Document X7qYd1Geb9eZmrGarr3v6Mx5w

DDORANFOTT CITE OR QUOTE NwDAwecSwem.Rebpeevar.ige2ow0v0/D3nrcaefat/dioxin ofE2x,3p,o7s,8u-rTeeaatnrndadcRhHeloularmtoeaddnibCHeonemzaolpt-hpou-RDnedioasxssines(sTmCenDtD) 2,3,7P,8a-TrteItIrIa:chIlnotreogdriabteendzSou-pm-Dmiaorxyinan(TdCRDisDk)CahnadrRacetlearteizdatCioonmfpoorunds NOTICE UATimH.gSpeI.lSniEccDayntvOipoioCrnolsiUnc.myM.eEnINttaiTsl PbISreoiAntegcPtcRiiorEncLuAlIaMgteeIdnNcfAyorRancYodmDshmRoAeunlFdtTon.notIittashttatehscinhsonstitcabageleeanbcecfoucrromancasyltlrayunerdedlpetooalsirecedyprbeysetnhte National U.S. ECRneevnsitereaorWrnfcmoahrsehaEnintnnadgvltiDPoroenrnov, mteDelcoeCtnpitomanlenAAtsgseenscsyment DISCLAIMER EArhraaesunctmsmivaeoaidsanriseonnammnslTeemeydxhnfpreoiotasnorffhtstdSraa,ueoslcrdgceiPboeuureetnlmooeasctnteeendonsciorrotetyt(ixlNioreasiennaAnaps.dASreded)ogrs.,taeehWftnnethctrehfyoapidlrpoefroirlanitelfchiavtcyelidyepNai.woocAtIxsiptiSiotunhinorarr.penseov,aHbsisaeeeosnewswednsoesiipnsvsmrlebnyoereov,naitinEtndig(dPen2Adtcd0eoo0fnwno3eddsrievlurdnleecocrvttstooeiidencoswotneainnrnotvsudotreeiuttoauhinttsteshteiteNwlhUreaaod.tSbrfrikioa.ansfntatioalsvlraeoegrrdseuinoccneys) IrtaahnevslefsaaoioitrrlceamridbeaaglttWeteouidoldhdanuaiitlotoneQaxrcytuetihhnarreatleaaitNstinmynpdAotGeydSneuitstooriidtebxhdveiielneliiiett-nEeiwleierPksmsAi,esiitsnchuIsoenenumfdteaohedpgrermoebwsnuyatacntryyiOdeonswaMn.gnitQBdlhl.uncoaTooflnithfthtiyeinenaGAueleuvgrieieiddtanseesclnscyiecnuwseersrsiimelnlanenptcndorptonrthpahsaociedstsigeicbnroeegvaeoelnrlfernsgiusumutsciluleahienztdodti-n,rawygtianiatdhmaceentiedobenetissntg 12/23/03 ii DRAFT--DO NOT CITE OR QUOTE ofE2x,3p,7o,s8u-rTeeaatnrndadcRhHeloularmtoeaddnibCHeonemzaolpt-hpou-RDneidoasxssines(sTmCeDntD) TABLE OF CONTENTS-OVERVIEW Part I: Part II: Part III: Estimating Exposure to Dioxin-Like Compounds (Draft Final) Volume 1: SCohuarpcteesrso1f Dthirooxuignh-L1i3ke Compounds in the United States Volume 2: PCrhoappetretrises1, Ethnrvoiurgohnm6ental Levels, and Background Exposures Volume 3: CSihtea-pStepresci1fitchrAosusgehss8ment Procedures HRCCCCCCCCChhhhhhhhheelaaaaaaaaaaappppppppplttttttttttteheeeeeeeeedrrrrrrrrrA243567981Cs.........soemsspDCEDMImAmTDCopaeieouseocorimvcdpcxnumnseheoiuiettdlnceapmo-nsfso,nRiopoEotigiuSimotersqoeonsumlunn2eoxpdbini(,igosvcca3cstynhani)ai,t7/tsrlldyHyoeoe,8anfnPouMn-cAihfmTcdyaTo,ceaRrFtdCatnmireeanoDaDlpcadnitccrDnsaooCohgtrdkalihsonfuiron(rcoATreotnitEdn2ivicciF,ie3mbs)T,eT7afono,lox8szxri-oicTDc-ipiCtityo-yDdxiDionxainnd(TRCelDatDed) and I2(Nn,3tA,e7gS,r8Ra-TteevedtierSwaucmhDlrmoarfaot,rdyDibaeecnnedzmoRb-ipesr-kD2C0io0hx3ai)nra(cTteCrDizDat)ioanndfoRrelated Compounds 12/23/03 iii DRAFT--DO NOT CITE OR QUOTE CONTENTS LLALIIIUSSSTTTTHOOOOFFF RATFSIACG.R.B.U.O.L.R.NE..E.YS..SM..........S......,......A.........B.........B.........R......E.........V.........I...A.........T.......I.....O.........N.........S......,......A.........N.........D............S.......Y...........M...........B........O...........L......S.................................................................................................................................................................................................x.viiiixxii 1. 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ROUDDT111111D......ONEI333333UO......FXD123456XCI......IENCITRNIAAPMSSITES-OltudrLIaeeQTemOmNsacIaAUmKdhmNi.UynaN.IEa.aVn-i.OnD.sSroi.CAydts.FtrIe.tae.NOLirT.trDc.e.eE.G.Mitd..IsDh.NB.Os..eD.EP.ouo.C.X..sXeOCd..oY.e.Iy..PuCsUN..M..erOFB..o-vN...L..A.nSe.ue...D.I.cU..tr.CK...re.dS...R..iT.E.n..e...c.....Et.O..n..s.rC...../..a...s..DR....O..t..........i...O.S.....Mo................nS.........P.......s.E.........O.........................R..U......................E....N.................L..........D............A..............S...........T........................I............O.............................N.............................S......................H.............................I...........P.......................S....................................F.....................O..............................R.....................................................................................................................................................................................................1111111.1.--------1111111111--320576735 2. 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ECTBA222...SID222O...VS123C...UEHRMRI2222222222222CEmS.............Mea2222222222222MEpnm.............3311122311223IrcACEo.............eu1213534424123dFrARn.............uFoLYcADEEPIRCOCAHEEOO.t.mto.l.ppRxCieneahtnutt..avh.hh.xiimpvnpiimau..TEddememee..riecer.s.eeuScorrrS.a.leraiaa.a.mmoniidbnDr..DDcPnlmtlI..polu..ytHiNidOeEa.F.aaCemoolce...ottt..ar.DliltnMNfaaa..aH.oeogiin..z.ftvz.r..neggiaRRRaSd.e.U.ocace..v.tliri..ic.dEieeeatccM..de.nnAEEi..llt.lelS.l.o.aaagsFoS..(ofC.Anaf..ttt.n.s.fsg..piee.e.f.ntieh..)..N..n.ume.e.dddm....d.ca.......odn..dc.tS....r.a.ttt.e.s..R.f.a.iioo.o.t..i.l..nc.n....Asec.C.He.......Eti.D.IC...gt.s.p.a.t....N.ame.a......y..fs.l.re.a.r...r..z...f.o..D.....cmiv..E.r....a....e..z..d....i..c.e....r.......ncau..f..Au....i..d.l.......t....oftnon.....c......i..s..e.......NgCoo.p.o.t.............i...c....e.nl..mg....v.h.......Io......n...t.....e..M.ea.......sge......i.......n.r.......c....n.i..E.......a......c...e.A.........t.....Ac....f.....a..s............Ef.t........L.....li....e.e.........c..s...f..........ra.c...S.....f.......t....i........n.t.e........zi........s.............cd..o.....a....................t....H....t.......n..s...........i................o.....a..............................n.z.................................a.................................r.......................d............................................................................................................................................................................................................................................................................................................................................................................................................................2.222222.22222222....-------22----2----2123322333312213----113333357404067776 12/23/03 iv DRAFT--DO NOT CITE OR QUOTE CONTENTS (continued) 222...222...456... D2222CO....2222thiha....l6666eob..r..r1234eaE....tceffTnCOsEe.ehacx.l..yerti..sdd..vr..oi.a.ao..it..t.div...e..v.da...F..e.s.....G.cu...S...un...Gt...l..r.ca...e..r.tT...is...Do....s......n..i......s........e..........a............s.........e.....................................................................................................................................................................................................................................................................................................................................................................................................................................................2222222-------44334441379002 3. M33..12E..CHAM333G...NE222O...IN123DS...EMERAATMSVAhseEAFLescRreNIhRaZsSamDesEUncmeDiMeSsweptMiOnoMtcortDO.krEI.n.ECDC.tf.o.oHoE.O.rEn.LAmF.v.c.NaFa.De.tlO.IipuI.oS.OaRt.nM..t.X.e..Da...I.nMO..IN..dO..F.o..A.XM.d.A...e.IC.o.NC...od.T..T.e.fA..II..AO.oO.C....fc.NN.T..A.t...i.I.c..o.O....t....i.n....oN.........n...........--........................I..........m...................p............l......i......c............a..........t........i......o............n............s.................f.......o............r..............R.................i......s...........k..............................333333------133266 4. E44444.....X12345.....POS44444DEEBPSU.....ONNOA11E444R.....TVVVC12123UEE.....EIIKRRRCNLGVITIGCOOHTOnnRiaeENNIvtAsPaAOrnseSMMikMRuenaLUe.rebt.AEEEaLo.NiE.lLNNlNr.YCi.DysS.teTTT.Tyto.Hovi.AAEAEmu.ifeI.nXr.LLGLRR.lca.Ise.PHItFMenS..Ze..OltAO.LT.sae.EA....YkTSab.A..D.T..es.EsU...G..IEeeI...LA.O..RsrX..E.e.v......N.E..vAP.Sa.........e.OSt......N...il........s....oS......D..........n.E................s........FD.....................O....................P.........O............O.............D................P.....................U......C........................LO.......................A.......N....................T..........C...................I..........E.O....................N..........N....................T.........S....................R..............O........A....................R.........T.............................I...........O..............................N.............................S.................................................................................................................................................................................................................4444444....44-------441112111----11385659002 5. D55..O12..SE-RED55..EMO12S..S11PP..EIORMNCCI555C...aaSE222Aln...ETc111cLuR...eC123lrMaI...HCtBiOEEEBB.o(A.oS.nsssDoo.Rd)ttt.sddiii.EyA.mmmyyo.L..BC..aaafBB..Ittt..uENT.eee.uu..rfsss..rrEGd..fdd..eeoooR..ee..ncOfff..nnI..ts.Z.SSSissF..vB..lllABB..eoooI..a.N.pppTaa..Ds..eeessD.e.I.oee.Od..FFFIdd.s...VaaaNe.o.oo..ccc.nI..nn.ttt.D...ooo...a...AH..rrrU....sss..M....nu..A....aaa..im..e...mL.nnn....c....addd...h.aD..n.....la.RRR....A..n.D.D..iii....isss..T...s.kkk..a.a..t.A....i..tt..aaac....aa..ttt..S....M......CCC......E..........uuu...o...T......rrr......d..rrr....S...eee.....e......nnn.......l.......ttt................BBB........................aaa..............ccc...............kkk................ggg................rrr...........ooo................uuu................nnn................ddd........................................555.5....-55---551212----11849092 12/23/03 v DRAFT--DO NOT CITE OR QUOTE 55..34.. M5S.U2O.M2D.ME-NAOoRFnY-cAaDnCcOTeSIrOEEN-nRd-EBpSoAPinSOtEsNDS..DE...O.C..S.H.E..A-..R.R.E.A..S.C.P..TO...EN..R.S..IE..Z..MA...T.O..I.DO...NE...L......I..N.......G............................................................555---222646 6. RISK CHARACTERIZATION........................................................................................6-1 APPENDIX .............................................................................................................................. A-1 GLOSSARY ............................................................................................................................ G-1 REFERENCES ........................................................................................................................... R-1 12/23/03 Y1 DRAFT--DO NOT CITE OR QUOTE LIST OF TABLES 1-1. The toxic equivalency factor (TEF) scheme for I-TEQDF ..............................................1-19 1-2. The toxic equivalency factor (TEF) scheme for TEQpp-WHO^ ................................. 1-19 1-3. The toxic equivalency factor (TEF) scheme for TEQpp-WHO^ ................................. 1-20 1-4. TThEeQracnognetorfibthuetoinrsv..i.v..o...r..e..l.a.t..i.v..e...p..o..t.e..n..c.y...e..s..t.i.m...a..t.e..s...(.R...E..P..)...v..a..l.u..e.s...f..o..r..t.h..e...m...a..j.o..r.............. 1-21 1- 5. Comparison of administered dose and body burden in rats and humans........................1-22 2- 1. Effects of TCDD and related compounds in different animal species........................... 2-44 2.2. Some biochemical response to TCDD............................................................................ 2-45 2-3. hSiugmhmexapryosoufrethleevceolms,baisneddesccorhiboertdabnydIsAeRleCcte(1d9i9n7d)ust.r..i.a.l...c.o...h..o..r.t..s..t.u..d..i.e..s..w...i.t..h.............. 2-46 2-4. Tcuomnogreninecrisd.e..n..c..e...a.n..d...p..r..o..m...o..t.i.o..n...d...a.t.a...c..i.t.e..d...f..o..r..t.h..e...T..E...F..-.W....H...O...9.8...f.o..r..p..r..i.n..c..i.p..a.l.................2-47 3- 1. Early molecular events in response to dioxin ................................................................3-15 4- 1. Confidence rating scheme ...............................................................................................4-25 4-2. UInnvietendtoSrytaotefsen.v..i.r.o..n..m...e..n..t.a..l..r..e.l..e.a..s..e..s..(..g..r.a..m...s./.y..e..a..r.)...o..f..T..E...Q...D..F.-.W....H...O...9.8...i.n...t.h..e....................4-26 4-3. Sources that are currently unquantifiable (Category E ) ..................................................4-30 4-4. eSnuvmirmonamryeonftaNl omrtehdiAamanedricfaonoCd.D...D.../.C..D...F....a.n...d...P..C..B....T...E..Q...-.W....H...O...9.8...l.e..v..e.l.s...i.n..................... 4-31 4-5. Background serum levels in the United States 1995-1997 .......................................... 4-33 4-6. Adult contact rates and background intakes of dioxin-like compounds ....................... 4-34 4-7. Variability in average daily toxic equivalent (TEQ) intake as a function of ag e.........4-35 12/23/03 vii DRAFT--DO NOT CITE OR QUOTE LIST OF TABLES (continued) 5-1. Pcoeahkosretrsu..m....d..i.o..x..i.n...l..e.v..e..l.s...i.n...t.h..e...b..a..c..k..g..r.o..u..n..d...p..o..p..u..l.a..t.i..o..n...a..n..d...e.p..i..d..e.m...i..o..l.o..g..i.c..a.l................ 5-31 5-2. Pfourbmlisuhleade.c..a..n..c.e..r...e.p..i..d..e.m....i.o..l.o..g..y...a..n..d...b..i.o..a..s.s..a..y...d..a..t.a..i..n...d..o..s.e..-.r..e..s.p..o..n..s..e...............................5-34 5-3. All cancer risk in humans throughage 75 ........................................................................5-36 5-4. Summary of all sitecancer ED0i andslope factor calculations........................................5-37 5-5. m2D-ooysdeeeaslrsyaine.i.lm.d..ia.n.l.g.c..a.1.r%.c..i.n.e.ox..gc..ee..sn..si.c.r.i.it.sy.k..s.(.t.9u..5d..%i.e..s.l.ou..ws..i.ne..rg...cs.o.i.mn..f.p.i.dl.e.e..nm..c.ue..l.bt..io.s.ut.a.n.g.d.e.)..(.b.P.a.o.s.re.t.di.e..ur..p.e.ot..n.a.l...,...1..9..8..4..)...5-38 5-6. Bdaoidlyyibnutradkeen.s..f..o..r..c..r.i..t.i.c..a.l...e.n..d..p..o..i.n..t..s..i.n....a.n..i..m...a.l..s..w...i.t.h...h..u..m....a.n....e.q..u..i..v..a.l..e.n..t........................5-39 12/23/03 viii DRAFT--DO NOT CITE OR QUOTE LIST OF FIGURES 1-1. Chemical structure of 2,3,7,8-TCDD and related compounds.......................................1-23 2-1. Cellular mechanism for AhR action............................................................................... 2-48 4-1. EUsntiitmedatSedtatCeDs,D1/9C9D5.F...I..-.T..E...Q....e..m...i.s.s..i.o..n..s...t.o...a..i.r..f..r.o..m....c..o..m...b..u..s..t.i.o..n...s..o..u..r.c..e..s..i.n....t.h..e............ 4-36 4-2. fCoormrepfaerriesnocneoyfeeasrstim19a8te7saonfda1n9n9u5al...I.-.T...E..Q....e..m...i.s..s.i.o..n..s...t.o...a..i.r..(..g..r.a..m...s...I.-..T..E..Q.../.y..r..)............. 4-37 4-3. Bplaorotidcilpeavnetlss i(nI-tThEeQCDfoCr C(2D0D00/C).D...F...+....W....H...O..9..4.)..v..e..r.s..u..s...a..g..e..o...f..a...s.u..b..s..e..t..o..f...................... 4-38 4-4. Panreaddicutletdpodpisutlraibtiuotniofnosr afondurayveearrasg:e1T9E65Q, 19-8W5,H1O995,caonndce2n0t3ra0t.i.o..n..s....w..i..t.h..i.n................ 4-39 4-5. Dnaenumdrsobinnogsdtysracbteiunorandreioonfsstdh(Buer)minoogfdiaenlfliaffnoetrtsiemrveeas.lu.u.l.at.i.tn.i.ng..g..f.ri.mo..m.p..a..vc..at.sr..i.oo..un..s.l.i.np..ui.d.r.s.c.i.no..gn..c.s.ec..ne..tn.r.aa..rt.ii.oo..sn..s...(.A...).............4-40 5-1. Choympoptahreitsiocnalobfalcifkegtrimouenadvaenradgoecbcoudpyatbiounrdalenscaenndarairoesa...u..n..d..e.r...t.h..e...c..u..r.v..e...i.n....................... 5-41 5-2. Pepeiadkemdiiooxliongbicoadlycobhuordrtesn(bleavcekl-scainlcbualactkegdr)oun..d...p..o..p..u...l.a..t.i.o..n..s...a.n..d......................................5-42 12/23/03 ix DRAFT--DO NOT CITE OR QUOTE LIST OF ACRONYMS, ABBREVIATIONS, AND SYMBOLS AAAAAAAAABBBBBDCCCCCCDDDECCDaDDIMFLWDTYYDhHLSYhTUmFEHNPRDTTLPKNSDFPPDCFPCATtDD111(sBAARu1b12sc ript) EEEEEFSGPDDGHAFCF01R/VC HHHHgGGIDACpGFCDTHDDD AaaaaaaaarlrllrsrgtkayyyepeneaalllarnliherhhuintcdnyyyaneyedddtdhearrrfpeeomoooarhpcccrmiottaaanahTsrrriocepbnbboethooooxrclaanltnniurucntraarrlsvneSaesfercecseufeerbfeapposrstcttaeooaisrnrecneusclaenadr translocator Disease Registry bbpbbCccccerohhoyeoeonnllntldnoooymzcfyttrrbioehodiiiwrr[nnnmxeosaaaaeinm]actttfipceeergoiekyTdddnhrrtiadDdeddlntyoniiietibbbmsesedeeeeerpvnnnadhazszzioelbooocefddCuyniiootrozeaxnoxnitfinnruorlanand Prevention Ucccdd5deeeeefgoyyyfftppiiear.hofefalStttoii-eeltyoooddmxdix.hccclccceeiiytyetEnhlhhhrriienrlmmvsvynrrrin-e,oooeebdvsiaafmmmotrtidlldduriornmiooeeeooggrtcuasenssrrhuPPPcansooeemll44lmt4swwoaeoa,555etriistttiP0icn00nhhtndte11tC1ehgaearffBAAecB/loaahvi1cc1n2Psd1oittenro%oreeeoymrrnnntlrzerzzoeecycyynschmtmmepieloooepeenrntiosdAreegleenvceyl hhhhggeyaeeaxlpsmpotatoagamcxtcehiiahonalolna-goirtlnerdouoddadtdayuiambicbreioyebnmlnlzetzoarofat-i-apncpc-s-tdhfodeiyriordoaxrxsioeinncarbons 12/23/03 x DRAFT--DO NOT CITE OR QUOTE LIST OF ACRONYMS, ABBREVIATIONS, AND SYMBOLS (continued) hIIIIIIDA-Pg-rPTACRESCQ kLLgABB mNNLLLLMMHMOEHHRORDAAANSLE0ETNA1LSES NNNNnOgITOOCOPDAESLDEHL pPPPPPPPPPPPPPPgCCCeAOBBBCCeKOCCBPQDDDDPHDTDDKWDDFFDF hkIiiiIillmmmNNnNNnnpppppppppppppppllllomnniimouionniaoiohooooooeehuaeooctfnaaaalitaeicwtwetteinnnnt-lylalllllb-iomtenmeeeettttrrsoaryyyyyyyniototrotiiiitsrliaeeglgrriaiscgaoooaaocbcccmnbcitbenumubimnnrrsgertcihcoccynnnhrhhhnirsirsinatnnsoaaarnlbzzaahoo-hohalselcaaaellllaetaymottofooogeicomooooilmnlliilomllllrlrmn-ogsoooaooirdgodbevrrrvru-orcfHHTIuogivlniiinnirrrirpikesieennnonnnwnnmecooposdeoaepaaauderirdhdsabaakaxaaanddppirlorillxrnaam-tu-obttttbatlvutpoieiirhamToreeileeAPeeleleltbbregeotelcotemytdaetfdudddddmfdihruEinieseeodogvnfsnnnvcotstbrseannzubFel-tqetdeuddodhtaoebegioirctaaAAoazzrniluivciinonierielorfptesgdbbsgboo-bcsclaae(odanededpchevlyeeeeee-Ae-ytmtreihdhypip-ednenfN-nmenpcvdPyTfeOrefn--morzzzzobpepeoufdiefsdmroyoSsoaoocuschufloehnretirecflddefDecrtxorear-ogetuRuiiiciadueiorixvdnctrToRrworantnmfeipenaaiaeyaxoxfdins)lnmaonrnseleaCinieodbtrsnncvciapkouohotEoertssneencllekxeemhadiSavnlamiueboetcSrlnytaitvainhlcEfeCaeeSytPatia1ynoAf%cneaetinSynrrdeu(s1rWHp9vo8eeHan9ylOsteh)level 12/23/03 xi DRAFT--DO NOT CITE OR QUOTE LIST OF ACRONYMS, ABBREVIATIONS, AND SYMBOLS (continued) pPRRRT2TTTTTTtSSSp,VARCMEEDCDEfeER4DtFQBQP,qCBPDGI5RC-D--WwT Hh Oo9948 UTTTWPNSRHHAPLO-LPS pprrrUu2tss2tttttttWd11hroooerheeethoa,n,i99ii.at4fl3lylxxyoecnSrolriaa99een,y,tiirtrxaehi.rt5t748rrccoodtviipdpilraler-,Evvndiioiai8WWebeeneotddsnere-rrrPcqqr-lcpkHeldioyetbaiHsHcuurpeAhdteikpleitnrlihziiodetsieOnOiehadvv'cbromelltnksavdaoelloahaelydPtiyieocneuuirlSlnslhlolneClelooyhmxoeoplcc-npnnagrpOltldBlydii(iooehittcehndpiaEgrsnrryocnnetgteootlPseaercganoafpdiblkAelaooblntohiioesocxbtnu)Ailolyztyeylotrdaioahsnramnrtvcaafeczietociooetispthcnnot-aoirhepetcerea-yIvdra-iiTcBiodoiEeoudxasFilrnydscehsetambelistoheindcTluEdFes 1f3orddioioxxinin-lsi,kfeuPraCnBs,sand >< maglgleeprrssieepcssaarrttttooeehhxgrraairnnttmahhmoaaarnnteeloyqrueaqlutoal to 1CTZQ IA IV 12/23/03 xii DRAFT--DO NOT CITE OR QUOTE AUTHORS AOUWWc.fSiaftlisi.lcnihEaegimnnoDgvfHtieoRrp.oneunF,stmaDeyraeClArancnsthsadilasPntadrnoDtteAecvdtiemolnoinpAimsgterenanttcoyr for Science NOULDERxie.afinSrfpsteidi.eecocaarEentiroSnmacor.vlhfeBiHnRrToitereranainslamlebntTahaegorunlcaxmethnaicdPlaoaPnElrodrknog,vDtyNeirecDoovtnireiotvmlhnoisepCAinmoatgnareeolnnlEticnfyfaects Laboratory NOUDEWx.afaSafptvisi.ociohdEesniunnaHorgvlef.tiCoRrCAoneelnn,nesamtvDeeleayeCrrrsnlcfiytohsarlaaEPnnnddrovRDtierieocsvntkiemoClnoehpnAamtragaelecnAnttecsrysizeasstimonenGt roup NMOUERCxhe.afiSfpsticiie.eehcofarEea,nirenmaPcolvlhhfeJiHa.nRrTrotDermeaniaslaemalenVtTcahegooirnltcakxeotnhiaincdPlaeoaPnEtlridorkncog,vsDtyNeiBrecDoovrtniareiotvmnlhnoicsephCAinmoatgnareeolnnlEticnfyfaects Laboratory NMOUEWx.afaSafpttisi.otcohhEesnieunnaowrgvleftiCNoRrAone.enn,nsLamtDeeolayeCrrrsnbcfitoehsarrlaaEPnnnddrovRDtierieocsvntkiemoClnoehpnAamtragaelecnAnttecsrysizeasstimonenGt roup NUBMWOr.afeSauftdsii.ccohieEecninaDnaolgvl.ftOiCoRrRofneoefn,nidscmtDeaeeaneCrrrncf(toRharleaEsPnendraovrDticerheocv)nt/iemSolenoenpnAimtoagrelenHAntcesyaseltshsmSceinetntist 12/23/03 xiii DRAFT--DO NOT CITE OR QUOTE AUTHORS (continued) NUJEIWOmon.afhSafmvtnisi.icohreEeLonidnnn.aiogavlmSfttiCecoRreohnneOenan,tsaumftDelfemaieCrcErncefntohagorliafEnPntehndreoevrDtiDereocivntviemiolsnoieopnAnmtagDelenAnirtcesycsetosrs-mWeansthington NULWOSpi.afnSafetisdi.ccohaiEenainCnlaogvlA.ftiCTosRrosnueeinn,xssmttDeeeanaeCrnrntcftoharlaEPnndrovDtiereocvntiemolnoepnAmtagelenAntcsysessment UDDDWOO.iwiffSaroffesiia.xccchiiEeentinonnooLrgPvff.toioPPrWloniorcne,liyvlnmDuetPeteCnirrnotositnojaelnPc,PrteProvetesentcitctiiioodnnesaA,nagdneTdnocTxyoicxsic Substances 12/23/03 xiv DRAFT--DO NOT CITE OR QUOTE 1. INTRODUCTION 1 This document presents an integrated summary of available information related to 2 exposure to and possible health effects of dioxin and related compounds. It also presents a short 3 risk characterization, which is a concise statement of dioxin science and the public health 4 implications of both general population exposures from environmental "background"1and 5 incremental exposures associated with proximity to sources of dioxin and related compounds. 6 Even though this document is a summary of key findings developed in the exposure and health 7 assessment portions (Parts I and II, respectively) of the U.S. Environmental Protection Agency's 8 (EPA or Agency) dioxin reassessment, it is meant to be detailed enough to stand on its own for 9 the average reader. Readers are encouraged to refer to the more detailed documents, cited below, 10 for further information on the topics covered here and to see complete literature citations. 11 12 Estimating Exposure to Dioxin-Like Compounds: This document, hereafter referred to as 13 Part I, the Exposure Document, is divided into 3 volumes: (1) Sources of Dioxin-Like 14 Compounds in the United States; (2) Properties, Environmental Levels, and Background 15 Exposures; and (3) Site-Specific Assessment Procedures. 16 17 Health Assessmentfor 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and Related 18 Compounds: This document, hereafter referred to as Part II, the Health Document, 19 contains two volumes with nine chapters covering pharmacokinetics, mechanisms of 20 action, epidemiology, animal cancer and various noncancer effects, toxic equivalency 21 factors (TEFs), and dose-response. 22 23 Parts of this integrative summary and risk characterization go beyond individual chapter 24 findings to reach general conclusions about the potential impacts of dioxin-like compounds on 25 human health. This document specifically identifies issues concerning the risks that may be 26 occurring in the general population at or near population background exposure levels. It* regularly'Tochceurtsertmo m"beamcbkgerrsouonfdtheexgpeonseurrael"phoapsublaeteinonusferodmtheroxupoghsuoruet mtheisdiraea(sfsoeosds,maeirn,tstooild, eestcc.r)ibtehaetxhpaovseurdeiothxaint concentrations within the normal background range. Most (> 95%) background exposure results from the presence ooff mthiinsubtaecakmgroouunntds oexfpdoiosxuirne-liiskferocmomthproeuencdasteingodriieetsaroyf fsaot,urpcreism: anrailtyurfarlolymftohremceodmdmioexricnisa,l afontohdrospuopgpelyn.icTdhioexoinrisgin from contemporary sources , and dioxins from reservoir sources . The term "background expo sure" as used in this document should not be interpreted as indicating the significance or acceptability of risk associated with such expo sures. 12/23/03 1-1 DRAFT--DO NOT CITE OR QUOTE 1 articulates the strengths and weaknesses ofthe available evidence for possible sources, 2 exposures, and health effects, and it presents assumptions made and inferences used in reaching 3 conclusions regarding these data. The final risk characterization provides a synopsis of dioxin 4 science and its implications for characterizing hazard and risk for use by risk assessors and 5 managers inside and outside the EPA and by the general public. 6 This document (Part III) is organized as follows: 7 8 1. Introduction. This chapter describes the purpose/organization of and the process for 9 developing the report, defines dioxin-like compounds in the context of the EPA 10 reassessment, and explains the toxic equivalence (TEQ) concept. 11 12 2. Effects Summary. This chapter summarizes the key findings of the Health Document 13 and provides links to relevant aspects of exposure, mechanisms, and dose-response. 14 15 3. Mechanisms and Mode of Dioxin Action. This chapter discusses the key findings on 16 effects in terms of mode of action. It uses the "Mode-of-Action Framework" recently 17 described by the World Health Organization/(WHO) International Programme on 18 Chemical Safety (IPCS) Harmonization of Approaches to Risk Assessment Project and 19 contained in the Agency's draft guidelines for carcinogen risk assessment as the basis for 20 the discussions. 21 22 4. Exposure Characterization. This chapter summarizes the key findings of the 23 Exposure Document and links them to the effects, mechanisms, and dose-response 24 characterization. 25 26 5. Dose Response Characterization. This chapter summarizes approaches to dose27 response that are found in the Health Document and provides links to relevant aspects of 28 exposure and effects. 29 30 6. Risk Characterization. This chapter presents conclusions that are based on an 31 integration of the exposure, effects, mechanisms, and dose-response information. It also 32 highlights key assumptions and uncertainties. 33 34 The process for developing this risk characterization and companion documents has been 35 open and participatory. Each ofthe documents has been developed in collaboration with 12/23/03 1-2 DRAFT--DO NOT CITE OR QUOTE 1 scientists from inside and outside the Federal Government. Each document has undergone 2 extensive internal and external review, including review by EPA's Science Advisory Board 3 (SAB). In September 1992, early drafts of all the background chapters underwent external peer 4 review. This was followed by extensive revision and re-review of the epidemiology chapter in 5 September 1993. In September 1994, drafts of each document, including an earlier version of 6 this risk characterization, were made available for public review and comment, which included a 7 150-day comment period and 11 public meetings around the country to receive oral and written 8 comments. These comments, along with those of the SAB, have been considered in the drafting 9 of this final document. The dose-response chapter of the Health Document underwent peer 10 review in 1997; an earlier version of this Integrated Summary and Risk Characterization 11 underwent development and review in 1997 and 1998, and comments have been incorporated. 12 In addition, as requested by the SAB, a chapter on toxic equivalency has been developed 13 and underwent external peer review in parallel with the Integrated Summary and Risk 14 Characterization in July 2000. Review by the SAB of the dose-response chapter, the toxic 15 equivalency chapter, and the Integrated Summary and Risk Characterization occurred in 16 November 2000. The report of that review was submitted to the EPA Administrator on May 31, 17 2001. These sections of the document, as well as a few of the other background chapters in Parts 18 I and II, have been revised to reflect the comments of the SAB and the public. The 19 comprehensive set of background documents and this integrative summary and risk 20 characterization are now being published as final reports to replace previous dioxin assessments 21 as the scientific basis for EPA decision making. 22 23 1.1. DEFINITION OF DIOXIN-LIKE COMPOUNDS 24 As defined in Part I of this document, this assessment addresses specific compounds in 25 the following chemical classes: polychlorinated dibenzo-p-dioxins (PCDDs or CDDs), 26 polychlorinated dibenzofurans (PCDFs or CDFs), polybrominated dibenzo-p-dioxins (PBDDs or 27 BDDs), polybrominated dibenzofurans (PBDFs or BDFs), and polychlorinated biphenyls (PCBs); 28 these chemicals are described as "dioxin-like." Dioxin-like refers to the fact that these 29 compounds have similar chemical structure and physical-chemical properties, and they invoke a 30 common battery of toxic responses. Because of their hydrophobic nature and resistance towards 31 metabolism, these chemicals persist and bioaccumulate in fatty tissues of animals and humans. 32 The CDDs include 75 individual compounds; CDFs include 135 different compounds. 33 These individual compounds are referred to technically as congeners. Likewise, the BDDs 34 include 75 different congeners, and the BDFs include an additional 135 congeners. Only 7 of the 35 75 congeners of CDDs or ofBDDs are thought to have dioxin-like toxicity: those with 12/23/03 1-3 DRAFT--DO NOT CITE OR QUOTE 1 chlorine/bromine substitutions in, at a minimum, the 2, 3, 7, and 8 positions. Only 10 of the 135 2 possible congeners of CDFs or of BDFs are thought to have dioxin-like toxicity; also those with 3 substitutions in the 2, 3, 7, and 8 positions. This suggests that 17 individual CDDs/CDFs and an 4 additional 17 BDDs/BDFs exhibit dioxin-like toxicity. The database on many of the brominated 5 compounds regarding dioxin-like activity has been less extensively evaluated, and these 6 compounds are not explicitly considered in this assessment. (For a review of this topic see 7 Birnbaum et al., 2003.) 8 There are 209 PCB congeners, only 12 of which are thought to have dioxin-like toxicity: 9 PCBs with four or more lateral chlorines, with one or no substitution in the ortho position. These 10 compounds are sometimes referred to as coplanar, meaning that they can assume a flat 11 configuration, with rings in the same plane. Similarly configured polybrominated biphenyls 12 (PBBs) are likely to have similar properties. However, the database on these compounds with 13 regard to dioxin-like activity has been less extensively evaluated, and these compounds are not 14 explicitly considered in this assessment. Mixed chlorinated and brominated congeners of 15 dioxins, furans, and biphenyls also exist, increasing the number of compounds potentially 16 considered dioxin-like within the definitions of this assessment. The physical/chemical 17 properties of each congener vary according to the degree and position of chlorine and/or bromine 18 substitution. Very little is known about occurrence and toxicity of the mixed (chlorinated and 19 brominated) dioxin, furan, and biphenyl congeners. Again, these compounds are not explicitly 20 considered in this assessment. 21 Generally speaking, this assessment focuses on the 17 CDDs/CDFs and a few of the 22 coplanar PCBs that are frequently encountered in source characterization or environmental 23 samples. The Agency recognizes that other dioxin-like compounds exist in the chemical classes 24 discussed above (e.g., brominated or chlorinated/brominated congeners) or in other chemical 25 classes (e.g., polyhalogenated naphthalenes or benzenes, azo- or azoxybenzenes), but this 26 evaluation focuses on the two dozen chlorinated congeners that are generally considered to be 27 most associated with environmental and human health risks. 28 The chlorinated dibenzodioxins and dibenzofurans are tricyclic aromatic compounds with 29 similar physical and chemical properties. Certain of the PCBs (the so-called coplanar or mono 30 ortho coplanar congeners) are also structurally and conformationally similar. The most widely 31 studied of this general class of compounds is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). This 32 compound, often simply called "dioxin," represents the reference compound for this class of 33 compounds. The structure of TCDD and several related compounds is shown in Figure 1-1. 34 Although sometimes confusing, the term "dioxin" is often also used to refer to the complex 35 mixtures of TCDD and related compounds emitted from sources or found in the environment or 12/23/03 1-4 DRAFT--DO NOT CITE OR QUOTE 1 in biological samples. It can also be used to refer to the total TCDD "equivalents" found in a 2 sample. This concept of toxic equivalency is discussed extensively in Part II, Chapter 9, Section 3 9.4, and is summarized below. 4 5 1.2. TOXIC EQUIVALENCY FACTORS 6 CDDs, CDFs, and PCBs are commonly found as complex mixtures when detected in 7 environmental media and biological tissues or when measured as environmental releases from 8 specific sources. Humans are likely to be exposed to variable distributions of CDDs, CDFs, and 9 dioxin-like PCB congeners that vary by source and pathway of exposures. This complicates the 10 human health risk assessment that may be associated with exposures to variable mixtures of 11 dioxin-like compounds. In order to address this problem, the concept of toxic equivalency has 12 been considered and discussed by the scientific community, and TEFs have been developed and 13 introduced to facilitate risk assessment of exposure to these chemical mixtures. 14 On the most basic level, TEFs compare the potential toxicity of each dioxin-like 15 compound in the mixture to the well-studied and understood toxicity of TCDD, the most toxic 16 member of the group. The use of the TEF methodology has been EPA policy since 1987, when 17 the Agency "adopted an interim procedure, based on dioxin `toxicity equivalence' factors 18 (TEFs), for estimating the hazard and dose-response of complex mixtures containing CDDs and 19 CDFs in addition to 2,3,7,8-TCDD" (EPA 1987, 1989a). The background and historical 20 perspective regarding this procedure is described in detail in Part II, Chapter 9, Section 9.1, 9.2, 21 and in Agency documents (U.S. EPA, 1987, 1989a, 1991a). This procedure involves assigning 22 individual TEFs to the 2,3,7,8-substituted CDD/CDF congeners and dioxin-like PCBs. To 23 accomplish this, scientists have reviewed the toxicological databases and considered chemical 24 structure, persistence, and resistance to metabolism and have agreed to ascribe specific "order of 25 magnitude" TEFs for each dioxin-like congener relative to TCDD, which is assigned a TEF of 26 1.0. The other congeners have TEF values ranging from 1.0 to 0.00001. Thus, these TEFs are 27 the result of scientific judgment of a panel of experts who used all of the available data, and they 28 are selected to account for uncertainties in the available data and to avoid underestimating risk. 29 In this sense, they can be described as "public health-conservative" values. 30 It is important to understand that this process results in values that represent the scientific 31 judgment of experts working with specified criteria. As described below, these values rely more 32 heavily on in vivo than in vitro data and on chronic or subchronic exposures rather than acute 33 exposures. Attempts to replicate or critique individual TEF values on the basis of distributional 34 analysis of relative potency (REP) estimates from individual endpoints or all data have been 35 undertaken (Finley et al., 2003), suggesting possible benefits from the analysis of REP 12/23/03 1-5 DRAFT--DO NOT CITE OR QUOTE 1 distributions. It remains important, however, to recognize the emphasis placed by WHO on the 2 above noted weighting factors and on the expert scientific judgment used to derive the existing 3 TEF values. 4 The TEQ concept is applied by multiplying the TEF of each congener present in a 5 mixture by the respective mass concentration and the products are summed to represent the 6 2,3,7,8-TCDD TEQ of the mixture, as determined by equation 1-1. 7 8 TEQ s [Congene^ y.7EFi 'j+\Ccmgenef/x TE}>', 'j+.......fCongeners x TEFK j (1-1) 9 10 The TEF values for PCDDs and PCDFs were originally adopted by international 11 convention (U.S. EPA, 1989a). Subsequent to the development of the first international TEFs 12 for CDD/CDFs, these values were further reviewed and/or revised and TEFs were also developed 13 for PCBs (Ahlborg et al., 1994; van den Berg et al., 1998). A problem arises in that past and 14 present quantitative exposure and risk assessments may not have clearly identified which of three 15 TEF schemes was used to estimate the TEQ. This reassessment introduces a new uniform TEQ 16 nomenclature that clearly distinguishes between the different TEF schemes and identifies the 17 congener groups included in specific TEQ calculations. The nomenclature uses the following 18 abbreviations to designate which TEF scheme was used in the TEQ calculation: 19 20 1. I-TEQ refers to the International TEF scheme adopted by EPA in 1989 (U.S. EPA, 21 1989a). See Table 1-1. 22 23 2. TEQ-WHO94 refers to the 1994 WHO extension of the I-TEF scheme to include 13 24 dioxin-like PCBs (Ahlborg et al., 1994). The TEF values for the dioxins and furans 25 are identical to the I-TEQ. See Table 1-2. 26 27 3. TEQ-WHO98refers to the 1998 WHO update to the previously established TEFs for 28 dioxins, furans, and dioxin-like PCBs (van den Berg et al., 1998). There are numerous 29 changes in the TEF values for the dioxins, furans and PCBs. See Table 1-3. 30 31 The nomenclature also uses subscripts to indicate which family of compounds is included 32 in any specific TEQ calculation. Under this convention, the subscript D is used to designate 33 dioxins, the subscript F to designate furans, and the subscript P to designate PCBs. For example, 34 "TEQdf-WHO98" would be used to describe a mixture for which only dioxin and furan congeners 35 were determined and where the TEQ was calculated using the WHO98scheme. If PCBs had also 12/23/03 1-6 DRAFT--DO NOT CITE OR QUOTE 1 been determined, the nomenclature would be "TEQDFP-WHO98." Note that the designations 2 TEQ -WHO and I-TEQ are interchangeable, as the TEFs for dioxins and furans are the same 3 in each scheme. Note also that in the current draft of this document, I-TEQ sometimes appears 4 without the D and F subscripts. This indicates that the TEQ calculation includes both dioxins 5 and furans. 6 This reassessment recommends that the WHO TEF scheme be used to assign toxic 7 equivalency to complex environmental mixtures for assessment and regulatory purposes. Later 8 sections of this document describe the mode(s) of action by which dioxin-like chemicals mediate 9 biochemical and toxicological actions. These data provide the scientific basis for the TEF/TEQ 10 methodology. In the 20-year history of the TEF/TEQ concept, the approach has evolved, and 11 decision criteria supporting the scientific judgment and expert opinion used in assigning TEFs 12 have become more transparent. Numerous states and countries and several international 13 organizations have studied and consequently adopted this approach to evaluating complex 14 mixtures of dioxin and related compounds (Part II, Chapter 9, Section 9.2). It has become the 15 accepted methodology, although the need for research to explore alternative approaches is widely 16 endorsed. Clearly, basing risk on TCDD alone or assuming that all chemicals are equally as 17 potent as TCDD is inappropriate on the basis of available data. Although uncertainties in the use 18 of the TEF methodology have been identified and are described later in this document and in 19 detail in Part II, Chapter 9, Section 9.5, one must examine the use of this method in the broader 20 context of the need to evaluate the potential public health and environmental impact of complex 21 mixtures ofpersistent, bioaccumulative chemicals. 22 It can be generally concluded that the use of TEF methodology for evaluating complex 23 mixtures of dioxin-like compounds decreases the overall uncertainties in the risk assessment 24 process, as compared to alternative approaches. Use of the latest consensus values for TEFs 25 assures that the most recent scientific information informs this "useful, interim approach" (U.S. 26 EPA, 1989a; Kutz et al., 1990) to dealing with complex environmental mixtures of dioxin-like 27 compounds. As stated by the EPA's SAB (U.S. EPA, 1995), "The use of the TEFs as a basis for 28 developing an overall index of public health risk is clearlyjustifiable, but its practical application 29 depends on the reliability of the TEFs and the availability of representative and reliable exposure 30 data." EPA will continue to work with the international scientific community to update these 31 TEF values to ensure that the most up-to-date and reliable data are used in their derivation and to 32 evaluate their use on a periodic basis. 33 A chemical is assigned a TEF value on the basis of all the available data comparing the 34 REP of a chemical to 2,3,7,8-TCDD. REP values are obtained from individual studies available 35 in the peer-reviewed literature. In addition, there are weighting criteria that place more emphasis 12/23/03 1-7 DRAFT--DO NOT CITE OR QUOTE 1 on REP values from chronic and subchronic studies that examine toxic endpoints (van den Berg 2 et al., 1998). There is a broad range in the quantity and quality of the data available for 3 individual congeners. For example, the TEF for PCB 126 is based on over 60 REP values from 4 in vivo endpoints that examine responses as diverse as enzyme induction, developmental 5 toxicity, immunotoxicity, hepatic toxicity, alterations in hormones, and tumor promotion, 6 whereas the TEF for 3,4,4',5-tetrachlorobiphenyl (PCB 81) is based on REP values for in vitro 7 CYP1A induction and QSAR calculations. Fortunately, the uncertainty in the PCB 81 TEF 8 based on limited data has minimal effect on the risk characterization of complex mixtures of 9 dioxin-like compounds since it does not contribute significantly to human TEQ exposures. 10 Five congeners contribute approximately 80% of the total TEQ in humans: 2,3,7,811 TCDD; 1,2,3,7,8-PCDD; 1,2,3,6,7,8-HxCDD; 2,3,4,7,8-PCDF; and PCB 126 (see Part I, Volume 12 2 and Section 4.4.3 of this document). With the exception of 1,2,3,6,7,8-HxCDD, the TEFs for 13 these chemicals are based on a number of different endpoints examined in multiple studies 14 performed in different laboratories (Table 1-4). The TEF for 1,2,3,6,7,8-HxCDD is based 15 heavily on a two-year bioassay in which rats were exposed to a mixture of 1,2,3,6,7,8-HxCDD 16 and 1,2,3,7,8,9-HxCDD. The TEFs for 2,3,4,7,8-PCDF and PCB 126 are similar to the mean 17 REP value for all in vivo endpoints and are similar to their REPs for tumor promotion. The TEF 18 for 1,2,3,7,8-PCDD is based largely on its REP for tumor promotion in rats, supported by studies 19 of its biochemical effects in a subchronic mouse study (DeVito et al., 1997). 20 From these data, it is clear that the chemicals that contribute approximately 80% to the 21 total human TEQ are well studied and that the assigned TEFs provide reasonable estimates of the 22 relative potency of these chemicals. In contrast, although some chemicals in the TEF 23 methodology have minimal data sets with which to reliably assess their relative potency, they do 24 not contribute substantially to the background human blood TEQ. 25 The ability of the TEF methodology to predict the biological effects ofmixtures 26 containing dioxin-like chemicals has been evaluated in a number of experimental systems. These 27 studies generally demonstrate that the assumption of additivity provides a reasonable estimate of 28 the dioxin-like potential of a mixture (Part II, Chapter 9, Section 9.4). Hamm et al. (2003) 29 demonstrated that a mixture of TCDD, PeCDD, TCDF, 1-PeCDF, 4-PeCDF, OCDF, and PCBs 30 77, 126 and 169 at doses approximating the relative abundance in the food supply, as described 31 by Birnbaum and DeVito (1995), induced a similar spectrum of reproductive toxicity in rat 32 offspring as does TCDD, and that the TEF methodology did reasonably well at predicting the 33 dose-response relationship of the mixture. A close relationship was evident for maternal EROD 34 enzyme induction between TCDD and the equivalent TEQ mixture, with a slightly lowered dose35 response for fetal effects from the mixture (~2 fold lower), attributed to decreased transfer of 12/23/03 1-8 DRAFT--DO NOT CITE OR QUOTE 1 mixture components to the offspring. A recent statistical modeling exercise of EROD enzyme 2 induction in the NTP bioassays (Toyoshiba et al., 2004) reported that from a statistical standpoint 3 the consensus WHO98TEFs were "significantly different from the maximum likelihood-based 4 estimates, but not very different in actual magnitude." Graphing of the non-log-scaled summary 5 data reported in Toyoshiba et al. (2004) reveals differences of less than 2 - 3 fold from predicted 6 TEQ-based activities, for individual congeners and the mixture. There are examples of 7 nonadditive interactions between dioxins and nondioxins. Both greater-than-additive and less8 than-additive interactions have been observed in these studies. In general the nonadditive 9 interactions between the dioxins and nondioxins have been observed at doses that are 10 considerably higher than present background human exposures (Part II, Chapter 9, Section 9.4). 11 There are a number of natural chemicals that bind and activate the aryl hydrocarbon (Ah) 12 receptor (AhR) and induce some dioxin-like effects. It has been proposed by some scientists that 13 these chemicals contribute significantly to total TEQ exposures and that these exposures far 14 outweigh those from PCDDs, PCDFs, and PCBs (Safe, 1995a). There are several limitations to 15 these analyses, as detailed in Part II, Chapter 9, Section 9.3.5. The hypothesis is built on AhR 16 binding studies and a few other in vitro studies that compared natural ligands to the dioxin-like 17 chemicals. Under these circumstances, neither biological half-life nor toxicity profile is 18 considered. 19 The in vivo data on the natural AhR ligands is limited to enzyme induction and a single 20 developmental study. Few if any toxicology studies demonstrating clear dioxin-like toxicities 21 have been published. The natural AhR ligands are rapidly metabolized and result in both 22 transient tissue concentrations and transient effects. More recent data demonstrate that these 23 potent in vitro AhR agonists (e.g., indolo[2,3-b]carbazole) neither elicit dioxin-like toxicity nor 24 alter the effects of dioxin in vivo (Pohjanvirta et al., 2002). This may occur because of short 25 persistence times in target organs or inadequate/inappropriate conformational changes induced as 26 a result ofAhR-ligand binding (Henry and Gasiewicz, 2003). The natural ligands also have their 27 own distinct biological effects that are independent of the AhR, and it is not clear as to the role of 28 the AhR in the biological effects of these chemicals. Because of the relative concentration of 29 these compounds in the daily diet, their in vitro binding characteristics, and the limited 30 toxicological information in vivo, this issue requires further research in order to better understand 31 the uncertainty surrounding the relative potential health effects of dioxin and related chemicals as 32 compared to natural AhR ligands. 33 One of the limitations of the use of the TEF methodology in risk assessment of complex 34 environmental mixtures is that the risk from nondioxin-like chemicals is not evaluated in concert 35 with that of dioxin-like chemicals. Another limitation of the TEF methodology is the application 12/23/03 1-9 DRAFT--DO NOT CITE OR QUOTE 1 of TEFs to nonbiological samples. The fate and distribution of PCDDs, PCDFs, and PCBs are 2 not necessarily related to their TEFs. Thus, the use of the TEF for assessing potential hazard and 3 risk based on dioxin-like compounds passing through nonbiological media must be done 4 cautiously. Fate and transport of the mixture and likelihood and route of exposure will have 5 important impacts on such assessments. Future approaches to the assessment of environmental 6 mixtures should focus on the development of methods that will allow risks to be predicted when 7 multiple mechanisms are present from a variety of contaminants coming into contact with 8 humans and other environmental receptors through multiple routes. 9 There are a number of uncertainties in the application of the TEF methodology which are 10 discussed in greater detail in Part II, Chapter 9. In 1998, the U.S. EPA and the U.S. Department 11 of the Interior sponsored a workshop on the use of the TEF methodology in ecological risk 12 assessment. This workshop involved panel members from academia, industry and state and 13 federal governments. This panel concluded that "the uncertainties associated with using RePs or 14 TEFs are not thought to be larger than other sources of uncertainty within the [ecological] risk 15 assessment process (e.g., dose-response assessment, exposure assessment, and risk 16 characterization)" (U.S. EPA, 2001a). In addition, despite the uncertainties in the TEF 17 methodology, the use of this methodology decreases the overall uncertainty of the risk 18 assessment. The panel had difficulty in quantitatively expressing the uncertainty in the TEF 19 methodology. While the panel supported the use of the TEF methodology, they also 20 recommended continued research focusing on a better understanding of the uncertainty in the 21 TEF methodology. 22 23 1.3. UNDERSTANDING EXPOSURE/DOSE RELATIONSHIPS FOR DIOXIN-LIKE 24 COMPOUNDS 25 Risk assessment requires the scaling of exposure/dose across endpoints and across 26 species. Given the many responses to TCDD and its congeners, the selection of dose metrics for 27 use in quantitative risk assessments is a complex problem. The biochemical and toxicological 28 responses to TCDD and related chemicals are initiated by their interaction with the Ah receptor. 29 Some responses, such as enzyme induction, require short periods (minutes to hours) of AhR 30 activation. Other responses, such as cancer, require prolonged (months to many years) activation 31 of this pathway. Still other responses, such as the developmental toxicities, require receptor 32 activation during specific windows of sensitivity. Because of the different mechanisms involved 33 in these diverse responses, it is unlikely that a single dose metric will be adequate for all of these 34 endpoints. 12/23/03 1-10 DRAFT--DO NOT CITE OR QUOTE 1 A number of studies have proposed a variety of dose metrics for a number of different 2 responses. These studies have taken different approaches, ranging from simple curve-fitting 3 exercises (Hurst et al., 2000; van Birgelen et al., 1996) to more complex physiologically based 4 pharmacokinetic (PBPK) modeling approaches (Jusko et al., 1995; Andersen et al., 1997; Kohn 5 et al., 1993; Portier and Kohn, 1996). Area under the curve (AUC) has been used traditionally in 6 the drug literature as a dose metric of choice when the dose and the time related to effects in 7 humans are known. 8 The choice of dose metric not only considers mechanistic data but must consider 9 pragmatic approaches as well. The use of the dose metric plays a role in its choice. Because of 10 differences in lifespan and uncertainties in the windows of sensitivity for various endpoints, 11 lifetime AUC may not be a useful dose metric for cross-species extrapolation in the risk 12 assessment of dioxin and related compounds. For instance, reported interspecies differences in 13 rat liver versus human lung cancer risks based on lifetime AUC are heavily influenced by 14 different lifespans of humans (~70 yrs) versus rats (~2 years), and are mitigated though the use of 15 peak levels or average concentrations (Aylward et al., 1996). Notably, there are no interspecies 16 differences in risk calculations between humans and rats when applying average body burden to 17 the same endpoint, all cancers combined, coupled with more detailed exposure data from the 18 epidemiology studies (see Table 5-4). Because cross-species scaling is not required when the 19 analysis is confined to humans, lifetime AUC has been used in the analysis of human cancer data 20 on TCDD (Becher et al., 1998) and may be a useful dose metric when applied to accidental or 21 occupational exposures. 22 The choice of dose metric is also dependent on the data available. A number of dose 23 metrics, such as AhR occupancy, induction of CYP1A2, and decreases in epidermal growth 24 factor (EGF) receptor (EGFR) have been proposed on the basis of PBPK models (Jusko et al., 25 1995; Andersen et al.,1997; Kohn et al., 1993; Portier and Kohn, 1996). Although these dose 26 metrics have been useful in hypothesis testing in experimental systems, they are not useful in 27 animal-to-human extrapolations due to the difficulty in measuring these parameters in humans. 28 In the following section, the strengths and weaknesses of a variety of proposed dose metrics are 29 presented. 30 12/23/03 1-11 DRAFT--DO NOT CITE OR QUOTE 1 1.3.1. Administered Dose 2 In experimental studies, animals are administered a defined dose through a variety of 3 routes. A default method used by EPA (U.S. EPA, 1992a, 1996) to estimate the human 4 equivalent dose when scaling across species is to use allometric scaling based on the following 5 equation: 6 7 Dosehuman = Doserat (W r a / ^ h u m a n f 25 8 (1-2) 9 where BW is the body weight in kilograms and Dose is the daily administered dose in rats or the 10 scaled human daily dose expressed as mg/kg/day, or in the case ofTCDD ng/kg/day. This 11 method, in the absence of data to select a more appropriate dose metric, is thought to scale 12 administered dose in such a way as to result in equivalent effective doses in humans and 13 experimental animals (U.S. EPA, 1992). Using this equation, a dose of 1ng TCDD/kg/day in a 14 0.35 kg rat would result in a scaled human dose of 0.27 ng TCDD/kg/day for a 70 kg human. If 15 this scaling method applies to TCDD and related chemicals, then 1ng TCDD/kg/day in the rat 16 should produce similar effective doses in a human exposed to 0.27 ng TCDD/kg/day, some 3.8 17 times lower. However, this method fails to take into account differences in the elimination half 18 life of the chemical in the two species. In the case of dioxin-like compounds, this is an important 19 consideration. 20 Assuming similar sensitivity between rats and humans at the tissue level, effective doses 21 should be a function of tissue concentration. Tissue concentrations of TCDD and related 22 chemicals are directly related to the concentration of TCDD in the body. The steady-state 23 concentration of TCDD in the body, or steady-state body burden, can be estimated in rats and 24 humans using the following equation. 25 26 Steady-state body burden (ng/kg) = [Dose (ng TEQ/kg)*half-life (days)] * F (1-3) 27 Ln(2) 28 29 where Dose is the daily administered dose, F is the fraction absorbed, and t1/2is the species- 30 specific half-life of TCDD. In the present example, we will assume that the species-specific half 31 life of TCDD is 25 days for rats and 2593 days for humans. We also assume for this illustration 32 that F is 50% for both human and animal studies. The fraction absorbed varies from ~50-100% 33 of administered dose, depending on dosing matrix (pellets, oil, food, breast milk; greater 34 variability from soil) and study species. For standardization elsewhere in Part III, Risk 35 Characterization, the Agency has adopted 50% absorption from animal food pellets and 80% 12/23/03 1-12 DRAFT--DO NOT CITE OR QUOTE 1 from human dietary intake (see Part II, Chapter 1; Poiger and Schlatter, 1986; Abraham et al., 2 1996). The fraction absorbed linearly impacts the calculation of resulting body burden, with 80% 3 absorption leading to a 1.6-fold higher value than 50% absorption. 4 Starting with an administered dose of 1ng/kg/day in rats and the scaled human dose of 5 0.27 ng/kg/day, the steady-state body burdens are presented in Table 1-5. The steady-state body 6 burden of TCDD using the scaled human dose is approximately 28 times that of the steady-state 7 body burden in the rat (Table 1-5). Using equation 1-3 to estimate equivalent steady-state body 8 burdens (i.e., 18 ng/kg), a human equivalent administered dose comparable to 1ng/kg/day 9 administered to the rat was estimated at 0.0096 ng/kg/day, over 100 times less. 10 Clearly, the default scaling method results in an estimated human equivalent dose that 11 produces much greater estimated human tissue concentrations (505 ng/kg) than the rat's tissue 12 concentration (18 ng/kg). The default scaling approach accounts for a difference of ~ 3.7 times, 13 based on allometric considerations, yet the half-life of TCDD in humans alone is approximately 14 100-fold greater than in rats. This exercise suggests that administered dose may not provide a 15 useful dose metric for cross-species extrapolation even if the dose is scaled using the EPA 16 default methodology. However, administered dose can be used to compare chronic exposures 17 between human populations in order to describe potential human health risks, because the species 18 differences in half-life would not exist in this case. Adjustments will still need to be made, 19 however, to compare short-term exposures expressed as intake as a function of body weight per 20 day to more typical daily intake values in the general population. 21 22 1.3.2. Area Under the Curve 23 AUC is frequently used as a dose metric for reversible responses of pharmaceutical 24 agents. Typically, these agents have half-lives on the order of minutes to hours. In addition, the 25 pharmacological actions of the drug and the length of time ofthe response is clearly defined in 26 both animals and humans. For example, for anesthetics, sleep time is used as the length of time 27 for determining the AUC. In essence, plasma concentrations are readily determined and the time 28 span is easily defined. In contrast, TCDD has a prolonged half-life in both humans and 29 experimental animals and some of the adverse effects that are of concern in the hazard 30 characterization are not reversible responses. Because of these differences it is unclear whether 31 the AUC is the best dosemetric. 32 Mechanistic considerations suggest that AUC may be a useful dose metric for 33 carcinogenesis. TCDD and related chemicals are thought to induce tumors through promotional 34 mechanisms as opposed to acting as direct initiators. The promotional effects of TCDD and 35 related chemicals are associated with altered gene expression, resulting in alterations in growth 12/23/03 1-13 DRAFT--DO NOT CITE OR QUOTE 1 and differentiation. This promotional process requires sustained tissue concentrations of TCDD 2 sufficient to maintain increased gene expression. One recent study examined AUC as a dose 3 metric for the tumor promotional responses of TCDD. Kim et al. (2003) compared AUC and 4 peak concentrations in rats as a dose metric for liver tumor promotion. Animals receiving a 5 single high exposure to TCDD had greater numbers of altered hepatic foci than animals receiving 6 repeated low dose exposures, even though the AUC was equivalent between the two exposures. 7 These data suggest that the peak concentrations of TCDD may play a significant role in TCDD 8 carcinogenicity and that future dose-response modeling exercises should incorporate measures of 9 dose timing and peak concentrations. 10 It is possible that AUC could be an appropriate dose metric for cancer in humans, and it 11 may also involve the incorporation of a threshold concentration (Hays et al., 1997). However, 12 the use of AUC for species extrapolation for TCDD is more complicated. Although blood or 13 plasma concentrations of TCDD can be determined in both humans and animals, the 14 determination of the time span for which the AUC is to be calculated is much less certain. For 15 some of the toxic responses to TCDD, such as induction of cleft palate, the window of sensitivity 16 is clearly defined in rodents and humans. For other responses, such as the developmental 17 reproductive alterations observed in male rats, the window of sensitivity has been narrowed to 18 exposures between gestational day 15 and 20 in the rats, but the human window of sensitivity is 19 uncertain. For many of the chronic toxic effects of TCDD, the length of time required to induce 20 the response remains uncertain in both experimental animals and humans. In order to apply 21 AUC for species comparisons of sensitivity to TCDD, one must have a better understanding of 22 the species differences in the windows of sensitivity to the various biological effects of TCDD. 23 In addition, differences in lifespan also must be considered. Brody and Reid (1967) 24 proposed that the biological activity of a drug is related to its plasma concentrations. If animals 25 and humans had the same plasma concentrations for their entire lives, the human AUC would be 26 greater because humans have a longer half-life of elimination for TCDD. However, because the 27 plasma concentrations would be the same, according to Brody and Reid (1967), the responses 28 should be similar. Hence, in order to use AUC for chronic toxicities, such as cancer, a correction 29 for the difference in lifespan must be applied. Typically, this involves the derivation of a lifetime 30 average serum lipid concentration, which is calculated by dividing the AUC by the time period of 31 exposure (Aylward et al., 1996). An estimation of the average daily AUC is directly related to 32 steady-state body burdens. Hence, once the AUC is corrected for life-span differences, these 33 values are equivalent to steady-state body burdens. 34 Although AUC may not be an appropriate dose metric for animal-to-human 35 extrapolations, it may be a useful tool for comparing populations exposed to high concentrations 12/23/03 1-14 DRAFT--DO NOT CITE OR QUOTE 1 of dioxins over a short period of time to the background population. Becher et al. (1998) and 2 Steenland et al. (2001) used this approach to examine dose-response relationships for cancer in 3 occupationally exposed cohorts. One difficulty in determining AUC is the accuracy of the intake 4 measurements. Past exposures through the diet are uncertain, although they have been estimated 5 (Pinsky and Lorber, 1998). Future exposures are thought to be decreasing, although the exact 6 magnitude of this decrease is uncertain. Hence, determination of AUC carries a number of 7 uncertainties that must be considered. 8 9 1.3.3. Plasma or Tissue Concentrations 10 Brodie and Reid (1967) have argued that the response to a drug is determined by the 11 amount bound to its biological receptor, and because the drug-receptor complex is in dynamic 12 equilibrium with the free drug in the plasma, the biological response of a drug will be related to 13 its plasma concentrations. There is no reason to believe that this relationship will not be true for 14 TCDD and related chemicals. However, there are several data gaps that may prohibit the use of 15 plasma or blood concentrations for species extrapolation. First, few animal studies have 16 determined blood or plasma concentrations of TCDD, particularly in the subchronic, chronic, and 17 lifetime exposures. PBPK models can be used to estimate blood concentrations and should 18 provide reasonable estimates of these values. In contrast, the human exposure data are based 19 predominantly on blood, serum, or plasma dioxin concentrations. 20 One limitation of the human data is that it is mostly presented on a lipid-adjusted basis. 21 Hence, in order to compare the human and animal plasma or blood concentrations, one would 22 have to first estimate the blood concentrations in the animals using a PBPK model. Then, either 23 the animal data would have to be expressed as a lipid basis or the human data would have to be 24 expressed as a wet-weight basis. In either case, assumptions of the percent lipid in the blood 25 would have to be applied, as would a number of other assumptions typically used in the 26 construction of PBPK models. Recent work by Salvan et al. (2001) has attempted to account for 27 some of these assumptions in an analysis of cancer mortality in the National Institute for 28 Occupational Safety and Health (NIOSH) cohort (Steenland et al., 1999, 2001) using data on age29 related body mass index (BMI) and historical background exposures and tissue half-lives from 30 the Ranch Hand cohort (Michalek and Tripathi, 1999). 31 The use of tissue concentrations as a dose metric has also been examined by van Birgelen 32 et al. (1996) and Hurst et al. (1998, 2000). van Birgelen et al. presented data demonstrating that 33 target tissue concentrations provided an accurate prediction of enzyme induction regardless of the 34 exposure scenario (i.e., acute vs. subchronic). Similarly, Hurst et al. (2000) presented data 35 demonstrating that fetal tissue concentrations of TCDD on gestation day 16 predicted decreases 12/23/03 1-15 DRAFT--DO NOT CITE OR QUOTE 1 in sperm counts, delays in puberty in males, urethra-phallus distance, and the incidence of 2 vaginal threads in rats prenatally exposed to TCDD on either gestational day 9 or 15. These data 3 suggest that target tissue concentrations may be a reasonable dose metric for these responses. 4 Although target tissue concentrations may aid in estimating risks, these data are unlikely to be 5 collected in humans in sufficient numbers to be useful, particularly for fetal concentrations. 6 Plasma (or serum) concentrations are also a useful tool for comparing exposures in 7 different human populations. Application of plasma concentration as a dose metric for species 8 extrapolation requires some level of assumptions, as described above, but reasonable 9 comparisons could be made, particularly for steady-state in humans and animals. Comparing 10 plasma or blood concentrations following acute exposures in experimental animals directly to 11 steady-state human blood or plasma concentrations is problematic. 12 One problem with the use of plasma, blood, or target tissue concentrations as a dose 13 metric is the limitations of current human PBPK models to predict these values on the basis of 14 changes in intake patterns. Further work will be required to develop such models. 15 16 1.3.4. Steady-State Body Burdens 17 Body burden is defined as the concentration of TCDD and related chemicals in the body 18 and is typically expressed as ng/kg body weight. In animals, these values are calculated from 19 studies at or approaching steady-state. These values are calculated on the basis of knowledge of 20 the species-specific half-life and the exposure or they are estimated on the basis of the TCDD 21 tissue concentration, the size of the tissues, and the weight of the animal. In humans the values 22 are typically presented as steady-state body burdens and are estimated on the basis of an intake 23 rate and the half-life of TCDD in humans. Alternatively, body burdens in humans are estimated 24 on the basis of lipid-adjusted serum or adipose tissue TCDD or TEQ concentrations (See Part I, 25 Volume 2, Chapter 4). 26 Steady-state body burdens provide a useful dose metric for several reasons. First, tissue 27 and blood concentrations are directly related to body burdens. Thus, body burdens are surrogates 28 for tissue concentrations. Second, the differences in the half-life of TCDD between species are 29 accounted for, because these body burdens are estimated at steady-state conditions. Third, 30 DeVito et al. (1995) have demonstrated that for a multitude of in vitro, biochemical, and toxic 31 responses, including chloracne and cancer, species have similar rates of responses when dose is 32 expressed on a body burden basis. Finally, body burdens provide flexibility, because they can be 33 estimated on the basis of either intake rates or on measured tissue concentrations. 34 Use of steady-state body burdens also has some limitations. In order to estimate steady35 state body burdens from lipid-adjusted tissue concentrations, an assumption of the percent body 12/23/03 1-16 DRAFT--DO NOT CITE OR QUOTE 1 fat must be used. In the reassessment, a value of 25% has been used for humans. It should be 2 noted that there are human populations with body fat compositions as low as 10% and greater 3 than 35%. Also, when estimating the body burden on the basis of intake rates and half-lives, the 4 uncertainty ofthese parameters should be considered. In the reassessment, the estimated current 5 steady-state body burden of approximately 5 ng TEQDFP-WHO98/kg is based on measured serum 6 concentrations from several populations in the mid 1990's. 7 Although measured concentrations should eliminate some of the uncertainties in 8 estimates using intake rates and half-life assumptions, it is likely that these measured values 9 represent a past history of higher exposure, and we must anticipate a continued downward trend 10 to represent a "true" lifetime average concentration associated with current dose intake rates. 11 Caution must be used when using body burden as a dose metric for species extrapolation when 12 comparing short-term animal studies to steady-state human exposures. Under acute exposure 13 conditions in the animals, the relationship between tissue concentrations and body burden may 14 not be the same as under the steady-state conditions. 15 16 1.3.5. Mechanistic Dose Metrics 17 Several groups have proposed a variety of dose metrics based on mechanistic 18 considerations, such as concentration of occupied AhR (Jusko, 1995), induced CYP1A2 19 (Andersen et al., 1997; Kohn et al., 1993) and reduced EGFR (Portier and Kohn, 1996). 20 Although these dose metrics are intellectually appealing, it must be kept in mind that they are 21 still hypothesized dose metrics and require further research to demonstrate their utility for cross 22 species extrapolations. In addition, these dose metrics are unlikely to be measured in sufficient 23 human samples to be useful. 24 25 1.3.6. Summary 26 A variety of dose metrics have been proposed for estimating potential human health 27 effects following exposure to dioxins. Many ofthem, such as tissue concentrations and the 28 mechanistic dose metrics, have practical limitations that inhibit their use. Others, such as AUC, 29 have limited utility for species extrapolations because of our limited understanding of the concept 30 of physiological time. Some, such as AUC and administered dose, can be used to compare 31 different human exposures, but are not necessarily suitable for cross-species extrapolations. 32 Others, such as steady-state body burdens or blood concentrations, are useful for species 33 extrapolations because they are directly related to tissue concentrations and can be estimated in 34 both animals and humans. All of these dose metrics require more research to improve cancer and 12/23/03 1-17 DRAFT--DO NOT CITE OR QUOTE 1 noncancer risk prediction. This research could include efforts to quantify impacts of dose timing, 2 peak concentrations, and AUC above a baseline. 3 The use of any of these dose metrics requires a number of assumptions, discussed above 4 and in various chapters in Parts I and II. The choice of dose metric requires an understanding of 5 the data available and their application in the intended use of the dose metric. Future research 6 efforts could provide better guidance in choosing the dose metrics for dioxins and related 7 chemicals. However, in the meantime, the use of steady-state body burdens can provide a 8 reasonable description of dose for use in species extrapolations and risk assessments for many 9 chronic effects and is clearly preferable to intake levels. 12/23/03 1-18 DRAFT DO NOT CITE OR QUOTE 21 Table 1-1. The toxic equivalency factor (TEF) scheme for I-TEQ F 3 Dioxin congener TEF Furan congener TEF 14068957 2111111,,,,,,,3222222,,,,,,,7333333,,,,,,,8774644-,,,,,,877866T,-,,,,C98877P---,,De88HHHC,-D9xxxHD-CCCpODDDDCCDDDDDDD 0000001.......1110500101 2221111111,,,,,,,,,,3332222222,,,,,,,,,,7443333333,,,,,,,,,,8767446744-,,,,,,,,,878677867T-,-,,,,,,C8889787PP----,,,Dee898HHHHCC--,F9xxxxHHDD-CCCCppOFFDDDDCCCFFFFDDDFFF 0000000000..........111110050011051 11111111257364 aNote that the scheme does not include dioxin-like PCBs. The nomenclature for this scheme is I-TEQDF, where "I" represents "International," TEQ represents the 2,3,7,8-TCD D toxic equivalence of the mixture, and the subscript DF indicates that only dioxins (D) and furans (F) are included in the TEF scheme. 1189 Table 1-2. The toxic equivalency factor (TEF) scheme for TEQDFP-WHO94a 20 Dioxin congener TEF Furan congener TEF DioPxCinB-like TEF 2222222212573684 2111111,,,,,,,3222222,,,,,,,7333333,,,,,,,8746744-,,,,,,86787T6-,,,,,C89787P---,,De88HHHC,D-9xxxHD-CCCpODDDDCCDDDDDDD 0000001....0...111050011 2221111111,,,,,,,,,,3332222222,,,,,,,,,,7443333333,,,,,,,,,,8767446744-,,,,,,,,,878,77867T6-,-,,,,,C8,88978PP7----,,Dee,89HHHH8CC--F,xxxxHHDD9CCCC-ppFFODDDDCCCFFFFDDDFFF 0000000000..........111115000011051 PPPPPPPPPPPPPCCCCCCCCCCCCCBBBBBBBBBBBBB-------------11111111111172012655617887358696774009 0000000000000.............1000000000000100000000000000000000001111100555511 333332120394 aTeqhueivnaolmenecnycloaftuthree fmorixtthuirse,TaEnFdstchheesmuebsicsriTpEtQDDFFPP-WindHiOca9t4e,swthheartedTioExiQnsre(pDre),sefunrtasntshe(F2),,3a,7n,d8 d-TioCxDinD-litkoexiPcCB s (P) are included in the TEF scheme. The subscript 94 following WHO displays the year changes were made to the TEF scheme. 12/23/03 1-19 DRAFT--DO NOT CITE OR QUOTE 21 Table 1-3. The toxic equivalency factor (TEF) scheme for TEQDFP-WHO98a 3 Dioxin congener TEF Furan congener TEF DioPxCinB-like TEF 1110468957 2111111,,,,,,,3222222,,,,,,,7333333,,,,,,,8746744-,,,,,,8778T66-,,,,,C88977P---,,De88HHHC,-D9xxxHD-CCCpODDDDCCDDDDDDD 0000011.......11100001001 2221111111,,,,,,,,,,3332222222,,,,,,,,,,7443333333,,,,,,,,,,8767446744-,,,,,,,,,878677867T-,-,,,,,,C8889787PP----,,,Dee898HHHHCC--,F9xxxxHHDD-CCCCppOFFDDDDCCCFFFFDDDFFF 0000000000..........1111100500115001 PPPPPPPPPPPPCCCCCCCCCCCCBBBBBBBBBBBB------------8111711111111201726556183586967749 000000000000............10000000000010000000000000000000011111105551 2222221111111112350234574689 aTeqhueivnaolmenecnycloaftutrhee fmorixtthuirse,TEanFdstchheemsuebsiscrTipEtQDDFFPP-WindHicOa9t8e,swthheartedTioExQinsre(pDr)e,sefunrtasntshe(F2),,3a,7n,d8-dTioCxDinD-litkoexiPcCBs (P) are included in the TEF scheme. The subscript 98 following WHO displays the year changes were made to the TEF scheme. Note that the changes to the TEFs since 1994 are as follows: ffoorr O1,C2,D3,D7,,8t-hPeenCeDwDW, tHheOnTewEFWisH0O.0T00E1F aisnd1tahnedI-tTheEFI-TisE0F.0is010;.5; ffoorr OPCCBDF7,7,ththeennewewWTHEOF iTsE0F.0i0s001.;0001 and the I-TEF is 0.001; the addition of PCB 81 (i.e., 3,4,4',5-TCB); and for the two di-ortho substituted HpCBs in the 1994 TEF scheme (i.e., PCBs 170 and 180), no TEFs have been assigned in the new WHO TEF scheme. 26 27 12/23/03 1-20 DRAFT--DO NOT CITE OR QUOTE 321 Tfoarbtlhee1m-4a. joTrhetorxaicngeequoifvtahleenicnyvcivoontrreilbautitvoerspotency estimates (REP) values 4 Chemical vNivuomebnedrpoofinints R(amngeaenof RstEdP)s suebncNdhpuroominnbitcesrsftoruofdmies (mReRaannEgPessotfd) TEF 65 P1C,2D,3D,7,8- 22 (00.5.16-00..292) 16 (0.05.319-00..924) 1 87 2P,C3D,4F,7,8- 40 (00..0418-04..70) 20 (00.2.0018-00..163) 0.5 109 81-,2H,3x,C6D,7D, 3 0.015-0.16 1 0.04 0.1 11 PCB 126 62 (00..020024-00..2908) 1111156234 TEF = toxic equivalency factor 31 (00..10304-00..1183) 0.1 12/23/03 1-21 DRAFT DO NOT CITE OR QUOTE 321 Tanadblheu1m-5a.nCsaomparison of administered dose and body burden in rats 4 addRmobasuit(enrA/didbs)aetoeindlryyed Hadudmbmousiae(nrnB/dibs)estoncedarbyleedd adedqmbHouusiu(einrvCm/dibas)eatolneendnrcyetd Rhrs(auadcAtatmoi-/losBteaeod)on-f Rhr(auaAttmi/-oCtao)on-f equivalent Dose 65 D(nogs/ekg/day) 1 0.27 0.0096 3.7 104 222221111111111113220034574689897 B(nogd/kygb)urden 18 505 18 0.036 1 aTinhdiiscamteastrtihxactoamdpoasreesofth1enegf/fkegct/sdaoyf tdoifaferraetnlteiandtsertsopaecsiteesadscya-slitnagtefbaoctdoyrsbbuerdtwenee(nBBra)tsoafn1d8hnugm/kagn,s.usCinogluthmen A fsocramlinuglafBacBto=rshtaolfc-olinfev*edrtotshee*raabtsdoorpsteioton afrhauctmioann(e0q.5u)i/vlanl2e.ntCdoolsuem. nCs oBluamnnd BC uthseens buosedydiwffeeirgehntt tionttehresp3e/c4iepsower aesquthiveailnetnetrshpuemciaens ssccaalleidngdofascetoorf t0o.2c7onnvge/krtgt/hdeayr,atwdhoicseh oinf t1unrng/ckogr/rdeasypo(nfrdosmtothaehcuomluamnnboAdydobsuerrdoewn)otfo5t0h5e ng/kg bbausreddenonasththeehiunmtearsnpheaclife-slifsecaolifn7g.1faycetoarrstoancdonfv=er0t.5the(ursaetdbiondtyhibsutradbelen foofr1c8onnsgi/sktgen(cfyro).mCcoolluummnn CA ubsoedsybboudryden rboowd)y tboutrhdeene,qiu.eiv.,a0le.0n0t 9168 nngg//kkgg/dBaBy.inThhuemfaifntsh,caonldumthnendidveidrievsescothluemhnumAarnesduolstse bthyatcowluomulnd Bcorrerseuspltos,ndrevweiathlinthgis tchoaltumthne BCWre3s/u4litnst,erresvpeeacliiensgfathcatot rwlheeadnsbtooday rbaut/rhduemn aisnursaetido aosfth3.e7-infoteldrs.peTchieeslassctaclionlgumfanctdoirvtihdeesractodluomseniAs obvyer 100 times the equivalent human dose. bAssumes administered dose scales across species as a function of BW3/4 cAssumes administered dose scales across species as a function of equivalent body burdens 12/23/03 1-22 DRAFT--DO NOT CITE OR QUOTE 2,3,7,8-Tetrachlorodibenzo-p dioxin L s/.a-Tetractiloffuiibaizofuriii 1,2,3,7,8 -Pentacn lorod ibenzo-p-dioxin -:;3 ,4,7,8-P enta ch! orodi benzoftira n 3,3,4,4,5,ff-Hexachlorobiphenv! i,3 ,4,4, & Pentach loros? ip henyi 1 Figure 1-1. Chemical structure of 2,3,7,8-TCDD and related compounds. 12/23/03 1-23 DRAFT--DO NOT CITE OR QUOTE 1 2. EFFECTS SUMMARY 2 3 Since the identification in 1957 of 2,3,7,8-TCDD as a chloracnegen, more than 5000 4 publications have discussed its biological and toxicological properties. A large number of the 5 effects of dioxin and related compounds have been discussed in detail throughout the chapters in 6 Part II of this assessment. These discussions illustrate the wide range of effects produced by this 7 class of compounds. The majority of effects have been identified in experimental animals; some 8 have also been identified in exposed human populations. Although past EPA risk assessments 9 have focused on cancer estimates based on extrapolation models as the major concern for dioxin 10 and related compounds, more recent data suggest that noncancer effects may be occurring at or 11 near human background steady-state body burden levels in animals and in humans. Evaluation 12 of noncancer effects and their relationship to past and current body burdens and intake levels is 13 an important feature of this reassessment. Direct comparisons between various noncancer effects 14 and cancer in animals and humans and exposures of interest are presented in the form of margins 15 ofexposure (MOE). 16 Cross-sectional studies have been conducted to evaluate the prevalence or extent of 17 disease in living 2,3,7,8-TCDD-exposed groups (Suskind and Hertzberg, 1984; Moses et al., 18 1984; Lathrop et al., 1984, 1987; Roegner et al., 1991; Grubbs et al., 1995; Sweeney et al., 1989; 19 CDC Vietnam Experience Study, 1988; Webb et al., 1989; Ott and Zober, 1994). The limitations 20 of the cross-sectional study design for evaluating hazard and risk are discussed in Part II, Chapter 21 7b, Section 7.11. Many of the earliest studies were unable to define exposure-outcome 22 relationships owing to a variety of shortcomings, including small sample size, poor participation, 23 short latency periods, selection of inappropriate controls, and the inability to quantify exposure to 24 2,3,7,8-TCDD or to identify confounding exposures. 25 Cohort and case-control studies have been used to investigate hypothesized increases in 26 malignancies among the various 2,3,7,8-TCDD-exposed populations (Fingerhut et al., 1991a, b; 27 Manz et al., 1991; Eriksson et al., 1990). In more recent analyses of occupational cohorts 28 (Steenland et al., 1999; Ott and Zober, 1996; Flesch-Janys et al., 1998), cross-sectional studies of 29 U.S. chemical workers (Sweeney et al., 1989), U.S. Air Force Ranch Hand personnel (Roegner et 30 al., 1991; Grubbs et al., 1995), and Missouri residents (Webb et al., 1989), serum or adipose 31 tissue levels of 2,3,7,8-TCDD were measured to evaluate 2,3,7,8-TCDD-associated effects in 32 exposed populations. The ability to measure tissue or serum levels of 2,3,7,8-TCDD for all or a 33 large sample of the subjects confirmed exposure to 2,3,7,8-TCDD and permitted the investigators 34 to test hypothesized dose-response relationships. 35 12/23/03 2-1 DRAFT--DO NOT CITE OR QUOTE 1 A large number of effects of exposure to TCDD and related compounds have been 2 documented in the scientific literature. Although many effects have been demonstrated in 3 multiple species (see Table 2-1), other effects may be specific to the species in which they are 4 measured and may have limited relevance to the human situation. Although the potential 5 species-specific responses are an important consideration for characterizing potential hazard, all 6 the observed effects of 2,3,7,8-TCDD illustrate the multiple sequelae that are possible when 7 primary impacts are at the level of signal transduction and gene transcription. Even though not 8 all observed effects may be characterized as "adverse" (i.e., some may be responses within the 9 normal range or adaptive or compensatory and ofunknown or neutral consequence), they 10 represent a continuum of response expected from the fundamental changes in biology caused by 11 exposure to dioxin-like compounds. As discussed in the following sections, the doses associated 12 with this plethora of effects are best compared across species using a common measurement unit 13 of steady-state body burden of 2,3,7,8-TCDD and other dioxin-like compounds, as opposed to 14 the level or rate of exposure/intake. 15 The low end of the range of experimental lowest-observed-adverse-effect levels 16 (LOAELs), no-observed-adverse-effect levels (NOAELs), and effective doses at the 1% response 17 level (ED01s) for critical endpoints from animal studies is compiled in Table 5-6 and Appendix 18 A. These selected endpoints cover a spectrum from overt toxicity (e.g., fetal mortality, cancer), 19 through developmental and reproductive toxicity endpoints, to enzyme induction as a marker of 20 intracellular dioxin activity. Many of the studies report multiple statistically significant effects 21 related to dioxin exposure. From these results, the values tabulated were selected on the basis of 22 the lowest dose at which significant effects occurred--findings that were generally highlighted 23 by the authors of the publication. In the event that multiple endpoints were elicited at the same 24 dose, the effect considered of most consistency across studies and relevance to human risk 25 assessment was selected (e.g., decreased sperm counts). 26 A variety ofmethods were employed to estimate body burdens corresponding to the 27 LOAELs/NOAELs/ED01s, including using measured body burden and lipid concentration data, 28 absorption adjustments for single-dose studies, and first-order pharmacokinetic modeling 29 estimates using absorbed dose and halflife. Additional details on study design, endpoint 30 selection, and calculation of body burdens are included in Appendix A and can also be found in 31 Sections 5.2 and 6.0 of this document and in other chapters of the dioxin reassessment. Human 32 equivalent intakes for the body burden endpoints were calculated according to formulae 33 discussed in Part II, Chapter 8 of this report and are displayed in order corresponding to the 34 preceding three results columns in Table 5-6 and Appendix A. These comparisons result in the 35 finding that, when animal data associated with effects at the low end of the range of experimental 12/23/03 2-2 DRAFT--DO NOT CITE OR QUOTE 1 observation (NOAELs/LOAELs/ED01s) are compared to current average human body burdens of 2 approximately 5 ng TEQFP-WHO98/kg--representing lifetime average intake values of 3 approximately 3 pg TEQDFP-WHO98/kg/day--or to current intake values of 1pg TEQDFP4 WHO /kg/day, relatively small MOEs are obtained. Similarly, some human noncancer effects 5 (e.g., developmental delay, neurobehavioral outcomes, and impact on thyroid function in Dutch 6 children) and cancer outcomes show comparatively small MOEs. 7 In the following sections which discuss these general effects, the focus is on developing 8 an understanding of dioxin hazard and risk. This discussion is, by its nature, selective of findings 9 that inform the risk assessment process. Readers are referred to the more comprehensive 10 chapters for further discussion of the broader epidemiologic and toxicologic database. 11 12 2.1. BIOCHEMICAL RESPONSES (Cross-reference: Part II, Chapters 2, 3, and 8) 13 As described later in Section 3, mechanistic studies can reveal the biochemical pathways 14 and types of biological events that contribute to adverse effects from exposure to dioxin-like 15 compounds. For example, much evidence indicates that 2,3,7,8-TCDD acts via an intracellular 16 protein, AhR, which is a ligand-dependent transcription factor that functions in partnership with 17 a second protein (known as the AhR nuclear translocator, or Amt) to alter gene expression. In 18 addition, receptor binding may result in release of cytoplasmic proteins that, in turn, alter the 19 expression or activity of cell-regulatory proteins (e.g., increases in Src activity). Therefore, from 20 a mechanistic standpoint, TCDD's adverse effects appear likely to reflect alterations in gene 21 expression or protein activity that occur at an inappropriate time and/or for an inappropriate 22 length of time. Mechanistic studies also indicate that several other proteins (e.g. hif a, Rb, relA, 23 src, sim, etc.) contribute to TCDD's gene-regulatory effects and that the response to 2,3,7,824 TCDD involves a relatively complex interplay between multiple genetic and environmental 25 factors. This model is illustrated in Figure 2-1 (from Part II, Chapter 2). Comparative binding 26 studies and other data suggest that biochemical events observed in response to TCDD exposure 27 are also seen with other dioxin-like compounds in proportion to their TEFs. 28 Comparative data from animal and human cells and tissues suggest a strong qualitative 29 similarity across species in response to dioxin-like chemicals. This further supports the 30 applicability to humans of the generalized model of initial events in response to dioxin exposure. 31 These biochemical and biological responses are sometimes considered adaptive or reflective of 32 exposure to dioxin-like compounds. When they are seen within normal homeostatic limits, these 33 biochemical changes are often not considered adverse in and of themselves. However, many of 34 these changes are potentially on a continuum of dose-response relationships that leads to adverse 35 responses and, considering the potential to shift population distributions in response, may be of 12/23/03 2-3 DRAFT--DO NOT CITE OR QUOTE 1 concern. Because of the distribution of responses and sensitivity within a population, it is 2 possible that adaptive responses for some are frankly adverse for those at the tails of the 3 distribution. For this reason, a balanced approach must be used when describing these events, 4 recognizing that they may be adaptive or simply biomarkers of exposure to dioxin-like 5 compounds, or they may represent early events in a pathway resulting in a risk of adverse effects 6 in some humans. 7 If, as we can infer from the evidence, 2,3,7,8-TCDD and other dioxin-like compounds 8 operate through these mechanisms, there are constraints on the possible models that can plausibly 9 account for dioxin's biological effects and also on the assumptions used during the risk 10 assessment process. For instance, the linear relationship expected between ligand concentration 11 and receptor binding may or may not be reflective of dose-response relationships for downstream 12 events requiring complex interactions of other regulatory proteins with the activated receptor. 13 Puga et al. (2000a) have shown that interactions of TCDD with the AhR alters expression of over 14 300 genes in a single cell line at one time point and one dose. These data suggest that 15 mechanisms of toxic action may be very complicated and that additional research will be 16 necessary to further unravel the mechanistic relationships underpinning dioxin's toxicity. 17 Mechanistic knowledge of dioxin action may also be useful in other ways. For example, 18 knowledge of genetic polymorphisms that influence 2,3,7,8-TCDD responsiveness may also 19 allow the identification of individuals either refractory to or at particular risk from exposure to 20 dioxin. In addition, knowledge of the biochemical pathways that are altered by dioxin-like 21 compounds may help in the development of approaches to intervention or to drugs that can 22 prevent dioxin's adverse effects. 23 As described in Part II, Chapter 2, biochemical and genetic analyses of the mechanisms 24 by which dioxin modulates particular genes have revealed the outline of a novel regulatory 25 system whereby a chemical signal can alter cellular regulatory processes. Future studies of 26 dioxin action have the potential to provide additional insights into mechanisms of mammalian 27 gene regulation that are of relatively broad interest. Additional perspectives on dioxin action can 28 be found in several recent reviews (Birnbaum, 1994a, b; Schecter, 1994; Hankinson, 1995; 29 Schmidt and Bradfield, 1996; Rowlands and Gustafsson, 1997; Gasiewicz, 1997; Hahn, 1998; 30 Denison et al., 1998; Wilson and Safe, 1998; Schecter and Gasiewicz, 2003). 31 The ability of 2,3,7,8-TCDD and other dioxin-like compounds to modulate a number of 32 biochemical parameters in a species-, tissue-, and temporal-specific manner is well recognized. 33 Despite the ever-expanding list of these responses from the past 20 years and the elegant work on 34 the molecular mechanisms mediating some of these, there still exists a considerable gap between 35 our knowledge of individual biochemical changes and the degree to which they are related to the 12/23/03 2-4 DRAFT--DO NOT CITE OR QUOTE 1 more complex biological and toxicological endpoints elicited by these chemicals. A framework 2 for considering these responses in a mode of action context is discussed later in this document. 3 TCDD-elicited activation of the AhR has been clearly shown to mediate altered 4 transcription of a number of genes, including several oncogenes and those encoding growth 5 factors, receptors, hormones, and drug-metabolizing enzymes. Table 2-2 provides an illustrative 6 list of gene products whose regulation or activity is modulated by 2,3,7,8-TCDD. Although this 7 list is not meant to be exhaustive, it demonstrates the range of potential dioxin impacts on 8 pathways with potential to lead to adverse effects. 9 As discussed in Part II, Chapter 2, it is possible that the TCDD-elicited alteration of 10 activity of these genes may occur through a variety of mechanisms. The transcription of some 11 genes may be directly regulated by the activated AhR. Other alterations in gene expression may 12 be secondary to the initial biochemical events directly regulated transcriptionally by the AhR. 13 Some of the changes may also occur by post-transcriptional processes such as messenger 14 ribonucleic acid (mRNA) stabilization or altered protein phosphorylation (Gaido et al., 1992; 15 Matsumura, 1994). Nie et al. (2001) described cross-talk between Arnt-requiring pathways 16 resulting in interactions between the AhR and the hypoxia signaling pathways. Thus, the 17 molecular mechanisms by which many if not most of the biochemical processes discussed herein 18 are altered by 2,3,7,8-TCDD treatment remain to be determined. Nevertheless, it is assumed, 19 based on the cumulative evidence available, that all of these processes are mediated by the 20 binding of 2,3,7,8-TCDD to the AhR. Although evidence has accumulated for the involvement 21 of the AhR in many but not all of these processes, structure-activity relationships, genetic data, 22 and reports from the use of biological models such as "knockout" mice that are lacking the AhR 23 (AhR'Q are consistent with the involvement of the AhR as the initial step leading to these 24 biochemical alterations. In fact, for every biochemical response that has been well studied, the 25 data are consistent with the particular response being dependent on the AhR. 26 The dioxin-elicited induction of certain drug-metabolizing enzymes such as CYP1A1, 27 CYP1A2, and CYP1B1 is clearly one of the most sensitive responses observed in a variety of 28 different animal species, including humans, and it occurs at body burdens as low as 3-8 ng 29 TCDD/kg in animals (see Part II, Chapter 8, Sections 8.3 and 8.4). These and other enzymes are 30 responsible for the metabolism of a variety of exogenous and endogenous compounds. Several 31 lines of experimental evidence suggest that these enzymes may be responsible for either 32 enhancing or protecting against the toxic effects of a variety of agents, including known 33 carcinogens as well as endogenous substrates such as hormones. These interactive effects are 34 dependent on the compounds and the experimental system examined. 12/23/03 2-5 DRAFT--DO NOT CITE OR QUOTE 1 Several reports (Kadlubar et al., 1992; Esteller et al., 1997; Ambrosone et al., 1995; 2 Kawajiri et al., 1993) provide evidence that human polymorphisms in CYPIA1 and CYPIA2 that 3 result in higher levels of enzyme activity are associated with increased susceptibility to 4 colorectal, endometrial, breast, and lung tumors. Also, exposure of AhR-deficient ("knockout") 5 mice to benzo[a]pyene (BaP) results in no tumor response, suggesting a key role for the 6 AhR--and perhaps CYPIA1 and CYPIA2--in BaP carcinogenesis (Dertinger et al., 1998; 7 Shimizu et al., 2000). Modulation of these enzymes by dioxin may play a role in chemical 8 carcinogenesis. However, the exact relationship between the induction of these enzymes and any 9 toxic endpoint observed following dioxin exposure has not been clearly established. 10 In addition to what is known about the P450 isozymes (CYP1A1, CYP1A2, and 11 CYP1B1), there exists some evidence from experimental animal data to indicate that the 12 alteration of certain other biochemical events might have a more direct relationship to sensitive 13 toxic responses observed following TCDD exposure. Some ofthese may be relevant to 14 responses observed in humans, and further work in these areas is likely to lead to data that would 15 assist in the risk characterization process. For example, changes in EGFR have been observed in 16 tissues from dioxin-exposed animals and humans (see Part II, Chapter 3, Section 3.5, and 17 Chapter 6, Section 6.5 ). EGF and its receptor possess diverse functions relevant to cell 18 transformation and tumorigenesis, and changes in these functions may be related to a number of 19 dioxin-induced responses, including neoplastic lesions, chloracne, and a variety of reproductive 20 and developmental effects. Likewise, the known ability of TCDD to directly or indirectly alter 21 the levels and/or activity of other growth factors and hormones, such as estrogen, thyroid 22 hormone, testosterone, and gonadotropin-releasing hormone and their respective receptors as 23 well as enzymes involved in the control of the cell cycle (Safe, 1995b), may affect growth 24 patterns in cells/tissues, leading to adverse consequences. In fact, most of the effects that the 25 dioxins produce at the cellular and tissue levels are due not to cell/tissue death but to altered 26 growth patterns (Birnbaum, 1994b). Many of these alterations may occur at critical times in 27 development and/or maturation and thus may be irreversible. 28 There does not yet exist a precise understanding of the relationships between the 29 alteration of specific biochemical processes and particular toxic responses observed in either 30 experimental animals or humans exposed to the dioxins. This is due predominantly to our 31 incomplete understanding of the complex and coordinated molecular, biochemical, and cellular 32 interactions that regulate tissue processes during development and under normal homeostatic 33 conditions. A further understanding of these processes and how 2,3,7,8-TCDD may interfere 12/23/03 2-6 DRAFT--DO NOT CITE OR QUOTE 1 with them remains an important goal that would greatly assist in the risk characterization process. 2 In particular, knowledge of the causal association of these responses coupled with dose-response 3 relationships may lead to a better understanding of sensitivity to various exposure levels of the 4 dioxin-like compounds. Nevertheless, it is important to recognize that many of the biochemical 5 and biological changes observed are consistent with the notion that 2,3,7,8-TCDD is a powerful 6 growth dysregulator. This hypothesis may play a considerable role in the risk characterization 7 process by providing a focus on those processes, such as development, reproduction, immunity, 8 and carcinogenesis, that are highly dependent on coordinated growth regulation. 9 10 2.2. ADVERSE EFFECTS IN HUMANS AND ANIMALS 11 2.2.1. Cancer (Cross-reference: Part II, Chapters 6, 7, and 8) 12 2.2.1.1. Epidem iologic Studies 13 Since the last formal EPA review in 1988 of the human database relating to the 14 carcinogenicity of TCDD and related compounds, a number of new follow-up mortality studies 15 have been completed. This body of information is described in Part II, Chapter 7a, Section 7.5, 16 of this assessment, and summaries appear in an International Agency for Research on Cancer 17 monograph (IARC, 1997), the Agency for Toxic Substances and Disease Registry (ATSDR) 18 ToxProfile (ATSDR, 1999a), and the National Toxicology Program's report on carcinogens 19 (NTP, 2001). Among the most important of these are the ones by Fingerhut et al. (1991a) and 20 Steenland et al. (1999, 2001) from NIOSH of 5172 U.S. chemical manufacturing workers and the 21 independent analyses by Aylward et al. (1996) and Salvan et al. (2001) and followup of the Dow 22 sub-cohort by Bodner et al. (2003); a study of 2479 German workers involved in the production 23 of phenoxy herbicides and chlorophenols by Becher et al. (1996, 1998) and by others in separate 24 publications (Manz et al., 1991; Nagel et al., 1994; Flesch-Janys et al., 1995, 1998); a study of 25 more than 2000 Dutch workers in two plants involved in the synthesis and formulation of 26 phenoxy herbicides and chlorophenols (Bueno de Mesquita et al., 1993) and subsequent follow 27 up and expansion by Hooiveld et al., 1998); a smaller study by Zober et al. (1990) of 247 workers 28 involved in a chemical accident cleanup and subsequent follow-up (Ott and Zober, 1996b); and 29 an international study by Saracci et al. (1991) of more than 18,000 workers exposed to phenoxy 30 herbicides and chlorophenols, with subsequent follow-up and expansion by Kogevinas et al. 31 (1997). Recent reports also indicate increased cancer risks among the Seveso population 32 (Bertazzi et al. 2001a, Warner et al. 2002). 33 Although uncertainty remains in interpreting these cohort results because not all potential 34 confounders have been ruled out and coincident exposures to other carcinogens are likely (see 35 Cole et al., 2003 for a critique), all provide support for an association between exposure to dioxin 12/23/03 2-7 DRAFT--DO NOT CITE OR QUOTE 1 and related compounds and increased cancer mortality. Strong inference regarding carcinogenic 2 hazard often relies on the availability of studies with well-documented exposures. One of the 3 strengths of these studies is that each has some exposure information that permits an assessment 4 of dose response. Some of these data have, in fact, served as the basis for fitting the dose5 response models in Part II, Chapter 8, Section 8.4. 6 In addition, during the development of its monograph on PCDDs/PCDFs (IARC, 1997), 7 the IARC Working Group abstracted from the published literature data concerning the most 8 highly exposed populations in the world. The group focused its attention on the most exposed 9 subcohorts within cohorts with adequate latency. IARC suggests that if associations between 10 exposure and risk are truly causal, they will become more apparent in these highly exposed 11 subcohorts with adequate latency. Increased risk for all cancers combined and lung cancer 12 mortality were consistent findings in the occupational cohort studies. Although the increase was 13 generally low (20-50%), it was highest in the subcohorts with the presumed heaviest exposure. 14 The results of the IARC Working Group's analysis regarding all cancer and lung cancer mortality 15 in the recent studies are summarized in Table 2-3. Observed numbers of cases, standardized 16 mortality ratios (SMR) and 95% confidence intervals (CI) are given for each of these two 17 findings for each study. 18 In addition, the Working Group developed overall SMRs for the combined studies. The 19 group state clearly that, although these total SMRs are low (1.4, 95% CI = 1.2-1.6 for all cancers 20 and 1.4, 95% CI = 1.1-1.7 for lung cancer), these results are unlikely to be due to chance, nor can 21 confounding by cigarette smoking likely account for the increase in lung cancer. Positive dose22 response trends in the German studies and increased risk in the longer duration U.S. subcohort 23 and the most heavily exposed Dutch workers support this view. In the opinion of these experts, 24 increases of this magnitude in all cancers combined have rarely been found in occupational 25 cohorts. These results are also supported by significantly increased mortality from lung and liver 26 cancers subsequent to the Japanese rice oil poisoning accident where exposure to high levels of 27 PCDFs and PCBs occurred (Kuratsune et al., 1988; Kuratsune, 1989). 28 Although smoking as a confounder cannot be totally eliminated as a potential explanation 29 of the occupational studies results, analyses conducted to date (Fingerhut et al., 1991b; Ott and 30 Zober, 1996b) suggest that smoking is not likely to explain the entire increase in lung cancer and 31 may even suggest synergism between occupational exposure to dioxin and smoking. These 32 analyses have not been deemed entirely satisfactory by some reviewers of the literature. The 33 question of confounding exposures such as to asbestos and other chemicals in addition to 34 smoking has not been entirely ruled out and must be considered as potentially adding to the 35 observed increases. Although increases of cancer at other sites (e.g., non-Hodgkin's lymphoma, 12/23/03 2-8 DRAFT--DO NOT CITE OR QUOTE 1 soft tissue sarcoma, gastrointestinal cancer) have been reported (see Part II, Chapter 7a, Section 2 7.5), the data for an association with exposure to dioxin-like chemicals are less compelling due to 3 the limited numbers of observed tumors at any specific site. 4 As discussed by IARC (McGregor et al., 1998) and Smith and Lopipero (2001), it is 5 unusual for a cancer hazard characterization to focus on the "all cancers combined" category of 6 epidemiological results, and continuing uncertainties regarding site-specific cancer increases 7 following dioxin exposure remain a factor in concluding that the epidemiological information is 8 limited. McGregor et al. (1998) note, however, that the predominant cancer promotion 9 mechanism of action for dioxin will theoretically elicit pre-existing initiated cell lines. These 10 promotional effects would be expected in multiple tissues, especially those most sensitive to the 11 effects of dioxin. In epidemiological studies, there may not be a statistically increased tumor 12 site(s), but rather a pattern of smaller increases that could vary across study populations because 13 of differences in life histories, exposures, and pre-existing initiating events. 14 The cancer-promotion mechanism may also serve to accentuate existing tumor rate 15 increases following other carcinogenic exposures, thereby acting in a synergistic manner. Timing 16 of tumor induction may differ between a cancer promoter and initiator, where the effects of a 17 promoter may not be monotonic with time, but rather may exhibit an earlier onset, harvesting 18 effect, where the total cancer burden may not have changed but the onset has been accelerated. 19 These timing issues are exacerbated by the pharmacokinetics of dioxin elimination, where initial 20 peak body burdens during employment or after accidental exposures decline gradually after 21 cessation of exposure. 22 Mathematically, a net carcinogenic effect in one or more organ sites must, by definition, 23 increase the "all cancers combined" risk for the exposed population if the exposed and control 24 groups are matched (i.e., they have the same background cancer rate absent the exposure). Thus, 25 an increase in the all cancers category should be considered an expected result of a carcinogen 26 exposure, not an unusual event. The statistical power of a study to detect such an effect is, 27 however, the limiting factor in the presence of stochastic events and imperfect matching. This 28 constraint is particularly applicable to rare tumor sites, but it also occurs for common tumor sites 29 such as lung, colon, breast (&), and prostate (%) or for mechanistically linked sites (e.g., 30 hormonally related breast, ovary, uterus), where substantial increases in site-specific relative 31 risks are necessary to impact the all cancer category. 32 Ionizing radiation (a mutagenic carcinogen) provides an example where small increased 33 relative risks at multiple sites lead to a significantly increased relative risk for "all nonleukemic 34 cancers." In atomic bomb survivors, the relative risk for all nonleukemic cancers at 100 rads was 35 1.17 (p<0.01), comprised principally of small but statistically significant increases in stomach 12/23/03 2-9 DRAFT--DO NOT CITE OR QUOTE 1 (relative risk [RR] = 1.11), lung (1.33), breast (1.69), ovary (1.52), and bladder-kidney (1.55) 2 cancers and nonstatistically significant increases in esophagus (1.23), liver (1.35), ovary (1.52), 3 and multiple myeloma (1.51). Although the relative risk for leukemia was 3.95 (p<0.01), the 4 excess cancer burden from nonleukemic sites in the exposed population was over twice that due 5 to the leukemias (Hoel, 1987). 6 Some studies that are discussed in Part II, Chapter 7a, report small or no increased risk of 7 cancer from exposure to 2,3,7,8-TCDD or its congeners. These studies generally suffer from one 8 or more deficiencies that limit their ability to determine the carcinogenic hazard of dioxins. 9 These deficiencies fall into the following categories: little statistical power to detect an effect of 10 exposure because the measured exposures are lower than those seen in the studies cited above 11 and are more similar to those of the comparison population; no measurements of internal 12 exposure to 2,3,7,8-TCDD and potential for misclassification of exposure; and inadequate 13 latency or follow-up. 14 The Ranch Hand study of U.S. Air Force personnel who sprayed the defoliant Agent 15 Orange during the Vietnam War provides an illustrative example of statistical power constraints 16 in the presence of low predicted relative risks. Statistical power is the ability of a study to detect 17 a real difference between two groups at pre-defined levels of statistical significance (usuallyp# 18 0.05) and relative risk. Statistical power analysis based on the detailed dosimetry and health 19 status data available for this cohort indicates insufficient statistical power to detect an elevated 20 all-cancers risk at levels consistent with the occupational dose-response data. A predicted 21 relative risk for all cancers combined can be estimated for the Ranch Hands by calculating the 22 difference between their dose and that of the control group (mean background of 4.25 ppt TCDD 23 in lipid) (Michalek et al., 1998) and then multiplying this dose increment by an estimated cancer 24 risk slope factor for TCDD. The median AUC increment value for the overall Ranch Hand group 25 is 468 ng TCDD/kg lipid * years, and for the high dioxin group the median is 2280 ng TCDD/kg 26 lipid * years. Using the Becher et al. (1998) linear formula (RR = 1 + 0.000016 x AUC ng27 TCDD/kg lipid * years, which equals ~ 3 x 10-3risk/pg/kg/day) described in Section 5.3 and 28 Table 5-2 of this document, the estimated all-cancers relative risk for the overall Ranch Hand 29 cohort is approximately 1.01, and for the high-exposure group it is 1.04 as compared to the 30 control population. Using formulae in Fleiss (1981) and Cohen (1977) and assuming two-sided 31 testing at a significance level of 5%, the study has no power to detect 1to 4% increases in 32 relative risk. Data on the overall prevalence of cancer in the comparison group (18.9%) and 33 sample sizes (all Ranch Hand 845 vs. 1224 controls; high category 241 vs. 1200 controls) used in 34 the above analysis were obtained from the 1997 Ranch Hand morbidity report 35 (http://www.brooks.af.mil/AFRL/HED/hedb/afhs/.html). 12/23/03 2-10 DRAFT--DO NOT CITE OR QUOTE 1 Recent suggestive cancer findings from the Ranch Hand database are consistent with 2 these calculations, both in the magnitude of the risk ratios under review and in the constraints on 3 statistical methods to detect such levels of incremental risk. Akhtar et al. (2003) provide results 4 that suggest exposure to dioxin-contaminated herbicides may be associated with cancer, based on 5 a statistically significant positive trend in "any site" cancer relative risk with exposure group, 6 accompanied by a non-significant increase in the any site cancer standardized incidence ratio of 7 1.09 (Obs. 134, Exp 123.34, p=0.34). 8 In addition, one of the earliest reported associations between exposure to dioxin-like 9 compounds in dioxin-contaminated phenoxy herbicides and increased cancer risk involved an 10 increase in soft tissue sarcomas (Hardell and Sandstrom, 1979; Eriksson et al., 1981; Hardell and 11 Eriksson, 1988; Eriksson et al., 1990). In this and in other recent evaluations of the 12 epidemiologic database, many of the earlier epidemiological studies that suggested an association 13 between dioxin exposure and soft tissue sarcoma have been criticized for a variety of reasons. 14 Arguments regarding selection bias, lack of exposure or differential exposure misclassification, 15 confounding, and chance in each individual study, which increases uncertainty around this 16 association, have been presented in the scientific literature. Nonetheless, the incidence of soft 17 tissue sarcoma is elevated, although not statistically so, in several of the most recent studies 18 (Bertazzi et al., 1993, 1997, 1999; Fingerhut et al., 1991a; Hertzman et al., 1997; Kogevinas et 19 al., 1997; Lampi et al., 1992; Lynge, 1998; Pesatori et al., 1999; Saracci et al., 1999; Vineis et al., 20 1986). It is probable that soft tissue sarcomas are not unlike other site-specific cancers whose 21 risks from exposure to TCDD are difficult to define because of small numbers and lack of 22 measures of internal exposure. 23 The accidental exposure of the population at Seveso, Italy, serves as an example of a 24 more highly exposed group where, in previous assessments, latency was considered to be 25 inadequate. Although Bertazzi and coworkers published results of cancer mortality after 10 and 26 15 years of latency, results are suggestive but not definitive regarding an association between 27 exposure to TCDD and cancer deaths. Results of the analysis of 20 years of follow-up have 28 recently been published (Bertazzi et al., 2001). This more recent follow-up of the same group of 29 residents in zones A and B was completed after 20.5 years to December 31, 1996. The authors 30 stated that their results support the evaluation of TCDD as a human carcinogen, especially with 31 the increased estimates of relative risk for all cancer mortality and for several specific sites of 32 cancer in the >15 year latency period. No soft tissue sarcomas were observed in zones A and B. 33 However, less than one case would have been expected to occur by the end of the follow-up. In 34 Zone A, where exposure was highest, the expectation of a soft tissue sarcoma was only 0.1. 35 There was little power to detect a significant risk in that region. 12/23/03 2-11 DRAFT--DO NOT CITE OR QUOTE 1 In a commentary by Smith and Lopipero (2001) on this study, two "key" problems were 2 identified. The "likely" exposure levels back-calculated to the time when the exposures occurred 3 indicate that the weighted average for the two highest exposure zones in Seveso is only 136 4 ng/kg TCDD (lipid adjusted) versus a mean of 3600 ng/kg TCDD (lipid adjusted) in the 5 combined U.S. industrial cohorts. This interpretation is consistent with the data in Figure 5-1 of 6 this document. On this basis, one would not expect to find significant increases in all cancers 7 combined based on extra risk estimates from the occupational cohorts. This situation is not 8 unlike the one described above for the Ranch Hand cohort. However, in this case, associations 9 with exposure to TCDD and cancer risk are being reported. 10 The other issue raised by these authors is the potential for smoking-related causes of 11 disease to be confounders in this study. The relatively low dioxin exposure and the increase in 12 major smoking-related causes of death raise questions regarding the attribution of these cancer 13 effects to TCDD exposure. Other data are consistent with potential dioxin hazard in this exposed 14 population, for example, the finding of increased diabetes mortality among women. Bertazzi 15 (2001b) takes exception to these interpretations and argues against the perception of "low" 16 exposure and smoking as a confounder. It is clear that the question of whether the Bertazzi 17 (2001a) study contributes to the weight of evidence for carcinogenicity awaits further follow-up 18 and improved exposure assessment. 19 In general, both past and more recent human studies have focused on males. Although 20 males comprise all the case-control studies and the bulk of the cohort study analyses, animal and 21 mechanism studies suggest that males and females might respond differently to TCDD. There 22 are now, however, some limited data suggesting carcinogenic responses associated with dioxin 23 exposure in females. The only report of a female cohort that had good TCDD exposure surrogate 24 information was that of Manz et al. (1991), which found a borderline statistically significant 25 increase in breast cancer. Although Saracci et al. (1991) did report reduced female breast and 26 genital organ cancer mortality, the finding was based on few observed deaths and on 27 chlorophenoxy herbicide rather than TCDD exposures. In the later update and expansion of this 28 cohort, Kogevinas et al. (1997) provided evidence of a reversal of this deficit and reported a 29 borderline significant excess risk ofbreast cancer in females. 30 Bertazzi et al. (1993, 1997, 1998) reported nonsignificant decreases in breast cancer and 31 endometrial cancer in women living in geographical areas around Seveso that were contaminated 32 by dioxin. Breast cancer rates in women who had been exposed as infants at the time of the 33 Seveso explosion were increased. On the basis of 15 (1.5%) confirmed breast cancer cases in the 34 Seveso Women's Health Study, a Cox proportional hazard ratio for breast cancer of 2.1 fold 35 (95% CI 1.0 - 4.6) was reported for a ten-fold increase in serum TCDD levels (Warner et al., 12/23/03 2-12 DRAFT--DO NOT CITE OR QUOTE 1 2002). Although Kogevinas et al. (1993) saw an increase in cancer incidence among female 2 workers most likely exposed to TCDD, no increase in breast cancer was observed in their small 3 cohort. In short, TCDD cancer experience for women may differ from that ofmen, but currently 4 there are few data to adequately address this question. 5 Both laboratory animal data and mechanistic inferences suggest that males and females 6 may respond differently to the carcinogenic effects of dioxin-like chemicals. Further data will be 7 needed to address this question of differential response between sexes, especially to hormonally 8 mediated tumors. In addition, studies by Brown et al. (1998) demonstrated that prenatal 9 exposure of rats to 2,3,7,8-TCDD enhances their sensitivity as adults to chemical carcinogenesis. 10 A mechanistic understanding of the impact of gestational dioxin exposure on mammary tissue 11 development has been provided by the work of Fenton and coworkers (Fenton et al., 2002; 12 Vorderstrasse et al., 2004). The experimental data in laboratory animals suggest that exposure to 13 women or perinatal exposures may result in carcinogenic responses. The epidemiological data 14 examining the association between exposure of adult women to dioxin and cancer is limited. No 15 epidemiological data are available to address the question of the potential impact of exposure to 16 dioxin-like compounds on childhood cancers or the effects of perinatal exposures on the 17 development of cancers later in life. The epidemiological data to date have not adequately 18 addressed these issues. 19 In summary, 2,3,7,8-TCDD and, by inference from more limited data, other dioxin-like 20 compounds are described as potentially multisite carcinogens in the more highly exposed human 21 populations--consisting primarily of adult males that have been studied. Although the 22 epidemiologic data by themselves are not sufficient to infer a causal association between 23 exposure to TCDD and other dioxin-like chemicals and increased cancer in humans (IARC, 24 1997; ATSDR, 1999a; DHHS, 2001), this "limited" epidemiologic database has been 25 strengthened by emerging data that reflect further follow-up and better exposure metrics. 26 Although uncertainty remains, the cancer findings in the epidemiologic literature are generally 27 consistent with results from studies of multiple laboratory animal species, where dioxin-like 28 compounds have clearly been identified as multisite carcinogens and tumor promoters. 29 2,3,7,8-TCDD has also been demonstrated to promote dose-dependent clonal expansion 30 and neoplastic transformation in human epidermal keratinocytes immortalized by simian 31 adenovirus SV40 exposure, leading to fixed alterations in regulatory gene expression (Yang et 32 al., 1999) and squamous cell carcinoma when inoculated into athymic nude mice (Yang et al., 33 1992). These phenomena did not occur in the absence of SV40 virus induction or in control cell 34 lines, including the immortalized cell culture. 12/23/03 2-13 DRAFT--DO NOT CITE OR QUOTE 1 Thus, the findings of increased risk at multiple sites in occupationally exposed humans 2 appear to be plausible, given what is known about mechanisms of dioxin action and the 3 fundamental level at which this class of compounds appears to act on gene expression and 4 cellular regulation in target tissues. Although several studies found a positive trend in dose5 response and have been the subject of empirical risk modeling (see Part II, Chapter 8, and Becher 6 et al., 1998, and Steenland et al., 2001), the epidemiologic data alone provide little insight into 7 the shape of the dose-response curve below the range of observation in these occupationally 8 exposed populations. However, Mackie et al. (2003) suggest that there is no evidence of a dioxin 9 cancer threshold from the epidemiology data. Steenland and Deddens (2003) also reported that 10 the results of quantitative exposure-response analyses for low environmental levels based on the 11 NIOSH cohort are consistent with the results from the Becher cohort and demonstrate that a 12 doubling of background levels of exposure will increase lifetime risk of cancer death between 0.1 13 and 1%. The issue of the shape of the dose-response curve in occupational cohorts is further 14 discussed in Section 5.2.1 ofthis document. 15 16 2.2.I.2. Animal Carcinogenicity (Cross-reference, Part II: Chapters 6 and 8) 17 An extensive database on the carcinogenicity of dioxin and related compounds in 18 laboratory studies exists and is described in detail in Part II, Chapter 6. There is adequate 19 evidence that 2,3,7,8-TCDD is a carcinogen in laboratory animals, based on long-term bioassays 20 conducted in both sexes of several strains of rats and mice, hamsters, and fish (U.S. EPA, 1985; 21 Huff et al., 1991; Zeise et al., 1990; IARC, 1997; DHHS, 2001). All the studies produced 22 positive results, leading to conclusions that TCDD is a multi-site carcinogen that increases the 23 incidence of tumors at sites distant from the site of treatment and at doses well below the 24 maximum tolerated dose. Since this issue was last reviewed by the Agency, in 1988, TCDD has 25 been shown to be a carcinogen in hamsters (Rao et al., 1988), which are relatively resistant to the 26 lethal effects of TCDD. Other preliminary data have also shown TCDD to be a liver carcinogen 27 in the small fish Medaka (Johnson et al., 1992). 28 In the past, limited attempts had been made to demonstrate the carcinogenicity of other 29 dioxin-like compounds. A mixture of two isomers of hexachlorodibenzo-p-dioxin (HCDDs) 30 produced liver tumors in both sexes of rats and mice when given by the gavage route (NTP, 31 1980), but not by the dermal route in Swiss mice (NTP, 1982a,b). Reports from Rozman (1999, 32 2000) and Rozman et al. (2000) demonstrated lung cancer in female rats given gavage exposures 33 of 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin(HpCDD). 34 Recently, the National Toxicology Program (NTP, 2003 a-d) has conducted chronic 35 bioassays to test the relative carcinogenic potency of four dioxin-like congeners (TCDD, 12/23/03 2-14 DRAFT--DO NOT CITE OR QUOTE 1 2,3,4,7,8-PeCDD, PCB 118, and PCB 126), both alone and in combination. In these studies, 2 TCDD, PCB 126 and 2,3,4,7,8-PeCDF, were tested individually or in an equally potent mixture 3 of all three chemicals in a 2-year bioassay in female Sprague-Dawley rats. The NTP study also 4 included PCB 118, but the results and interpretation of this bioassay remain under review due to 5 substantial contamination by PCB 126. Initial reports from the NTP study indicate that there is 6 clear evidence of carcinogenicity for both TCDD and PCB 126. In these studies, both TCDD and 7 PCB 126 exposures increases the incidence of cholangiocarcinoma of the liver, cystic 8 keratinizing epithelioma of the lung, and gingival squamous cell carcinoma of the oral mucosa. 9 Under the conditions of the 2-year study, there was some evidence of carcinogenic activity for 10 the 2,3,4,7,8-PeCDF based on increased incidences of cholangiocarcinoma of the liver, cystic 11 keratinizing epithelioma of the lung and gingival squamous cell carcinoma of the oral mucosa. 12 The results from the mixture study also indicate clear evidence of carcinogenicity as evidenced 13 by dose dependent increases in cholangiocarcinomas in the liver and cystic keratinizing 14 epitheliomas of the lung. The data on the three individual chemicals and mixtures demonstrate 15 consistent increases in the incidence of three tumor types. This evidence provides support that 16 the carcinogenicity of dioxin-like chemicals is mediated through their interactions with the Ah 17 receptor and that the TEF methodology may provide a useful tool in estimating the potential 18 carcinogenic risks of dioxin-like chemicals. 19 TCDD is characterized as a nongenotoxic carcinogen because it is negative in most 20 assays for DNA-damaging potential and is a potent "promoter" and a weak initiator or 21 noninitiator in two-stage initiation-promotion (I-P) models for liver, skin, and lung. The liver 22 response is characterized by increases in altered hepatocellular foci (AHF), which are considered 23 to be preneoplastic lesions because increases in AHFs are associated with liver cancer in rodents. 24 The results of the multiple I-P studies enumerated in Table 6-5 and in Part II, Chapter 6, Section 25 6.3, have been interpreted as showing that induction of AHFs by TCDD is dose-dependent 26 (Maronpot et al., 1993; Teeguarden et al., 1999), exposure-duration dependent (Dragan et al., 27 1992; Teeguarden et al., 1999; Walker et al., 2000), and partially reversible after cessation of 28 treatment (Dragan et al., 1992; Tritscher et al., 1995; Walker et al., 2000). 29 Other studies indicate that other dioxin-like compounds have the ability to induce AHFs. 30 These studies showed that the compounds demonstrate a rank-order of potency for AHF 31 induction that is similar to that for CYP1A1 (Flodstrom and Ahlborg, 1992; Waern et al., 1991; 32 Schrenk et al., 1994). Non-ortho-substituted, dioxin-like PCBs have also induced the 33 development of AHFs according to their potency to induce CYP1A1 (Hemming et al., 1995; van 34 der Plas et al., 1999). It is interesting to note that liver I-P studies carried out in ovariectomized 35 rats demonstrated the influence that the intact hormonal system has on AHF development. AHF 12/23/03 2-15 DRAFT--DO NOT CITE OR QUOTE 1 were significantly reduced in the livers of ovariectomized female rats (Graham et al., 1988; 2 Lucier et al., 1991). 3 I-P studies on skin have demonstrated that TCDD is a potent tumor promoter in mouse 4 skin as well as rat liver. Early studies demonstrated that TCDD is at least two orders of 5 magnitude more potent than the "classic" promoter tetradecanoyl phorbol acetate (Poland et al., 6 1982), that TCDD skin tumor promotion is AhR dependent (Poland and Knutsen, 1982), that 7 TCDD had weak or no initiating activity in the skin system (DiGiovanni et al., 1977), and that 8 TCDD's induction of drug-metabolizing enzymes is associated with both metabolic activation 9 and deactivation of initiating agents, as described by Lucier et al. (1979). More recent studies 10 show that the skin tumor-promoting potencies of several dioxin-like compounds reflect relative 11 AhR binding and pharmacokinetic parameters (Hebert et al., 1990). 12 Although few I-P studies have demonstrated lung tumors in rats or mice, the study by 13 Clark et al. (1991) is particularly significant because of its use of ovariectomized animals. In 14 contrast to liver tumor promotion, lung tumors were seen only in initiated (diethylnitrosamine 15 [DEN]), TCDD-treated rats. No tumors were seen in DEN-only, TCDD-only, control, or 16 DEN/TCDD intact rats. Liver tumors are ovary dependent, but ovaries appear to protect against 17 TCDD-mediated tumor promotion in female rat lung. Perhaps the use oftransgenic animal 18 models will allow further understanding of the complex interaction of factors associated with 19 carcinogenesis in rodents and, by extension, in humans. Several such systems are being 20 evaluated (Eastin et al., 1998; van Birgelen et al., 1999; Dunson et al., 2000). 21 The tumor-promoting ability of a number of dioxin-like chemicals has been examined. As 22 discussed in Part II, Chapter 6, Section 6, 1,2,3,7,8-PCDD; 1,2,3,4,6,7,8-HpCDD; 2,3,4,7,823 PCDF; 1,2,3,4,7,8-HCDF; PCB126; and PCB105 all promote the development of AHF within 24 rodent liver, suggesting that they, like TCDD, are tumor promoters. (For a summary of positive 25 tumor-promotion studies for PCDDs and PCDFs in rats, see Part II, Chapter 6, Table 6-5). In 26 addition, complex mixtures of dioxins and furans and commercial PCB mixtures act as 27 promoters of liver AHF. For the five principle dioxins, furans, and coplanar PCBs that comprise 28 approximately 80% of the current, total dioxin/furan/PCB TEQ in human blood, all are positive 29 in either rodent bioassays or rodent liver tumor-promotion studies or mouse skin tumor 30 promotion studies. Although the majority of dioxin-like congeners have not been tested for 31 carcinogenicity in chronic rodent bioassays, these data suggest that it is likely that those 32 individual congeners and mixtures of dioxin-like compounds that comprise the majority of the 33 dioxin-like activity in human tissues are likely to be carcinogenic to rodents. 34 van den Berg et al. (2000) present a summary of the data (their Table 1) relied on by 35 WHO's European Centre for Environment and Health (WHO-ECEH) and IPCS in their joint 12/23/03 2-16 DRAFT--DO NOT CITE OR QUOTE 1 consensus re-evaluation of the TEFs for PCDDs, PCDFs, and dioxin-like PCBs for mammals. 2 These TEFs were derived using a tiered approach in which in vivo toxicity data were given more 3 weight than in vitro data, toxicity more than biochemical endpoints, and chronic more than acute 4 data. Table 2-4 summarizes the tumor incidence and promotion data that were cited in the 5 development of these TEFsDFP-WHO98. The data presented are for those congeners that are 6 principal contributors to the background body burden of dioxin TEQs in the United States (see 7 Part I, Chapter 3). For 1,2,3,7,8-PeCDF and 2,3,4,7,8-PeCDF, the TEF was used to adjust the 8 dose from the studies by Waern et al. (1991), and for PCB 126 similar dose adjustments are 9 included from Hemming et al. (1995; their Fig. 4). For the comparison of TCDD to the 10 HxCDDs, the primary TCDD data points from the Kociba et al. (1978) bioassay were graphed for 11 both the original tumor count data and for the revised tumor counts from Goodman and Sauer 12 (1992). This presentation ofboth the original and the revised tumor counts for TCDD reflects 13 the contemporaneous performance and analysis of the HxCDD and TCDD bioassays and 14 pathology and the recognition that the HxCDD pathology has not been re-analyzed. 15 Table 2-3 illustrates the comparability of the TCDD and other congener data sets based 16 on TEFs. This analysis also demonstrates that the development of the TEFs for all of the 17 congeners that contribute substantially to the background dioxin TEQ appropriately reflect either 18 cancer bioassay or tumor promotion data. Furthermore, when one considers the impact of current 19 TEF values on compounds that made up the majority of the TEQ prior to 1990, it is clear that 20 more than 80% of the TEQ for either dioxins/furans or PCBs was made up of compounds for 21 which the current TEF is supported by data on relative potencies which included tumor 22 promotion or carcinogenic endpoints. This point is illustrated in Part II, Chapter 6, Table 6-10. 23 24 2.2.I.3. Plausible M ode(s) o f Carcinogenic Action 25 Several potential mechanisms for TCDD carcinogenicity are discussed above and in Part 26 II, Chapter 6, Section 6.4. These include oxidative stress, indirect DNA damage, endocrine 27 disruption/growth dysregulation/altered signal transduction, and cell replication/apoptosis 28 leading to tumor promotion. All of these mechanisms are biologically plausible as contributors 29 to the carcinogenic process in humans, and none are mutually exclusive. Several biologically 30 based models that encompass many of these activities are described in Part II, Chapter 8, Section 31 8.4. Further work is needed to elucidate a detailed mechanistic model for any particular 32 carcinogenic response in animals or in humans; however, plausible modes of action with 33 probable relevance to human carcinogenicity are discussed below. 34 TCDD is a potent tumor promoter in rat and mouse liver and in initiated human skin 35 cells. In general terms, it is believed that cancer is likely due to the clonal expansion of damaged 12/23/03 2-17 DRAFT--DO NOT CITE OR QUOTE 1 cells that have a heritable genetic defect. Increased growth and accumulation of damage in 2 critical genes ultimately aid in the progression into tumors. Consequently, promotion of 3 carcinogenesis by TCDD may occur at several steps: (1) increased formation of 4 initiated/susceptible cells through DNA mutation and/or increase rate of fixation of damaged 5 DNA into the genome, (2) reduced loss of initiated cells through a suppression of apoptosis, (3) 6 increase in growth rate and clonal expansion of initiated cells, and (4) accumulation of DNA 7 damage in critical genes resulting in the progression of clonally expanded cell populations into 8 tumors. Within this framework, it is hypothesized that TCDD may be acting as a tumor promoter 9 through multiple mechanisms. Primarily, the activation of the AhR leads to alteration in genes 10 that are involved in normal cell growth and differentiation pathways. 11 TCDD may contribute to the formation and accumulation of DNA damage via an indirect 12 mechanism involving the production of reactive oxygen species. These reactive oxygen species 13 may be formed as a result of autooxidation during futile metabolism of TCDD by the induction 14 of CYP1 enzymes or via the CYP1-dependent production of estrogen metabolites capable of 15 redox cycling. The clonal expansion of these damaged cells by TCDD and related chemicals is 16 likely to occur through the altered expression and activity of a number of genes that regulate the 17 cell-cycle. Activation of the AhR by TCDD results in altered expression or activity of the EGF 18 receptor, retinoblastoma protein, TGF-beta, and many others. These proteins all regulate the cell 19 cycle, and alterations of these proteins would alter cell growth properties. 20 The contribution of these two pathways in the carcinogenic actions of TCDD remains 21 uncertain. However, Portier et al. (1996) have proposed a model in which the contribution of 22 TCDD to the number ofDNA damaged or initiated cells plays a significant role in its 23 carcinogenic response. In contrast, Conolly and Andersen (1997) have proposed a tumor 24 promotion model based on a negative selection mechanism in which the actions of TCDD are 25 focused on its ability to alter cell growth properties. Descriptions of these models are provided in 26 Part II, Chapter 8. Interestingly, the use of the model by Portier and colleagues leads to a result 27 that is consistent with low-dose linearity, whereas the Andersen and Conolly model predicts 28 highly nonlinear dose response relationships in the low-dose region. Presently, the available data 29 do not allow for adequate discrimination between these two models. 30 TCDD causes a dose-related increase in thyroid follicular cell adenomas and carcinomas 31 in rats and mice. One hypothesis for the induction of thyroid tumors involves the disruption of 32 thyroid hormone homeostasis via the induction of the phase II enzymes UDP33 glucuronosyltransferases (UGTs) (Hurley, 1998; Hill et al., 1998). Dioxin-like compounds 34 induce the synthesis of UDP-glucuronosyltransferase-1 (UGT1) mRNA by an AhR-dependent 35 transcriptional mechanism (Bock et al., 1998; Nebert et al., 1990). It is proposed that dioxin-like 12/23/03 2-18 DRAFT--DO NOT CITE OR QUOTE 1 chemicals increase the incidence ofthyroid tumors through an extrathyroidal mechanism. 2 Dioxin-like chemicals induce hepatic UGT, resulting in increased conjugation and elimination of 3 thyroxine (T4) and leading to reduced serum T4 concentrations. T4 production is controlled by 4 thyroid stimulating hormone (TSH), which is under negative and positive regulation from the 5 hypothalamus, pituitary, and thyroid by thyrotrophin releasing hormone (TRH), TSH itself, 6 thyroxine (T4), and triiodothyronine (T3). Consequently, the reduced serum T4 concentrations 7 would lead to a decrease in the negative feedback inhibition on the pituitary gland. This would 8 then lead to a rise in secreted TSH and stimulation of the thyroid. The persistent induction of 9 UGT by dioxins and subsequent prolonged stimulation of the thyroid would result in thyroid 10 follicular cell hyperplasia and hypertrophy of the thyroid, thereby increasing the risk of 11 progression to neoplasia. 12 In support of this hypothesis, Kohn et al. (1996) modeled the effect of 2,3,7,8-TCDD on 13 UGTs and thyroid hormones in female rats within the framework of a PBPK model. This 14 mathematical model described release and uptake of thyroid hormones, metabolism, 2,3,7,815 TCDD induction of UGT1, regulation of TSH release from the pituitary by T4, and feedback on 16 TRH and somatostatin, which inhibits TSH release. The model successfully reproduced the 17 observed effects of 2,3,7,8-TCDD on serum T3, T4, and TSH and UGT1 mRNA and enzyme 18 activity, suggesting that this is a plausible mechanism for an indirect role of 2,3,7,8-TCDD on the 19 thyroid. This model is supported by the more recent experimental work of Schuur et al. (1997), 20 which demonstrated the extrathyroidal effects of 2,3,7,8-TCDD on thyroid hormone turnover. 21 Although this discussion illustrates that there is no defined molecular mechanism leading 22 to cancer in either liver or thyroid, it does demonstrate the concept of "mode of action" as 23 defined in the Agency's proposed cancer guidelines (U.S. EPA, 1996, 1999, 2003). In each case, 24 critical "key events" that correlate with carcinogenicity can be identified and measured, and these 25 same events occur in both animals and humans. Although these relationships and linkages 26 remain to be detailed, they form plausible, testable hypotheses whose acceptance by the scientific 27 community is growing. 28 Despite this lack of a defined mechanism at the molecular level, there is a consensus that 29 2,3,7,8-TCDD and related compounds are receptor-mediated carcinogens in that (1) interaction 30 with the AhR is a necessary early event; (2) 2,3,7,8-TCDD modifies a number of receptor and 31 hormone systems involved in cell growth and differentiation, such as the EGFR and estrogen 32 receptor; and (3) sex hormones exert a profound influence on the carcinogenic action of 2,3,7,833 TCDD. 34 12/23/03 2-19 DRAFT--DO NOT CITE OR QUOTE 1 2.2.I.4. Other D ata R elated to Carcinogenesis 2 Despite the relatively large number ofbioassays on 2,3,7,8-TCDD, those by Kociba et al. 3 (1978) and NTP (1982a), because oftheir multiple dose groups and wide dose range, continue to 4 be the focus of dose-response modeling efforts and of additional review. Goodman and Sauer 5 (1992) reported a re-evaluation of the female rat liver tumors in the Kociba study using the latest 6 pathology criteria for such lesions. The review confirmed only approximately one-third of the 7 tumors of the previous review (Squire, 1980). Although this finding did not change the 8 determination of carcinogenic hazard--as 2,3,7,8-TCDD induced tumors in multiple sites in this 9 study--it did have an effect on evaluation of dose-response and on estimates of risk at low doses. 10 These issues are discussed in a later section of this document. 11 One of the more intriguing findings in the Kociba bioassay was reduced tumor incidences 12 of the pituitary, uterus, mammary gland, pancreas, and adrenals in exposed female rats as 13 compared to controls. Although this finding, coupled with evaluation of epidemiologic data, has 14 led some authors to conclude that dioxin possesses "anticarcinogenic" activity (Kayajanian, 15 1997, 1999), it should be noted that in the Kociba study, the decreased incidence of tumors, with 16 the exception of mammary gland tumors, is associated with significant weight loss in these rats. 17 Examination of the data from NTP also demonstrates a significant decrease in these tumor types 18 when there is a concomitant weight loss in the rodents, regardless of the chemical administered 19 (Haseman and Johnson, 1996). It is also worth noting that the decrease in mammary tumors was 20 only observed in one of seventeen rodent carcinogenesis studies, and was not observed in the 21 recent NTP studies on TCDD, PCB 126, and 2,3,4,7,8-PeCDF (NTP, 2003 a-d). 22 As discussed in Section 3.2.3, under certain circumstances exposure to 2,3,7,8-TCDD 23 may elicit beneficial effects. For example, 2,3,7,8-TCDD protects against the subsequent 24 carcinogenic effects of polycyclic aromatic hydrocarbons (PAHs) in mouse skin, possibly 25 reflecting induction of detoxifying enzymes (Cohen et al., 1979; DiGiovanni et al., 1980). In 26 other situations, 2,3,7,8-TCDD-induced changes in estrogen metabolism may alter the growth of 27 hormone-dependent tumor cells, producing a potential anticarcinogenic effect (Spink et al., 1990; 28 Gierthy et al., 1993). While TCDD has been shown to inhibit the growth of certain breast cancer 29 cell lines, Warner et al. (2002) have demonstrated an increase in breast cancer in highly exposed 30 women from Seveso. Because the mechanism of the decreases in the tumor cells is unknown, 31 extrapolation of these effects to humans is premature. 32 In considering overall risk, one must take into account factors such as the range of doses 33 to target organs and hormonal state to obtain a complete picture of hazard and risk. Although 34 exposure to dioxins may influence cancer response directly or indirectly and positively or 35 negatively, it is unlikely that such data will be available to argue that dioxin exposure provides a 12/23/03 2-20 DRAFT--DO NOT CITE OR QUOTE 1 net benefit to human health. It is also important to note that the doses at which the incidence of 2 certain tumors may decrease is in the same range at which adverse noncancer effects occur (see 3 Appendix A). 4 5 2.2.I.5. Cancer Hazard Characterization 6 TCDD, CDDs, CDFs, and dioxin-like PCBs are a class of well-studied compounds whose 7 human cancer potential is supported by a large database, including "limited" epidemiological 8 support, unequivocal animal carcinogenesis, and biologic plausibility based on mode of action 9 data. In 1985, EPA classified 2,3,7,8-TCDD and related compounds as "probable" human 10 carcinogens, based on the available data. During the intervening years, the database relating to 11 the carcinogenicity of dioxin and related compounds has grown and strengthened considerably. 12 In addition, EPA guidance for carcinogen risk assessment has evolved (U.S. EPA, 1996, 1999, 13 2003). Under EPA's current approach, complex mixtures of dioxin and related compounds are 14 considered "likely to be carcinogenic to humans," as are individual dioxin-like congeners other 15 than TCDD. This descriptor is based primarily on the concept of toxic equivalency but also on 16 the data available to support this characterization for individual congeners. Positive lifetime 17 bioassays are available for a number of the principal congeners contributing to human TEQ body 18 burden, specifically TCDD, 2,3,4,7,8-PeCDF, 1,2,3,6,7,8-HxCDD, 1,2,3,7,8,9-HxCDD, and PCB 19 126 (Kociba et al., 1978; NTP, 1980; NTP, 2003 a-d). 20 2,3,7,8-TCDD is best characterized as "carcinogenic to humans." This means that, based 21 on the weight of all of the evidence (human, animal, mode of action), 2,3,7,8-TCDD meets the 22 stringent criteria that allows EPA and the scientific community to accept a causal relationship 23 between exposure and cancer hazard. The guidance (see EPA, 2003, section 2.6) suggests that 24 "carcinogenic to humans" is an appropriate descriptor of carcinogenic potential when there is an 25 absence of conclusive epidemiologic evidence to clearly establish a cause-and-effect relationship 26 between human exposure and cancer but there is compelling carcinogenicity data in animals and 27 mechanistic information in animals and humans demonstrating similar modes of carcinogenic 28 action. 29 The "carcinogenic to humans" descriptor is suggested for 2,3,7,8-TCDD because all of 30 the following conditions are met: 31 32 Occupational epidemiologic studies all show an association between 2,3,7,8-TCDD 33 exposure and increases in the all-cancers-combined category, in lung cancer, and 34 perhaps in cancers at other sites, but the data are insufficient on their own to 35 demonstrate a causal association. 12/23/03 2-21 DRAFT--DO NOT CITE OR QUOTE 1 2 There is extensive carcinogenicity in both sexes of multiple species of animals at 3 multiple sites. 4 5 There is general agreement that the mode of 2,3,7,8-TCDD's carcinogenicity is AhR 6 dependent and proceeds through modification of the action of a number of receptor 7 and hormone systems involved in cell growth and differentiation, such as the EGFR 8 and estrogen receptors. 9 10 The human AhR and the rodent AhR are similar in structure and function and, once 11 transformed, both bind to the same DNA response elements, designated DRE's. 12 13 Human and rodent tissue and organ cultures respond to TCDD and related chemicals 14 in a similar manner and at similar concentrations. 15 16 Other dioxin-like compounds are characterized as "likely to be carcinogenic to humans," 17 primarily because of the lack of epidemiological evidence associated with their carcinogenicity, 18 although there is a strong inference based on toxic equivalency that they would behave in humans 19 as 2,3,7,8-TCDD does. Each of the congeners that contributes substantially to human body 20 burden has been evaluated in vivo in cancer bioassays or tumor promotion assays. Each has a 21 large database demonstrating AhR-mediated dioxin-like activities. Each has physico-chemical 22 properties that contribute to their persistence. For each congener, the degree of certainty of 23 carcinogenic hazard is dependent on the available congener-specific data and its consistency with 24 the generalized mode of action that underpins toxic equivalency for 2,3,7,8-TCDD and related 25 compounds. For the congeners most frequently encountered in human blood, milk, and adipose 26 tissue, the database in support of 2,3,7,8-TCDD-like carcinogenic hazard is strong; those with 27 weaker data supporting 2,3,7,8-TCDD-like carcinogenicity contribute relatively little to total 28 TEQ. 29 On the basis of this logic, all complex environmental mixtures of 2,3,7,8-TCDD and 30 dioxin-like compounds would be characterized as "likely" carcinogens, but the degree of 31 certainty ofthe cancer hazard would be dependent on the major constituents of the mixture. For 32 instance, the hazard potential, although still considered "likely," would be characterized 33 differently for a mixture whose TEQ was dominated by octachlorodibenzo-p-dioxin as compared 34 to one dominated by other PCDDs. 35 12/23/03 2-22 DRAFT--DO NOT CITE OR QUOTE 1 2.2.2. Reproductive and Developmental Effects 2 Several sections of this reassessment (Part II, Chapter 5 and Chapter 7b) have focused on 3 the variety of effects that dioxin and dioxin-like agents can have on human reproductive health 4 and development. The emphasis in each of these chapters has been on the discussion of the more 5 recent reports of the impact of dioxin-like compounds on reproduction and development. These 6 reports have been put into context with previous reviews of the literature applicable in risk 7 assessment (Hatch, 1984; Sweeney, 1994; Kimmel, 1988) to develop a profile of the potential for 8 dioxin and dioxin-like agents to cause reproductive or developmental toxicity, based on the 9 available literature. An earlier version of the literature review and discussion contained in Part 10 II, Chapter 5, has been previously published (Peterson et al., 1993). 11 The origin of concerns regarding a potential link between exposure to chlorinated dioxins 12 and adverse developmental events can be traced to early animal studies reporting increased 13 incidence of developmental abnormalities in rats and mice exposed early in gestation to 2,4,514 trichlorophenoxyacetic acid (2,4,5-T) (Courtney and Moore, 1971). 2,4,5-T is a herbicide that 15 contains dioxin and related compounds as impurities. Its use was banned in the late 1970s, but 16 exposure to human populations continued as a result of past production, use, and disposal. 17 18 2.2.2.1. H um an Effects 19 The literature base with regard to potential human effects is detailed in Part II, Chapter 20 7b, Section 7.13. In general, there is limited epidemiological evidence to make a direct 21 association between exposure to TCDD or other dioxin-like compounds and effects on human 22 reproduction or development. One effect that may illustrate this relationship is the altered sex 23 ratio (increased females) seen in the 6 years after the Seveso, Italy, accident (Mocarelli et al., 24 1996, 2000), and in a heavily exposed occupational cohort in Russia (Ryan et al., 2002). 25 Particularly intriguing in these evaluations is the observation that exposure before and during 26 puberty is linked to this sex ratio effect, and predominantly through the paternal side. Other sites 27 have been examined for the effect of TCDD exposure on sex ratio with mixed results but with 28 smaller numbers of offspring. Data on these sites are still preliminary, but effects similar to the 29 Seveso findings are being reported. Continued evaluation of the Seveso population may provide 30 other indications of impacts on reproduction and development but, for now, such data are limited 31 and further research is needed. 32 Positive human data on developmental effects of dioxin-like compounds are limited to a 33 few studies of populations exposed to a complex mixture of potentially toxic compounds (e.g., 34 developmental studies from the Netherlands and effects of ingestion of contaminated rice oil in 35 Japan [Yusho] and Taiwan [Yu-Cheng]). In the latter studies, however, all four manifestations 12/23/03 2-23 DRAFT--DO NOT CITE OR QUOTE 1 of developmental toxicity (reduced viability, structural alterations, growth retardation, and 2 functional alterations) were observed to some degree following exposure to dioxin-like 3 compounds as well as other agents. Data from the Dutch cohort of children exposed to PCBs and 4 dioxin-like compounds (Huisman et al., 1995a, b; Koopman-Esseboom et al., 1994a-c; 1995a, b, 5 1996; Pluim et al., 1992, 1993, 1994; Weisglas-Kuperus et al., 1995; Patandin et al., 1998, 1999; 6 ten Tusscher et al., 2003; Vreugdenhil et al., 2002) suggest impacts of background levels of 7 dioxin and related compounds on neurobehavioral outcomes, thyroid function, immune function, 8 and liver enzymes aspartate aminotransferase (AST) and alanine aminotransferase (ALT). 9 Although these effects cannot be attributed solely to dioxin and related compounds, 10 several associations suggest that these are, in fact, likely to be AhR-mediated effects. Similarly, 11 it is highly likely that the developmental effects in human infants exposed to a complex mixture 12 of PCBs, PCDFs, and polychlorinated quaterphenyls (PCQs) in the Yusho and Yu-Cheng 13 poisoning episodes may have been caused by the combined exposure to those PCB and PCDF 14 congeners that are AhR agonists (Lu and Wong, 1984; Kuratsune, 1989; Rogan, 1989). 15 However, it is not possible to determine the relative contributions of individual chemicals to the 16 observed effects. 17 The incidents at Yusho and Yu-Cheng resulted in increased perinatal mortality and low 18 birth weight in infants born to women who had been exposed. Rocker bottom heal was observed 19 in Yusho infants, and functional abnormalities have been reported in Yu-Cheng children. Not all 20 the effects that were seen are attributable only to dioxin-like compounds. The similarity of 21 effects observed in human infants prenatally exposed to this complex mixture with those reported 22 in adult monkeys exposed only to TCDD suggests that at least some of the effects in the Yusho 23 and Yu-Cheng children are due to the TCDD-like congeners in the contaminated rice oil ingested 24 by the mothers of these children. The similar responses include a clustering of effects in organs 25 derived from the ectodermal germ layer, referred to as ectodermal dysplasia, including effects on 26 the skin, nails, and Meibomian glands and developmental and psychomotor delay during 27 developmental and cognitive tests (Chen et al., 1992). Some investigators believe that because 28 some of the effects in the Yusho and Yu-Cheng cohorts do not correlate with TEQ, such effects 29 could be exclusively due to nondioxin-like PCBs or to an interaction between the dioxins and the 30 nondioxin-like congeners. 31 Ofparticular interest is the common developmental origin (ectodermal layer) of many of 32 the organs and tissues that are affected in humans. An ectodermal dysplasia syndrome involving 33 hyperpigmentation, deformation of the fingernails and toenails, conjunctivitis, gingival 34 hyperplasia, and abnormalities of the teeth has been clearly associated with the Yusho and Yu35 Cheng episodes, and in the non-human primate studies. Alaluusua et al. (1996, 1999) 12/23/03 2-24 DRAFT--DO NOT CITE OR QUOTE 1 investigated dioxin exposure and tooth development in Finnish children as a result of studies of 2 dental effects in dioxin-exposed rats, mice, and nonhuman primates (Part II, Chapter 5, Section 3 5.2) and in PCB-exposed children (Rogan et al., 1988). The Finnish investigators examined 4 enamel hypomineralization of permanent first molars in 6-7-year-old children. The length of 5 time that infants breast-fed was not significantly associated with either mineralization changes or 6 with TEQ levels in the breast milk. However, when the levels and length of breast-feeding were 7 combined in an overall score, a statistically significant association was observed (r= 0.3, 8 p=0.003, regression analysis). These data are discussed further in Part II, Chapter 7b, Section 9 7.13. Follow-up mechanistic studies on tooth development in TCDD sensitive and resistant rats 10 revealed a relatively high dose impact on epithelial-mesenchymal interactions, particularly the 11 mesenchymal odontocytes. This effect that was not associated with differential resistance to 12 acute TCDD toxicity (Kiukkonen et al., 2002). 13 Other investigations into noncancer effects of human exposure to dioxin have provided 14 human data on TCDD-induced changes in circulating reproductive hormones. This was one of 15 the effects judged as having a positive relationship with exposure to TCDD in Part II, Chapter 16 7b, Section 7.13. Levels of reproductive hormones have been measured with respect to exposure 17 to 2,3,7,8-TCDD in three cross-sectional medical studies. Testosterone, luteinizing hormone 18 (LH), and follicle-stimulating hormone (FSH) were measured in trichlorophenol (TCP) and 19 2,4,5-T production workers from the NIOSH cohort (Egeland et al., 1994), in Army Vietnam 20 veterans (CDC Vietnam Experience Study, 1988), and in Air Force Ranch Hands, who handled 21 and/or sprayed Agent Orange during the Vietnam War (Roegner et al., 1991; Grubbs et al., 22 1995). A recent study also demonstrated an inverse correlation between TCDD levels and 23 prolactin in 2,4,5,-T herbicide sprayers (Johnson et al., 2001). Alterations in breast development 24 have been reported in young women, where a doubling of the serum dioxin concentration 25 (CALUX assay) increased the odds of not having reached the adult stage of breast development 26 by 2.3 fold (P<0.02) in the women (~17 yo) studied (Den Hond et al., 2002). Alterations in 27 menstrual duration and flow have been reported in women exposed as premenarcheal girls 20 28 years previously as a result of the Seveso incident (Eskenazi et al., 2002a). 29 The risk of abnormally low testosterone was two to four times higher in exposed workers 30 who had serum 2,3,7,8-TCDD levels above 20 ng/g than in unexposed referents (Egeland et al., 31 1994). In both the 1987 and 1992 examinations, mean testosterone concentrations were slightly 32 but not significantly higher in Ranch Hands (Thomas et al., 1990; Grubbs et al., 1995). FSH and 33 LH concentrations were no different between the exposed and comparison groups. No 34 significant associations were found between Vietnam experience and altered reproductive 12/23/03 2-25 DRAFT--DO NOT CITE OR QUOTE 1 hormone levels (CDC Vietnam Experience Study, 1988). Only the NIOSH study (Egeland et al., 2 1994) found an association between serum 2,3,7,8-TCDD level and increases in serum LH. 3 The findings of the NIOSH and Ranch Hand studies are plausible, given the 4 pharmacological and toxicological properties of2,3,7,8-TCDD in animal models, which are 5 discussed in Part II, Chapters 5 and 7. One plausible mechanism responsible for the effects of 6 dioxins may involve their ability to influence hormone receptors. The AhR, to which 2,3,7,87 TCDD binds, and the hormone receptors are signaling pathways that regulate homoeostatic 8 processes. These signaling pathways are integrated at the cellular level, and there is considerable 9 "cross-talk" between these pathways. For example, studies suggest that 2,3,7,8-TCDD 10 modulates the concentrations of numerous hormones and/or their receptors, including estrogen 11 (Romkes and Safe, 1988; Romkes et al., 1987), progesterone (Romkes et al., 1987), 12 glucocorticoid (Ryan et al., 1989), and thyroid hormones (Gorski and Rozman, 1987; Pavuk et 13 al., 2003). 14 In summary, the results from both the NIOSH and the Ranch Hand studies are limited by 15 the cross-sectional nature of the data and the type of clinical assessments conducted. However, 16 the available data provide evidence that small alterations in human male reproductive hormone 17 levels are associated with serum 2,3,7,8-TCDD. 18 19 2.2.2.2. ExperimentalAnimal Effects 20 The extensive experimental animal database with respect to reproductive and 21 developmental toxicity of dioxin and dioxin-related agents is discussed in Part II, Chapter 5. 22 Dioxin exposure has been observed to result in both male and female reproductive effects as well 23 as developmental effects. These latter effects are among the most responsive health endpoints to 24 dioxin exposure (see Part II, Chapter 8, Section 8.3). In general, the prenatal and developing 25 postnatal animal is more sensitive to the effects of dioxin than is the adult. In several instances 26 (e.g., fetotoxicity in hamsters, rats, mice, and guinea pigs), the large species differences seen in 27 acute toxicity are greatly reduced when developing animals are evaluated. Most of the data 28 reviewed are from studies of six genera of laboratory animals. Although much of the data come 29 from animals exposed only to TCDD, more recent studies of animals exposed to mixtures of 30 PCDD/PCDF/ PCB congeners provide results that are consistent with the studies of TCDD 31 alone. 32 33 2.2.2.2.I. Developmental toxicity. Dioxin exposure results in a wide variety of developmental 34 effects; these are observed in three different vertebrate classes and in several species within each 35 class. All four of the manifestations of developmental toxicity have been observed following 12/23/03 2-26 DRAFT--DO NOT CITE OR QUOTE 1 exposure to dioxin: reduced viability, structural alterations, growth retardation, and functional 2 alterations. As summarized previously (Peterson et al., 1993), increased prenatal mortality (rat 3 and monkey), functional alterations in learning (rat, mouse, and monkey) and sexual behavior 4 (rat), and changes in the development of the reproductive system (rat, hamster, and mouse) occur 5 at the lowest exposure levels tested (see also Part II, Chapter 8, Section 8.3). 6 Dioxin exposure has resulted in reduced prenatal or postnatal viability in virtually every 7 species in which it has been tested. Previously, increased prenatal mortality appeared to be 8 observed only at exposures that also resulted in maternal toxicity. However, the studies of Olson 9 and McGarrigle (1990) in the hamster and Schantz and Bowman (1989) in the monkey suggested 10 that this was not the case in all species. Although the data from these two studies were limited, 11 prenatal death was observed in cases where no maternal toxicity was evident. In the rat, 12 Peterson's laboratory (Bjerke et al., 1994a, b; Roman et al., 1995) reported increased prenatal 13 death following a single exposure to TCDD during gestation that did not cause maternal toxicity, 14 and Gray et al. (1995a) observed a decrease in postnatal survival under a similar exposure 15 regimen. Although identifying the presence or absence of maternal toxicity may be instructive as 16 to the specific origin of the reduced prenatal viability, it does not alter the fact that pre- and 17 postnatal deaths were observed. In either case, the Agency considers these effects as being 18 indicators of developmental toxicity in response to the exposure (U.S. EPA, 1991b). 19 Some of the most striking findings regarding dioxin exposure relate to the effects on the 20 developing reproductive system in laboratory animals. Only a single, low-level exposure to 21 TCDD during gestation is required to initiate these developmental alterations. Mably et al. 22 (1992a-c) originally reported that a single exposure of the Holtzman maternal rat to as little as 23 0.064 :g/kg could alter normal sexual development in the male offspring. A dose of 0.064 :g/kg 24 in these studies resulted in a maximal body burden in the maternal animal of 64 ng/kg during 25 critical windows in development. More recently, these findings of altered normal sexual 26 development have been further defined (Bjerke et al., 1994a, b; Gray et al., 1995a; Roman et al., 27 1995) and extended to female offspring and other strains (Faqi et al., 1998; Ohsako et al., 2001) 28 and species (hamsters and mice) (Gray et al., 1995b; Theobald et al., 1997). In general, the 29 findings of these later studies have produced qualitatively similar results that define a significant 30 effect of dioxin on the developing reproductive system. 31 In the developing male rat, TCDD exposure during the prenatal and lactational periods 32 results in delay of the onset of puberty, as measured by age at preputial separation. There is a 33 reduction in testis weight, sperm parameters, and sex accessory gland weights. In the mature 34 male exposed during the prenatal and lactational periods, there is an alteration of normal sexual 35 behavior and reproductive function. Males exposed to TCDD during gestation are 12/23/03 2-27 DRAFT--DO NOT CITE OR QUOTE 1 demasculinized. Feminization of male sexual behavior and a reduction in the number of 2 implants in females mated with exposed males have also been reported, although these effects 3 have not been consistently found. These effects do not appear to be related to reductions in 4 circulating androgens, which were shown in the most recent studies to be unaffected by TCDD. 5 Most of these effects have occurred in a dose-related fashion, some at doses of 0.05 :g/kg and 6 0.064 :g/kg, the lowest doses tested (Mably et al., 1992c; Gray et al., 1997a). 7 In Part II, Chapter 8, ED0i values were estimated from the Mably et al. (1992a-c) and 8 Gray et al. (1997a) reports. In these two studies more than 44 data sets were modeled, and 17 of 9 these data sets had body burden ED0is lower than 50 ng/kg. For the 12 endpoints in the Mably et 10 al. studies that were modeled in Part II, Chapter 8, the median body burden EDmestimate is 5.2 11 ng TCDD/kg. Although not modeled in Part II, Chapter 8, the data from Faqi et al. (1998) and 12 Ohsaka et al. (2001) have LOAELs and NOAELs for developmental reproductive effects of 13 TCDD in male rats ranging from body burdens of 12.5-200 ng TCDD/kg, which is consistent 14 with the Mably et al. and Gray et al. studies. 15 In the developing female rat, Gray and Ostby (1995) demonstrated altered sexual 16 differentiation in both the Long Evans and Holtzman strains. The effects observed depended on 17 the timing of exposure. Exposure during early organogenesis altered the cyclicity, reduced 18 ovarian weight, and shortened the reproductive lifespan. Exposure later in organogenesis 19 resulted in slightly lowered ovarian weight, structural alterations of the genitalia, and a slight 20 delay in puberty. However, cyclicity and fertility were not affected with the later exposure. The 21 most sensitive dose-dependent effects of TCDD in the female rat were the structural alterations 22 of the genitalia that occurred at 0.20 :g TCDD/kg administered to the dam (Gray et al., 1997b). 23 As described above, studies demonstrating adverse health effects from prenatal exposures 24 often involved a single dose administered at a discrete time during pregnancy. The production of 25 prenatal effects at a given dose appears to require exposure during critical times in fetal 26 development. This concept is well supported by a recent report (Hurst et al., 2000) that 27 demonstrated the same incidence of adverse effects in rat pups born to dams with a single 28 exposure of 0.2 :g TCDD/kg body weight on gestation day 15 versus 1.0 :g TCDD/kg body 29 weight on gestation day 8. Both ofthese experimental exposure paradigms resulted in the same 30 fetal tissue concentrations and body burdens during the critical window of sensitivity. For 31 example, exposure to 0.2 :g TCDD/kg on day 15 resulted in 13.2 pg TCDD/g fetal tissue on 32 day16; exposure to 1.0 :g TCDD/kg on day 8 resulted in 15.3 pg TCDD/g fetus on day 16. This 33 study demonstrates the appropriateness of the use of body burden to describe the effects of 34 TCDD when comparing different exposure regimens. The uncertainties introduced when trying 35 to compare studies with steady-state body burdens with single-dose studies may make it difficult 12/23/03 2-28 DRAFT--DO NOT CITE OR QUOTE 1 to determine a lowest effective dose. Application of pharmacokinetic models (described in Parts 2 I and II) to estimate body burdens at the critical time of development is expected to be a sound 3 method for relating chronic background exposures to the results obtained from single-dose 4 studies. 5 Structural malformations, particularly cleft palate and hydronephrosis, occur in mice 6 administered TCDD. The findings, although not representative of the most sensitive 7 developmental endpoints, indicate that exposure during the critical period of organogenesis can 8 affect the processes involved in normal tissue formation. The TCDD-sensitive events appear to 9 require the AhR. Mouse strains that produce AhRs with relatively high affinity for TCDD 10 respond to lower doses than do strains with relatively low-affinity receptors. Moreover, 11 congeners that have a greater affinity for the AhR are more developmentally toxic than those that 12 have a lower affinity. This is consistent with the rank ordering of toxic potency based on affinity 13 for the receptor, as discussed in Part II, Chapter 9, Section 9.3. In addition, mice in which the Ah 14 receptor has been knocked out do not develop cleft palate. 15 Recent work, not elaborated upon here, has demonstrated that developmental exposure of 16 rodents to dioxin also permanently alters the development of the prostate in wild type but not 17 AhR null mutant mice (Lin et al., 2003), and mammary development in rats and mice (Fenton et 18 al, 2002; Vorderstrasse et al., 2003). The key role of the Ah receptor has also been demonstrated 19 in the developing heart of AhR null mice (Lund et al., 2003). 20 21 2.2.2.2.2. Adultfemale reproductive toxicity. The primary effects of TCDD on female 22 reproduction in animals appear to be decreased fertility, inability to maintain pregnancy for the full 23 gestational period, and, in the rat, decreased litter size. In some studies of rats and of primates, 24 signs of ovarian dysfunction such as anovulation and suppression of the estrous cycle have been 25 reported (Kociba et al., 1976; Barsotti et al., 1979; Allen et al., 1979; Li et al., 1995a, b). Although 26 the majority of reproductive effects are associated with high-dose exposures in experimental 27 animals, the induction of endometriosis in primates occurs at body burdens near background 28 human exposures. This effect is discussed further below. 29 30 2.2.2.2.3. Adult male reproductive toxicity. TCDD and related compounds decrease testis and 31 accessory sex organ weights, cause abnormal testicular morphology, decrease spermatogenesis, 32 and reduce fertility when given to adult animals in doses sufficient to reduce feed intake and/or 33 body weight. In the testes of these different species, TCDD effects on spermatogenesis are 34 characterized by loss of germ cells, the appearance of degenerating spermatocytes and mature 35 spermatozoa within the lumens of seminiferous tubules, and a reduction in the number of tubules 12/23/03 2-29 DRAFT--DO NOT CITE OR QUOTE 1 containing mature spermatozoa (Allen and Lalich, 1962; Allen and Carstens, 1967; McConnell et 2 al., 1978; Chahoud et al., 1989). This suppression of spermatogenesis is not a highly sensitive 3 effect when TCDD is administered to postweanling animals, as an exposure of 1 :g/kg/day over 4 a period of weeks appears to be required to produce these effects. 5 6 2.2.2.3. Other Data Related to Developmental and Reproductive Effects 7 2.2.2.3.I. Endometriosis. The association of dioxin with endometriosis was first reported in a 8 study of rhesus monkeys that had been exposed for 4 years to dioxin in their feed and then held 9 for an additional 10 years (Rier et al., 1993). There was a dose-related increase in both the 10 incidence and severity of endometriosis in the exposed monkeys as compared to controls. 11 Follow-up on this group of monkeys revealed a clear association with total TEQ. A study in 12 which rhesus monkeys were exposed to PCBs for up to 6 years failed to show any enhanced 13 incidence of endometriosis (Arnold et al., 1996). However, many of these monkeys were no 14 longer cycling, and the time may not have been adequate to develop the response. In the TCDD 15 monkey study, it took 7 years before the first case of endometriosis was noted (Rier et al., 1993). 16 A recent study in Cynomolgus monkeys showed promotion of surgically induced 17 endometriosis by TCDD within 1year after surgery (Yang et al., 2000). Studies using rodent 18 models for surgically induced endometriosis have also shown the ability of TCDD to promote 19 lesions in a dose-related manner (Cummings et al., 1996, 1999; Johnson et al., 1997; Bruner20 Tran et al., 1999). This response takes at least 2 months to be detected (Cummings et al., 1996, 21 1999; Johnson et al., 1997). Another study in mice that failed to detect dioxin promotion of 22 surgically induced endometriosis held the mice for only 1month, not long enough to detect a 23 response (Yang et al., 1997). Prenatal exposure of mice also enhanced the sensitivity of the 24 offspring to the promotion of surgically induced endometriosis by TCDD (Cummings et al., 25 1999). 26 The effects of TCDD in the murine model of endometriosis appear to be AhR-mediated, 27 as demonstrated in a study in which AhR ligands were able to promote the lesions, whereas non 28 AhR ligands, including a nondioxin-like PCB, had no effect on surgically induced endometriosis 29 (Johnson et al., 1997). Dioxin has also been shown to result in endometriosis with human 30 endometrial tissue implanted in nude mice (Bruner-Tran et al., 1999). 31 Data on the relationship of dioxins to endometriosis in humans is intriguing, but 32 preliminary. Studies in the early 1990s suggested that women who had higher levels of persistent 33 organochlorines were at increased risk for endometriosis (Gerhard and Runnebaum, 1992). This 34 was followed by the observation that Belgian women, who have the highest levels of dioxins in 35 their background population, had higher incidences of endometriosis than those reported from 12/23/03 2-30 DRAFT--DO NOT CITE OR QUOTE 1 other populations (Koninckx et al., 1994). A study from Israel then demonstrated that there was 2 a correlation between detectable TCDD in women who had surgically confirmed endometriosis 3 in comparison to those who had no endometriosis (Mayani et al., 1997). 4 Recent studies from Belgium indicate that women with higher body burdens, based on 5 serum TEQ determinations, are at greater risk for endometriosis (Pauwels et al., 1999). No 6 association was seen with total PCBs in this study. A small study in the United States that did 7 not involve surgically confirmed endometriosis saw no association between TCDD and 8 endometriosis (Boyd et al., 1995). Likewise, a study in Canada saw no association between total 9 PCBs and endometriosis (Lebel et al., 1998). The lack of an association with total PCBs is not 10 surprising, because the rodent studies have indicated that this response is AhR-mediated 11 (Johnson et al., 1997). The Seveso Women's Health Study reported "...a doubled, non 12 significant risk for endometriosis among women with serum TCDD levels of 100 ppt or higher, 13 but no clear dose-response. Unavoidable disease misclassification in a population-based study 14 may have led to an underestimate of the true risk of endometriosis"(Eskenazi et al., 2002b). 15 The animal results lend biological plausibility to the epidemiology findings (Birnbaum 16 and Cummings, 2002). Endometriosis is not only an endocrine disorder, it is also associated with 17 immune system alterations (Rier et al., 1995; Rier and Foster, 2002). Dioxins are known to be 18 potent modulators of the animal immune system and to affect estrogen homeostasis. Further 19 studies are clearly needed to provide additional support to this association of endometriosis and 20 dioxins, as well as to demonstrate causality. 21 22 2.2.2.3.2. Androgenic deficiency. The effects of TCDD on the male reproductive system when 23 exposure occurs in adulthood are believed to be due in part to an androgenic deficiency. This 24 deficiency is characterized in adult rats by decreased plasma testosterone and 25 5a-dihydrotestosterone concentrations, unaltered plasma LH concentrations, and unchanged 26 plasma clearance of androgens and LH (Moore et al., 1985, 1989; Mebus et al., 1987; Moore and 27 Peterson, 1988; Bookstaff et al., 1990a). The cause of the androgenic deficiency was believed to 28 be due to decreased testicular responsiveness to LH and increased pituitary 29 responsiveness to feedback inhibition by androgens and estrogens (Moore et al., 1989, 1991; 30 Bookstaff et al., 1990a, b; Kleeman et al., 1990). The single dose used in some of those earlier 31 studies (15 :g TCDD/kg body weight) is now known to affect Leydig cells (Johnson et al., 32 1994). 33 12/23/03 2-31 DRAFT--DO NOT CITE OR QUOTE 1 2.2.2.4. Developmental and Reproductive Effects Hazard Characterization 2 There is limited direct evidence addressing the issues of how or at what levels humans 3 will begin to respond to dioxin-like compounds with adverse impacts on development or 4 reproductive function. The series of published Dutch studies suggest that pre- and early postnatal 5 exposures to PCBs and other dioxin-like compounds may impact developmental milestones at 6 levels at or near current average human background exposures. Although it is unclear whether 7 these measured responses indicate a clearly adverse impact, if humans respond to TCDD 8 similarly to animals in laboratory studies, there are indications that exposures at relatively low 9 levels might cause developmental effects and at higher levels might cause reproductive effects. 10 There is especially good evidence for effects on the fetus from prenatal exposure. The Yusho 11 and Yu-Cheng poisoning incidents are clear demonstrations that dioxin-like compounds can 12 produce a variety of mild to severe developmental effects in humans that resemble the effects of 13 exposure to dioxins and dioxin-like compounds in animals. 14 Humans do not appear to be particularly sensitive or insensitive to effects of dioxin 15 exposure in comparison to other animals. Therefore, it is reasonable to assume that human 16 responsiveness would lie across the middle ranges of observed responses. This assumption still 17 does not address the issues surrounding the potentially different responses that humans (or 18 animals) might have to the more complex and variable environmental mixtures of dioxin-like 19 compounds. One additional key point is that most of the epidemiology studies have focused on 20 TCDD, and not the total TEQ. Eskenazi et al. (2004) have shown that background exposure to 21 dioxins, furans and PCBs in the referent population (zone non-ABR) cohort at Seveso was 22 substantial,with non-ABR residents having average serum 2,3,7,8-TCDD and TEQ levels of 20.2 23 ppt and 100.4 ppt, respectively. The exposure zone A median serum TCDD level was 272 ppt 24 and zone B was 47 ppt. The authors suggest that previous Seveso studies "that considered only 25 TCDD exposure, may have underestimated health effects due to total TEQ concentrations." 26 TCDD and related compounds have reproductive and developmental toxicity potential in 27 a broad range of wildlife and domestic and laboratory animals. Many of the effects have been 28 shown to be TCDD dose-related. The effects on perinatal viability and male reproductive 29 development are among the most sensitive effects reported, occurring at a single prenatal 30 exposure range of as little as 0.05-0.075 :g/kg, resulting in calculated fetal tissue concentrations 31 of 3-4 ng/kg in the rat (Hurst et al., 2000). In these studies, effects were often observed at the 32 lowest exposure level tested, thus a NOAEL has not been established for several of these 33 endpoints. In general, the structure-activity results are consistent with an AhR-mediated 34 mechanism for the developmental effects that are observed in the low-dose range. The structure35 activity relationship in laboratory mammals appears to be similar to that for AhR binding. This 12/23/03 2-32 DRAFT--DO NOT CITE OR QUOTE 1 is especially the case with cleft palate in the mouse, but has also been seen with hydronephrosis 2 in the mouse, and developmental reproductive effects in rats. 3 It is assumed that the responses observed in animal studies are indicative of the potential 4 for reproductive and developmental toxicity in humans. This is an established assumption in the 5 risk assessment process for developmental toxicity (U.S. EPA, 1991b). It is supported by the 6 number of animal species and strains in which effects have been observed. The limited human 7 data are consistent with an effect following exposure to TCDD or TCDD-like agents. In 8 addition, the phylogenetic conservation of the structure and function of the AhR also increases 9 our confidence that these effects may occur in humans. 10 There is extensive evidence in experimental animals (mice, rats, monkeys) that exposure 11 to dioxin-like chemicals during development produces neurobehavioral effects. In fact, recent 12 studies in rodents demonstrate effects on brain development (Zareba et al., 2002), attention 13 (Markowski et al., 2002), and behavior (Hojo et al., 2002) at doses close to current human body 14 burdens. The situation in humans is more complex. Studies in humans demonstrate associations 15 between dioxin exposure and alterations in neurological development. These same studies often 16 show similar associations between exposure to nondioxin-like PCBs and these same effects. On 17 the basis of the human studies, it is possible that the alterations in neurological development are 18 due to an interaction between the dioxins and the nondioxin-like PCBs. At present there are 19 limited data that define the roles ofthe dioxins versus the nondioxin-like PCBs in these effects 20 on neurological development. 21 In general, the structure-activity results on dioxin-like compounds are consistent with an 22 AhR-mediated mechanism for many of the developmental effects that are observed. The 23 structure-activity relationship in laboratory mammals appears to be similar to that for AhR 24 binding. This is especially the case with teratogenesis in the mouse. However, a direct 25 relationship with AhR binding has not yet been proven for those involving the developing 26 nervous system. 27 28 2.2.3. Immunotoxicity 29 2.2.3.I. Epidemiologic Findings 30 The available epidemiologic studies on immunologic function in humans relative to 31 exposure to 2,3,7,8-TCDD do not describe a consistent pattern of effects among the examined 32 populations. Two studies of German workers in which one cohort was exposed to 2,3,7,8-TCDD 33 (Ott et al., 1994), and the other to 2,3,7,8-tetrabrominated dioxin and furan (Zober et al., 1992), 34 found dose-related increases of complements C3 or C4, whereas the Ranch Hands have 35 continued to exhibit elevations in immunoglobulin A (IgA) (Roegner et al., 1991; Grubbs et al., 12/23/03 2-33 DRAFT--DO NOT CITE OR QUOTE 1 1995). Other studies of groups with documented exposure to 2,3,7,8-TCDD have not examined 2 complement components to any great extent or observed significant changes in IgA. Suggestions 3 of immunological disturbances have been observed in a small group of exposed workers (Tonn et 4 al., 1996) and in perinatally exposed children (ten Tusscher et al., 2003), providing support for a 5 testable hypothesis to be evaluated in other exposed populations. 6 Comprehensive evaluation ofimmunologic status and function of the NIOSH (Halperin 7 et al., 1998), Ranch Hand (Michalek et al., 1999b), and Hamburg chemical workers (Jung et al., 8 1998; Ernst et al., 1998) cohorts found no consistent differences between exposed and unexposed 9 groups for lymphocyte subpopulations, response to mitogen stimulation, or rates of infection. 10 However, recent data from the Seveso experience demonstrate subtle effects on immune function 11 (Baccarelli et al., 2002). 12 More comprehensive evaluations ofimmunologic function with respect to exposure to 13 2,3,7,8-TCDD and related compounds are necessary to assess more definitively the relationships 14 observed in nonhuman species. Longitudinal studies of the maturing human immune system may 15 provide the greatest insight, particularly because animal studies have found significant results in 16 immature animals, and human breast milk is a source of 2,3,7,8-TCDD and other related 17 compounds. The studies of Dutch infants (ten Tusscher et al., 2003) described earlier provide an 18 example of such a study design. Additional studies of highly exposed adults may also shed light 19 on the effects of long-term chronic exposures through elevated body burdens. Therefore, there 20 appears to be too little information to suggest definitively that 2,3,7,8-TCDD, at the levels 21 observed, causes long-term adverse effects on the immune system in adult humans. 22 23 2.2.3.2. Animal Findings 24 Cumulative evidence from a number of studies indicates that the immune system of 25 various animal species is a target for toxicity of TCDD and structurally related compounds, 26 including other PCDDs, PCDFs, and PCBs. Both cell-mediated and humoral immune responses 27 are suppressed following TCDD exposure, suggesting that there are multiple cellular targets 28 within the immune system that are altered by TCDD. Evidence also suggests that the immune 29 system is indirectly targeted by TCDD-induced changes in nonlymphoid tissues. TCDD 30 exposure of experimental animals results in decreased host resistance following challenge with 31 certain infectious agents, which likely result from TCDD-induced suppression of immunological 32 functions. 33 The primary antibody response to the T cell-dependent antigen, sheep red blood cells 34 (SRBCs), is the most sensitive immunological response that is consistently suppressed in mice 35 exposed to TCDD and related compounds. The degree of immunosuppression is related to the 12/23/03 2-34 DRAFT--DO NOT CITE OR QUOTE 1 potency of the dioxin-like congeners. There is remarkable agreement among several different 2 laboratories for the potency of a single acute dose of TCDD (i.e., suppression at a dose as low as 3 0.1 :g TCDD/kg with an average 50% immunosupressive dose [ID50] value of approximately 4 0.7 :g TCDD/kg) to suppress this response in Ah-responsive mice. Results of studies that have 5 compared the effects of acute exposure to individual PCDDs, PCDFs, and PCB congeners 6 (which differ in their binding affinity for the AhR) on this response have provided critical 7 evidence that certain dioxin-like congeners are also immunosuppressive. The degree of 8 immunosuppression has been found to be related to potency of the dioxin-like congeners. 9 Antibody responses to T cell-independent antigens such as trinitrophenyl-lipopolysaccharide and 10 the cytotoxic T lymphocyte (CTL) response are also suppressed by a single acute exposure to 11 TCDD, albeit at higher doses than those that suppress the SRBC response. Although a thorough 12 and systematic evaluation of the immunotoxicity of TCDD-like congeners in different species 13 and for different immunological endpoints has not been performed, it can be inferred from the 14 available data that dioxin-like congeners are immunosuppressive. 15 Perinatal exposure of experimental animals to TCDD results in suppression of primarily 16 T cell immune functions, with suppression persisting into adulthood. In mice, the effects on T 17 cell functions appear to be related to the fact that perinatal TCDD exposure alters thymic 18 precursor stem cells in the fetal liver and bone marrow and thymocyte differentiation in the 19 thymus. These studies suggest that perinatal development is a critical and sensitive period for 20 TCDD-induced immunotoxicity. Further efforts should be made to determine the consequences 21 of perinatal exposure to TCDD and related compounds and mixtures on immune system 22 integrity. 23 24 2.2.3.3. Other Data Related toImmunologic Effects 25 In addition to the TCDD-like congener results, studies using strains ofmice that differ in 26 the expression of the AhR have provided critical evidence to support a role for Ah-mediated 27 immune suppression following exposure to dioxin-like compounds. Recent in vitro work also 28 supports a role for Ah-mediated immune suppression. Other in vivo and in vitro data, however, 29 suggest that non-Ah-mediated mechanisms may also play some role in immunotoxicity induced 30 by dioxin-like compounds. However, more definitive evidence remains to be developed to 31 support this latter view. 32 The immunosuppressive potency ofindividual dioxin-like compounds in mice is related 33 to their structural similarity to TCDD. However, the immunotoxicity of TCDD and related 34 congeners can be modified by co-exposure to nondioxin-like PCBs in simple binary or more 35 complex mixtures, resulting in additive or antagonistic interactions. There is a need for the 12/23/03 2-35 DRAFT--DO NOT CITE OR QUOTE 1 generation of dose-response data of acute, subchronic, and chronic exposure to the individual 2 congeners in a mixture and for the mixture itself in order to fully evaluate potential synergistic, 3 additive, or antagonistic effects of environmentally relevant mixtures. A preliminary report 4 demonstrating that the immunotoxicity of a food-like mixture of dioxins was well-predicted by 5 the TEQ has been presented (Smialowicz et al., 1997). 6 Animal host resistance models that mimic human disease have been used to assess the 7 effects of TCDD on altered host susceptibility. TCDD exposure increases susceptibility to 8 challenge with bacteria, viruses, parasites, and tumors. Mortality is increased in TCDD-exposed 9 mice challenged with certain bacteria. Increased parasitemia occurs in TCDD-exposed mice and 10 rats challenged with parasitic infections. Low doses of TCDD also alter resistance to virus 11 infections in rodents. Increased susceptibility to infectious agents is an important benchmark of 12 immunosuppression; however, the role that TCDD plays in altering immune-mediated 13 mechanisms important in murine resistance to infectious agents remains to be elucidated. Also, 14 because little is known about the effects that dioxin-like congeners have on host resistance, more 15 research is recommended in this area. 16 Studies in nonhuman primates exposed acutely, subchronically, or chronically to 17 halogenated aromatic hydrocarbons (HAH) have revealed variable alterations in lymphocyte 18 subpopulations, primarily T lymphocyte subsets. In three separate studies in which monkeys 19 were exposed subchronically or chronically to PCBs, the antibody response to SRBC was 20 consistently found to be suppressed. These results in nonhuman primates are important because 21 they corroborate the extensive database of HAH-induced suppression of the antibody response to 22 SRBC in mice and thereby provide credible evidence for immunosuppression by HAHs across 23 species. In addition, these data indicate that the primary antibody response to this T cell24 dependent antigen is the most consistent and sensitive indicator of HAH-induced 25 immunosuppression. 26 The available database derived from well-controlled animal studies on TCDD 27 immunotoxicity can be used for the establishment ofNOELs. As the antibody response to 28 SRBCs has been shown to be dose-dependently suppressed by TCDD and related dioxin-like 29 compounds, this database is best suited for the development of dose-response modeling. 30 31 2.2.3.4. Immunologic Effects Hazard Characterization 32 Accidental or occupational exposure of humans to TCDD and/or related compounds 33 variably affects a number of immunological parameters. Unfortunately, the evaluation of 34 immune system integrity in humans exposed to dioxin-like compounds has provided data that are 35 inconsistent across studies. The broad range of "normal" responses in humans due to the large 12/23/03 2-36 DRAFT--DO NOT CITE OR QUOTE 1 amount of variability inherent in such a heterogenous population, the limited number and 2 sensitivity of tests performed, and poor exposure characterization of the cohorts in these studies 3 compromise any conclusions about the ability of a given study to detect immune alterations. 4 Consequently, there are insufficient clinical data from these studies to fully assess human 5 sensitivity to TCDD exposure. Nevertheless, based on the results of the extensive animal work, 6 the database is sufficient to indicate that immune effects could occur in the human population 7 from exposure to TCDD and related compounds at some dose level. At present, it is EPA's 8 scientific judgment that TCDD and related compounds should be regarded as nonspecific 9 immunosuppressants and immunotoxicants until better data to inform this judgment are 10 available. 11 It is interesting that a common thread in several human studies is the observed reduction 12 in CD4+ T helper cells, albeit generally within the "normal" range, in cohorts exposed to dioxin 13 like compounds. Even though these reductions may not translate into clinical effects, it is 14 important to note that these cells play an important role in regulating immune responses and that 15 their reduction in clinical diseases is associated with immunosuppression. It is also important to 16 realize that those at the extremes of the population distribution may be at special risk of such 17 alterations. Another important consideration is that a primary antibody response following 18 immunization was not evaluated in any of the human studies. Because this immune parameter 19 has been revealed to be the most sensitive in animal studies, it is recommended that TCDD and 20 related compounds be judged immunosupressive and that this parameter be included in future 21 studies of human populations exposed to TCDD and related compounds. It is also recommended 22 that research focused on delineating the mechanism(s) underlying dioxin-induced 23 immunotoxicity and immunosuppression continue. 24 25 2.2.4. Chloracne 26 Chloracne and associated dermatologic changes are widely recognized responses to 27 TCDD and other dioxin-like compounds in humans. Along with the reproductive hormones 28 discussed above and gamma glutamyl transferase (GGT) levels, which are discussed below, 29 chloracne is one of the noncancer effects that has a strong positive association with exposure to 30 TCDD in humans (see Part II, Chapter 7b, Section 7.13). Chloracne is a severe acne-like 31 condition that develops within months of first exposure to high levels of dioxin and related 32 compounds. For many individuals, the condition disappears after discontinuation of exposure, 33 despite initial serum levels of dioxin in the thousands of parts per trillion; for others, it may 34 remain for many years. The duration of persistent chloracne is on the order of 25 years, although 12/23/03 2-37 DRAFT--DO NOT CITE OR QUOTE 1 cases of chloracne persisting for more than 40 years have been noted (see Part II, Chapter 7b, 2 Section 7.13). 3 In general, chloracne has been observed in most incidents where substantial dioxin 4 exposure has occurred, particularly among TCP production workers and Seveso residents (see 5 Part II, Chapter 7b). The amount of exposure necessary for development of chloracne has not 6 been resolved, but studies suggest that high exposure (both high acute and long-term exposure) to 7 2,3,7,8-TCDD increases the likelihood of chloracne, as evidenced by chloracne in TCP 8 production workers and Seveso residents who had documented high serum 2,3,7,8-TCDD levels 9 (Beck et al., 1989; Fingerhut et al., 1991a; Mocarelli et al., 1991; Neuberger et al., 1991) or in 10 individuals who had a work history with long duration of exposure to 2,3,7,8-TCDD11 contaminated chemicals (Bond et al., 1989). 12 In earlier studies, chloracne was considered to be a "hallmark of dioxin intoxication" 13 (Suskind, 1985). However, in only two studies were risk estimates calculated for chloracne. 14 Both were studies of different cohorts of TCP production workers, one of which was employed 15 in a West Virginia plant (Suskind and Hertzberg, 1984), the other in a plant in Michigan (Bond et 16 al., 1989). Of the 203 West Virginia workers, 52.7% (p<0.001) were found to have clinical 17 evidence of chloracne, and 86.3% reported a history of chloracne (p<0.001). None of the 18 unexposed workers had clinical evidence or reported a history of chloracne. Among the 19 Michigan workers, the relative risk for cases of chloracne was highest for individuals with the 20 longest duration of exposure ($ 60 months; RR = 3.5, 95% CI = 2.3-5.1), those with the highest 21 cumulative dose of TCDD (based on duration of assignment across and within 2,3,7,8-TCDD22 contaminated areas in the plant) (RR = 8.0, 95% CI = 4.2-15.3), and those with the highest 23 intensity of 2,3,7,8-TCDD exposure (RR = 71.5, 95% CI = 32.1-159.2). 24 Studies in multiple animal species have been effective in describing the relationship 25 between 2,3,7,8-TCDD and chloracne, particularly in rhesus monkeys (McNulty, 1977; Allen et 26 al., 1977; McConnell et al., 1978). Subsequent to exposure to 2,3,7,8-TCDD, monkeys 27 developed chloracne and swelling ofthe meibomian glands, the modified sebaceous glands in the 28 eyelid. The histologic changes in the meibomian glands are physiologically similar to those 29 observed in human chloracne (Dunagin, 1984). 30 In summary, the evidence provided by the various studies convincingly supports what is 31 already presumed--that chloracne is a common sequel of high levels of exposure to 2,3,7,832 TCDD and related compounds. More information is needed to determine the level and frequency 33 of exposure to dioxin-like compounds needed to cause chloracne and whether personal 34 susceptibility plays a role in the etiology. Finally, it is important to recall that the absence of 35 chloracne does not imply lack of exposure (Mocarelli et al., 1991). 12/23/03 2-38 DRAFT--DO NOT CITE OR QUOTE 1 2.2.5. Diabetes 2 Diabetes mellitus is a heterogeneous disorder that is a consequence of alterations in the 3 number or function of pancreatic beta cells responsible for insulin secretion and carbohydrate 4 metabolism. Diabetes and fasting serum glucose levels were evaluated in more recent cross 5 sectional medical studies because of the apparently high prevalence of diabetes and abnormal 6 glucose tolerance tests in one case report of 55 TCP workers (Pazderova-Vejlupkova et al., 7 1981). Recent epidemiology studies, as well as early case reports, have indicated a weak 8 association between serum concentrations of dioxin and diabetes. This association was first 9 noted in the early 1990s when a decrease in glucose tolerance was seen in the NIOSH cohort. 10 This was followed by a report of an increase in diabetes in the Ranch Hand cohort (Michalek et 11 al., 1999a; Longnecker and Michalek, 2000). An increase in diabetes in other occupational 12 cohorts (Steenland et al., 1999; Vena et al., 1998) as well as in the Seveso population (Pesatori et 13 al., 1998) has also been reported. There was not a significant increase in diabetes in the NIOSH 14 mortality study, although 6 of the 10 most highly exposed workers did have diabetes (Calvert et 15 al., 1999). However, mortality studies are limited in their ability to assess risk from diabetes 16 mellitus because the prevalence of disease may not be available from death certificates. 17 A paper by Longnecker and Michalek (2000) found a pattern suggesting that low levels of 18 dioxin may influence the prevalence of diabetes. However, these results did not show an 19 exposure-response relationship. Because it is the only study of its type to have been published, 20 additional population-based studies are warranted to validate its findings. A recent update of the 21 Ranch Hand study shows a 47% excess of diabetes in the most heavily exposed group of veterans 22 (Michalek et al., 1999a). 23 Most of the data suggest that the diabetes observed in the studies is Type II, or adult-onset 24 diabetes, rather than insulin dependent, or Type I. Aging and obesity are the key risk factors for 25 Type II diabetes. However, dioxins may shift the distribution of sensitivity, putting people at risk 26 at younger ages or when they have less weight. Dioxin alters lipid metabolism in multiple 27 species, including humans (Sweeney et al., 1997; Pohjanvirta and Tuomisto, 1994), and it also 28 alters glucose uptake into both human and animal cells in culture (Enan and Matsumura, 1994; 29 Olsen et al., 1994). Mechanistic studies have demonstrated that dioxin affects glucose transport 30 (Enan and Matsumura, 1994), a property under the control of the hypoxia response pathway 31 (Ouiddir et al., 1999). A key regulatory protein in this pathway is the partner of the AhR, Amt 32 (also known as HIF1-beta) (Gu et al., 2000; Taylor and Zhulin, 1999). Activation of the AhR by 33 dioxin may compete with other pathways for Arnt, such as the hypoxia-inducible factor (HIF) 34 pathway (Gradin et al., 1992). Dioxin has also been shown to downregulate the insulin growth 35 factor receptor (Liu et al., 1992). These three issues--altered lipid metabolism, altered glucose 12/23/03 2-39 DRAFT--DO NOT CITE OR QUOTE 1 transport, and alterations in the insulin signaling pathway--all provide biological plausibility to 2 the association of dioxins with diabetes. 3 A causal relationship between diabetes and dioxin has not been established, although both 4 the toxicologic and epidemiological data are suggestive of a plausible association (Remillard and 5 Bunce, 2002). Many questions have yet to be answered. For example, does diabetes alter the 6 pharmacokinetics of dioxin? Diabetes is known to alter the metabolism of several drugs in 7 humans (Matzke et al., 2000) and may also alter dioxin metabolism and kinetics. Because adult8 onset diabetes is also associated with being overweight, and body composition has been shown to 9 modify the apparent half-life of dioxin, could the rate of elimination of dioxins be lowered in 10 people who have diabetes, causing them to have higher body burdens? This may be relevant to 11 the background population, but it is hardly likely to be an explanation in highly exposed 12 populations. 13 Key research needs are twofold. The first is to develop an animal model with which to 14 study the association between dioxins and diabetes and glucose perturbation. Several rodent 15 models for Type II diabetes exist and may be used. The second is to conduct population-based 16 incidence studies that take into account dioxin levels as well as the many known factors 17 associated with diabetes. Although diabetes may cause the underlying pathology leading to 18 death, it is often not attributed as the cause of death and thus limits the utility of mortality 19 studies. 20 21 2.2.6. Other Effects 22 2.2.6.I. Elevated GGT 23 As mentioned above, there appears to be a consistent pattern of increased GGT levels 24 among individuals exposed to 2,3,7,8-TCDD-contaminated chemicals. Elevated levels of serum 25 GGT were observed within a year after exposure in Seveso children (Caramaschi et al., 1981; 26 Mocarelli et al., 1986) and 10 or more years after cessation of exposure among TCP and 2,4,5-T 27 production workers (May, 1982; Martin, 1984; Moses et al., 1984; Calvert et al., 1992) and 28 among Ranch Hands (Roegner et al., 1991; Grubbs et al., 1995). All of these groups had a high 29 likelihood of substantial exposure to 2,3,7,8-TCDD. In addition, for those studies that evaluated 30 dose-response relationships with 2,3,7,8-TCDD levels, the effect was observed only at the 31 highest levels or categories of2,3,7,8-TCDD and, in the NIOSH study, only in workers who 32 reported drinking high levels of alcohol. 33 In contrast, although background levels of serum 2,3,7,8-TCDD suggested minimal 34 exposure in Army Vietnam veterans, GGT was increased at borderline significance among 35 Vietnam veterans as compared to non-Vietnam veterans (CDC Vietnam Experience Study, 12/23/03 2-40 DRAFT--DO NOT CITE OR QUOTE 1 1988). In addition, despite the increases observed in some studies of occupational cohorts, other 2 studies ofTCP production workers from West Virginia or Missouri residents measured but did 3 not report elevations in GGT levels (Suskind and Hertzberg, 1984; Webb et al., 1989). 4 In clinical practice, GGT is often measured because it is elevated in almost all 5 hepatobiliary diseases and is used as a marker for alcoholic intake (Guzelian, 1985). In 6 individuals with hepatobiliary disease, elevations in GGT are usually accompanied by increases 7 in other hepatic enzymes, for example, AST and ALT, and metabolites, for example, uro- and 8 coproporphyrins. Significant increases in hepatic enzymes other than GGT and metabolic 9 products were not observed in individuals whose GGT levels were elevated 10 or more years 10 after exposure ended, suggesting that the effect may be GGT-specific. These data suggest that in 11 the absence of increases in other hepatic enzymes, elevations in GGT are associated with 12 exposure to 2,3,7,8-TCDD, particularly among individuals who were exposed to high levels. 13 The animal data with respect to 2,3,7,8-TCDD-related effects on GGT are sparse. 14 Statistically significant changes in hepatic enzyme levels, particularly AST, ALT, and alkaline 15 phosphatase, have been observed after exposure in rats and hamsters (Gasiewicz et al., 1980; 16 Kociba et al., 1978; Olson et al., 1980). Only one study evaluated GGT levels (Kociba et al., 17 1978); moderate but statistically nonsignificant increases were noted in rats fed 0.10 :g/kg 18 2,3,7,8-TCDD daily for 2 years, and no increases were observed in control animals. 19 In summary, GGT is the only hepatic enzyme examined that was found in a number of 20 studies to be chronically elevated in adults exposed to high levels of 2,3,7,8-TCDD. The 21 consistency of the findings in a number of studies suggests that the elevation may reflect a true 22 effect of exposure, but its clinical significance is unclear. Long-term pathological consequences 23 of elevated GGT have not been illustrated by excess mortality from liver disorders or cancer or in 24 excess morbidity in the available cross-sectional studies. 25 It must be recognized that the absence of an effect--for example, liver enzymes--in a 26 cross-sectional study does not obviate the possibility that the enzyme levels may have increased 27 concurrently with the exposure but declined after cessation. The apparently transient elevations 28 in ALT levels among the Seveso children suggest that hepatic enzyme levels other than GGT 29 may react in this manner to 2,3,7,8-TCDD exposure. 30 31 2.2.6.2. Thyroid Function 32 Many effects of 2,3,7,8-TCDD exposure in animals resemble signs of thyroid dysfunction 33 or significant alterations of thyroid-related hormones. In the few human studies that have 34 examined the relationship between 2,3,7,8-TCDD exposure and hormone concentrations in 35 adults (CDC Vietnam Experience Study, 1988; Roegner et al., 1991; Grubbs et al., 1995; 12/23/03 2-41 DRAFT--DO NOT CITE OR QUOTE 1 Suskind and Hertzberg, 1984), the results are mostly equivocal. Cross-sectional analysis of the 2 Ranch Hand cohort (Pavuk et al., 2003) found signs of elevated TSH means among the high 3 TCDD exposure group in the 1985 and 1987 follow-ups, with an increasing trend across the 4 decade 1982 - 1992, but no association with the occurrence of thyroid disease. Concentrations of 5 thyroid binding globulin also appeared to be positively correlated with current levels of 2,3,7,86 TCDD in the BASF accident cohort (Ott et al., 1994). Little additional information on thyroid 7 hormone levels has been reported for production workers and none for Seveso residents, two 8 groups with documented high serum 2,3,7,8-TCDD levels. 9 Thyroid hormones play important roles in the developing nervous system in all vertebrate 10 species, including humans--to the extent that all infants in the United States are tested for 11 hypothyroidism shortly after birth. Several studies of nursing infants suggest that ingestion of 12 breast milk with a higher dioxin TEQ may alter thyroid function (Pluim et al., 1993; Koopman13 Esseboom et al., 1994c; Nagayama et al., 1997). These findings suggest a possible shift in the 14 distribution of thyroid hormones, particularly T4, and point out the need for collection of 15 longitudinal data to assess the potential for long-term effects associated with developmental 16 exposures. 17 The exact processes that account for these observations in humans are unknown, but 18 when put in perspective of animal responses, the following might apply: dioxin increases the 19 metabolism and excretion of thyroid hormone, mainly T4, in the liver, and reduced T4 levels 20 stimulate the pituitary to secrete more TSH, which enhances thyroid hormone production. Early 21 in the disruption process, the body can overcompensate for the loss of T4, which may result in a 22 small excess of circulating T4 to the increased TSH. In animals given higher doses of dioxin, the 23 body is unable to maintain homeostasis, TSH levels remain elevated, and T4 levels decrease. 24 A plausible mode of action for thyroid effects is described in Section 2.2.1.3. 25 26 2.2.6.3. Cardiovascular Disease 27 Elevated cardiovascular disease has been noted in several occupational cohort studies 28 (Steenland et al., 1999; Sweeney et al., 1997; Flesch-Janys et al., 1995) and in the Seveso 29 (Pesatori et al., 1998) and the rice oil poisoning studies. This appears to be associated with 30 ischemic heart disease and in some cases with hypertension. Recent data from the Ranch Hand 31 study indicate that dioxin may be a possible risk factor for the development of essential 32 hypertension (Grubbs et al., 1995). Elevated blood lipids have also been seen in several cohorts. 33 The association of dioxins with heart disease in humans has biological plausibility, given the data 34 in animals. First is the key role ofhypoxia in heart disease and the potential for involvement of 35 the activated AhR in blocking an hypoxic response (Gradin et al., 1996; Gu et al., 2000). Dioxin 12/23/03 2-42 DRAFT--DO NOT CITE OR QUOTE 1 has been shown to perturb lipid metabolism in multiple laboratory species (Pohjanvirta and 2 Tuomisto, 1994). The heart--in fact the entire vascular system--is a clear target for the adverse 3 effects of dioxin in fish and birds (Hornung et al., 1999; Cheung et al., 1981). Recent studies 4 have demonstrated that the heart is also a target in mammals ( Lund et al., 2003; NTP 2003a). In 5 mammals, dioxin has been shown to disturb heart rhythms at high doses in guinea pigs (Gupta et 6 al., 1973; Pohjanvirta and Tuomisto, 1994). 7 8 2.2.6.4. Oxidative Stress 9 Several investigators have hypothesized that some of the adverse effects of dioxin and 10 related compounds may be associated with oxidative stress. Induction of CYP1A isoforms has 11 been shown to be associated with oxidative DNA damage (Park et al., 1996). Altered 12 metabolism of endogenous molecules such as estradiol can lead to the formation of quinones and 13 redox cycling. This has been hypothesized to play a role in the enhanced sensitivity of female 14 rats to dioxin-induced liver tumors (Tritscher et al., 1996). Lipid peroxidation, enhanced DNA 15 single-strand breaks, and decreased membrane fluidity have been observed in liver as well as in 16 extrahepatic tissues following exposure to high doses of TCDD (Stohs, 1990). A dose- and time17 dependent increase in superoxide anion in peritoneal macrophages following exposure to TCDD 18 (Alsharif et al., 1994). A recent report that low-dose (0.15 ng TCDD/kg/day) subchronic 19 exposure can lead to oxidative changes in several tissues in mice (Slezak et al., 2000) suggests 20 that this mechanism or mode of toxicity deserves further attention. 12/23/03 2-43 DRAFT--DO NOT CITE OR QUOTE 21 Table 2-1. Effects of TCDD and related compounds in different animal species 3 Effect Guinea Humans Monkey pig Rat Mouse Hamster Cow Rabbit Chicken Fish Avian wildlife Marine mammals Mink 4 Presence of AhR + + 0 ++ + ++ ++ + ++ 5 Binding of TCDD: 6 AhR complex to the 7 DRE (enhancer) + + ++ + ++ ++ 8 Enzyme induction + + + ++ + + ++ + ++ 9 Acute lethality 0 + + ++ + ++ ++ + ++ 10 W asting syndrome + + + ++ + ++ ++ ++ 1112 Teratogenesis/fetal +/- + + ++ + toxicity, mortality + ++ + ++ 13 Endocrine effects +/- + ++ ++ ++ 14 Im m unotoxicity +/- + + + + + + ++ + 15 Carcinogenicity +/- ++ + + 16 Neurotoxicity ++ ++ + 1178 Chloracnegenic effects ++ + ++ + 19 Porphyria + 0 0 ++ 0 + 20 Hepatotoxicity + + +/- + + +/- + + ++ + ++ 21 Edema + 0 0+ + ++ 22 Testicular atrophy + + ++ 2234 Bone marrow hypoplasia ++ +/- + 33222221567089 Teeth + + + = observed. +/- = observed to limited extent, or +/- results. 0 = not observed. Blank cells = no data. + 21 Table 2-2. Some biochemical responses to TCDD 3 CYP1A1 Human chorionic gonadotrophin 4 CYP1A2 Interleukin-1beta 5 CYP1B1 Gastrin 6 GST Ya TNF alpha 7 GST Yb TGF-beta 8 GST Yc EGF 9 UDP glucuronyl transferase Fibrinogen 10 QR quinone reductase/ Nmo Plastin 11 Aldehyde dehydrogenase EGFR 12 Ornithine decarboxylase c-erbA related hormone receptor 13 Malic enzyme Estrogen receptor 14 Phospholipase A2 25Dx-putative progesterone receptor 15 60kDa microsomal esterase MDR-1 multidrug resistance 16 Aminolevulinic acid synthetase Aryl hydrocarbon binding protein 17 Choline kinase c-fos 18 EctoATPase c-jun 19 Prostaglandin synthetase -2 (COX-2) Cystatin-like protein 20 Plasminogen activator inhibitor-2 MHC-Q1 21 Urokinase plasminogen activator Protein kinase C 22 Nedd-4-like ubiquitin protein ligase pp60 c-src protein kinase 23 PEPC kinase p21 ras 24 Terminal transferase p27/Kip1 25 Testosterone 7alpha hydroxylase bcl-2 22227689 Note: This list is not a comprehensive list of all responses known to be affected by TCDD. Source: Sutter et al., 1992; Lai et al., 1996. 12/23/03 2-45 DRAFT--DO NOT CITE OR QUOTE 321 Tstaubdliees2-w3i.thShuimghmeaxrypoosfutrheelecvoemlsb,ianseddecsochriobretdanbdy IsAelRecCted(1i9n9d7u)astrial cohort All cancers Lung cancer 4 Reference Observed SMR 95% CI Observed SMR 95% CI 5 International cohort 67 K(1o9g9e7v)binas et al. 394 1.2 1.1-1.3 127 1.2 1.0-1.4 8 Industrial populations (high-exposure subcohorts) 109 F(1in9g91erah)cut(UetSaAl.) 114 1.5 1.2-1.8 40 1.4 1.0-1.9 1112 B(1e9c9h6e)rde(tGaelr.many) 105 [1.3] [1.0-1.5] 33 [1.4] [1.0-2.0] 111534 H(1o9o9i6v)eeld et al. (Netherlands) 51 1.5 1.1-1.9 14 1 0.5-1.7 111768 O((1Bt9tA9aS6nFbd)afZcocbideernt) 18 1.9 1.1-3.0 7 2.4 1.0-5.0 19 TOTAL [288] [1.4] [1.2-1.6] [94] [1.4] [1.1-17] 20 p value <0.001 <0.01 22322222221257036894 aAdapted from IARC; Table 38 (1997); non-Hodgkin's lymphoma, soft-tissue sarcoma, and gastrointestinal results not shown. TOTALs were calculated by the IARC Working Group. bBMeecnhearndetwaolm. (a1n99>62),0Hyoeoarisveslidnceet failr.s(t1e9x9p6oas)u,rteh.e TohriegsienadlaItAa RinCclucdoehotrhte(cSoahraocrctsi oetf aFl.i,ng1e9r9h1u)t, eatnadl.o(t1h9e9r 1cao,hbo),rts. cMen $ 20 years latency and $ 1 year exposure. dMen, cohorts I and II, summed (Boehringer-Ingelheim, Bayer-Uerdingen cohorts). efMcMaenennc,eacrnshdlcoowrmaocbmnienenesd,u.Fbgacrotourpy, A$.20 years latency. Data presented for lung cancer are all respiratory tract 12/23/03 2-46 DRAFT--DO NOT CITE OR QUOTE 321 Tfoarbpleri2n-c4i.paTlucmonogreinnecrisdence and promotion data cited for the TEF-WHO98 % of adipose 4 TEF-W HO98 tumor incidence/promotion Congener citationa TEF-WHO W Ht eOq98dtfips-sue Dose-response graphs: dose conc.b adjusted to reflect TEF multiplier 65 2T,C3,D7D,8- TEF Standard 18 87 P1e,2C,3D,7D,8- Waern et al. (1991) 1 15 109 2,3,4,7,8- Waern et al. (1991) PeCDF 0.5 1112 H1,x2C,3D,6D,7, NTP (1980); 0.1 111:..222..m33..i67x..t78u..r89e--;HxCDDH;xCDD/ long-term bioassays, Osborne-Mendel rats 1134 H1,x2C,3D,7D,8,9- iiSnnpNrKaTogcPuiebs-atDueadtwiealsle,.y(1ra9t7s8) 0.1 15 PCB 126 Hemming et al. (1995) 0.1 7 10 2 33 111768 bavSaene dPeanrtBIIe,rgCheatpatle.,r 240,0T0a.blHesex4a--4C6D, 4D-4r7eferenced to previous TEF reviews. 12/23/03 2-47 DRAFT--DO NOT CITE OR QUOTE 43256 rAhFdeeiihtogaiRxntuio,srnhbea-olrr2ayec-slsk1tpho.poymrndCoasrteioepvlicrlenauo;retlbepaleoi,rnmnsm;ierNteenecscFt;eh-opBkaftBnTopi,rFhs;nmosA,uspbcIfPlhaoe,soraararAlystltshriroazaRcnanitssaaiccotcrerntiidip;pottAiinimoo.mnnmTtf,fuaCaAnccDotthoopDRrrh;s,i;nHl2iuTn,I3cFA-,ll,7eiTkha,8Aeyr-p,tptreoDratoxnrNtaiseaclAiohinncl;rodaehrtucooscoprdig9bipnb0lreieo,tnitf9oeza0inocn-tks;opierRl-q;odBudiDoea,RnxltciEone,n;. 12/23/03 2-48 DRAFT--DO NOT CITE OR QUOTE 1 3. MECHANISMS AND MODE OF DIOXIN ACTION 2 3 Mechanistic studies can reveal the biochemical pathways and types of biological and 4 molecular events that contribute to dioxin's adverse effects (See Part II, Chapter 2, for a detailed 5 discussion). For example, much evidence indicates that TCDD acts via an intracellular protein 6 (the AhR), which functions as a ligand-dependent transcription factor in partnership with a 7 second protein (Amt). Therefore, from a mechanistic standpoint, TCDD's adverse effects appear 8 likely to reflect alterations in gene expression that occur at an inappropriate time and/or for an 9 inappropriately long time. Mechanistic studies also indicate that several other proteins contribute 10 to TCDD's gene regulatory effects and that the response to TCDD probably involves a relatively 11 complex interplay between multiple genetic and environmental factors. If TCDD operates 12 through such a mechanism, as all evidence indicates, then there are certain constraints on the 13 possible models that can plausibly account for TCDD's biological effects and, therefore, on the 14 assumptions used during the risk assessment process (e.g., Poland, 1996; Limbird and Taylor, 15 1998). 16 Mechanistic knowledge of dioxin action may also be useful in other ways. For example, 17 a further understanding of the ligand specificity and structure of the AhR will likely assist in the 18 identification of other chemicals to which humans are exposed that may add to, synergize, or 19 block the toxicity of TCDD. Knowledge of genetic polymorphisms that influence TCDD 20 responsiveness may also allow the identification of individuals at greater risk from exposure to 21 dioxin. In addition, knowledge of the biochemical pathways that are altered by TCDD may help 22 identify novel targets for the development of drugs that can antagonize dioxin's adverse effects. 23 As described below, biochemical and genetic analyses of the mechanisms by which 24 dioxin may modulate particular genes have revealed the outline of a novel regulatory system 25 whereby a chemical signal can alter cellular regulatory processes. Future studies of dioxin action 26 have the potential to provide additional insights into mechanisms of mammalian gene regulation 27 that are of a broader interest. Additional perspectives on dioxin action can be found in several 28 reviews (Birnbaum, 1994a, b; Schecter, 1994; Hankinson, 1995; Schmidt and Bradfield, 1996; 29 Gasiewicz, 1997; Rowlands and Gustafsson, 1997; Denison et al., 1998; Hahn, 1998; Wilson and 30 Safe, 1998; Schecter and Gasiewicz, 2003; Matsumura, 2003; Carlson and Perdew, 2002). 31 Knowledge of the mode(s) of action by which the broad class of chemicals known as 32 dioxins act may facilitate the risk assessment process by contributing to the weight of the 33 evidence for hazard characterization and by imposing bounds on the models used to describe 34 possible responses of humans resulting from exposure to mixtures of these chemicals (see 12/23/03 3-1 DRAFT--DO NOT CITE OR QUOTE 1 Sections 2 and 5 of this document). The relatively extensive database on TCDD, as well as the 2 more limited database on related compounds, has been reviewed, with emphasis on the role of 3 the specific cellular receptor for TCDD and related compounds--the AhR--in the postulated 4 mode(s) of action. This discussion focuses on summarizing the elements of the mode(s) of 5 dioxin action that are relevant for understanding and characterizing dioxin risk for humans. 6 These elements include: 7 8 Similarities between humans and other animals with regard to receptor structure 9 and function; 10 11 The relationship between receptor binding and toxic effects; and 12 13 The extent to which the purported mechanism(s) or mode(s) of action might 14 contribute to the diversity of biological responses seen in animals and, to some 15 extent, in humans. 16 17 In addition, this section identifies important and relevant knowledge gaps and 18 uncertainties in the understanding of the mechanism(s) of dioxin action and indicates how these 19 may affect the approach to risk characterization. 20 21 3.1. MODE VERSUS MECHANISM OF ACTION 22 In the context of revising its carcinogen risk assessment guidelines, EPA has proposed 23 giving greater emphasis to use of all of the data in hazard characterization, dose-response 24 characterization, exposure characterization, and risk characterization (U.S. EPA, 1996, 1999, 25 2003). One aid to the use of more information in risk assessment has been the definition of mode 26 versus mechanism of action. Mechanism of action is defined as the detailed molecular 27 description of key events in the induction of cancer or other health endpoints. Mode of action 28 refers to the description of key events and processes, starting with interaction of an agent with the 29 cell through functional and anatomical changes, resulting in cancer or other health endpoints. 30 Despite a desire to construct detailed biologically based toxicokinetic and toxicodynamic 31 models to reduce uncertainty in characterizing risk, few examples have emerged. Use of a mode 32 of action approach recognizes that, although all of the details may not have been worked out, 33 prevailing scientific thought supports moving forward using a hypothesized mode of action 34 supported by data. This approach is consistent with advice offered by the National Academy of 12/23/03 3-2 DRAFT--DO NOT CITE OR QUOTE 1 Sciences'National Research Council in its report entitled Science and Judgment in Risk 2 Assessment (NAS/NRC, 1994). 3 Mode of action discussions help to provide answers to the questions: How does the 4 chemical produce its effect? Are there mechanistic data to support this hypothesis? Have other 5 modes of action been considered and rejected? In order to demonstrate that a particular mode of 6 action is operative, it is generally necessary to outline the hypothesized sequence of events 7 leading to effects, to identify key events that can be measured, to outline the information that is 8 available to support the hypothesis, and to discuss those data that are inconsistent with the 9 hypothesis or support an alternative hypothesis. Following this, the information is weighed to 10 determine whether there is a causal relationship between key precursor events associated with the 11 mode of action and cancer or other toxicological endpoint in animals, and ultimately whether this 12 inference can be extended to humans. 13 14 3.2. GENERALIZED MODEL FOR DIOXIN ACTION 15 Dioxin and related compounds are generally recognized to be receptor-mediated 16 toxicants. The generalized model has evolved over the years to appear as illustrated in Table 3-1 17 and Figure 2-1. 18 19 3.2.1. The Receptor Concept 20 One of the fundamental concepts that influences our approach to risk assessment of 21 dioxin and related compounds is the receptor concept. The idea that a drug, hormone, 22 neurotransmitter, or other chemical produces a physiological response by interacting with a 23 specific cellular target molecule, that is, a "receptor," evolved from several observations. First, 24 many chemicals elicit responses that are restricted to specific tissues. This observation implies 25 that the responsive tissue (e.g., the adrenal cortex) contains a "receptive" component whose 26 presence is required for the physiologic effect (e.g., cortisol secretion). Second, many chemicals 27 are quite potent. For example, picomolar to nanomolar concentrations of numerous hormones 28 and growth factors elicit biological effects. This observation suggests that the target cell contains 29 a site(s) to which the particular chemical binds with high affinity. Third, stereoisomers of some 30 chemicals (e.g., catecholamines, opioids) differ by orders of magnitude in their ability to produce 31 the same biological response. This observation indicates that the molecular shape of the 32 chemical strongly influences its biological activity. This, in turn, implies that the binding site on 33 or in the target cell also has a specific, three-dimensional configuration. Together, these types of 34 observations support the prediction that the biological responses to some chemicals involve 12/23/03 3-3 DRAFT--DO NOT CITE OR QUOTE 1 stereospecific, high-affinity binding of the chemicals to specific receptor sites located on or in the 2 target cell. Many of these characteristics have been noted for TCDD and related compounds. 3 The availability of compounds of high specific radioactivity has permitted quantitative 4 analyses of their binding to cellular components in vitro. To qualify as a potential receptor, a 5 binding site for a given chemical must satisfy several criteria: (1) the binding site must be 6 saturable, that is, the number of binding sites per cell should be limited; (2) the binding should be 7 reversible; (3) the binding affinity measured in vitro should be consistent with the potency of the 8 chemical observed in vivo; (4) if the biological response exhibits stereospecificity, so should the 9 in vitro binding; (5) for a series of structurally related chemicals, the rank order for binding 10 affinity should correlate with the rank order for biological potency; and (6) tissues that respond to 11 the chemical should contain binding sites with the appropriate properties. 12 The binding of a chemical ("ligand") to its specific receptor is assumed to obey the law of 13 mass action; that is, it is a bimolecular, reversible interaction. The concentration of the liganded, 14 or occupied, receptor [RL] is a function of both the ligand concentration [L] and the receptor 15 concentration [R] as shown in equation 3-1: 16 ki 17 18 [L] + [R] [RL] (3-1) 19 k2 20 21 Inherent in this relationship is the fact that the fractional occupancy (i.e., [RL]/[R]) is a 22 function of ligand concentration [L] and the apparent equilibrium dissociation constant KD, which 23 is a measure of the binding affinity of the ligand for the receptor, that is, [RL]/[R] = [L]/(KD+ 24 [L]), where KD= [L] [RJ/[LR] = k2/k1. Therefore, the relationship between receptor occupancy 25 and ligand concentration is hyperbolic. At low ligand concentrations (where [L]<<KD), a small 26 increase in [L] produces an approximately linear increase in fractional receptor occupancy. At 27 high ligand concentration (where [L]>>K), the fractional occupancy of the receptor is already 28 very close to 1, that is, almost all receptor sites are occupied. Therefore, a small increase in [L] 29 is likely to produce only a slight increase in receptor occupancy. These issues are discussed in 30 regard to TCDD binding to the AhR and dose-response in Part II, Chapter 8. 31 Ligand binding constitutes only one aspect of the receptor concept. By definition, a 32 receptor mediates a response, and the functional consequences of the ligand-receptor binding 33 represent an essential aspect of the receptor concept. Receptor theory attempts to quantitatively 34 relate ligand binding to biological responses. The classic "occupancy" model of Clark (1933) 12/23/03 3-4 DRAFT--DO NOT CITE OR QUOTE 1 postulated that (1) the magnitude of the biological response is directly proportional to the fraction 2 of receptors occupied, and (2) the response is maximal when all receptors are occupied. 3 However, analyses of numerous receptor-mediated effects indicate that the relationship between 4 receptor occupancy and biological effect is not as straightforward as Clark envisioned. 5 In certain cases, no response occurs even when there is some receptor occupancy. This 6 suggests that there may be a threshold phenomenon that reflects the biological "inertia" of the 7 response (Ariens et al., 1960). In other cases, a maximal response occurs well before all 8 receptors are occupied, a phenomenon that reflects receptor "reserve" (Stephenson, 1956). 9 Therefore, one cannot simply assume that the relationship between fractional receptor occupancy 10 and biological response is linear. Furthermore, for a ligand (such as TCDD) that elicits multiple 11 receptor-mediated effects, one cannot assume that the binding-response relationship for a simple 12 effect (such as enzyme induction) will necessarily be identical to that for a different and more 13 complex effect (such as cancer). 14 The cascades of events leading to different complex responses (e.g., altered immune 15 response to pathogens or development of cancer) are likely to be different, and other rate-limiting 16 events likely influence the final biological outcome, resulting in different dose-response curves. 17 Thus, even though ligand binding to the same receptor is the initial event leading to a spectrum 18 of biological responses, ligand-binding data may not always mimic the dose-effect relationship 19 observed for particular responses. 20 Another level of complexity is added when one considers different chemical ligands that 21 bind to the same receptor. Relative potencies are determined by two properties of the ligand: 22 affinity for the receptor and capacity to confer a particular response in the receptor (e.g., a 23 particular conformational change), also called efficacy (Stephenson, 1956). Ligands with 24 different affinities and the same degree of efficacy would be expected to produce parallel dose25 response curves with the same maximal response within a particular model system. However, 26 ligands of the same affinity with different efficacies may result in dose-response curves that are 27 not parallel or that differ in maximal response. These issues relate particularly to Ah receptor 28 ligands that are not "dioxins," where different efficacies or an inability to elicit the suite of 29 dioxin-like responses compound differences in binding affinity for the Ah receptor. This 30 complicates the use of the toxic equivalency approach, particularly for extrapolation purposes 31 beyond the closely related congener groups. As described previously, this argues strongly for the 32 use of all available information in setting TEFs and highlights the important role that scientific 33 judgment plays in addressing uncertainty in the face of incomplete mechanistic understanding. 34 12/23/03 3-5 DRAFT--DO NOT CITE OR QUOTE 1 3.2.2. A Framework to Evaluate Mode of Action 2 In its revised proposed guidelines for carcinogen risk assessment (U.S. EPA, 1999, 2003), 3 EPA recommends the use of a structured approach to evaluating mode of action. This approach 4 is similar to and builds upon an approach developed within the WHO/IPCS Harmonization 5 Project (WHO, 2000). Fundamentally, the approach uses a modification of the "Hill Criteria" 6 (Hill, 1965), which have been used in the field of epidemiology for many years to examine 7 causality between associations of exposures and effects. The framework calls for a summary 8 description of the postulated mode of action, followed by the identification of key events that are 9 thought to be part of the mode of action. These key events are then evaluated as to strength, 10 consistency, and specificity of association with the endpoint under discussion. Dose-response 11 relationships between the precursor key events are evaluated and temporal relationships are 12 examined to be sure that "precursor" events actually precede the induction of the endpoint. 13 Finally, biological plausibility and coherence of the data with the biology are examined and 14 discussed. All of these "criteria" are evaluated and conclusions are drawn with regard to 15 postulated mode of action. 16 In the case of dioxin and related compounds, elements of such an approach are found for 17 a number of effects, including cancer, in Part II. Application of the framework to dioxin and 18 related compounds may now proceed in a step-wise fashion to evaluate the association between 19 the chemical or complex mixture and clearly adverse effects. The approach can be applied 20 sequentially to early events, for example, receptor binding and intermediate events such as 21 enzyme induction or endocrine impacts. Additional data will be required to extend the 22 framework to most effects, but several have data that would support a framework analysis, a 23 number of which are discussed below. 24 25 3.2.3. Mechanistic Information and Mode of Action--Implications for Risk Assessment 26 A substantial body of evidence from investigations using experimental animals indicates 27 that the AhR mediates the biological effects of TCDD. The key role ofthe AhR in the effects of 28 dioxin and related compounds is substantiated by four lines of research: (1) structure/activity 29 relationships, (2) responsive versus nonresponsive mouse strains, (3) mutant cell lines, and (4) 30 the development oftransgenic mice in which the gene for the AhR has been "knocked out" 31 (Birnbaum, 1994a; Fernandez-Salguero et al., 1996; Lahvis and Bradfield, 1998). Dioxin 32 appears not to cause effects in the AhR knockout mouse (Fernandez-Salguero et al., 1996; Lahvis 33 and Bradfield, 1998; Peters et al., 1999). 12/23/03 3-6 DRAFT--DO NOT CITE OR QUOTE 1 It is clear that the AhR is necessary, but not sufficient, for essentially all of the well2 studied responses to dioxin. The AhR functions as a ligand-activated transcription factor, 3 controlling the expression of specific genes via interaction with defined nucleotide sequences in 4 the promoter regions. In order to control transcription, the TCDD-AhR complex interacts with 5 another protein, Amt, to bind to the dioxin response element. This complex is also bound by 6 other nuclear coactivators and/or corepressors to bind to the transcriptional complex and initiate 7 transcription (Gu et al., 2000). However, Arnt has many other partners that control hypoxia 8 response, neuronal differentiation, morphological branching, etc. (Gu et al., 2000). 9 It is possible that there are other mechanisms that impact how dioxin initiates its toxic 10 effects, apart from its direct transcriptional activation of drug metabolizing genes. It may be that 11 the adverse effects of dioxin may result from competition of the ligand-activated AhR with other 12 Arnt partners (Gradin et al., 1996). The AhR, Arnt, and Arnt partners are all members of the Per13 Arnt-Sim (PAS) family of basic helix-loop-helix proteins that function as nuclear regulatory 14 proteins (Gu et al., 2000). The PAS proteins are highly conserved, with homologous proteins 15 being present in prokaryotes. They play key roles in circadian rhythms and development. The 16 embryolethality of Arnt knockout mice, as well as the reduced fertility and viability of the AhR 17 knockout mice (Abbott et al., 1999), point to a key role of these proteins in normal physiology. 18 Another potential mechanism by which TCDD can cause effects involves the 19 protein/protein interactions of the AhR. When not bound to a ligand, the AhR exists in a 20 multimeric protein complex that involves two molecules of heat shock protein 90 as well as other 21 proteins, including AIP/XAP2/ara9, ara3, ara6, src, rel, and Rb (Carver et al., 1998; Enan and 22 Matsumura, 1996; Puga et al., 2000b). AIP/XAP2/ara9 is a 37 kilodalton protein that is related 23 to known immunophilins and is involved in the control of signal transduction processes. C-src 24 has been shown to be associated with the AhR in several tissues and is a tyrosine kinase (Enan 25 and Matsumura, 1996). Dioxin has been shown to cause a rapid increase in phosphorylation 26 upon exposure. Recent studies have shown that rel, which is a key component of the NF-kappaB 27 complex that controls apoptosis, binds to the AhR complex (Tian et al., 1999; Puga et al., 28 2000c). Similarly, several investigators have demonstrated an association between the AhR and 29 the retinoblastoma protein; this has been shown to affect cell cycling (Puga et al., 2000b). 30 Thus, the AhR may act as a negative regulator ofkey regulator molecules involved in 31 phosphorylation, cell cycling, and apoptosis in its unliganded state. Upon binding of TCDD, 32 these other proteins are now able to exert their effects. In addition, dioxin may act by competing 33 for Arnt, thus blocking key roles of other PAS regulatory proteins. Both of these mechanisms for 34 the effects of dioxin are in addition to the direct role of the ligand-bound form ofthe receptor in 12/23/03 3-7 DRAFT--DO NOT CITE OR QUOTE 1 control of transcription via the well-studied mechanism of binding to a dioxin-response element 2 in DNA. 3 Although studies using human tissues are much less extensive, it appears reasonable to 4 assume that dioxin's mode of action to produce effects in humans includes receptor-mediated key 5 events. Studies using human organs and cells in culture are consistent with this hypothesis. A 6 receptor-based mode of action would predict that, except in cases where the concentration of 7 TCDD is already high (i.e., [TCDD]~Kd), incremental exposure to TCDD will lead to some 8 increase in the fraction of AhRs occupied. However, it cannot be assumed that an increase in 9 receptor occupancy will necessarily elicit a proportional increase in all biological response(s), 10 because numerous molecular events (e.g., cofactors, other transcription factors, genes) that 11 contribute to the biological endpoint are integrated into the overall response. That is, the final 12 biological response should be considered as an integration of a series of dose-response curves, 13 with each curve dependent on the molecular dosimetry for each particular step. 14 Dose-response relationships that will be specific for each endpoint must be considered 15 when using mathematical models to estimate the risk associated with exposure to TCDD. It 16 remains a challenge to develop models that incorporate all the complexities associated with each 17 biological response. Furthermore, the parameters for each mathematical model may apply only 18 to a single biological response within a given tissue and species. 19 Given TCDD's widespread distribution, its persistence, and its accumulation within the 20 food chain, it is likely that most humans are exposed to some level of dioxin; thus, the population 21 at potential risk is large and genetically heterogeneous. By analogy with the findings in inbred 22 mice, polymorphisms in the AhR probably exist in humans. Therefore, a concentration of TCDD 23 that elicits a particular response in one individual may not do so in another. For example, studies 24 of humans exposed to dioxin following an industrial accident at Seveso, Italy, failed to reveal a 25 simple and direct relationship between blood TCDD levels and the development of chloracne 26 (Mocarelli et al., 1991). These differences in responsiveness to TCDD may reflect genetic 27 variation either in the AhR or in some other component of the dioxin-responsive pathway. 28 Therefore, analyses of human polymorphisms in the AhR and Arnt genes have the potential to 29 identify genotypes associated with higher (or lower) sensitivities to dioxin-related effects. Such 30 molecular genetic information may be useful in the future for accurately predicting the health 31 risks posed by dioxin to humans. 32 Complex responses (such as cancer) probably involve multiple events and multiple genes. 33 For example, a homozygous recessive mutation at the hr (hairless) locus is required for TCDD's 34 action as a chloracnegen and tumor promoter in mouse skin (Poland et al., 1982). Thus, the hr 12/23/03 3-8 DRAFT--DO NOT CITE OR QUOTE 1 locus influences the susceptibility of a particular tissue (in this case, skin) to a specific effect of 2 dioxin (tumor promotion). An analogous relationship may exist for the effects of TCDD in other 3 tissues. For example, TCDD may produce porphyria cutanea tarda only in individuals who have 4 inherited uroporphyrinogen decarboxylase deficiency (Doss et al., 1984). Such findings suggest 5 that, for some adverse effects of TCDD, the population at risk may be limited to individuals who 6 have a particular genetic predisposition. 7 Other factors can influence an organism's susceptibility to TCDD. For example, female 8 rats are more prone to TCDD-induced liver neoplasms than are males; this phenomenon is 9 related to the hormonal status of the animals (Lucier et al., 1991). In addition, hydrocortisone 10 and TCDD synergize in producing cleft palate in mice (Abbott et al., 1992). Retinoic acid and 11 TCDD produce a similar synergistic teratogenic effect (Couture et al., 1990). These findings 12 indicate that, in some cases, TCDD acts in combination with hormones or other chemicals to 13 produce adverse effects. Such phenomena might also occur in humans. If so, the difficulty in 14 assessing risk is increased, given the diversity among humans in hormonal status, lifestyle (e.g., 15 smoking, diet), and chemical exposure. 16 Dioxin's action as a tumor promoter and developmental toxicant presumably reflects its 17 ability to alter cell proliferation and differentiation processes. There are several plausible 18 mechanisms by which this could occur. First, TCDD might activate a gene (or genes) that is 19 directly involved in tissue proliferation. Second, TCDD-induced changes in hormone 20 metabolism may lead to tissue proliferation (or lack thereof) and altered differentiation secondary 21 to altered secretion of a trophic hormone. Third, TCDD-induced changes in the expression of 22 growth factor or hormone receptors may alter the sensitivity of a tissue to proliferative stimuli. 23 Fourth, TCDD-induced toxicity may lead to cell death, followed by regenerative proliferation. 24 These mechanisms likely differ among tissues and period of development, and they may be 25 modulated by different genetic and environmental factors. 26 The parallels between animal and human data relating to dioxin's tumor-promotion 27 potential can assist in informing determinations of human risk, recognizing that the complexity 28 of these intracellular processes limits our current mechanistic understanding. Using a weight-of29 evidence approach, the Agency considers the cancer promotion data from in vitro and in vivo 30 animal studies to be relevant and informative to humans. Although the specific mechanism(s) by 31 which dioxin causes cancer remains to be established (as, indeed, for cancer in general), the 32 intracellular factors and mechanistic pathways involved in dioxin's cancer-promotion mode of 33 action all have parallels between animals and humans. No qualitative differences have been 12/23/03 3-9 DRAFT--DO NOT CITE OR QUOTE 1 reported to indicate that humans should be considered fundamentally different from the multiple 2 animal species in which bioassays have demonstrated dioxin-induced neoplasia. Notably: 3 4 the intracellular molecular protein, DNA, and RNA factors and mechanisms 5 postulated in dioxin cancer promotion are common to animals and humans, 6 reflecting intracellular functions that have been preserved phylogenetically over 7 millions of years. These factors include the AhR, Amt heterodimerization, 8 cellular growth and differentiation functions, dioxin responsive elements, DNA 9 transcription mechanisms, and oxidative enzyme induction; and, 10 11 similar dioxin-induced toxic outcomes are evident between animals and humans 12 across a variety of endpoints, progressing from enzyme induction, altered 13 intracellular regulatory proteins, dermal lesions, and liver function and porphyria 14 through to in vitro neoplastic cell promotion and clonal expansion following viral 15 or chemical induction (in addition to the epidemiological cancer results following 16 occupational exposures). 17 18 As detailed in Part II, Chapter 2 (mechanism of action), the mode of action parallels 19 between humans and animals can be traced through dioxin's impacts at the subcellular level, as 20 follows: 21 22 AhR binding: The AhR has been phylogenetically retained over hundreds of millions of 23 years of evolution in humans and animals (Hahn, 1998) and is highly expressed in developing 24 tissues (Abbott et al., 1995), pointing to a fundamental role in cellular growth, differentiation 25 and/or endogenous/xenobiotic metabolism. Species-specific AhR molecular structures reveal 26 them to be members of a family of transcription-activating proteins that exhibit a basic helix 27 loop-helix (bHLH) DNA binding motif, PAS domain for dimerization and ligand binding, and a 28 C-terminal transactivation domain related to transcription induction and associated with a variety 29 of toxic endpoints. 30 Notable similarities exist in the AhR across animal taxa, particularly at the bHLH and 31 PAS sites (Fujii-Kuriyama et al., 1995), with human AhR being structurally most closely related 32 to that of the guinea pig (75% base homology) and other sensitive animal strains (Korkalainen et 33 al., 2001). Dioxin-resistant strains of rats and hamsters exhibit mutations in the AhR and/or 34 increased homology differences, particularly in the C-terminal transactivation domain and Q-rich 12/23/03 3-10 DRAFT--DO NOT CITE OR QUOTE 1 subdomain (Korkalainen et al., 2001). Human AhR binding affinities vary ~20-fold (Kd ~ 2 0.3-38.8 nM) (Okey et al. 1997), encompassing the range from sensitive C57BL/6 mice (0.27 3 nM) to relatively resistant DBA/2 mice (1.5 nM) (Ema et al., 1994). Evidence suggests that 4 within species, the AhR binding affinity correlates with biochemical effects and toxicity 5 (Birnbaum et al., 1990, Poland and Glover, 1980), whereas between species, relative AhR 6 binding affinities do not determine dioxin sensitivity because multiple downstream events 7 intercede (DeVito and Birnbaum, 1995). Differences in conformational changes in the AhR 8 following ligand binding are also likely to impact toxicity (Henry and Gasiewicz, 2003). 9 10 TCDD-AhR binding to Amt: Following ligand binding, the TCDD-Arnt complex 11 translocates to the nucleus, where it heterodimerizes (joins) with the bHLH-PAS transcription 12 partner protein, Amt. Amt has been phylogenetically retained over evolutionary time in both 13 humans and animals in several related forms and is essential for fetal survival. Amt molecular 14 weights vary across species from 85 kDa for the mouse, 87 kDa for humans, and 88 kDa for the 15 rat (Pohjanvirta et al., 1999). The Amt protein also dimerizes with other receptor/transcription 16 pathways in the cell nucleus, indicating its importance and fundamental role in regulating DNA 17 transcription (Schmidt and Bradfield, 1996; Zaher et al., 1998; Ge and Elferink, 1998; Tian et al., 18 1999). 19 20 Cross-talk among intracellular regulatory proteins: As noted, cancer is inherently a loss 21 of the regulation of normal cell growth, differentiation, and death (apoptosis) that is locked into 22 the genetic coding through clonal expansion. Central to the control of cell cycling and 23 programmed cell death are numerous regulatory proteins (e.g., EGF, HIF-1a, TNF-a, TGF-$j, 24 NF-kB, RB), whose functional roles, although being rapidly elucidated, remain uncertain. These 25 regulatory proteins are expressed in humans and animals and can be impacted by dioxin 26 exposure, as in the role of EGF in dioxin-induced cleft palate in mice (Bryant et al., 2001). The 27 Arnt protein is a common co-transcription factor for many bHLH-PAS regulatory proteins in 28 addition to its role in the TCDD-AhR transcription pathway. The potential exists, therefore, for 29 prolonged, inappropriate TCDD-AhR induction to impact multiple Arnt-related functions in the 30 nucleus, thereby altering other regulatory pathways. 31 Competition for the Amt protein has been demonstrated regarding the hypoxia inducible 32 factor 1 (HIF-1a) pathway following dioxin administration and Amt cross-talk (Gradin et al., 33 1996; Nie et al., 2001). In addition, dioxin-induced clonal expansion in human and animal cell 34 cultures has resulted in fixed changes to the intranuclear expression of plasminogen activation 12/23/03 3-11 DRAFT--DO NOT CITE OR QUOTE 1 inhibitor (PAI-2), tumor necrosis factor alpha (TNF-a), and transforming growth factor $ (TGF2 $), although it remains to be determined whether these changes were cause or effect of the 3 dioxin-promoted clonal expansion (Yang et al., 1999). 4 5 Dioxin response elements (DREs): In the well-studied pathway of cytochrome mixed 6 function oxidase induction (e.g., CYP1A1, 1A2), the ligand-AhR-Arnt heterodimer binds 1:1 to 7 DREs upstream of the DNA gene battery transcription site (Denison et al., 1989). This 8 mechanism is common to the mouse (six DREs) (Lusska et al. 1993), the rat (three DREs), and 9 humans (two DREs) (Swanson and Bradfield, 1993), and is based on the 3'A-CGCAC5' DNA 10 sequence. Subsequent to DRE binding, the C-terminal transactivation domain of the AhR alters 11 histone proteins and causes unwinding ofthe chromatin, exposing the dioxin promoter and aryl 12 hydrocarbon hydroxylase (AHH) gene battery to constitutively expressed DNA transcription 13 proteins (Whitlock et al., 1996). 14 15 Enzyme induction: At least seven enzyme genes, and likely more, are included in the 16 AhR-Arnt induced gene battery: three oxidative P450 cytochromes (CYP1A1, 1A2 ,1B1) and 17 four non-P450 enzymes responsive to reactive oxygenated metabolites and oxidative stress (for 18 example, a quinone oxidoreductase, aldehyde dehydrogenase, glucuronosyltransferase, and 19 glutathione transferase [Nebert et al., 2000; Zhang et al., 1998]). These enzymes are expressed in 20 humans and animals. Similar EC50s were reported for CYP1A1 induction in lymphocytes in 21 mice (1.3 nM) and humans (1.8nM) (Clark et al., 1992). However, substantial interspecies 22 differences have been noted between cultured human and mouse embryonic palatal cells 23 regarding CYP1A1 induction and morphological effects. Paralleling a ~200-fold lower 24 sensitivity for morphological and cellular effects on embryonic palatal tissue, human cell cultures 25 expressed ~350-fold fewer receptors and exhibited ~1500-fold lower dioxin-induced CYP1A1 26 m-RNA induction than mice (Abbott et al., 1999). Notably, though, effects on human and rat 27 embryonic palatal shelf tissue occur at similar in vitro concentrations as compared to the much 28 higher sensitivity shown in mice, suggesting that mice may exhibit a particular sensitivity to 29 effects on palatal differentiation (Abbott and Birnbaum, 1990, 1991; Couture et al., 1990). 30 For CYP1A2 there is a ~40-fold variability in protein and enzyme activity levels in the 31 human population (Eaton et al., 1995; Nebert et al., 1996). The importance of CYP1A2 to dioxin 32 toxicity in rodents has been demonstrated in knockout mice, where dioxin-induced porphyrin 33 changes did not occur in the absence of CYP1A2, and hepatic toxicity was substantially reduced 12/23/03 3-12 DRAFT--DO NOT CITE OR QUOTE 1 (Smith et al., 2001). This is likely due to the lack of hepatic sequestration in the absence of 2 CYP1A2 (Diliberto et al., 1999). 3 Recent human epidemiological data have reported long-term hepatic enzyme and 4 porphyrin ratio changes many years after industrial dioxin exposure (Neuberger et al., 1999). 5 The prolonged up-regulation of mixed-function oxidase (MFO) enzymes has been postulated to 6 impact the carcinogenic potential of xenobiotics that are metabolically activated, such as the 7 PAHs. Indeed, carcinogenicity from PAHs is absent in AhR-knockout mice, presumably from 8 lack of induction of the mixed-function oxidases. In a related mechanistic postulate, emphasis 9 has been placed on the existence of both MFOs (CYP1A1, 1A2) and detoxifying/scavenging 10 phase II transferase enzymes in the dioxin-induced gene battery, suggesting an evolutionary 11 mechanism that creates reactive oxidative products through the MFOs (possibly as a result of 12 endogenous ligand metabolism) yet provides a protective mechanism for mitigating the resulting 13 oxidative stress through the phase II transferase enzymes. Abnormal regulation ofthis 14 mechanism could cause oxidative stress that is related both to DNA damage and cell 15 cycling/apoptosis regulation (Nebert et al., 2000). 16 17 Toxic effects and clonal proliferation: A spectrum of toxic effects has been demonstrated 18 in both animals and humans following dioxin exposure, including developmental impacts, 19 hormonal changes, skin lesions, and liver damage (DeVito et al., 1995). Dioxin has also been 20 demonstrated to promote neoplastic changes and clonal expansion in human and animal cell 21 cultures following viral induction. Exposure of normal human keratinocytes in vitro leads to 22 accelerated differentiation, increased cell proliferation, and decreased senescence in 23 differentiating cells (Ray and Swanson, 2003). These changes were accompanied by decreased 24 levels of a number of cell regulatory proteins, including p53, supporting the concept that dioxin 25 may exert its tumor promoting effects, in part, through this mechanism. 26 In Yang et al. (1992), human epidermal keratinocytes immortalized by adenovirus 12 27 simian virus 40 exposure (SV40) underwent neoplastic transformation after 2 weeks of dioxin 28 exposure in vitro at $ 0.1 nM, exhibiting increased saturation density, colony formation on soft 29 agar, and squamous cell carcinoma when inoculated into athymic nude mice. These phenomena 30 did not occur in the absence of SV40 virus induction or in control cell lines, including the 31 immortalized cell culture. Both the neoplastic cell transformation and AHH induction in the 32 untransformed cells were dose dependent. Follow-up analyses demonstrated alterations in 33 growth regulatory gene expression (PAI-2, TNF-a, and TGF-$) that became fixed in the genome 34 following successive division in TCDD-damaged cells (Yang et al., 1999). 12/23/03 3-13 DRAFT--DO NOT CITE OR QUOTE 1 Conversely, under certain circumstances, exposure to TCDD may elicit beneficial effects 2 in selected tissue or cells. For example, TCDD protects against the subsequent carcinogenic 3 effects of PAHs in mouse skin, possibly reflecting induction of detoxifying enzymes (Cohen et 4 al., 1979; DiGiovanni et al., 1980). In other situations, TCDD-induced changes in estrogen 5 metabolism may alter the growth of hormone-dependent tumor cells, producing a potential 6 anticarcinogenic effect (Spink et al., 1990; Gierthy et al., 1993). However, several recent studies 7 in mice indicate that the AhR has an important role in the genetic damage and carcinogenesis 8 caused by components in tobacco smoke, such as BaP, through its ability to regulate CYP1A1 9 gene induction (Dertinger et al., 1998; Shimizu et al., 2000). TCDD's biological effects likely 10 reflect a complicated interplay between genetic and environmental factors. These issues 11 complicate the risk assessment process for dioxin. 12 Thus, it is clear that the robust database on mode(s) of dioxin action related to 13 biochemical effects and to clearly adverse effects supports an understanding of dioxin's impact 14 on biological and cellular processes. This database is among the best available for xenobiotic 15 chemicals. The short-comings described above will stimulate additional research to further 16 elucidate details in this understanding of the impact of dioxins, but they should not detract from 17 the recognition that, among the data available to aid hazard characterization and risk assessment, 18 these are remarkably consistent and useful findings. 12/23/03 3-14 DRAFT--DO NOT CITE OR QUOTE 1 Table 3-1. Early molecular events in response to dioxin' 4 Diffusion into the cell 5 Binding to the AhR protein 6 Impacts on cytoplasmic phosphorylation 7 Dissociation from hsp90 8 Active translocation from cytoplasm to nucleus 9 Association with Arnt protein 10 Competition for Arnt with other nuclear cofactors 11 Conversion of liganded receptor to the DNA-binding form 12 Binding of liganded receptor heteromer to enhancer DNA 13 Enhancer activation 14 Altered DNA configuration 15 Histone modification 16 Recruitment of additional proteins 17 Nucleosome disruption 18 Increased accessibility of transcriptional promoter 19 Binding of transcription factors to promoter 20 Enhanced mRNA and protein synthesis 222123 aThese events are discussed in detail in Part II, Chapter 2. 24 25 26 12/23/03 3-15 DRAFT--DO NOT CITE OR QUOTE 1 4. EXPOSURE CHARACTERIZATION 2 3 This section summarizes key findings developed in the exposure portion of the Agency's 4 dioxin reassessment. These findings are developed in the companion document entitled Part I: 5 Estimating Exposure to Dioxin-Like Compounds, which is divided into three volumes: (1) 6 Sources of Dioxin in the United States, (2) Properties, Environmental Levels, and Background 7 Exposures, and (3) Site-Specific Assessment Procedures. Readers are encouraged to examine the 8 more detailed companion document for further information on the topics covered here and to see 9 complete literature citations. The characterization discussion provides cross-references to help 10 readers find the relevant portions of the companion document. 11 This discussion is organized as follows: (1) sources, (2) fate, (3) environmental media 12 and food concentrations, (4) background exposures, (5) potentially highly exposed populations, 13 and (6) trends. The key findings are presented in italics. 14 15 4.1. SOURCES (Cross-reference: Part I, Volume 1: Sources of Dioxin-Like 16 Compounds in the United States) 17 CDD/CDFs have never been intentionally produced other than on a laboratory-scale basis 18 for use in scientific analysis. Rather, they have been generated as unintended by-products in 19 trace quantities in various combustion, industrial, and biological processes. PCBs, on the other 20 hand, were commercially produced in large quantities, but they are no longer commercially 21 produced in the United States. EPA has classified sources of dioxin-like compounds into five 22 broad categories:1 23 24 1. Combustion Sources. CDD/CDFs are formed in most combustion systems, which can 25 include waste incineration (such as municipal solid waste, sewage sludge, medical 26 waste, and hazardous wastes), burning of various fuels (such as coal, wood, and 27 petroleum products), other high temperature sources (such as cement kilns), and 28 poorly or uncontrolled combustion sources (such as forest fires, building fires, and 29 open burning of wastes). Some evidence exists that very small amounts of dioxin-like 30 PCBs are produced during combustion, but they appear to be a small fraction of the 31 total TEQs emitted. 32 12/23/03 4-1 DRAFT--DO NOT CITE OR QUOTE 1 2. Metals Smelting, Refining, and Processing Sources. CDD/CDFs can be formed 2 during various types of primary and secondary metals operations, including iron ore 3 sintering, steel production, and scrap metal recovery. 4 5 3. Chemical Manufacturing. CDD/CDFs can be formed as by-products from the 6 manufacture of chlorine-bleached wood pulp, chlorinated phenols (e.g., 7 pentachlorophenol, or PCP), PCBs, phenoxy herbicides (e.g., 2,4,5-T), and 8 chlorinated aliphatic compounds (e.g., ethylene dichloride). 9 10 4. Biological and Photochemical Processes. Recent studies suggest that CDD/CDFs 11 can be formed under certain environmental conditions (e.g., composting) from the 12 action of microorganisms on chlorinated phenolic compounds. Similarly, CDD/CDFs 13 have been reported to be formed during photolysis of highly chlorinated phenols. 14 15 5. Reservoir Sources. Reservoirs are materials or places that contain previously formed 16 CDD/CDFs or dioxin-like PCBs and have the potential for redistribution and 17 circulation of these compounds into the environment. Potential reservoirs include 18 soils, sediments, biota, water, and some anthropogenic materials. Reservoirs become 19 sources when they have releases to the circulating environment. 20 21 The development ofnational estimates of annual environmental releases to air, water, and 22 land is complicated by the fact that only a few facilities in most industrial sectors have been 23 evaluated for CDD/CDF emissions. Thus, an extrapolation is needed to estimate national 24 emissions. The extrapolation method involves deriving an estimate of emissions per unit of 25 activity (i.e., an emission factor) at the tested facilities and multiplying this by the total activity 26 level in the untested facilities. 27 In order to convey the level of uncertainty in both the measure of activity and the 28 emission factor, EPA developed a qualitative confidence rating scheme. The confidence rating 29 scheme, presented in Table 4-1, uses qualitative criteria to assign a high, medium, or low 30 confidence rating to the emission factor and activity level for those source categories for which 31 emission estimates can be reliably quantified. The overall "confidence rating" assigned to a 32 quantified emission estimate was determined by the confidence ratings assigned to the 33 corresponding "activity level" and "emission factor." If the lowest rating assigned to either the 34 activity level or the emission factor terms is "high," then the category rating assigned to the 12/23/03 4-2 DRAFT--DO NOT CITE OR QUOTE 1 emission estimate is high (also referred to as "A"). If the lowest rating assigned to either the 2 activity level or emission factor terms is "medium," then the category rating assigned to the 3 emission estimate is medium (also referred to as "B"). If the lowest rating assigned to either the 4 activity level or emission factor terms is "low," then the category rating assigned to the emission 5 estimate is low (also referred to as "C"). 6 For many source categories, either the emission factor information or the activity level 7 information were inadequate to support development of reliable quantitative release estimates for 8 one or more media. For some of these source categories, sufficient information was available to 9 make preliminary estimates of environmental releases of CDD/CDFs or dioxin-like PCBs; 10 however, the confidence in the activity level estimates or emission factor estimates was so low 11 that the estimates cannot be included in the sum of quantified emissions from sources with 12 confidence ratings of A, B, or C. These estimates were given an overall confidence class rating 13 of D. For other sources, some information exists suggesting that they may release dioxin-like 14 compounds; however, the available data were judged to be insufficient for developing any 15 quantitative emission estimate. These estimates were given an overall confidence class rating of 16 E. 17 18 4.1.1. Inventory of Releases 19 This dioxin reassessment has produced an "inventory" of sources of environmental 20 releases of dioxin-like compounds for the United States (Table 4-2). The inventorywas 21 developed by considering all sources identified in the published technical and scientific literature 22 and by the incorporation of results from numerous individual emissions test reports of individual 23 industrial and combustion source facilities. In order to be representative of the United States, 24 data generated from U.S. sources of information were always given first priority for developing 25 emission estimates. Data from other countries were used for making estimates in only a few 26 source categories where foreign technologies were judged similar to those found in the United 27 States and the U.S. data were judged to be inadequate. The inventory is limited to sources whose 28 releases can be reliably quantified (i.e., those with confidence ratings of A, B, or C, as defined 29 above). As discussed below, this document does provide preliminary estimates of releases from 30 Class D sources, but they are presented separately from the inventory. 31 The inventory presents the environmental releases in terms of two reference years: 1987 32 and 1995. The year 1987 was selected primarily because little empirical data existed for making 33 source-specific emission estimates prior to this time; 1995 represents the latest year that could 34 reasonably be addressed within the timetable for producing the rest of this document. EPA 12/23/03 4-3 DRAFT--DO NOT CITE OR QUOTE 1 expects to conduct periodic revisions and updates to the source inventory in the future to track 2 changes in environmental releases over time. 3 Figure 4-1 displays the emission estimates to air for sources included in the inventory and 4 shows how the emission factors and activity levels were combined to generate emission 5 estimates. Figure 4-2 compares the annual mean I-TEQ emission estimates to air for the two 6 reference years (1987 and 1995). 7 The following conclusions are made for sources of dioxin-like compounds included in the 8 inventory: 9 10 EPA's best estimates ofreleases of CDD/CDFs to air, water, and landfrom 11 reasonably quantifiable sources were approximately 3300 g TEQDF-WHO98(3000 gI12 TEQ) in 1995 and 14,000 g TEQDF-WHO98(12,800 g I-TEQ) in 1987. This finding is 13 derived directly from Table 4-2. 14 15 The inventory indicates that, between 1987 and 1995, there was approximately a 76% 16 decrease in total environmental releases of CDDs/CDFsfrom known sources in the 17 United States. EPA is currently evaluating source releases for the year 2000. 18 Preliminary indications support the observation of a continued reduction in total 19 environmental releases from 1995 levels. The inventory updated for the year 2000 20 will undergo scientific peer review. 21 22 The environmental releases of CDD/CDFs in the United States occurfrom a wide 23 variety ofsources, but they are dominated by releases to the airfrom combustion 24 sources. The current (1995) inventory indicates that emissions from combustion 25 sources are more than an order ofmagnitude greater than emissions from the sum of 26 emissions from all other categories. Approximately 70% of all quantifiable 27 environmental releases were contributed by air emissions from just three source 28 categories in 1995: municipal waste incinerators (representing 38% of total 29 environmental releases); backyard burning of refuse in barrels (19%); and medical 30 waste incinerators (14%). 31 32 The decrease in estimated releases of CDD/CDFs between 1987 and 1995 33 (approximately 76%) was dueprimarily to reductions in air emissionsfrom 34 municipal and medical waste incinerators, andfurther reductions are anticipated. 12/23/03 4-4 DRAFT--DO NOT CITE OR QUOTE 1 For both categories, these emission reductions have occurred from a combination of 2 improved combustion and emission controls and from the closing of a number of 3 facilities. EPA's regulatory programs estimate that full compliance with recently 4 promulgated regulations should result in further reductions in emissions from the 5 1995 levels of more than 1800 I-TEQ. These reductions will occur in the following 6 source types: municipal waste combustors, medical waste incinerators, and various 7 facilities that burn hazardous waste (see Part I, Volume 1, for further details about 8 these reductions). No federal regulations are in place or currently under development 9 for limiting dioxin emissions from backyard burning of refuse in barrels. A number 10 of states have general restrictions on the practice of backyard trash burning. 11 12 Insufficient data are available to comprehensively estimatepoint source releases of 13 dioxin-like compounds to water. Sound estimates of releases to water are available 14 only for chlorine bleached pulp and paper mills (356 g I-TEQDFor TEQDF-WHO98for 15 1987 and 20 g I-TEQDFor TEQDF-WHO98for 1995) and the manufacture of ethylene 16 dichloride (EDC)/vinyl chloride monomer (VCM) (< 1 g I-TEQDFor TEQDF-WHO98 17 in 1995). Other releases to water bodies that cannot be quantified on the basis of 18 existing data include effluents from publicly owned treatment works (POTW) and 19 most industrial/commercial sources. EPA's Office of Water estimates that when full 20 compliance with limitations on effluent discharges of CDD/CDF from chlorine 21 bleached pulp and paper mills is achieved, annual emissions will be reduced to 5 g I22 TEQDF or TEQDF-WHO98. 23 24 Based on the available information, the inventory includes only a limited set of 25 activities that result in direct environmental releases to land. Total releases to land 26 quantified in the national inventory are estimated at 110 g TEQDF-WHO98in 1995 and 27 are principally from municipal wastewater treatment sludge (76.6 g) and the use of 28 2,4-D (28.9 g). Not included in the inventory's definition of an environmental release 29 is the disposal of sludge and ashes into approved landfills. 30 31 Significant amounts of dioxin-like compoundsproduced annually are not considered 32 environmental releases and, therefore, are not included in the national inventory. 33 Examples include dioxin-like compounds generated internal to a process but 34 destroyed before release, waste streams that are disposed of in approved landfills and 12/23/03 4-5 DRAFT--DO NOT CITE OR QUOTE 1 are therefore outside the definition of annual environmental releases, and products 2 that contain dioxin-like compounds but for which environmental releases, if any, 3 cannot be estimated. 4 5 Theprocedures and results of the U.S. inventory may have underestimated releasesfrom 6 contemporary sources. A number of investigators have suggested that national inventories may 7 underestimate emissions because of the possibility of unknown sources. This claim has been 8 supported with mass balance analyses that suggest that deposition exceeds emissions (Rappe, 9 1991; Harrad and Jones, 1992; Bruzy and Hites, 1995); however, the uncertainty, in both the 10 emissions and deposition estimates for the United States prevents the use of this approach for 11 reliably evaluating the issue. 12 A variety of other arguments indicate that the inventory could underestimate emissions of 13 dioxin-like compounds: 14 15 A number of sources lacked sufficient data to include in the inventory but 16 there were limited evidence indicating that these sources can emit CDD/CDFs. 17 These sources are listed in Tables 4-3 and 4-4 and include various components 18 of the metals industries, such as electric arc furnaces and foundries and 19 uncontrolled or minimally controlled combustion practices (e.g., accidental 20 fires at landfills). 21 22 The possibility remains that truly unknown sources exist. Many of the sources 23 that are well-accepted today were discovered only in the past 10 years. For 24 example, CDD/CDFs were found unexpectedly in the wastewater effluent 25 from bleached pulp and paper mills in the mid 1980s. Ore sintering is now 26 listed as one of the leading sources of CDD/CDF emissions in Germany, but it 27 was not recognized as a source until the early 1990s. 28 29 4.1.2. General Source Observations 30 For any given time period, releases from both contemporary formation sources and 31 reservoir sources determine the overall amount of the dioxin-like compounds that are being 32 released to the open and circulating environment. Because existing information is incomplete 33 with regard to quantifying contributions from contemporary and reservoir sources, it is not 34 currently possible to estimate the total magnitude of release for dioxin-like compounds from all 12/23/03 4-6 DRAFT--DO NOT CITE OR QUOTE 1 sources into the U.S. environment. For example, in terms of 1995 releases from reasonably 2 quantifiable sources, this document estimates releases of 3300 g TEQDF-WHO98(3000 g I3 TEQdf) for contemporary formation sources and 2900 g I-TEQDFor TEQDF-WHO98for reservoir 4 sources. 5 In addition, there remain a number of unquantifiable and poorly quantified sources. No 6 quantitative release estimates can be made for agricultural burning or for most CDD/CDF 7 reservoirs or for any dioxin-like PCB reservoirs. The preliminary 1995 estimate of releases from 8 poorly characterized contemporary formation sources is 1400 g I-TEQDFor TEQDF-WHO98. 9 The preliminary release estimates for contemporary formation sources and reservoir sources are 10 presented in Table 4-2. Table 4-3 lists all the sources that have been reported to release dioxin 11 like compounds but cannot be characterized on even a preliminary basis. 12 Additional observations and conclusions about all sources of dioxin-like compounds are 13 summarized below: 14 15 The contribution ofdioxin-like compounds to waterwaysfrom nonpoint source 16 reservoirs is likely to be greater than the contributionfrom point sources. Current 17 data are only sufficient to support preliminary estimates of nonpoint source 18 contributions of dioxin-like compounds to water (i.e., from urban storm water runoff 19 and rural soil erosion). These estimates suggest that, on a nationwide basis, total 20 nonpoint releases are significantly larger than point source releases. 21 22 Current emissions ofCDD/CDFs to the U.S. environment resultprincipallyfrom 23 anthropogenic activities. Evidence that supports this finding includes matches in 24 time of rise of environmental levels with time when general industrial activity began 25 rising rapidly (see trend discussion in Part I, Volume 2, Chapter 6), the lack of any 26 identified large natural sources, and observations of higher CDD/CDF body burdens 27 in industrialized versus less industrialized countries (see discussion on human tissue 28 levels in Part I, Volume 2, Chapter 4). 29 30 Although chlorine is an essential componentfor theformation of CDD/CDFs in 31 combustion systems, the empirical evidence indicates thatfor commercial-scale 32 incinerators, chlorine levels infeed are not the dominant controllingfactorfor rates 33 of CDD/CDF stack emissions. Important factors that can affect the rate of CDD/CDF 34 formation include the overall combustion efficiency, post-combustion flue gas 12/23/03 4-7 DRAFT--DO NOT CITE OR QUOTE 1 temperatures and residence times, and the availability of surface catalytic sites to 2 support CDD/CDF synthesis. Data from bench-, pilot- and commercial-scale 3 combustors indicate that CDD/CDF formation can occur by a number of mechanisms. 4 Some of these data, primarily from laboratory and pilot-scale combustors, have shown 5 direct correlation between chlorine content in fuels and rates of CDD/CDF formation. 6 Other data, primarily from commercial-scale combustors, show little relation between 7 availability of chlorine in feeds and rates of CDD/CDF formation. 8 9 The conclusion that chlorine in feed is not a strong determinant of CDD/CDF 10 emissions applies to the overall population of commercial-scale combustors. For any 11 individual commercial-scale combustor, circumstances may exist in which changes in 12 chlorine content of feed could affect CDD/CDF emissions. For uncontrolled 13 combustion, such as open burning of household waste, the chlorine content of the 14 waste may play a more significant role in rates of CDD/CDF formation and release 15 than is observed at commercial-scale combustors. The full discussion on this issue is 16 presented in Part I, Volume 1, Chapter 2. 17 18 Dioxins arepresent in some ball clays, but insufficient data are available to estimate 19 whether environmental releases occur during mining and use. Recent studies in the 20 United States and Europe have measured dioxins (principally CDDs) in some ball 21 clays and other related clays. As discussed in Part I, Volume 1, Chapter 13, it is likely 22 that the dioxin present in ball clay is of a natural origin. Ball clay is principally used 23 in the manufacture of ceramics, which involves firing the clay in high-temperature 24 kilns. This activity may cause some portion of the CDDs contained in the clay to be 25 released into the air, but emission tests have not yet been conducted that would allow 26 characterizing these releases. 27 28 Data are available to estimate the amounts ofCDD/CDFs contained in only a limited 29 number ofcommercialproducts. No systematic survey has been conducted to 30 determine levels of dioxin-like compounds in commercial products. The available 31 data do, however, allow estimates to be made of the amounts of dioxin-like 32 compounds in bleached pulp (40 g I-TEQDFor TEQDF-WHO98in 1995), POTW sludge 33 used in fertilizers (3.5 g I-TEQDFor 2.6 g TEQDF-WHO98in 1995), 34 pentachlorophenol-treated wood (8400 g I-TEQDFor 4800 g TEQDF-WHO98in 1995), 12/23/03 4-8 DRAFT--DO NOT CITE OR QUOTE 1 dioxazine dyes and pigments (< 1 g I-TEQDFor TEQDF-WHO98in 1995), and 2,4-D 2 (18.4 g I-TEQdf or 28.9 g TEQdf-WH098in 1995). 3 4 No significant release ofnewlyformed dioxin-like PCBs is occurring in the United 5 States. Unlike CDD/CDFs, PCBs were intentionally manufactured in the United 6 States in large quantities from 1929 until production ceased in 1977. Although it has 7 been demonstrated that small quantities of coplanar PCBs can be produced during 8 waste combustion, no strong evidence exists that the dioxin-like PCBs make a 9 significant contribution to TEQ releases during combustion. The occurrences of 10 dioxin-like PCBs in the U.S. environment most likely reflect past releases associated 11 with PCB production, use, and disposal. Further support for this finding is based on 12 observations of reductions since the 1980s in PCBs in Great Lakes sediment and other 13 areas. 14 15 It is unlikely that the emission rates of CDD/CDFsfrom known sources correlate 16 proportionally with generalpopulation exposures. Although the inventory shows the 17 relative contribution of various sources to total emissions, it cannot be assumed that 18 these sources make the same relative contributions to human exposure. It is quite 19 possible that the major sources of dioxin in food (see the discussion in Part I, Volume 20 2, Chapter 2, indicating that diet is the dominant exposure pathway for humans) may 21 not be those sources that represent the largest fractions of current total emissions in 22 the United States. It is important to consider the geographic locations of sources 23 relative to the areas from which much of the beef, pork, milk, and fish come. That is, 24 many of the agricultural areas that produce dietary animal fats are not located near or 25 directly downwind of the major sources of dioxin and related compounds. 26 27 The contribution ofreservoir sources to human exposure may be significant. Several 28 factors support this finding: 29 1. Because the magnitude of releases from current sources of newly formed PCBs 30 are most likely negligible, human exposure to the dioxin-like PCBs is thought to 31 be derived almost completely from reservoir sources. Key pathways involve 32 releases from both soils and sediments to both aquatic and terrestrial food chains. 33 As discussed in Part I, Volume 2, Chapter 4, one-third of general population 12/23/03 4-9 DRAFT--DO NOT CITE OR QUOTE 1 TEQdfp exposure is due to PCBs. Thus, at least one-third of the overall risk from 2 dioxin-like compounds comes from reservoir sources. 3 4 2. CDD/CDF releases from soil via soil erosion and runoff to waterways may be 5 significant. These releases appear to be greater than releases to water from the 6 primary sources included in the inventory. CDD/CDFs in waterways can 7 bioaccumulate in fish, leading to human exposure via their consumption. As 8 discussed in Part I, Volume 2, Chapter 4, fish consumption makes up about one9 fifth of the total general population CDD/CDF TEQ exposure. This suggests that 10 a significant portion of the CDD/CDF TEQ exposure could be due to releases 11 from the soil reservoir. It is not known, however, how much of the soil erosion 12 and runoffrepresents recently deposited CDD/CDFs from primary sources or 13 longer-term accumulation. Much of the eroded soil comes from tilled agricultural 14 lands, which would include a mix of CDD/CDFs from various deposition times. 15 The age of CDD/CDFs in urban runoffis less clear. 16 17 3. Potentially, soil reservoirs could have vapor and particulate releases that deposit 18 on plants and enter the terrestrial food chain. The magnitude of this contribution, 19 however, is unknown. 20 21 Collectively, these three factors suggest that reservoirs are a significant source of current 22 background TEQ exposure, perhaps contributing half or more of the total. 23 24 4.2. ENVIRONMENTAL FATE (Cross-reference: Part I, Volume 2, Chapter 2) 25 The estimates of environmental releases are presented above in terms of TEQs. This is 26 done for convenience in presenting summary information and to facilitate comparisons across 27 sources. For purposes of environmental fate modeling, however, it is important to use the 28 individual CDD/CDF and PCB congeners values rather than TEQs because the physical/chemical 29 properties of individual dioxin congeners vary and will behave differently in the environment. 30 For example, the relative mix of congeners released from a stack cannot be assumed to remain 31 constant during transport through the atmosphere and deposition to various media. The full 32 congener-specific release rates for most sources are given in an electronic database that is 33 available as a companion to this document (U.S. EPA, 1998) Database of Sources of 34 Environmental Releases of Dioxin-Like Compounds in the United States. EPA/600/P-98/002Ab. 12/23/03 4-10 DRAFT--DO NOT CITE OR QUOTE 1 In Part I, Volume 3, site-specific procedures are provided for estimating the impact of 2 emissions on local populations, and this section emphasizes that congener specific emission 3 values should be used in modeling their environmental fate. Finally, it is important to recognize 4 that this document does not use source release estimates to generate background population 5 intake/risk estimates; rather, these estimates are derived primarily from food levels and 6 consumption rates. 7 Dioxin-like compounds are widely distributed in the environment as a result ofa number 8 ofphysical and biologicalprocesses. The dioxin-like compounds are essentially insoluble in 9 water, they are generally classified as semivolatile, and they tend to bioaccumulate in animals. 10 Some evidence has shown that these compounds can degrade in the environment, but in general 11 they are considered to be very persistent and relatively immobile in soils and sediments. These 12 compounds are transported through the atmosphere as vapors or attached to airborne particulates 13 and can be deposited on soils, plants, or other surfaces (by wet or dry deposition). The dioxin 14 like compounds enter water bodies primarily via direct deposition from the atmosphere or by 15 surface runoff and erosion. From soils, these compounds can reenter the atmosphere as either 16 resuspended soil particles or vapors. In water, they can be resuspended into the water column 17 from sediments, they can be volatilized out of the surface waters into the atmosphere, or, they 18 can become buried in deeper sediments. Immobile sediments appear to serve as permanent sinks 19 for the dioxin-like compounds. Although anthropogenic materials (such as PCP) are not always 20 considered an environmental compartment, dioxin-like compounds are also found in such 21 materials, and from there they have the potential to be released into the broader environment. 22 Atmospheric transport and deposition ofthe dioxin-like compounds are a primary means 23 oftheir dispersal throughout the environment. The dioxin-like compounds have been measured 24 in wet and dry deposition in most locations, including remote areas. Numerous studies have 25 shown that they are commonly found in soils throughout the world. Industrialized countries tend 26 to show similar elevated concentrations in soil, and detectable levels have been found in 27 nonindustrialized countries. The only satisfactory explanation available for this distribution is air 28 transport and deposition. Finally, by analogy these compounds would be expected to behave 29 similarly to other compounds that have similar properties, and this postulated mechanism of 30 global distribution is becoming widely accepted for a variety of persistent organic compounds. 31 The two primary pathwaysfor the dioxin-like compounds to enter the ecologicalfood 32 chains and human diet are air-to-plant-to-animal and water/sediment-to-fish. Vegetation 33 receives these compounds via atmospheric deposition in the vapor and particle phases. The 34 compounds are retained on plant surfaces and bioaccumulated in the fatty tissues of animals that 12/23/03 4-11 DRAFT--DO NOT CITE OR QUOTE 1 feed on these plants. Vapor phase transfers onto vegetation have been experimentally shown to 2 dominate the air-to-plant pathway for the dioxin-like compounds, particularly for the lower 3 chlorinated congeners. In the aquatic food chain, dioxins enter water systems via direct 4 discharge or deposition and runoff from watersheds. Fish accumulate these compounds through 5 their direct contact with water, suspended particles, and bottom sediments and through their 6 consumption of aquatic organisms. 7 Although these two pathways are thought to normally dominate contribution to the 8 commercial food supply, others can also be important. Elevated dioxin levels in cattle resulting 9 from animal contact with PCP-treated wood have been documented by the U.S. Department of 10 Agriculture. Animal feed contamination episodes have led to elevations of dioxins in poultry in 11 the United States, milk in Germany, and meat/dairy products in Belgium (see Part I, Volume 2, 12 Chapter 5). 13 14 4.3. ENVIRONMENTAL MEDIA AND FOOD CONCENTRATIONS (Cross-reference: 15 Part I, Volume 2, Chapter 3) 16 Background levels of dioxin-like compounds in various environmental media, including 17 food, are presented in Table 4-4 in terms of means, variability, and sample sizes used to support 18 the estimates. Estimates for background levels of dioxin-like compounds in environmental 19 media are based on a variety of studies conducted at different locations in North America. Of the 20 studies available for this compilation, only those conducted in locations representing 21 "background" were selected. The amount and representativeness of the data vary, but in general 22 they were derived from studies that were not designed to estimate national background means. 23 The environmental media concentrations were similar to those in studies from Western Europe. 24 These data are the best available for comparisons with site-specific values. Because of the 25 limited number of locations examined, it is not known whether these estimates adequately 26 capture the full national variability. As new data are collected, these ranges are likely to be 27 expanded and refined. The limited data on dioxin-like PCBs in environmental media are 28 summarized in Part I, Volume 2, Chapter 3. 29 Estimates for levels of dioxin-like compounds in food are based on data from a variety of 30 studies conducted in North America. Beef, pork, and poultry estimates were derived from 31 statistically based national surveys. Milk estimates were derived from a survey of a nationwide 32 milk sampling network. Dairy estimates were derived from milk fat concentrations, coupled with 33 appropriate assumptions for the amount of milk fat in dairy products. The background egg 34 concentrations were based on an analysis of 15 egg samples collected from retail stores in eight 12/23/03 4-12 DRAFT--DO NOT CITE OR QUOTE 1 states (CA, OH, GA, NY, PA, OR, MN, WS; two samples per state except one in OR), where 2 each sample was a composite of 24 individual eggs (i.e., 15 samples represented 360 eggs). The 3 fish data, as discussed below, were derived from multiple studies, with samples collected both 4 directly from water bodies and from retail outlets. All fish concentrations were expressed on the 5 basis of fresh weight in edible tissue. As with other environmental media, food levels found in 6 the United States were similar to levels found in Europe. 7 The procedure to evaluate background fish exposures emphasizes the use of both species8 specific consumption rates and species-specific concentrations. EPA's national bioaccumulation 9 study (U.S. EPA, 1992b) provides some species-specific information on freshwater/estuarine fish 10 caught in the wild at various locations in the United States. Additional species-specific data on 11 store-bought fish are available from studies conducted by the U.S. Food and Drug Administration 12 (FDA) during the mid to latter 1990s (Jensen and Bolger, 2000; Jensen et al., 2000). An 13 important aspect of the FDA studies is that they include data on store-bought catfish, tuna, 14 shellfish, and salmon, which are some of the most highly consumed species. Accordingly, the 15 data used to characterize CDD/CDF fish levels are much improved over previous estimates, with 16 more than 300 individual samples and good representation of the most highly consumed species. 17 However, the levels of dioxins in fish remain more uncertain than those in the other foods. 18 The compilation of data from different studies still lacks the geographic coverage and 19 statistical power of the other food surveys. The EPA and FDA studies did not address dioxin 20 like PCBs; rather, these are based on a much smaller data set derived from the open literature. 21 Also, the estimates of dioxin intake resulting from fish consumption do not include consumption 22 of fish oils. Currently, insufficient data are available to support estimates of dioxin intake from 23 direct fish oil consumption. 24 The general population dioxin intake calculations used in this document are a function of 25 both consumption rate and dioxin concentration in food. The concentration data used in this 26 document were measured in raw foods; therefore, if cooking significantly alters the dioxin 27 concentration in consumed portions it must be accounted for in estimating dioxin intake. 28 This issue has been examined in a number of studies that measured the effects of cooking 29 on the levels of CDDs, CDFs, and PCBs in foods (see Part I, Volume 2, Chapter 3). These 30 studies have a range of results, depending on food type and cooking method. Most of the 31 cooking experiments suggested that cooking reduces the total amount of dioxins in food but 32 causes relatively little change in its concentration. 33 Although some cooking experiments have shown increases and others have shown 34 decreases in dioxin concentrations, the relative prevalence of these impacts have not been 12/23/03 4-13 DRAFT--DO NOT CITE OR QUOTE 1 established. Therefore, given that most experiments show little change and others show change 2 in both directions, the most reasonable assumption that can be made from the existing data is that 3 dioxin concentration in uncooked food is a reasonable surrogate for dioxin concentration in 4 cooked food. Although cooking in general does not reduce dioxin concentration in food, some 5 specific food preparation practices can be adopted that can reduce dioxin intake by significantly 6 reducing overall animal fat consumption. For example, carefully trimming fat from meat, 7 removing skin from chicken and fish, and avoiding cooking in animal fats should reduce both 8 animal fat and dioxin intake. 9 Some evidence from Europe suggests that during the 1990s a decline occurred in 10 concentrations of dioxins and furans in food products, particularly dairy products (see Part I, 11 Volume 2, Chapter 6). For example, the United Kingdom's Ministry of Agriculture, Fisheries, 12 and Food collected milk samples in 1990 and again from similar locations in 1995. In 1990, the 13 I-TEQdfranged from 1.1 to 3.3 ppt, whereas the 1995 I-TEQDFranged from 0.7 to 1.4. In 14 Germany, a sampling of 120 dairy products in 1994 found I-TEQdf concentrations that were 25% 15 lower than those in a similar sampling program in 1990. Liem et al. (2000) reports on a 16 European cooperative study coordinated by the National Institute of Public Health and the 17 Environment in the Netherlands and the Swedish National Food Administration. Ten countries 18 supplied data on food concentrations, food consumption patterns, and other data used to evaluate 19 exposure to dioxins in Europe. Some of the data suggested reductions in concentrations over 20 time, but the available information was insufficient to draw general conclusions. 21 No systematic study of temporal trends in dioxin levels in food has been conducted in the 22 United States. Although not statistically based, one U.S. study examined dioxin levels in 14 23 preserved food samples from various decades in the 20th century (Winters et al., 1998). It was 24 found that meat samples of the 1950s through the 1970s had concentrations that were two-three 25 times higher for the CDD/CDF TEQs and about 10 times higher for the PCB TEQs, as compared 26 to current meat concentrations. 27 The food data and associated exposure estimates presented here reflect a mid-1990's time 28 frame. New studies underway now or recently completed could be used in future updates to this 29 report to make exposure estimates for a new reference year, such as 2000. The following studies 30 on dioxin levels in food were not completed in time to be included in this document and should 31 be considered in future updates: 32 33 The milk levels used in Tables 4-4 and 4-6 are based on a study by Lorber et al. 34 (1998) where milk samples were collected in 1996. A very similar milk survey was 12/23/03 4-14 DRAFT--DO NOT CITE OR QUOTE 1 conducted by Schaum et al. (2003) involving the collection and analysis of TEQDFPin 2 cow milk samples from 45 dairy plants in July of 2000 and again in January 2001. 3 This study reported TEQFPlevels in whole milk which were about half the levels 4 found by Lorber et al. (1998). Follow-up work by Schuda et al. (2004), which 5 addressed CDD/Fs only, allowed estimation of 2000/2001 TEQDFmilk levels on a 6 lipid basis. This approach showed similar TEQ levels in milk lipid, or perhaps a 7 slight decrease, when comparing CDD/F TEQs in the two sampling times (0.71 pg 8 TEQDF/g lipid in 2000/2001 compared to 0.82 pg TEQDF/g lipid in 1996). 9 10 USDA is currently conducting a nationwide survey of dioxin levels in beef, pork and 11 poultry. Samples were collected in 2002 and 2003 and data analysis is now 12 underway. The survey design and data analysis are structured in a similar way to the 13 earlier USDA surveys used in this report and should allow for trend analysis. 14 15 The Institute ofMedicine of the National Academies published a review of dioxin 16 levels in foods in 2003 (Institute ofMedicine of the National Academies, 2003). This 17 document presents policy options for reducing dietary exposure to dioxins in food and 18 related research recommendations. Appendix B of the Institute of Medicine's report 19 summarizes FDA's Total Diet Survey of dioxin levels in food collected in 2001. A 20 wide variety of foods were sampled including dairy products, eggs, meats, fish, fruits, 21 vegetables and fats/oils. 22 23 The food consumption rates used here are based primarily on USDA's 1994-1996 Continuing 24 Survey of Food Intakes by Individuals. As new USDA survey data come available, these should 25 be incorporated into future updates of this report. 26 27 4.4. BACKGROUND EXPOSURES (Cross-reference: Part I, Volume 2, Chapter 4) 28 4.4.1. Tissue Levels 29 The average CDD/CDF/PCB tissue levelfor the general adult U.S. population appears to 30 be declining, and the best estimate ofcurrent (late 1990s) levels is 25ppt (TEQDFP-WHO98, lipid 31 basis). 32 The tissue samples collected in North America in the late 1980s and early 1990s showed 33 an average TEQDFP-WHO98level of about 55 pg/g lipid. This finding is supported by a number of 34 studies--all conducted in North America--that measured dioxin levels in adipose, blood, and 12/23/03 4-15 DRAFT--DO NOT CITE OR QUOTE 1 human milk. However, the number of participants in most ofthese studies was relatively small 2 and they were not statistically selected in ways that ensure their representativeness of the general 3 U.S. adult population. One study, the 1987 National Human Adipose Tissue Survey, involved 4 more than 800 individuals and provided broad geographic coverage, but it did not address 5 coplanar PCBs. Similar tissue levels of these compounds have been measured in Europe and 6 Japan during similar time periods. 7 Because dioxin levels in the environment have been declining since the 1970s (see the 8 trends discussion in Part I, Volume 2, Chapter 6), it is reasonable to expect that levels in food, 9 human intake, and, ultimately, human tissue have also declined over this period. The changes in 10 tissue levels are likely to lag the decline seen in environmental levels, and the changes in tissue 11 levels cannot be assumed to occur proportionally with declines in environmental levels. 12 CDC (2000) summarizes levels of CDDs, CDFs, and PCBs in human blood collected 13 between 1995 to 1997 from 316 U.S. residents (ages 20-70 years). The individuals sampled had 14 no known exposures to dioxin other than normal background. Although the samples in this data 15 set were not collected in a manner that can be considered statistically representative of the 16 national population and they lack wide geographic coverage, they are judged to provide a better 17 indication of current tissue levels in the United States than the earlier data. 18 PCBs 105, 118, and 156 are missing from the blood data for the comparison populations 19 reported by CDC (2000). These congeners account for 62% of the total PCB TEQ estimated in 20 the early 1990s. Assuming that the missing congeners from the CDC study data contribute in the 21 same proportion to the total PCB TEQ as in earlier data, they would increase the estimate of 22 current body burdens by another 3.3 pg TEQ/g lipid, for a total PCB TEQ of 5.3 pg/g lipid and a 23 total of 25.4 pg TEQDFP-WHO98/g lipid (i.e., the TEQDF-WHO98concentration was 20.1 pg/g 24 lipid, and the TEQP-WHO98concentration was estimated at 5.3 pg/g lipid). A summary of the 25 CDC (2000) data is shown in Table 4-5. 26 A portion of the CDC blood data were plotted as a function of age. This plot, shown in 27 Figure 4-3, indicates that blood levels generally increase with age, as does the variability in blood 28 levels. 29 The calculation of a current tissue level of 25.4 pg/g lipid TEQDFP-WHO98is further 30 supported by the observation that this mean tissue level is consistent with the best estimate of 31 current adult intake, 66 pg TEQDFP-WHO98/d. Using this intake in a one-compartment, steady32 state pharmacokinetic model yields a tissue level estimate of about 11.3 pg TEQDFP/g lipid 33 (assumes TEQDFPhas an effective half-life of 7.1 years, 80% of ingested dioxin is absorbed into 34 the body, and lipid weight is 25% of the adult assumed body weight of 70 kg, or 17.5 kg). 12/23/03 4-16 DRAFT--DO NOT CITE OR QUOTE 1 Because intake rates appear to have declined in recent years, and steady-state is not likely to have 2 been achieved, it is reasonable to observe higher measured tissue levels, such as the 25.4 pg 3 TEQ/g lipid, than those predicted by the model. 4 Characterizing national background levels of dioxins in tissues is uncertain because the 5 current data cannot be considered statistically representative of the general population. It is also 6 complicated by the fact that tissue levels are a function ofboth age and birth year. Because 7 intake levels have varied over time, the accumulation of dioxins in a person who turned 50 years 8 old in 1990 is different than that in a person who turned 50 in 2000. As discussed in Part I, 9 Volume 2, Chapter 6, exposure to dioxin-like compounds peaked during the 1960s, with 10 declining exposures since then. Therefore, a person born in 1910 will see a rise in body levels 11 that peaks at 50 to 70 years old. At the other end of the spectrum, a person born in 1970 will 12 experience a higher body concentration very early in life, with declining levels in later years. 13 A pharmacokinetic (PK) modeling framework was developed to study trends in 14 population body burdens of CDDs/CDFs throughout the 20thcentury and into the 21st century 15 (Lorber, 2002). It was assumed that individuals within a population were exposed to doses rising 16 from 0.50 pg WHO98-TEQDF/kg-day during the 1940s to about 6.5 pg WHO98-TEQDF/kg-day by 17 the late 1960s, down to 1.0 pg WHO98-TEQDF/kg-day by 1980, and finally to 0.50 pg WHO9818 TEQ /kg-day by 2000, remaining constant at that level into the 21st century. It was found that a 19 modeled population tissue level distribution will vary, depending on the year the modeled 20 population is sampled. The results of this analysis are presented in Figure 4-4, which shows 21 modeled population tissue level distributions for four years. An "age trend" is seen in the figure 22 for modeled populations sampled in 1985 and 1995, as was seen in the CDC monitoring study of 23 actual blood measurements of WHO98-TEQDFP(see Fig. 4-3). Figure 4-4 also suggests that this 24 age trend will disappear in the 21st century and that the CDD/CDF tissue level will drop below 10 25 ppt TEQ -WHO98lipid basis by 2030. 26 Monitoring studies which are currently underway should help determine whether the 27 decline in body burdens has been continuing into the 21st century, as suggested by modeling. 28 Results from the National Health and Nutrition Examination Survey of 1999-2000 (NHANES 29 1999-2000) were recently made available (CDC, 2003). NHANES 1999-2000 included data on 30 dioxin-like compounds in the blood of 1921 sampled individuals, aged 12 and higher, and 31 sampled from numerous locations around the country. These compounds included the 17 dioxin 32 and furan congeners, as well as PCB congeners 126, 77, 169, and 81. 33 The current estimate of background body burden is based on 6 different studies totaling 34 316 individuals around the country which measured concentrations of these compounds in 12/23/03 4-17 DRAFT--DO NOT CITE OR QUOTE 1 populations characterized as "background" (CDC, 2000). Often these populations were selected 2 the "background" population for studies which targeted other potentially exposed populations. 3 The dates of these surveys, as noted above, were from about 1995 to 1997. In addition to being 4 more recent, the NHANES 1999-2000 sampled population was much larger, but perhaps most 5 importantly, NHANES was statistically designed to be representative of U.S. background after 6 several years of data collection while the merged population from the 6 studies was not. 7 However, the amount of blood serum available for individual measurements in NHANES 8 1999-2000 was too small to be able to detect and characterize current levels of dioxin like 9 compounds in the population. A large majority of the measurements were nondetects. For this 10 reason, an effort is underway to pool remaining, available individual samples from NHANES and 11 measure them for dioxin-like compounds, which would provide an updated measure of average 12 concentrations of these compounds in the blood of U.S. citizens (ages 12 and greater, circa 1999 13 2000, and with all other delimiters relevant to the pooled samples, of course). 14 15 4.4.2. Intake Estimates 16 Adult daily intakes of CDD/CDFs and dioxin-like PCBs are estimated to average 43 and 17 23pg TEQDFP-WHO98/day, respectively, for a total intake of 66pg/day TEQDFP-WHO98. Daily 18 intake is estimated by combining exposure media concentrations (food, soil, and air) with contact 19 rates (ingestion, inhalation). Table 4-6 summarizes the media concentrations, contact rates, and 20 resulting intake estimates. 21 The intake estimate is supported by an extensive database on food consumption rates and 22 estimates of dioxin-like compounds in food (as discussed above). PK modeling provides further 23 support for the intake estimates. Applying a simple steady-state PK model to an adult average 24 blood level of 25 ppt TEQDFP-WHO98(on a lipid basis) yields a daily intake of 146 pg TEQDFP25 WHO98/day (assumes TEQFPhas an effective half-life of 7.1 years, 80% of ingested dioxin is 26 absorbed into the body, and lipid weight is 25% of the adult assumed body weight of 70 kg, or 27 17.5 kg). This PK-modeled CDD/CDF/PCB intake estimate is about 2.2 times higher than the 28 direct intake estimate of 66 pg TEQDFP-WHO98/day. This difference is to be expected with this 29 application of a simple steady-state PK model to current average adipose tissue concentrations. 30 Current adult tissue levels reflect intakes from past exposure levels, which are thought to be 31 higher than current levels (Lorber, 2002; also in Part I, Volume 2, Chapter 6). Because the 32 direction and magnitude of the difference in intake estimates between the two approaches are 33 understood, the PK-derived value is judged supportive of the pathway-derived estimate. It 12/23/03 4-18 DRAFT--DO NOT CITE OR QUOTE 1 should be recognized, however, that the pathway-derived value will underestimate exposure if it 2 has failed to capture all the significant exposure pathways. 3 4 4.4.3. Variability in Intake Levels 5 CDD/CDF and dioxin-like PCB intakesfor the generalpopulation may extend to levels at 6 least three times higher than the mean. Variability in general population exposure is primarily 7 the result of the differences in dietary choices that individuals make. These are differences in 8 both quantity and types of food consumed. An increased background exposure can result from 9 either a diet that favors consumption of foods high in dioxin content or a diet that is 10 disproportionately high in overall consumption of animal fats. 11 The best data available to determine the variability of total fat consumption come from 12 several analyses of the Bogalusa Heart Study (Cresanta et al., 1988; Nicklas et al., 1993, 1995, 13 Nicklas, 1995; Frank et al., 1986). These data show that the 95thpercentile of total fat 14 consumption is about twice the mean and the 99thpercentile is approximately three times the 15 mean. For a diet that has a broad distribution of animal fats (as does the typical U.S. diet), this 16 same distribution can be assumed for dioxin intake. 17 Although body burden data cannot be assumed to be perfectly representative of current 18 intakes (because they reflect past exposures as well as current ones), they also provide some 19 support for this finding, based on the observation that the 95thpercentile blood level in the CDC 20 (2000) study was almost twice the mean level. 21 Intakes of CDDs/CDFs and dioxin-like PCBs are more than three times higherfor a 22 young child thanfor an adult, on a body-weight basis. This figure is based on combining age23 specific food consumption rate and average food concentrations, as was done above for adult 24 intake estimates (see Table 4-7). 25 Only 4 of the 17 toxic CDD/CDF congeners and 1 ofthe 11 toxic PCBs accountfor most 26 ofthe toxicity in human tissue concentrations: 2,3,7,8-TCDD, 1,2,3,7,8-PCDD, 1,2,3,6,7,827 HxCDD, and 2,3,4,7,8-PCDF and PCB 126. This finding is derived directly from the data 28 described earlier on human tissue levels and is supported by intake estimations that indicate that 29 these congeners are also the primary contributors to dietary dose. These five compounds make 30 up about 80% of the total TEQDFP-WHO98tissue level. 31 12/23/03 4-19 DRAFT--DO NOT CITE OR QUOTE 1 4.5. POTENTIALLY HIGHLY EXPOSED POPULATIONS OR DEVELOPMENTAL 2 STAGES (Cross-reference: Part I, Volume 2, Chapter 5) 3 As discussed earlier, background exposures to dioxin-like compounds may extend to 4 levels at least three times higher than the mean. This upper range is assumed to result from the 5 normal variability of diet and human behaviors. Exposures from local elevated sources or 6 exposures resulting from unique diets would be in addition to this background variability. Such 7 elevated exposures may occur in small segments of the population, such as individuals living 8 near discrete local sources. Nursing infants represent a special case: for a limited portion of their 9 lives, these individuals may have elevated exposures on a body-weight basis when compared 10 with nonnursing infants and adults. 11 Dioxin contamination incidents involving the commercial food supply have occurred in 12 the United States and in other countries. For example, in the United States, contaminated ball 13 clay was used as an anticaking agent in soybean meal, which resulted in elevated dioxin levels in 14 some poultry and catfish. This incident, which occurred in 1998, involved a small faction of the 15 national poultry production, and the use of contaminated ball clay has since been eliminated. 16 Elevated dioxin levels have also been observed in a few beef and dairy animals, where the 17 contamination was associated with contact with pentachlorophenol-treated wood. Evidence of 18 this kind of elevated exposure was not detected in the national beef survey. Consequently, its 19 occurrence is likely to be low, but it has not been determined. 20 These incidents may have led to small increases in dioxin exposure to the general 21 population. However, it is unlikely that they have led to disproportionate exposures to 22 populations living near where they occurred because in the United States meat and dairy products 23 are highly distributed on a national scale. If contamination events were to occur in foods that are 24 predominantly distributed on a local or regional scale, then such events could lead to more highly 25 exposed local populations (see Part I, Volume 2, Chapter 5). 26 Elevated exposures associated with the workplace or with industrial accidents have also 27 been documented. U.S. workers in certain segments of the chemical industry had elevated levels 28 of TCDD exposure, with some tissue measurements in the thousands of part per trillion TCDD. 29 There is no clear evidence that elevated exposures are currently occurring among U.S. workers. 30 Documented examples of past exposures for other groups include certain Air Force personnel 31 exposed to Agent Orange during the Vietnam War and people exposed as a result of industrial 32 accidents in Europe and Asia. 12/23/03 4-20 DRAFT--DO NOT CITE OR QUOTE 1 Consumption ofbreast milk by nursing infants leads to higher levels of exposure and 2 higher body burdens ofdioxins during earlyyears oflife as compared with those ofnonnursing 3 infants (Part I, Volume 2, Chapter 5). 4 Kreuzer et al. (1997) and Abraham et al. (1994, 1995, 1998, 2000) compared dioxin 5 levels in infants who were breast-fed with those who were formula-fed. All the studies showed 6 elevations in the concentrations of dioxins in the breast-fed infants. Collectively, these studies 7 included more than 100 infants, and they found that blood levels in infants aged 4-12 months 8 were generally higher than 20 pg TEQDF-WHO98/g lipid in nursing infants and lower than 5 pg 9 TEQDF-WHO98/g lipid in formula fed infants. Limited data suggest a similar difference for 10 dioxin-like PCBs. Abraham et al. (1995) reported that at 11 months a breast-fed infant had a 11 concentration of 31.4 pg TEQP-WHO98/g lipid, compared to 2.5 pg TEQP-WHO98/g lipid for the 12 formula-fed infant. 13 U.S. dioxin intakes from nursing were calculated using time-dependent values for breast 14 milk concentrations, consumption rates, and body weights. These calculations estimated an 15 intake immediately after birth of 242 pg TEQDFP-WHO98/kg/day. This level dropped to 18 pg 16 TEQ -WHO /kg/day after 12 months of nursing. The average intake over 1-year of nursing 17 was calculated to be 87 pg TEQDFP-WHO98/kg/day. The cumulative intake for a 1year nursing 18 scenario represented about 13% ofthe total lifetime cumulative intake (see Lorber and Phillips, 19 2002, and Part I, Volume 2, Chapter 5, for details on these calculations). 20 CDC (1997) reported that in 1995, 55% of all babies experienced some breast-feeding, 21 with about half of those breast-feeding beyond 5 months. The average duration of breast-feeding 22 was 28.7 weeks. In a policy statement, the American Academy of Pediatrics (1997) stated that 23 exclusive breast feeding provides ideal nutrition and is sufficient to support optimal growth and 24 development for 6 months after birth. It recommended that breast-feeding continue for at least 25 12 months and thereafter for as long as mutually desired. 26 To better evaluate the impact of nursing on infants, changes in body burden were 27 calculated using a one-compartment, first-order pharmacokinetic model (Lorber and Phillips, 28 2002). First, the model was validated using data from Abraham et al. (1998). Dioxin and furan 29 concentrations for six mother/infant pairs were provided, including two breast milk 30 measurements while the mother was feeding her infant and a blood measurement for the infant 31 at about 1year. These mothers' milk concentrations were used as the independent source term 32 for the model, and the infant blood concentrations served as dependent model prediction. Other 33 required parameters included the infant's body weight and lipid fraction over time (assigned 34 average male and female infant values), absorption fraction (assigned a constant value of 0.80), 12/23/03 4-21 DRAFT--DO NOT CITE OR QUOTE 1 and, most importantly, an assumption of a rapid dissipation rate ofTEQs in the infant (half-life 2 < 1year) during the early months of life. This dissipation rate was developed by Kreuzer et al. 3 (1997), and it contrasts the more typical 7-year half-life found in adults for TCDD. 4 The average observed infant concentration was 24 pg TEQDF-WHO98/g lipid, compared to 5 a predicted concentration of 26 pg TEQDF-WHO98/g lipid. The observed high and low 6 concentrations were 5 and 44 pg TEQDF-WHO98/g lipid, compared to predicted high and low 7 concentrations in these infants of 10 and 36 pg TEQDF-WHO98/g lipid. When the model was 8 rerun at a higher TEQ dissipation rate of 7 years, the average predicted concentration rose to 39 9 pg TEQDF-WHO98/g lipid. This demonstrated the appropriateness and importance ofthe 10 assignment of a rapid dissipation rate of TEQs in infants. 11 This framework was used to evaluate various nursing scenarios: formula only and 6 12 weeks, 6 months, 1year, and 2 years nursing. These scenarios reasonably capture the range of 13 current nursing practices. This modeling effort required using the intake assumptions described 14 earlier--242 pg TEQDFP-WHO98/kg/day at birth and an average of 87 pg TEQDFP-WHO98/kg/day 15 over a year of breast-feeding--and other parameters noted above including the fraction of the 16 oral dose that is absorbed into the body, changes in body weight over time, and changes in body 17 fat fraction over time. For the infant, the half-life was less than 1year, and during adulthood the 18 half-life increased as the fraction of body fat increased. The longer half-life during the later 19 years of life was based on a model presented in Michalek et al. (1996). The complete set of input 20 values is listed in Lorber and Phillips (2002) as well as in Part I, Volume 2, Chapter 5. 21 The modeling results in terms of changes in lipid concentrations and body burdens as a 22 function of age are shown in Figure 4-5. Some key observations include: 23 24 For the 6-month, 1-year, and 2-year nursing scenarios, lipid concentrations peaked at 25 around 9 weeks at 44 ppt TEQ -WHO . For the formula-fed infants they peaked at 26 less than 10 ppt after the first year. 27 28 In all four scenarios, the lipid concentrations merged at about 10 years of age at a 29 concentration of about 13 ppt TEQDFP-WHO98. Lipid and body burdens declined 30 slightly from age 10 to about age 20 and then rose gradually through adulthood. This 31 rise was due to the increase in half-life with age. At age 70, the modeled lipid and 32 body burden concentrations were 13 ppt TEQDFP-WHO98lipid and 5 ppt TEQDFP33 WHO98whole body weight. 34 12/23/03 4-22 DRAFT--DO NOT CITE OR QUOTE 1 Breast-feeding leads to higher total lifetime exposures to TEQs as compared to 2 formula feeding. Using an AUC approach, 70-year cumulative lifetime exposures 3 were evaluated. The results suggest that breast-feeding added between 3% (for the 64 week breast-feeding scenario) and 18% (for the 2-year scenario) more accumulated 5 exposure to TEQs as compared to formula-feeding. 6 7 The above analysis indicates that the average annual infant intake resulting from 1 year of 8 nursing, 87 pg TEQDFP-WHO98/kg/day, significantly exceeds the currently estimated adult intake 9 of 1pg TEQDFP-WHO98/kg/day. The impact of nursing on infant body burdens, however, is much 10 less, that is, infant body burdens will not exceed adult body burdens by 87 times. Rather, the 11 modeling suggests that peak infant body burdens are only about two times the current adult body 12 burdens (44 vs. 25 pg TEQDFP-WHO98/g lipid). The reduced impact on body burden levels in 13 nursing infants (relative to the intake) is due to the rapidly expanding infant body weight and 14 lipid volume, and the faster elimination rate in infants. Body burden levels in nursing infants 15 should decline in the future if, as discussed earlier, general population exposures decline. 16 Consumption offish, meat, or dairyproducts containing elevated levels ofdioxins and 17 dioxin-like PCBs can lead to elevated exposures in comparison with the generalpopulation. 18 The above discussion identified the general population distribution as extending up to roughly 19 three times the mean. Most people will have exposures within this range even if they have 20 unusual diets in terms of meat and dairy products. This is because (1) most people eat food from 21 multiple sources, which tends to average out the contamination levels, and (2) meat and dairy 22 products have similar dioxin levels, so substitution of one type of meat for another should not 23 have a great impact on total exposure. Clearly, elevated exposures are possible in unusual 24 situations, such as when an individual consumes large quantities of meat or dairy products that 25 have significantly increased dioxin levels. 26 Elevated exposures resulting from fish consumption can occur in different situations. 27 Concentrations in freshwater fish are significantly greater than in meat and dairy products; 28 therefore, individuals who consume large quantities of freshwater fish at background 29 contamination levels may have intakes higher than the general population distribution. A simple 30 scenario was devised to evaluate this hypothesis. Through a review of the literature, EPA (U.S. 31 EPA, 1997) concluded that a range of consumption of 59 to 170 g/day describes subsistence fish 32 consumption behavior. These consumption rates were adopted to characterize the range of 33 exposures in this scenario. Further, it is assumed that freshwater fish is the primary source of 34 protein, that is, no meat or eggs are consumed. Assuming that all other exposure pathways stay 12/23/03 4-23 DRAFT--DO NOT CITE OR QUOTE 1 the same and using background exposure media concentrations, adult daily intake in this 2 subsistence fisher scenario is calculated to range from 2.2 to 5.7 pg TEQDFP-WHO98/kg-day. 3 These intakes are about two to six times higher than the adult general population mean daily 4 intake of 0.93 pg TEQDFP-WHO98/kg-day. If subsistence fishers obtain their fish from areas 5 where the concentration of dioxin-like chemicals in the fish is elevated, their exposure could be 6 higher. Although this scenario appears reasonable, no clearly supportive data could be found to 7 confirm that such highly exposed subpopulations exist in the United States. 8 One study that measured dioxin-like compounds in the blood of sport fishers in the Great 9 Lakes area showed elevations over mean background but within the range of normal variability. 10 However, another study that measured 90 PCB congeners (seven of which were dioxin-like 11 PCBs, although PCB 126 was not measured) in the blood of sport fishers who consume high 12 amounts of fish caught from Lake Michigan (> 26 pounds of sport fish per year) did find 13 significant elevations of PCBs in their blood as compared to a control population (individuals 14 consuming < 6 pounds of sport fish per year). The average total concentration of PCBs in the 15 blood of the sport fishers was more than three times higher than that of the control population. 16 Similarly, elevated levels of coplanar PCBs have been measured in the blood of fishers on the 17 north shore of the Gulf of the St. Lawrence River who consume large amounts of seafood. 18 Elevated CDD/CDF levels in human blood have been measured in Baltic fishermen. For further 19 details on these studies see Part I, Volume 2, Chapter 5. 20 High exposures to dioxin-like compounds as a result of consuming meat and dairy 21 products would most likely occur in situations where individuals consume large quantities of 22 these foods and the level of these compounds is elevated. Most people eat meat and dairy 23 products from multiple sources, and even if large quantities are consumed they are not likely to 24 have unusually high exposures. Individuals who raise their own livestock for basic subsistence 25 have the potential for higher exposures if local levels of dioxin-like compounds are high. One 26 study in the United States showed elevated levels in chicken eggs near a contaminated soil site. 27 European studies at several sites have shown elevated CDD/CDF levels in milk and other animal 28 products near combustion sources, and some ofthese studies have also documented elevations in 29 the levels of dioxin-like compounds in blood from families who consume their own home 30 products. 12/23/03 4-24 DRAFT--DO NOT CITE OR QUOTE 21 Table 4-1. Confidence rating scheme CO Confidence category Confidence rating Activity level estimate Emission factor estimate 5 Categories/media for which emissions can be reasonably quantified 6 A High Dsuerrvievyed from comprehensive Derived from comprehensive survey 7 B Medium pBlaasnetdaoctniveistytimleavteelsaonfdanvuermagbeer of Derived from testing at a limited but reasonable number of facilities plants or limited survey believed to be representative of source category 8 C Low Based on data judged possibly Derived from testing at only a few, nonrepresentative. possibly nonrepresentative facilities or from similar source categories 9 Categories/media for which emissions cannot be reasonably quantified 10 D Preliminary estimate Based on extremely limited data, jnuodngreedprteosebnetactlievaer.ly Based on extremely limited data, jnuodngreedprteosebnetactlievaer.ly 11 E Not quantified No data. 12 (1) Argument based on theory but no d(2a)taData indicating dioxin formation but not in a form that allows developing an emission factor 12/23/03 4-25 DRAFT DO NOT CITE OR QUOTE 321 TTaEbQledf4--W2.HIOnv98einntothrye of environmental United States releases (grams/year) of Confidence ratinga Confidence ratinga reference year 1995 reference year 1987 4 5 67 Emission source category A B C Releases (g TEQ/yr) to air Waste incineration Municipal waste incineration 1250 D AB C 8877 8 Hazardous waste incineration 5.8 5 9 Boilers/industrial furnaces 0.39 0.78 1110 Minceidniecraaltiwonaste/pathological 488 2590 12 Crematoria 9.1b 5.5b 13 14 Sewage sludge incineration Tire combustion 14.8 0.11 6.1 0.11 1156 111789 Pulp and paper mill sludge incineratorsc Power/energy generation V-elheiacdleedfduel combustion 20 21 2223 - unleaded - diesel W-oroedsicdoemntbiaulstion 2 5.6 33.5 62.8b 37.5 3.6 27.8 89.6b 24 - industrial 27.6 26.4 2256 Coal combustion - utility boilers 27 - residential 60.1 50.8 30 28 - commercial/Industrial 40 3209 Oil combustion - industrial/utility 10.7 17.8 31 - residential 6 333234 Other high temperature sources wCeamsteenbtukrinlinnsg)(hazardous 156.1 117.8 3356 3378 bLuigrnhitnwgeihgahztaardgoguresgwataestkeilns Cement kilns (nonhazardous waste burning) 3.3b 17.8 2.4b 13.7 4309 Petroleum refining catalyst regeneration 2.21 2.24 12/23/03 4-26 DRAFT--DO NOT CITE OR Table 4-2. Inventory of environmental releases (grams/year) of TEQDF-WHO98in the United States (continued) Confidence rating" reference year 1995 Confidence ratinga reference year 1987 1 432 Emission source category A Releases (g TEQ/yr) to air (continued) O(ctohnetrinhuiegdh)temperature sources Cigarette combustion B CD 0.8 AB C 1 5 Carbon reactivation furnaces 0.08b 0.06b 6 Kraft recovery boilers 2.3 2 7 Combustion of landfill gas 7 8 Biogas combustion <1 11109 Minimally controlled or uncontrolled combustion6 Backyard barrel burningf 628 604 12 Landfill fires 1000 13 Accidental fires (structural) < 20 14 Accidental fires (vehicles) 30 15 Forest and brush fires 200 111768 Metallurgical processes Ferrous metal smelting/refining 19 - sintering plants 28 32.7 20 21 - electric arc furnaces - foundries 40 20 2223 24 Nsmoenlfteinrrgo/uresfimnientagl - primary copper < 0.5b < 0.5b 25 - secondary aluminum 29.1 16.3 26 27 - secondary copper - secondary lead 271 1.72 983 1.29 28 - primary magnesium 15 29 Coke production 7 30 Drum and barrel reclamation 0.08 0.08 3333312534 Chemical manufacturing/processing souErtcheyslene dichloride/vinyl chloride 11.2b 36 TOTAL RELEASES TO AIRg 3125 13515 12/23/03 4-27 DRAFT--DO NOT CITE OR Table 4-2. Inventory of environmental releases (grams/year) of TEQDF-WHO98in the United States (continued) Confidence rating" reference year 1995 Confidence rating" reference year 1987 1 Emission source category Releases (g TEQ/yr) to water A B CD AB C 4325 Chemical manufacturing/ processing sources Bleached chemical wood pulp and paper mills 19.5 356 67 wPOasTteWwa(tmerunicipal) 10 89 Ethylene dichloride/vinyl chloride 0.43b 1110 Reservoir sources Urban runoff to surface water 190 1123 Rwuartearl soil erosion to surface 2700 1154 TOTAL RELEASES TO WATERg 19.93 356 16 Releases (g TEQ/yr) to land 21110789 2212 Chemical manufacturing/ processing sources Banledapcahpeedrcmheilml iscluadl gweood pulp 1.4 Ethylene dichloride/vinyl chloride 0.73b 14.1 2234 tMreuantmiceipnatlswluadsgteewater 76.6 76.6 2256 Cseowmamgeerscluiadlglye marketed 2.6 2.6 2278 2,4-Dichlorophenoxy acetic acid 28.9 33.4 3209 TOTAL RELEASES TO LANDg 110.23 126.7 333333333125374689 OVERALL RELEASES (g/yr) TO THE OPEN AND CIRCULATING ENVIRONMENT 3255 (SUM OF COLUMNS A, B, C ) 13,998 (SUM OF COLUM NS A, B, C ) aThe most reliable estimates of environmental releases are those sources within Categories A, B, and C, which are defined as: A= wChitahraHcitgehrizCatoinonfidoefnthcee iSnouthreceECmaitsesgioonryFjuadcgtoerdatondbeHAigdheCquoantfeidfeonrcQe uinaAntcittaivtiitvye LEesvtieml.ation 12/23/03 4-28 DRAFT--DO NOT CITE OR QUOTE TTaEbQledf4--W2.HIOnv98einntotrhye of environmental releases United States (continued) (grams/year) of 11111111111527036894643789251 B= C= D= CwhiathraMcteedriizuamtionCoonfftihdeenScoeuricnethCeatEemgoirsysijoundgFeadcttoorbeanAddaetqleuaastteMfoerdQiuumanCtoitnaftiidveenEcsetiimn Aatcitoinvity PCwLrheieatvhlrieamLlc.toienwraizrCaytoiInonnfdidoicefantthcieeonSinoouefirttchheeerCPtaohtteeegnEotmiraylisjMusidoagngendFitautocdteboerofAaInd-dTe/qEourQatDhtFeeEAfomcritsiQvsiiuotaynnsLtfiertovametilv."eUEnsqtuimanatitfiioend" (i.e., Category D) Sources be clearly nonrepresenta in Reference tive. Year 1995 . Based on extrem ely lim ited data, judged to bcefgdTpITecTCLnomrhhOoeocniiainslhTstsudgristArodbeeeieoldeinLrftmndeseefrpsrrudwes-ereesfeicitllpsntofeithpeefictimcircrhtcnsoioseafadtneilotoUcluesvynt.cetenilhtfmnymiioetotteairihnbostdCeesunaiSrDafotnnoltondDaitprnstat/eoWghlCdsle.loaDooutf(mfoatFStardhaewneeenesCtmeuieScrdofiesoseematsncnnciimbttttooriuiuonotaarsntlslaete,.ivws4oona.anomf1isltma-tafedbodioinleirtoendo;dxiurnbeitsnhvatttaererheirihliameIssi-ll.c.Tsi)rsl.eEespiQeoonnretgs.sintcioemsnatrrteeoqlw.uiaVrsineugrsyeledfeaawdseodaffstuuhererlosfgooaurtrheciefgsohrwlitshatyeedTusiEneQthhDaFivs-eWinbHveeOenn9t8ory 12/23/03 4-29 DRAFT--DO NOT CITE OR QUOTE 21 Table 4-3. Sources that are currently unquantifiable (Category E)a 3 Category Unquantified sources 4 Combustion sources UAgnrciocnutlrtoulrlaeldbcuornminbgustion of PCBs 5 Metal smelting and refining PPrriimmaarryy naliuckmeilnum 6 Chemical manufacturing MPDT2CC,eahhi4onolll-lnootxDaoorracooii-zchlbbi-thlnoeiboplenaorthzsoerdeeeotpynrdnphaeyehescllsienhsqanolun(oollidrexdoayppskiohasga/cemspenpestoiincllsltssa)cid 7 Biological and photochemical processes Composting 8 Reservoir sources ASWPBeCiiaordPttiea-mrtreenattsed wood O CD 11 aThere exist no or insufficient data characterizing environmental releases from these sources . Therefore , it is currently not possible to arrive at an estimate of annual environmental releases. 12/23/03 4-30 DRAFT--DO NOT CITE OR QUOTE 321 lTeavbellse i4n-4e.nvSiuromnmmaernytaolfmNeodritah aAnmdefroiocdaan CDD/CDF and PCB TEQ-WHO98 4 Media CDD/CDFsb PCBsb 5 Urban soil, ppt Ra9n.n3g=e2=71200.-221 n 2=.399 6 Rural soil, ppt n Range ==2.3075.141-5.7 n0=.5692 7 Sediment, ppt Ran5g.3ne==11<5.18-20 0.5n3= 101.69 8 Urban air, pg/m3 Ra0n.g1en2==1000.6.0039-40.2 0n.0=05039 9 Rural air, pg/m3 Range =0n.=0061.00304-0.02 0.n0=050371 1110 Fshreelslhfiwsha,teprpfticsh and 1.n0=(2N2A2d) samn p=le1sc1po.l2muesp(N6osAciotde)mopfo1si0tes 1123 pMpatcrine fish and shellfish, 0.2n6=1(N58Ad) samn p=le1s0cp.o2lmu5sp(5NoscAiotdem)opfo1s3ites 14 Water, ppq 0.00056 n=0.20306079 (NAd) NAd 1111157689 M4(CsNa0Dmi+olDktpUe,l/:eFp.Ses/p)Pa.tcCrheBgcioocomnmaplporsiisteedfoorf n=8 c0o.m01p8oesites n = 80.c0o0m8p8oesites 2210 Dairy, pptf n = 8 0co.1m2eposites n = 80c.o0m58peosites 22222534 E2(CN4gDogeDtsge,/g:Fpsep)datachtaccoommpporsisiteedfoofr n=150c.o0m81peosites n = 180p.l1u0se6(NcoAmd)posites 12/23/03 4-31 DRAFT--DO NOT CITE OR QUOTE lTeavbellse i4n-4e.nvSiuromnmmaernytaolfmNeodritah aAnmdefroiocdan(cCoDntDin/uCeDdF) and PCB TEQ-WHO98 Media CDD/CDFsb PCBsb 1 Beefppt Ran0g.e1n8==06.301.11-10.95 n0.=08643 2 Pork, ppt Ran0g.2e8n==7080.1.258-1.8 n0.=01728 3 Poultry, ppt Ra0n.g0e68n==07.800.30-700.43 n0.=02768 4 111111203468957 Vegetable fats, ppt 0.056 n0=.3204g(NAd) n = 50c.o0m37peosites aWhole-weight basis; concentrations provided in parenthesis for food products are calculated at ND = 0. bcToVfhaedlueTteeEscQatirodefnft,ihseehxaccreoiptnhtcmfeonerttrisacotimiol neasanndreTCpEoDQrDtes/dCanhDdeFresstaainnredvaserpgdeecdtaieebvsli-eastpfiaoetcnsisff.iocrNiwnoghneidcsehttieoncnotsnradwteeeterwectessiegwthtetoeredonasevet-ehtroaaglzfeetsrh.oe. limit dNA = not available; congener-specific PCB data and data to calculate TEQ concentrations at ND = 0 are limited. efTSEtaQndcaarldcudleavtieadtiboynssectotiunlgd nnoont dbeeteccatlscutolazteedrod. ue to limitations associated with the data (i.e., composite analyses). gDairy concentration calculated from milk lipid concentrations and then assuming a fat fraction for dairy. 15 16 17 18 19 20 21 22 23 24 25 26 27 28 12/23/03 4-32 DRAFT--DO NOT CITE OR QUOTE 1 2 Table 4-5. Background serum levels in the United States 1995-1997 3 4 Value 5 Median 6 Mean 7 95thPercentile TEQd f p -WHO,8 (pg/g lipid) 18.7 22.1a 38.8 2,3,7,8-TCDD (pg/g lipid) 1.9 2.1 4.2 1111120389 aAfter adjusting to account for missing PCBs, the mean is 25.4 pg/g lipid. Source: CDC, 2000 12/23/03 4-33 DRAFT DO NOT CITE OR QUOTE 4321 Tcoamblpeo4u-n6d. sAdult contact rates and background intakes of dioxin-like Dioxins and furans Dioxin-like PCBS Total 22222222111111111111257625036034574689897 Exposure route Contact rate iSnogielstion 50 mg/d Soil dermal 12 g/d Ffsihrseehsllhafnwisdhataer 5.9 g/d Mashnaedrllifnieshfaish 9.6 g/d Inhalation 13.3 m3/d Milk 175 g/d Dairy 55 g/d Eggs 0.24 g/kg-d Beef 0.67 g/kg-d Pork 0.22 g/kg-d Poultry 0.5 g/kg-d Other meats 0.35 g/kg-d Vfaetgetable 17 g/d Water 1.4 L/d Total Concentration TEQD F-WHO98 9.3 pg/g 9.3 pg/g 1.0 pg/g 0.26 pg/g 0.12 pg/m3 0.018 pg/g 0.12 pg/g 0.081 pg/g 0.18 pg/g 0.28 pg/g 0.068 pg/g 0.18 ppt 0.056 pg/g 0.0005 pg/L Intake (pg TEQd fW H O 98/kg-d) 0.0066 0.0016 0.084 0.036 0.023 0.045 0.094 0.019 0.13 0.062 0.034 0.062 0.014 0.000011 0.61 Intake Concentration TEQP-W HO98 W(HpgOt98e/kqg-pd- ) 2.3 ppt 0.0016 2.3 ppt 1.2 pg/g 0.00039 0.1 0.25 pg/g 0.034 NA 0.0088 pg/g 0.058 pg/g 0.10 pg/g 0.084 pg/g 0.012 pg/g 0.026 pg/g 0.041 pg/g 0.037 pg/g NA NA 0.022 0.046 0.024 0.06 0.0026 0.013 0.014 0.009 NA 0.33 Intake W(pHgOt98e/qkgd-fdp -) 0.0082 0.002 0.18 0.07 0.023 0.067 0.14 0.043 0.19 0.065 0.047 0.076 0.023 0.000011 0.94 (43 pg/d) (23 pg/d) (66 pg/d) 322089 aThe TEQ^ fish concentrations rep orted here are species-specific ingestion rate weighted averages. 12/23/03 4-34 DRAFT--DO NOT CITE OR QUOTE 21 Ta afubnlect4i-o7n. oVfaargieability in average daily toxic equivalent (TEQ) intake as CO 5 Age range 6 1-5 years 7 6-11 years 8 12-19 years 9 Adult 1110 pgInTtaEkQeD, FmPa-WssHbOas9i8s/d 50 54 61 66 IpngtaTkEeQ, bDoFdPy-WwHeiOg9h8t/bkags-dis 3.3 1.8 1.1 0.9 12/23/03 4-35 DRAFT--DO NOT CITE OR QUOTE Emission Source (tested/total units) Best Estim ate of l-TEQ Em ission Factor (ng/kg or ng/L) Municipal Solid Waste Incineration (39/130) Backyard Barrel Burning (NA) Medical Waste Incineration (20/2,400) Secondary Copper Smelting (2/3) Cement Kilns Burning Haz Waste (10/34) Residential Wood Burning (7/25,000,000) Utility / Industrial Coal Combustion (11/?) On-Road Diesel Fuel Combustion (NA) Secondary Aluminum Smelting (6/76) Industrial Wood Burning (9/?) Iron Ore Sinter Plante (2/11) Cement Kilns Not Burning Haz Waste (15/17B) Sewage Sludge Incineration (13/257) Manufacture of EDC/VC (?/?) Utility / Industrial Oil Combustion (>2/?) Crematoria (16/1,555) Hazardous Waste I n c i n e r a t i o n ( 1 7 / 1 6 2 ) On-Road Unleaded Gas Fuel Combustion (?/?) On-Road Leaded Gas Fuel Combustion (?/?) Total A nnual "Activity" (thousand m etric tons/yr or million L/yr) A nnual l-TEQ Em ission (g l-TEQ/yr) T he figures include s o u rc e s with ann ual l-TEQ em ission e stim a te s g re a te r th a n 5 g l-TEQ/yr in one or both of Reference Y ear 1995 and Reference Y ear 1987. Derivations of emission factors an d an n u a l "activity1e stim a te s (e.g., kg of w a ste incinerated) a re p re se n te d in th e following c h a p te rs of th is report. T he d ifference in b a r sh ad in g ind icates th e d e g re e of con fid en ce in the estim ate. The set of num bers following the source categories indicates the num ber of facilities/sites for which em ission test data are available versus the num ber of facilities/sites in th e category. A question m ark (?) indicates that the precise num ber of facilities/sites could not be estim ated. L egend Low Confidence M edium C o n fid en ce H igh C o n fid en ce 1 Figure 4-1. Estimated CDD/CDF I-TEQ emissions to air from combustion sources 32 in the United States, 1995. 4 12/23/03 4-36 DRAFT--DO NOT CITE OR QUOTE Municipal Solid Waste Incineration Backyard Barrel Burning Medical Waste Incineration Secondary Copper Smelting Cement Kilns Burning Haz Waste Residential Wood Burning ^ Utility/Industrial Coal Combustion On-Road Diesel Fuel Combustion Secondary Aluminum Smelting Industrial Wood Burning Iron Ore Sinter Plants Cement Kilns Not Burning Haz Waste Sewage Sludge Incineration ^ Manufacture of ED C/V C Utility/lndustrial Oil Combustion Crematoria ^ Hazardous Waste Incineration On-Road Unleaded G as Fuel Combustion On-Road Leaded G as Fuel Combustion ^ 1 -------- 1 --------- , i m -------------. j = 1 _____________ |___________________________ |___________________________ | 10 100 1000 10000 1995 1987 1 32 FTiEgQur/eyr4)-2fo. rCreofmerpeanrciseoyneaorfse1st9i8m7aatensdo1f9a9n5n.ual I-TEQ emissions to air (grams I- 12/23/03 4-37 DRAFT--DO NOT CITE OR QUOTE TEQ, pg/g lipid 1 Figure 4-3. Blood levels (I-TEQ for CDD/CDF + WHO94) versus age of a subset of participants in the CDC (2000). 2 Source: ATSDR, 1999b 43251 wFoniigltyhu,irnneoa4tn-P4aC. dBPusrl)et.dpiocpteudladtiiostnrifbourtifoonusr ayneadrsa:ve1r9a6g5e, T19E8Q5,D1F9-9W5,HanOd982c0o3n0c.e(nCtrDaDtio/CnDs Fs Source: Adapted from Lorber, 2002 12/23/03 4-39 DRAFT--DO NOT CITE OR QUOTE 1 2 3 4 5 6 (A) 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 (B) 24 25 26 27 28 29 30 31 333234 Fcscoiegnnucarereniot4rs-a5td.iuoDrnisenmg(Aoa)nlasifnterdatitmbiooend. yofbtuhredemnosd(eBl)foorf ienvfaalnutastirnegsuilmtipnagcftsroomn vliapriidous nursing 12/23/03 4-40 DRAFT--DO NOT CITE OR QUOTE 1 5. DOSE-RESPONSE CHARACTERIZATION 2 3 Previous sections of this integrated summary focused on characterizing the hazards of and 4 exposure to dioxin-like compounds. In order to bring these issues together and provide an 5 adequate characterization of risk, the relationships of exposure to dose and, ultimately, to 6 response must be evaluated. Key questions to be asked include: (1) What can be said about the 7 shape of the dose-response function in the observable range and what does this imply about 8 dose-response in the range of environmental exposures? and (2) What is a reasonable limit 9 (critical dose or point of departure [POD]) at the lower end of the observable range and what risk 10 is associated with this exposure? In addition, one can address the issue of extrapolation beyond 11 the range of the data in light of the answers to the above questions. Although extrapolation of 12 risks beyond the range of observation in animals and/or humans is an inherently uncertain 13 enterprise, it is recognized as an essential component of the risk assessment process (NAS/NRC, 14 1983). The level of uncertainty is dependent on the nature (amount and scope) of the available 15 data and on the validity of the models that have been used to characterize dose-response. These 16 form the bases for scientific inference regarding individual or population risk beyond the range of 17 current observation (NAS/NRC, 1983, 1994). 18 Dose-response analysis can be implemented in a variety of ways in risk assessment, 19 depending on the extent and quality of the available data. At the basic level, dose-response 20 information comes from a comparison of doses or levels at which there are no observed adverse 21 effects with those at which the lowest adverse effect is observed. Such an analysis can be 22 enhanced through the application ofmathematical models to interpolate between empirically 23 measured data points (plus incorporating their statistical variability), with the option for 24 extrapolation below these data points subject to model shape assumptions when going beyond 25 the range of known data. One such form of modeling is the benchmark dose (BMD) analysis, 26 where a mathematical model is used to calculate the dose necessary to elicit a predetermined 27 response rate (e.g., an effective dose [ED] for a 1% response: ED01). Ultimately, the 28 development and use ofphysiologically-based pharmacokinetic PBPK models and biologically29 based dose response models goes beyond the mathematical replication of data points by linking 30 the model to relevant and measurable biological parameters in the species of interest, and 31 potentially between species (Kim et al., 2002). 32 These dose-response concepts are developed in Part II, Chapter 8, where the body of 33 literature concerning dose-response relationships for TCDD is presented. Among other things, 34 this chapter addresses the important concept of selecting an appropriate metric for cross-species 12/23/03 5-1 DRAFT--DO NOT CITE OR QUOTE 1 scaling of dose and presents the results of empirical modeling for many of the available data sets 2 on TCDD exposures in humans and in animals. Although not all human observations or animal 3 experiments on TCDD are amenable to this level of dose-response modeling, more than 200 data 4 sets were evaluated for shape, leading to an effective dose value expressed as a percent response 5 being presented for each endpoint being evaluated. 6 The analysis of dose-response relationships for TCDD, considered within the context of 7 toxic equivalency, mechanism of action, and background human exposures, helps elucidate the 8 common ground and the boundaries of the science and science policy components inherent in 9 this risk characterization for the broader family of dioxin-like compounds. For instance, the 10 dose-response relationships provide a basis to infer a POD for extrapolation for cancer and 11 noncancer risk for a complex mixture of dioxin-like congeners given the assumption of toxic 12 equivalency as discussed in Part II, Chapter 9, Section 9.6. Similarly, these relationships provide 13 insight into the shape of the dose-response at the POD, which can help inform choices for 14 extrapolation models for both TCDD and total TEQ. Dose-response modeling also provides a 15 perspective on the relationship between the level at which effects are seen in experimental 16 systems or epidemiologic studies and background exposures and body burdens for dioxin and 17 related compounds. 18 In evaluating the dose-response relationships for TCDD as a basis for assessing this 19 family of compounds, both empirical dose-response modeling approaches and mode of action 20 based approaches have been developed and applied (see Part II, Chapter 8, Section 8.3 and 8.4; 21 Portier et al., 1996; Kim et al., 2003). Empirical models have advantages and disadvantages 22 relative to more ambitious mechanism-based models. Empirical models provide a simple 23 mathematical model that adequately describes the pattern of response for a particular data set; 24 they can also provide the means for hypothesis testing and interpolation between data points. In 25 addition, they can provide qualitative insights into underlying mechanisms. However, the major 26 disadvantage of empirical models is their inability to quantitatively link data sets in a 27 mechanistically meaningful manner. On the other hand, mechanism-based modeling can be a 28 powerful tool for understanding and combining information on complex biological systems. Use 29 of a truly mechanism-based approach can, in theory, enable more reliable and scientifically sound 30 extrapolations to lower doses and between species. However, any scientific uncertainty about the 31 mechanisms that the models describe is inevitably reflected in uncertainty about the predictions 32 of the models. 33 PBPK models have been validated in the observable response range for numerous 34 compounds in both animals and humans. The development of PBPK models for disposition of 12/23/03 5-2 DRAFT--DO NOT CITE OR QUOTE 1 TCDD in animals has proceeded through multiple levels ofrefinement, with newer models 2 showing increasing levels of complexity by incorporating data for disposition ofTCDD and its 3 molecular actions with the AhR and other proteins, as well as numerous physiological parameters 4 (Part II, Chapter 1). These models have provided insights into key determinants of TCDD 5 disposition in treated animals. Development of such models continues and the current generation 6 of dioxin PBPK models are being submitted for publication (DeVito et al., personal 7 communication). Pharmacokinetic models have been extended to generate predictions for early 8 biochemical consequences of tissue dosimetry of TCDD, such as induction of CYP1A1, and are 9 being developed to address the impacts of enzyme induction (e.g., CYP1A2) on TCDD storage 10 and half-life. It is anticipated that these enhanced PBPK models will improve the understanding 11 of early phase human distributional and half-life kinetic data. However, extension of these 12 models to more complex responses is more uncertain at this time, particularly regarding selection 13 of the appropriate tissue metric to link to the effect(s) under consideration. Differences in 14 interpretation of the mechanism of action embodied in these pharmacodynamic models lead to 15 varying estimates of dose-dependent behavior for similar responses. The shape of the 16 dose-response curves governing extrapolation to low doses are determined by these hypotheses 17 and assumptions. 18 At this time, the knowledge of the mechanism of action of dioxin, receptor theory, and 19 the available dose-response data do not firmly establish a scientific basis for replacing a linear 20 procedure for estimating cancer potency. Consideration of this same information indicates that 21 the use of different procedures to estimate the risk of exposure for cancer and noncancer 22 endpoints may not be appropriate. Both the cancer and noncancer effects of dioxin appear to 23 result from qualitatively similar modes of action. Initial steps in the process of toxicity are the 24 same, and many early events appear to be shared. Thus, the inherent potential for low dose 25 significance of either type of effect (cancer or noncancer) should be considered equal and 26 evaluated accordingly. In the observable range around 1% excess response, the quantitative 27 differences are relatively small. Below this response, the different mechanisms can diverge 28 rapidly. The use of predicted biochemical responses as dose metrics for toxic responses is 29 considered a potentially useful application of these models. However, greater understanding of 30 the linkages between these biochemical effects and toxic responses is needed to reduce the 31 potentially large uncertainty associated with these predictions. 32 12/23/03 5-3 DRAFT--DO NOT CITE OR QUOTE 1 5.1. DOSE METRIC(S) 2 One of the most difficult issues in risk assessment is determining the dose metric to use 3 for animal-to-human extrapolations. An appropriate animal-to-human extrapolation of tissue 4 dose is required to provide significant insight into differences in sensitivity among species. As 5 noted in Section 1.3, the most appropriate dose metric should reflect both the magnitude and 6 frequency of exposure, and it should be clearly related to the toxic endpoint of concern by a 7 well-defined mechanism. However, this is often difficult, because human exposures with 8 observable responses may be very different from highly controlled exposures in animal 9 experiments. In addition, comparable exposures may be followed by very different 10 pharmacokinetics (absorption, distribution, metabolism and/or elimination) in animals and 11 humans. Finally, the sequelae of exposure in the form of a variety of responses related to age, 12 organ, and species sensitivity complicate the choice of a common dose metric. Despite these 13 complexities, relatively simple default approaches, including body surface or body weight scaling 14 of daily exposures, have often been recommended (U.S. EPA, 1992a, 1996; ATSDR, 1999). 15 As discussed in Section 1.3, dose can be expressed in a number of ways. For TCDD and 16 other dioxin-like compounds, attention has focused on the consideration of dose expressed as 17 daily intake (ng/kg/day), body burden (ng/kg), or AUC (DeVito et al., 1995; Aylward et al., 18 1996). The concept of physiological time (lifetime of an animal) complicates the extrapolation, 19 as the appropriate scaling factor is uncertain for toxic endpoints. Because body burden 20 incorporates differences between species in TCDD half-life (these differences are large between 21 rodent species and humans [see Part II, Chapter 8, Table 8.2]), this dose metric appears to be the 22 most practical for many effects of this class of compounds (DeVito et al., 1995). 23 Average lifetime body burden is best suited for steady-state conditions, with difficulties 24 arising when this dose metric is applied to the evaluation of acute exposures, such as those 25 occurring in the 1976 accidental exposure in Seveso, Italy (Bertazzi and di Domenico, 1994). In 26 cases such as this one, increased body burden associated with the acute exposure event is 27 expected to decline (half-life for TCDD is approximately 7 years) until it begins to approach a 28 steady-state level associated with the much smaller daily background intake. In general, daily 29 excursions in human exposure are relatively small and have minor impact on average body 30 burden. Instead, PBPK models suggest that human body burdens increase over time and begin to 31 approach steady-state after approximately 25 years with typical background doses. Occupational 32 exposures represent the middle ground where daily excursions during the working years can 33 significantly exceed daily background intakes for a number of years, resulting in elevated body 34 burdens. 12/23/03 5-4 DRAFT--DO NOT CITE OR QUOTE 1 The relationship between occupational exposures and body burden and between body 2 burden and AUC are demonstrated in Figure 5-1. This figure graphs two hypothetical body 3 burden scenarios during the 70-year lifespan of an individual. The first is a continuation to 70 4 years of age of the background body burden scenario discussed--with caveats and 5 assumptions-- in Part I, Volume 3, Chapter 5. In this scenario, an infant is breast-fed for 6 6 months by a mother who has a background dioxin body burden level and is subsequently exposed 7 to the average current level of dioxin in the food supply (1 pg/kg/day). This background scenario 8 leads to a 70 year lifetime area under the curve (AUC) of 184 ng/kg*Y, equivalent to a lifetime 9 average body burden (LABB) of 2.6 ng/kg (~184/70 years). 10 In the second scenario, the same individual incurs an additional occupational exposure 11 between 20 and 30 years of age of 100 pg/kg/day--100 times background--which then ceases. 12 The buildup of dioxin body burden is evident in the peak level and shark fin appearance. AUC in 13 this occupational scenario is 3911 ng/kg*Y, and LABB is 55.9 ng/kg. Note that in the 14 occupational scenario the AUC and LABB are only 21 times background. 15 Table 5-1 and Figure 5-2 summarize literature on average levels of dioxin TEQs in the 16 background human population and peak levels in commonly cited epidemiological cohorts. 17 Table 5-1 collates data on tissue lipid levels (ppt lipid adjusted) in populations, principally from 18 serum, and tabulates either current levels for the background population or back-calculated peak 19 levels for the exposed cohorts. Figure 5-2 graphs the estimated range and central tendency of the 20 total TEQdfp body burden (ng/kg whole body), combining the range of measured 2,3,7,8-TCDD 21 values with the estimate of the background non-2,3,7,8-TCDD TEQ level from the U.S. 22 population in the late 1980s/early 1990s. TEQ levels are calculated for PCDD, PCDF, and 23 PCBs, based on TEQDFP-WHO98values, and assume a constant 25% body fat ratio when 24 converting from serum lipid ppt to ng/kg body burden. Total TEQ values for the Hamburg 25 cohort women were calculated by the authors, but did not include a dioxin-like PCB contribution. 26 Seveso values reported by Needham et al. (1999) are based on stored serum samples from 27 subjects undergoing medical examinations contemporaneous with the exposure and were not 28 back-calculated. Additional information consistent with Figure 5-2 has recently been published 29 (Eskenazi et al., 2004) that demonstrate similar Seveso Zones A and B initial levels, with an 30 important further measurement of background 2,3,7,8-TCDD (20.2 ppt serum lipid) and other 31 congener TEQ contributions (80.2 ppt) in the unexposed background population (non-ABR 32 women) in this time period. 33 As discussed earlier, using background total body burden (TEQDFP-WHO98) as a point of 34 comparison, these often-termed "highly exposed" populations have peak body burdens that are 12/23/03 5-5 DRAFT--DO NOT CITE OR QUOTE 1 relatively close to general population backgrounds at the time. When compared with background 2 body burdens of the late 1980s, many ofthe median values and some ofthe mean values fall 3 within a range of one order of magnitude (factor of 10) and all fall within a range of two orders 4 of magnitude (factor of 100). General population backgrounds at the time are likely to have been 5 higher than present background body burdens. 6 One uncertainty in comparing peak body burdens is the use of a first-order elimination 7 rate with an overall half-life of 7.1 years. Recent evidence suggests that the elimination of 8 TCDD may be dependent on the level of exposure, in addition to an early distributional or 9 sequestration phase. Populations with high exposures may have half-lives significantly less than 10 7.1 years. Relatively rapid early elimination was noted in two highly exposed Austrian women 11 (initial half-lives of ~1.5 and 2.9 years; Geusau et al., 2002). Supportive data are also available 12 through an analysis of the Seveso populations (Michalek et al., 2002). In this analysis, a period 13 of fast elimination within the first 0.27 years after the exposure in Seveso was observed, followed 14 by a period of slower elimination between 3 and 16.35 years from exposure. The mean TCDD 15 half-life in the first 0.27 years after exposure in the Seveso cohort was 0.34 years in males (n=6) 16 and 0.43 years in females (n=10). From 3 years onward in the Seveso cohort, the half-life in 17 males was 6.9 years (n=9) and 9.6 years in females (n=13). For Ranch Handers, the half-life was 18 7.5 years (n=97) between 9 and 33 years after exposure. This analysis indicates that dioxin body 19 burdens and elimination kinetics may be more complex at higher doses than represented by a 20 single first-order half-life, including issues of tissue distribution and dose-dependent elimination. 21 This is consistent with the limited data available in rodents that also indicates a dose-dependent 22 elimination. 23 There are a number of physiologically-based pharmacokinetic models ofTCDD in both 24 experimental animals and humans. Several of the rodent models assume that the elimination rate 25 of TCDD is a constant (Wang et al., 1997; 2000; Emond et al., 2004). One model by Anderson 26 et al. (1993) has a dose dependent doubling of the elimination rate which is dependent upon Ah 27 receptor occupancy. Kohn et al. (1993; 1996) has the elimination rate increasing in proportion to 28 body weight and includes an increased elimination of TCDD from the liver at high doses due to 29 hepatocyte cell death. The Carrier et al. (1995a, b) model describes a dose-dependent 30 elimination of TCDD and other dioxins due to a dose-dependent hepatic sequestration ofthese 31 chemicals. While these models use different approaches, they all provide reasonable fits to the 32 available experimental data. 33 Attempts to develop pharmacokinetic models for TCDD in humans have also resulted in 34 a variety ofmathematical descriptions of the elimination rate. Maruyama et al. (2002, 2003) 12/23/03 5-6 DRAFT--DO NOT CITE OR QUOTE 1 have assumed that the elimination rate is constant. Van der Molen et al. (1998; 2000) multiply a 2 constant elimination rate by the ratio of liver fat/body fat. This results in an overall change in the 3 elimination of TCDD based on body composition and body weight. Gentry et al. (2003) and 4 Clewell et al. (2004) describe the elimination of TCDD in proportion to hepatic CYP1A2 5 expression. Aylward et al. (2004) modified the Carrier et al. (1995a, b) model to include an 6 elimination of dioxins directly into the large intestine based on lipid partitioning. This model 7 provided reasonable fits to data from Seveso patients as well as three Austrian patients. Finally, 8 Michalek et al. (2002) used a classical pharmacokinetic approach to describe the Seveso data. 9 This work suggests that there is an early distribution phase that results in a rapid loss of TCDD 10 from the blood (half-life of 0.37 years) followed by a prolonged terminal elimination phase (half 11 life approximately 6.9 years). 12 Hence, there are a number of pharmacokinetic models available that describe the 13 absorption, distribution and elimination of TCDD in animals and humans. While these models 14 provide reasonable fits to the available data, they employ a wide range of descriptions of the 15 elimination of TCDD. Some assume first order elimination, while others assume dose-dependent 16 pharmacokinetics. Others suggest that body composition significantly influences the elimination 17 of dioxins. Presently, it is difficult to determine which of these model structures provides the 18 most accurate description of the pharmacokinetics ofTCDD and other dioxins. 19 Advances in understanding the dose-dependency of the pharmacokinetics of TCDD and 20 related chemicals will improve our ability to describe the relationship between exposure, dose 21 and response. The development of more accurate models may affect both exposure group 22 assignment in epidemiology studies and the calculation of dose-response curves, although the 23 magnitude and direction of these postulated impacts remains to be quantified. Estimates of back24 calculated doses are important because the ability to detect effects in epidemiologic studies is 25 dependent on a sufficient difference between control and exposed populations. Using published 26 first-order back-calculation procedures, the relatively small difference (< 10-100-fold) in body 27 burden between exposed and controls in the dioxin epidemiology studies makes exposure 28 characterization in the studies a particularly serious issue. This point also strengthens the 29 importance of measured blood or tissue levels in the epidemiologic analyses, despite the 30 uncertainties associated with calculations extending the distribution of measured values to the 31 entire cohort and assumptions involved in back-calculations. 32 As a bounding exercise on the impact of half-lives on back-extrapolated exposure 33 estimates, EPA has compared the impacts of varying half-life values on back-calculated peak and 34 AUC results. This scenario is constructed by calculating the peak body burden 20 years prior to a 12/23/03 5-7 DRAFT--DO NOT CITE OR QUOTE 1 terminal level for various half-lives versus a 7.1 year fixed half-life, assuming first order kinetics 2 (Ct = C0e-rt). A constant dosing regimen is then constructed to simulate an occupational exposure 3 that would achieve these same peak body burdens following 10 years exposure, maintaining the 4 same half-life as in the 20 year follow-up. For each half-life value, a different dose level is 5 necessary and was mathematically derived to reach the required peak level after ten years 6 occupational exposure. 7 In this occupational scenario, peak and AUC ratios (AUCvariablehalf.life/AUC71years) varied in 8 a non-linear manner depending on the input half-life. Half-life values of 4 years and longer had 9 low, single digit numerical impacts on the peak and AUC ratios compared to the 7.1 year half-life 10 results (e.g., at a 4 year half-life, the ratio for the peak value = 4.6, the AUC ratio = 3.8; at a 5 11 year half-life, the ratio for peak = 2.3, AUC = 2). At half-lives below 4 years, peak and AUC 12 ratios rose dramatically to approximately 1 and 2 orders of magnitude for 3 and 2 year half-lives, 13 respectively. The terminal body burden did not influence the ratio because the mathematical 14 function remained constant. More complex PBPK models, where half-life varies with body 15 burden, are under development and will be more influenced by the terminal body burden for each 16 individual. This bounding exercise suggests that impacts on back-calculated peak and AUC 17 values may become significant if the models predict prolonged periods with half-lives of less 18 than 4 years. 19 5.1.1. Calculations of Effective Dose 20 Comparisons across multiple endpoints, multiple species, and multiple experimental 21 protocols are too complicated to be made on the basis of the full dose-response curve. As 22 discussed above, comparisons of this sort can be made by either choosing a given exposure and 23 comparing the responses or choosing a particular response level and comparing the associated 24 exposures. In the analyses contained in Chapter 8, Section 8.3, and elsewhere in the 25 reassessment, emphasis is placed on comparing responses using estimated exposures associated 26 with a given level of excess response or risk. To avoid large extrapolations, this common level 27 of excess risk was chosen such that for most studies the estimated exposure is in or near the 28 range of the exposures seen in the studies being compared, with extra weight given to the human 29 data. A common metric for comparison is the effective dose, which is the dose resulting in an 30 excess response over background in the studied population. This excess response rate can be 31 calculated as a fraction of the minimum to maximum response (e.g., 1% increase in risk). 32 Alternatively, for continuous data the dose can be calculated as the amount necessary to move an 33 additional percentage of distribution of the response past a predetermined "effect" level. EPA 12/23/03 5-8 DRAFT--DO NOT CITE OR QUOTE 1 has suggested this approach in calculating BMDs (Allen et al., 1994) and in its proposed 2 approaches to quantifying cancer risk (U.S. EPA, 1996, 1999, 2003). 3 Although effective dose evaluation at the 10% response level (ED10or lower bound on 4 ED10[LED10]) is somewhat the norm, given the power of most chronic toxicology studies to 5 detect an effect, this level is actually higher than those typically observed in the exposed groups 6 in studies of TCDD impacts on humans. To illustrate, lung cancer mortality has a background 7 lifetime risk of approximately 4% (smokers and nonsmokers combined), so that even a relative 8 risk of 2.0 (two times the background lifetime risk) represents approximately a 4%, or 4 in 100, 9 increased lifetime risk (see Chapter 8 for a comprehensive elaboration of formulae). On the basis 10 of this observation, and recognizing that many of the TCDD-induced endpoints studied in the 11 laboratory include 1% effect levels in the experimental range, Chapter 8 presents effective doses 12 of 1%, or ED01, and 10%, or ED10, values. 13 The use of effective dose values below 10% is consistent with the Agency's guidance on 14 the use of mode of action in assessing risk, as described in the proposed carcinogen risk 15 assessment guidelines (U.S. EPA, 1996, 1999, 2003) and in the evaluation framework discussed 16 in Section 3.3, in that the observed range for many "key events" for TCDD extends down to or 17 near the 1% response level. Determining the dose at which key events for dioxin toxicity begin 18 to be seen in a heterogeneous human population provides important information for decisions 19 regarding risk and safety. 20 21 5.2. EMPIRICAL MODELING OF INDIVIDUAL DATA SETS 22 As described in Chapter 8, Section 8.3, empirical models have advantages and 23 disadvantages relative to more ambitious mechanism-based models. Empirical models provide a 24 simple mathematical model that adequately describes the pattern of response for a particular data 25 set and that can also provide the means for hypothesis testing and interpolation between data 26 points. In addition, they can provide qualitative insights into underlying mechanisms. However, 27 the major disadvantage is their inability to quantitatively link data sets in a mechanistically 28 meaningful manner. 29 Data available for a number of biochemical and toxicological effects of TCDD and for its 30 mechanism of action indicate that there is good qualitative concordance between responses in 31 laboratory animals and humans (see Table 2-1). In addition, as described below, human data on 32 exposure and cancer response appear to be qualitatively consistent with animal-based risk 33 estimates derived from carcinogenicity bioassays. These and other data presented throughout this 34 reassessment would suggest that animal models are generally an appropriate basis for estimating 12/23/03 5-9 DRAFT--DO NOT CITE OR QUOTE 1 human responses to dioxin-like compounds. Nevertheless, there are clearly differences in 2 exposures and responses between animals and humans, and recognition of these is essential when 3 using animal data to estimate human risk. The level of confidence in any prediction of human 4 risk depends on the degree to which the prediction is based on an accurate description of these 5 interspecies extrapolation factors. See Chapter 8, Section 8.3, for a further discussion of this 6 point. 7 Almost all dioxin research data are consistent with the hypothesis that the binding of 8 TCDD to the AhR is the first step in a series of biochemical, cellular, and tissue changes that 9 ultimately lead to toxic responses observed in both experimental animals and humans (see Part II, 10 Chapter 2, Section 2.3). Therefore, an analysis of dose-response data and models should use, 11 whenever possible, information on the quantitative relationships among ligand (i.e., TCDD) 12 concentration, receptor occupancy, and biological response. However, it is clear that multiple 13 dose-response relationships are possible when considering ligand receptor-mediated events. For 14 example, dose-response relationships for relatively simple responses, such as enzyme induction, 15 may not accurately predict dose-response relationships for complex responses such as 16 developmental effects and cancer. 17 Cell- or tissue-specific factors may determine the quantitative relationship between 18 receptor occupancy and the ultimate response. Indeed, for TCDD there are much experimental 19 data from studies using animal and human tissues to indicate that this is the case. This serves as 20 a note of caution, as empirical data on TCDD are interpreted in the broader context of complex 21 exposures to mixtures of dioxin-like compounds as well as to nondioxin-like toxicants. 22 As for other chemical mechanisms where high biological potency is directed through the 23 specific and high-affinity interaction between chemical and critical cellular target, the 24 supposition of a response threshold for receptor-mediated effects is a subject for scientific 25 debate. The basis of this controversy has been summarized by Sewall and Lucier (1995). 26 Based on classic receptor theory, the occupancy assumption states that the magnitude of 27 biological response is proportional to the occupancy of receptors by drug molecules. The 28 "typical" dose-response curve for such a receptor-mediated response is sigmoidal when plotted 29 on a semilog graph or hyperbolic if plotted on an arithmetic plot. Implicit in this relationship is 30 low-dose linearity (0-10% fractional response) through the origin. Although the law ofmass 31 action predicts that a single molecule of ligand can interact with a receptor, thereby inducing a 32 response, it is also widely held that there must be some dose that is so low that receptor 33 occupancy is trivial and, thus, no perceptible response is obtainable. 12/23/03 5-10 DRAFT--DO NOT CITE OR QUOTE 1 Therefore, the same receptor occupancy assumption of the classic receptor theory is 2 interpreted by different parties as support for and against the existence of a threshold. It has been 3 stated that the occupancy assumption cannot be accepted or rejected on experimental or 4 theoretical grounds (Goldstein et al., 1974). To determine the relevance of receptor interaction 5 for TCDD-mediated responses, one must consider (1) alternatives as well as limitations of the 6 occupancy theory, (2) molecular factors contributing to measured endpoints, (3) limitations of 7 experimental methods, (4) contribution of measured effect to a relevant biological/toxic 8 endpoint, and (5) background exposure. 9 Throughout this reassessment, each of these considerations has been explored within the 10 current context of the understanding of the mechanism of action of TCDD, of the methods for 11 analysis of dose-response for cancer and noncancer endpoints, and of the available data sets of 12 TCDD dose and effect for several rodent species, as well as humans who were occupationally 13 exposed to TCDD at levels exceeding the exposure of the general population. 14 15 5.2.1. Cancer 16 As discussed in Section 2.2.1.4, TCDD is characterized as carcinogenic to humans when 17 using a weight-of-evidence approach, and is a carcinogen in all species and strains of laboratory 18 animals tested. The epidemiological database for TCDD, described in detail in Part II, Chapter 19 7a, suggests that exposure may be associated with increases in all cancers combined and 20 respiratory cancer and with the possibility ofelevated risks at other sites. Although there are 21 sufficient data in animal cancer studies to model dose-response for a number of tumor sites, as 22 with many chemicals it is generally difficult to find human data with sufficient information to 23 model dose-response relationships. For TCDD, three studies of human occupational exposure 24 have sufficient information to perform a quantitative dose-response analysis: Becher et al. (1998) 25 (the Hamburg cohort); Ott and Zober (1996) (the BASF cohort); and Steenland et al. (2001) (the 26 NIOSH cohort). 27 The all-cancer mortality ED01/LED01results from these three studies are detailed in Part 28 II, Chapter 8, Section 8.3, and tabulated and graphed in Table 5-2, along with the bioassay results 29 for liver cancer in female Sprague-Dawley rats (Kociba et al., 1978). Table 5-2 includes only the 30 results and mathematical formulae that were published by the primary authors in the peer31 reviewed literature. These calculations and formulae were chosen because they are based on the 32 full primary data set and not on secondary analyses using summary results. In order to graph 33 results for the occupational cohort studies, the central points for data ranges were requested from, 12/23/03 5-11 DRAFT--DO NOT CITE OR QUOTE 1 and kindly provided by, the authors (Drs. Steenland, Zober and Becher) and are included in the table. 2 Slightly different approaches are used for modeling cancer in humans than are used for 3 modeling in animal studies. The modeling approach used in the analysis of the human 4 epidemiology data for all cancers combined and lung cancer involves applying the estimated 5 human body burden-to-cancer response and estimating parameters in a mathematical risk model 6 for each data set. For the three occupational cohort studies, exposure subgroups were defined by 7 the authors using measured and then back-extrapolated TCDD levels in a subset of workers to 8 inform exposure calculations for the remainder of the cohort. None of the studies sampled 9 TCDD blood serum levels for more than a fraction of its cohort, and these samples were 10 generally taken decades after the last known exposure. In each study, serum fat or body fat levels 11 of TCDD were back-calculated using a first-order model. The assumed half-life of TCDD used 12 in the model varied from study to study. 13 Steenland et al. and Becher et al. used the measured and back-extrapolated TCDD 14 concentrations to refine and quantitate job exposure matrices, which were then used to estimate 15 dioxin cumulative dose for each member of their entire cohort. Ott and Zober (1996a) used 16 regression procedures with data on time spent at various occupational tasks to estimate TCDD 17 levels for all members of the cohort. The cohorts were then divided into exposure groups on the 18 basis of the estimated TCDD levels. As noted, central measures of the ranges from the primary 19 data were provided to the Agency by the authors, removing the need to estimate this parameter 20 from the upper and lower range points in the literature. 21 Risk outcomes in these cohorts were expressed as standardized mortality ratios (SMRs) 22 or rate ratios. SMRs are calculated by comparing the cancer rates in the subcohorts to the age23 and gender-matched general community in that time period. SMR results are usually expressed 24 as a ratio, with SMR = 100 set as the community, or expected, cancer death rate. Rate ratios are 25 calculated from within cohort data using the lowest exposed group as the control value for both 26 dose and risk. Although the lowest exposed group is defined to have a risk equal to unity (rate 27 ratio = 1), this low group may not, in fact, have an SMR equal to the general community (it could 28 be either lower or higher). 29 The three occupational cohort studies provide best fit dose-response models within the 30 range of their data. These models and the resulting formulae allow for the calculation of 31 ED /LED values, from which a linear extrapolation can be performed, consistent with the 32 EPA's draft cancer guidelines. There are several assumptions and uncertainties involved in 33 modeling these data, including extrapolation of dosage (both in back-calculation and in 12/23/03 5-12 DRAFT--DO NOT CITE OR QUOTE 1 elimination kinetics), the type of extrapolation model employed, and whether the origin point 2 should be fixed (i.e., SMR = 100) or allowed to float. 3 Based on the model formulae using the full data set as provided in the primary literature 4 (Steenland et al., 2001; Ott and Zober, 1996; Becher et al., 1998; detailed in Chapter 8), the 5 calculated ED0i central estimates for all cancers combined range from 1.4 to 62 ng TCDD/kg 6 LABB (Table 5-3). The lower bounds on these doses (based on a modeled 95% CI) range from 7 0.71 ng TCDD/kg to 30.5 ng TCDD/kg (not available for models published by Becher et al., 8 1998, due to the absence of statistical parameter measures). A parallel measure of unit excess 9 risk per one part per trillion TCDD body burden above background (assumed 5 ppt) is also 10 tabulated. These values are strongly dependent on the study chosen and the model used, and it 11 must be recognized that the risks posed to some members of the population from TCDD may be 12 zero, depending on the model chosen to extrapolate results below the range of observation. Male 13 and female values do not match because of differences in the input variable of background 14 lifetime all-cancer mortality risk. 15 Analysis of model results indicates that the power model applied to the Steenland et al. 16 (2001) data leads to unreasonably high risks at low exposure levels, based on calculations of the 17 attributable risk that this model would predict from background dioxin levels in the general 18 population. This result is due to the very steep slope of this power curve at low environmental 19 levels. The steep dose-response curve also makes the power model very sensitive to the 20 background dose that is incorporated into the calculations and the location of the calculation 21 point on the dose-response curve. Exclusion of the Steenland et al. power model reduces the 22 ED0i range to 6-62 ng TCDD/kg LABB and the LED0i range to 11.5-31 ng TCDD/kg LABB 23 (lower confidence values were unavailable for the Becher et al. 1998 data). For the purposes of 24 this assessment, the piecewise linear formula published by Steenland et al. (2001) is the preferred 25 model from this data set. 26 These epidemiologically derived ED values are summarized in Table 5-4 (additional 27 details in Part II, Chapter 8), along with the resulting cancer slope factors. The results of the 28 Kociba et al. (1978) cancer bioassay are also included in Table 5-4 for comparison purposes, 29 using the Goodman and Sauer (1992) revision to the liver tumor pathology results. Dose30 response modeling for this bioassay used the EPA Benchmark Dose software and multistage 31 model to calculate the ED /LED . The similarity between the cancer bioassay ED results in 32 rodents (Kociba et al. 1978) and the human epidemiology results is noteworthy when the 33 exposure metric is based on lifetime average body burden (LABB). LABB is calculated as the 34 AUC divided by lifetime years, and it equilibrates tissue doses across species. 12/23/03 5-13 DRAFT--DO NOT CITE OR QUOTE 1 The epidemiological data and dose-response models have stimulated considerable 2 contemporary interest and statistical analysis, particularly the option of performing a pooled or 3 meta-analysis on the entire occupational cohort data set. In reviewing this literature, care should 4 be taken to note which published analyses form the basis for the statistical tests, the recent 5 provision of data-derived central dose estimates for the ranges given in the literature (courtesy of 6 the primary authors), and the availability ofmore detailed primary dose-response literature 7 (Steenland et al., 2001; Becher et al., 1998), which supercede studies used previously (Aylward 8 et al., 1996; Flesch-Janys et al., 1998). For instance, the dose-response pattern for the NIOSH 9 cohort summary data, as published by Aylward et al. (1996), demonstrates a different high dose 10 point from the more recent and detailed analysis of the full dataset, as published by Steenland et 11 al. (2001). 12 Starr (2001, 2003) reviewed meta-analysis data and results that were included in the 13 external review draft of the EPA dioxin reassessment, and the analysis performed by Crump et al. 14 (2003; see below). The draft EPA meta-analysis was based on summary results published by 15 Aylward et al. (1996; NIOSH), Ott and Zober (1996; BASF), and Flesch-Janys et al. (1998). 16 Exposure range midpoints were either obtained from the original publication (Aylward et al., 17 1996) or were based on a log-normal fit to the data ranges to estimate the midpoint (for Ott and 18 Zober, 1996; Flesch-Janys et al., 1998). On the basis of these earlier data sets and the application 19 of a linear model, Starr concluded that the assumption of a fixed origin at an SMR = 100 should 20 be rejected on statistical grounds. Although a significantly increased cancer risk was evident in 21 these cohorts, the overall results using an unconstrained linear model (not fixed to the SMR = 22 100 point) were concluded to be consistent with the null hypothesis of no dose-response 23 relationship between TCDD and the cancer rate. 24 In a subsequent dioxin meta-analysis performed as part of the Joint European 25 Commission on Food Additives, Crump et al. (2003) performed similar and expanded statistical 26 analyses on a more recent data set using data-derived central estimates of exposure levels for Ott 27 and Zober (1996; Hamburg cohort) and from Steenland et al. (2001; NIOSH cohort). Fitting a 28 linear model to the data again indicated that the baseline SMR = 100 assumption could be 29 rejected, based on statistical tests. 30 Goodness of fit trend tests for this linear model were statistically significant both with the 31 background SMR set equal to 100 and with the background SMR estimated (p=0.01). A further 32 series of trend tests were performed by successively removing the highest cumulative exposure to 33 determine the lowest exposure for which there remained statistically significant evidence for an 34 effect. This progressive analysis of the data was considered by Crump et al. to provide a more 12/23/03 5-14 DRAFT--DO NOT CITE OR QUOTE 1 robust test for trends than a linear goodness of fit test. The analysis demonstrated an increase in 2 total cancer at cumulative TEQ serum levels that would result from a lifetime average intake of 7 3 pg TEQ/kg body weight/day (assuming 50% uptake, t1/27.6 years, 25% body fat), with no trend 4 for increase at 6 pg/kg/day. 5 The pooled analysis of the Ott and Zober (1996), Flesch-Janys et al. (1998), and 6 Steenland et al. (2001) data yielded ED01estimates of 51 ng/kg body burden (baseline SMR fixed 7 at 100) and 91 ng/kg body burden (baseline SMR estimated), corresponding to ED01daily intake 8 estimates of 25 and 45 (95% CI = 21-324) pg/kg/day, respectively, above current background 9 TCDD-TEQ for all cancers combined (calculated using the half-life and absorption assumptions 10 in Crump et al.). These results are consistent with the range of ED0is in Part II, Chapter 8, and 11 Tables 5-3 and 5-4. On the basis of their results and comparison to other published analyses, 12 Crump et al. (2003) concluded that they could not see a clear choice between their ED01estimate 13 of 45 pg/kg/day and the Steenland et al. (2001) estimate of 7.7 pg/kg/day, citing advantages to 14 each study. 15 The choice of model is central to the above statistical analyses of the individual studies 16 and the meta-analysis. The epidemiological data are not sufficient to mandate the selection of 17 any particular model shape. The published literature includes power, linear, piecewise linear, 18 and multiplicative models (see Table 5-2). The EPA's draft carcinogen risk assessment 19 guidelines (U.S. EPA, 1999) propose applying a standard curve-fitting procedure within the 20 range of the data (e.g., Benchmark Dose software), recognizing that more elaborate models will 21 be appropriate for more complex information and that, ultimately, biologically based 22 pharmacokinetic models would be preferred. 23 The curve-fitting procedure is used to determine a POD, generally at the 10% response 24 level, but where more sensitive data are available, a lower point for linear extrapolation can be 25 used to improve the assessment (e.g., 1% response for dioxin, ED0i). Extrapolation from the 26 POD to lower doses is conducted using a straight line drawn from the POD to the origin--zero 27 incremental dose, zero incremental response--to give a probability of extra risk. The linear 28 default is selected on the basis of the agent's mode of action when the linear model cannot be 29 rejected and there is insufficient evidence to support an assumption of nonlinearity. Additional 30 important uncertainties in the human epidemiological data are discussed in Part II, Chapter 8, 31 Section 8.3, and include the representativeness and precision of the dose estimates that were 32 used, the choice of half-life and whether it is dose dependent, and potential interactions between 33 TCDD and smoking or other toxicants. 12/23/03 5-15 DRAFT--DO NOT CITE OR QUOTE 1 For the animal data, both empirical and mechanistic models have been applied to examine 2 cancer dose-response. Portier et al. (1984) used a simple multistage model of carcinogenesis 3 with up to two mutation stages affected by exposure to model the five tumor types observed to be 4 increased in the 2-year feed study by Kociba et al. (1978) (Sprague-Dawley rats) and the eight 5 tumor types observed to be increased in the 2-year gavage cancer study conducted by NTP 6 (1982a) (Osborne-Mendel rats and B6C3F mice). The findings from this analysis, which 7 examined cancer dose-response within the range of observation, are presented in Part II, Chapter 8 8, Table 8.3., which is reproduced with slight modifications as Table 5-5. All but one of the 9 estimated ED s are above the lowest dose used in the experiment (approximately 1ng 10 TCDD/kg/day in both studies) and are thus interpolations rather than extrapolations. The 11 exception, liver cancer in female rats from the Kociba study, is very near the lowest dose used in 12 this study and is only a small extrapolation (from 1ng TCDD/kg/day to 0.77 ng TCDD/kg/day). 13 Steady-state body burden calculations were also used to derive doses for comparison across 14 species. Absorption was assumed to be 50% for the Kociba et al. (feed experiment) and 100% 15 for the NTP study (gavage experiment). 16 The shapes of the dose-response curves as determined by Portier et al. (1984) are also 17 presented in Table 5-5. The predominant shape of the dose-response curve in the experimental 18 region for these animal cancer results is linear. This does not imply that a nonlinear model such 19 as the quadratic or cubic--or for that matter a "J-shaped" model--would not fit these data. In 20 fact, it is unlikely that in any one case a linear model or a quadratic model could be rejected 21 statistically. These studies had only three experimental dose groups; hence, these shape 22 calculations are not based on sufficient doses to guarantee a consistent estimate, and they should 23 be viewed with caution. 24 The ED01steady-state body burdens range from a low value of 14 ng/kg, based on the 25 linear model associated with liver tumors in female rats, to as high as 1190 ng/kg, based on a 26 cubic model associated with thyroid follicular cell adenomas in female rats. Lower bounds on 27 the steady-state body burdens in the animals range from 10 ng TCDD/kg to 224 ng/kg. The 28 corresponding estimates of daily intake level at the ED obtained from an empirical linear model 29 range from 0.77 to 43 ng TCDD/kg body weight/day, depending on the tumor site, species, and 30 sex of the animals investigated. Lower confidence bounds on the estimates of daily intake level 31 at the ED0i in the animals range from 0.57 to 14 ng TCDD/kg body weight/day. 32 In addition, using a mechanistic approach to modeling, Portier and Kohn (1996) 33 combined the biochemical response model by Kohn et al. (1993) with a single initiated34 phenotype two-stage model of carcinogenesis to estimate liver tumor incidence in female 12/23/03 5-16 DRAFT--DO NOT CITE OR QUOTE 1 Sprague-Dawley rats from the 2-year cancer bioassay by Kociba et al. (1978). By way of 2 comparison, the ED0i estimate obtained from this linear mechanistic model was 0.15 ng 3 TCDD/kg body weight/day, based on intake, which is equivalent to 2.7 ng TCDD/kg steady-state 4 body burden. No lower bound on this modeled estimate of steady-state body burden was 5 provided. 6 As discussed in Part II, Chapter 8, Section 8.2, the use of different dose metrics can lead 7 to widely diverse conclusions. For example, the ED01intake for the animal tumor sites presented 8 above ranges from less than 1to tens of ng/kg/day, and the lowest dose with an increased 9 tumorigenic response (thyroid tumors) in a rat is 1.4 ng TCDD/kg/day (NTP, 1982a). The daily 10 intake of dioxins in humans is estimated at approximately 1pg TEQ/kg/day. This implies that 11 humans are exposed to doses 1400 times lower than the lowest tumorigenic daily dose in rat 12 thyroid. However, 1.4 ng TCDD/kg/d in the rat leads to a steady-state body burden of 13 approximately 25 ng TCDD/kg, assuming a half-life of TCDD of 25 days and absorption from 14 feed of 50%2. If the body burden of dioxins in humans is approximately 20 ng TEQ/kg lipid, or 5 15 ng TEQ/kg body weight (assuming about 25% of body weight is lipid), "average" humans are 16 exposed to about five times less TCDD than the minimal carcinogenic dose for the rat. The 17 difference between these two estimates is entirely due to the approximately 100-fold difference in 18 the half-life of TCDD in humans and rats. At least for this comparison, if cancer is a function of 19 average levels in the body, the most appropriate metric for comparison is the average or steady20 state body burden, because this accounts for the large differences in animal and human half-lives. 21 Comparisons of human and animal ED0is from Part II, Chapter 8, Section 8.3, for cancer 22 response on a body burden basis show similar potential for the carcinogenic effects of TCDD. In 23 humans, cancer ED0is ranged from approximately 6 ng/kg to 62 ng/kg (excluding the Steenland 24 et al., 2001, power model). This is similar to the empirical modeling estimates from the animal 25 studies, which ranged from 14 ng/kg to 1190 ng/kg (most estimates were in the range of 14 to 26 500 ng/kg). The lower bounds on the human body burdens at the ED01s (based on a modeled 27 95% CI) ranged from 11.5 ng TCDD/kg to 31 ng TCDD/kg (again, the lower values that would 28 have resulted from the Becher et al., 1998, analysis could not be included because error bounds 29 on the models were unavailable). Lower bounds on the steady-state body burdens in the animals 30 ranged from 10 ng TCDD/kg to 224 ng/kg. The estimate for the single mechanism-based model 31 presented earlier (2.7 ng/kg) is below the lower end of the human EDmestimates. 2Steady-state body burden (ng/kg) = (daily dose (ng/kg/day) * (half-life)/Ln(2)) ( f ), where f is the fraction absorbed from the exposure route (unitless) and half-life is the half-life in days. 12/23/03 5-17 DRAFT--DO NOT CITE OR QUOTE 1 Using human and animal cancer ED01s, their lower bound estimates, and the value of 2.7 2 ng TCDD/kg from the single mechanism-based model, slope factors and comparable risk 3 estimates for a human background body burden of approximately 5 ng TEQ/kg (20 ng TEQ/kg 4 lipid) can be calculated using the following equations: 5 Slope factor (per pg TEQ/kgBW/day) = risk at ED01/ intake (pg TEQ/kgBW/day) 6 associated with human equivalent steady-state body burden at ED where: 7 8 Risk at ED0i = 0.01; and 9 10 Intake (pg TEQ/kg BW/day) = [body burden at ED01(ng TEQ/kg)* Ln(2)] * 1000 (pg/ng) 11 half-life (days) x f (5-1) 12 13 half-life = 2593 days in humans and 25 days in rats (see Table 8.1 in Part II, Chapter 8) 14 f = fraction of dose absorbed; assumed to be 0.8 (80%) 15 and 16 Upper bound on excess risk at human background body burden = (human (5-2) 17 background body burden (ng/kg))(risk at ED01)/lower bound on human 18 equivalent steady-state body burden (ng/kg) at ED01, where: 19 Risk at ED = 0.01 20 21 Use of these approaches reflects methodologies being developed within the context of the 22 revised draft carcinogen risk assessment guidelines (U.S. EPA, 1999, 2003). Under these draft 23 guidelines (EPA, 2003, section 5.4), risk estimates may be based on linear extrapolation or 24 nonlinear hazard quotients, depending on the mode of action, accompanied by a statement on the 25 extent of extrapolation generally expressed as the margin of exposure (MOE = POD/exposure). 26 The formulae used in this quantitative linear analysis for dioxin are approximate for a number of 27 the cancer slope factors derived from human data in Table 5.4 because of the calculation of risk 28 for 1pg TCDD/kg body weight/day above background, the use of lifetable analysis to derive the 29 expected cancer rates, and the changing gradient of the dose-response curves as body burden 30 increases, especially for the power formulae. As discussed below, these methods can be 31 compared to previous approaches using the linearized multistage (LMS) procedure to determine 32 whether the chosen approach has significantly changed the estimation of slope. The estimates of 33 ED /LED represent the human-equivalent body burden for 1% excess cancer risk based on 34 exposure to TCDD and are assumed for purposes of this analysis to be equal for TCDD 12/23/03 5-18 DRAFT--DO NOT CITE OR QUOTE 1 equivalents (total TEQ). This assumption is based on the toxic equivalency concept discussed 2 throughout this report and in detail in Part II, Chapter 9. All cancer slope factors can be 3 compared to the Agency's previous slope factor of 1.6 x 10-4per pg TCDD/kg body weight/day, 4 which is equivalent to 1.6 x 105per mg TCDD/kg body weight/day (U.S. EPA, 1985). 5 6 5.2.1.1. Estimates ofSlope Factors and Risk at Current Background Body Burdens 7 Based on Human Data 8 Traditionally, EPA has relied on central estimates of risk from epidemiological studies 9 rather than on upper bound estimates, which can exhibit substantial statistical spread in these 10 results. This practice developed because epidemiological data were most often from high-end 11 occupational exposures--as with the principal dioxin literature--where the data were likely to 12 provide upper estimates of cancer slope and where all excess cancer increases were attributed to 13 the single exposure of interest, amidst a variety of other potential carcinogenic exposures. For 14 the analyses conducted herein, the Agency has presented both central (e.g., ED01) and upper 15 bound (e.g., LED0i) estimates where these are available. 16 The estimates of slope factors (risk per pg TCDD/kg body weight/day) calculated from 17 the human ED0is presented in Part II, Chapter 8, Table 8.3.1, range from 5.1 x 10-3if the EDmfor 18 all cancer deaths in the Hamburg cohort is used to 0.57 x 10-3if the ED0i for all cancer deaths in 19 the smaller BASF cohort is used. All of the other slope factors for all cancer deaths in the three 20 cohorts fall within this range (Table 5-4). The meta-analysis by Crump et al. (2003) leads to 21 similar results, with the reported ED01of 46 ng/kg (95% lower bound = 31 ng/kg) BB, resulting 22 in a cancer slope factor of 0.65 (95% upper confidence limit = 0.97) x 10-3risk per pg 23 TCDD/kgBW/day (adopting the EPA assumptions of baseline SMR = 100, halflife = 7.1 years, 24 80% absorption; alternatively, adopting a floating SMR results in a CSF = 0.37 (0.69) x 10-3). 25 There is no compelling reason to choose one slope factor over the next from among those 26 calculated, given that each study had particular strengths and weaknesses (See Part II, Chapter 27 7a). The results cluster around a cancer slope factor of 10~3risk/pgTCDD/kg body weight/day 28 above background, which represents EPA's most current upper bound slope factor for estimating 29 human cancer risk based on human data. By inference, this risk value could also apply to total 30 TEQ intake. As described in Section 4.4.2, current intakes in the United States are 31 approximately 1pg TEQDFP-WHO98/kg body weight/day, and body burdens are approximately 5 32 ng TEQDFP-WHO98/kg body weight (which equates to a serum level of approximately 20 pg/g 33 lipid). Uncertainties associated with these estimates from human studies are discussed in Part II, 34 Chapter 8, Section 8.3, and in Becher et al. (1998). 12/23/03 5-19 DRAFT--DO NOT CITE OR QUOTE 1 These estimates compare well with the published estimates of cancer slope and risk for 2 the Hamburg and NIOSH cohorts by Becher et al. (1998) and Steenland et al. (2001), 3 respectively. The risk estimates by Becher et al. were derived from data on TCDD exposure to 4 male workers with a 0 or 10-year latency. These estimates range from 1.3 x 10-3to 5.6 x 10-3per 5 pg TCDD/kg body weight/day, and were calculated using German background cancer rates. The 6 fraction of dioxin assumed absorbed is not stated by Becher et al. but, presumably, if the 7 absorption fraction was set at 100%, this would contribute to the slight differences to the EPA 8 values in Table 5.5. The Steenland et al. calculations were performed for either no lag or a 159 year lag. The authors calculated a lifetime all cancer excess risk above background of between 5 10 x 10-4(piecewise linear) to 9.4 x 10-3(power model) per pgTCDD/kg/day. The Steenland et al. 11 results are lower than those presented in Table 5-4 because the authors assumed 50% absorption 12 and a lower additional dose (i.e., incorporating a two-fold doubling of dose over background into 13 the Steenland et al. results reproduces their calculations). 14 In both analyses, all excess cancers are attributed to TCDD exposure, despite significant 15 levels of other dioxin-like compounds in blood measurements. Notable, though, is the Becher et 16 al. determination of a very similar slope coefficient for total TEQ and TCDD, based on their 17 measured data, which is consistent with the TEF methodology. The results from Steenland et al. 18 are more consistent with a reduced cancer slope factor when based on TEQ. Although risk 19 estimates using TCDD alone in these cohorts might suggest an overestimate of risk because dose 20 is underestimated, no evidence for this has emerged from the analysis because TCDD dominates 21 the total TEQ in these occupational cohorts. 22 23 5.2.I.2. Estimates ofSlope Factors and Risk at Current Background Body Burdens Based 24 on Animal Data 25 Upper bound slope factors (per pg TCDD/kg body weight/day) for human cancer risk 26 calculated from lower bounds on ED0is (LED0is) for the animal cancers presented in Table 5-5 27 range from 3 x 10-3to 0.1 x 10-3, that is, from 19 times greater than the previous upper bound 28 estimate on cancer slope (1.6 x 10-4[U.S. EPA, 1985]) to less than 50% of this value. The 29 highest slope factor is derived from the same study as the 1985 estimate; that is, the slope factor 30 derived from the female liver cancer in the Kociba et al. (1978) study continues to give the 31 highest slope factor. 32 12/23/03 5-20 DRAFT--DO NOT CITE OR QUOTE 1 5.2.1.2.1. Reconciling the Portier (1984) and EPA (1985) slope estimates. In attempting these 2 comparisons, two issues became apparent. First, the body burden and the intake at the ED01from 3 Portier et al. (1984) does not result in the same slope factor as EPA's (U.S. EPA, 1985). Despite 4 the use of the same study results, a slope factor of 1.8 x 10-5per pg TCDD/kg body weight/day 5 results when using the LMS approach in Portier et al. (1984), which is approximately a factor of 6 10 lower than EPA's estimate of the slope (U.S. EPA, 1985). The differences are attributable to 7 the aims ofthe respective calculations at the time. Portier et al. calculated "virtually safe doses" 8 assuming that rodent and human doses scaled on a mg/kg basis, and they used the original tumor 9 counts from the study. EPA, on the other hand, used (body weight) b to arrive at a human 10 equivalent dose and the pathology results from a reread of the original Kociba study (U.S. EPA, 11 1980). In addition, EPA adjusted tumor counts for early mortality in the study. The factor to 12 adjust for (body weight) b scaling in the rat is 5.8. The correction for early mortality can be 13 accounted for with a factor of 1.6 (this is the ratio of the intake values at the EDmwith and 14 without the early mortality correction). If the Portier et al. slope factor (1.8 x 10-5per pg 15 TCDD/kg body weight/day) is multiplied by these two factors, a slope of 1.7 x 10-4per pg 16 TCDD/kg body weight/day is calculated. This is essentially equivalent to the EPA estimate of 17 1.6 x 10-4per pg TCDD/kg body weight/day. Reconciling these issues is important to ensuring 18 appropriate comparisons of slope factor estimates. 19 20 5.2.1.2.2. Calculating a revised estimate of cancer slope from Kociba et al. (1978). Of greater 21 consideration is the calculation of slope factor estimates using current methods of analysis that 22 recognize the importance of the dose metric and the differences in half-life of dioxins in the 23 bodies of laboratory animals and humans (see Part II, Chapter 8, Section 8.2, for detailed 24 discussion). The major difference between the approaches used to calculate risks in the mid25 1980s (Portier et al., 1984; U.S. EPA, 1985) and the current approach is the use ofbody burden 26 as the dose metric for animal-to-human dose equivalence. The decision to use body burden 27 accounts for the approximately 100-fold difference between half-lives of TCDD in humans and 28 rats (2593 days vs. 25 days [see Part II, Chapter 8, Table 8.1]). 29 The use of equation 5-1 results in an estimated body burden at the LED0i of 6.1 ng 30 TEQ/kg, derived from the EPA (U.S. EPA, 1985) Kociba et al. tumor counts. This compares 31 favorably with the Portier estimate of 10 ng TEQ/kg found in Table 5-5. The difference is 32 entirely accounted for by the early deaths adjustment by EPA. Use of these body burdens at the 33 LED01results in slope factor estimates of 3.3 x 10-3per pg TCDD/kg body weight/day and 4.9 x 34 10-3per pg TCDD/kg body weight/day for the Portier at al. (1984) (10 ng/kg) and the newly 12/23/03 5-21 DRAFT--DO NOT CITE OR QUOTE 1 derived body burden (6.1 ng/kg), respectively. Again, the difference is due solely to the 2 adjustment for early mortality, which EPA considers a better estimate of upper bound lifetime 3 risk than the unadjusted estimate. EPA's revised slope factor (4.9 x 10-3per pg TCDD/kg body 4 weight/day) would be 31 times greater than the slope factor from 1985. 5 However, a second issue with the modeling of the Kociba et al. data relates to the use of 6 the appropriate tumor counts. As mentioned in Section 2.2, Goodman and Sauer (1992) reported 7 a second re-evaluation ofthe female rat liver tumors in the Kociba et al. study using the latest 8 pathology criteria for such lesions. Results of this review are discussed in more detail in Part II, 9 Chapter 6, Section 6.2. The review confirmed only approximately one-third of the tumors seen 10 in the previous review (U.S. EPA, 1980). Although this finding did not change the determination 11 of carcinogenic hazard, because TCDD induced tumors in multiple sites in this study, it does 12 have an effect on evaluation of dose-response and on estimates of risk. Because neither the 13 original EPA slope factor estimate (U.S. EPA, 1985) nor that of Portier et al. (1984) reflect this 14 reread, it is important to factor these results into the estimate of the EDmand slope factor. 15 Using the LMS procedure used by EPA in 1985 and the tumor counts as reported in Part 16 II, Chapter 6, Table 6.2, the revised slope factor is reduced by approximately 3.6-fold to yield a 17 slope factor of 4.4 x 10-5per pg TCDD/kg body weight/day. However, because the original 18 estimates used a (body weight)2/3scaling, an adjustment must also be made to remove this 19 interspecies scaling factor in order to obtain a correct result when comparing with body burden as 20 the interspecies metric. When dose is adjusted and equation 5-1 is used, an LED01of 22.2 ng 21 TEQ/kg and a slope factor of 1.4 x 10-3per pg TCDD/kg body weight/day are derived. This 22 represents EPA's most current upper bound slope factor for estimating human cancer risk based 23 on animal data. It is 8.7 times larger than the slope factor calculated in U.S. EPA (1985). This 24 number reflects the increase in slope factor based on the use of the body burden dose metric (31 25 times greater) and the Goodman and Sauer (1992) pathology (3.6 times less). These results can 26 also be obtained using EPA's Benchmark Dose software and entering adjusted tumor counts and 27 dose data to obtain a BMDL from which an LED body burden of 22 ng/kg can be derived (see 28 Tables 5-2, 5-4). 29 30 5.2.I.3. Estimates ofSlope Factors and Risk at Current Background Body Burdens Based 31 on a Mechanistic Model 32 As discussed above, Portier and Kohn (1996) combined the biochemical response model 33 of Kohn et al. (1993) with a single initiated-phenotype two-stage model of carcinogenesis to 34 estimate liver tumor incidence in female Sprague-Dawley rats from the Kociba et al. (1978) 12/23/03 5-22 DRAFT--DO NOT CITE OR QUOTE 1 bioassay. The model is described in more detail in Part II, Chapter 8, Section 8.4. This model 2 adequately fit the tumor data, although it overestimated the observed tumor response at the 3 lowest dose in the Kociba et al. study. The shape of the dose-response curve was approximately 4 linear, and the estimated ED01value for this model was 1.3 ng/kg/day. The corresponding body 5 burden giving a 1% increased effect was 2.7 ng/kg. 6 The model authors believe that the use of CYP1A2 as a dose metric for the first mutation 7 rate is consistent with its role as the major TCDD-inducible estradiol hydrolase in liver and with 8 its hypothesized role in the production of estrogen metabolites leading to increased oxidative 9 DNA damage and increased mutation (Yager and Liehr, 1996; Hayes et al., 1996; Dannan et al., 10 1986; Roy et al., 1992). Although no lower bound estimate of the ED01is calculated, a 11 maximum likelihood estimate of the slope factor of 7.1 x 10-3per pg TCDD/kgBW/day can be 12 calculated. This estimate represents an example of the type of modeling based on key events in a 13 mode of action for carcinogenesis that is consistent with the future directions in dose-response 14 modeling described in EPA's revised proposed cancer risk assessment guidelines (U.S. EPA, 15 1999). Although a number of uncertainties remain regarding structure and parameters of the 16 model, the slope estimate is consistent with those derived from humans and animals. More 17 details on this model can be found in Part II, Chapter 8, Section 8.4. 18 An alternative mechanistic model has been proposed (Conolly and Andersen, 1997). This 19 model was developed for focal lesion growth, based on two types of initiated cells and applying 20 the negative selection mechanism for hepatic tumor promotion proposed by Jirtle et al. (Jirtle and 21 Meyer, 1991; Jirtle et al., 1991). In this model, even though the two types of initiated cells 22 express the same biochemical marker, they respond differently to promotional stimulation in the 23 liver. The model presumes that a promotional stimulus to the liver is countered by mito24 inhibitory signals generated by the liver to constrain proliferation. One set of mutated cells is 25 sensitive to this mito-inhibition, whereas the other set of mutated cells is insensitive and 26 responds only to the promotional stimulus. The result is that, under increasing doses of the 27 promoter, one group of focal lesions is decreasing in size--and hence, number of cells--whereas 28 the other group is increasing in size. 29 The Conolly and Andersen model is different from the Portier and Kohn (1996) model in 30 that it can result in U-shaped dose-response curves for the total number and mean size of 31 observable focal lesions without using U-shaped parametric forms for the mutation rates or the 32 birth rates. Conolly and Andersen did not apply their model to cancer risk estimation. Presently, 33 there are insufficient experimental data to support or refute the use of either the Portier and Kohn 34 or the Conolly and Andersen model. 12/23/03 5-23 DRAFT--DO NOT CITE OR QUOTE 1 2 5.2.2. Noncancer Endpoints 3 The analysis of noncancer endpoints following dioxin exposure uses the same dose 4 metrics as for the preceding cancer analysis, although with increased emphasis on LOAELs and 5 NOAELs. Summarized here are noncancer results based on the 200+ ED0i calculations 6 performed in Part II, Chapter 8, combined with a tabulation (Table 5-6; Appendix A) of the 7 lower range of measured, empirical, LOAEL/NOAEL results. Noncancer endpoints following 8 dioxin exposure present similar--lower for some effects--PODs as compared to cancer ED01s, 9 with many of the PODs falling in a range of ~10-50 ng/kg BB and lower still for subclinical 10 endpoints. 11 Before presenting these results, consideration should be give to a number of difficulties 12 and uncertainties associated with comparing the same or different endpoints across species, such 13 as differences in sensitivity of endpoints, times of exposure, exposure routes, and species and 14 strains; the use ofmultiple or single doses; and variability between studies even for the same 15 response. The estimated ED s may be influenced by experimental design, suggesting that 16 caution should be used when comparing values from different designs. Caution should also be 17 used when comparing studies that extrapolate ED0is outside the experimental range. 18 Furthermore, it may be difficult to compare values across endpoints. For example, the human 19 health risk for a 1% change of body weight may not be equivalent to a 1% change in enzyme 20 activity. Similarly, a 1% change in response in a population for a dichotomous endpoint is 21 different from a 1% change in a continuous endpoint, where the upper bound of possible values 22 may be very large, leading to a proportional increase in what constitutes the 1% effect level. 23 Finally, background exposures are often not considered in these calculations simply because they 24 were not known. 25 Part II, Chapter 8, presents estimated ED0is for more than 200 data sets. These data sets 26 were categorized by exposure regimen (single exposure vs. multiple exposures), effect 27 (biochemical, hepatic, tissue, immune, and endocrine) and developmental stage (adult vs. 28 developmental). The Hill model was fit to a majority of the data sets. This model not only 29 provides estimates of the ED01, it also provides insight into the shape of the dose-response curve 30 in the form of a shape parameter. The shape parameter, or the Hill coefficient, can be used to 31 determine whether the dose-response curve is linear or threshold-like. An analysis of the shape 32 parameters for the different response categories implies that many dose-response curves are 33 consistent with linearity over the range of doses tested. This analysis does not imply that the 34 curves would be linear outside this range of doses, but it does inform the choices for 12/23/03 5-24 DRAFT--DO NOT CITE OR QUOTE 1 extrapolation. This is particularly true when body burdens or exposures at the lower end of the 2 observed range are close to body burdens or exposures of interest for humans, which is the case 3 with dioxin-like chemicals and biochemical effects. 4 Several general trends were observed and discussed in Part II, Chapter 8, relating to the 5 ED0i results. The lowest ED01s tended to be for biochemical effects, followed by hepatic 6 responses, immune responses, and responses in tissue weight. However, there was a wide range 7 of ED0is within each category. For example, in the immune category, there was a range of 8 almost six orders of magnitude in the ED0i estimates. In addition, some of the lowest ED01 9 estimates were for changes in immune function in adult mice, with ED0is ranging from 2 to 25 ng 10 TCDD/kg. Overall shape parameter data suggest that biochemical responses to TCDD are more 11 likely to be linear within the experimental dose range. The more complex responses are more 12 likely to assume a nonlinear shape. Nonetheless, a large number (> 40%) of the more complex 13 responses have shape parameters that are more consistent with linearity than with nonlinearity. 14 Table 5-6 summarizes the range of experimental LOAEL, NOAEL, and ED0i values for 15 critical endpoints from animal studies. The published data supporting these values are presented 16 in Appendix A. These endpoints were chosen because they are considered adverse (e.g., 17 developmental or reproductive toxicity) or are on the critical path for cancer and noncancer 18 effects. In addition, these effects were chosen because the body burdens at which the effects 19 occur are approximately 50 ng/kg or lower. The use of ED0is and NOAELs and/or LOAELs in 20 this analysis provides a "point of departure" for a discussion ofmargins of exposure for a variety 21 of health endpoints. No one endpoint has been chosen as the "critical effect," as is often done in 22 RfD calculations. For the effects listed in Table 5-6 and Appendix A, the MOE is approximately 23 10 or less. In some cases, particularly for ED0i values for the developmental toxicities of TCDD 24 in rats (Mably et al., 1992a-c; Gray et al., 1997a, b; Faqi et al., 1998; Markowski et al., 2001), the 25 MOE is less than 1. These estimates of the MOE assume a background human body burden of 5 26 ng TEQ/kg body weight. 27 Results from the analysis of ED0is and an examination of LOAELs in additional studies 28 suggest that noncancer effects can occur at body burden levels in animals equal to or less than 29 body burdens calculated for tumor induction in animals. This is especially true when considering 30 biochemical changes that may be on the critical path for both noncancer and cancer effects, such 31 as enzyme induction or impacts on growth factors or their receptors. Although human noncancer 32 effects were not modeled in Part II, Chapter 8, the observation of effects in the Dutch studies 33 (discussed in Section 2.2.2 in this document) suggest that subtle but important noncancer human 12/23/03 5-25 DRAFT--DO NOT CITE OR QUOTE 1 effects may be occurring at body burden levels equivalent to those derived for many 2 biochemical--and some clearly adverse--effects in animals. 3 4 5.3. MODE-OF-ACTION-BASED-DOSE-RESPONSE MODELING 5 As described in Part II, Chapter 8, Section 8.3, mechanism-based modeling can be a 6 powerful tool for understanding and combining information on complex biological systems. Use 7 of a truly mechanism-based approach can, in theory, enable reliable and scientifically sound 8 extrapolations to lower doses and between species. However, any scientific uncertainty about the 9 mechanisms that the models describe is inevitably reflected in uncertainty about the predictions 10 of the models. The assumptions and uncertainties involved in the mechanistic modeling 11 described in Chapter 8 are discussed at length in that chapter and in cited publications. 12 The development and continued refinement of PBPK models of the tissue dosimetry of 13 dioxin has provided important information concerning the relationships between administered 14 dose and dose-to-tissue compartments (Part II, Chapter 8, Section 8.2). Aspects of these models 15 have been validated in the observable response range for multiple tissue compartments, species, 16 and class of chemical. These models will continue to provide important new information for 17 future revisions of this health assessment document. Such information will likely include 18 improved estimates of tissue dose for liver and other organs where toxicity has been observed, 19 improved estimates of tissue dose(s) in humans, and improved estimates of tissue dose for 20 dioxin-related compounds. 21 In this reassessment, the development of biologically based dose-response models for 22 dioxin and related compounds has led to considerable and valuable insights regarding both 23 mechanisms of dioxin action and dose-response relationships for dioxin effects. These efforts, 24 described in some detail in Part II, Chapter 8, Section 8.3, have provided additional perspectives 25 on traditional methods such as the linearized multistage procedure for estimating cancer potency 26 or the uncertainty factor approach for estimating levels below which noncancer effects are 27 unlikely to occur. These methods have also provided a biologically based rationale for what had 28 been primarily statistical approaches. The development of models like those in Chapter 8 allows 29 for an iterative process of data development, hypothesis testing, and model development. 30 31 5.4. SUMMARY OF DOSE-RESPONSE CHARACTERIZATION 32 All humans tested contained detectable body burdens of TCDD and other dioxin-like 33 compounds that are likely to act through the same mode of action. The receptor modeling theory 34 outlined in Chapter 8 indicates that xenobiotics that operate through receptor binding 12/23/03 5-26 DRAFT--DO NOT CITE OR QUOTE 1 mechanisms, such as dioxin, will follow a linear dose-response binding in the 1-10% receptor 2 occupancy region. This theoretical basis suggests--and this is supported by empirical 3 findings--that the proximal biochemical and transcription reactions for dioxins, such as effects 4 on DNA transcription and enzyme induction, may also follow linear dose-response kinetics. 5 More distal toxic effects could be linear or sublinear/threshold depending on (1) the toxic 6 mechanism, (2) location on the dose-response curve, and (3) interactions with other processes 7 such as intracellular protein binding and co-factor induction/repression. 8 Empirical data provide dose-response shape information down to approximately the 1% 9 effect level for many toxic endpoints. Many examples of adverse effects experienced at these 10 low levels have too much data variability to clearly distinguish on a statistical basis (goodness of 11 fit) between dose-response curve options and whether dose-response follows linear, 12 supra/sublinear, power curve, or threshold kinetics. Toxic effects seen only at higher doses are 13 presumably more likely to result from multiple cellular perturbations and are thus less likely to 14 follow linear relationships. 15 Empirical dose-response data from cancer studies--both human epidemiological and 16 bioassays--do not provide consistent or compelling information supportive of either threshold or 17 supralinear models (see Tables 2-3 and 5-2) and are insufficient to move from EPA's default 18 linear extrapolation policy in the proposed carcinogen risk assessment guidelines (U.S. EPA, 19 1996, 1999, 2003). This policy indicates that, for cancer dose-response, the data are to be 20 modeled within the observed range and a POD calculated from which a linear extrapolation to 21 the origin is generated. For noncancer endpoints, EPA proposes using an MOE approach, rather 22 than an RfD approach, due to the inability to determine levels that are likely to be without 23 appreciable effects of lifetime exposure to the population (including susceptible subpopulations) 24 for all adverse effects, particularly given the current level of background exposure and human 25 body burdens. Data on background levels of dioxins, furans and coplanar PCBs (see Part I, 26 Volume 3, and Section 4.4 in this document) indicate that current levels in humans are already 27 substantially along the dose-response curve. Thus, theoretical issues regarding increases from 28 zero body burden levels are moot, and assessments must consider both background and 29 additional increments of dose to this background level. 30 MOEs between population levels and the empirically observed (not modeled) 1% effect 31 levels for a number of biochemical/toxic endpoints are on the order of less than 1 to 2 orders of 32 magnitude. Thus, the extrapolation between observed effects and background levels is not large, 33 with any increments to background further advancing along the dose-response curve through or 34 toward the observed range. This further reduces the level of uncertainty when evaluating the 12/23/03 5-27 DRAFT--DO NOT CITE OR QUOTE 1 significance of MOEs. It is possible that any additional exposure above current background body 2 burdens will be additive to ongoing responses. The magnitude of the additional response will be 3 a function of the toxic equivalency of the incremental exposure. This observation, the relatively 4 small MOE for "key events" potentially on the pathway to cancer and noncancer effects, and the 5 high percentage of observed linear responses suggest that a proportional model should be used 6 when extrapolating beyond the range ofthe experimental data. Short of extrapolating linearly 7 over one to two orders of magnitude to estimate risk probabilistically for cancer and noncancer 8 effects in the face of the uncertainties described above, a simple MOE approach may be useful to 9 decision makers when discussing risk management goals. However, this decision would have to 10 be based on a policy choice, because this analysis does not strongly support either approach. 11 Because human data for cancer dose-response analysis were available and because of a 12 strong desire to stay within the range of responses estimated by these data, the risk chosen for 13 determining a POD was the 1% excess risk. Doses and exposures associated with this risk (the 14 ED01s) were estimated from the available data using both mechanistic and empirical models. 15 Comparisons were made on the basis of body burdens to account for differences in half-life 16 across the numerous species studied. 17 In humans, restricting the analysis to log-linear models resulted in cancer ED s ranging 18 from 6.0 ng/kg to 62 ng/kg. These were similar to the estimates from empirical modeling of the 19 animal studies, which ranged from 14 ng/kg to 1190 ng/kg (most estimates were in the range of 20 14 to 500 ng/kg), and 2.7 ng/kg for the single mechanism-based model. Lower bounds on these 21 ED0i estimates were used to calculate upper bound slope factors and risk estimates for average 22 background body burdens. 23 Table 5-4 summarizes the ED01/LED0i and slope factor calculations for the occupational 24 cohort and bioassay studies. The slope factor calculations are performed by linearly 25 extrapolating the ED/LED values to the background response rates, consistent with procedures 26 outlined in the draft proposed guidelines for carcinogen risk assessment (U.S. EPA, 1996, 1999, 27 2003). A slope factor estimate of approximately 1 x 10-3per pg TCDD/kg body weight/day 28 represents EPA's most current upper bound slope factor for estimating human cancer risk based 29 on human data. A slope factor of 1.4 x 10-3per pg TCDD/kg body weight/day represents EPA's 30 most current upper bound slope factor for estimating human cancer risk based on animal data. 31 Details on the specific procedures and calculations are provided in the footnotes. Additional 32 details on the study characteristics and dose-response data and graphs are available in Section 5.2 33 and Table 5-2. The Agency, although fully recognizing the range and the public health34 conservative nature of the slope factors that make up the range, suggests the use of 1 x 10-3per 12/23/03 5-28 DRAFT--DO NOT CITE OR QUOTE 1 pg TEQ/kg body weight/day as an estimator of upper bound cancer risk for both background 2 intakes and incremental intakes above background. 3 Upper bound slope factors allow the calculation of the high end (greater than 95%) ofthe 4 probability of cancer risk in the population. This means that there is a greater than 95% chance 5 that cancer risks will be less than the upper bound. Use of the ED0i rather than the LED01to 6 provide more likely estimates based on the available epidemiological and animal cancer data 7 result in slope factors and risk estimates that are within a factor of2 from the upper bound 8 estimates. Even though there may be individuals in the population who might experience a 9 higher cancer risk on the basis of genetic factors or other determinants of cancer risk not 10 accounted for in epidemiologic data or animal studies, the vast majority of the population is 11 expected to have less risk per unit of exposure, and some may have zero risk. On the basis of 12 these slope factor estimates (per pg TEQ/kg body weight/day), upper bound cancer risk at 13 average current background body burdens (5 ng TEQ/kg body weight) exceed 10-3(1 in 1000). 14 Current background body burdens reflect higher average intakes from the past (approximately 3 15 pg TEQ/kg body weight/day). For a very small percentage of the population (< 1%), estimated 16 upper bound risks may be two to three times higher than this upper bound, based on average 17 intake, if their individual cancer risk slope is represented by the upper bound estimate and they 18 are among the most highly exposed (among the top 5%), based on dietary intake of dioxin and 19 related compounds. 20 Estimates for noncancer endpoints show greater variability. In general, when compared 21 on a body burden basis, the noncancer endpoints displayed lower ED01s and NOAELs and/or 22 LOAELs for short-term exposures versus longer-term exposures and for simple biochemical 23 endpoints versus more complex endpoints such as tissue weight changes or toxicity. A number 24 of significant, adverse, noncancer responses occurred at LOAEL/NOAEL/ED0is of < 10-50 25 ng/kg, levels that are similar to the ED0is estimated for cancer effects (see Tables 5-4, 5-6 and 26 Appendix A). The mechanism-based models for noncancer endpoints gave a lower range of 27 ED01s (0.17 to 105 ng/kg) when compared to the broader noncancer data set. Although most of 28 these estimates were based on a single model, the estimate from a different model--the hepatic 29 zonal induction model--gave an ED0i for CYP1A2 induction of 51 ng/kg and, hence, was within 30 the same range. 31 Although highly variable, these estimates suggest that any choice ofbody burden of more 32 than 100 ng/kg as a POD would likely yield > 1% excess risk for some endpoint in humans, 33 including those with clear clinical significance. Also, choosing a POD of less than 1ng/kg 34 would likely be an extrapolation below the range of these data. Any choice in the middle range 12/23/03 5-29 DRAFT--DO NOT CITE OR QUOTE 1 of 1 to 100 ng/kg would be supported by the analyses, although the data provide the greatest 2 support in the range of 10 to 50 ng/kg. This range of body burdens should also provide a useful 3 point of comparison when evaluating impacts ofrisk management on average body burdens in 4 the general population or on estimates of impact of incremental exposures above background on 5 individual body burdens at various ages. 12/23/03 5-30 DRAFT DO NOT CITE OR QUOTE 21 Table 5-1. Peak serum dioxin levels in the background population and epidemiological cohorts Total TEQ (ppt lipid) 2,3,7,8-TCDD (ppt lipid) Non-2,3,7,8-TCDD PCBs TEQ (ppt lipid) 3 Cohort Central Mean No. Lower Tendency Upper Central Tendency TEQ Central Tendency Comment 4657 pCoDpCulactoimonp,aUriSsoAn (12909050-)1997; CDC 316 2a 25.4 meanb 50a (95%12.9.1UmCmeLedai=ann4.2) 5.3 (est.)b 23.3 mean Ts1e0Er5uQ,mD1;F1pm8-W,is1sH5in6Og98P; CBs estimated 1089 A~B1as9sce9ks0gssrmouenndt,, UDSioAxin preosoulletsd 30 5552.8memdeiaann 70 S5D.2~m1e.3a2nc 2108.m8 emdeiaann 47.6 mean bTserEerQuamDstF,mPa-diWlikpHdoOs9e8, ; 11 Back-calculated 111234 RK(1ae9nt9cc9hh)uHmaentda,ll.ow; 276 (r5a2n.3gem2e7d-i9a4n) serum 111576 RK(1ae9nt9cc9hh)uHmaentda,lh. igh; 283 (ra1n9g5e.79m4-e3d,i2a9n0) serum 211089 wHetoaamml.be(nu1;r9gF9lc9eo)shcohr-tJ,anys 66542t,3e,7q,8 19.3 17821.18.2mmedeiaannee 6789.1 (ran15g20e56.82.8.4mm-e6ed3ai9an7n.4) 304.4 meane Ifsu-eTrrauEnmQTsE, Qdiooxnilny;and 2212 NIOSH, Fingerhut et 253 al. (1991b), NTIS (ran2g,0e0f02-m32e,a0n00) serum 222534 Bc(1hA9lo9Sr3Fa),cnsee;veOrett et al. 56 (1ra0n0g8egge2o0m-1. 3m3e6a0n) serum Table 5-1. Peak serum dioxin levels in the background population and epidemiological cohorts (continued) Total TEQ (ppt lipid) 2,3,7,8-TCDD (ppt lipid) Non-2,3,7,8-TCDD PCBs TEQ (ppt lipid) Cohort Central Mean No. Lower Tendency Upper Central Tendency TEQ Central Tendency Comment 321 Bc(1hA9lo9Sr3Fa),cnmeo; dOetrtateet al. 59 (4r2an0g.8e8g2eo.7m2.-4m9e1a5n) serum 45 BOAttSeFt ,anl.o(1c9h9lo3r)acne; 139 (r3a8n.g4eg8e2o.m72.-m29e8an1) serum 67 LSeavnedsioetZaoln.e(1A9;98) 7 (r2a3n30g2e5g.e94o1mm.2e.-d3mi9ae9na.n7) serum 1089 maSle.evd(e1isc9oa9l9Z; )NohneeedAh,am et 296 (r3a8n1g-e4819.5-m5e6d,0ia0n0) nuSsesoaritmunbmgpal;yceks-DtcaLaklecnula1t9e7d6;, 1112 LSeavnedsioetZaoln. e(1B9;98) 51 4(7ra.55n2g.g5eeom5m.e3.d-i2ma7ne3a)n serum 111534 maSle.evd(e1isc9oa9l9Z; )NohneeedBh,am et 80 (8r7an-1g4e71m.8e-7d2ia5n) nuSsesoaritmnubmgpal;yceks-DtcaLaklecnula1t9e7d6;, 111768 maSle.evd(e1isc9oa9l9Z; )NohneeedRh,am et 48 (1r5a-n8g9e m1-e5d4ia5n) nuSseosaritmnubgmpal;yce2ks-DtcaLaklecnula1t9e7d6;; 2109 LSeavnedsioetNaol.nA(1B9R98;) 52 (4r.a9n5.gg5eeom1me.0.d-im1a8ne.a1n) serum Table 5-1. Peak serum dioxin levels in the background population and epidemiological cohorts (continued) Total TEQ (ppt lipid) 2,3,7,8-TCDD (ppt lipid) Non-2,3,7,8-TCDD PCBs TEQ (ppt lipid) Cohort Central Mean No. Lower Tendency Upper Central Tendency TEQ Central Tendency Comment 321 DH(1uo9to9ci6hv)eAldcceitdaeln.t; 14 11(48r3a43n1.g8.8eg3aer0oit1mh-..3m6m8ee3aa)nn serum 4657 DPruotdcuhcMtioanin; H(1o9o9i6v)eld et al. 5 268(0r5a8.n9.2ggeaer1oit7mh-..1mm16ee0aa)nn serum 22111111111111053746890289 aEstimated from ATSDR (1999b) Calcasieu comparison population graph. bCDC data scaled upward to adjust for missing data on PCB congeners 105, 118 and 156 by matching to PCB congener ratios measured in the early 1990 s. c SD approximated from unweighted estimate. dfWoretiogthatledTEaQver(aPgCeBlecvoenlstrfiboruttihoensnuobtseatdojufssteedrufmorlimpiidssiTnEgQcsonwgeernee4rs.5).4 ng/kg for 2,3,7,8-TCDD and 55.4 ng/kg ePCDD- and PCD F-derived TEQ only, using I-TEFs. fgLRoawngeer ienstteimrvaatleodnfrcoumrreenxtploenveenl.tial log distribution graph. hRanges for median values for Seveso result from age groupings in original publication (Needham et al., 1999; Tables 1, 2, 5) 21 Table 5-2. Published cancer epidemiology and bioassay data and dose-response formulae Central estimate of range All cancer deaths 3 Study Egxrpoouspusre (ngy/ekagrsf)aat x o(lbasteernvceyd) 4 Hamburg 5 cohort, 6 Becher et al. 7 (1998) 0-1 1-4 4-8 8-16 0 2000 5657 11314 1.00 RR 1.12 (0-yr lag)b 1.42 P trend = 0.03 1.77 16-64 32000 1.63 64+ 96000 2.19 :g/kg fat*Years n = 1189 male; measured = 275; cancer deaths = 124 Harmonic mean, 1.5 x upper limit Power: _p=0.026 RR = ( 0 .0 0 0 1 7 x + 1 ) A0 .3 2 6 Additive: _p=0.031 RR = 1+0.000016 x M ultiplicative: ^=0.043 RR = exp(0.00000869 x) 8 NIOSH 9 cohort, 10 Steenland et 11 al. (2001) <335 335-<520 520-<1212 1212-<2896 2896-<7568 7568-<20455 >20455 260 402 853 1895 4420 12125 59838 ppt lipid *Years M edian n = 3538 male; measured = 199; cancer deaths = 256 12 BASF 13 cohort, Ott 14 and Zober 15 (1996) <0.1 0.1-0.99 1.0-1.99 2.0+ 598 19407 55057 148800 :g/kg bw. peak; n = 243 male; measured = 138; cancer deaths = 31 Arithmetic mean 1.00 RR 1.26 (15-yr lag) 1.02 1.43 1.46 1.82 1.62 Power: _p=0.003 RR = (x/background)A0.097 Piecewise linear, <40000:c RR = exp(0.000015 x) 0.80 SMR 1.2 (0-yr lag) 1.4 2.0 Conditional risk ratio = 1.22 (95% CI 1.00-1.50)d RR = exp(0.00000503 x) II 1 __' ^ ---- :=fcer1a-il p ew n Eterla~il h i E t c ri ^3 2mm duo] = Cum ulail w TCDDngiTig lipid e ;;#ari 12/23/03 5-34 DRAFT--DO NOT CITE OR QUOTE Tdoasbel-ere5s-p2.onPsuebfloisrmheudlacean(ccoenrteinpuideedm) iology and bioassay data and Central estimate of range All cancer deaths Study Egxrpoouspusre (ng/kg fat x years)" o(lbasteernvceyd) 1 S-D Rats, 2 Kociba et al. 3 (1978); 4 Goodman 5 and Sauer 6 (1992) 7 pathology 0 0.001 0.01 0.1 :g/kg/day 0 540 1700 8100 ng/kg lipid, not AUC 2/86 Tumors 1/50 9/50 18/45 89 a Central estimates provided courtesy o f Drs. Steenland, Zober, and Becher. 10 b RR data provided only for the zero-lag analysis in Becher et al. (1998) 11 c Coefficient for the piecewise linear m odel (0.000015) provided by Dr. Steenland. The initial slope in the 12 piecewise regression is applicable only to 40,000 ng/kg lipid years. 13 d Slope factor calculated from the conditional risk ratio, CR=1.22; see Chapter 8 12/23/03 5-35 DRAFT--DO NOT CITE OR QUOTE 21 Table 5-3. All cancer risk in humans through age 75a 4365 S(2te0e0n1Sl)taunddyet al. Model and Sex power male power female piecewise linear male EDni 1.38 1.84 18.6 9(u5lpo%pweeCrr),I 0.71, 8.95 0.92, 14.9 11.5, 48.3 Unbitoedxbycaebcsuksrgrdriesonkunafodbrov1eppt 0.0079 (0.0027, 0.0132) 0.0064 (0.0022, 0.0107) 0.00052 (0.00020, 0.00084) 87 Becher et al. (1998) piecewise linear female 23.1 power-male 5.971 power-female 7.58 14.3, 59.8 0.00042 (0.00016, 0.00067) 0.0018 0.0014 additive-male 18.22 0.00055 additive-female 22.75 0.00044 multiplicative-male 32.16 0.0003 109 Ott and Zober (1996) multiplicative-female multiplicative-male multiplicative-female 39.82 50.9 62.1 25.0, 30.5, 0.00024 0.00019 (0, 0.00039) 0.00015 (0, 0.00032) 111123 aUnits are constant body burden in ng/kg not adjusted for lipid: see Part III, Chapter 8, Table 8-2, for details. 12/23/03 5-36 DRAFT--DO NOT CITE OR QUOTE 21 Table 5-4. Summary of all site cancer ED01and slope factor calculations 3 Study 4 H a m b u r g c o h o rt, B e c h e r et al. (1 9 9 8 ), p o w e r ED01 (LED01) (ng/kg) 6 Cancer slope factor for 1 pg/kg/day above background" (UCL) 5.1 E -3 5 H a m b u r g coh ort, B e c h e r et al. (1 9 9 8 ), ad d itiv e 6 H a m b u r g co h o rt, B e c h e r et al. (1 9 9 8 ), m u ltip lic a tiv e 7 N I O S H c o h o r t, S te e n la n d et al. (2 0 0 1 ), p ie c e w is e lin ea rb 1 8 .2 3 2 .2 18.6 (1 1 .5 ) 1.6 E -3 0.8 9 E-3 1.5 E -3 (2 .5 E -3 ) 8 B A S F cohort, from O tt and Z ob er (1 9 9 6 ), m u ltip licative 5 0 .9 (25.0) 0 .5 7 E-3 (1.2 E -3) 9 1110 S p r a g u e - D a w l e y r a t s , K o c i b a e t a l . ( 1 9 7 8 ) ; G ood m an and Sauer (1992), pathology 3 1 .9 (2 2 )c B M D dose 0 .9 7 E -3 (1 .4 E -3) 38 (27.5) 0 .8 E -3 (1.1 E -3) B M D ad ip ose 1123 aA s s u m e s 2 5 % o f b o d y w e i g h t i s l i p i d ; 8 0 % o f d i o x i n d o s e i s a b s o r b e d f r o m t h e n o r m a l d i e t i n h u m a n s ; t h e T C D D 14 h a l f - l i f e i s 7 . 1 y e a r s i n h u m a n s . B a c k g r o u n d a l l c a n c e r m o r t a l i t y r a t e c a l c u l a t e d t h r o u g h l i f e t a b l e a n a l y s i s t o 7 5 15 y e a r s . S u m m a r y r e s u l t s a r e f o r m a l e a l l c a n c e r r i s k , b e c a u s e t h e m a l e l i f e t i m e ( t o 7 5 y e a r s ) a l l c a n c e r r i s k i s g r e a t e r 16 t h a n f o r f e m a l e s , l e a d i n g t o c o r r e s p o n d i n g l y h i g h e r c a n c e r s l o p e f a c t o r s . A s d e t a i l e d i n P a r t I I I , C h a p t e r 8 , 17 (ED01) (0dose)R e l R i s k = 0 .99 + 0 .0 1 /R isk . B a sed o n th e m an n er in w h ich the d o se-resp o n se data w ere calcu lated u sin g 18 C o x R e g r e s s i o n r a t e r a t i o a n a l y s e s , r i s k s a r e g i v e n a s c a n c e r s l o p e f a c t o r s f o r 1 p g / k g / d a y a b o v e b a c k g r o u n d , 19 a s s u m e d 5 p p t T C D D i n l i p i d . 20 b S t e e n l a n d e t a l . ( 2 0 0 1 ) p o w e r m o d e l r e s u l t s a r e n o t i n c l u d e d , a s t h i s f o r m u l a p r e d i c t s u n r e a s o n a b l y h i g h 21 a t t r i b u t a b l e r i s k s a t b a c k g r o u n d d i o x i n l e v e l s i n t h e c o m m u n i t y d u e t o t h e s t e e p s l o p e o f t h e p o w e r c u r v e f o r m u l a 22 a t v e r y l o w l e v e l s . 23 cM o d e l e d u s i n g U . S . E P A B e n c h m a r k D o s e S o f t w a r e , v e r s i o n 1 . 2 , w i t h e i t h e r d o s e o r a d i p o s e c o n c e n t r a t i o n a s t h e 24 m e t r i c . A b s o r p t i o n f r o m f o o d p e l l e t s i n a n i m a l s is a s s u m e d to b e 5 0 % . B M D = 0 . 0 0 1 7 6 8 4 9 u g / k g / d a y . B M D L = 25 01 010 . 0 0 1 2 2 5 1 7 u g / k g / d a y . T h e r e f o r e , r a t L E D = 1 . 2 2 5 1 x 2 5 x 0 . 5 / l n 2 = 2 2 n g / k g ; h u m a n e q u i v a l e n t L E D = 2 2 x 2276 l n 2 x 1 0 0 0 / 2 5 9 3 / 0 . 8 = 7 . 3 8 p g / k g / d a y ; s l o p e f a c t o r = 0 . 0 1 / 7 . 3 8 = 1 . 4 E - 3 r i s k / p g / k g / d a y . 12/23/03 5-37 DRAFT--DO NOT CITE OR QUOTE 4321 b(TPaaosberltdeie5ur-p5eo.tnaD2l.o,-sy1ee9sa8yr4ia)enlmdimiondagell1cs%'a1rceixncoegsesnriicsikty(9st5u%dieloswuseirncgosnifmidpelnecme ublotiusntadg)e ED01 Animal intake for 1% Steady-state body excess risk in burden in ng/kg at 5 Tumor ng/kg/day (95% lower ED01 (95% low er Shape confidence bound) confidence bound) 6 L iv er ca n cer in fe m a le rats (K o c ib a ) L inear 0 .7 7 (0.57) 14 (10) 7 S q u a m o u s cell ca rcin o m a o f the to n g u e in m a le 8 rats (K ocib a) L inear 14.1 (5 .9 ) 254 (106) 109 S q u a m o u s c e l l c a r c i n o m a o f t h e n a s a l t u r b i n a t e s or h ard p alate in m a le rats (K o c ib a ) C ubic 4 1 .4 (1.2) 746 (22) 1112 S q u a m o u s c e l l c a r c i n o m a o f t h e l u n g i n f e m a l e rats (K o cib a ) C ubic 4 0 .4 (2.7) 730 (48) 1134 S q u a m o u s c e l l c a r c i n o m a o f t h e n a s a l t u r b i n a t e s or h ard p alate in fe m a le rats (K o c ib a ) L inear 5 .0 (2.0) 90 (36) 1156 T h y r o i d f o l l i c u l a r c e l l a d e n o m a i n m a l e r a t s (N T P ) L inear 4 .0 (2.1) 144 (76) 17 T h y r o i d f o l l i c u l a r c e l l a d e n o m a i n f e m a l e r a t s 18 ( N T P ) C ubic 33 .0 (3.1) 1190 (112) 2109 L i v e r a d e n o m a s a n d c a r c i n o m a s i n f e m a l e r a t s (N T P ) Q uadratic 13.0 (1.7) 469 (61) 2212 L i v e r a d e n o m a s a n d c a r c i n o m a s i n m a l e m i c e (N T P ) L inear 1.3 (0 .8 6 ) 2 0 .6 (13.6) 2234 L i v e r a d e n o m a s a n d c a r c i n o m a s i n f e m a l e m i c e (N T P ) L inear 15.1 (7 .8 ) 239 (124) 2256 T h y r o i d f o l l i c u l a r c e l l a d e n o m a s a n d c a r c i n o m a s in fem ale m ice (N T P ) L inear 30.1 (1 4 .0 ) 478 (222) 27 S u b c u t a n e o u s t i s s u e s a r c o m a s i n f e m a l e m i c e 28 ( N T P ) L in-C ubic 43 .2 (14.1) 686 (224) 29 L e u k e m i a s a n d l y m p h o m a s i n f e m a l e m i c e ( N T P ) L inear 10.0 (5 .4 ) 333120 a R e p r i n t e d w i t h s l i g h t m o d i f i c a t i o n s f r o m P a r t I I , C h a p t e r 8 , T a b l e 8 . 3 . 2 . 159 (86) 12/23/03 5-38 DRAFT--DO NOT CITE OR QUOTE 321 Teqaubilvea5le-6n.tBdoaidlyy binutradkeens for critical endpoints in animals with human 4 Animal Endpoint 5 Rats Cancer 67 Rhesus monkeys Fetal mortality Developmental neurotoxicity Study Kociba et al. (1978) Bowm an et al. (1989) Schantz et al. (1992) Estimated body burden (ng/kg) LOAEL 180 NOAEL 18 E D 01 32 90 21 NC 21 - NC Human equiv.a intakes (pg/kg/day) 60; 6; 11 30; 7 7 8 Rats 9 Rats Endometriosis Reproductive tox. (m ultigeneration al) Developmental/ reproductive toxicity Rier et al. (1993) M urray et al. (1979) M ably et al. (1992) Gray et al. (1997) 21 180 18 38 30 - NC 7 NC 60; 6 0.34 13; 0.1 0.08 10; 0.03 Faqi et al. (1998) 25 - 0.6 8; 0.2 Ohsako et al. (2001) 30 8 NC 10; 3 10 Rats Developmental im m un otoxicity Gehrs and Smialowicz (1999) 60 - NC 20 11 Rats Developmental M arkow ski et al. (2001) 108 36b 0.7 36; 12; 0.2 Neurotoxicity 12 Mice Immunological effects Burleson et al. (1996) 6 3 NC 2; 1 (adult) Smialowicz et al. (1994) 300 - 2.9 100; 1 N arasim han et al. (1994) 100 50b 1.5 33; 17; 0.5 13 Rats 14 Mice Thyroid effects CYP1A1/1A2 enzyme inducti on Vecchi et al. (1983) Sewall et al. (1995) DeVito et al (1994) Diliberto et al. (2001) 1200 76 22 24 2.8 - 7 401; 2 26 25; 7; 8 22 8; 7 67 0.9; 22 Vogel et al. (1997) 5.1 0.51 0.003 1.6; 0.16; 0.001 15 Rats CYP1A1/1A2 enzyme inducti on Narasimhan et al (1994) van Birgelen et al. (1995) Schrenk et al. (1994) 25 243 72 10 - 3 8; 3; 2; 1 19 81; 6 26 24; 9 Sewall et al. (1995) 82 3.5 3; 0.7; 1 16 W alker et al. (1999) 76 - 59 25; 20 12/23/03 5-39 DRAFT--DO NOT CITE OR QUOTE 1111111114257036342568971 iTnatbaklee5(-c6o.nBtionduyedb)urdens for critical endpoints in animals with human equivalent daily aH(buomdyanbuerqdueinva(lnegn/tkign)t*akLens2*w1e0r0e0e)s/t(itm'Aa*taebdsaocrpcotirodni)ngwhtoertehet'Afo=llo2w59in3gdeaqyusaatinodn:abdsaoilryptiinotnakfera(cptgio/kng=/d0ay.8) (=Poiger and Schlatter 1986; see Section II). Corresponding human equivalent intake values are arranged in sequence from the previous three columns. bNOAEL values are based on the highest individual dose group in which there are no statistically significant clehvaenlgse--s.20Staantdist6i0canllgy/ksgigonrifailclayn--t idnosaellrfeisxpeodn-rsaetitoretnedsst gprlouuspaspipnarMenatrkdoewclsinkeisetarael.a(l2s0o0e1v)idanendtianttahlel d5o0sneg/kg dose group in Narasimhan et al. (1994). - - = no NOAEL value, as effects seen in the lowest dose group in the study. NprCese=nNtaotitocnalocfutlhaeteddadtaueintogrianpsuhficfiacliefonrtmdowseithreosuptotnasbeuliantfioornmoaftimonea(nleassndthvaanritahnrecee edsotsimesaatensd. a control) or due to Note: This table is reproduced in Appendix A with explanatory details of study design, results, and calculation procedures, formulae, and assumptions. 12/23/03 5-40 DRAFT--DO NOT CITE OR QUOTE Bdy hunier, ng TEQ/kg 2222222111111111111250364257036894436892571 Fhyigpuortehe5t-i1c.alCboamckpgarroisuonndoafnldifeotcimcuepaavtieornaaglesbcoednyarbiousr.den and area under the curve in 12/23/03 5-41 DRAFT DO NOT CITE OR QUOTE Body Burden ng/kg whole body, 25% lipid 111111111142503367468258971 FpprbbrvedceTt2Tflheieroapooeaae,imCCos3sigctsrnrppisppmw,idiDDihiutuu7avsetebreellrDDb,iecocaitama8obeeshdittrftt-liuifn;ieiaTiiv5TvttoTototthhnt-etieEhyUCnnhEhlo2eedeoQ.sebcieDn..QSnbcgloacs(moToxDa.Psil,rChobcwe,cm-hpeebomsaaDvakcteaoeiaercxbhlez-ebtCnrpckkicilleecnispno/aung;ans(motduulawlol~rraUauahcpidtasoenn4tioetsueoloSipuodi-d7roxolr2teeAnniaa.nnhitsanb6sr,dnts3hoenopt.eoo~sip,atU/(odftmbh7e1gfdtbTprrtsoao,.9eeteheata8tShtwdimdopp9itdec-ole.meeyrmiiT0oknppdpdueolswaC-obisoeeopd)ocpdftetm,pwiDurpeiar,ofttnstudtehhirileiDtrhect1odclroretraraeti1itunelm2ahbohctbeTo.lbinn9,euhenrsaaog3eEaegttrtmanni,tiliortpQ,ee7comeohnsgrfdanne,vtneo/e8raatlcaia)okesshenf-ltvomn:clngeeT(pebdsnanoS-ntsrbeaCibir2hotiheecetsirclanos,enDaeosyai3cktbcde-btrthb2k,DgTo2touhtny7ihe,garlr,ntete3a,i3eobsicr8attcxbot,o,vruyuk7-hnmro7pinluTaner,bdegem,ios8dnrip8ndCur;nisru-e5dr-baotauTDitnTetnpi-ibmhhnuorU1snoCpCDeieeganen)anlue.sD.tinDeSstd2-,smrtil2t2y.Dh,oeoiDFtn3ps5,thapvnfof3eoh,o%edrole7csTtn,reeoop7oioltp,b-nvEst8imfa,utbn2uhma8age-Qdttolt,lerTll-hh3aaanadjsdTwueaiTCtb,ttoioyn7iimeCttnaEnooarDiled,hococf8Ds-nen2QdaDka2tnwb-a,siteDnvTg3,w)oos.m3eso;oer,ua-Cndtr7i,ofndNinar7etyb,mD2uhert-ena8,dehoe28d,nirbdsD-a3enpeti,-duTuetv3,niTrte7rnmtrCheTe,UheddtC7,asdeh8EtDdeee,.dehDoa8S-anuQTndDreitn-s.D.epnteEsutsgpdth.-QrtFhietheeotheorsedoner 12/23/03 5-42 DRAFT--DO NOT CITE OR QUOTE 1 6. RISK CHARACTERIZATION 2 3 Characterizing risks from dioxin and related compounds requires the integration of 4 complex data sets and the use of science-based inferences regarding hazard, mode of action, dose 5 response, and exposure. It also requires consideration of incremental exposures in the context of 6 an existing background exposure that, for the majority of the population, is independent of local 7 sources and dominated by exposure through the food supply. Finally, this characterization must 8 consider risks to special populations and developmental stages (subsistence fishers, children, 9 etc.) as well as to the general population. It is important that this characterization convey the 10 current understanding of the scientific community regarding these issues, highlight uncertainties 11 in this understanding, and specify where assumptions have been used or inferences made in the 12 absence of data. Although characterization of risk is inherently a scientific exercise, it must by 13 nature go beyond empirical observations and draw conclusions in untested areas. In some cases, 14 these conclusions are, in fact, untestable, given the current capabilities in analytical chemistry, 15 toxicology, and epidemiology. This situation should not detract from one's confidence in the 16 conclusions of a well-structured and well-documented characterization of risk, but it should serve 17 to confirm the importance of considering risk assessment as an iterative process that benefits 18 from evolving methods and data collection and is subject to change as the knowledge base 19 improves. 20 21 Dioxin and related compounds can produce a wide variety of effects in animals and may 22 produce many of the same effects in humans. 23 There is adequate evidence, based on all the available information, as discussed in Parts I 24 and II of this Reassessment and in this Integrated Summary, to support the inference that the 25 potential exists for humans to respond with a broad spectrum of effects from exposure to dioxin 26 and related compounds, depending on the magnitude and duration of exposure. This inference is 27 based on the similarities in receptor and receptor binding and their sequellae observed in animals 28 and in humans. Effects will likely range from detection of biochemical changes at or near 29 background levels of exposure to detection of adverse effects with increasing severity as body 30 burdens increase above background levels. Data presented in Part II, Chapter 8, and illustrated in 31 Table 5-6 and Appendix A support this general conclusion. 32 Enzyme induction, changes in hormone levels, and indicators of altered cellular function 33 seen in humans and laboratory animals represent effects of unknown clinical significance but that 34 may be early indicators of toxic response. Induction of activating/metabolizing enzymes at or 12/23/03 6-1 DRAFT--DO NOT CITE OR QUOTE 1 near background levels, for instance, may be adaptive and, in some cases, beneficial, or it may be 2 considered adverse. Induction may lead to more rapid metabolism and elimination ofpotentially 3 toxic compounds, or it may lead to increases in reactive intermediates and may potentiate toxic 4 effects. Examples of both ofthese situations are available in the published literature, and events 5 of this type formed the basis for a biologically based model discussed in Part III, Section 5. 6 Subtle effects, such as the impacts on neurobehavioral and developmental outcomes in 7 laboratory animals and humans, the thyroid function and immune system alterations seen in the 8 Dutch children exposed to background levels of dioxin and related compounds, or the changes in 9 circulating reproductive hormones in men exposed to TCDD, illustrate the types of responses 10 that support the finding of subtle yet arguably adverse effects at or near background body 11 burdens. Clearly adverse effects, including, perhaps, cancer, may not be detectable until 12 exposures contribute to body burdens that exceed current background by one or two orders of 13 magnitude (10 or 100 times). MOEs in this range are considerably less than those typically seen 14 for environmental contaminants of toxicologic concern, particularly when the health endpoint is 15 cancer, as observed in epidemiologic studies. 16 Clear mechanistic relationships between biochemical and cellular changes seen at or near 17 background body burden levels and production of adverse effects detectable at higher levels 18 remain uncertain, but modes of action consistent with available data have been discussed in 19 several chapters in Part II. Information on these mechanistic relationships and modes ofaction is 20 useful in hazard characterization, and data are accumulating to suggest refined mode of action 21 hypotheses for further testing. 22 It is well known that individual species vary in their sensitivity to any particular dioxin 23 effect. Laboratory rodents (typically strains ofrats and mice) are not necessarily the most 24 sensitive responders for several well-studied effects. However, the evidence available to date 25 indicates that humans most likely fall in the middle rather than at either extreme of the range of 26 sensitivity for individual effects among animals. In other words, evaluation ofthe available data 27 suggests that humans, in general, are neither extremely sensitive nor insensitive to the individual 28 effects of dioxin-like compounds. 29 Human data provide direct or indirect support for evaluation of likely effect levels for 30 several of the endpoints observed in laboratory studies (e.g., cancer and neurobehavioral and 31 endocrine endpoints), although the influence of variability among humans remains difficult to 32 assess. Discussions have highlighted certain prominent, biologically significant effects of TCDD 33 and related compounds. In TCDD-exposed men, subtle changes in biochemistry and physiology, 34 such as enzyme induction, altered levels of circulating reproductive hormones, or reduced 12/23/03 6-2 DRAFT--DO NOT CITE OR QUOTE 1 glucose tolerance and, perhaps, diabetes, have been detected in a limited number of 2 epidemiologic studies. 3 These findings, coupled with the knowledge derived from animal experiments, suggest 4 the potential for adverse impacts on human metabolism and developmental and/or reproductive 5 biology and, perhaps, other effects in the range of current human exposures. These biochemical, 6 cellular, and organ-level endpoints have been shown to be affected by TCDD, but specific data 7 on these endpoints do not generally exist for other congeners. Despite this lack of congener8 specific data, there is reason to infer that these effects may occur for all dioxin-like compounds, 9 based on the concept of toxic equivalency. 10 In this document, dioxin and related compounds are characterized as developmental, 11 reproductive, immunological, endocrinological, and carcinogenic hazards. The deduction that 12 humans are likely to respond with noncancer effects from exposure to dioxin-like compounds is 13 based on the finding that these compounds impact cellular regulation at a fundamental level and 14 on the demonstration of adverse effects among a broad range of species. For example, because 15 developmental toxicity following exposure to TCDD-like congeners occurs in fish, amphibians, 16 reptiles, birds, and mammals, it is likely to occur at some level in humans. 17 It is not currently possible to state exactly how or at what levels individuals will respond 18 with specific adverse impacts on development or reproductive function, but the analyses of the 19 Dutch cohort data and laboratory animal studies suggest that some effects may occur at or near 20 background levels. Fortunately, there have been few human cohorts identified with TCDD 21 exposures high enough to raise body burdens significantly over background levels (see Table 5-1 22 and Figure 5-2 in this document), and when these cohorts were examined, relatively few 23 clinically significant effects were detected. However, the power ofthese studies to detect these 24 effects remains an issue. The lack of sufficient exposure gradients and adequate human 25 information and the focus ofmost currently available epidemiologic studies on occupationally 26 TCDD-exposed adult males make it difficult to evaluate the inference that noncancer effects 27 associated with exposure to dioxin-like compounds may be occurring in the broader human 28 population. It is important to note, however, that when exposures to very high levels of dioxin 29 like compounds have been studied--such as in the Yusho and Yu-Cheng cohorts--a spectrum of 30 adverse effects have been detected in men, women, and children. Many of these effects are 31 similar to what has been observed not only in small laboratory animals, but in wildlife and in 32 nonhuman primates. 33 Some have argued that in the absence of better human data, deducing that a spectrum of 34 noncancer effects will occur in humans overstates the science; however, most of the scientists 12/23/03 6-3 DRAFT--DO NOT CITE OR QUOTE 1 involved as authors and reviewers in the reassessment have indicated that such inference is 2 reasonable, given the weight of evidence from available data. As presented, this logical 3 conclusion represents a testable hypothesis that may be evaluated by further data collection. 4 EPA, its federal colleagues, and others in the general scientific community are continuing to fill 5 critical data gaps, which will reduce our uncertainty regarding both hazard and risk 6 characterization for dioxin and related compounds. However, as discussed by EPA's SAB (U.S. 7 EPA, 2001b) "neither knowledge breakthroughs nor fully developed techniques for producing 8 more unbiased risk assessments can be expected to be available in the near future." 9 10 Dioxin and related compounds are structurally related and elicit their effects through a 11 common mode of action. 12 The scientific community has identified and described a series of common biological 13 steps that are necessary for most, if not all, of the observed effects of dioxin and related 14 compounds in vertebrates, including humans. Binding of dioxin-like compounds to a cellular 15 protein called the aryl hydrocarbon receptor (AhR) represents the first step in a series of events 16 attributable to exposure to dioxin-like compounds, including biochemical, cellular, and tissue17 level changes in normal biological processes. Binding to the AhR appears to be necessary for all 18 well-studied effects of dioxin, but it is not sufficient in and of itselfto elicit these responses. 19 There remains some uncertainty as to whether every dioxin response is AhR-mediated. 20 Some data from the use of sensitive biological tools, such as AhR-deficient (AhR-/-) mice, 21 suggest a small residual of effects from exposure to TCDD, and, thus, we cannot rule out 22 receptor-independent alternative pathways. However, these reported non-AhR-mediated 23 responses occur in animals at doses that are orders of magnitude higher than current human 24 exposures and require much higher doses than other AhR-mediated effects in animals. Thus, 25 these putative non-AhR-mediated mechanisms are unlikely to impact any of the assumptions 26 made in this reassessment. 27 Exposure of animals--and in some cases humans--to chemicals whose structure and 28 AhR binding characteristics are similar to those of 2,3,7,8-TCDD can elicit similar effects. In the 29 past 5 years, significant data have accumulated that support the concept of toxic equivalence, a 30 concept that is at the heart of risk assessment for the complex mixtures of dioxin and related 31 compounds encountered in the environment. These data have been analyzed and summarized in 32 Part II, Chapter 9. This chapter was added to EPA's dioxin reassessment to address questions 33 raised by the SAB in 1995. The SAB suggested that, because the TEQ approach was a critical 34 component of risk assessment for dioxin and related compounds, the Agency should be explicit 12/23/03 6-4 DRAFT--DO NOT CITE OR QUOTE 1 in its description of the history and application of the process and go beyond reliance on the 2 Agency's published reference documents on the subject (U.S. EPA, 1987, 1989a). 3 The analyses in Parts II and III of this document demonstrate that, although variability in 4 the data underpinning the scientific judgments regarding toxic equivalency exists, when data are 5 restricted to longer exposure and in vivo data, the empirical analysis strongly supports the 6 judgment of experts in setting TEF values. This is particularly true for the use of TEFs for 7 assessing the animal cancer endpoint but will likely apply even more strongly to noncancer 8 effects as additional congener-specific data are collected. A focus on the five congeners that 9 make up greater than 80% ofhuman body burden on a TEQ basis reveals rather robust data sets, 10 which form the basis for assigned TEFs. This focus reduces the impact ofthe uncertainties in 11 TEFs assigned to less-studied congeners. In its recent review (U.S. EPA, 2001b), EPA's SAB 12 agreed that the general framework for calculating TEFs and applying them to obtain a TEQ is 13 well described in Part II, Chapter 9. The Board recognized that uncertainties remained regarding 14 toxicities ofjoint exposures that are not dominated by well-studied congeners, and recommended 15 further development of the TEF methodology (e.g., development of probability density functions 16 around experimental results to assist future expertjudgment in reviewing and revising TEFs) (see 17 Finley et al., 2003). 18 19 EPA and the international scientific community have adopted toxic equivalency of dioxin 20 and related compounds as prudent science policy. 21 Dioxin and related compounds always exist in nature as complex mixtures. As discussed 22 in the exposure document, these complex mixtures can be characterized through analytic 23 methods to determine concentrations of individual congeners. Dioxin and related compounds 24 can be quantified and biological activity of the mixture can be estimated using relative potency 25 values and an assumption of dose additivity. Such an approach has evolved over time to form 26 the basis for the use of TEQ in risk assessment for this group of compounds. Although such an 27 approach is dependent on critical assumptions and scientific judgment, it has been characterized 28 by the SAB as a "useful, interim" way to deal with the complex mixture problem, and it has been 29 accepted by numerous countries and several international organizations. Alternative approaches, 30 including the assumption that all congeners carry the toxic equivalency of 2,3,7,8-TCDD or that 31 all congeners other than 2,3,7,8-TCDD can be ignored, have been rejected as inadequate for risk 32 assessment purposes. 33 Significant additional literature is now available on the subject of toxic equivalency of 34 dioxin and related compounds, as summarized (through 2000) in Part II, Chapter 9. An 12/23/03 6-5 DRAFT--DO NOT CITE OR QUOTE 1 international evaluation of all of the available data (van den Berg et al., 1998) reaffirmed the 2 TEQ approach and provided the scientific community with the latest values for TEFs for PCDDs, 3 PCDFs, and dioxin-like PCBs. Consequently, we can infer with greater confidence that humans 4 will respond to the cumulative exposure of AhR-mediated chemicals. This reassessment 5 recommends that the WHO98TEF scheme be used to assign toxic equivalency to complex 6 environmental mixtures for assessment and regulatory purposes. Further research is needed to 7 address remaining uncertainties inherent in the current approach, in particular those regarding the 8 impact of actual exposures compared to measured body burdens of highly persistent congeners 9 and the continuing debate regarding the role of other Ah-agonists in the diet on the toxicity of 10 dioxin-like compounds. WHO has suggested that the TEQ scheme be reevaluated on a periodic 11 basis and that TEFs and their application to risk assessment be reanalyzed to account for 12 emerging scientific information. EPA supports this suggestion and intends to participate in 13 future re-evaluations. 14 15 Complex mixtures of dioxin and related compounds are highly potent, "likely" 16 carcinogens. 17 A weight-of-evidence evaluation suggests that mixtures of dioxin and related compounds 18 (CDDs, CDFs, and dioxin-like PCBs) are strong cancer promoters and weak direct or indirect 19 initiators and that they are likely to present a cancer hazard to humans. Because dioxin and 20 related compounds always occur in the environment and in humans as complex mixtures of 21 individual congeners, it is appropriate that the characterization apply to the mixture. According 22 to the Agency's revised proposed guidelines for carcinogen risk assessment, the descriptor 23 "likely to be carcinogenic to human" is appropriate when the available tumor effects and other 24 key data are adequate to demonstrate carcinogenic potential to humans (U.S. EPA, 1999, 2003) 25 yet are not sufficient to infer a cause-and-effect relationship. 26 "Adequate data" are recognized to span a wide range. Even though the database from 27 cancer epidemiologic studies remains a point of scientific discussion, it is the view of this 28 reassessment that this body of evidence is supported by the laboratory data that indicate that 29 TCDD increases cancer mortality of several types. Although not all confounders were ruled out 30 in any one study, positive associations between surrogates of dioxin exposure, either length of 31 occupational exposure or proximity to a known source combined with some information based 32 on measured blood levels, and cancer have been reported. 33 These epidemiologic data strongly suggest a role for dioxin exposure to contribute to a 34 carcinogenic response but are not sufficient to confirm a causal relationship between exposure to 12/23/03 6-6 DRAFT--DO NOT CITE OR QUOTE 1 dioxin and increased cancer incidence. Available human studies alone cannot demonstrate 2 whether a cause-and-effect relationship between dioxin exposure and increased incidence of 3 cancer exists. Therefore, evaluation of cancer hazard in humans must include an evaluation of all 4 of the available animal and in vitro data as well as the data from exposed human populations. 5 The data for complex mixtures of dioxin and related compounds represent a case that, 6 according to discussions in the draft guidelines, would approach the strong-evidence end ofthe 7 adequate data spectrum. Epidemiologic observations of an association between exposure and 8 cancer responses (TCDD); unequivocal positive responses in both sexes, multiple species, 9 multiple sites, and different routes in lifetime bioassays or initiation-promotion protocols or other 10 shorter-term in vivo systems such as transgenic models (TCDD plus numerous PCDDs, PCDFs, 11 dioxin-like PCBs); and mechanistic or mode-of action data that are assumed to be relevant to 12 human carcinogenicity, including, for instance, initiation-promotion studies (PCDDs, PCDFs, 13 dioxin-like PCBs) all support the description of complex mixtures of dioxin and related 14 compounds as likely to be human carcinogens. On the basis of these observations, complex 15 environmental mixtures of TCDD and dioxin-like compounds should be characterized as "likely" 16 carcinogens, with the degree of certainty of the characterization being dependent on the 17 constituents of the mixture, when known. For instance, the hazard potential, although "likely," 18 would be characterized differently for a mixture whose TEQ was dominated by octaCDD as 19 compared with one dominated by pentaCDF. 20 As discussed in Section 2.2.1.5, under EPA's current approach for carcinogen risk 21 assessment, individual congeners can also be characterized as to carcinogenic hazard. 2,3,7,822 Tetrachlorodibenzo-p-dioxin (TCDD) is best characterized as "carcinogenic to humans." This 23 means that, on the basis of the weight of all of the evidence (human, animal, mode of action), 24 TCDD meets the criteria that allow EPA and the scientific community to accept a causal 25 relationship between TCDD exposure and cancer hazard. The guidance suggests that 26 "carcinogenic to humans" is an appropriate descriptor of human carcinogenic potential when 27 there is an absence of conclusive epidemiologic evidence to clearly establish a cause-and-effect 28 relationship between human exposure and cancer but there is compelling evidence of 29 carcinogenicity in animals and mechanistic information in animals and humans demonstrating 30 similar modes of carcinogenic action. The "carcinogenic to humans" descriptor is suggested for 31 TCDD because all of the following conditions are met: 32 33 There is strong and consistent evidence from occupational epidemiologic studies for an 34 association between TCDD exposure and increases in cancer at all sites, in lung cancer 12/23/03 6-7 DRAFT--DO NOT CITE OR QUOTE 1 and, perhaps, at other sites, but the data are insufficient on their own to support a causal 2 association. This point was discussed in detail by the International Agency for Research 3 on Cancer (IARC, 1997). 4 5 There is extensive carcinogenicity in both sexes of multiple species at multiple sites. 6 7 There is general agreement that the mode of TCDD's carcinogenicity is as an AhR8 dependent promoter and proceeds through gene expression and/or a modification of the 9 action of a number of receptor and hormone systems involved in cell growth and 10 differentiation, such as the epidermal growth factor receptor and the estrogen receptor. 11 12 The human AhR and the rodent AhR are similar in structure and function and, once 13 activated, both bind to the same DNA response elements, designated DREs. 14 15 Human and rodent tissue and organ cultures respond to TCDD and related chemicals in a 16 similar manner and at similar concentrations. TCDD has the ability to transform 17 immortalized human and rodent cells that then have demonstrable tumorigenicity. 18 19 Other individual dioxin-like compounds are characterized as "likely to be carcinogenic to 20 humans" primarily because of the lack of epidemiological evidence associated with their 21 carcinogenicity, although the inference based on toxic equivalency is strong that they would 22 behave in humans as TCDD does. Other factors, such as the available congener-specific chronic 23 bioassays, also support this characterization. For each congener, the degree of certainty is 24 dependent on the available congener-specific data and their consistency with the generalized 25 mode of action that underpins toxic equivalency for TCDD and related compounds. 26 Although uncertainties remain regarding quantitative estimates of upper-bound cancer 27 risk from dioxin and related compounds, efforts of this reassessment to bring more data into the 28 evaluation of cancer potency have resulted in evaluation of the slope of the dose-response curve 29 at the low end of the observed range (using the LED ) using a simple proportional (linear) model 30 and a calculation of both upper-bound risk and MOE based on human equivalent background 31 exposures and associated body burdens. Evaluation of shape parameters (used to estimate degree 32 of linearity or nonlinearity of dose-response within the range of observation) for biochemical 33 effects that can be hypothesized as key events in a generalized dioxin mode-of-action model do 12/23/03 6-8 DRAFT--DO NOT CITE OR QUOTE 1 not argue for significant departures from linearity below a calculated ED01, extending down to at 2 least one to two orders of magnitude lower exposure. 3 Risk estimates for intakes associated with background body burdens or incremental 4 exposures based on this slope factor represent a plausible upper bound on risk, based on the 5 evaluation of animal and human data. The slope factors, based on the most sensitive cancer 6 responses calculated by authors of peer-reviewed publications and presented in Part II, Chapter 8, 7 and Section 5 for both animals and humans, fall in a range of approximately 0.6 x 10-3to 5 x 10-3 8 per pg TEQ/kg body weight/day. 9 The ranges of estimates ofupper-bound cancer potency calculated from the human and 10 animal data overlap. The range above is bounded on the upper end by the estimate of slope from 11 the Hamburg cohort epidemiology study and on the lower end by the estimates from the Ott and 12 Zober epidemiology study, with the NIOSH piece-wise linear epidemiology model and the 13 reanalyzed Kociba rat study falling intermediate in this range. Consequently, the Agency, 14 although fully recognizing this range and the public health-conservative nature of the slope 15 factors that make up the range, suggests the use of 1 x 10-3per pg TEQ/kg body weight/day as an 16 estimator ofupper-bound cancer risk for both background intakes and incremental intakes above 17 background. 18 This decision reflects the weight given to the individual estimates from the human studies 19 and the comparability ofthe revised estimate from the animal data. A recently published meta 20 analysis (Crump, 2003) is consistent with this estimate. In addition, this decision reflects the 21 judgment that, because ED0i estimates require little extrapolation from the range of observation 22 and current body burdens are within a factor of 10 of the ED estimates, use of a linear model is 23 both consistent with the data and unlikely to require more than an order of magnitude 24 extrapolation. This bounding on extrapolation would apply to both estimates of risk at current 25 background exposures and to additional increments above current background. Application of 26 upper-bound slope factors allows the calculation of a high-end bounding estimate of the 27 probability of cancer risk in the population. This means that there is greater than a 95% chance 28 that "true" population cancer risks will be less than the upper-bound estimate. 29 Use of the human ED0is rather than the LED0is to provide more likely upper-bound 30 estimates based on the available epidemiological data is a matter of EPA science policy and 31 compares well with upper-bound animal cancer data. Use of either ED or LED results in 32 slope factors and risk estimates that are within a factor of 2; well within the inherent uncertainty 33 of these estimates. Although there may be individuals within a population who may experience a 34 higher cancer risk on the basis of genetic factors or other determinants of cancer risk not 12/23/03 6-9 DRAFT--DO NOT CITE OR QUOTE 1 accounted for in epidemiologic data or animal studies, the vast majority of the population is 2 expected to have less risk per unit of exposure than the bounding estimate would suggest, and 3 some may have zero risk. 4 On the basis of these slope factor estimates (per pg TEQ/kg body weight/day), upper5 bound risks at average current background body burdens (5 ng TEQ/kg body weight) that result 6 from historical average intakes of approximately 3 pg TEQ/kg body weight/day may exceed 10-3 7 (1 in a 1000). A very small percentage of the population (< 1%) has estimated risks that are a 8 few times higher than an upper bound based on average intake if their individual cancer risk 9 slope is represented by the upper bound estimate and they are among the most highly exposed 10 (among the top 5%), based on dietary intake of dioxin and related compounds. This estimate of 11 the range of upper-bound risk for the general population has increased by approximately an order 12 of magnitude from the estimate described at background exposure levels in EPA's earlier draft of 13 this reassessment (10-4-10-3) (U.S. EPA, 1994). This has occurred because, despite the fact that 14 average intakes and body burdens are going down, estimates of upper-bound risk per unit dose 15 have gone up by a factor of approximately 6 over the Agency's 1985 estimate and the range of 16 exposure through the diet has been characterized. 17 EPA's approach to the development of an upper-bound estimate on cancer risk is 18 consistent with its own past practices described above and with FDA's approach. In its recent 19 report (U.S. EPA, 2001b), the SAB agreed that the treatment of the range of upper-bound risks 20 obtained for the general population in this assessment is consistent with past EPA practice. 21 FDA's past estimates of a risk-specific dose associated with a one-in-a-million risk (0.057 pg/kg 22 body weight/day) (FDA 1990) have been based on animal data and have differed from EPA's 23 only in minor ways regarding tumor counts and in the approach to cross-species scaling. In 1992, 24 while EPA's reassessment was underway, FDA's risk-specific dose was adopted by the U.S. 25 Public Health Service's Committee to Coordinate Environmental Health and Related Programs 26 (CCEHRP) as the risk-specific dose for TEQ. In 1998, ATSDR used this risk-specific dose as a 27 line of support for its policy guideline on dioxin and dioxin-like compounds in soil. 28 WHO and a number of individual countries have taken a different science-policy 29 approach and have treated dioxins as nongenotoxic carcinogens and assumed that a safety factor 30 approach, based on noncancer effects observed at lower doses than cancer in animals, would be 31 adequate to account for concerns for both cancer and noncancer effects. This approach assumes 32 that there is a virtual threshold for cancer effects above those for many noncancer effects. This 33 position has been reiterated as recently as June 2001 by the Joint FAO/WHO Expert Committee 34 on Food Additives (JECFA). The differences between EPA (plus a number of other U.S. federal 12/23/03 6-10 DRAFT--DO NOT CITE OR QUOTE 1 agencies) and these international organizations in their approach to assessing potential cancer 2 risk reflect differences in science policy. 3 Despite EPA's use of the epidemiology data to describe an upper bound on cancer risk, 4 the peer panels who met to review earlier drafts of the cancer epidemiology chapter suggested 5 that the epidemiology data alone were not adequate to support the characterization of dioxin and 6 related compounds as "known" human carcinogens but that the results from the human studies 7 were largely consistent with observations from laboratory studies of dioxin-induced cancer and, 8 therefore, should be weighed in the assessment. Other scientists, including those who attended 9 the peer panel meetings, felt either more or less strongly about the weight of evidence from 10 cancer epidemiology studies, representing the range of opinions that still exists on the 11 interpretation of these studies. Similar opinions were expressed in the comments documented in 12 the SAB's reports in 1995 and in 2001 (U.S. EPA, 1995, 2001b). 13 In its reevaluation of the cancer hazard of dioxin and related compounds, IARC (1997) 14 found that whereas the epidemiologic database for 2,3,7,8-TCDD was still "limited," the overall 15 weight of the evidence provided by human, animal and mechanistic data was sufficient to 16 characterize 2,3,7,8-TCDD as a Category 1 "known" human carcinogen. Other related members 17 of the class of dioxin-like compounds were considered to have "inadequate" epidemiologic data 18 to factor into hazard categorization. A similar classification of 2,3,7,8-TCDD as a "known" 19 carcinogen has been published within the context of the Department of Health and Human 20 Services' report on carcinogens (NTP, 2001). Here, too, the characterization is based on the 21 weight of the human, animal, and mode of action information in humans and animals. 22 Therefore, given that 2,3,7,8-TCDD is contained in complex mixtures of dioxin and 23 related compounds and that the TEQ approach has been adopted as a reasonable approach to 24 assessing risks of these complex mixtures, it is also reasonable to apply estimates of upper-bound 25 cancer potency derived from epidemiology studies where 2,3,7,8-TCDD was associated with 26 excess cancer risk to complex mixtures of dioxin and related compounds. 27 The current evidence suggests that both receptor binding and most early biochemical 28 events such as enzyme induction demonstrate linearity of dose-response within the range of 29 observation. The mechanistic relationship of these early events to the complex process of 30 carcinogenesis remains uncertain, although modes of dioxin action have been proposed. If these 31 findings imply low-dose linearity in biologically based cancer models under development, then 32 the probability of cancer risk may also be linearly related to exposure to TCDD. Until the 33 mechanistic relationship between early cellular responses and the parameters in biologically 12/23/03 6-11 DRAFT--DO NOT CITE OR QUOTE 1 based cancer models is better understood, the shape of the dose-response curve for cancer below 2 the range of observation can be inferred only with uncertainty. 3 Initial attempts to construct a biologically based model for certain dioxin effects as 4 described in this reassessment will need to be continued and expanded to accommodate more of 5 the available biology and to apply to a broader range of potential health effects associated with 6 exposure to dioxin-like compounds. Associations between exposure to dioxin and certain types 7 of cancer have been noted in occupational cohorts with average body burdens of TCDD 8 approximately one to three orders of magnitude (10 to 1000 times) higher than average TCDD 9 body burdens in the general population. In terms of TEQ, the average body burden in these 10 occupational cohorts level is within one to two orders of magnitude (10 to 100 times) of average 11 background body burdens in the general population (see Table 5-1 and Figure 5-2). Thus, there 12 is no need for large-scale, low-dose extrapolations when applying models based on curve-fitting 13 empirical data in order to evaluate background intakes and body burdens, and there are few if any 14 data to suggest large departures from linearity in this somewhat narrow window between the 15 lower end of the range of observation and the range of general population background exposures. 16 Nonetheless, the relationship of apparent increases in cancer mortality in these worker 17 populations to calculations of general population risk remains a source of uncertainty. 18 19 Use of a "margin of exposure" approach to evaluate risk for noncancer and cancer 20 endpoints. 21 The likelihood that noncancer effects may be occurring in the human population at 22 environmental exposure levels has received increased attention in recent years and is a major 23 focus of this reassessment. This likelihood is often evaluated using an MOE approach. An MOE 24 is calculated by dividing a "point of departure" at the low end of the range of observation in 25 human or animal studies (the human-equivalent LOAEL, NOAEL, BMD, or effective dose 26 [EDxx]) by the comparable surrogate of human exposure at the level of interest. It differs from a 27 reference dose (RfD), which establishes a level of exposure below which the Agency considers it 28 unlikely that any adverse effects will occur. The Agency has used the MOE approach for a 29 number of years in its noncancer assessment of the safety of pesticides. The MOE concept has 30 also been incorporated into the Draft Final Guidelinesfor Carcinogen Risk Assessment (U.S. 31 EPA, 2003) as an alternative approach to dose-response analysis if the shape of the dose32 response curve is uncertain. These draft cancer guidelines recommend differing approaches and 33 default assumptions for linear versus nonlinear cancer data, where linear data can be 34 approximated through the cancer slope factor and nonlinear data through an RfD and Hazard 12/23/03 6-12 DRAFT--DO NOT CITE OR QUOTE 1 Index approach. For both linear and nonlinear approaches to cancer characterization, the Agency 2 recommends a statement ofthe extent of extrapolation of risk estimates from observed data to 3 exposure levels of interest and its implications for certainty or uncertainty in quantifying risk. 4 The extent of this extrapolation can be expressed as a margin ofexposure (MOE). 5 As the exposure of interest approaches the range of observation of effects and MOEs get 6 smaller, reaching any conclusion regarding the certainty of no harm is much more difficult and 7 relies heavily on scientific judgment regarding the adequacy of the available data. In order for a 8 decision relying on the MOE to be adequately protective of health, information is provided to 9 allow the decisionmaker, to the extent information allows, to take into account the nature of the 10 effect at the POD; the shape and slope of the dose-response curve; the adequacy of the overall 11 database to assess human hazard; interindividual variability in the human population with regard 12 to exposure, metabolism, and toxic response; and other factors. Background exposures should be 13 factored into the calculation. Considering MOEs based on estimates of incremental exposure 14 alone divided by the human exposure of interest is not considered to give an accurate portrayal of 15 the implications of that exposure unless background exposures are insignificant. 16 One of the difficulties in assessing the potential health risk of exposure to dioxins is that 17 background exposures are often a significant component of total exposure when based on TEQ. 18 The average levels of background intake and current average body burdens of dioxin-like 19 compounds in terms of TEQs in the general population (1 pg TEQ/kg body weight/day and 5 ng 20 TEQ/kg body weight, respectively) are within a factor of 10 of human-equivalent levels 21 associated with NOELS, LOAELs, or ED values derived from studies in laboratory animals 22 exposed to TCDD or TCDD equivalents for both cancer and noncancer toxic effects (see Table 23 5-6 and Appendix A). Therefore, in many cases, the MOE compared to background using these 24 toxic endpoints is a factor of 10 or less. These estimates and others are presented and discussed 25 in Part II, Chapter 8. 26 As discussed in Chapter 8, these data, although variable, suggest that choosing a human27 equivalent body burden associated with an ED01value above 100 ng/kg as a point of departure 28 would likely yield a greater than 1% excess risk for some toxicity endpoint in humans. Also, 29 choosing a POD below 1ng/kg would likely be an extrapolation below the range of these data. 30 Given the nature of the data and the range of uncertainty around individual data sets, any choice 31 for a 1% effect point of departure in the middle range of 1ng/kg to 100 ng/kg would be 32 supported by the analyses, although the data provide the greatest support for defining a point of 33 departure consistent with principles of safety assessment in the range of 10 ng/kg to 50 ng/kg. 34 This range also includes body burdens consistent with the empirically derived NOAELs and 12/23/03 6-13 DRAFT--DO NOT CITE OR QUOTE 1 LOAELs for many of the effects that have traditionally been used as a POD for safety assessment 2 by WHO, JECFA, and ATSDR. 3 Although somewhat dependent on experimental design or the model chosen to derive the 4 ED0i, NOAEL, and LOAEL values, this range provides a perspective on the nature and variety of 5 effects that have been evaluated within approximately an order of magnitude, from biochemical 6 markers of exposure to more clearly adverse effects in animals. This range of body burdens 7 should also provide a useful point of comparison when evaluating impacts of risk management 8 on average body burdens in the general population or on estimates of impact of incremental 9 exposures above background on the range of individual body burdens at various ages. 10 Because of the relatively high background levels as compared to effect levels, the Agency 11 is not recommending the derivation of a reference dose (RfD) for dioxin and related compounds. 12 Although RfDs are often useful because they represent a health risk goal below which there is 13 likely to be no appreciable risk ofnoncancer effects over a lifetime of exposure, their primary use 14 by the Agency is to evaluate increments of exposure from specific sources when background 15 exposures are low. Any RfD that the Agency would recommend using a traditional approach for 16 setting an RfD using uncertainty factors to account for limitations of knowledge is likely to be 17 below--perhaps significantly below (by a factor of 10 or more)--current background intakes and 18 body burdens. Because exceeding the RfD is not a statement of risk, comparing an incremental 19 exposure to an RfD when the RfD has already been exceeded by average background exposures 20 has little value for evaluating possible risk management options. In addition, the calculation of 21 an RfD (with its traditional focus on a single "critical" effect) distracts from the large array of 22 effects associated with similar body burdens of dioxin. 23 The Agency's SAB, in its comments on an earlier draft of this document, remarked that 24 there might be value in calculating an RfD, despite a recognition of these concerns. The RfD 25 could be used for purposes of comparison with other chemical-specific RfDs, to ensure that 26 proper emphasis was given to noncancer effects and to set a goal for future exposure reductions. 27 These comments notwithstanding, the Agency feels that all of these ends can be accomplished 28 without the establishment of an RfD. 29 As discussed earlier, a range of values has been presented that indicates that dioxin and 30 related compounds can produce effects, some of which are indicative of a biological response to 31 dioxin exposure and some of which are arguably adverse, at or near current background body 32 burdens or intake levels. Several of the studies within this range could logically be chosen as the 33 "critical" effect upon which an RfD could be set. No one effect provides the obvious choice, as 34 evidenced by approaches taken by WHO, JECFA and ATSDR, all of which chose different 12/23/03 6-14 DRAFT--DO NOT CITE OR QUOTE 1 effects upon which to base their tolerable or minimal risk levels. A range of ED01s has been 2 described in Chapter 8 and a summary ofNOAELs, LOAELs, and ED0is for low-dose effects is 3 presented in Table 5-6 and Appendix A. 4 Depending on the choice of the endpoint, a composite uncertainty factor would need to be 5 determined in order to set an RfD. This composite uncertainty factor should account for, at a 6 minimum, pharmacodynamic aspects of cross-species scaling (traditionally, a factor of 7 3)--because pharmacokinetic factors are assumed to be accounted for by cross-species scaling on 8 the basis of body burden--and interindividual human variability (traditionally, a factor of 10). In 9 addition, selection of a LOAEL within the range would suggest an additional factor of 10 uncertainty as large as 10. Recently published results also indicate neurobehavioral impacts on 11 adult rats exposed perinatally at levels that yield body burden ED01s below current average 12 human body burdens and as low as the lowest noncancer effects previously evaluated 13 (Markowski et al., 2001). In addition, many of the developmental reproductive effects observed 14 in rats (Mably et al., 1992a-c) have EDmvalues less than current background exposures. These 15 results suggest that there may be additional database needs regarding risks to children. The 16 above considerations would traditionally yield a composite uncertainty factor in the range of 30 17 to 100 or more. 18 Coupled with the relatively narrow range of possible "critical" effects discussed above, 19 the range of plausible composite uncertainty factors make the selection of any particular value as 20 the Agency's RfD more difficult than usual and probably unnecessary, particularly in light of the 21 fact that any value that the Agency might choose using traditional approaches would be below 22 current background body burden or intake levels. 23 When evaluating incremental exposures associated with specific sources, knowing the 24 increment relative to background may help in understanding the impact of the incremental 25 exposure. For instance, it would be misleading to focus on only the incremental exposure in 26 evaluating the potential impact on human health when a relatively large background body burden 27 of dioxin already exists in the exposed population. In these circumstances, the incremental 28 exposure needs to be evaluated in the context of these background levels to aid in determining 29 whether these incremental exposures have regulatory significance. This approach would parallel 30 the Agency's approach to evaluating lead exposures. Other parallel science and management 31 issues between dioxin-like compounds and lead are under discussion within the Agency. 32 Providing guidance on the how to judge the significance of incremental increases to background 33 using the MOE approach is beyond the science scope of the reassessment and will have to be 34 addressed elsewhere by EPA. However, it is clear, in light of relatively high background 12/23/03 6-15 DRAFT--DO NOT CITE OR QUOTE 1 exposures, that the MOE approach is more useful than an RfD for characterizing dioxin 2 noncancer risks. 3 Other national and international bodies have chosen to define "safe" or "tolerable" levels 4 for dioxin and related compounds (e.g., WHO, 1998; ATSDR, 1999a; SCF, 2000). These 5 estimates cluster within a factor of 4 of current average intake levels, although estimates in the 6 past have spanned many orders of magnitude. Some commenters on earlier drafts of this 7 reassessment have suggested that EPA's approach is inconsistent with these efforts and overly 8 "conservative." Two distinctions can help in understanding these apparent differences. First, in 9 its reassessment, EPA has not tried to establish a tolerable or acceptable level ofrisk. Rather, it 10 has tried to provide a science-based description of hazard and potential risk without making a 11 policy judgment of acceptability. Second, whether one is providing a risk descriptor or an 12 acceptable risk determination, a number ofjudgments need to be made as one moves from 13 experimental observation to conclusion. Apparently subtle differences in these judgments can 14 result in significantly different conclusions. These differences in judgment fall into three major 15 areas: (1) the original focus on cancer rather than noncancer effects as the primary endpoint of 16 regulatory concern and the assumption by some that all nongenotoxic compounds have 17 thresholds below which cancer risk is minimal or nonexistent; (2) the use of intake as the cross 18 species dose metric despite the large difference in half-life in animals versus humans (for TCDD, 19 for instance, the difference between rats and humans is over a factor of 100); and (3) the size of 20 the "safety" factor or "uncertainty" factors used to derive a "safe or "tolerable" level. 21 The latter factor is currently the most widely divergent. More recent assessments have 22 taken noncancer endpoints into account and have applied a range of uncertainty factors. For 23 instance, ATSDR (1999a) set a minimal risk level (MRL), which is defined similarly to EPA's 24 RfD, for dioxin and related compounds of 1.0 pg TEQ/kg body weight/day. The ATSDR 25 assessment is based on the results of Schantz et al. (1992), a study that is included in Table 5-6 26 and Appendix A. ATSDR used intake as the interspecies dose metric and a composite 27 uncertainty factor of 90, accounting for intraindividual human variability (10), a minimal 28 LOAEL/NOAEL (3), and residual pharmacodynamic differences (3). 29 Hypothetically, had ATSDR relied on the TCDD body burdens measured during this 30 series of rhesus monkey experiments (see Bowman et al., 1989) and had all other factors been 31 equal, the MRL would likely have been determined to be in the range of 0.07 pg TEQ/kg body 32 weight/day (see Table 5-6 and Appendix A), or more than 10 times lower than the existing 33 ATSDR MRL and current average intake levels. The ATSDR assessment, however, selects a 12/23/03 6-16 DRAFT--DO NOT CITE OR QUOTE 1 single "critical" effect from among a number of choices and uses "traditional" uncertainty 2 factors, but it uses intake rather than body burden as the dose metric. 3 Several recent assessments have recognized the value of body burden rather than daily 4 intake as the preferred dose metric. WHO (1998) has set a tolerable daily intake (TDI) of 1-4 pg 5 TEQ/kg body weight/day using a range of effects and body burden and has indicated that, 6 although current exposures in that range are "tolerable" (a decision taking into account risk 7 management in addition to traditional hazard assessment), efforts should be made to ultimately 8 reduce intake levels to the lower end of the range and perhaps further. Findings in this 9 reassessment and comments made by the SAB (U.S. EPA, 2001b) are consistent with this 10 recommendation. The WHO assessment relied on an evaluation of the most sensitive effects that 11 are considered adverse (hormonal, reproductive, and developmental effects) and were seen at low 12 doses in animal studies (rats and monkeys). Body burden was used as a dose metric, and a 13 composite uncertainty of 10 was recommended to account for a number of factors, including the 14 use of a LOAEL rather than a NOAEL, differences in animal-to-human susceptibility, and 15 differences in half-lives of elimination for the different components of the TEQ mixture. 16 In May 2001, the European Commission Scientific Committee on Food (SCF, 2000) 17 established a tolerable weekly intake of 14 pg TEQ/kg body weight/week (equivalent to a TDI of 18 2 pg TEQ/kg body weight/day), based on several new studies, which are also now included in 19 EPA's range of low-dose effects, and on a composite uncertainty factor of 9.6. This factor 20 accounts for interindividual variability in toxicokinetics (a factor of 3.2) and marginal effects 21 close to a NOAEL (a factor of 3). The committee concluded that no uncertainty factor needed to 22 be applied for differences in toxicodynamics between experimental animals and humans and for 23 interindividual variation among humans. In June 2001, WHO JECFA determined a provisional 24 tolerable monthly intake (PTMI) of 70 pg TEQ/kg body weight/month (equivalent to 2.33 pg 25 TEQ/kg body weight/day), based on an approach similar to that used by the SCF. The same two 26 studies and safety factors of 3.2 or 9.6 were used, but two models were used to extrapolate the 27 maternal body burden at the NOEL/LOEL of the studies. The committee chose the PTMI as the 28 mid-point of the range ofvalues from its analysis. 29 It should be clear from the discussion above that there is a consensus that sensitive animal 30 responses falling within a relatively narrow range of body burdens can be used as a POD for 31 regulatory guidance, but the choice of individual studies varies. The EPA assessment is the only 32 one to bound the full range of effects (from arguably adaptive and questionably adverse to 33 arguably adverse to clearly adverse) observed through the application of a uniform modeling 34 approach, as well as through evaluating experimental LOAELs and NOAELs. There is also an 12/23/03 6-17 DRAFT--DO NOT CITE OR QUOTE 1 emerging consensus that body burden should often be used as a cross-species dose metric. This 2 has implications for ATSDR's current MRL derivation. Finally, there is no consensus on the size 3 or nature of uncertainty factors to be applied. Traditional approaches that might be applied by 4 EPA or that have been applied by ATSDR would likely require additional information to support 5 the choice or removal of uncertainty factors as performed by WHO, SCF, and JECFA. In 6 particular, the focus on accounting for residual toxicodynamic differences in cross-species 7 scaling and interindividual variability in the general population to account for sensitive 8 individuals, including children, would suggest larger uncertainty factors than have been proposed 9 by these groups if EPA were to set an RfD. 10 The choice of any composite uncertainty factor greater than 10 applied to effect levels 11 based on body burden in any of the analyses described above would result in TDIs or MRLs 12 below current background intakes. The use of uncertainty factors in the range of 30 to 100 or 13 more, as traditionally used by EPA, would result in values even further below some current 14 background body burdens or intake levels than the values presented by other organizations. 15 Given the range of choices for a POD, the range of potential composite uncertainty factors and 16 the uninformative nature of an RfD below current background levels, the Agency has chosen to 17 continue to focus on MOE analyses and to not establish an RfD for dioxin and related 18 compounds. 19 20 Children's risk from exposure to dioxin and related compounds may be increased, but 21 more data are needed to fully address this issue. 22 The issue of children's risk from exposure to dioxin-like compounds has been addressed 23 in a number of sections throughout this reassessment. Data suggest a sensitivity of response in 24 both humans and animals during the developmental period, both prenatal and postnatal. 25 However, these data are limited. Because evaluation of the impacts of early exposures on both 26 children's health and health later in life is important for a complete characterization of risk, 27 collection of additional data should be a high priority in order to reduce uncertainties in future 28 risk assessments. 29 Data from the Dutch cohort of children exposed to PCBs and dioxin-like compounds 30 suggest subtle impacts on neurobehavioral outcomes, thyroid function, and immune system 31 alterations from prenatal--and perhaps postnatal--exposure to 1980s background levels of 32 dioxin and related compounds. Although these effects cannot be attributed solely to dioxin and 33 related compounds, several associations suggest that these effects are, in fact, likely to be Ah34 mediated. An investigation of background dioxin exposure and tooth development was done in 12/23/03 6-18 DRAFT--DO NOT CITE OR QUOTE 1 Finnish children as a result of studies of dental effects in dioxin-exposed rats, mice, and 2 nonhuman primates and in PCB-exposed children. The Finnish investigators examined enamel 3 hypomineralization ofpermanent first molars in 6- and 7-year-old children. The length of time 4 that infants breast fed was not significantly associated with either mineralization changes or with 5 TEQ levels in the breast milk. However, when the levels and length of breast feeding were 6 combined in an overall score, a statistically significant association was observed. 7 In addition, effects have been seen in cases where significantly elevated exposure 8 occurred. The incidents at Yusho and Yu-Cheng resulted in increased perinatal mortality and 9 low birth weight in infants born to women who had been exposed. Rocker bottom heal was 10 observed in Yusho infants, and functional abnormalities have been reported in Yu-Cheng 11 children. The similarity of effects observed in human infants prenatally exposed to the complex 12 mixture in Yusho and Yu-Cheng and those reported in adult monkeys exposed perinatally to only 13 TCDD suggests that at least some of the effects on children are due to the TCDD-like congeners 14 in the contaminated rice oil ingested by the mothers of these children. The similar responses 15 include a clustering of effects in organs derived from the ectodermal germ layer, referred to as 16 ectodermal dysplasia, including effects on the skin, nails, and Meibomian glands, and 17 developmental and psychomotor delay during developmental and cognitive tests. 18 Some investigators believe that because all of the effects in the Yusho and Yu-Cheng 19 cohorts do not correlate with TEQ, some of the effects are due exclusively to nondioxin-like 20 PCBs or to a combination of all the congeners. In addition, on the basis of these data, the extent 21 of the association between overt maternal toxicity and embryo/fetal toxicity in humans is still not 22 clear. Further studies in the offspring as well as follow-up of the Seveso incident may shed 23 further light on this issue. In addition to the chloracne and acute responses to TCDD exposure 24 seen in Seveso children, elevated levels of serum GGT have been observed within a year after 25 exposure in some of the more highly exposed Seveso children. Long-term pathologic 26 consequences of elevated GGT have not been illustrated by excess mortality from liver disorders 27 or cancer or in excess morbidity, but further follow-up is needed. It must be recognized that the 28 absence of an effect thus far does not obviate the possibility that the enzyme levels increased 29 concurrently with the exposure but declined after cessation. The apparently transient elevations 30 in ALT levels among the Seveso children suggest that hepatic enzyme levels other than GGT 31 may react in this manner to TCDD exposure. Recent studies in Seveso have also demonstrated 32 an altered sex ratio in the second generation (Mocarelli et al., 2000). 33 Impacts on thyroid hormones provide an example of an effect of elevated postnatal 34 exposure to dioxin and related compounds. Several studies of nursing infants suggest that 12/23/03 6-19 DRAFT--DO NOT CITE OR QUOTE 1 ingestion of breast milk that has a higher dioxin TEQ may alter thyroid function. Thyroid 2 hormones play important roles in the developing nervous system of all vertebrate species, 3 including humans. In the United States, all infants are tested for hypothyroidism shortly after 4 birth. Results from the studies mentioned above suggest a possible shift in the population 5 distribution of thyroid hormone levels, particularly T4, and point out the need for collection of 6 longitudinal data to assess the potential for long-term effects associated with developmental 7 exposures. 8 A large number of studies in animals, including studies of single congeners and exposures 9 to complex mixtures, have addressed the question of effects of dioxin-like chemicals after in 10 utero or lactational exposure. However, the vast majority of the data are derived from studies of 11 2,3,7,8-TCDD, single congeners (e.g., PCB 77), or commercial mixtures of PCBs. Exposure 12 patterns have included single doses to the dams as well as dosing on multiple days during 13 gestation beginning as early as the first day of gestation. These studies are discussed in detail in 14 Part II, Chapter 5. The observed toxic effects include developmental toxicity, neurobehavioral 15 and neurochemical alterations, endocrine effects, and developmental immunotoxicity. For 16 instance, results of this body of work suggest that 2,3,7,8-TCDD clearly has the potential to 17 produce alterations in male reproductive function (rats, mice, hamsters), male sexual behavior 18 (rats), and female genitalia (rats, hamsters) after prenatal exposure. In addition, impacts on 19 neuromotor and cognitive behavior as well as on development of the immune system have been 20 indicated in a number of studies. 21 No epidemiological data and limited animal data are available to address the question of 22 the potential impact of exposure to dioxin-like compounds on childhood cancers or on cancers of 23 later life. The direct impacts of increased early postnatal exposure on the carcinogenic process 24 may be small, noting the limited impact of nursing on total body burden (see the discussion of 25 breast milk exposures and body burdens below), the assumption that cancer risk is a function of 26 average lifetime body burden, and the possibility that, because dioxin is a potent cancer promoter 27 rather than a direct initiator of the cancer process, exposures later in life might be more important 28 than those received earlier. However, recent studies of Brown et al. (1998) suggest that prenatal 29 exposure of rats to dioxin and related compounds may indirectly enhance their sensitivity as 30 adults to chemical carcinogenesis from other chemical carcinogens. Further work is needed to 31 evaluate this issue. 32 Fetuses, infants, and children are exposed to dioxins through several routes. The fetus is 33 exposed in utero to levels of dioxin and related compounds that reflect the body burden of the 34 mother. It is important to recognize that the greatest impact on the mother's body burden is from 12/23/03 6-20 DRAFT--DO NOT CITE OR QUOTE 1 of her lifetime exposure history rather than from the individual meals she eats during pregnancy. 2 Good nutrition, including a diet with appropriate levels of fat, has consequences on dietary intake 3 and consequent body burdens of dioxin and related compounds. Nursing infants represent 4 special cases because for a limited portion of their lives they may have elevated exposures on a 5 body-weight basis when compared with non-nursing infants and with adults (see discussion 6 below). 7 In addition to breast milk exposures, intakes of CDD/CDFs and dioxin-like PCBs are 8 more than three times higher for a young child than for an adult, on a body-weight basis. Table 9 4-7 in Section 4 of this document describes the variability in average intake values as a function 10 of age using age-specific food consumption rates and average food concentrations, as was done 11 for adult intake estimates. However, as with the nursing infants, the differences in body burden 12 between children and adults are expected to be much less than the differences in daily intake. 13 Assuming that body burden is the relevant dose metric for most if not all effects, there is some 14 assurance that these short-term increased intake levels will have limited additional impact on risk 15 as compared with overall lifetime exposure. 16 17 Background exposures to dioxin and related compounds need to be considered when 18 evaluating both hazard and risk. 19 The term "background exposure" has been used throughout this reassessment to describe 20 exposure of the general population to environmental media (food, air, soil, etc.) that have dioxin 21 concentrations within the normal background range. Adult daily intakes of CDD/CDFs and 22 dioxin-like PCBs are estimated to average 43 and 23 pg TEQDFP-WHO98/day, respectively, for a 23 total intake of 66 pg/day TEQDFP-WHO98. On a body-weight basis, this corresponds to 24 approximately 1pg TEQDFP-WHO98/kg-day. Daily intake is estimated by combining exposure 25 media concentrations (food, soil, air) with contact rates (ingestion, inhalation). Table 4-6 26 summarizes the intake rates derived by this method. The intake estimate is supported by an 27 extensive database on food consumption rates and food data. Pharmacokinetic modeling 28 provides further support for the intake estimates. Current adult tissue levels reflect intakes from 29 past exposure levels, which are thought to be higher than current levels. 30 CDD/CDF and dioxin-like PCB intakes for the general population may extend to levels at 31 least three times higher than the mean. Variability in general population exposure is primarily a 32 result of differences in the dietary choices that individuals make in terms of both quantity and 33 types of food consumed. A diet that is disproportionately high in animal fats will result in an 34 increased background exposure over the mean. Data on the variability of fat consumption 12/23/03 6-21 DRAFT--DO NOT CITE OR QUOTE 1 indicate that the 95thpercentile is about twice the mean and the 99thpercentile is approximately 2 three times the mean. Additionally, a diet that substitutes meat sources that are low in dioxin 3 (e.g., beef, pork, or poultry) with sources that are high in dioxin (e.g., freshwater fish) could 4 result in elevated exposures. 5 Evidence of widespread background exposure can also be seen by examining data on 6 human tissue. These data indicate that the average CDD/CDF tissue level for the general adult 7 U.S. population appears to be declining. A pharmacokinetic modeling evaluation of this 8 declining trend suggests that the CDD/CDF tissue level will drop below 10 ppt TEQDF-WHO98, 9 lipid basis, by 2030 (Lorber, 2002). The best estimate of current (mid to late 1990s) levels is 25 10 ppt (TEQDFP-WHO98, lipid basis). The tissue samples collected in North America in the late 11 1980s and early 1990s showed an average TEQDFP-WHO98level of about 55 pg/g lipid. This 12 finding is supported by a number of studies, all conducted in North America, that measured 13 dioxin levels in adipose tissue, blood, and human milk. However, the number of people in most 14 of these studies is relatively small, and the participants were not statistically selected in ways that 15 ensured their representativeness of the general U.S. adult population. One study, the 1987 16 National Human Adipose Tissue Survey (NHATS), involved more than 800 individuals and 17 provided broad geographic coverage, but it did not address coplanar PCBs. Similar tissue levels 18 of these compounds were measured in Europe and Japan during similar time periods. 19 Because dioxin levels in the environment have been declining since the 1970s, it is 20 reasonable to expect that levels in food, human intake, and, ultimately, human tissue have also 21 declined over this period. The changes in tissue levels are likely to lag the decline seen in 22 environmental levels, and the changes in tissue levels cannot be assumed to occur proportionally 23 with declines in environmental levels. CDC (2000) summarized levels of CDDs, CDFs, and 24 PCBs in human blood collected between 1995 and 1997. The individuals sampled were all U.S. 25 residents who had no known exposures to dioxin other than normal background. The blood was 26 collected in six different locations from 316 individuals ranging in age from 20 to 70 years. All 27 TEQ calculations were made assuming that nondetects were equal to half the detection limit. 28 Although these samples were not collected in a manner that can be considered statistically 29 representative of the national population and they lack wide geographic coverage, they are judged 30 to provide a better indication of current tissue levels in the United States than the earlier data (see 31 Table 4-5). 32 PCBs 105, 118, and 156 are missing from the blood data for the comparison populations 33 reported by CDC (2000). These congeners account for 62% of the total PCB TEQ estimated in 34 the early 1990s. Assuming that the missing congeners from the CDC study data contribute the 12/23/03 6-22 DRAFT--DO NOT CITE OR QUOTE 1 same proportion to the total PCB TEQ as in earlier data, they would increase the estimate of 2 current body burdens by another 3.3 pg TEQ/g lipid, for a total PCB TEQ of 5.3 pg/g lipid and a 3 total TEQdfp-WHO98of 25.4 pg/g lipid. 4 As noted, characterizing national background levels of dioxins in tissues is uncertain 5 because the current data cannot be considered statistically representative of the general 6 population. The task is also complicated by the fact that tissue levels are a function of both age 7 and birth year. Because intake levels have varied over time, the accumulation of dioxins in a 8 person who turned 50 in 1990 is different from that in a person who turned 50 in 2000. Future 9 surveys should help to characterize national levels of CDD/CDF/PCBs during the last years of 10 the 20thcentury and into the 21st century. The National Health and Nutrition Examination Survey 11 (NHANES) conducted in 1999-2000 included measurements of dioxin blood levels in 1921 12 individuals, aged 12 and higher, from numerous locations around the country (CDC, 2003). 13 Unfortunately, not enough blood serum was available per individual to be able to quantify the 14 dioxin concentrations at low background levels, so the majority of measurements were 15 nondetects. An effort is currently underway to pool remaining NHANES 1999-2000 samples and 16 reanalyze them. This will allow for an estimate of average background body burdens of dioxin 17 like compounds representative of the turn of the century, and in future years should provide a 18 picture of dioxin levels in the general U.S. population. 19 As described above, current intake levels from food sources are estimated in this 20 reassessment to be approximately 1pg TEQ/kg body weight/day. Certain segments of the 21 population may be exposed to additional increments of exposure by being in proximity to point 22 sources or because of dietary practices. These types of exposure are described below. 23 24 Evaluating the exposure of "special" populations and developmental stages is critical to 25 risk characterization. 26 As discussed above, background exposures to dioxin-like compounds may extend to 27 levels at least three times higher than the mean. This upper range is assumed to result from the 28 normal variability of diet and human behaviors. Exposures from local elevated sources or unique 29 diets would be added to this background variability. Elevated exposures may occur in small 30 segments of the population, such as individuals living near discrete local sources or subsistence 31 or recreational fishers. Nursing infants represent a special case. For a limited portion of their 32 lives, they may have elevated exposures on a body-weight basis when compared to non-nursing 33 infants and to adults. This exposure will be discussed in a separate section. 12/23/03 6-23 DRAFT--DO NOT CITE OR QUOTE 1 Dioxin contamination incidents involving the commercial food supply have occurred in 2 the United States and other countries. For example, in the United States, contaminated ball clay 3 was used as an anticaking agent in soybean meal, resulting in elevated dioxin levels in some 4 poultry and catfish. This incident involved only a small fraction of national poultry production 5 and the practice has since been eliminated. Elevated dioxin levels have also been observed in a 6 few beef and dairy animals, where the contamination was associated with contact with 7 pentachlorophenol-treated wood. This type of elevated exposure was not detected in the national 8 beef survey; consequently, its occurrence is likely to be low, although it has not been determined. 9 These incidents may have led to small increases in dioxin exposure to the general 10 population; however, it is unlikely that they have led to disproportionate exposures to 11 populations living near where they occurred because, in the United States, meat and dairy 12 products are highly distributed on a national scale. If contamination events were to occur in 13 foods that are predominantly distributed on a local or regional scale, then such events could lead 14 to higher exposure among local populations. 15 Elevated exposures associated with the workplace or with industrial accidents have also 16 been documented. U.S. workers in certain segments of the chemical industry had elevated levels 17 of TCDD exposure, with some tissue measurements in the thousands of parts per trillion TCDD. 18 There is no clear evidence that elevated exposures are currently occurring among U.S. workers. 19 Documented examples of past exposures for other groups include certain Air Force personnel 20 exposed to Agent Orange during the Vietnam War and individuals exposed as a result of 21 industrial accidents in Europe and Asia. 22 The discussion in Section 4.5 identified the general population distribution of exposure as 23 extending up to roughly three times the mean. Most people will have exposures within this range 24 even if they have unusual diets in terms of meat and dairy products because most people eat food 25 from multiple sources, which tends to average out the contamination levels, and meat and dairy 26 products have similar dioxin levels, so substitution of one type of meat for another should not 27 have a great impact on total exposure. Clearly elevated exposures are possible in unusual 28 situations where an individual consumes high quantities of meat or dairy products that have 29 significantly increased dioxin levels. Elevated exposures resulting from fish consumption can 30 occur in different situations because concentrations in freshwater fish are significantly greater 31 than in meat and dairy products. Therefore, people who consume large quantities of freshwater 32 fish at background contamination levels may have intakes elevated above the general population 33 distribution. 12/23/03 6-24 DRAFT--DO NOT CITE OR QUOTE 1 Consumption of fish, meat, or dairy products containing elevated levels of dioxins and 2 dioxin-like PCBs can lead to elevated exposures in comparison to the general population. Most 3 people eat some fish from multiple sources, both fresh and salt water. If individuals obtain their 4 fish from areas where the concentration ofdioxin-like chemicals is elevated, they may constitute 5 a highly exposed subpopulation. Although this scenario seems reasonable, very little supporting 6 data could be found for such a highly exposed subpopulation in the United States. One study that 7 measured dioxin-like compounds in blood of sports fishers in the Great Lakes area showed 8 elevations over mean background but within the range ofnormal variability. 9 Another study that measured 90 PCB congeners--of which 7 were dioxin-like mono 10 ortho PCBs (although PCB 126 was not measured)--in Lake Michigan "sport-fish eaters" 11 showed a significant elevation in these PCBs versus a control group (little or no sport fish 12 consumption). Significantly elevated concentrations of dioxins, furans, and coplanar PCBs were 13 measured in Great Lakes fish by the Ontario Ministry of the Environment, although this study 14 was conducted in known or suspected hot spots for the purpose of setting consumption 15 advisories. It is not known to what extent individuals would be consuming fish at the high 16 concentrations measured. Elevated CDD/CDF levels in human blood have been measured in 17 Baltic fishermen. Similarly, elevated levels of coplanar PCBs have been measured in the blood 18 of fishers on the north shore of the Gulf of the St. Lawrence River who consume large amounts 19 of seafood. 20 High exposures to dioxin-like chemicals as a result of consuming meat and dairy products 21 would most likely occur in situations where individuals consume large quantities of these foods 22 and the level of these compounds is elevated. Most people eat meat and dairy products from 23 multiple sources, and even if large quantities are consumed, unusually high exposures are not 24 likely. Individuals who raise their own livestock for basic subsistence have the potential for 25 higher exposures if local levels of dioxin-like compounds are high. One study in the United 26 States showed elevated levels in chicken eggs near a contaminated soil site. European studies at 27 several sites have shown elevated CDD/CDF levels in milk and other animal products near 28 combustion sources. 29 In summary, in addition to general population exposure, some individuals or groups of 30 individuals may also be exposed to dioxin-like compounds from local discrete sources or 31 pathways within their environment. Examples of these "special" exposures include 32 contamination incidents, occupational exposures, direct or indirect exposure to local populations 33 from discrete sources, or exposures to subsistence or recreational fishers. 34 12/23/03 6-25 DRAFT--DO NOT CITE OR QUOTE 1 Breast-feeding infants have higher intakes of dioxin and related compounds for a short but 2 developmentally important part of their lives; however, the benefits of breast feeding are 3 widely recognized to outweigh the risks. 4 Three studies have compared dioxins in infants who were breast fed with those who were 5 formula fed, and all have shown elevations in the concentrations of dioxins in infants being 6 breast fed. Formula-fed infants had lipid-based concentrations < 5 ppt TEQDF-WHO98, whereas 7 breast-fed infants had average lipid-based concentrations > 20 ppt TEQDF-WHO98. A similar 8 disparity is seen in more limited data on dioxin-like PCBs. 9 The dose to the infant varies as a function of infant body weight, the concentration of 10 dioxins in the mother's milk, and the trend of dioxins in the mother's milk to decline over time. 11 Using typical values for these parameters, dioxin intakes at birth were estimated to equal 242 pg 12 TEQDFP-WHO98/kg/day, which would drop to 18 pg TEQDFP-WHO98/kg/day after 12 months. The 13 average infant dose over a year was calculated to be 87 pg TEQDFP-WHO98/kg/day. Although this 14 dose exceeds the currently estimated adult dose of 1pg TEQDFP-WHO98/kg/day, the effect on 15 infant body burdens is expected to be less dramatic, that is, infant body burdens will not exceed 16 adult body burdens by 87 times. This is due to the rapidly expanding infant body weight and 17 lipid volume, the decrease in concentration of dioxins in the mother's milk over time, and more 18 rapid elimination in infants. 19 A pharmacokinetic exercise comparing 6-month, 1-year, and 2-year nursing scenarios 20 with formula feeding showed peak infant lipid concentrations of 44 ppt TEQDFP-WHO98at 9 21 weeks of age, compared with peak lipid concentrations of less than 10 ppt for the formula-fed 22 infants and average adult lipid concentrations of 25 ppt TEQDFP-WHO98. The dioxin 23 concentrations in breast-fed and formula-fed children were predicted to merge at about 10 years 24 of age, at a lipid concentration of about 13 ppt TEQDFP-WHO98. Breast feeding for 1year was 25 predicted to result in a lifetime accumulated exposure about 13% higher as compared to formula 26 feeding only. 27 The American Academy of Pediatrics (1997) has made a compelling argument for the 28 diverse advantages of breast feeding for infants, mother, families, and society. These include 29 health, nutritional, immunologic, developmental, psychological, social, economic, and 30 environmental benefits. Breast milk is the point of comparison for all infant food, and the breast 31 fed infant is the reference for evaluation of all alternative feeding methods. In addition, 32 increasing the rates ofbreast-feeding initiation is a national health objective and one of the goals 33 of the United States Government's Healthy People 2010. WHO (1988) maintained that the 12/23/03 6-26 DRAFT--DO NOT CITE OR QUOTE 1 evidence did not support an alteration of its recommendations that promote and support breast 2 feeding. A more recent consultation in 1998 (WHO, 2000) reiterated these conclusions. 3 Although it is important that the recommendations of these groups continue to be 4 reevaluated in light of emerging scientific information, the Agency does not believe that the 5 findings contained in this reassessment provide a scientific basis for initiating such a 6 reevaluation. This conclusion is based on the fact that stronger data have been presented that 7 body burden, not intake, is the best dose metric; that many of the noncancer effects, particularly 8 those seen in children, are more strongly associated with prenatal exposure and the mother's 9 body burden than with postnatal exposures and breast milk levels; and that dioxin-like 10 compounds are strong promoters of carcinogenicity, a mode of action that depends on late-stage 11 impacts rather than on early-stage impacts on the carcinogenic process. 12 13 Many dioxin sources have been identified and emissions to the environment are being 14 reduced. 15 Current emissions of CDDs/CDFs/PCBs to the United States environment result 16 principally from anthropogenic activities. Evidence for this finding includes matches in time of 17 the rise of environmental levels with the rise in general industrial activity (see discussion in 18 Section 4.1), lack of any identified large natural sources, and observations of higher 19 CDD/CDF/PCB body burdens in industrialized versus less industrialized countries (see 20 discussion on human tissue levels in Section 4.4). 21 The principal identified sources of environmental releases are (1) combustion and 22 incineration sources; (2) chemical manufacturing/processing sources; (3) industrial/municipal 23 processes; (4) biological and photochemical processes; and (5) reservoir sources. Development 24 of national estimates of annual environmental releases to air, water, and land is complicated by 25 the fact that only a few facilities in most industrial sectors have been evaluated for CDD/CDF 26 emissions. Thus, an extrapolation is needed to estimate national emissions. The extrapolation 27 method involves deriving an estimate of emissions per unit of activity (i.e., an emission factor) at 28 the tested facilities and multiplying this by the total activity level in the untested facilities. 29 In order to convey the level of uncertainty in both the measure of activity and the 30 emission factor, EPA developed a qualitative confidence rating scheme. The confidence rating 31 scheme, presented in Section 4, Table 4-1, uses qualitative criteria to assign a high, medium, or 32 low confidence rating to the emission factor and activity level for those source categories for 33 which emission estimates can be reliably quantified. The dioxin reassessment has produced an 34 inventory of source releases for the United States (Table 4-2). The inventory is limited to 12/23/03 6-27 DRAFT--DO NOT CITE OR QUOTE 1 sources whose releases can be reliably quantified (i.e., those with confidence ratings of A, B, or 2 C, as defined in Table 4-1). The inventory presents the environmental releases in terms of two 3 reference years: 1987 and 1995. For both of these periods, emissions from combustion and 4 incineration sources dominated total releases. EPA's best estimates of releases of CDD/CDFs to 5 air, water, and land from reasonably quantifiable sources were approximately 3300 g (7 pounds) 6 TEQDF-WHO98in 1995 and 14,000 g (31 pounds) TEQDF-WHO98in 1987. The decrease in 7 estimated releases of CDD/CDFs between 1987 and 1995 (approximately 76%) was due 8 primarily to reductions in air emissions from municipal and medical waste incinerators. 9 Although this inventory is one of the most comprehensive and well-documented in the 10 world, it is likely to underestimate total releases because a number of known sources lacked 11 sufficient data to be included in the inventory and the possibility remains that truly unknown 12 sources exist. 13 Further reductions in environmental releases since the inventory for 1995 can be 14 anticipated as a result of EPA regulations for waste combustion sources and pulp and paper 15 facilities. EPA's regulatory programs estimate that, under full compliance with these regulations, 16 an additional 1800 g I-TEQ reduction in CDD/CDF emissions should occur. With these 17 anticipated emission reductions, uncontrolled burning of household waste would become the 18 largest quantifiable source. Although the full magnitude of reservoir releases remains uncertain, 19 their relative contribution to total annual releases be can reasonably anticipated to increase as 20 contemporary formation sources continue to decrease. 21 No significant release of newly formed dioxin-like PCBs is occurring in the United 22 States. Unlike CDD/CDFs, PCBs were intentionally manufactured in the United States in large 23 quantities from 1929 until production was banned in 1977. Although it has been demonstrated 24 that small quantities of coplanar PCBs can be produced during waste combustion, no strong 25 evidence exists that the dioxin-like PCBs make a significant contribution to TEQ releases during 26 combustion. The occurrences of dioxin-like PCBs in the U.S. environment most likely reflect 27 past releases associated with PCB production, use, and disposal. Further support for this finding 28 is based on observations of reductions since the 1980s in PCBs in Great Lakes sediment and in 29 other areas. 30 As described in Section 4.1, combustion appears to be the most significant process of 31 CDD/CDF formation today. Important factors that can affect the rate of dioxin formation include 32 overall combustion efficiency, post-combustion flue gas temperatures and residence times, and 33 the availability of surface catalytic sites to support dioxin synthesis. Although chlorine is an 34 essential component for the formation of CDDs/CDFs in combustion systems, the empirical 12/23/03 6-28 DRAFT--DO NOT CITE OR QUOTE 1 evidence indicates that, for commercial-scale incinerators, chlorine levels in feed are not the 2 dominant controlling factor for rates of CDD/CDF stack emissions. The conclusion that chlorine 3 in feed is not a strong determinant of dioxin emissions applies to the overall population of 4 commercial scale combustors. For any individual commercial-scale combustor, circumstances 5 may exist in which changes in chlorine content of feed could affect dioxin emissions. For 6 uncontrolled combustion, such as open burning of household waste, chlorine content of wastes 7 may play a more significant role than commercial-scale combustors in levels of dioxin emissions. 8 9 Dioxins are widely distributed in the environment at low concentrations, primarily as a 10 result of air transport and deposition. 11 The dioxin-like compounds are essentially insoluble in water, they are generally classified 12 as semivolatile, and they tend to bioaccumulate in animals. Once introduced into the 13 environment, they are widely distributed in the environment as a result of a number of physical 14 and biological processes. There is some evidence that these compounds can degrade in the 15 environment, but in general they are considered very persistent and relatively immobile in soils 16 and sediments. 17 The dioxin-like compounds are transported through the atmosphere as vapors or attached 18 to airborne particulates and they can be deposited on soils, plants, or other surfaces (by wet or dry 19 deposition). 20 They enter water bodies primarily via direct deposition from the atmosphere or by surface 21 runoff and erosion. From soils, these compounds can reenter the atmosphere as resuspended soil 22 particles or as vapors. In water, they can be resuspended into the water column from sediments, 23 volatilized out of the surface waters into the atmosphere, or buried in deeper sediments. 24 Immobile sediments appear to serve as permanent sinks for the dioxin-like compounds. 25 Anthropogenic materials (such as pentachlorophenol), although not always considered an 26 environmental compartment, may also contain these compounds, and they have the potential to 27 be released from these materials into the broader environment. 28 The two primary pathways by which dioxin-like compounds enter the ecological food 29 chains and human diet are air to plant to animal and water/sediment to fish. Vegetation receives 30 these compounds via atmospheric deposition in the vapor and particle phases. The compounds 31 are retained on plant surfaces and bioaccumulated in the fatty tissues of animals that feed on 32 these plants. In the aquatic food chain, dioxins enter water systems via direct discharge or 33 deposition and runoff from watersheds. Fish accumulate these compounds through direct contact 12/23/03 6-29 DRAFT--DO NOT CITE OR QUOTE 1 with water, suspended particles, and bottom sediments and through the consumption of aquatic 2 organisms. 3 Although these two pathways are thought to normally dominate contribution to the 4 commercial food supply, others can also be important. Animal feed contamination episodes have 5 led to elevations of dioxins in poultry in the United States, in milk in Germany, and in meat/dairy 6 products in Belgium. Gaining a quantitative understanding of how dioxin moves in the 7 environment will be particularly important in understanding the relative contributions of 8 individual point sources to the food chain and assessing the effectiveness of control strategies to 9 reduce human exposure. Although the emissions inventory shows the relative contribution of 10 various sources to total emissions, it is unlikely that these sources make the same relative 11 contributions to human exposure. 12 It is quite possible that the major contributors of dioxin to food may not be those sources 13 that represent the largest fractions of total emissions in the United States (see discussion in 14 Section 4.4 indicating that the diet is the dominant exposure pathway for humans). The 15 geographic locations of sources relative to the areas from which much of the beef, pork, milk, 16 and fish are produced should be considered. Most of the agricultural areas that produce dietary 17 animal fats are not located near or directly downwind of the major sources of dioxin and related 18 compounds. 19 The contribution of reservoir sources to human exposure is likely to be significant. 20 Several factors support this finding. First, human exposure to the dioxin-like PCBs is thought to 21 be derived almost completely from reservoir sources. Because approximately one-third of 22 general population TEQ intake is due to PCBs, then at least one-third of the calculated overall 23 risk from dioxin-like compounds comes from reservoir sources. Second, CDD/CDF releases 24 from soil via soil erosion and runoff to waterways appear to be greater than releases to water 25 from the primary sources included in the inventory. CDD/CDFs in waterways can bioaccumulate 26 in fish, leading to human exposure via consumption of fish. This suggests that a significant 27 portion of the CDD/CDF TEQ exposure could be due to releases from the soil reservoir. Finally, 28 soil reservoirs could have vapor and particulate releases that deposit on plants and enter the 29 terrestrial food chain. However, the magnitude of this contribution is unknown. Collectively, 30 these three factors suggest that reservoirs are a significant source of current background TEQ 31 exposure, perhaps contributing half or more of the total. 32 12/23/03 6-30 DRAFT--DO NOT CITE OR QUOTE 1 Environmental levels, emissions, and human exposures have declined during recent 2 decades. 3 The most compelling supportive evidence of a general decline in environmental levels for 4 CDD/CDF/PCBs comes from dated sediment core studies. CDD/CDF/PCB concentrations in 5 sediments began to increase around the 1930s and continued to increase until about 1970. 6 Decreases began in 1970 and have continued to the time of the most recent sediment samples 7 (about 1990). Sediment studies in lakes located in several European countries have shown 8 similar trends. 9 It is reasonable to assume that sediment core trends are driven by a similar trend in 10 emissions to the environment. The period of increase generally matches the time when a variety 11 of industrial activities began rising, and the period of decline appears to correspond with growth 12 in pollution abatement. Decreases in dioxin emissions will presumably have resulted from many 13 of these abatement efforts, which included elimination of most open burning, particulate controls 14 on combustors, phase-out of leaded gas, and bans on PCBs, 2,4,5-T, hexachlorophene and 15 restrictions on the use of pentachlorophenol. Also, the national source inventory of this 16 assessment documented a significant decline in emissions from the late 1980s to the mid-1990s. 17 Evidence of declines in human exposure can be inferred from the overall declines in 18 environmental levels and emissions, and it is directly supported by limited data on concentrations 19 in food and human tissues (see Sections 4.3 and 4.4). Because of the lag between environmental 20 levels and body burdens, it is anticipated that further declines in tissue concentrations should 21 occur as individuals with higher body burdens from past exposure age out of the population. A 22 pharmacokinetic modeling exercise suggested that levels of TEQDF-WHO98in the U.S. 23 population should decline from levels of about 20 ppt lipid-basis measured in the mid-1990s 24 CDC study to below 10 ppt lipid-basis by 2030. This analysis includes CDD/CDFs only, not 25 PCBs. Dioxin-like PCBs currently make up approximately 20% of the current total TEQ body 26 burden but may increase in percentage as CDD/CDFs decline. This modeling result is based on 27 the assumption that current CDD/CDF intakes remain the same into the 21st century. 28 29 Risk Characterization Summary Statement 30 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD; "dioxin") is highly toxic to many animal 31 species, producing a variety of noncancer and cancer effects. Other 2,3,7,8-substituted 32 polychlorinated dibenzo-p-dioxins and dibenzofurans and coplanar polychlorinated biphenyls 33 (PCBs) exhibit similar effects, albeit at different doses and with different degrees of confidence 34 in the database. 12/23/03 6-31 DRAFT--DO NOT CITE OR QUOTE 1 The similarities in toxicity between species and across different dioxin congeners stem 2 from a common mode of action via initial binding to the aryl hydrocarbon (AhR) receptor. This 3 common mode of action is supported by the consistency in effects evident from multiple 4 congener databases, although uncertainty remains due to data gaps for some congeners. The 5 databases supportive of dioxin-like toxicity, both cancer and noncancer, are strongest for those 6 congeners that are the major contributors to the risk to human populations. This has led to an 7 international scientific consensus that it is prudent science policy to use the concept of toxic 8 equivalency factors (TEFs) to sum the contributions of individual PCDD, PCDF, and coplanar 9 PCB congeners with dioxin-like activity. 10 In addressing receptor-mediated responses resulting from complex mixtures of dioxin 11 like congeners, this assessment has provided a basis for the use of integrated measures of dose 12 such as lifetime average body burden as more appropriate default metrics than average lifetime 13 daily intake. Although average body burden over a lifetime appears to be the most useful dose 14 metric for chronic effects, average body burden during the window of sensitivity may be the most 15 appropriate metric for developmental effects. The Agency recognizes, therefore, that the final 16 choice of the appropriate metric may depend on the endpoint under evaluation. 17 Dioxin and related compounds have been shown to be developmental, reproductive, 18 immunological, endocrinological, and cancer hazards, among others in multiple animal species. 19 There is no reason to expect, in general, that humans would not be similarly affected at some 20 dose, and indeed, a growing body of data supports this assumption. On the basis of the animal 21 data, current margins of exposure are lower than generally considered acceptable, especially for 22 more highly exposed human populations. The human database supporting this concern for 23 potential effects near background body burdens is less certain. Occupational and industrial 24 accident cohorts exposed at higher levels show correlations with exposure for cancer and a 25 number ofnoncancer effects consistent with those seen in the animal studies. 26 For cancer outcomes, the epidemiological evidence provides consistent findings of 27 statistically significant elevations, with dose-response trends for all cancers combined and lung 28 cancer risk in occupational cohorts along with evidence of possible additional tissue-specific 29 cancer rate elevations. Given this substantial yet still not definitive epidemiological data, the 30 positive cancer bioassays at multiple sites and in all animal species tested, in vitro studies, and 31 the mechanistic considerations common to animals and humans for dioxin carcinogenicity, EPA 32 characterizes 2,3,7,8-tetrachlorodibenzo-p-dioxin as "carcinogenic to humans." On the basis of 33 similarities of response in multiple positive animal bioassays for non-TCDD congeners and 34 mixtures, mode of action studies, and consistent with the concept of toxic equivalency, complex 35 mixtures of dioxin and related compounds are considered highly potent "likely" carcinogens. 12/23/03 6-32 DRAFT--DO NOT CITE OR QUOTE 1 The calculated body burdens of dioxin and dioxin-like substances leading to an estimated 2 1% increase (ED0i) in the lifetime risk of cancer in the three occupational studies with the best 3 exposure information fall within a 10-fold range, and those calculated from the animal bioassay 4 data fall in the middle of this range. The ED0i for all cancers combined from the three 5 occupational cohorts range from 6 to 62 ngTCDD/kg body weight (excluding the NIOSH power 6 model calculation), depending on the study and the model used. By comparison, current 7 background body burdens in the United States are approximately 5 ngTEQ/kg body weight, 8 suggesting little margin of exposure (MOE) at today's body burden levels. 9 From these same occupational and animal cancer studies, EPA estimates an upper bound 10 on the lifetime risk of all cancers combined of 1 x 10-3per pgTEQ/kg/day. This cancer slope 11 factor is based on a statistical estimate of risks from occupational exposures--principally to 12 healthy, adult, male workers--and it must be coupled with a recognition that a small number of 13 people may be both more susceptible and consume up to three times the average level of fat per 14 day (the principal exposure pathway for dioxins in the general population). Conversely, this risk 15 estimate is based on assumptions that the extra cancer risk seen in the occupational cohorts is 16 attributable to dioxin and not other chemical agents present; that the appropriate metric for 17 cancer risk is lifetime average body burden and not a measure of peak exposure, which would 18 tend to mitigate risks at low exposures; and that the dose-response model curve continues below 19 the range of statistically significant data and does not then exhibit some nonlinearity. Using the 20 best available estimates of cancer risks, the upper bound on general population lifetime risk for 21 all cancers might be on the order of 1 in 1000 or more. Upper-bound risk estimates allow the 22 calculation of the high end of the probability of cancer risk in the population. This means that 23 there is greater than a 95% chance that cancer risks will be less than the upper bound, and it 24 could be as low as zero in some individuals. 25 For noncancer effects, EPA generally calculates an RfD/RfC value that represents an 26 estimate (with uncertainty spanning perhaps an order of magnitude) of a daily exposure to the 27 human population (including sensitive subgroups) that is likely to be without an appreciable risk 28 of deleterious effects during a lifetime. RfD/RfCs are generally calculated by estimating a point 29 of departure dose just below the lower end of the range of observed adverse effects, and dividing 30 this by uncertainty factors to account for extrapolation issues and database deficits. Applying 31 these standard procedures to the data reviewed in this assessment would result in an RfD/RfC 32 below the current estimated average dose to the U.S. population (~1 pgTEQ/kg/day), and would, 33 therefore, be uninformative for a safety assessment. 34 EPA has chosen instead to characterize the MOEs for noncancer endpoints in order to 35 better inform risk management decisions. The MOE is the ratio of the effect level in the 12/23/03 6-33 DRAFT--DO NOT CITE OR QUOTE 1 comparison species (ED0i or low effect level; animal or human) to the human body burden. For 2 the most sensitive endpoints identified, MOEs range from, for example, less than 1 for enzyme 3 induction in mice and rats, < 4 for developmental effects, and 4 for endometriosis in non-human 4 primates. In evaluating MOEs, consideration should be given to uncertainties in distinguishing 5 between adaptive biochemical changes and adverse effects, both on an individual level and as 6 these changes impact whole populations. The risks from dioxin and related compounds may be 7 greater for children than for adults, but more data are needed to fully address this issue. 8 Releases of dioxins to the environment from characterized sources have decreased 9 significantly over the last decade and are expected to continue to decrease. Other sources are still 10 poorly characterized, and an environmental reservoir of dioxins from both man-made and natural 11 sources has been recognized. Human body burdens have also declined and are anticipated to be 12 further reduced as additional, recently implemented, dioxin emission controls impact 13 environmental and food levels and, ultimately, human exposure, although the relationship with 14 reservoir sources remains uncertain. 12/23/03 6-34 DRAFT--DO NOT CITE OR QUOTE 1 APPENDIX A 2 345 TeqaubilveaAle-n1t. dBaoildyyinbtuarkdeens for critical endpoints in animals with human 6 Animal Endpoint Study 7 Rats Cancer Kociba et al. (1978)1 8 Rhesus 109 monkeys Fetal Mortality Developmental Neurotoxicity Bowm an et al. (1989)2 Schantz et al. (1992)3 Estimated body burden (ng/kg) LOAEL 180 90 21 NOAEL 18 21 - ED01 32 NC NC Human equiv.a intakes (pg/kg/day) 60; 6; 11 30; 7 7 Endometriosis Rier et al. (1993)4 11 Rats Reproductive Tox. M urray et al. (1979)5 (m ultigeneration al) 12 Rats Developmental/ M ably et al. (1992a, b, c)6 Reproductive Toxicity G ray et al. (1997)7 21 - NC 7 180 18 NC 60; 6 38 - 0.34 13; 0.1 30 - 0.08 10; 0.03 Faqi et al. (1998)8 25 - 0.6 8; 0.2 Ohsako et al. (2001)9 30 8 NC 10; 3 13 Rats Developmental Gehrs and Sm ialowicz (1999)10 60 - NC 20 Im m uno to xicity 14 Rats Developmental M arkowski et al. (2001)11 108 36b 0.7 36; 12; 0.2 Neurotoxicity 15 M ice Im m unological Effects Burleson et al. (1996)12 6 3 NC 2; 1 (adult) Sm ialowicz et al. (1994)13 300 - 2.9 100; 1 N arasim han et al. (1994)14 100 50b 1.5 33; 17; 0.5 V ecchi et al. (1983)15 16 Rats Thyroid Effects Sewall et al. (1995)16 17 M ice CY P1A1/1A2 Enzyme DeVito et al. (1994)17 Induction D iliberto et al. (2001)18 1200 76 22 24 2.8 - 7 401; 2 26 25; 7; 8 22 8; 7 67 0.9; 22 Vogel et al. (1997)19 5.1 0.51 0.003 1.6; 0.16; 0.001 N arasim han et al (1994)14 18 Rats CYP1A1/1A2 Enzyme van Birgelen et al. (1995)20 Induction Schrenk et al. (1994)21 25 10 3 8; 3; 2; 1 243 - 19 81; 6 72 - 26 24; 9 Sewall et al. (1995)16 8 2 3.5 3; 0.7; 1 W alker et al. (1999)22 76 - 59 25; 20 12/23/03 A-1 DRAFT--DO NOT CITE OR QUOTE TeqaubilveaAle-n1t. dBaoildyyinbtuarkdee(ncsonfotrincureitdi)cal endpoints in animals with human 21 a H u m a n e q u i v a l e n t i n t a k e s w e r e e s t i m a t e d a c c o r d i n g t o t h e f o l l o w i n g e q u a t i o n : d a i l y i n t a k e ( p g / k g / d a y ) 3 = ( b o d y b u r d e n ( n g /k g ) * L n 2 * 1 0 0 0 ) /( t ! /2 * a b s o r p tio n ) w h e r e t% = 2 5 9 3 d a y s a n d a b s o r p tio n fr a c tio n = 0 .8 4 (P o ig e r an d S ch la tter 1 9 8 6 ; see S e c tio n II). C o r r e sp o n d in g h u m a n eq u iv a le n t in ta k e v a lu e s are arran ged 5 in se q u en ce fro m th e p rev io u s th ree co lu m n s. 67 b N O A E L v a l u e s a r e b a s e d o n t h e h i g h e s t i n d i v i d u a l d o s e g r o u p i n w h i c h t h e r e a r e n o s t a t i s t i c a l l y s i g n i f i c a n t 8 ch a n g es. S ta tistic a lly sig n ifica n t d o se r e sp o n se tren d s p lu s ap p a ren t d e c lin e s are a lso e v id e n t at a ll d o se 9 le v e ls -- 2 0 a n d 6 0 n g /k g o r a lly -- in a ll fix ed -ra tio te st g ro u p s in M a rk o w sk i et a l. (2 0 0 1 ) an d in th e 50 n g /k g 10 d o s e g r o u p i n N a r a s i m h a n e t a l . ( 1 9 9 4 ) . 1112 - - = N o N O A E L v a l u e , a s e f f e c t s s e e n i n t h e l o w e s t d o s e g r o u p i n t h e s t u d y . 1134 N C = N o t c a l c u l a t e d d u e t o 15 i n s u f f i c i e n t d o s e r e s p o n s e i n f o r m a t i o n ( l e s s t h a n t h r e e d o s e s a n d a c o n t r o l ) o r d u e t o p r e s e n t a t i o n o f t h e d a t a 221111107689 i n g r a p h i c a l f o r m w i t h o u t t a b u l a t i o n o f m e a n a n d v a r i a n c e e s t i m a t e s . 22 Kociba et al. (1978)1 . . I n c r e a s e d c a n c e r i n f e m a l e S p r a g u e 23 D a w l e y r a t s e x p o s e d f o r 2 y e a r s t o T C D D i n t h e f o o d m a t r i x . 24 S t a t is t i c a l L O A E L a n d N O A E L b o d y b u r d e n e s t im a t e s m o d e l e d 25 a s s u m i n g 5 0 % a b s o r p t i o n f r o m t h e f o o d m a t r i x a n d a 2 5 - d a y h a l f 26 l i f e . C o m p a r e t o m e a s u r e d l i p i d l e v e l s i n t h e K o c i b a e t a l. ( 1 9 7 8 ) 27 r a t s o f 5 4 0 a n d 1 7 0 0 p p t a t 1 a n d 1 0 n g / k g / d a y d o s e r a t e s a n d t o 28 m e a s u r e d b o d y b u r d e n s i n t h e H u r s t e t a l. ( 2 0 0 0 ) s u b c h r o n i c 5 / 7 d a y 29 g a v a g e s t u d y in f e m a l e L o n g - E v a n s r a t s o f 1 9 a n d 1 2 0 n g / k g a t 1 a n d 30 1 0 n g / k g / d a y d o s e r a t e s . E D 01 c a l c u l a t e d f o r f e m a l e r a t t u m o r s u s i n g 31 a m u l t i s t a g e f o r m u l a a n d E P A B e n c h m a r k D o s e S o f t w a r e r e s u l t i n a n 32 E D 01 ( L E D 01) o f 3 1 . 9 ( 2 2 ) n g / k g b o d y b u r d e n u s i n g K o c i b a e t a l. 33 ( 1 9 7 8 ) d a t a a n d G o o d m a n a n d S a u e r ( 1 9 9 2 ) p a t h o l o g y . Ko ciba et al. 1978: T um ors 12/23/03 A-2 DRAFT--DO NOT CITE OR QUOTE TeqaubilveaAle-n1t. dBaoildyyinbtuarkdee(ncsonfotrincureitdi)cal endpoints in animals with human 1 Bowman et al. (1989)2 . . O f f s p r i n g p e r c o h o r t s i g n i f i c a n t l y 2 r e d u c e d at th e 2 5 p p t d o se g r o u p in c o h o r ts I a n d II (L O A E L ) b u t 3 n o t in th e 5 p p t d o se g r o u p (N O A E L ; p u b lic a tio n F ig . 5 a tta c h ed ). 4 E stim a te d m a tern a l b o d y b u rd en s are c a lc u la te d a t p a rtu ritio n o f th e 5 2 5 p p t co h o rt II g ro u p fo r th e L O A E L (lo w e s t v a lu e o f 2 5 p p t 6 co h o rts I and II) and th e 5 p p t co h o rt I fo r th e N O A E L (h ig h e st 7 v a lu e o f 5 p p t c o h o rts I an d II). M a tern a l T C D D fa t le v e ls are 8 e stim a te d a c c o r d in g to th e e m p ir ic a l fo r m u la a n d d a ta su p p lie d in 9 B o w m a n e t a l. (1 9 8 9 ; se e p u b lic a tio n fig u r e s 3 a n d 5): y = 1 4 .9 + 10 4 . 2 9 x ( r = 0 . 9 2 4 ) , w h e r e y = P C D D / f a t p p t i n f a n t a t w e a n i n g a n d 11 x = T C D D / f a t p p t m o t h e r a t p a r t u r i t i o n . T h e m e a s u r e d T C D D f a t 12 l e v e l s i n o f f s p r i n g ( " y " v a l u e ) o f t h e 5 p p t c o h o r t s I a n d I I a t 13 p a r t u r i t i o n w e r e 3 7 7 1 4 1 p p t a n d 3 2 3 7 0 p p t , r e s p e c t i v e l y , 14 r e s u l t i n g i n e s t i m a t e d m a t e r n a l f a t l e v e l s a t p a r t u r i t i o n o f c o h o r t s I 15 a n d I I o f 8 4 a n d 7 2 p p t , r e s p e c t i v e l y . F o l l o w i n g t h e a u t h o r s ' 16 r e c o m m e n d a t i o n , t h e f a t l e v e l i n t h e 2 5 p p t d o s e g r o u p i s c a l c u l a t e d 17 f o l l o w i n g a 5 : 1 r a t i o t o t h e 5 p p t g r o u p s , i . e . , 4 2 0 a n d 3 6 0 p p t f o r 18 c o h o r t s I a n d I I r e s p e c t i v e l y . M e a s u r e d m a t e r n a l d a t a i n t h e 2 5 p p t 19 d o s e g r o u p a t t h e t i m e o f b i r t h o f c o h o r t I I I ( 4 8 8 d a y s p o s t c e s s a t i o n 20 o f T C D D d o s e ) w e r e 3 3 5 1 1 9 p p t ( 3 n o n - b r e d f e m a l e s ) a n d 2 1 9 7 5 21 p p t ( a l l 7 m o n k e y s ) i n f a t . A 2 5 % b o d y l i p i d w a s a s s u m e d i n 2223 c o n v e r t i n g t o h u m a n e q u i v a l e n t b o d y b u r d e n . Bow man et al. 1989: Infant Survival 24 Schantz et al. (1992)3 . . I n c r e a s e d r o u g h - t u m b l e p l a y ( p u b l i c a t i o n 25 F i g . 2 a t t a c h e d ) , f e w e r r e t r e a t s d u r i n g p l a y b o u t s , a n d f e w e r 26 d i s p l a c e m e n t s f r o m p r e f e r r e d p o s i t i o n s i n t h e 5 p p t c o h o r t I 27 o f f s p r i n g . M a t e r n a l T C D D f a t l e v e l s a r e e s t i m a t e d a c c o r d i n g t o t h e 28 e m p i r i c a l f o r m u l a a n d d a t a s u p p l i e d i n B o w m a n e t a l. ( 1 9 8 9 ; s e e 29 F i g s . 3 a n d 5 ) : y = 1 4 . 9 + 4 . 2 9 x ( r = 0 . 9 2 4 ) , w h e r e y = P C D D / f a t p p t 30 in f a n t a t w e a n i n g a n d x = T C D D / f a t p p t m o t h e r a t p a r t u r i t io n . T h e 31 m e a s u r e d T C D D f a t l e v e l i n o f f s p r i n g ( " y " v a l u e ) o f t h e 5 p p t c o h o r t 32 I g r o u p a t p a r t u r i t i o n w a s 3 7 7 1 4 1 p p t , r e s u l t i n g i n a n e s t i m a t e d 33 m a t e r n a l f a t l e v e l a t p a r t u r i t io n o f 5 p p t c o h o r t I o f 8 4 p p t . F a t l e v e l 34 c o n v e r t e d to b o d y b u r d e n b y d iv id in g b y 4 , a p p r o x im a t in g 2 5 % b o d y 35 f a t in a h u m a n e q u i v a l e n t c o m p a r i s o n . Schantz et al. 1992 : Ro ug h-tu m ble Play 12/23/03 A-3 DRAFT--DO NOT CITE OR QUOTE TeqaubilveaAle-n1t. dBaoildyyinbtuarkdee(ncsonfotrincureitdi)cal endpoints in animals with human 1 Rier et al. (1993)4 . . I n c r e a s e d i n c i d e n c e , s e v e r i t y a n d d o s e 2 r e s p o n s e fo r r h e su s m o n k e y s w ith e n d o m e tr io sis in th e 5 a n d 2 5 p p t 3 d o se g ro u p s (rA F S c la ssific a tio n ; p u b lica tio n fig u r e 2 a tta ch ed , * 4 p < 0 .1 7 , ** p < 0 .0 5 ). L O A E L (n o N O A E L ) b o d y b u rd en a d o p ted 5 fro m th e h ig h e st m a tern a l fa t le v e l ca lcu la ted a c co rd in g to th e 6 fo r m u la su p p lie d b y B o w m a n e t a l. (1 9 8 9 ; s e e fo o tn o te 2 ) o f 8 4 p p t 7 fo r th e 5 p p t d o se g ro u p o c c u r r in g at th e p a rtu ritio n o f c o h o r t I. F o r 8 co m p a riso n , th e a v era g e o f e ig h t m ea su red m a tern a l fa t le v e ls at the 9 b irth o f th e 5 p p t c o h o r t III (4 8 8 d a y s p o st c e ssa tio n o f T C D D ) w a s 10 5 4 1 1 p p t f a t . A 2 5 % b o d y l i p i d w a s a s s u m e d i n c o n v e r t i n g t o 11 h u m a n e q u i v a l e n t b o d y b u r d e n . Rie r et al. 1993 : En do metrio sis W N fR O ii 25 p i* 12 M urray et al. (1979)5 . . S i g n i f i c a n t r e d u c t i o n s i n f e r t i l i t y ( g r a p h 13 o f p u b l i c a t i o n t a b l e 1 d a t a a t t a c h e d ) , l i t t e r s i z e , g e s t a t i o n s u r v i v a l , 14 a n d n e o n a t a l s u r v i v a l a n d g r o w t h i n t h e 1 0 n g / k g / d a y f o o d m a t r i x 15 m a t e r n a l d o s e g r o u p i n a t h r e e - g e n e r a t i o n r e p r o d u c t i o n s t u d y i n 16 S p r a g u e - D a w l e y r a t s . M a t h e m a t i c a l l y e s t i m a t e d b o d y b u r d e n o f 17 1 8 0 n g / k g a t 1 0 n g / k g / d a y ( h a l f - l i f e = 2 5 d a y s , 5 0 % a b s o r p t i o n f r o m 18 f o o d m a t r i x ) . C o m p a r i s o n e m p i r i c a l m e a s u r e m e n t s f r o m a s i m i l a r 19 d o s e r e g i m e n i n t h e r e l a t e d c a n c e r s t u d y b y K o c i b a e t a l . ( 1 9 7 8 ) 20 w e r e 1 7 0 0 p p t T C D D i n l i p i d i n t h e 1 0 n g / k g / d a y d o s e g r o u p , a n d 21 t h e m e a s u r e d b o d y b u r d e n i n H u r s t e t a l . ( 2 0 0 0 ) s u b c h r o n i c 5 / 7 d a y 22 g a v a g e s t u d y i n f e m a l e L o n g - E v a n s r a t s w a s 1 2 0 n g / k g a t t h e 1 0 23 n g / k g / d a y d o s e r a t e . T h e f e r t i l i t y i n d e x in t h e f 0 g e n e r a t i o n w a s s o 24 l o w t h a t f u r t h e r s t u d i e s w i t h t h is d o s e g r o u p w e r e d i s c o n t i n u e d . 25 T h u s , t h e s t u d y i s e s s e n t i a l l y t w o d o s e l e v e l s a n d a c o n t r o l a n d w a s 26 n o t m o d e l e d b e c a u s e o f t h e l i m i t e d d o s e r e s p o n s e r e l a t i o n s h i p d a t a . M urray et al. 1979: Rat Fertility Index 12/23/03 A-4 DRAFT--DO NOT CITE OR QUOTE TeqaubilveaAle-n1t. dBaoildyyinbtuarkdee(ncsonfotrincureitdi)cal endpoints in animals with human 1 M ably et al. (1992a,b,c)6 . . D e c r e a s e d d a i l y s p e r m p r o d u c t i o n 2 (p u b lica tio n F ig . 5 a tta ch ed ), ca u d a e p id id y m a l sp erm , e p id id y m is 3 w e ig h ts an d a ltered se x u a l b e h a v io r in o ffsp r in g a t 6 4 n g /k g o r a lly to 4 H o ltzm a n rat d a m s o n g esta tio n d a y 1 5 . L O A E L (n o N O A E L ) b o d y 5 b u r d e n b a se d o n H u r st e t a l. (2 0 0 0 ) G D 1 6 b o d y b u rd e n fr a c tio n o f 6 60% fo llo w in g sin g le G D 1 5 5 0 n g /k g g a v a g e d o se to fe m a le L o n g 7 E v a n s r a t s . E D 01 v a l u e m o d e l e d f o r c a u d a l s p e r m c o u n t o f 0 . 3 4 8 n g /k g b o d y b u rd en at d a y 63 u sin g E P A B en ch m ark D o se S o ftw a re 9 V e r s i o n 1 . 3 , 6 0 % a b s o r p t i o n . E D 01 m o d e l i n g o f M a b l y e t a l . ( 1 9 9 2 ) 10 u s i n g E P A B e n c h m a r k D o s e S o f t w a r e V e r s i o n 1 . 3 r e s u l t s i n a b r o a d 11 r a n g e o f E D 01s , f r o m 0 . 3 4 n g / k g f o r d a i l y s p e r m p r o d u c t i o n o n P N D 12 6 3 t o 4 6 1 n g / k g f o r p i n n a d e t a c h m e n t , w i t h a m e d i a n v a l u e o f 3 . 1 1134 n g / k g f o r 1 5 d i f f e r e n t e n d p o i n t s . Mab ly et al. 1992: Epididymal Spe rm 15 Gray et al. (1997)7 . . D e c r e a s e i n e j a c u l a t e d s p e r m n u m b e r s i n 16 m a l e o f f s p r i n g , p o o l e d r e s u l t s f r o m t w o s t u d i e s ( s e e p u b l i c a t i o n F i g . 17 1 ; r e s u l t s p o o l e d w i t h G r a y e t a l . 1 9 9 5 ; a t t a c h e d g r a p h o f d a t a f r o m 18 p u b l i c a t i o n t e x t p . 1 5 ) a t 5 0 n g / k g s i n g l e d o s e , d a y 1 5 o f g e s t a t i o n t o 19 f e m a l e L o n g - E v a n s r a t s . L O A E L ( n o N O A E L ) b o d y b u r d e n b a s e d 20 o n H u r s t e t a l . ( 2 0 0 0 ) G D 1 6 b o d y b u r d e n f r a c t i o n o f 6 0 % f o l l o w i n g 21 s i n g l e G D 1 5 5 0 n g / k g g a v a g e d o s e t o f e m a l e L o n g - E v a n s r a t s . E D 01 22 m o d e l i n g o f G r a y e t a l . ( 1 9 9 7 ) u s i n g E P A B e n c h m a r k D o s e 23 S o f t w a r e V e r s i o n 1 . 3 , 6 0 % a b s o r p t i o n , r e s u l t s in a b r o a d r a n g e o f 24 E D 01s f r o m 0 . 0 8 n g / k g f o r e p i d i d y m a l s p e r m c o u n t o n D 4 9 t o 3 2 7 25 n g / k g f o r d a i l y s p e r m p r o d u c t i o n o n D 4 9 , w i t h a m e d i a n v a l u e o f 8 0 2276 n g / k g f o r 3 2 d i f f e r e n t e n d p o i n t s . Gra y et al. 1997 : Ejacu lated S perm 12/23/03 A-5 DRAFT--DO NOT CITE OR QUOTE TeqaubilveaAle-n1t. dBaoildyyinbtuarkdee(ncsonfotrincureitdi)cal endpoints in animals with human 1 Faqi et al. (1998)8 . . D e c r e a s e d d a i l y s p e r m p r o d u c t i o n ( g r a p h 2 a tta ch ed o f d ata fro m p u b lic a tio n T a b le 3 ), ca u d a ep id id y m u s sp erm , 3 sp erm tra n sit ra te, an d p e r ce n t a b n o rm a l sp erm in o ffsp r in g o f 4 2 5 /5 n g /k g (lo a d in g /w e e k ly m a in te n a n c e ) m a tern a l W ista r rat 5 g ro u p . M a in ten a n ce d o se o f 5 n g /k g /w e e k su b cu ta n eo u s 6 a d m in iste r e d to m a in ta in b o d y b u rd en o f 2 5 n g /k g . A d d itio n a l 7 d a ta o n T C D D le v e ls m e a su r e d in m a te r n a l fa t a t g e sta tio n d a y 2 1 8 estim a te d fro m p u b lic a tio n F ig u re 1 at 1 5 0 n g /k g in 2 5 /5 g ro u p . ^ 9 D e c r e a se s in cau d a e p id id y m a l sp erm n u m b ers (P N D 1 7 0 ) an d 10 d a i l y s p e r m p r o d u c t i o n ( P N D 7 0 a n d 1 7 0 ) w e r e o b s e r v e d a t a l l 11 d o s e s . I n a d d i t i o n , i n c r e a s e s i n s p e r m t r a n s i t r a t e a n d p e r c e n t 12 a b n o r m a l s p e r m w e r e o b s e r v e d a t a l l d o s e l e v e l s a t P N D 1 7 0 . 13 E D 01 v a l u e o f 0 . 6 n g / k g f o r d e c r e a s e s i n d a i l y s p e r m p r o d u c t i o n , 14 o n P N D 7 0 a n d m o d e l e d u s i n g E P A B e n c h m a r k D o s e S o f t w a r e 15 V e r s i o n 1 . 3 . Faq i et al. 1998; Daily Sp erm Production 16 Ohsako et al. (2001)9 . . D e c r e a s e d a n o - g e n i t a l d i s t a n c e i n m a l e 17 o f f s p r i n g o f H o l t z m a n r a t d a m s r e c e i v i n g 5 0 n g / k g s i n g l e d o s e o r 18 g r e a t e r o n g e s t a t i o n d a y 1 5 ( p u b l i c a t i o n F i g . 7 a t t a c h e d ) . N O A E L a t 19 1 2 . 5 n g / k g s i n g l e d o s e . D o s e - d e p e n d e n t d e c r e a s e s i n a n d r o g e n 20 r e c e p t o r m R N A l e v e l s i n v e n t r a l p r o s t a t e in a l l d o s e g r o u p s 21 ( p u b l i c a t i o n F i g . 8 a t t a c h e d ) . N o c h a n g e s i n d a i l y s p e r m p r o d u c t i o n 22 o r s p e r m r e s e r v e . L O A E L / N O A E L b o d y b u r d e n s b a s e d o n H u r s t e t 23 a l . ( 2 0 0 0 ) g e s t a t i o n d a y ( G D ) 1 6 b o d y b u r d e n f r a c t i o n o f 6 0 % 24 f o l l o w i n g s i n g l e G D 1 5 5 0 n g / k g g a v a g e d o s e t o f e m a l e L o n g - E v a n s 25 r a t s . E D 01 v a l u e s f o r t h i s s t u d y w e r e n o t c a l c u l a t e d b e c a u s e t h e 26 s i g n i f i c a n t d a t a w e r e n o t p r e s e n t e d i n t a b u l a r f o r m a t . 3333333322212577036894 Ohsako et al. 2001: Androgen Receptor Ohsako et al. 2001: Ano-genital Distance 12/23/03 A-6 DRAFT--DO NOT CITE OR QUOTE TeqaubilveaAle-n1t. dBaoildyyinbtuarkdee(ncsonfotrincureitdi)cal endpoints in animals with human 1 Gehrs and Smialowicz (1999)1 0 . . D e c r e a s e d d e l a y e d - t y p e 2 h y p e r se n sitiv ity (D T H ; p u b lic a tio n F ig . 2 a a tta ch ed ; d o se u n its fo r 3 c o lu m n s are 0 , 1 0 0 , 3 0 0 , an d 1 0 0 0 n g /k g ) in m a le o ffsp r in g 4 fo llo w in g sin g le m a tern a l o ra l d o se o f 1 0 0 n g /k g o n g esta tio n d a y 14 5 to F 3 4 4 rats. L O A E L (n o N O A E L ) b o d y b u rd en b a se d o n H u rst et 6 a l. (2 0 0 0 ) G D 1 6 b o d y b u rd e n fr a c tio n o f 6 0 % fo llo w in g sin g le 7 G D 1 5 50 n g /k g g a v a g e d o se to fe m a le L o n g -E v a n s rats. B en ch m ark 8 d o se a n a ly sis w a s n o t p erfo rm ed o n th is stu d y b e c a u se th e data w ere 9 p resen ted in g ra p h ica l fo rm a t. Gehrs and Sm ialowicz 1999: Delayed-Type Hypersensitivity AGE Cmc-nllUl 10 M arkow ski et al. (2001)1 1 . P e r i n a t a l T C D D e x p o s u r e p r o d u c e d a s i g n i f ic a n t d o s e - r e l a t e d r e d u c t i o n i n t h e 11 n u m b e r o f e a r n e d o p p o r t u n i t i e s t o r u n , l e v e r r e s p o n s e r a t e , a n d t o t a l n u m b e r o f r e v o l u t i o n s i n t h e w h e e l i n 12 o f f s p r i n g o f H o l t z m a n r a t s e x p o s e d t o s i n g l e o r a l T C D D d o s e s o n G D 1 8 . S t a t i s t i c a l l y s i g n i f i c a n t d o s e g r o u p 13 e f f e c t s a t 1 8 0 n g / k g d o s e ( L O A E L ) . N O A E L a t 6 0 n g / k g d o s e g r o u p , w h e r e a p p a r e n t d e c l i n e s a r e n o t s t a t i s t i c a l l y 14 s i g n i f i c a n t ( s e e p u b l i c a t i o n F i g . 2 a t t a c h e d ; p u b l i c a t i o n T a b l e 3 ) . E D 01 r e s u l t s m o d e l e d b y t h e a u t h o r s . T a b l e 15 i n c l u d e s r e s u l t f o r t o t a l w h e e l r e v o l u t i o n s . B o d y b u r d e n s b a s e d o n 1 8 0 a n d 6 0 n g / k g s i n g l e o r a l d o s e s a n d H u r s t 16 e t a l . ( 2 0 0 0 ) G D 1 6 b o d y b u r d e n f r a c t i o n o f 6 0 % f o l l o w i n g s i n g l e G D 1 5 5 0 n g / k g g a v a g e d o s e t o f e m a l e L o n g 17 E v a n s r a t s . 3333322222222221111225703036894489 Markowski et al. 2001: Operant Conditioning 35 Burleson et al. (1996)1 2 . . I n c r e a s e d s u s c e p t i b i l i t y t o i n f l u e n z a 36 i n f e c t i o n c h a l l e n g e i n B 6 C 3 F 1 m i c e f o l l o w i n g 1 0 n g T C D D / k g 37 ( L O A E L ) a n d h i g h e r s i n g l e o r a l g a v a g e d o s e t o 8 - w e e k - o l d m i c e 38 ( p u b l i c a t i o n F i g . 1 a t t a c h e d ) . N o s i g n i f i c a n t e f f e c t s s e e n a t 1 a n d 5 39 n g / k g d o s e s ( N O A E L ) . A s s u m e 6 0 % a b s o r p t i o n . B e n c h m a r k d o s e 40 a n a l y s is w a s n o t p e r f o r m e d o n s t u d y b e c a u s e t h e d a t a w e r e n o t 41 p r e s e n t e d i n t a b u l a r f o r m a t . Burleson et al. 1996: Influenza Susc eptibility 12/23/03 A-7 DRAFT--DO NOT CITE OR QUOTE TeqaubilveaAle-n1t. dBaoildyyinbtuarkdee(ncsonfotrincureitdi)cal endpoints in animals with human 1 Sm ialowicz et al. (1994)1 3 . . D o s e - r e l a t e d s u p p r e s s i o n o f a n t i b o d y 2 p la q u e fo r m in g c e ll (P F C ; p u b lic a tio n F ig . 1 a tta c h ed ) r e sp o n se in 3 a d u lt fe m a le B 6 C 3 F 1 m ic e at 3 0 0 n g /k g sin g le in tra p erito n ea l 4 in je c tio n a n d h ig h e r. P F C in c r e a se s rep o rted in h ig h -d o se -g r o u p 5 m a le F 3 4 4 an d fem a le L o n g -E v a n s rat sp e c ie s tested , a cc o m p a n ie d 6 b y a l t e r a t i o n s t o s p l e n i c C D 4 -C D 8 + l y m p h o c y t e s . E D 01 v a l u e s f o r 7 m ic e c a lc u la te d fo r p la q u e fo r m in g c e lls p e r m illio n c e lls o f 2 .9 8 n g /k g b o d y b u rd en u sin g E P A B en ch m a rk D o se S o ftw a re V e r sio n 9 1 .3 . Smialowicz et al. 1994: PFC Immune Response 10 N arasim han et al. (1994)1 4 . . D e c r e a s e d s p l e n i c a n t i b o d y p l a q u e 11 f o r m i n g c e l l ( P F C ; g r a p h o f p u b l i c a t i o n T a b l e 5 d a t a a t t a c h e d ) 12 r e s p o n s e f o l l o w i n g s i n g l e i n t r a p e r i t o n e a l d o s e a d m i n i s t e r e d t o 13 f e m a l e B 6 C 3 F 1 m i c e ( 7 - 9 w e e k s o l d ) . L O A E L f o r d e c r e a s e d S R B C 14 a n d s p l e n i c P F C r e s p o n s e s a t 1 0 0 n g / k g , n o n s t a t i s t i c a l l y s i g n i f i c a n t 15 d e c r e a s e e v i d e n t a t 5 0 n g / k g , N O A E L a t 2 5 n g / k g . C Y P 1 A 1 16 L O A E L ( N O A E L ) a t 2 5 ( 1 0 ) n g / k g d o s e ( g r a p h o f p u b l i c a t i o n t a b l e 17 1 d a t a a t t a c h e d ) . E D 01 v a l u e s c a l c u l a t e d f o r s p l e e n P F C / m i l l i o n c e l l s 18 o f 1 . 5 n g / k g b o d y b u r d e n a n d f o r C Y P 1 A 1 m R N A i n d u c t i o n o f 3 22211209 n g / k g u s i n g E P A B e n c h m a r k D o s e S o f t w a r e V e r s i o n 1 . 3 . Narasimhan et al. 1994: PFC Imm une Response 12/23/03 A-8 DRAFT--DO NOT CITE OR QUOTE TeqaubilveaAle-n1t. dBaoildyyinbtuarkdee(ncsonfotrincureitdi)cal endpoints in animals with human 1 V ecchi et al. (1983)1 5 . . D e c r e a s e d p l a q u e - f o r m i n g c e l l s ( P F C ) p e r 2 m illion and P F C /sp leen (graph o f p u b lication table 2 data attached) 3 at all d o ses tested in aryl h yd rocarb on h y d ro x y la se sen sitive m o u se 4 strains (B 6, C 3 ) fo llo w in g sin g le in trap eriton eal d o ses. L ess 5 se n sitiv ity in o th er strains (e .g . D B A /2 a n d A K R ). L O A E L (n o 6 N O A E L ) o f 1 2 0 0 n g / k g . E D 01 c a l c u l a t e d f o r P F C / m i l l i o n 7 sp len ocytes o f 7 ng/k g for B 6 m ice u sin g E P A B en ch m ark D o se 8 S o ftw a re V ersio n 1.3. Vecchi et al. 1983: PFC Immune Response 9 Sewall et al. (1995)1 6 . . S t a t i s t i c a l l y s i g n i f i c a n t d e c r e a s e d r a t i o o f 10 t h y r o i d p a r e n c h y m a l a r e a t o t h y r o i d f o l l i c l e a r e a ( p u b l i c a t i o n F i g . 6 11 a t t a c h e d ) w a s r e p o r t e d i n f e m a l e S p r a g u e - D a w l e y r a t s f o l l o w i n g o r a l 12 g a v a g e b i w e e k l y d o s i n g f o r 3 0 w e e k s a t d a i l y e q u i v a l e n t d o s e s o f 13 0 . 1 - 1 2 5 n g / k g / d a y . L O A E L ( N O A E L ) o f 3 . 5 ( 1 ) n g / k g / d a y f o r 14 t h y r o i d p a r e n c h y m a / f o l l i c l e r a t i o , c a l c u l a t i n g t o a p p r o x i m a t e b o d y 15 b u r d e n s o f 7 6 a n d 2 2 n g / k g f o r t h e L O A E L a n d N O A E L , 16 r e s p e c t i v e l y . T h e s e c a l c u l a t i o n s a s s u m e a h a l f - l i f e o f 2 5 d a y s a n d 17 6 0 % b o d y b u r d e n f r a c t i o n f o l l o w i n g g a v a g e d o s e , b a s e d o n H u r s t e t 18 a l . ( 2 0 0 0 ) . S i g n i f i c a n t i n c r e a s e s w e r e a l s o r e p o r t e d f o r t h y r o i d 19 s t i m u l a t i n g h o r m o n e , w i t h a L O A E L o f 3 . 5 n g / k g / d a n d a N O A E L o f 20 1 n g / k g / d . S e r u m t h y r o x i n e w a s s i g n i f i c a n t l y d e c r e a s e d a t 1 0 . 5 21 n g / k g / d a y a n d a t h i g h e r d o s e s . E D 01 v a l u e s w e r e n o t c a l c u l a t e d f o r 22 t h y r o i d p a r e n c h y m a l / f o l l i c l e r a t i o . E D 01 f o r d e c r e a s e s i n s e r u m 23 t h y r o x i n o f 4 3 n g / k g b o d y b u r d e n u s i n g E P A B e n c h m a r k D o s e 24 S o f t w a r e V e r s i o n 1 . 3 . T h e E D 01 f o r i n c r e a s e d s e r u m t h y r o i d 25 s t i m u l a t i n g h o r m o n e i s 2 6 n g / k g . L O A E L ( N O A E L ) f o r C Y P 1 A 1 26 m R N A i n d u c t i o n o f 0 . 3 5 ( 0 . 1 ) n g / k g / d a y , a p p r o x i m a t i n g t o 8 ( 2 ) 27 n g / k g b o d y b u r d e n ( a s s u m i n g 6 0 % a b s o r p t i o n , 2 5 d a y h a l f l i f e ) . 28 E D 01 f o r i n c r e a s e s i n C Y P 1 A 1 m R N A w a s 3 . 5 n g / k g u s i n g E P A 3209 B e n c h m a r k D o s e S o f t w a r e V e r s i o n 1 . 3 . Sew all et a l. 1995: T hyro id Histology TCOO DSE IniAgJdeyl 12/23/03 A-9 DRAFT--DO NOT CITE OR QUOTE TeqaubilveaAle-n1t. dBaoildyyinbtuarkdee(ncsonfotrincureitdi)cal endpoints in animals with human 1 DeVito et al. (1994)1 7 . . L O A E L ( n o N O A E L ) o f 1 . 5 n g / k g / d a y 2 for in d u ction o f C Y P 1 A 1 an d C Y P 1 A 2 (p u b lication Fig. 2 attached) 3 and in crea sed p h o sp h o ry la tio n o f p h o sp h o ty r o sy l p rotein s in fem a le 4 B 6 C 3 F 1 m ice g a va g e fed 1 .5 -1 5 0 n g/kg/day, 5 days per w eek , for 5 13 w e e k s . A p p r o x im a te b o d y b u rd en after 13 w e e k s at 1.5 6 n g / k g / d a y o f 2 4 n g / k g , b a s e d o n D i l i b e r t o e t a l . ( 2 0 0 1 ) . E D 01 v a l u e 7 c a lc u la te d at 22 n g /k g for C Y P 1 A 1 in d u ctio n in th e liver u sin g E P A 8 B en ch m a rk D o se S oftw are V e r sio n 1.3. DeVito et al. 1994: Enzyme Induction 9 Diliberto et al. (2001)1 8 . . D o s e r e s p o n s e r e l a t i o n s h i p f o r 10 C Y P 1 A 1 i n d u c t i o n i n f e m a l e B 6 C 3 F 1 m i c e ( 6 0 d a y s o l d ) a t a l l o r a l 11 g a v a g e d o s e s f r o m 0 . 1 5 n g / k g / d a y ( 5 / 7 d a y s , 1 3 w e e k s ) a n d h i g h e r , 12 c o r r e s p o n d i n g t o a r a d i o l a b e l m e a s u r e d b o d y b u r d e n o f 2 . 7 5 n g / k g . 13 H e p a t i c C Y P 1 A 1 a c t i v i t y ( p u b l i c a t i o n T a b l e 5 , g r a p h o f l i v e r E R O D 14 d a t a a t t a c h e d ) m o d e l e d u s i n g E P A B M D S S o f t w a r e V e r s i o n 1 . 3 15 r e s u l t s i n a n E D 01 o f 9 . 7 n g / k g / d a y . B o d y b u r d e n i n t e r p o l a t e d u s i n g 16 l i n e a r r e g r e s s i o n o f d a t a f r o m D i l i b e r t o e t a l . ( 2 0 0 1 ; T a b l e 4 ) w i t h 17 f o r m u l a : b o d y b u r d e n = 6 . 8 7 8 2 * d a i l y d o s e ( M - F ) ( R 2 = 0 . 9 9 9 4 ; 18 M i c r o s o f t E x c e l ) , r e s u l t i n g i n e s t i m a t e d E D 01 b o d y b u r d e n o f 6 7 19 n g / k g . Diliberto et al. 2001: EROD Induction 12/23/03 A-10 DRAFT--DO NOT CITE OR QUOTE TeqaubilveaAle-n1t. dBaoildyyinbtuarkdee(ncsonfotrincureitdi)cal endpoints in animals with human 1 V ogel et al. (1997)1 9 . . L O A E L ( N O A E L ) f o r C Y P 1 A 1 E R O D 2 in d u ction (graph o f p u b lication T a b le 3 data attached) at 0.34 3 (0 .0 3 4 ) n g /k g /d a y to C 5 7 fe m a le m ic e a d m in istered 1, 10, 100 n g /k g 4 load in g d oses fo llo w e d b y w e e k ly in jection s o f 0.2, 2, and 20 n g /k g 5 for 135 d ays, calcu latin g to 4 .9 (0 .4 9 ) n g /k g b o d y burden (assu m in g 6 1 0 0 % a b s o r p t i o n , 1 0 d a y h a l f l i f e ) . E D 01 v a l u e c a l c u l a t e d f o r 7 C Y P 1 A 1 E R O D in d u ction o f 0 .0 0 3 n g/k g b o d y b u rd en u sin g E P A 8 B e n c h m a r k D o s e S o ftw a re V e r sio n 1.3. Vogel et al. 1997: EROD Induction 9 van Birgelen et al. (1995)2 0 . . S i g n i f i c a n t i n c r e a s e s i n C Y P 1 A 1 10 ( g r a p h o f l i v e r E R O D d a t a f r o m p u b l i c a t i o n t a b l e 3 a t t a c h e d ) a n d 11 C Y P 1 A 2 , p l u s d e c r e a s e d r e l a t i v e t h y m u s w e i g h t s a n d l o s s o f h e p a t i c 12 r e t i n o i d s , a t a l l d o s e s t e s t e d i n 8 w e e k o l d f e m a l e S p r a g u e - D a w l e y 13 r a t s e x p o s e d t o d i e t a r y m a t r i x i n t a k e s o f 0 , 0 . 2 , 0 . 4 , 0 . 7 , 5 , 2 0 14 : g T C D D / k g d i e t , c o r r e s p o n d i n g t o 0 , 1 3 . 5 , 2 6 . 4 , 4 6 . 9 , 3 2 0 a n d 1 0 2 4 15 n g / k g / d a y o r a l i n t a k e . L O A E L ( n o N O A E L ) c a l c u l a t e d f r o m 1 3 . 5 16 n g / k g / d a y d o s e t o b e 2 4 3 n g / k g b o d y b u r d e n ( 5 0 % a b s o r p t i o n f r o m 17 d i e t a r y m a t r i x , 2 5 d a y h a l f l i f e ) . C a l c u l a t e d n o e f f e c t l e v e l s ( C N E L ) 18 b y t h e a u t h o r s o f 0 . 7 t o 4 n g T C D D / k g / d a y ( H i l l a n d W e i b u l l 19 m o d e l s , b a s e d o n t h e m e a s u r e d c o n t r o l v a l u e p l u s t w i c e t h e s t a n d a r d 20 d e v i a t i o n : m a t h e m a t i c a l c a l c u l a t e d c o r r e s p o n d i n g b o d y b u r d e n s a r e 21 1 3 a n d 7 2 n g / k g a t 5 0 % a b s o r p t i o n , h a l f l i f e 2 5 d a y s ) . M e a s u r e d 22 l e v e l s b y a u t h o r s i n l i v e r a n d f a t o f 1 4 0 0 a n d 6 2 0 p p t , r e s p e c t i v e l y . 23 E D 01 v a l u e c a l c u l a t e d f o r C Y P 1 A 1 o f 1 9 n g / k g b o d y b u r d e n u s i n g 24 E P A B e n c h m a r k D o s e S o f t w a r e V e r s i o n 1 . 3 . van Birgelen et al. 1995: EROD Induction 25 Schrenk et al. (1994)2 1 . . C Y P 1 A 1 i n d u c t i o n i n f e m a l e W i s t a r r a t s 26 e x p o s e d v i a b i w e e k l y s u b c u t a n e o u s i n j e c t i o n t o a v e r a g e d a i l y d o s e s 27 o f 2 , 2 0 , a n d 2 0 0 n g / k g / d a y f o r 1 3 w e e k s . L O A E L ( n o N O A E L ) f o r 28 C Y P 1 A 1 E R O D i n d u c t i o n o f 2 n g / k g / d a y ( g r a p h o f p u b l i c a t i o n 29 t a b l e 1 d a t a a t t a c h e d ) , a p p r o x i m a t i n g t o 7 2 n g / k g b o d y b u r d e n ( 2 5 30 d a y h a l f l i f e , 1 0 0 % a b s o r p t i o n ) . E D 01 f o r C Y P 1 A 1 i n d u c t i o n o f 2 6 31 n g / k g b o d y b u r d e n u s i n g E P A B e n c h m a r k D o s e S o f t w a r e V e r s i o n 44333333331257036894 1 .3 . Schrenk et al. 1994: EROD Induction 12/23/03 A-11 DRAFT--DO NOT CITE OR QUOTE TeqaubilveaAle-n1t. dBaoildyyinbtuarkdee(ncsonfotrincureitdi)cal endpoints in animals with human 1 W alker et al. (1999)2 2 . . D o s e - d e p e n d e n t e x p r e s s i o n o f C Y P 1 A 1 2 (grap h o f p u b lication table 3 data attach ed ) and C Y P 1 A 2 R N A 3 (C Y P 1 B 1 le ss sen sitiv e) in fem a le S p ra g u e -D a w le y rats g a v a g e fed 4 b iw e e k ly for 30 w e e k s to a verage d aily d o ses o f 3.5 - 125 5 n g /k g /d a y . L O A E L v a lu e o f 3.5 n g /k g /d a y (n o N O A E L ), ca lcu la tes 6 to 76 ng/kg b od y burd en (assu m in g h alflife o f 25 d ays, 60% 7 absorption fo llow in g g avage). M easured liver lev el o f 4 4 7 n g/k g. 8 E D 01 v a l u e s c a l c u l a t e d f o r C Y P 1 A 1 m R N A a n d C Y P 1 A 2 m R N A a t 9 59 and 2 7 0 n g /k g b od y burd en s, resp ectively, u sing E P A 10 B e n c h m a r k D o s e S o f t w a r e V e r s i o n 1 . 3 . H i g h m a x i m a l i n d u c t i o n 1112 p o t e n t i a l o f e n z y m e s c o n t r i b u t e s t o h i g h 1 % e f f e c t i v e d o s e ( E D 01). W alker et al. 1999: CYP1A1 mRNA 13 12/23/03 A-12 DRAFT--DO NOT CITE OR QUOTE 222222221111111111112570436257036843689492571 333334444442233333112032589570344689 GLOSSARY Advtahedredsipeteioerffnfoaerlcmte:annvAcireoboniomfcthehneemtawlihccoahllaecllhoearngngagene.i,sfmunocrtiroendaulciemspaaniromrgeannt,isomr 'psaatbhiolliotygitco lreessipoonntdhatot aafnfects AresauUmnmdaerrytmheeaCsuurrevteha(At iUntCeg):raAtersesaeurinadlearsstheesscmoennctesnotrfaatiodnosveerosvuesrttihmeedcuurarvtieo.nTohfethAeUstCudiys.a Aryrtlreahcneyspdctrrooirpctnaiuorcnbloefanacrrttoerarcnethsplatotocfraut(noAcrthi(RoAn)ms: ti)An. npairnttnrearcsehlliuplwaripthroatesiencothnadt pisroateliigna, nthde-daerpyelnhdyednrtocarbon Aryhfluyhndycrtodicoroanrcsbaaorsnbaorentrcaernepsctcoerrpip(ttothiroennAufhacRclet)oa.rritnrathneslcoecllaitnorpa(Artnrnetr)s:hipAwn iitnhtraacseelcluonladr pprrootteeiinn,tthhaet aryl Bacpptcsdsskhohuoorigeoeuocmprsxhrunuoecmilolnneeudaressxcntmn:riepdfoconorainootalasefmultbxbfumrrefpaoerorcoaiisemonknl.ssldugtueyeetrrrsrexofveupopu:oaprronmeipmrsTtdleuoysehdrruo.deaenunadTetrmsgscixhoeieepoen.xsdofd.ioisMniadrucsTii(aro,gohfetsixaoientnntiohnt(gtode>h-a,flrttrimh9oatkrheie5peri"g%o,sscbugisbo)galoeaamcnonicrklii,flpfkgcyiboegcrdatouoraccoicnun.ok)ucdncxgunetsdihrrdniosoaensurtextofxndpahrpcdioaomecovsmteeuesaexpumrrcdpyetroabeio"ofbnesaiaxiturstlsesi,rinmfteuporyosrcprfieoemoomtdsfnhruaarectilhinrretsygirsnkleteythsfenraoriafeosscurtrsmaioradooctmloencetgcihssatuo,ehwtmreaeiidneetdshnwitonitfh Benpbcarhecmdkegatrerorkumndidon.seed(cBhManDge):inAresstpaotinstsiecarlatleowoferancoandfvideresneceeflfiemcti,t toynpitchaelldyo1se-1t0h%at,pcroodmupcaerseda to BodtbbbcIoooyhnaiaunrfeolsbrkhTctcidbhunusuEheoemorlenoQaddwmbsfatyeealntciindehscnaosdi:eannsfhtglrdhcTBuooeoeeiCmmfonrsovDadtatftraonsyynaDtltxhptsuuibiineieodctuactisnioraarsseedsplslkasol.uereeyegeanecsriteittcaeciiyxosmatsopperl-ndiarsarcaceeptepaneefsespildnsdcnplretyieootordfhadnpiancetacsriatseeohhhhsssninaaene.t,lglhngffbt/I-e-thkanlelsiisgectdffaieoeessbdaaniodadooszcndyieffestdy-iTntlosoeitCpttwfnarhaiadt,DtedehteyitiDegheoa-ashxedntntiistpjadns.uoeotsesfhasuIvtunrTueebaersdmlCoaeu,adn,DasesayienossnmDrsorbdua.acturmahtlierAnhsaed,tdecoyleetatrwndheraleacsrerewlnduesaiaaeilgitnepattehvhisdtodvettasieedalomecuilrhtyfeoetahei,tnsteeshmebssreatdouthiricadeeemoanynTblaismaCtteshianDdiels.D Canacbenro:rmAafl,amunilcyonotfrodlilseedasgersoawffthecotifncgelcles.ll growth and differentiation, characterized by an 12/23/03 G-1 DRAFT--DO NOT CITE OR QUOTE 44443333333333222222222211111111111111225703257036890368944425703689368942571 Carcinogen: An agent capable of inducing cancer. Caregcviinveionngtgemrnioesdseiifstoi:esaTtphhoeepogureliangtoiinomnoeroapfnradol/tdoeurrecodtitohcneerllomsf.oalbeecnuilgarncoornmtroalligmneacnhtatnuimsmors. oTfhtheectaarrcgientocgeelnlsic, Chrtoimniecienffreeclat:tioAnntoeftfheectlitfheatitmoeccoufrtshaesoargreansuislmt o.f repeated exposures over a long period of Chrsoingnicifeicxapnotsfurarec:tioMn uolftitphleeaenxipmoaslu'sreosrothcecuirnrdinivgidouvaelr'salnifeextitmened. ed period of time or a Chrcohneimc isctauld. y: A toxicity study designed to measure the (toxic) effects of chronic exposure to a Chroofncichrtoonxiiccietxyp:osTuhree.capacity of a substance to cause adverse human health effects as a result Cohmcooermdt:imcAaolngincrovhueapsraticogtfaetariinosintmi.caalsndofththaet issasmtuedsipedecoievse,rinacpleurdiiondgohfutmimaensa,stphaatrtisofidaensctiifeinetdifbicyoar Convcfoaidrniesatnbrclueec.tiendtesrovtahla(tCthIi)s: rAangraenhgaesoafsvpaeluciefsiefdorpraovbaarbiailbitlye ooff iinntcelruedsitn,gfotrheextraumepvlael,uaeroatfet,he Cona(afansostueoruxncepidaoertsiersu:dkrweAfaiotcchftooidnnritdsfeioerteairossdtne.i.soeTrahvsieas)riamasbsaloyecmitahataiktoenisibtbeoftatwlhseeaelynriasthkpepfeaeacxrtpotorhsafuotrrtehdoeisfeeixanpsteeorsaeunsrtdeaionsfdainsthstoeercceioasttneifdsouwnidther Concgheenmeircsa:l fCaommilpieosunds that have similar chemical structures or belong to closely related Copalsasnuamre: aDfelasctrciopntifvigeutreartmionre,fwerirtihngrintogsthien ftahcetstahmatemsuplattii-arlinpglaendec.hemical structures can Diopm2txhh,i3eenyms,-s7elii,bck8cea-ehrlT:se-cCmoAhDifecntmDahal.eisdcadjpBelieceoprtcxsiraviiosnuept,seteafhrnutoaidretafsbndthi,eaoesanaicndrcrdcihibunyPemvdCsoruBocklopeafmhtaaeompbcionioilucmyfnnaamdtartstyeoutntrhtieeasbrstmaauhntteeadesdvrryeoe"sdfosiiaifsomnttxaoiimnilxnacia-rcellicsrtkhoeaeeswn"pmdaoiirnnhcdasutshelmmisssataernrsutesaca.dbtsouosCerleiseessrsmatman,idennt. 12/23/03 G-2 DRAFT--DO NOT CITE OR QUOTE 4444422333333333322222222111111111111112572257003680343689249403574364689258971 Effeiocnvtierverelbaatdicooksngetro(oEueDnxdp):ercaTtteehdseoldervoaseelpsethorcafetancntoairnrdecvsreepraossenedebsfeftetowcatentehniantbccareacanksgbere,oeudxnepfdirneaesnsddeadmsaaasxpiamepracelercrnaettneitnscr.erespasoense, EffeEiIuscnsftifsicnevoagcmesteitedhvswoeewshldehoa0oe1wtsrt(eeehEreetDhvvneaa0o1ll)udru:meaa.ttT,aioghSanieulvlcaodehtwnotsihtseehevtecha1opel0ruo%rcaweatsisrepoeeronsfonpoafdortimnn2asgo,el3os,tlt7woec,ve8aher-rlT1oe(%CfnEfiDeDcicnDt1tc0oi.vrxoeeiracsdloeoolwsoiengeylraenbsvtoeauuldd,nvitedehsreostenAo eEgdfeeDfnete1cc0cyt.t[LsauEngDegf1ef0se]t)cst. Epidesepremciaalllgyr,obwutthnofat cetxocrlu(sEivGeFly),: eApitmheitloiagl.enic polypeptide active on a variety of cell types, Follhpoicoivtlrauemriitsaaotnrniymefoguslltllaiaimnctidlune.lsgaIt(nheesogwgrtomhsm)eoaepnnnredo, d(fsFuoticlSmltiHicuol)lne:atsoeFtfsiSmstHphueelirasmrteia.nlnegaashceoidromifcoegsnlteyrocsgotiepmnrosu.tleaiItnnessmethecnere,dtfeeodvllebilcyolpethmseteiamnntutoelarfitoinrg Halfs-pleifcei:fieAd cmheeamsuicraeloinf tthheetbimodeyr.equired to reduce to one-half the original concentration of a Hortmhaotneex:erCt tohnetirrohl icghhelmy iscpaelcsifpircoedfufceectdsboyntoistshueerstiosrsuoersgaonfsthspeebcoidalyi.zed for that function and LatehneaclythPeefrfieocdt:ofTihnetetriemste. between first exposure to an agent and manifestation or detection of a Ligasuncdh: aAs nayhomromleocnueleorthnaetubrointrdasntsomainttoetrhtehra. tIbninndosrmtoaal uresacgepe,toar,suolsuuballelymwoiltehchuilgeh affinity. Lowccehhreemmlimiiccaaitll ononereteodfef1de%cttoiovpfertohddeousmcee0a1xa(iLm1E%aDlir0ne1c)s:rpeoTanshseeeo9rfe5al%antialvodewvteeorrscecooennftffrieodcle.tnincethliomseiteoxfptohseeddotsoethoef a Lowsetexaspttio-sosteibcdsaelplroyvpesudiglanatdiifovincearansnetdieniftcfsreeacaptspelersovipenrlif(arLteeOqcuAoennEtcLryo)l:ogrTrsoheuvepe.lroitwyeostf aedxvpeorssuereeflfeevcetlsabtewtwheicehn tthheere are Lutetoinsitziminuglahtoersmexonheor(mLoHn)e: rAelehaoserm. one that acts with the follicle stimulating hormone (FSH) Maragcitnuaolfoerxpproojseucrteed(MenOviEro):nmTehnetaLlEeDxp10o,sLuEreD/d0o1,soeroofthinetrepreositn,teoxfpdreespsaerdtuarseadriavtiidoe.d by the 12/23/03 G-3 DRAFT--DO NOT CITE OR QUOTE 4433333333334442222222222111111111111112572570368204036892574930368443492689571 Minriisomulitakelealrynisdtkodlbueervaewtlioi(tnMhooRuftLeax)p:ppoArseuncrieea.sbtliemraistek ooffdaadivlyerhsuemnoannceaxnpcoesruhreeatlothaehfafezcatrsdoovuesrsaubsspteacnicfieedthat No-bseotxubapttsioteshsrteievcydeadalpl-royeapdsnuivogleatnrticisfooeincneasafninfdtedeicrnitetcdslreeavaapdesplveres(oNrispneOritoaAhtreeEtfoLcroe)bn:qeturTpeorhnle;eccysuhoriomgsrohesreesesvfttfeoeerxciatptdysovmoseufrasrayeedbvleeefevfrepescrelotased.tfufwechcetdicbhaetttwthheeirseenleatvrheeeln,o No-psoiobgpsnueiflraivcteiaodnn-teiafnfncedrceitatslseeavspepilnr(oNtphOeriaEftrLeeq)c:uoenAntrcnoyle.oxrpsoesvuerreitlyevoeflaantywehfifcehcttbheetrwe eaerennthoesetaxtpisotsiceadlly Phaaerblmismaocirnpoatkitoiionnne, )td.icisst:ribTuhtieonq,uamnetittaabtoivliesmde,sacnridpteixocnreotfiothne(pmreotcaebsosliosfmchaenmd iecxacl rdeitsiopnoseitqiounal: Phymctsohieoactlraooabngcostiteclriraucilzclaeytnapdbhmaoasatrehmsdesa-rpbcphaorlakoaricnnmeceseatsicecfosrabktmehihnaeaetwvttiohicoerrk(cPofhoBferamPtKchihce)aePlmmBuioncPddaKele.lr:mgAooPvedhsaeyiwlls.aiibothlleoingdiaectaaacllhoyncbobamlsoepodadmrtfmolodewenltruaastreeesduastnoedd Poinbothtobeusoelnforddvwaeoetpniroabanrnotuauonnrbeddset(ohPrnveOetbDhdeeg)in:dincoTinsdiheenengacsdoseoofsoceari-alrooteenwsdpa-owdnnoiesstsheetipsemuoxactirnthaetpdatonhilnaiatnctiimcodidneaner.kncTsechetfi.hsreopmlooiwantedirossemen-doresostfpotofhnteesneratmnhgeoedueoplfpoerr Promofoctaerrc:inAogneangeesnist sthtiamtuislanteost cthaerccinloongaelneicxpitasneslifobnuot fththatewinhietinataeddmcienllisttoerperdodauftceer aanneinoiptilaatsomr. Recstehepeletobcirtni:vdeAinbgmin(odfloienrcgeuxolaafrmasptsrlpuee,cctsiuefrieecawsruyiblthshitynadnarcoecceaalnlrbdooranosrnpeetchceiepfitccoerpl)l.h'syssiuorlfoagciectehfafteicst cthhaatraacctceormizepdanbiyes Rec(elipgtaonrds)itien:terTahcetsp. ortion of the receptor molecule or structure with which the compound RefeottfaoorsrfoesbrameneesfdcslaweaemicNildetythoOnloostiAsmeur.atEi(ltRaLaentf,xiDopaapno)L:pssOuroAerAefcniEttaheoLbesl,ttedhiomaerrtiahasatkueubmsoe(ewnfadncdi.htehpmlGoeutapenernurckelieaordrtautoilasolsiynene,fut(yfwisenescicdtpthlsauinnuddnnuiEnircngiPengrAgstpea'aneisnrslnhtiiyotfaienvpftcaeismcaastneounc.rbeosgrIrrtgdhoceeeuanrapnelostrbh)afelmtlhydaaeagtrpniispvitleuliidedkdee)ly 12/23/03 G-4 DRAFT--DO NOT CITE OR QUOTE 222222222233333344444333341111111111111122575225036890374403346074689548923689571 Relatsottuixvdiecya,pnsotptieencnitcehysa,t(oRsrpEmePcai)ft:ricixTs,hteuetdcrya.,;tiaaoncdoofnntochteepaptvoestiremangicelaydrottoof tothobextacicionneagqeugnievenarelrteoanlctthyoexbsiucttaenbqdausaiervddaloenncaysivnaglluee. Relauaotmnfive2oxenmpgroeisstahekneds(epRtxhoRpapt)ou:tslhaeTetdihoedenxisvpreioidlnsaeetdaidvbcgeoyrmhotouherpeatsrhsuataurtseedtyoow.ffittcThheheetehddreiiesffeldeaairtssieeevnaeacsmeerisironiknsrkgiisstakhdseebtfhueienntweeudxenpeeanoxsspttehhodees.eredaAxtpgeroreoosluefapddti.ivaseneadrsisek ResCwrteherDalevetsDeoaersi/,recCasosDnmotdoFupsrstochooueemrnscd:edisiraoRcinxnuetitlshnoaer-troiltvnihpkogeoeigreePsennCnvvairiiBcrreoosmmnnamamanttedeeernnrhiittaaa..lvlssP.eootRtrheeepnsltpeaioracvlteeosrnietrtshsieaabrltvefcocooiorrnmsrteaiedninicssolptuurrdierbecvueistosiouowisnlslhy,aesnnfedodtrhcimmeiryeceduhnlatasvt,eiboinotoaf, Riskeeoxxn(ppeinor(esrtseuhspreeerdectsooiennnavttecianxhlugteemotshfierchaaucnlemgaritgnaaenginnttfhyroeoratmhlatahzmte)h:riaxortTmu(rhreeewpoprielrflsoceobhncaetcbimunilrigi)ct.yathlsoe.fciIennrjtuqariuyna,tnydtiittshaeataitvsheea,troemrrmdwesia,ltlrhinsfokrtoisomccur) to Sloproeeeexxnsppfetoarhrevcsesutesoirdenerdcs:froiceAnroaunsrusreneeudisptipcsnpaooentnrhfcdebpeionrrloogurpiwnstodok-r,dtrfiogirosseoknenmse(reorlaeagfsllilasioyfnpethatooipapmnpfuretlho1aeextixiniodmpno1oa)s0ste0uia-n.frrgfeeestocpotroeaednnxspceaeegrreeedmnlaitng.tig/okTnaghs/9idhs5aip%ye,s,tticihsmoangtafetiiesnd,,eeufrnoasclruleyallliymit, Stanbtpchodeoetnpawtrurredelolaeialtzntifeioovtdnhresema.rniesoIyxtkrpdtiioasinfslffiebretdeyorqetarhnunaceddtneiesotulfnyii(nneScixtaMoipgonoeRnvs,e)eas:rdnetexdTpd,ohiantpionstuedailr/sapoptrtireheorrtencaasrcetieenoilntanbbt.eaiytvcwTemohemhuiesolnetrmaittpsheluseyatrsiueenudxgorypef.tohtishsTeeehudresadautiiSfnaofMdlelbyrtReyhnset1icasr0ene0sdfi.inemarrreidilnsaiczkreetdo to Staticcinohsftnaliunvcecaenenlctscieioognutnh,lideafiaecdxapifpnrfliceaoerire:nincicTthehoobenicelpeytrwoo5eb%feaanboditlfiwifttfhyoeertgehtrinaomttuseaptsaroetriisssluteuilsctssaum.laalsSlyiytgubncdeioyfindcdsuaeiendsecitgoreencldehcvsoaetnnalcs.tiiesdtaeiclroaantlileoy.nssBigmynaifyicant if Thyhaarcnootdriimdvdaoestncetiresmescau(esTlreat3aTtiianSnnHgadchpTtoiro4orn)md.suoTicnnt3ietohan(ynTwrdSohTiHde4)nc:beTllAol3sohadlenoaldredmvTieon4lngseltefoevseeepcdlrsrobeadatreucedckhtbioioygnnhtt.hahenedahnryetpeleroiatohsreaplomitfuutisht/aepritythuygirtloaanridydgthlaantd ToleTdrrhaienbklteeinrmgdawiilsayuteisnrettdahkafrteecq(aTuneDnbIte)ly:iniAgneWTstDeodrIlddisaHialnyeaeolstvhteimrOaargtleiafnoeitfzimtahteeiowanmi(tWohuoHnuttOoa)fshaigecanolitfnhitcaaamsnstienhsasenmatletihnntrfsio.sokTd. hoer 12/23/03 G-5 DRAFT--DO NOT CITE OR QUOTE 222221111111111112030442573689368942571 2222257689 utgenernamvero"aitldolaylebcrlaoybnalneso"stoeicsi"uaatsceecdde,wpatiasthbclotehn"etoabmra"sirniicasknctofsnredseou.m"nopttisoenrvoef afonoidntaennddewdaftuern.ctTioonlearnabdleasdionetaskneoits Toxpsiucremesqemnuetidvinatolaernmecpiexret(usTerEenQtmt)hu:eltTi2p,h3lie,e7td,o8xb-iyTcCtehDqeuDrievstaoplxeeicnctcievyqefuamicvataoslrse(ncTcoEenFcoe)fnotthrfeaetmaiocinhx.tduTiroehx.einp-rloikdeucctosmapreound ToxTcaaicorcCecmeDotqphuDuoeni,utrvtneuahsdnleuecplmnetrcreootysasfeitfennatxttocipiextneosircratinm(smTctehiiEmxeentFbuat)ierv:feraicioTtlojafEubttdFhhlgeseemcdwgoaeretomnalult.p-pusa,tsruwienditgithehedaltplhaoeontdfeTtnwEhteFiealallo-vtufoa2nxil,di3aceb,ir7ltsey,t8od-ooTafdtCeataDoacxnDhdicdbtiiateoykixnioingnfg-21lii.,kn3teT,o7E,8F-s Traansscartiepmtipolna:te,Twheithprroecseuslstinogf ctroannsstfreurctoinfggeanmetiecssinenfogremr aRtNioAn tmoothleecmuleesusesninggeraRDNNAA. molecule Traptnhrsaoctcreiisspset.ifofenctfiavcetoinr:thAe isnuibtisattaionnce, ,stuimsuuallalytioanp,roortetienr,mthinaattiisondeovfetlhoepegdenweittihcintrathnescorirpgtainoinsm and Uppuesruablolyunnodt: aAtrupelasutsaitbisleticuaplpceornlfiimdeitntcoetlhime ittr.ue value of a quantity or response. This is Weiiciagnnanhcfuoaltsu-rgeomdesfina-natetgnivmohiandadu,yevmbnecoacrantseuhe,:spaeeAnofdfisnemiisctaieatvp,al,epsseauraoncniadnhdcmhahnsueeumcgcsaaheantadnicnvsef.eiors,,rmiicnnhodhafeuraatmcectrtaimeonrnsiinz., iisnnTugghpwetphohaerpetepttxhrhteoeeranhcatyhntpdocoouwtnhnhsediisedcirhesrwttshhhaaeatltlaavcsncaoiianelgdanebittnilifeoticndsata, 12/23/03 G-6 DRAFT--DO NOT CITE OR QUOTE 321 REFERENCES FOR PART IIIA b b o t t B D , B i r n b a u m , L S . ( 1 9 9 0 ) R a t e m b r y o n i c p a l a t a l s h e l v e s r e s p o n d t o T C D D i n o r g a n c u l t u r e . T o x i c o l A p p l 4 Pharm acol 103(3):441-51 65 A b b o t t , B D , B i r n b a u m , L S . ( 1 9 9 1 ) T C D D e x p o s u r e o f h u m a n e m b r y o n i c p a l a t a l s h e l v e s i n o r g a n c u l t u r e a l t e r s t h e 7 d ifferen tiation o f m ed ia l ep ith elial cells. T era to lo g y 4 3 (2 ):1 1 9 -3 2 . 89 A b b o t t , B D ; H a r r i s , M W ; B i r n b a u m , L S . ( 1 9 9 2 ) C o m p a r i s o n s o f t h e e f f e c t s o f T C D D a n d h y d r o c o r t i s o n e o n g r o w t h 10 f a c t o r e x p r e s s i o n p r o v i d e i n s i g h t i n t o t h e i r i n t e r a c t i o n i n t h e e m b r y o n i c m o u s e p a l a t e . T e r a t o l o g y 4 5 ( 1 ) : 3 5 - 5 3 . 1112 A b b o t t , B D ; B i r n b a u m , L S ; P e r d e w , G H . ( 1 9 9 5 ) D e v e l o p m e n t a l e x p r e s s i o n o f t w o m e m b e r s o f a n e w c l a s s o f 13 t r a n s c r i p t i o n f a c t o r s : I . e x p r e s s i o n o f a r y l h y d r o c a r b o n r e c e p t o r i n t h e C 5 7 B L / 6 N m o u s e e m b r y o . D e v D y n 14 2 0 4 ( 2 ) : 1 3 3 - 4 3 1156 A b b o t t , B D ; H e l d , G A ; W o o d , C R ; e t a l . ( 1 9 9 9 ) A h R , A R N T , a n d C Y P 1 A 1 m R N A q u a n t i t a t i o n i n c u l t u r e d h u m a n 17 e m b r y o n i c p a l a t e s e x p o s e d t o T C D D a n d c o m p a r i s o n w i t h m o u s e p a l a t e i n v i v o a n d i n c u l t u r e . T o x i c o l S c i 18 4 7 ( 1 ) : 6 2 - 7 5 2109 A b b o t t , B D ; S c h m i d , J E ; P i t t , J A ; e t a l . ( 1 9 9 9 ) A d v e r s e r e p r o d u c t i v e o u t c o m e s i n t h e t r a n s g e n i c A h R - d e f i c i e n t 21 m o u s e . T o x i c o l A p p l P h a r m a c o l 1 5 5 ( 1 ) : 6 2 - 7 0 . 2223 A b r a h a m , K ; K r o w k e , R ; N e u b e r t , D . ( 1 9 8 8 ) P h a r m a c o k i n e t i c s a n d b i o l o g i c a l a c t i v i t y o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o 24 p - d i o x i n . 1 . d o s e - d e p e n d e n t t i s s u e d i s t r i b u t i o n a n d i n d u c t i o n o f h e p a t i c e t h o x y r e s o r u f i n O - d e e t h y l a s e i n r a t s 25 f o l l o w i n g a s i n g l e i n j e c t i o n . A r c h T o x i c o l 6 2 : 3 5 9 - 3 6 8 . 2276 A b r a h a m , K ; P a p k e , O ; B a l l , M ; e t a l . ( 1 9 9 4 ) C o n c e n t r a t i o n s o f P C D D s , P C D F s a n d c o p l a n a r P C B s i n b l o o d f a t o f a 28 b r e a s t - f e d a n d a f o r m u l a - f e d i n f a n t . O r g a n o h a l o g e n C o m p o u n d s 2 1 : 1 6 3 - 1 6 5 . 3209 A b r a h a m , K ; P a p k e , O ; B a l l , M ; e t a l . ( 1 9 9 5 ) C h a n g e s i n b l o o d l i p i d c o n c e n t r a t i o n o f P C D D s , P C D F s , a n d c o p l a n a r 31 P C B s i n a b r e a s t - f e d a n d a f o r m u l a - f e d i n f a n t i n t h e s e c o n d y e a r o f l i f e . O r g a n o h a l o g e n C o m p o u n d s 2 6 : 2 2 3 - 2 2 5 . 3323 A b r a h a m , K ; P a p k e , O ; G r o s s , A ; e t a l . ( 1 9 9 8 ) T i m e c o u r s e o f P C D D / P C D F / P C B c o n c e n t r a t i o n s i n b r e a s t - f e e d i n g 34 m o t h e r s a n d t h e i r i n f a n t s . C h e m o s p h e r e 3 7 : 1 7 3 1 - 1 7 4 . 3356 A b r a h a m , K ; P a p k e , O ; W a h n , U ; e t a l . ( 2 0 0 0 ) P O P a c c u m u l a t i o n i n i n f a n t s d u r i n g b r e a s t - f e e d i n g . O r g a n o h a l o g e n 37 C o m p o u n d s 4 8 , 2 5 - 2 6 . 3389 A h l b o r g , V G ; B e c k i n g , G C ; B i r n b a u m , L S ; e t a l . ( 1 9 9 4 ) T o x i c e q u i v a l e n c y f a c t o r s f o r d i o x i n - l i k e P C B s . 40 C h e m o s p h e r e 2 8 ( 6 ) : 1 0 4 9 - 1 0 6 7 . 4412 A l a l u u s u a , S ; L u k i n m a a , P - L ; V a r t i a i n e n , T ; e t a l . ( 1 9 9 6 ) P o l y c h l o r i n a t e d d i b e n z o - p - d i o x i n s a n d d i b e n z o f u r a n s v i a 43 m o t h e r ' s m i l k m a y c a u s e d e v e l o p m e n t a l d e f e c t s i n t h e c h i l d 's t e e t h . E n v i r o n T o x i c o l P h a r m a c o l 1 : 1 9 3 - 1 9 7 . 4454 A k h t a r , F . Z , G a r a b r a n t , D . H . , M i c h a l e k , J . E . ( 2 0 0 3 ) C a n c e r i n U S A i r F o r c e V e t e r a n s o f t h e V i e t n a m W a r . 46 O r g a n o h a l o g e n C o m p o u n d s 6 4 : S e c t i o n II. V i e t n a m S t u d i e s 4478 A l a l u u s u a , S ; L u k i n m a a , P - L ; T o r p p a , T ; e t a l . ( 1 9 9 9 ) D e v e l o p i n g t e e t h a s b i o m a r k e r o f d i o x i n e x p o s u r e . L a n c e t 49 3 5 3 : 2 0 6 . 5510 M a c a c a m u la ttaA l l e n , J R ; C a r s t e n s , L A . ( 1 9 6 7 ) L i g h t a n d e l e c t r o n m i c r o s c o p i c o b s e r v a t i o n s i n 5523 f a t . A m J V e t R e s 2 8 : 1 5 1 3 - 1 5 2 6 . m o n k ey s fed toxic 12/23/03 R-1 DRAFT--DO NOT CITE OR QUOTE 1 A lle n , JR .; L a lich , JJ. (1 9 6 2 ) R e sp o n se o f ch ic k e n s to p r o lo n g e d fe e d in g o f cru d e "to x ic fa t." P ro c S o c E x p B io l 2 M ed 109:48-51. 43 A l l e n , J R ; B a r s o t t i , D A ; V a n M i l l e r , J P ; e t a l . ( 1 9 7 7 ) M o r p h o l o g i c a l c h a n g e s i n m o n k e y s c o n s u m i n g a d i e t 5 containin g lo w lev els o f 2,3,7,8-tetrach lorod ib en zod ioxin . F o o d C o sm et T o x ico l 1 5 :4 01 -4 1 0 . 67 A l l e n , J R . ; B a r s o t t i , D A ; L a m b r e c h t , L K ; e t a l . ( 1 9 7 9 ) R e p r o d u c t i v e e f f e c t s o f h a l o g e n a t e d a r o m a t i c h y d r o c a r b o n s 8 on n on h u m an prim ates. A n n N Y A ca d S ci 3 2 0 :4 1 9 -4 2 5 . 109 A l l e n , B C ; K a v l o c k , R J ; K i m m e l , C A ; e t a l . ( 1 9 9 4 ) D o s e - r e s p o n s e a s s e s s m e n t f o r d e v e l o p m e n t a l t o x i c i t y . I I . 11 c o m p a r i s o n o f g e n e r i c b e n c h m a r k d o s e e s t i m a t e s w i t h n o o b s e r v e d a d v e r s e e f f e c t l e v e l s . F u n d a m A p p l T o x i c o l 12 2 3 : 4 8 7 - 4 9 5 . 1134 A l s h a r i f , N Z ; L a w s o n , T ; S t o h s , S J . ( 1 9 9 4 ) O x i d a t i v e s t r e s s i n d u c e d b y 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i s 15 m e d i a t e d b y t h e a r y l h y d r o c a r b o n ( A h ) r e c e p t o r c o m p l e x . T o x i c o l o g y 9 2 : 3 9 - 5 1 . 1176 A m e r i c a n A c a d e m y o f P e d i a t r i c s . ( 1 9 9 7 ) B r e a s t f e e d i n g a n d t h e u s e o f h u m a n m i l k . P e d i a t r i c s 1 0 0 ( 6 ) : 1 0 3 5 - 1 0 3 9 1189 A m b r o s o n e , C B ; F r e u n d e n h e i m , J L ; G r a h a m , S ; e t a l . ( 1 9 9 5 ) C y t o c h r o m e P 4 5 0 I A 1 a n d g l u t a t h i o n e - s - t r a n s f e r a s e 20 ( M 1 ) g e n e t i c p o l y m o r p h i s m s a n d p o s t - m e n o p a u s a l b r e a s t c a n c e r r i s k . C a n c e r R e s 5 5 : 3 4 8 3 - 3 4 8 5 . 2212 A n d e r s e n , M E ; M i l l s , J J ; G a r g a s , M L ; e t a l . ( 1 9 9 3 ) M o d e l i n g r e c e p t o r - m e d i a t e d p r o c e s s e s w i t h d i o x i n : i m p l i c a t i o n s 23 f o r p h a r m a c o k i n e t i c s a n d r i s k a s s e s s m e n t . R i s k A n a l 1 : 2 5 - 3 6 . 2254 A n d e r s e n , M E ; B i r n b a u m , L S ; B a r t o n , H A ; e t a l . ( 1 9 9 7 ) R e g i o n a l h e p a t i c C Y P 1 A 1 a n d C Y P 1 A 2 i n d u c t i o n w i t h 26 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n e v a l u a t e d w i t h a m u l t i - c o m p a r t m e n t g e o m e t r i c m o d e l o f h e p a t i c z o n a t i o n . 27 T o x i c o l A p p l P h a r m a c o l 1 4 4 : 1 4 5 - 1 5 5 . 2298 A r i e n s , E J ; v a n R o s s u m , J M ; K o o p m a n , P C . ( 1 9 6 0 ) R e c e p t o r r e s e r v e a n d t h r e s h o l d p h e n o m e n a . I . T h e o r y a n d 30 e x p e r i m e n t s w i t h a u t o n o m i c d r u g s t e s t e d o n i s o l a t e d o r g a n s . A r c h I n t P h a r m a c o d y n 1 2 7 : 4 5 9 - 4 7 8 . 3312 A r n o l d , D L ; N e r a , E A ; S t a p l e y , R ; e t a l . ( 1 9 9 6 ) P r e v a l e n c e o f e n d o m e t r i o s i s i n r h e s u s ( M a c a c a m u l a t t a ) m o n k e y s 33 i n g e s t i n g P C B ( A r o c l o r 1 2 5 4 ) : r e v i e w a n d e v a l u a t i o n . F u n d a m A p p l T o x i c o l 3 1 ( 1 ) : 4 2 - 5 5 . 3354 A T S D R ( A g e n c y f o r T o x i c S u b s t a n c e s a n d D i s e a s e R e g i s t r y ) . ( 1 9 9 9 a ) T o x i c o l o g i c a l p r o f i l e f o r c h l o r i n a t e d 36 d i b e n z o - p - d i o x i n s . U n i t e d S t a t e s D e p a r t m e n t o f H e a l t h a n d H u m a n S e r v i c e s . 3378 A T S D R . ( 1 9 9 9 b ) H e a l t h c o n s u l t a t i o n ( e x p o s u r e i n v e s t i g a t i o n ) C a l c a s i e u E s t u a r y ( a k a M o s s v i l l e ) L a k e C h a r l e s , 39 C a l c a s i e u P a r i s h , L A . C e r c l i s N o . L A 0 0 0 2 3 6 8 1 7 3 . P r e p a r e d b y E x p o s u r e I n v e s t i g a t i o n a n d C o n s u l t a t i o n B r a n c h , 40 D i v i s i o n o f H e a l t h A s s e s s m e n t a n d C o n s u l t a t i o n . 4412 A y l w a r d , L L ; H a y s , S M ; K a r c h , N J ; e t a l . ( 1 9 9 6 ) R e l a t i v e s u s c e p t i b i l i t y o f a n i m a l s a n d h u m a n s t o t h e c a n c e r h a z a r d 43 p o s e d b y 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n u s i n g i n t e r n a l m e a s u r e s o f d o s e . E n v i r o n S c i T e c h n o l 3 0 : 3 5 3 4 - 3 5 4 3 . 4454 A y l w a r d , L ; H a y e s , S ; B r u n e t , R ; e t a l . ( 2 0 0 3 ) I m p a c t o f a c o n c e n t r a t i o n - d e p e n d e n t e l i m i n a t i o n r a t e f o r T C D D o n 46 d o s e e s t i m a t e s f o r t h e N I O S H c o h o r t . O r g a n o h a l o g e n C o m p o u n d s 6 4 : 1 2 8 - 1 3 1 . 4478 A y l w a r d , L L ; B r u n e t , R C ; C a r r i e r , G ; e t a l . ( 2 0 0 4 ) C o n c e n t r a t i o n - d e p e n d e n t T C D D e l i m i n a t i o n k i n e t i c s i n h u m a n s : 49 t o x i c o k i n e t i c m o d e l i n g f o r m o d e r a t e l y t o h i g h l y e x p o s e d a d u l t s f r o m S e v e s o , I t a l y , a n d V i e n n a , A u s t r i a , a n d i m p a c t 50 o n d o s e e s t i m a t e s f o r t h e N I O S H c o h o r t . J E x p o A n a l E n v i r o n E p i d e m i o l O n - l i n e p u b l i c a t i o n A p r i l 1 4 , 2 0 0 4 . 555123 (R eference a d d ed d u rin g P ro o f)B a c c a r e l l i , A ; M o c a r e l l i , P ; P a t t e r s o n , D G J r . ; e t a l . ( 2 0 0 2 ) I m m u n o l o g i c E f f e c t s o f D i o x i n : N e w R e s u l t s f r o m 54 S e v e s o a n d C o m p a r i s o n w i t h O t h e r S t u d i e s . E n v i r o n . H e a l t h P e r s p e c t . 1 1 0 : 1 1 6 9 - 1 1 7 3 . 12/23/03 R-2 DRAFT--DO NOT CITE OR QUOTE 21 B a r s o t t i , D A ; A b r a h a m s o n , L J ; A l l e n , J R . ( 1 9 7 9 ) H o r m o n a l a l t e r a t i o n s i n f e m a l e r h e s u s m o n k e y s f e d a d i e t 3 con tain in g 2 ,3 ,7 ,8-tetra ch lo ro d ib en zo -p -d io x in . B u ll E n viron C o n ta m T o x ic o l 2 1 :4 6 3 -4 6 9 . 45 B e c h e r , H ; F l e s c h - J a n y s , D ; K a u p p i n e n , T ; e t a l . ( 1 9 9 6 ) C a n c e r m o r t a l i t y i n G e r m a n m a l e w o r k e r s e x p o s e d t o 6 p h en o x y h erbicid es and dioxin s. C an cer C au ses C ontrol 7 :3 1 2 -3 2 1 . 87 B e c h e r , H ; S t e i n d o r f , K . ; F l e s c h - J a n y s , D . ( 1 9 9 8 ) Q u a n t i t a t i v e c a n c e r r i s k a s s e s s m e n t f o r d i o x i n s u s i n g a n 9 occu p ation al cohort. E nviron H ealth P erspect 1 0 6(2 ):6 6 3 -6 7 0 . 1110 B e c k , H ; E c k a r t , K ; M a t h a r , W ; e t a l . ( 1 9 8 9 ) L e v e l s o f P C D D ' s a n d P C D F ' s i n a d i p o s e t i s s u e o f o c c u p a t i o n a l l y 12 e x p o s e d w o r k e r s . C h e m o s p h e r e 1 8 : 5 0 7 - 5 1 6 . 1134 B e r t a z z i , P A ; d i D o m e n i c o . ( 1 9 9 4 ) C h e m i c a l , e n v i r o n m e n t a l , a n d h e a l t h a s p e c t s o f t h e S e v e s o , I t a l y , a c c i d e n t . I n : 15 S c h e c t e r , A . e d . D i o x i n s a n d h e a l t h . N e w Y o r k : P l e n u m P r e s s , p p . 5 8 7 - 6 3 2 . 1176 B e r t a z z i , P A ; P e s a t o r i , A C ; C o n s o n n i , D ; e t a l . ( 1 9 9 3 ) C a n c e r i n c i d e n c e i n a p o p u l a t i o n a c c i d e n t a l l y e x p o s e d t o 18 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p a r a - d i o x i n . E p i d e m i o l o g y 4 ( 5 ) : 3 9 8 - 4 0 6 . 2109 B e r t a z z i , P A ; Z o c c h e t t i , C ; G u e r c i l e n a , S ; e t a l . ( 1 9 9 7 ) D i o x i n e x p o s u r e a n d c a n c e r r i s k : a 1 5 - y e a r m o r t a l i t y s t u d y 21 a f t e r t h e " S e v e s o A c c i d e n t . " E p i d e m i o l o g y 8 ( 6 ) : 6 4 6 - 6 5 2 . 2223 B e r t a z z i , P A ; B e r n u c c i , I ; B r a m b i l l a , G ; e t a l . ( 1 9 9 8 ) T h e S e v e s o s t u d i e s o n e a r l y a n d l o n g - t e r m e f f e c t s o f d i o x i n 24 e x p o s u r e : a r e v i e w . E n v i r o n H e a l t h P e r s p e c t 1 0 6 ( 2 ) : 6 2 5 - 6 3 3 . 2256 B e r t a z z i , P A ; P e s a t o r i , A C ; C o n s o n n i , D ; e t a l . ( 1 9 9 9 ) E p i d e m i o l o g y o f l o n g - t e r m h e a l t h e f f e c t s o f d i o x i n e x p o s u r e 27 i n t h e S e v e s o p o p u l a t i o n . O r g a n o h a l o g e n C o m p o u n d s 4 4 : 3 3 7 - 3 3 8 . 2289 B e r t a z z i , P A ; C o n s o n n i , D ; B a c h e t t i , S ; e t a l . ( 2 0 0 1 a ) H e a l t h e f f e c t s o f d i o x i n e x p o s u r e : a 2 0 - y e a r m o r t a l i t y s t u d y . 30 A m J E p i d e m i o l 1 5 3 ( 1 1 ) : 1 0 4 8 . 3312 B e r t a z z i , P A ; C o n s o n n i , D ; B a c h e t t i , S ; e t a l . ( 2 0 0 1 b ) B e r t a z z i e t a l . r e s p o n d t o S m i t h a n d L o p i p e r o . A m J E p i d e m i o l 33 1 5 3 ( 1 1 ) : 1 0 3 1 - 1 0 4 4 . 3354 B i r n b a u m , L S . ( 1 9 8 3 ) D i s t r i b u t i o n a n d e x c r e t i o n o f 2 , 3 , 6 , 2 ' , 3 ' , 6 ' - a n d 2 , 4 , 5 , 2 ' 4 ' 5 ' - h e x a c h l o r o b i p h e n y l i n s e n e s c e n t 36 r a t s . T o x i c o l A p p l P h a r m a c o l 7 0 : 2 6 2 - 2 7 2 . 3378 B i r n b a u m , L S . ( 1 9 9 4 a ) E v i d e n c e f o r t h e r o l e o f t h e A h R i n r e s p o n s e s t o d i o x i n . I n : S p i t z e r , H L ; S l a g a , T J ; G r e e n l e e , 39 W F ; e t a l . , e d s . R e c e p t o r - m e d i a t e d b i o l o g i c a l p r o c e s s e s : i m p l i c a t i o n s f o r e v a l u a t i n g c a r c i n o g e n e s i s . P r o g r e s s i n 40 C l i n i c a l N e w Y o r k : W i l e y - L i s s , I n c . , p p . 1 3 9 - 1 5 4 . 4412 B i r n b a u m , L S . ( 1 9 9 4 b ) T h e m e c h a n i s m o f d i o x i n t o x i c i t y : r e l a t i o n s h i p t o r i s k a s s e s s m e n t . E n v i r o n H e a l t h P e r s p e c t 43 1 0 2 ( S u p p l 9 ) : 1 5 7 - 1 6 7 . 4454 B i r n b a u m , L S ; M c D o n a l d , M M ; B l a i r , P C ; e t a l . ( 1 9 9 0 ) D i f f e r e n t i a l t o x i c i t y o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n 46 ( T C D D ) i n C 5 7 B L / 6 J m i c e c o n g e n i c a t t h e A h L o c u s . F u n d a m A p p l T o x i c o l 1 5 ( 1 ) : 1 8 6 - 2 0 0 . 4478 B i r n b a u m , L S ; D e V i t o , M J . ( 1 9 9 5 ) U s e o f t o x i c e q u i v a l e n c y f a c t o r s f o r r i s k a s s e s s m e n t f o r d i o x i n s a n d r e l a t e d 49 c o m p o u n d s . T o x i c o l o g y 1 0 5 : 3 9 1 - 4 0 1 . 5510 B i r n b a u m , L S ; C u m m i n g s , A M . ( 2 0 0 2 ) D i o x i n s a n d E n d o m e t r i o s i s : A P l a u s i b l e H y p o t h e s i s . E n v i r o n . H e a l t h 555234 P e r s p e c t . 1 1 0 : 1 5 - 2 1 . 12/23/03 R-3 DRAFT--DO NOT CITE OR QUOTE 1 B irn b a u m , L S ; S task al, D F ; D ilib erto , JJ. (2 0 0 3 ) H ea lth E ffects o f p o ly b r o m in a te d d ib e n z o -p -d io x in s (P B D D s) and 2 dib enzofu rans (P B D F s). E n viron m ent International 2 9 :8 5 5 -8 6 0 . 43 B j e r k e , D L ; P e t e r s o n , R E . ( 1 9 9 4 ) R e p r o d u c t i v e t o x i c i t y o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n m a l e r a t s : d i f f e r e n t 5 e ffe c ts o f in u tero v e r su s la cta tio n a l e x p o su r e . T o x ic o l A p p l P h a rm a co l 1 2 7 :2 4 1 -2 4 9 . 67 B j e r k e , D L ; S o m m e r , R J ; M o o r e , R W ; e t a l . ( 1 9 9 4 a ) E f f e c t s o f i n u t e r o a n d l a c t a t i o n a l 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p 8 d io x in e x p o s u r e o n r e s p o n s iv e n e s s o f th e m a le rat r e p r o d u c tiv e sy ste m to te sto ste r o n e stim u la tio n in a d u lth o o d . 9 T oxicol A p p l P harm acol 127:250-257. 1110 B j e r k e , D L ; B r o w n , T J ; M a c L u s k y , N J ; e t a l . ( 1 9 9 4 b ) P a r t i a l d e m a s c u l i n i z a t i o n a n d f e m i n i z a t i o n o f s e x b e h a v i o r i n 12 m a l e r a t s b y i n u t e r o a n d l a c t a t i o n a l e x p o s u r e t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i s n o t a s s o c i a t e d w i t h 13 a l t e r a t i o n s i n e s t r o g e n r e c e p t o r b i n d i n g o r v o l u m e s o f s e x u a l l y d i f f e r e n t i a t e d b r a i n n u c l e i . T o x i c o l A p p l P h a r m a c o l 14 1 2 7 ( 2 ) : 2 5 8 - 6 7 . 1156 B o d n e r , K M ; C o l l i n s , J J ; B l o e m e n , L J ; e t a l . ( 2 0 0 3 ) C a n c e r r i s k f o r c h e m i c a l w o r k e r s e x p o s e d t o 2 , 3 , 7 , 8 17 t e t r a c h l o r o d i b e n z o - p - d i o x i n . O c c u p E n v i r o n M e d . 6 0 ( 9 ) : 6 7 2 - 5 . 1189 B o c k , K W ; G s c h a i d m e i e r , H ; H e e l , H ; e t a l . ( 1 9 9 8 ) A H r e c e p t o r - c o n t r o l l e d t r a n s c r i p t i o n a l r e g u l a t i o n a n d f u n c t i o n 20 o f r a t a n d h u m a n U D P - g l u c u r o n o s y l t r a n s f e r a s e i s o f o r m s . A d v E n z y m e R e g u l 3 8 : 2 0 7 - 2 2 2212 B o n d , G G ; M c L a r e n , E A ; B r e n n e r , F E ; e t a l . ( 1 9 8 9 ) I n c i d e n c e o f c h l o r a c n e a m o n g c h e m i c a l w o r k e r s p o t e n t i a l l y 23 e x p o s e d t o c h l o r i n a t e d d i o x i n s . J O c c u p M e d 3 1 : 7 7 1 - 7 7 4 . 2254 B o o k s t a f f , R C ; K a m e l , F ; M o o r e , R W ; e t a l . ( 1 9 9 0 a ) A l t e r e d r e g u l a t i o n o f p i t u i t a r y g o n a d o t r o p i n - r e l e a s i n g h o r m o n e 26 ( G n R H ) r e c e p t o r n u m b e r a n d p i t u i t a r y r e s p o n s i v e n e s s t o G n R H i n 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n - t r e a t e d m a l e 27 r a t s . T o x i c o l A p p l P h a r m a c o l 1 0 5 : 7 8 - 9 2 . 2289 B o o k s t a f f , R C ; M o o r e , R W ; P e t e r s o n , R E . ( 1 9 9 0 b ) 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n c r e a s e s t h e p o t e n c y o f 30 a n d r o g e n s a n d e s t r o g e n s a s f e e d b a c k i n h i b i t o r s o f l u t e i n i z i n g h o r m o n e s e c r e t i o n i n m a l e r a t s . T o x i c o l A p p l 31 P h a r m a c o l 1 0 4 : 2 1 2 - 2 2 4 . 3323 B o w m a n , R E ; S c h a n t z , S L ; W e e r a s i n g h e , N C A ; e t a l . ( 1 9 8 9 ) C h r o n i c d i e t a r y i n t a k e o f 2 , 3 , 7 , 8 - T e t r a c h l o r o d i b e n z o 34 p - d i o x i n a t 5 o r 2 5 p a r t s p e r t r i l l i o n i n t h e m o n k e y : T C D D k i n e t i c s a n d d o s e - e f f e c t e s t i m a t e o f r e p r o d u c t i v e t o x i c i t y . 35 C h e m o s p h e r e 1 8 ( 1 - 6 ) : 2 4 3 - 2 5 2 . 3376 B o y d , J A ; C l a r k , G C ; W a l m e r , D ; e t a l . ( 1 9 9 5 ) E n d o m e t r i o s i s a n d t h e e n v i r o n m e n t : b i o m a r k e r s o f t o x i n e x p o s u r e . 38 C o n f e r e n c e o n E n d o m e t r i o s i s 2 0 0 0 , M a y 1 5 - 1 7 . 4309 B r e s l o w , N E ; D a y , N E . ( 1 9 8 7 ) S t a t i s t i c a l m e t h o d s i n c a n c e r r e s e a r c h . V o l . I I : t h e d e s i g n a n d a n a l y s i s o f c o h o r t 41 s t u d i e s . I A R C S c i P u b l 8 2 : 1 - 4 0 6 . 4423 B r o d y , B B ; R e i d , W D . ( 1 9 6 7 ) F e d P r o c . 2 6 : 1 0 6 2 - 1 0 7 0 . 4454 B r o w n , N M ; M a n z o l i l l o , P A ; Z h a n g , J X ; e t a l . ( 1 9 9 8 ) P r e n a t a l T C D D a n d p r e d i s p o s i t i o n t o m a m m a r y c a n c e r i n t h e 46 r a t. C a r c i n o g e n e s i s 1 9 ( 9 ) : 1 6 2 3 - 1 6 2 9 . 4478 B r u n e r - T r a n , K L ; R i e r , S E ; E i s e n b e r g , E ; e t a l . ( 1 9 9 9 ) T h e p o t e n t i a l r o l e o f e n v i r o n m e n t a l t o x i n s i n t h e 49 p a t h o p h y s i o l o g y o f e n d o m e t r i o s i s . G y n e c o l O b s t e t I n v e s t 4 8 ( S u p p l S 1 ) : 4 5 - 5 6 . 5510 B r u z y , L P ; H i t e s , R A . ( 1 9 9 5 ) E s t i m a t i n g t h e a t m o s p h e r i c d e p o s i t i o n o f p o l y c h l o r i n a t e d d i b e n z o - p - d i o x i n s a n d 5523 d i b e n z o f u r a n s f r o m s o i l . E n v i r o n S c i T e c h n o l 2 9 : 2 0 9 0 - 2 0 9 8 . 12/23/03 R-4 DRAFT--DO NOT CITE OR QUOTE 1 B ryan t, P L ; S c h m id , JE ; F en to n , S E ; et al. (2 0 0 1 ) T er a to g e n ic ity o f 2 ,3 ,7 ,8 -te tr a c h lo r o d ib e n z o -p -d io x in (T C D D ) in 2 m ic e lacking the exp ression o f E G F an d/or T G F -alp h a. T o x ic o l S ci 6 2 (1 ):1 0 3 -1 4 . 43 B u e n o d e M e s q u i t a , H B ; D o o r n b o s , G ; v a n d e r K u i p , D M ; e t a l . ( 1 9 9 3 ) O c c u p a t i o n a l e x p o s u r e t o p h e n o x y 5 h erb icid es a n d ch lo ro p h en o ls a n d ca n cer m ortality in th e N eth erla n d s. A m J In d M e d 2 3 :2 8 9 -3 0 0 . 67 B u r l e s o n , G R ; L e b r e c , H ; Y a n g , Y G ; e t a l . ( 1 9 9 6 ) E f f e c t o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) o n 8 in flu e n z a v iru s h o st resista n ce in m ic e . F u n d a m A p p l T o x ic o l 2 9 (1 ):4 0 -7 . 109 C a l v e r t , G M ; H o r n u n g , R W ; S w e e n e y , M H ; e t a l . ( 1 9 9 2 ) H e p a t i c a n d g a s t r o i n t e s t i n a l e f f e c t s i n a n o c c u p a t i o n a l 11 c o h o r t e x p o s e d t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p a r a - d i o x i n . J A M A 2 6 7 : 2 2 0 9 - 2 2 1 4 . 1123 C a l v e r t , G M ; W i l l i e , K K ; S w e e n e y , M H ; e t a l . ( 1 9 9 6 ) E v a l u a t i o n o f s e r u m l i p i d c o n c e n t r a t i o n s a m o n g U . S . w o r k e r s 14 e x p o s e d t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n . A r c h E n v i r o n H e a l t h 5 1 ( 2 ) : 1 0 0 - 1 0 7 . 1156 C a l v e r t , G M ; S w e e n e y , M H ; D e d d e n s , J ; e t a l . ( 1 9 9 9 ) E v a l u a t i o n o f d i a b e t e s m e l l i t u s , s e r u m g l u c o s e , a n d t h y r o i d 17 f u n c t i o n a m o n g U n i t e d S t a t e s w o r k e r s e x p o s e d t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i - b e n z o - p - d i o x i n . O c c u p E n v i r o n M e d 18 5 6 ( 4 ) : 2 7 0 - 2 7 6 . 2109 C a r a m a s c h i , F ; D e l C a i n o , G ; F a v a r e t t i , C ; e t a l . ( 1 9 8 1 ) C h l o r a c n e f o l l o w i n g e n v i r o n m e n t a l c o n t a m i n a t i o n b y T C D D 21 i n S e v e s o , I t a l y . I n t J E p i d e m i o l 1 0 : 1 3 5 - 1 4 3 . 2223 C a r l s o n , D B ; P e r d e w , G . ( 2 0 0 2 ) . A d y n a m i c r o l e f o r t h e A h r e c e p t o r i n c e l l s i g n a l i n g ? I n s i g h t s f r o m a d i v e r s e g r o u p 24 o f A h r e c e p t o r i n t e r a c t i n g p r o t e i n s . J . B i o c h e m . M o l . T o x i c o l . 1 6 : 3 1 7 - 3 2 5 . 2256 C a r r i e r , G ; B r u n e t , R C ; B r o d e u r J . ( 1 9 9 5 a ) M o d e l i n g o f t h e t o x i c o k i n e t i c s o f p o l y c h l o r i n a t e d d i b e n z o - p - d i o x i n s a n d 27 d i b e n z o f u r a n s i n m a m m a l i a n s , i n c l u d i n g h u m a n s . I . N o n l i n e a r d i s t r i b u t i o n o f P C D D / P C D F b o d y b u r d e n b e t w e e n 28 l i v e r a n d a d i p o s e t i s s u e s . T o x i c o l A p p l P h a r m a c o l 1 ( 2 ) : 2 5 3 - 6 6 . 3209 C a r r i e r , G ; B r u n e t , R C ; B r o d e u r , J . ( 1 9 9 5 b ) M o d e l i n g o f t h e t o x i c o k i n e t i c s o f p o l y c h l o r i n a t e d d i b e n z o - p - d i o x i n s 31 a n d d i b e n z o f u r a n s i n m a m m a l i a n s , i n c l u d i n g h u m a n s . I I . K i n e t i c s o f a b s o r p t i o n a n d d i s p o s i t i o n o f P C D D s / P C D F s . 32 T o x i c o l A p p l P h a r m a c o l . 1 ( 2 ) : 2 6 7 - 7 6 . 3334 C a r v e r , L A ; L a P r e s , J J ; J a i n , S ; e t a l . ( 1 9 9 8 ) C h a r a c t e r i z a t i o n o f t h e A h R - a s s o c i a t e d p r o t e i n , A R A 9 . J B i o l C h e m 35 2 7 3 ( 5 0 ) : 3 3 5 8 0 - 3 3 5 8 7 . 3376 C D C ( C e n t e r s f o r D i s e a s e C o n t r o l a n d P r e v e n t i o n ) . ( 1 9 9 7 ) V i t a l a n d h e a l t h s t a t i s t i c s . F e r t i l i t y , f a m i l y p l a n n i n g , a n d 38 w o m e n ' s h e a l t h : n e w d a t a f r o m t h e 1 9 9 5 N a t i o n a l S u r v e y o f F a m i l y G r o w t h . N a t i o n a l C e n t e r f o r H e a l t h S t a t i s t i c s , 39 C D C , U . S . D e p a r t m e n t o f H e a l t h a n d H u m a n S e r v i c e s . S e r i e s 2 3 , N o . 1 9 . 4410 C D C . ( 2 0 0 0 ) P e r s o n a l c o m m u n i c a t i o n f r o m D . P a t t e r s o n , C D C , A t l a n t a , G A t o M . L o r b e r , U . S . E P A , W a s h i n g t o n , 42 D C . A p r i l , 2 0 0 0 . 4443 C D C ( 2 0 0 3 ) S e c o n d N a t i o n a l R e p o r t o n H u m a n E x p o s u r e t o E n v i r o n m e n t a l C h e m i c a l s . D e p a r t m e n t o f H e a l t h a n d 45 H u m a n S e r v i c e s , C e n t e r s f o r D i s e a s e C o n t r o l a n d P r e v e n t i o n , N C E H P u b N o . 0 2 - 0 7 1 6 . R e v i s e d M a r c h 2 0 0 3 . 4476 C D C V i e t n a m E x p e r i e n c e S t u d y . ( 1 9 8 8 ) H e a l t h s t a t u s o f V i e t n a m v e t e r a n s . I I . P h y s i c a l h e a l t h . J A M A 48 2 5 9 : 2 7 0 8 - 2 7 1 4 . 4590 C h a h o u d , I . ; K r o w k e , R . ; S c h i m m e l , A . ; e t a l . ( 1 9 8 9 ) R e p r o d u c t i v e t o x i c i t y a n d p h a r m a c o k i n e t i c s o f 2 , 3 , 7 , 8 51 t e t r a c h l o r o d i b e n z o - p - d i o x i n . I . E f f e c t s o f h i g h d o s e s o n t h e f e r t i l i t y o f m a l e r a t s . A r c h T o x i c o l 6 3 : 4 3 2 - 4 3 9 . 5523 C h e n , Y C J ; G u o , Y L L ; H s u , C C . ( 1 9 9 2 ) C o g n i t i v e d e v e l o p m e n t o f c h i l d r e n p r e n a t a l l y e x p o s e d t o p o l y c h l o r i n a t e d 54 b i p h e n y l s ( Y u - C h e n g c h i l d r e n ) a n d t h e i r s i b l i n g s . J F o r m o s a n M e d A s s o c 9 1 : 7 0 4 - 7 0 7 . 12/23/03 R-5 DRAFT--DO NOT CITE OR QUOTE 1 C h eu n g, M O ; G ilbert, EF; P eterson , R E . (1 9 8 1 ) C ard iovascu lar teratogen icity o f 2, 3, 7, 2 8-tetra ch lo ro d ib en zo-p -d iox in in the ch ick em b ryo. T o x ic o l A p p l P h arm acol 6 1 (2 ):1 9 7 -2 0 4 . 34 C l a r k , A J . ( 1 9 3 3 ) T h e m o d e o f a c t i o n o f d r u g s o n c e l l s . B a l t i m o r e , M D : W i l l i a m s a n d W i l k i n s . 65 C l a r k , G ; T r i t s c h e r , A ; B e l l , D ; e t a l . ( 1 9 9 2 ) I n t e g r a t e d a p p r o a c h f o r e v a l u a t i n g s p e c i e s a n d i n t e r i n d i v i d u a l 7 d ifferen ces in resp on siven ess to d ioxin s and structural an alogs. E n viron H ealth P ersp ect 9 8 :1 2 5 -3 2 . 98 C l a r k , G C ; T r i t s c h e r , A ; M a r o n p o t , R ; e t a l . ( 1 9 9 1 ) T u m o r p r o m o t i o n b y T C D D i n f e m a l e r a t s . I n : G a l l o , M ; 10 S c h e u p l e i n , R ; v a n D e r H e i j d e n , K , e d s . B a n b u r y r e p o r t 3 5 : b i o l o g i c a l b a s i s f o r r i s k a s s e s s m e n t o f d i o x i n a n d r e l a t e d 11 c o m p o u n d s . C o l d S p r i n g H a r b o r L a b o r a t o r y , C o l d S p r i n g H a r b o r , N Y . 1123 C l e w e l l , H J ; G e n t r y , P R ; C o v i n g t o n , T R ; e t a l . ( 2 0 0 4 ) E v a l u a t i o n o f t h e p o t e n t i a l i m p a c t o f a g e - a n d g e n d e r - s p e c i f i c 14 (R eference a d d ed d u rin g P ro o f)p h a r m a c o k i n e t i c d i f f e r e n c e s o n t i s s u e d o s i m e t r y . T o x i c o l S c i 7 9 ( 2 ) : 3 8 1 - 9 3 . 1156 C o h e n , G M ; B r a c k e n , W M ; I y e r , R P ; e t a l . ( 1 9 7 9 ) A n t i c a r c i n o g e n i c e f f e c t s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n 17 o n b e n z o ( a ) p y r e n e a n d 7 , 1 2 - d i m e t h y l b e n z ( a ) a n t h r a c e n e t u m o r i n i t i a t i o n a n d i t s r e l a t i o n s h i p t o D N A b i n d i n g . C a n c e r 18 R e s 3 9 : 4 0 2 7 - 4 0 3 3 . 2109 C o h e n , J . ( 1 9 7 7 ) S t a t i s t i c a l p o w e r a n a l y s i s f o r t h e b e h a v i o r a l s c i e n c e s , r e v . e d . N e w Y o r k : A c a d e m i c P r e s s . 2212 C o l e , P ; T r i c h o p o u l o s , D ; P a s t i d e s , H ; e t a l . ( 2 0 0 3 ) D i o x i n a n d c a n c e r : a c r i t i c a l r e v i e w . R e g u l T o x i c o l P h a r m a c o l . 23 3 8 ( 3 ) : 3 7 8 - 8 8 . 2254 C o n o l l y , R B ; A n d e r s e n , M E . ( 1 9 9 7 ) H e p a t i c f o c i i n r a t s a f t e r d i e t h y l n i t r o s a m i n e i n i t i a t i o n a n d 2 , 3 , 7 , 8 26 t e t r a c h l o r o d i b e n z o - p - d i o x i n p r o m o t i o n : e v a l u a t i o n o f a q u a n t i t a t i v e t w o - c e l l m o d e l a n d o f C Y P 1 A 1 / 1 A 2 a s a 27 d o s i m e t e r . T o x i c o l A p p l P h a r m a c o l 1 4 6 : 2 8 1 - 2 9 3 . 2298 C o u r t n e y , K D ; M o o r e , J A . ( 1 9 7 1 ) T e r a t o l o g y s t u d i e s w i t h 2 , 4 , 5 - T a n d 2 , 3 , 7 , 8 - T C D D . T o x i c o l A p p l P h a r m a c o l 30 2 0 : 3 9 6 - 4 0 3 . 3312 C o u t u r e , L A ; A b b o t t , B D ; B i r n b a u m , L S . ( 1 9 9 0 ) A c r i t i c a l r e v i e w o f t h e d e v e l o p m e n t a l t o x i c i t y a n d t e r a t o g e n i c i t y 33 o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n : r e c e n t a d v a n c e s t o w a r d u n d e r s t a n d i n g t h e m e c h a n i s m . T e r a t o l o g y 4 2 : 6 1 9 34 6 2 7 . 3356 C r e s a n t a , J L ; F a r r i s , R P ; C r o f t , J B ; e t a l . ( 1 9 8 8 ) T r e n d s i n f a t t y a c i d i n t a k e s o f 1 0 - y e a r - o l d c h i l d r e n , 1 9 7 3 - 1 9 8 2 . J 37 A m e r D i e t e t i c A s s o c 8 8 : 1 7 8 - 1 8 4 . 3398 C r u m p , K S ; C a n a d y , R ; K o g e v i n a s , M . ( 2 0 0 3 ) M e t a - a n a l y s i s o f d i o x i n c a n c e r d o s e - r e s p o n s e f o r t h r e e o c c u p a t i o n a l 40 c o h o r t s . E n v i r o n H e a l t h P e r s p e c t . 1 1 1 ( 5 ) : 6 8 1 - 6 8 7 . 4412 C u m m i n g s , A M ; M e t c a l f , J L ; B i r n b a u m , L . ( 1 9 9 6 ) P r o m o t i o n o f e n d o m e t r i o s i s b y 43 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n r a t s a n d m i c e : t i m e - d o s e d e p e n d e n c e a n d s p e c i e s c o m p a r i s o n . T o x i c o l A p p l 44 P h a r m a c o l 1 3 8 ( 1 ) : 1 3 1 - 1 3 9 . 4456 C u m m i n g s , A M ; H e d g e , J M ; B i r n b a u m , L S . ( 1 9 9 9 ) E f f e c t o f p r e n a t a l e x p o s u r e t o T C D D o n t h e p r o m o t i o n o f 47 e n d o m e t r i o t i c l e s i o n g r o w t h b y T C D D i n a d u l t f e m a l e r a t s a n d m i c e . T o x i c o l S c i 5 2 ( 1 ) : 4 5 - 9 . 4498 D a n n a n , G A ; P o r u b e k , D J ; N e l s o n , S D ; e t a l . ( 1 9 8 6 ) 1 7 b e t a - e s t r a d i o l 2 - a n d 4 - h y d r o x y l a t i o n c a t a l y z e d b y r a t 50 h e p a t i c c y t o c h r o m e P - 4 5 0 : r o l e s o f i n d i v i d u a l f o r m s , i n d u c t i v e e f f e c t s , d e v e l o p m e n t a l p a t t e r n s , a n d a l t e r a t i o n s b y 51 g o n a d e c t o m y a n d h o r m o n e r e p l a c e m e n t . E n d o c r i n o l o g y 1 1 8 : 1 9 5 2 - 1 9 6 0 . 5523 D a v i s , D ; S a f e , S . ( 1 9 8 8 ) I m m u n o s u p p r e s s i v e a c t i v i t i e s o f p o l y c h l o r i n a t e d d i b e n z o f u r a n c o n g e n e r s : q u a n t i t a t i v e 54 s t r u c t u r e - a c t i v i t y r e l a t i o n s h i p s a n d i n t e r a c t i v e e f f e c t s . T o x i c o l A p p l P h a r m a c o l 9 4 : 1 4 1 - 1 4 9 . 12/23/03 R-6 DRAFT--DO NOT CITE OR QUOTE 1 D e n H o n d , E; R o e ls , H A ; H o p p e n b r o u w e r s, K ; et al. (2 0 0 2 ) S e x u a l m a tu ra tio n in r ela tio n to p o ly c h lo r in a te d 2 a r o m a t i c h y d r o c a r b o n s : S h a r p e a n d S k a k k e b a c k 's h y p o t h e s i s r e v i s i t e d . E n v i r o n . H e a l t h P e r s p e c t . 1 1 0 : 7 7 1 - 7 7 6 43 D e n i s o n , M S ; F i s h e r , J M ; W h i t l o c k , J P , J r . ( 1 9 8 9 ) P r o t e i n - D N A i n t e r a c t i o n s a t r e c o g n i t i o n s i t e s f o r t h e d i o x i n - A h 5 receptor com p lex. J B io l C h em 2 6 4 (28 ):16 4 7 8 -1 64 8 2 . 67 D e n i s o n , M S ; P h e l a n , D ; E l f e r i n k , C J . ( 1 9 9 8 ) T h e A h R s i g n a l t r a n s d u c t i o n p a t h w a y . I n : D e n i s o n , M S ; H e l f e r i c h , 8 W G , eds. T o x ica n t-recep tor in teraction s. B ristol. P A : T aylor & Francis; pp. 3-33. 109 D e r t i n g e r , S D ; S i l v e r s t o n e , A E ; G a s i e w i c z , T A . ( 1 9 9 8 ) I n f l u e n c e o f a r o m a t i c h y d r o c a r b o n r e c e p t o r - m e d i a t e d e v e n t s 11 o n t h e g e n o t o x i c i t y o f c i g a r e t t e s m o k e c o n d e n s a t e . C a r c i n o g e n e s i s 1 9 : 2 0 3 7 - 2 0 4 2 . 1123 D e V i t o , M J ; B i r n b a u m , L S . ( 1 9 9 5 ) D i o x i n s : m o d e l c h e m i c a l s f o r a s s e s s i n g r e c e p t o r - m e d i a t e d t o x i c i t y . T o x i c o l o g y 14 1 0 2 ( 1 - 2 ) : 1 1 5 - 2 3 . 1156 D e V i t o , M J ; M a , X F ; B a b i s h , J G ; e t a l . ( 1 9 9 4 ) D o s e - r e s p o n s e r e l a t i o n s h i p s i n m i c e f o l l o w i n g s u b c h r o n i c e x p o s u r e 17 t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n : c y p 1 a 1 , c y p 1 a 2 , e s t r o g e n - r e c e p t o r , a n d p r o t e i n - t y r o s i n e p h o s p h o r y l a t i o n . 18 T o x i c o l A p p l P h a r m a c o l 1 2 4 : 8 2 - 9 0 . 2109 D e V i t o , M J ; B i r n b a u m , L S ; F a r l a n d , W H ; e t a l . ( 1 9 9 5 ) C o m p a r i s o n s o f e s t i m a t e d h u m a n - b o d y b u r d e n s o f d i o x i n l i k e 21 c h e m i c a l s a n d T C D D b o d y b u r d e n s i n e x p e r i m e n t a l l y e x p o s e d a n i m a l s . E n v i r o n H e a l t h P e r s p e c t 1 0 3 : 8 2 0 - 8 3 1 . 2223 D e V i t o , M J ; D i l i b e r t o , J J ; R o s s , D G ; e t a l . ( 1 9 9 7 ) D o s e - r e s p o n s e r e l a t i o n s h i p s f o r p o l y h a l o g e n a t e d d i o x i n s a n d 24 d i b e n z o f u r a n s f o l l o w i n g s u b c h r o n i c t r e a t m e n t i n m i c e . I . C Y P 1 A 1 a n d C Y P 1 A 2 e n z y m e a c t i v i t y i n l i v e r , l u n g , a n d 25 s k i n . T o x i c o l . A p p l . P h a r m a c o l . 1 4 7 : 2 6 7 - 2 8 0 . 2276 D i G i o v a n n i , J ; V i a j e , A ; B e r r y , D L ; e t a l . ( 1 9 7 7 ) T u m o r - i n i t i a t i n g a b i l i t y o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n 28 ( T C D D ) a n d A r o c l o r 1 2 5 4 i n t h e t w o - s t a g e s y s t e m o f m o u s e s k i n c a r c i n o g e n e s i s . B u l l E n v i r o n C o n t a m T o x i c o l 29 1 8 ( 5 ) : 5 5 2 - 7 . 3310 D i G i o v a n n i , J . ; B e r r y , D L ; G l e a s o n , G L ; e t a l . ( 1 9 8 0 ) T i m e - d e p e n d e n t i n h i b i t i o n b y 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p 32 d i o x i n o f s k i n t u m o r i g e n e s i s w i t h p o l y c y c l i c h y d r o c a r b o n s . C a n c e r R e s 4 0 : 1 5 8 0 - 1 5 8 7 . 3334 D i l i b e r t o , J J ; A k u b u e , P I ; L u e b k e , R W ; e t a l . ( 1 9 9 5 ) D o s e - r e s p o n s e r e l a t i o n s h i p s o f t i s s u e d i s t r i b u t i o n a n d i n d u c t i o n 35 o f C Y P 1 A 1 a n d C Y P 1 A 2 e n z y m a t i c - a c t i v i t i e s f o l l o w i n g a c u t e e x p o s u r e t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n 36 ( T C D D ) i n m i c e . T o x i c o l A p p l P h a r m a c o l 1 3 0 : 1 9 7 - 2 0 8 . 3378 D i l i b e r t o , J J ; B u r g i n , D E ; B i r n b a u m , L S ( 1 9 9 9 ) E f f e c t s o f C Y P 1 A 2 o n D i s p o s i t i o n o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p 39 d i o x i n , 2 , 3 , 4 , 7 , 8 - p e n t a c h l o r o d i b e n z o f u r a n , a n d 2 , 2 ' , 4 , 4 ' , 5 , 5 ' - h e x a c h l o r o b i p h e n y l i n C Y P 1 A 2 k n o c k o u t a n d p a r e n t a l 40 ( C 5 7 B L / 6 N a n d 1 2 9 / S v ) s t r a i n s o f M i c e . T o x c i o l . A p p l . P h a r m a c o l . 1 5 9 : 5 2 - 6 4 . 4412 D i l i b e r t o , J J ; D e V i t o , M J ; R o s s , D G ; e t a l . ( 2 0 0 1 ) S u b c h r o n i c e x p o s u r e o f [ 3 H ] 43 2 . 3 . 7 . 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) i n f e m a l e B 6 C 3 F 1 m i c e : r e l a t i o n s h i p o f s t e a d y - s t a t e l e v e l s t o 44 d i s p o s i t i o n a n d m e t a b o l i s m . T o x i c o l S c i 6 1 ( 2 ) : 2 4 1 - 5 5 . 4456 D o s s , M ; S a v e r , H ; v o n T i e p e r m a n n , R ; e t a l . ( 1 9 8 4 ) D e v e l o p m e n t o f c h r o n i c h e p a t i c p o r p h y r i a ( p o r p h y r i a c u t a n e a 47 t a r d a ) w i t h i n h e r i t e d u r o p o r p h y r i n o g e n d e c a r b o x y l a s e d e f i c i e n c y u n d e r e x p o s u r e t o d i o x i n . J B i o c h e m 1 6 : 3 6 9 - 3 7 3 . 4489 D r a g a n , Y P ; X u , X ; G o l d s w o r t h y , T L ; e t a l . ( 1 9 9 2 ) C h a r a c t e r i z a t i o n o f t h e p r o m o t i o n o f a l t e r e d h e p a t i c f o c i b y 50 2 . 3 . 7 . 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n t h e f e m a l e r a t . C a r c i n o g e n e s i s 1 3 ( 8 ) : 1 3 8 9 - 1 3 9 5 . 5512 D u n a g i n , W G . ( 1 9 8 4 ) C u t a n e o u s s i g n s o f s y s t e m i c t o x i c i t y d u e t o d i o x i n s a n d r e l a t e d c h e m i c a l s . J A m A c a d 5534 D e r m a t o l 1 0 ( 4 ) : 6 8 8 - 7 0 0 . 12/23/03 R-7 DRAFT--DO NOT CITE OR QUOTE 1 D u n so n , D B ; H a se m a n , JK ; v a n B ir g e le n , A P J M ; et al. (2 0 0 0 ) S ta tistical a n a ly sis o f sk in tu m o r d ata fr o m T g .A C 2 m o u se bioassays. T o x ico l S ci 5 5:293-302. 43 E a s t i n , W C ; H a s e m a n , J K ; M a h l e r , J F ; e t a l . ( 1 9 9 8 ) T h e N a t i o n a l T o x i c o l o g y P r o g r a m e v a l u a t i o n o f g e n e t i c a l l y 5 altered m ice as p red ictive m o d els for id en tifying carcin ogen s. T o x ic o l P ath ol 2 6 :4 6 1 -4 7 3 . 67 E a t o n , D L ; G a l l a g h e r , E P ; B a m m l e r , T K ; e t a l . ( 1 9 9 5 ) R o l e o f c y t o c h r o m e P 4 5 0 1 A 2 i n c h e m i c a l c a r c i n o g e n e s i s : 8 im p lic a tio n s fo r h u m a n va ria b ility in e x p r e ssio n a n d e n z y m e activity. P h a r m a c o g e n e tic s 5 (5 ):2 5 9 -2 7 4 . 109 E g e l a n d , G M ; S w e e n e y , M H ; F i n g e r h u t , M A ; e t a l . ( 1 9 9 4 ) T o t a l s e r u m t e s t o s t e r o n e a n d g o n a d o t r o p i n s i n w o r k e r s 11 e x p o s e d t o d i o x i n . A m J E p i d e m i o l 1 3 9 : 2 7 2 - 2 8 1 . 1123 E m a , M ; O h e , N ; S u z u k i , M ; e t a l . ( 1 9 9 4 ) D i o x i n b i n d i n g a c t i v i t i e s o f p o l y m o r p h i c f o r m s o f m o u s e a n d h u m a n 14 a r y l h y d r o c a r b o n r e c e p t o r s . J B i o l C h e m 2 6 9 ( 4 4 ) : 2 7 3 3 7 - 2 7 3 4 . 1156 E m o n d , C ; B i r n b a u m , L S ; D e V i t o , M J . ( 2 0 0 4 ) P h y s i o l o g i c a l l y b a s e d p h a r m a c o k i n e t i c m o d e l f o r d e v e l o p m e n t a l 17 (R eference a d d ed d u rin g P ro o f)e x p o s u r e s t o T C D D i n t h e r a t . T o x i c o l S c i . 8 0 ( 1 ) : 1 1 5 - 3 3 . 1189 E n a n , E ; M a t s u m u r a , F . ( 1 9 9 4 ) 2 , 3 , 7 , 8 - T e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) - i n d u c e d c h a n g e s i n g l u c o s e 20 t r a n s p o r t i n g a c t i v i t y i n g u i n e a p i g s , m i c e , a n d r a t s i n v i v o a n d i n v i t r o . J B i o c h e m T o x i c o l 9 ( 2 ) : 9 7 - 1 0 6 . 2212 E n a n , E ; M a t s u m u r a , F . ( 1 9 9 6 ) I d e n t i f i c a t i o n o f c - S r c a s t h e i n t e g r a l c o m p o n e n t o f t h e c y t o s o l i c A h R c o m p l e x , 23 t r a n s d u c i n g t h e s i g n a l o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) t h r o u g h t h e p r o t e i n p h o s p h o r y l a t i o n p a t h w a y . 24 B i o c h e m P h a r m a c o l 5 2 ( 1 0 ) : 1 5 9 9 - 1 6 1 2 . 2256 E r i k s s o n , M ; H a r d e l l , L ; B e r g , N O ; e t a l . ( 1 9 8 1 ) S o f t - t i s s u e s a r c o m a s a n d e x p o s u r e t o c h e m i c a l s u b s t a n c e s : a c a s e 27 r e f e r e n t s t u d y . B r J I n d M e d 3 8 : 2 7 - 3 3 . 2289 E r i k s s o n , M ; H a r d e l l , L ; A d a m , H . ( 1 9 9 0 ) E x p o s u r e t o d i o x i n s a s a r i s k f a c t o r f o r s o f t t i s s u e s a r c o m a : a p o p u l a t i o n 30 b a s e d c a s e - c o n t r o l s t u d y . J N a t l C a n c e r I n s t 8 2 : 4 8 6 - 4 9 0 . 3312 E r n s t , M ; F l e s c h - J a n y s , D ; M o r g e n s t e r n , I ; e t a l . ( 1 9 9 8 ) I m m u n e c e l l f u n c t i o n s i n i n d u s t r i a l w o r k e r s a f t e r e x p o s u r e 33 t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n : d i s s o c i a t i o n o f a n t i g e n - s p e c i f i c T - c e l l r e s p o n s e s i n c u l t u r e s o f d i l u t e d w h o l e 34 b l o o d a n d o f i s o l a t e d p e r i p h e r a l b l o o d m o n o n u c l e a r c e l l s . E n v i r o n H e a l t h P e r s p e c t 1 0 6 ( S u p p l 2 ) : 7 0 1 - 7 0 5 . 3356 E s k e n a z i , B ; M o c a r e l l i , P ; W a r n e r , M ; e t a l . ( 1 9 9 8 ) S e v e s o w o m e n ' s h e a l t h s t u d y : a s t u d y o f t h e e f f e c t s o f T C D D 37 o n r e p r o d u c t i v e h e a l t h . O r g a o n h a l o g e n c o m p o u n d s 3 8 : 2 1 9 - 2 2 2 . 3389 E s k e n a z i , B ; W a r n e r , M ; , M o c a r e l l i , P ; e t a l . ( 2 0 0 2 a ) S e r u m D i o x i n C o n c e n t r a t i o n s a n d M e n s t r u a l C y c l e 40 C h a r a c t e r i s t i c s . A m J E p i d e m i o l 1 5 6 : 3 8 3 - 3 9 2 . 4412 E s k e n a z i , B ; M o c a r e l l i , P ; W a r n e r , M ; e t a l . ( 2 0 0 2 b ) S e r u m D i o x i n C o n c e n t r a t i o n s a n d E n d o m e t r i o s i s : A C o h o r t 43 S t u d y i n S e v e s o , I t a l y . E n v i r o n . H e a l t h P e r s p e c t . 1 1 0 : 6 2 9 - 6 3 4 . 4454 E s k e n a z i , B ; M o c a r e l l i , P ; W a r n e r , M ; e t a l . ( 2 0 0 4 ) R e l a t i o n s h i p o f S e r u m T C D D C o n c e n t r a t i o n s a n d A g e a t 46 (R eference a d d ed d u rin g P ro o f)e x p o s u r e o f f e m a l e r e s i d e n t s o f S e v e s o , I t a l y . E n v i r o n . H e a l t h P e r s p e c t . 1 1 2 : 2 2 - 2 7 . 4478 E s t e l l e r , M ; G a r c i a , A ; M a t i n e z - P a l o n e s , J M ; e t a l . ( 1 9 9 7 ) G e r m l i n e p o l y m o r p h i s m s i n c y t o c h r o m e P 4 5 0 I A 1 49 ( C 4 8 8 7 C Y P I A 1 ) a n d m e t h y l e n e t e t r a h y d r o f o l a t e r e d u c t a s e ( M T H F R ) g e n e s a n d e n d o m e t r i a l c a n c e r s u s c e p t i b i l i t y . 50 C a r c i n o g e n e s i s 1 8 : 2 3 0 7 - 2 3 1 1 . 5512 F a q i , A S ; D a l s e n t e r , P R ; M e r k e r , H J ; e t a l . ( 1 9 9 8 ) R e p r o d u c t i v e t o x i c i t y a n d t i s s u e c o n c e n t r a t i o n s o f l o w d o s e s o f 53 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n m a l e o f f s p r i n g r a t s e x p o s e d t h r o u g h o u t p r e g n a n c y a n d l a c t a t i o n . T o x i c o l 54 A p p l P h a r m a c o l 1 5 0 ( 2 ) : 3 8 3 - 3 9 2 . 12/23/03 R-8 DRAFT--DO NOT CITE OR QUOTE 21 F e n t o n , S E ; H a m m , J: B i m b a u m , L S ; Y o u n g b l o o d , G L . ( 2 0 0 2 ) P e r s i s t e n t a b n o r m a l i t i e s i n t h e r a t m a m m a r y g l a n d 3 fo llo w in g g esta tio n a l an d lactation al ex p o su re to 2 ,3 ,7 ,8 - tetra ch lo ro d ib en zo -p -d io x in (T C D D ). T o x ic o lo g ic a l 4 S cien ces 67: 63-74. 65 F e r n a n d e z - S a l g u e r o , P M ; H i l b e r t , D M ; R u d i k o f f , S ; e t a l . ( 1 9 9 6 ) A r y l - h y d r o c a r b o n r e c e p t o r - d e f i c i e n t m i c e a r e 7 resistan t to 2 ,3 ,7 ,8 -te tr a ch lo r o d ib e n z o -p -d io x in -in d u c ed to x icity . T o x ic o l A p p l P h a r m a c o l 1 4 0 (1 ):1 7 3 -1 7 9 . 89 F i n g e r h u t , M A ; H a l p e r i n , W E ; M a r l o w , D A . ( 1 9 9 1 a ) C a n c e r m o r t a l i t y i n w o r k e r s e x p o s e d t o 2 , 3 , 7 , 8 10 t e t r a c h l o r o d i b e n z o - p - d i o x i n . N e w E n g l J M e d 3 2 4 : 2 1 2 - 2 1 8 . 1112 F i n g e r h u t , M A ; H a l p e r i n , W E ; M a r l o w , D ; e t a l . ( 1 9 9 1 b ) M o r t a l i t y a m o n g U n i t e d S t a t e s w o r k e r s e m p l o y e d i n t h e 13 p r o d u c t i o n o f c h e m i c a l s c o n t a m i n a t e d w i t h 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) . U . S . D e p a r t m e n t o f H e a l t h 14 a n d H u m a n S e r v i c e s , N a t i o n a l I n s t i t u t e f o r O c c u p a t i o n a l S a f e t y a n d H e a l t h . C i n c i n n a t i , O H N T I S # P B 9 1 - 1 2 5 9 7 1 . 1156 F i n l e y , B L ; C o n n o r , K T ; S c o t t , P K . ( 2 0 0 3 ) . T h e u s e o f t o x i c e q u i v a l e n c y f a c t o r d i s t r i b u t i o n s i n p r o b a b i l i s t i c r i s k 17 a s s e s s m e n t s f o r d i o x i n s , f u r a n s , a n d P C B s . J T o x i c o l E n v i r o n H e a l t h 6 6 ( 6 ) : 5 3 3 - 5 0 . 1189 F l e i s s , J L . ( 1 9 8 1 ) S t a t i s t i c a l m e t h o d s f o r r a t e s a n d p r o p o r t i o n s . N e w Y o r k : J o h n W i l e y . 2210 F l e s c h - J a n y s , D ; B e r g e r , J ; G u r n , P ; e t a l . ( 1 9 9 5 ) E x p o s u r e t o p o l y c h l o r i n a t e d d i o x i n s a n d f u r a n s ( P C D D / C D F ) a n d 22 m o r t a l i t y i n a c o h o r t o f w o r k e r s f r o m a h e r b i c i d e - p r o d u c i n g p l a n t i n H a m b u r g , F e d e r a l R e p u b l i c o f G e r m a n y . A m J 23 E p i d e m i o l 1 4 2 : 1 1 6 5 - 1 1 7 5 . 2254 F l e s c h - J a n y s , D ; S t e i n d o r f , K ; G u r n , P ; e t a l . ( 1 9 9 8 ) E s t i m a t i o n o f t h e c u m u l a t e d e x p o s u r e t o p o l y c h l o r i n a t e d 26 d i b e n z o - p - d i o x i n s / f u r a n s a n d s t a n d a r d i z e d m o r t a l i t y r a t i o a n a l y s i s o f c a n c e r m o r t a l i t y b y d o s e i n a n o c c u p a t i o n a l l y 27 e x p o s e d c o h o r t . E n v i r o n H e a l t h P e r s p e c t 1 0 6 ( S u p p l 2 ) : 6 5 5 - 6 6 2 . 2289 F l e s c h - J a n y s , D ; B e c h e r , J ; B e r g e r , J ; e t a l . ( 1 9 9 9 ) E p i d e m i o l o g i c a l i n v e s t i g a t i o n o f b r e a s t c a n c e r i n c i d e n c e i n a 30 c o h o r t o f f e m a l e w o r k e r s w i t h h i g h e x p o s u r e t o P C D D / C D F a n d H C H . O r g a n o h a l o g e n C o m p o u n d s 4 4 : 3 7 9 - 3 8 2 . 3312 F l o d s t r o m , S ; A h l b o r g , U G . ( 1 9 9 2 ) R e l a t i v e t u m o r p r o m o t i n g a c t i v i t y o f s o m e p o l y c h l o r i n a t e d d i b e n z o - p - d i o x i n - , 33 d i b e n z o f u r a n - , a n d b i p h e n y l c o n g e n e r s i n f e m a l e r a t s . C h e m o s p h e r e 2 5 : 1 ( 2 ) : 1 6 9 - 1 7 2 . 3354 F o o d a n d D r u g A d m i n i s t r a t i o n ( F D A ) . ( 1 9 9 0 ) C a r c i n o g e n i c r i s k a s s e s s m e n t f o r d i o x i n s a n d f u r a n s i n f i s h 36 c o n t a m i n a t e d b y b l e a c h e d - p a p e r m i l l s . R e p o r t o f t h e Q u a n t i t a t i v e R i s k A s s e s s m e n t C o m m i t t e e . F D A , W a s h i n g t o n , 37 D . C . . U S A . 3389 F r a n k , G C ; W e b b e r , L S ; F a r r i s , R P ; e t a l . ( 1 9 8 6 ) D i e t a r y d a t a b o o k : q u a n t i f y i n g d i e t a r y i n t a k e s o f i n f a n t s , c h i l d r e n , 40 a n d a d o l e s c e n t s , t h e B o g a l u s a h e a r t s t u d y , 1 9 7 3 - 1 9 8 3 . N a t i o n a l R e s e a r c h a n d D e m o n s t r a t i o n C e n t e r 41 A r t e r i o s c l e r o s i s , L o u i s i a n a S t a t e U n i v e r s i t y M e d i c a l C e n t e r , N e w O r l e a n s , L A . 4423 F u j i i - K u r i y a m a , Y ; E m a , M ; M i m u r a , J ; e t a l . ( 1 9 9 5 ) P o l y m o r p h i c f o r m s o f t h e A h r e c e p t o r a n d i n d u c t i o n o f t h e 44 C Y P 1 A 1 g e n e . P h a r m a c o g e n e t i c s 5 S p e c N o : S 1 4 9 - 5 3 . 4456 G a i d o , K W ; M a n e s s , S C ; L e o n a r d , L S ; e t a l . ( 1 9 9 2 ) 2 , 3 , 7 , 8 - T e t r a c h l o r o d i b e n z o - p - d i o x i n - d e p e n d e n t r e g u l a t i o n o f 47 t r a n s f o r m i n g g r o w t h f a c t o r s - a n d $ 2 e x p r e s s i o n i n a h u m a n k e r a t i n o c y t e c e l l l i n e i n v o l v e s b o t h t r a n s c r i p t i o n a l a n d 48 p o s t - t r a n s c r i p t i o n a l c o n t r o l . J B i o l C h e m 2 6 7 : 2 4 5 9 1 - 2 4 5 9 5 . 4590 G a s i e w i c z , T A . ( 1 9 9 7 ) D i o x i n s a n d t h e A h R : p r o b e s t o u n c o v e r p r o c e s s e s i n n e u r o e n d o c r i n e d e v e l o p m e n t . 51 N e u r o t o x i c o l o g y 1 8 : 3 9 3 - 4 1 4 . 5523 G a s i e w i c z , T A ; H o l s c h e r , M A ; N e a l , R A . ( 1 9 8 0 ) T h e e f f e c t o f t o t a l p a r e n t e r a l n u t r i t i o n o n t h e t o x i c i t y o f 2 , 3 , 7 , 8 54 t e t r a c h l o r o d i b e n z o - p - d i o x i n i n t h e r a t . T o x i c o l A p p l P h a r m a c o l 5 4 : 4 6 9 - 4 8 8 . 12/23/03 R-9 DRAFT--DO NOT CITE OR QUOTE 1 G e, N L ; E lferin k , CJ. (1 9 9 8 ) A d irect interaction b etw een th e aryl h ydrocarbon recep tor and retin ob lastom a protein. 2 L in k in g d io x in sign alin g to the cell cy cle. J B io l C h em 2 8 ;2 7 3 (3 5 ):2 2 7 0 8 -1 3 . 43 G e r h a r d , I ; R u n n e b a u m , B . ( 1 9 9 2 ) G r e n z e n d e r h o r m o n s u b s i t t u t i o n b e i s c h a d s t o f f b e l a s t u n g u n d f e r t i l i t a t s s t o r u n g e n . 5 Z ent B l G ynekol 114:593-602. 67 G e h r s , B C ; S m i a l o w i c z , R J . ( 1 9 8 9 ) P e r s i s t e n t s u p p r e s s i o n o f d e l a y e d - t y p e h y p e r s e n s i t i v i t y i n a d u l t F 3 4 4 r a t s a f t e r 8 p erinatal ex p o su re to 2 ,3 ,7 ,8-tetra ch lo ro d ib en zo -p -d io x in . T o x ic o lo g y 1 3 4 (1 ):7 9 -8 8 . 109 G e n t r y , P R ; C o v i n g t o n , T R ; C l e w e l l , H J . ( 2 0 0 3 ) 3 r d . E v a l u a t i o n o f t h e p o t e n t i a l i m p a c t o f p h a r m a c o k i n e t i c 11 d i f f e r e n c e s o n t i s s u e d o s i m e t r y i n o f f s p r i n g d u r i n g p r e g n a n c y a n d l a c t a t i o n . R e g u l T o x i c o l P h a r m a c o l 3 8 ( 1 ) : 1 - 1 6 . 1123 G e u s a u , A ; S c h m a l d i e n s t , S ; D e r f l e r , K ; e t a l . ( 2 0 0 2 ) . S e v e r e 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) 14 i n t o x i c a t i o n : k i n e t i c s a n d t r i a l s t o e n h a n c e e l i m i n a t i o n i n t w o p a t i e n t s . A r c h T o x i c o l 7 6 ( 5 - 6 ) : 3 1 6 - 2 5 . E p u b 2 0 0 2 15 M a y 0 4 . 1176 G i e r t h y , J F ; B e n n e t t , J A ; B r a d l e y , L M ; e t a l . ( 1 9 9 3 ) C o r r e l a t i o n o f i n v i t r o a n d i n v i v o g r o w t h s u p p r e s s i o n o f M C F 18 7 h u m a n b r e a s t c a n c e r b y 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n . C a n c e r R e s 5 3 : 3 1 4 9 - 3 1 5 3 . 2109 G o l d s t e i n , J A ; H i c k m a n , P ; J u e , D L . ( 1 9 7 4 ) E x p e r i m e n t a l h e p a t i c p o r p h y r i a i n d u c e d b y p o l y c h l o r i n a t e d b i p h e n y l s . 21 T o x i c o l A p p l P h a r m a c o l 2 7 ( 2 ) : 4 3 7 - 4 4 8 . 2223 G o o d m a n , D G ; S a u e r , R M . ( 1 9 9 2 ) H e p a t o t o x i c i t y a n d c a r c i n o g e n i c i t y i n f e m a l e S p r a g u e - D a w l e y r a t s t r e a t e d w i t h 24 2 . 3 . 7 . 8 - t e t r a c h l o r o r d i b e n z o - p - d i o x i n ( T C D D ) : a P a t h o l o g y W o r k i n g G r o u p r e e v a l u a t i o n . R e g u l T o x i c o l P h a r m a c o l 25 1 5 : 2 4 5 - 2 5 2 . 2276 G o r s k i , J R ; R o z m a n , K . ( 1 9 8 7 ) D o s e - r e s p o n s e a n d t i m e c o u r s e o f h y p o t h y r o x i n e m i a a n d h y p o i n s u l i n e m i a a n d 28 c h a r a c t e r i z a t i o n o f i n s u l i n h y p e r s e n s i t i v i t y i n 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) - t r e a t e d r a t s . T o x i c o l o g y 29 4 4 ( 3 ) : 2 9 7 - 3 0 7 . 3310 G r a d i n , K ; M c G u i r e , J ; W e n g e r , R H ; e t a l . ( 1 9 9 6 ) F u n c t i o n a l i n t e r f e r e n c e b e t w e e n h y p o x i a a n d d i o x i n s i g n a l 32 t r a n s d u c t i o n p a t h w a y s : c o m p e t i t i o n f o r r e c r u i t m e n t o f t h e A R N T t r a n s c r i p t i o n f a c t o r . M o l C e l l B i o l 33 1 6 ( 1 0 ) : 5 2 2 1 - 5 2 3 1 . 3354 G r a h a m , M J ; L u c i e r , G W ; L i n k o , P ; e t a l . ( 1 9 8 8 ) I n c r e a s e s i n c y t o c h r o m e P - 4 5 0 m e d i a t e d 1 7 b e t a - e s t r a d i o l 36 2 - h y d r o x y l a s e a c t i v i t y i n r a t l i v e r m i c r o s o m e s a f t e r b o t h a c u t e a d m i n i s t r a t i o n a n d s u b c h r o n i c a d m i n i s t r a t i o n o f 37 2 . 3 . 7 . 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n a t w o - s t a g e h e p a t o c a r c i n o g e n e s i s m o d e l . C a r c i n o g e n e s i s 9 : 1 9 3 5 - 1 9 4 1 . 3389 G r a y , L E , J r . ; O s t b y , J S . ( 1 9 9 5 ) I n u t e r o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) a l t e r s r e p r o d u c t i v e 40 m o r p h o l o g y a n d f u n c t i o n i n f e m a l e r a t o f f s p r i n g . T o x i c o l A p p l P h a r m a c o l 1 3 3 : 2 8 5 - 2 9 4 . 4412 G r a y , L E , J r . ; K e l c e , W R ; M o n o s s o n , E ; e t a l . ( 1 9 9 5 a ) E x p o s u r e t o T C D D d u r i n g d e v e l o p m e n t p e r m a n e n t l y a l t e r s 43 r e p r o d u c t i v e f u n c t i o n i n m a l e L o n g E v a n s r a t s a n d h a m s t e r s : r e d u c e d e j a c u l a t e d a n d e p i d i d y m a l s p e r m n u m b e r s a n d 44 s e x a c c e s s o r y g l a n d w e i g h t s i n o f f s p r i n g w i t h n o r m a l a n d r o g e n i c s t a t u s . T o x i c o l A p p l P h a r m a c o l 1 3 1 : 1 0 8 - 1 1 8 . 4456 G r a y , L E , J r . ; O s t b y , J ; W o l f , C ; e t a l . ( 1 9 9 5 b ) F u n c t i o n a l d e v e l o p m e n t a l t o x i c i t y o f l o w d o s e s o f 2 , 3 , 7 , 8 47 t e t r a c h l o r o d i b e n z o - p - d i o x i n a n d a d i o x i n - l i k e P C B ( 1 6 9 ) i n L o n g E v a n s r a t s a n d S y r i a n h a m s t e r s : r e p r o d u c t i v e , 48 b e h a v i o r a l a n d t h e r m o r e g u l a t o r y a l t e r a t i o n s . O r g a n o h a l o g e n C o m p o u n d s 2 5 : 3 3 - 3 8 . 4590 G r a y , L E ; O s t b y , J S ; K e l c e , W R . ( 1 9 9 7 a ) A d o s e - r e s p o n s e a n a l y s i s o f t h e r e p r o d u c t i v e e f f e c t s o f a s i n g l e 51 g e s t a t i o n a l d o s e o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n m a l e L o n g E v a n s h o o d e d r a t o f f s p r i n g . T o x i c o l A p p l 5523 P h a r m a c o l 1 4 6 ( 1 ) : 1 1 - 2 0 . 12/23/03 R-10 DRAFT--DO NOT CITE OR QUOTE 1 G ra y , L E ; W olf, C; M a n n , P ; et al. (1 9 9 7 b ) In u tero e x p o su r e to lo w d o se s o f 2 ,3 ,7 ,8 -te tr a c h lo r o d ib e n z o -p -d io x in 2 alters rep ro d u ctiv e d e v e lo p m e n t o f fem a le L o n g E van s h o o d e d rat offsp rin g. T o x ic o l A p p l P h a rm a col 1 4 6 (2 ):2 3 7 3 44. 45 G r u b b s , W D ; W o l f e , W H ; M i c h a l e k , J E ; e t a l . ( 1 9 9 5 ) A i r F o r c e h e a l t h s t u d y : a n e p i d e m i o l o g i c i n v e s t i g a t i o n o f 6 health effects in A ir F orce p erson n el fo llo w in g ex p o su re to h erb icid es. R ep o rt n u m b er A L -T R -9 2 0 1 0 7 . 87 G u , Y i - J ; H o g e n e s c h , J B ; B r a d f i e l d , C A . ( 2 0 0 0 ) T h e P A S S u p e r f a m i l y : s e n s o r s o f e n v i r o n m e n t a l a n d d e v e l o p m e n t a l 9 signals. A n n u R ev P h arm acol T o x ico l 4 0 :5 1 9 -5 6 1 . 1110 G u p t a , B N ; V o s , J G ; M o o r e , J A ; e t a l . ( 1 9 7 3 ) P a t h o l o g i c e f f e c t s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n l a b o r a t o r y 12 a n i m a l s . E n v i r o n H e a l t h P e r s p e c t 5 : 1 2 5 - 1 4 0 . 1134 G u z e l i a n , P S . ( 1 9 8 5 ) C l i n i c a l e v a l u a t i o n o f l i v e r s t r u c t u r e a n d f u n c t i o n i n h u m a n s e x p o s e d t o h a l o g e n a t e d 15 h y d r o c a r b o n s . E n v i r o n H e a l t h P e r s p e c t 6 0 : 1 5 9 - 1 6 4 . 1176 H a h n , M E . ( 1 9 9 8 ) T h e a r y l h y d r o c a r b o n r e c e p t o r : a c o m p a r a t i v e p e r s p e c t i v e . C o m p B i o c h e m P h y s i o l 1 2 1 : 2 3 - 5 3 . 1189 H a l p e r i n , W ; V o g t , R ; S w e e n e y , M H ; e t a l . ( 1 9 9 8 ) I m m u n o l o g i c a l m a r k e r s a m o n g w o r k e r s e x p o s e d t o 2 , 3 , 7 , 8 20 t e t r a c h l o r o d i b e n z o - p - d i o x i n . O c c u p E n v i r o n M e d 5 5 : 7 4 2 - 7 4 9 . 2212 H a m m , J T ; C h e n , C - Y ; B i r n b a u m , L S . ( 2 0 0 3 ) A m i x t u r e o f D i o x i n s , F u r a n s , a n d N o n - O r t h o P C B s B a s e d U p o n 23 C o n s e n s u s T o x i c E q u i v a l e n c y F a c t o r s P r o d u c e s D i o x i n - L i k e R e p r o d u c t i v e E f f e c t s . T o x i c o l o g i c a l S c i e n c e s 7 4 : 1 8 2 24 1 9 1 . 2256 H a n k i n s o n , O . ( 1 9 9 5 ) T h e a r y l h y d r o c a r b o n r e c e p t o r c o m p l e x . A n n R e v P h a r m a c o l T o x i c o l 3 5 : 3 0 7 - 3 4 0 . 2278 H a r d e l l , L ; E r i k s s o n , M . ( 1 9 8 8 ) T h e a s s o c i a t i o n b e t w e e n S T S s a n d e x p o s u r e t o p h e n o x y a c e t i c a c i d s : a n e w c a s e 29 r e f e r e n t s t u d y . C a n c e r 6 2 : 6 5 2 - 6 5 6 . 3310 H a r d e l l , L ; S a n d s t r m , A . ( 1 9 7 9 ) C a s e - c o n t r o l s t u d y : s o f t - t i s s u e s a r c o m a s a n d e x p o s u r e t o p h e n o x y a c e t i c a c i d s o r 32 c h l o r o p h e n o l s . B r J C a n c e r 3 9 : 7 1 1 - 7 1 7 . 3334 H a r p e r , N ; C o n n o r , K ; S t e i n b e r g , M ; e t a l . ( 1 9 9 4 ) A n e n z y m e - l i n k e d i m m u n o s o r b e n t a s s a y ( E L I S A ) s p e c i f i c f o r 35 a n t i b o d i e s t o T N P - L P S d e t e c t s a l t e r a t i o n s i n s e r u m i m m u n o g l o b u l i n s a n d i s o t y p e s w i t c h i n g i n C 5 7 B L / 6 a n d D B A / 2 36 m i c e e x p o s e d t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n a n d r e l a t e d c o m p o u n d s . T o x i c o l o g y 9 2 : 1 5 5 - 1 6 7 . 3378 H a r r a d , S J ; J o n e s , K C . ( 1 9 9 2 ) A s o u r c e i n v e n t o r y a n d b u d g e t f o r c h l o r i n a t e d d i o x i n s a n d f u r a n s i n t h e U n i t e d 39 K i n g d o m e n v i r o n m e n t . S c i e n c e o f t h e T o t a l E n v i r o n m e n t 1 2 6 : 8 9 - 1 0 7 . 4410 H a s e m a n , J K ; J o h n s o n , F M . ( 1 9 9 6 ) A n a l y s i s o f N a t i o n a l T o x i c o l o g y P r o g r a m r o d e n t b i o a s s a y d a t a f o r 42 a n t i c a r c i n o g e n i c e f f e c t s . M u t a t R e s 3 5 0 ( 1 ) : 1 3 1 - 1 4 1 . 4434 H a t c h , M . ( 1 9 8 4 ) R e p r o d u c t i v e e f f e c t s o f t h e d i o x i n s . I n : L o w r a n c e , W W , e d . P u b l i c h e a l t h r i s k s o f t h e d i o x i n s . L o s 45 A l t o s , C A : W i l l i a m K a u f m a n n ; p p . 2 5 5 - 2 7 5 . 4476 H a y e s , C L ; S p i n k , D ; S p i n k , B ; e t a l . ( 1 9 9 6 ) 1 7 - b e t a E s t r a d i o l h y d r o x y l a t i o n c a t a l y z e d b y h u m a n c y t o c h r o m e P 4 5 0 48 1 B 1 . P r o c N a t A c a d S c i 9 3 : 9 7 7 6 - 9 7 8 1 . 4590 H a y s , S M ; A y l w a r d , L L ; K a r c h , N J ; e t a l . ( 1 9 9 7 ) T h e r e l a t i v e s u s c e p t i b i l i t y o f a n i m a l s a n d h u m a n s t o t h e 51 c a r c i n o g e n i c h a z a r d p o s e d b y e x p o s u r e t o 2 , 3 , 7 , 8 - T C D D : a n a n a l y s i s u s i n g s t a n d a r d a n d i n t e r n a l m e a s u r e s o f d o s e . 5523 C h e m o s p h e r e 3 4 ( 5 - 7 ) : 1 5 0 7 - 1 5 2 2 . 12/23/03 R-11 DRAFT--DO NOT CITE OR QUOTE 1 H eb ert, C D ; H arris, M W ; E lw ell, M R ; et al. (1 9 9 0 ) R ela tiv e to x icity an d tu m o r-p ro m o tin g ab ility o f 2 2 .3 .7 .8 - tetrach lorod ib en zo-p -d ioxin (T C D D ), 2 ,3 ,4 ,7,8 -p en ta ch lo ro d ib en zo fu ran (P C D F ), and 3 1 .2 .3 .4 .7 .8 - h e x a c h lo r o d ib e n z o fu r a n (H C D F ) in h a irless m ic e . T o x ic o l A p p l P h a r m a c o l 1 0 2 :3 6 2 -3 7 7 . 45 H e m m i n g , H ; B a g e r , Y ; F l o d s t r o m , S ; e t a l . ( 1 9 9 5 ) L i v e r t u m o u r p r o m o t i n g a c t i v i t y o f 3 , 4 , 5 , 3 ' , 4 ' - p e n t a c h l o r o 6 b ip h e n y l a n d its in tera ctio n w ith 2 ,3 ,7 ,8 -te tr a c h lo r o d ib e n z o -p -d io x in . E u r J P h a r m a c o l 2 9 2 :2 4 1 -2 4 9 . 87 H e n r y , E C ; G a s i e w i c z T A . ( 2 0 0 3 ) . A g o n i s t b u t n o t a n t a g o n i s t l i g a n d s i n d u c e c o n f o r m a t i o n a l c h a n g e i n t h e m o u s e 9 aryl h yd rocarb on recep tor as d etected b y partial p roteolysis. M o l P h arm acol. 6 3 (2 ):3 9 2 -4 0 0 1110 H e r t z m a n , C ; T e s c h k e , K ; O s t r y , A ; e t a l . ( 1 9 9 7 ) M o r t a l i t y a n d c a n c e r i n c i d e n c e a m o n g s a w m i l l w o r k e r s e x p o s e d t o 12 c h l o r o p h e n a t e w o o d p r e s e r v a t i v e s . A m J P u b l H e a l t h 8 7 ( 1 ) : 7 1 - 7 9 . 1134 H i l l , A B . ( 1 9 6 5 ) T h e e n v i r o n m e n t a n d d i s e a s e : a s s o c i a t i o n o r c a u s a t i o n . P r o c R S o c M e d 5 8 : 2 9 5 - 3 0 0 . 1156 H i l l , R N ; C r i s p , T M ; H u r l e y , P M ; e t a l . ( 1 9 9 8 ) R i s k a s s e s s m e n t o f t h y r o i d f o l l i c u l a r c e l l t u m o r s . E n v i r o n H e a l t h 17 P e r s p e c t 1 0 6 ( 8 ) : 4 4 7 - 4 5 7 . 1189 H o e l , D . G . 1 9 8 7 . C a n c e r r i s k m o d e l s f o r i o n i z i n g r a d i a t i o n . E n v H e a l t h P e r s p e c t 7 6 : 1 2 1 - 1 2 4 . 2210 H o j o , R ; S t e r n , S ; Z a r e b a , G ; e t a l . ( 2 0 0 2 ) S e x u a l l y d i m o r p h i c b e h a v i o r a l r e s p o n s e s t o p r e n a t a l d i o x i n e x p o s u r e . 22 E n v i r o n . H e a l t h P e r s p e c t . 1 1 0 : 2 4 7 - 2 5 4 . 2234 H o o i v e l d , M ; H e e d e r i k , D ; B u e n o d e M e s q u i t a , H B . ( 1 9 9 6 ) P r e l i m i n a r y r e s u l t s o f t h e s e c o n d f o l l o w - u p o f a D u t c h 25 c o h o r t o c c u p a t i o n a l l y e x p o s e d t o p h e n o x y h e r b i c i d e s , c h l o r o p h e n o l s , a n d c o n t a m i n a n t s . O r g a n o h a l o g e n 26 C o m p o u n d s 3 0 : 1 8 5 - 1 8 9 . 2278 H o o i v e l d , M ; H e e d e r i k , D J J ; K o g e v i n a s , M ; e t a l . ( 1 9 9 8 ) S e c o n d f o l l o w - u p o f a D u t c h c o h o r t o c c u p a t i o n a l l y 29 e x p o s e d t o p h e n o x y h e r b i c i d e s , c h l o r o p h e n o l s , a n d c o n t a m i n a n t s . A m J E p i d e m i o l 1 4 7 ( 9 ) : 8 9 1 - 9 0 1 . 3310 H o r n u n g , M W ; S p i t s b e r g e n , J M ; P e t e r s o n , R E . ( 1 9 9 9 ) 2 , 3 , 7 , 8 - T e t r a c h l o r o d i b e n z o - p - d i o x i n a l t e r s c a r d i o v a s c u l a r 32 a n d c r a n i o f a c i a l d e v e l o p m e n t a n d f u n c t i o n i n s a c f r y o f r a i n b o w t r o u t ( O n c o r h y n c h u s m y k i s s ) . T o x i c o l S c i 33 4 7 ( 1 ) : 4 0 - 5 1 . 3354 H u f f , J E ; S a l m o n , A G ; H o o p e r , N K ; e t a l . ( 1 9 9 1 ) L o n g - t e r m c a r c i n o g e n e s i s s t u d i e s o n 36 2 . 3 . 7 . 8 - tetrach lorod ib en zo-p-dioxin and h exach lorod ib en zo-p -d ioxin s. C ell B io l T o x ico l 7(1):67-94. 3378 H u i s m a n , M ; K o o p m a n - E s s e b o o m , C ; L a n t i n g , C I ; e t a l . ( 1 9 9 5 a ) N e u r o l o g i c a l c o n d i t i o n i n 1 8 - m o n t h - o l d c h i l d r e n 39 p e r i n a t a l l y e x p o s e d t o p o l y c h l o r i n a t e d b i p h e n y l s a n d d i o x i n s . E a r l y H u m D e v 4 3 : 1 6 5 - 1 7 6 . 4410 H u i s m a n , M ; K o o p m a n - E s s e b o o m , C ; F i d l e r , V ; e t a l . ( 1 9 9 5 b ) P e r i n a t a l e x p o s u r e t o p o l y c h l o r i n a t e d b i p h e n y l s a n d 42 d i o x i n s a n d i t s e f f e c t o n n e o n a t a l n e u r o l o g i c a l d e v e l o p m e n t . E a r l y H u m D e v 4 1 ( 2 ) : 1 1 1 - 1 2 7 . 4434 H u r l e y , P M . ( 1 9 9 8 ) M o d e o f c a r c i n o g e n i c a c t i o n o f p e s t i c i d e s i n d u c i n g t h y r o i d f o l l i c u l a r c e l l t u m o r s i n r o d e n t s . 45 E n v i r o n H e a l t h P e r s p e c t 1 0 6 ( 8 ) : 4 3 7 - 4 4 5 . 4476 H u r s t , C H ; A b b o t t , B D ; D e V i t o , M J ; e t a l . ( 1 9 9 8 ) 2 , 3 , 7 , 8 - T e t r a c h l o r o d i b e n z o - p - d i o x i n i n p r e g n a n t L o n g E v a n s r a t s : 48 d i s p o s i t i o n to m a t e r n a l a n d e m b r y o / f e t a l t i s s u e s . T o x i c o l S c i 4 5 ( 2 ) : 1 2 9 - 1 3 6 . 4590 H u r s t , C H ; D e V i t o , M J ; S e t z e r , R W ; e t a l . ( 2 0 0 0 ) A c u t e a d m i n i s t r a t i o n o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n 51 ( T C D D ) i n p r e g n a n t L o n g E v a n s r a t s : a s s o c i a t i o n o f m e a s u r e d t i s s u e c o n c e n t r a t i o n s w i t h d e v e l o p m e n t a l e f f e c t s . 5523 T o x i c o l S c i 5 3 ( 2 ) : 4 1 1 - 4 2 0 . 12/23/03 R-12 DRAFT--DO NOT CITE OR QUOTE 1 IA R C (International A g e n c y for R esearch on C an cer). (1 9 9 7 ) IA R C m o n og ra p h s on th e evalu ation o f carcin ogen ic 2 risks to h u m an s. V o l. 69. P o lych lo rin a ted d ib en zo -p a ra -d io xin s an d p o ly ch lorin a ted d ib en zofu ran s. L y o n , F ran ce. 43 J e n s e n , E ; B o l g e r , P M . ( 2 0 0 0 ) E x p o s u r e a s s e s s m e n t o f d i o x i n s / f u r a n s c o n s u m e d i n d a i r y f o o d s a n d f i s h . F o o d 5 A d d itiv es and C ontam inants, subm itted. 67 J e n s e n , E . ; C a n a d y , R ; B o l g e r , P M . ( 2 0 0 0 ) E x p o s u r e a s s e s s m e n t f o r d i o x i n s a n d f u r a n s i n s e a f o o d a n d d a i r y f o o d s i n 8 th e U n ited States, 1 9 98 -9 9 . O rgan oh alogen C om p o u n d s 4 7 :3 1 8 -3 2 1 . 109 J i r t l e , R L ; M e y e r , S A . ( 1 9 9 1 ) L i v e r t u m o r p r o m o t i o n : e f f e c t o f p h e n o b a r b i t a l o n E G F a n d p r o t e i n k i n a s e C s i g n a l 11 t r a n s d u c t i o n a n d t r a n s f o r m i n g g r o w t h f a c t o r - b e t a 1 e x p r e s s i o n . D i g D i s S c i 3 6 : 6 5 9 - 6 6 8 . 1123 J i r t l e , R L ; M e y e r , S A ; B r o c k e n b r o u g h , J S . ( 1 9 9 1 ) L i v e r t u m o r p r o m o t e r p h e n o b a r b i t a l : a b i p h a s i c m o d u l a t o r o f 14 h e p a t o c y t e p r o l i f e r a t i o n . P r o g C l i n B i o l R e s 3 6 9 : 2 0 9 - 2 1 6 . 1156 J o h n s o n , E S ; S h o r t e r , C ; B e s t e r v e l t , L L ; e t a l . ( 2 0 0 1 ) . S e r u m h o r m o n e l e v e l s i n h u m a n s w i t h l o w s e r u m 17 c o n c e n t r a t i o n s o f 2 , 3 , 7 , 8 - T C D D . T o x i c o l . I n d u s t r i a l H e a l t h 1 7 : 1 0 5 - 1 1 2 . 1189 J o h n s o n , R D ; T i e t g e , J E ; B o t t s , S . ( 1 9 9 2 ) C a r c i n o g e n i c i t y o f 2 , 3 , 7 , 8 - T C D D t o M e d a k a . T h e T o x i c o l o g i s t 20 1 2 ( 1 ) : 1 3 8 . 2212 J o h n s o n , L ; W i l k e r , C E ; S a f e , S H ; e t a l . ( 1 9 9 4 ) 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n r e d u c e s t h e n u m b e r , s i z e , a n d 23 o r g a n e l l e c o n t e n t o f L e y d i g c e l l s i n a d u l t r a t t e s t e s . T o x i c o l o g y 8 9 : 4 9 - 6 5 . 2254 J o h n s o n , K L ; C u m m i n g s , A M ; B i r n b a u m L S . ( 1 9 9 7 ) P r o m o t i o n o f e n d o m e t r i o s i s i n m i c e b y p o l y c h l o r i n a t e d 26 d i b e n z o - p - d i o x i n s , d i b e n z o f u r a n s , a n d b i p h e n y l s . E n v i r o n H e a l t h P e r s p e c t 1 0 5 ( 7 ) : 7 5 0 - 7 5 5 . 2278 J u n g , D ; B e r g , P A ; E d l e r , L ; e t a l . ( 1 9 9 8 ) I m m u n o l o g i c f i n d i n g s i n w o r k e r s f o r m e r l y e x p o s e d t o 2 , 3 , 7 , 8 29 t e t r a c h l o r o d i b e n z o - p - d i o x i n a n d i t s c o n g e n e r s . E n v i r o n H e a l t h P e r s p e c t 1 0 6 ( 2 ) : 6 8 9 - 6 9 5 . 3310 J u s k o , W J . ( 1 9 9 5 ) P h a r m a c o k i n e t i c s a n d r e c e p t o r - m e d i a t e d p h a r m a c o d y n a m i c s o f c o r t i c o s t e r o i d s . T o x i c o l o g y 32 1 0 2 : 1 8 9 - 1 9 6 . 3334 K a d l u b a r , F F ; B u t l e r , M A ; K a d e r l i k , R K ; e t a l . ( 1 9 9 2 ) P o l y m o r p h i s m s f o r a r o m a t i c a m i n e m e t a b o l i s m i n h u m a n s : 35 r e l e v a n c e f o r h u m a n c a r c i n o g e n e s i s . E n v i r o n H e a l t h P e r s p e c t 9 8 : 6 9 - 7 4 . 3376 K a w a j i r i , K ; N a k a c h i , K ; I m a i , K ; e t a l . ( 1 9 9 3 ) G e r m l i n e p o l y m o r p h i s m s o f p 5 3 a n d C Y P I A 1 g e n e s i n v o l v e d i n 38 h u m a n l u n g c a n c e r . C a r c i n o g e n e s i s 1 4 ( 6 ) : 1 0 8 5 - 1 0 8 9 . 4309 K a y a j a n i a n , G M . ( 1 9 9 7 ) D i o x i n i s a p r o m o t e r b l o c k e r , a p r o m o t e r , a n d a n e t a n t i c a r c i n o g e n . R e g u l T o x i c o l 41 P h a r m a c o l 2 6 ( 1 ) : 1 3 4 - 1 3 7 . 4432 K a y a j a n i a n , G M . ( 1 9 9 9 ) D i o x i n i s a s y s t e m i c p r o m o t e r b l o c k e r , I I . E c o t o x i c o l E n v i r o n S a f 4 2 ( 2 ) : 1 0 3 - 1 0 9 . 4454 K e t c h u m , N S ; M i c h a l e k , J E ; B u r t o n J E . ( 1 9 9 9 ) S e r u m d i o x i n a n d c a n c e r i n v e t e r a n s o f O p e r a t i o n R a n c h H a n d . A m 46 J E p i d e m i o l 1 4 9 ( 7 ) : 6 3 0 - 6 3 9 . 4478 K i m . A H ; K o h n , M C ; P o r t i e r , C J ; W a l k e r , N J . ( 2 0 0 2 ) I m p a c t o f p h y s i o l o g i c a l l y b a s e d p h a r m a c o k i n e t i c m o d e l i n g 49 o n b e n c h m a r k d o s e c a l c u l a t i o n s f o r T C D D - i n d u c e d b i o c h e m i c a l r e s p o n s e s . R e g u l T o x i c o l P h a r m a c o l . 3 6 ( 3 ) : 2 8 7 50 9 6 . 5512 K i m m e l , G L . ( 1 9 8 8 ) A c a n c e r r i s k - s p e c i f i c d o s e e s t i m a t e f o r 2 , 3 , 7 , 8 , - T C D D , a p p e n d i x C . U . S . E P A , E x t e r n a l 5534 R e v i e w D r a f t . 12/23/03 R-13 DRAFT--DO NOT CITE OR QUOTE 1 K itchin, K T ; W o o d s, JS. (1 9 7 9 ) 2 ,3 ,7 ,8 -T etra ch lo ro d ib en zo -p -d io x in (T C D D ) effects on h epatic m icrosom al 2 cy to ch ro m e P -44 8 -m ed ia ted en zym e activities. T o x ic o l A p p l P h arm acol 4 7 :5 3 7 -5 4 6 . 43 K i u k k o n e n , A ; V i l u k s e l a , M ; S a h l b e r g , C ; e t a l . ( 2 0 0 3 ) R e s p o n s e o f t h e i n c i s o r t o o t h t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o 5 p -d io x in in a d io x in -resista n t an d a d io x in -se n sitiv e rat strain. T o x ic o l S c i. 6 9 (2 ):4 8 2 -9 . 67 K l e e m a n , J M ; M o o r e , R W ; P e t e r s o n , R E . ( 1 9 9 0 ) I n h i b i t i o n o f t e s t i c u l a r s t e r o i d o g e n e s i s i n 2 , 3 , 7 , 8 8 te tra ch lo ro d ib en zo -p -d io x in -trea ted rats: e v id e n c e that th e k e y le sio n o ccu rs prior to or d u rin g p r e g n e n o lo n e 9 form ation. T o x ico l A p p l P h arm acol 1 0 6 :1 1 2 -1 2 5 . 1110 K o c i b a , R J ; K e e l e r , P A ; P a r k , G N ; e t a l . ( 1 9 7 6 ) 2 , 3 , 7 , 8 - T e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) : r e s u l t s o f a 1 3 w e e k 12 o r a l t o x i c i t y s t u d y i n r a t s . T o x i c o l A p p l P h a r m a c o l 3 5 : 5 5 3 - 5 7 4 . 1134 K o c i b a , R J ; K e y e s , D G ; B e y e r , J E ; e t a l . ( 1 9 7 8 ) R e s u l t s o f a t w o - y e a r c h r o n i c t o x i c i t y a n d o n c o g e n i c i t y s t u d y o f 15 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n r a t s . T o x i c o l A p p l P h a r m a c o l 4 6 : 2 7 9 - 3 0 3 . 1176 K o g e v i n a s , M ; S a r a c c i , R ; W i n k e l m a n n , R ; e t a l . ( 1 9 9 3 ) C a n c e r i n c i d e n c e a n d m o r t a l i t y i n w o m e n o c c u p a t i o n a l l y 18 e x p o s e d t o c h l o r o p h e n o x y h e r b i c i d e s , c h l o r o p h e n o l s a n d d i o x i n s . C a n c e r C a u s e s C o n t r o l 4 : 5 4 7 . 2109 K o g e v i n a s , M ; B e c h e r , H ; B e n n , T ; e t a l . ( 1 9 9 7 ) C a n c e r m o r t a l i t y i n w o r k e r s e x p o s e d t o p h e n o x y h e r b i c i d e s , 21 c h l o r o p h e n o l s , a n d d i o x i n . A n e x p a n d e d a n d u p d a t e d i n t e r n a t i o n a l c o h o r t s t u d y . A m J E p i d e m i o l 1 4 5 ( 1 2 ) : 1 0 6 1 22 1 0 7 5 . 2234 K o h n , M C ; L u c i e r , G W ; C l a r k , G C ; e t a l . ( 1 9 9 3 ) A m e c h a n i s t i c m o d e l o f e f f e c t s o f d i o x i n o n g e n e e x p r e s s i o n i n t h e 25 r a t l i v e r . T o x i c o l A p p l P h a r m a c o l 1 2 0 : 1 3 8 - 1 5 4 . 2276 K o h n , M C ; S e w a l l , C H ; L u c i e r , G W ; e t a l . ( 1 9 9 6 ) A m e c h a n i s t i c m o d e l o f e f f e c t s o f d i o x i n o n t h y r o i d h o r m o n e s i n 28 t h e r a t . T o x i c o l A p p l P h a r m a c o l 1 3 6 : 2 9 - 4 8 . 3209 K o n i n c k x , P R ; B r a e t , P ; K e n n e d y , S H ; e t a l . ( 1 9 9 4 ) D i o x i n p o l l u t i o n a n d e n d o m e t r i o s i s i n B e l g i u m . H u m R e p r o d 31 9 ( 6 ) : 1 0 0 1 - 1 0 0 2 . 3323 K o o p m a n - E s s e b o o m , C ; W e i s g l a s - K u p e r u s , N ; d e R i d d e r , M A J ; e t a l . ( 1 9 9 5 b ) E f f e c t s o f P C B / d i o x i n e x p o s u r e a n d 34 f e e d i n g t y p e o n t h e i n f a n t 's v i s u a l r e c o g n i t i o n m e m o r y . I n : E f f e c t s o f p e r i n a t a l e x p o s u r e t o P C B s a n d d i o x i n s o n 35 e a r l y h u m a n d e v e l o p m e n t . D i s s e r t a t i o n . E r a s m u s U n i v e r s i t e i t R o t t e r d a m . 3376 K o o p m a n - E s s e b o o m , C ; W e i s g l a s - K u p e r u s , N ; d e R i d d e r , M A J ; e t a l . ( 1 9 9 6 ) E f f e c t s o f p o l y c h l o r i n a t e d 38 b i p h e n y l / d i o x i n e x p o s u r e a n d f e e d i n g t y p e o n t h e i n f a n t 's m e n t a l a n d p s y c h o m o t o r d e v e l o p m e n t . P e d i a t r i c s 9 7 : 7 0 0 39 7 0 6 . 4410 K o o p m a n - E s s e b o o m , C ; H u i s m a n , M ; W e i s g l a s - K u p e r u s , N ; e t a l . ( 1 9 9 4 a ) D i o x i n a n d P C B l e v e l s i n b l o o d a n d 42 h u m a n m i l k i n r e l a t i o n t o l i v i n g a r e a s i n T h e N e t h e r l a n d s . C h e m o s p h e r e 2 9 ( 9 - 1 1 ) : 2 3 2 7 - 2 3 3 8 . 4434 K o o p m a n - E s s e b o o m , C ; H u i s m a n , M ; W e i s g l a s - K u p e r u s , N ; e t a l . ( 1 9 9 4 b ) P C B a n d d i o x i n l e v e l s i n p l a s m a a n d 45 h u m a n m i l k o f 4 1 8 D u t c h w o m e n a n d t h e i r i n f a n t s . P r e d i c t i v e v a l u e o f P C B c o n g e n e r l e v e l s i n m a t e r n a l p l a s m a f o r 46 f e t a l a n d i n f a n t 's e x p o s u r e to P C B s a n d d i o x i n s . C h e m o s p h e r e 2 8 : 1 7 2 1 - 1 7 3 2 . 4478 K o o p m a n - E s s e b o o m , C ; M o r s e , D C ; W e i s g l a s - K u p e r u s , N ; e t a l . ( 1 9 9 4 c ) E f f e c t s o f d i o x i n s a n d p o l y c h l o r i n a t e d 49 b i p h e n y l s o n t h y r o i d h o r m o n e s t a t u s o f p r e g n a n t w o m e n a n d t h e i r i n f a n t s . P e d i a t r R e s 3 6 ( 4 ) : 4 6 8 - 4 7 3 . 5510 K o o p m a n - E s s e b o o m , C ; H u i s m a n , M ; T o u w e n , B C L ; e t a l . ( 1 9 9 5 a ) E f f e c t s o f P C B / d i o x i n e x p o s u r e a n d f e e d i n g 52 t y p e o n t h e i n f a n t ' s v i s u a l r e c o g n i t i o n m e m o r y . I n : D i s s e r t a t i o n . E f f e c t s o f p e r i n a t a l e x p o s u r e t o P C B s a n d d i o x i n s 5534 o n e a r l y h u m a n d e v e l o p m e n t . E r a s m u s U n i v e r s i t e i t R o t t e r d a m . 12/23/03 R-14 DRAFT--DO NOT CITE OR QUOTE 1 K o r k a la in e n , M ; T u o m is to , J; P o h ja n v irta , R . (2 0 0 1 ) T h e A H r e c e p to r o f th e m o s t d io x in -se n sitiv e sp e c ie s, g u in e a 2 p ig , is h ig h ly h o m o lo g o u s to th e h u m a n A H recep to r. B io c h e m B io p h y s R e s C o m m u n 2 8 5 (5 ):1 1 2 1 -1 1 2 9 . 43 K r e u z e r , P E ; C s a n a d y , G y , A ; e t a l . ( 1 9 9 7 ) 2 , 3 , 7 , 8 - T e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) a n d c o n g e n e r s i n i n f a n t s . 5 A to x ic o k in e tic m o d e l o f h u m a n lifetim e b o d y b u rd en b y T C D D w ith sp ecia l em p h a sis o n its u p tak e an d nutrition. 6 A rch T oxicol 71:383-400. 87 K u r a t s u n e , M ; I k e d a , M ; N a k a m u r a , Y ; e t a l . ( 1 9 8 8 ) A c o h o r t s t u d y o n m o r t a l i t y o f Y u s h o p a t i e n t s : a p r e l i m i n a r y 9 rep ort. In: M iller, R W ; et al., ed s. U n u s u a l o c c u r r e n c e s as c lu e s to c a n c e r e tio lo g y . Jp n S c i S o c P ress: T o k y o /T a y lo r 10 & F r a n c i s , L t d . , p p . 6 1 - 6 8 . 1112 K u r a t s u n e , M . ( 1 9 8 9 ) Y u s h o , w i t h r e f e r e n c e t o Y u - C h e n g . I n : K i m b r o u g h , R D ; J e n s e n , A A , e d s . H a l o g e n a t e d 13 b i o p h e n y l s , t e r p h e n y l s , n a p h t h a l e n e s , d i b e n z o d i o x i n s a n d r e l a t e d p r o d u c t s . 2 n d e d . N e w Y o r k : E l s e v i e r S c i e n c e p p . 14 3 8 1 - 4 0 0 . 1156 K u t z , F W ; B a r n e s , D G ; B r e t t h a u e r , E W ; e t a l . ( 1 9 9 0 ) T h e I n t e r n a t i o n a l T o x i c i t y E q u i v a l e n c y F a c t o r ( I - T E F ) m e t h o d 17 f o r e s t i m a t i n g r i s k s a s s o c i a t e d w i t h e x p o s u r e s t o c o m p l e x m i x t u r e s o f d i o x i n s a n d r e l a t e d c o m p o u n d s . T o x i c o l 18 E n v i r o n C h e m 2 6 : 9 9 - 1 0 9 . 2109 L a h v i s , G P ; B r a d f i e l d , C A . ( 1 9 9 8 ) A h r n u l l a l l e l e s : d i s t i n c t i v e o r d i f f e r e n t ? B i o c h e m P h a r m a c o l 5 6 ( 7 ) : 7 8 1 - 7 8 7 . 2212 L a i , Z W ; P i n e a u , T ; E s s e r , C . ( 1 9 9 6 ) I d e n t i f i c a t i o n o f d i o x i n - r e s p o n s i v e e l e m e n t s ( D R E s ) i n t h e 5 ' r e g i o n s o f 23 p u t a t i v e d i o x i n - i n d u c i b l e g e n e s . C h e m B i o l I n t e r a c t 1 0 0 : 9 7 - 1 1 2 . 2254 L a m p i , P ; H a k u l i n e n , T ; L u o s t a r i n e n , T ; e t a l . ( 1 9 9 2 ) C a n c e r i n c i d e n c e f o l l o w i n g c h l o r o p h e n o l e x p o s u r e i n a 26 c o m m u n i t y i n s o u t h e r n F i n l a n d . A r c h E n v i r o n H e a l t h 4 7 ( 3 ) : 1 6 7 - 1 7 5 . 2278 L a n d i , M T ; C o n s o n n i , D ; P a t t e r s o n , D G , J r . ; e t a l . ( 1 9 9 8 ) 2 , 3 , 7 , 8 - T e t r a c h l o r o d i b e n z o - p - d i o x i n p l a s m a l e v e l s i n 29 S e v e s o 2 0 y e a r s a f t e r t h e a c c i d e n t . E n v i r o n H e a l t h P e r s p e c t 1 0 6 ( 5 ) : 2 7 3 - 2 7 7 . 3310 L a t h r o p , G D ; W o l f e , W H ; A l b a n e s e , R A ; e t a l . ( 1 9 8 4 ) A n e p i d e m i o l o g i c i n v e s t i g a t i o n o f h e a l t h e f f e c t s i n A i r F o r c e 32 p e r s o n n e l f o l l o w i n g e x p o s u r e t o h e r b i c i d e s . B a s e l i n e m o r b i d i t y s t u d y r e s u l t s . U . S . A i r F o r c e S c h o o l o f A e r o s p a c e 33 M e d i c i n e , A e r o s p a c e M e d i c a l D i v i s i o n . B r o o k s A i r F o r c e B a s e , T X , u n p u b l i s h e d . 3354 L a t h r o p , G D ; W o l f e , W H ; M i c h a l e k , J E ; e t a l . ( 1 9 8 7 ) A n e p i d e m i o l o g i c i n v e s t i g a t i o n o f h e a l t h e f f e c t s i n A i r F o r c e 36 p e r s o n n e l f o l l o w i n g e x p o s u r e t o h e r b i c i d e s . F i r s t f o l l o w - u p e x a m i n a t i o n r e s u l t s , J a n u a r y 1 9 8 5 - S e p t e m b e r 1 9 8 7 . U . S . 37 A i r F o r c e S c h o o l o f A e r o s p a c e M e d i c i n e , A e r o s p a c e M e d i c a l D i v i s i o n . B r o o k s A i r F o r c e B a s e , T X , u n p u b l i s h e d . 3398 L e b e l , G ; D o d i n , S ; A y o t t e , P ; e t a l . ( 1 9 9 8 ) O r g a n o c h l o r i n e e x p o s u r e a n d t h e r i s k o f e n d o m e t r i o s i s . F e r t i l S t e r i l 40 6 9 ( 2 ) : 2 2 1 - 2 2 8 . 4412 L i , X ; J o h n s o n , D C ; R o z m a n , K K . ( 1 9 9 5 a ) E f f e c t s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) o n e s t r o u s 43 c y c l i c i t y a n d o v u l a t i o n in f e m a l e S p r a g u e - D a w l e y r a t s . T o x i c o l L e t t 7 8 : 2 1 9 - 2 2 2 . 4454 L i , X ; J o h n s o n , D C ; R o z m a n , K K . ( 1 9 9 5 b ) R e p r o d u c t i v e e f f e c t s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) i n 46 f e m a l e r a t s : o v u l a t i o n , h o r m o n a l r e g u l a t i o n a n d p o s s i b l e m e c h a n i s m ( s ) . T o x i c o l A p p l P h a r m a c o l 1 3 3 : 3 2 1 - 3 2 7 . 4478 L i e m , A K D ; A t u m a , S ; B e c k e r , W ; e t a l . ( 2 0 0 0 ) D i e t a r y i n t a k e o f d i o x i n a n d d i o x i n - l i k e P C B s b y t h e g e n e r a l 49 p o p u l a t i o n o f t e n E u r o p e a n c o u n t r i e s . R e s u l t s o f E U - S C O O P T a s k 3 . 2 . 5 . ( D i o x i n s ) . O r g a n o h a l o g e n C o m p o u n d s 50 4 8 : 1 3 - 1 6 . 5512 L i m b i r d , L E ; T a y l o r , P . ( 1 9 9 8 ) E n d o c r i n e d i s r u p t o r s s i g n a l t h e n e e d f o r r e c e p t o r m o d e l s a n d m e c h a n i s m s t o i n f o r m 5534 p o l i c y . C e l l 9 3 : 1 5 7 - 1 6 3 . 12/23/03 R-15 DRAFT--DO NOT CITE OR QUOTE 1 L in ,T M ; R a sm u sse n ,N T ; M o o r e ,R W ; et al. (2 0 0 3 ) R e g io n -sp e c ific in h ib itio n o f p rostatic e p ith elia l b u d fo rm a tio n in 2 th e u rogen ital sinus o f C 5 7 B L /6 m ice e x p o se d in utero to 2 ,3 ,7 ,8 -tetra ch lo ro d ib en zo -p -d io x in . T o x ic o l. S ci. 76: 1 7 1 3 181. 45 L o n g n e c k e r , M P ; M i c h a l e k , J E . ( 2 0 0 0 ) S e r u m d i o x i n l e v e l i n r e l a t i o n t o d i a b e t e s m e l l i t u s a m o n g A i r F o r c e v e t e r a n s 6 w ith b ack groun d levels o f exposu re. E p id em io lo g y 11:44-48. 87 L o r b e r , M . ( 2 0 0 2 ) A p h a r m a c o k i n e t i c m o d e l f o r e s t i m a t i n g e x p o s u r e o f A m e r i c a n s t o d i o x i n - l i k e c o m p o u n d s i n t h e 9 past, present, and future. S cien ce o f T o ta l E n viron 2 8 8 :8 1 -9 5 . 1110 L o r b e r , M ; P h i l l i p s , L . ( 2 0 0 2 ) I n f a n t e x p o s u r e t o d i o x i n - l i k e c o m p o u n d s i n b r e a s t m i l k . E n v i r o n H e a l t h P e r s p e c t 12 1 1 0 ( 6 ) : A 3 2 5 - A 3 3 2 . 1134 L i u , H ; B i e g e l , L ; N a r a s i m h a n , T R ; e t a l . ( 1 9 9 2 ) I n h i b i t i o n o f i n s u l i n - l i k e g r o w t h f a c t o r - I r e s p o n s e s i n M C F - 7 c e l l s 15 b y 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n a n d r e l a t e d c o m p o u n d s . M o l C e l l E n d o c r i n o l 8 7 ( 1 - 3 ) : 1 9 - 2 8 . 1176 L u , Y C ; W o n g , P N . ( 1 9 8 4 ) D e r m a t o l o g i c a l , m e d i c a l , a n d l a b o r a t o r y f i n d i n g s o f p a t i e n t s i n T a i w a n a n d t h e i r 18 t r e a t m e n t s . A m J I n d M e d 5 : 8 1 - 1 1 5 . 2109 L u c i e r , G W ; L u i , E M K ; L a m a r t i n i e r e , C A . ( 1 9 7 9 ) M e t a b o l i c a c t i v a t i o n / d e a c t i v a t i o n r e a c t i o n s d u r i n g p e r i n a t a l 21 d e v e l o p m e n t . E n v i r o n H e a l t h P e r s p e c t 2 9 : 7 - 1 6 . 2232 L u c i e r , G W ; T r i t s c h e r , A ; G o l d s w o r t h y , T ; e t a l . ( 1 9 9 1 ) O v a r i a n h o r m o n e s e n h a n c e T C D D - m e d i a t e d i n c r e a s e s i n 24 c e l l p r o l i f e r a t i o n a n d p r e n e o p l a s t i c f o c i i n a t w o s t a g e m o d e l f o r r a t h e p a t o c a r c i n o g e n e s i s . C a n c e r R e s 5 1 : 1 3 9 1 25 1 3 9 7 . 2276 L u n d , A K ; G o e n s , M B ; K a n a y , N L ; W a l k e r , M K . ( 2 0 0 3 ) . C a r d i a c h y p e r t r o p h y i n a r y l h y d r o c a r b o n r e c e p t o r n u l l m i c e 28 i s c o r r e l a t e d w i t h e l e v a t e d a n g i o t e n s i n I I , e n d o t h e l i n - 1 , a n d m e a n a r t e r i a l b l o o d p r e s s u r e . T o x i c o l . A p p l . P h a r m a c o l . 29 1 9 3 : 1 7 7 - 1 8 7 . 3310 L u s s k a , A ; S h e n , E ; W h i t l o c k , J P , J r . ( 1 9 9 3 ) P r o t e i n - D N A i n t e r a c t i o n s a t a d i o x i n - r e s p o n s i v e e n h a n c e r . A n a l y s i s o f 32 s i x b o n a f i d e D N A - b i n d i n g s i t e s f o r t h e l i g a n d e d A h r e c e p t o r . J B i o l C h e m . 2 6 8 ( 9 ) : 6 5 7 5 - 6 5 8 0 . 3334 L y n g e , E . ( 1 9 9 8 ) C a n c e r i n c i d e n c e i n D a n i s h p h e n o x y h e r b i c i d e w o r k e r s , 1 9 4 7 - 1 9 9 3 . E n v i r o n H e a l t h P e r s p e c t 35 1 0 6 ( 2 ) : 6 8 3 - 6 8 8 . 3376 M a b l y , T A ; M o o r e , R W ; P e t e r s o n , R E . ( 1 9 9 2 a ) I n u t e r o a n d l a c t a t i o n a l e x p o s u r e o f m a l e r a t s t o 2 , 3 , 7 , 8 38 t e t r a c h l o r o d i b e n z o - p - d i o x i n : 1 . e f f e c t s o n a n d r o g e n i c s t a t u s . T o x i c o l A p p l P h a r m a c o l 1 1 4 : 9 7 - 1 0 7 . 4309 M a b l y , T A ; M o o r e , R W ; G o y , R W ; e t a l . ( 1 9 9 2 b ) I n u t e r o a n d l a c t a t i o n a l e x p o s u r e o f m a l e r a t s t o 2 , 3 , 7 , 8 41 t e t r a c h l o r o d i b e n z o - p - d i o x i n : 2 . e f f e c t s o n s e x u a l b e h a v i o r a n d t h e r e g u l a t i o n o f l u t e i n i z i n g h o r m o n e s e c r e t i o n i n 42 a d u l t h o o d . T o x i c o l A p p l P h a r m a c o l 1 1 4 : 1 0 8 - 1 1 7 . 4434 M a b l y , T A ; B j e r k e , D L ; M o o r e , R W ; e t a l . ( 1 9 9 2 c ) I n u t e r o a n d l a c t a t i o n a l e x p o s u r e o f m a l e r a t s t o 2 , 3 , 7 , 8 45 t e t r a c h l o r o d i b e n z o - p - d i o x i n : 3 . E f f e c t s o n s p e r m a t o g e n e s i s a n d r e p r o d u c t i v e c a p a b i l i t y . T o x i c o l A p p l P h a r m a c o l 46 1 1 4 : 1 1 8 - 1 2 6 . 4478 M a c k i e , D ; L i u , J ; L o j , Y - S ; T h o m a s , V . ( 2 0 0 3 ) N o E v i d e n c e o f D i o x i n C a n c e r T h r e s h o l d . E n v i r o n . H e a l t h P e r s p e c t . 49 1 1 1 : 1 1 4 5 - 1 1 4 7 . 5510 M a n z , A ; B e r g e r , J ; D w y e r , J H ; e t a l . ( 1 9 9 1 ) C a n c e r m o r t a l i t y a m o n g w o r k e r s i n c h e m i c a l p l a n t c o n t a m i n a t e d w i t h 5523 d i o x i n . L a n c e t 3 3 8 : 9 5 9 - 9 6 4 . 12/23/03 R-16 DRAFT--DO NOT CITE OR QUOTE 1 M a r k o w s k i, V P ; Z a r e b a , G ; S tern , S; et al. (2 0 0 1 ) A lte r e d o p er a n t r e s p o n d in g fo r m o to r r e in fo r c e m e n t a n d th e 2 d eterm in atio n o f b en ch m a rk d o ses fo llo w in g p erin atal ex p o su re to lo w -le v el 2 ,3 ,7 ,8 -tetra ch lo ro d ib en zo -p -d io x in . 3 E n viron H ealth P ersp ect 1 0 9 (6 ):6 2 1 -6 2 7 . 45 M a r k o w s k i , V P ; C o x , C ; P r e s t o n , R ; W e i s s , B . ( 2 0 0 2 ) I m p a i r e d r e s p o n s e e f f i c i e n c y i n a n o p e r a n t v i s u a l 6 d iscrim in a tion p roced u re fo llo w in g p renatal ex p o su re to 2 ,3 ,7 ,8 -tetra ch lo ro d ib en zo -p -d io x in (T C D D ). 7 N eu ro to xicol. T eratol. 24: 2 0 9 -2 1 8 . 89 M a r o n p o t , R R ; F o l e y , J F ; T a k a h a s h i , K ; e t a l . ( 1 9 9 3 ) D o s e - r e s p o n s e f o r T C D D p r o m o t i o n o f h e p a t o c a r c i n o g e n e s i s 10 i n r a t s i n i t i a t e d w i t h D E N : h i s t o l o g i c , b i o c h e m i c a l , a n d c e l l p r o l i f e r a t i o n e n d p o i n t s . E n v i r o n H e a l t h P e r s p e c t 11 1 0 1 : 6 3 4 - 6 4 2 . 1123 M a r t i n , J V . ( 1 9 8 4 ) L i p i d a b n o r m a l i t i e s i n w o r k e r s e x p o s e d t o d i o x i n . B r J I n d M e d 4 1 : 2 5 4 - 2 5 6 . 1154 M a r u y a m a W , Y o s h i d a K , T a n a k a T , e t a l . ( 2 0 0 2 ) P o s s i b l e r a n g e o f d i o x i n c o n c e n t r a t i o n i n h u m a n t i s s u e s : 16 s i m u l a t i o n w i t h a p h y s i o l o g i c a l l y b a s e d m o d e l . J T o x i c o l E n v i r o n H e a l t h 6 5 ( 2 4 ) : 2 0 5 3 - 7 3 . 1178 M a r u y a m a W , Y o s h i d a K , T a n a k a T , e t a l . ( 2 0 0 3 ) S i m u l a t i o n o f d i o x i n a c c u m u l a t i o n i n h u m a n t i s s u e s a n d a n a l y s i s 19 o f r e p r o d u c t i v e r i s k . C h e m o s p h e r e 5 3 ( 4 ) : 3 0 1 - 1 3 . 2210 M a t s u m u r a , F . ( 1 9 9 4 ) H o w i m p o r t a n t i s t h e p r o t e i n p h o s p h o r y l a t i o n p a t h w a y i n t h e t o x i c e x p r e s s i o n o f d i o x i n - t y p e 22 c h e m i c a l s ? B i o c h e m P h a r m a c o l 4 8 ( 2 ) : 2 1 5 - 2 2 4 . 2234 M a t z k e , G R ; F r y e , R F ; E a r l y J J ; e t a l . ( 2 0 0 0 ) E v a l u a t i o n o f t h e i n f l u e n c e o f d i a b e t e s m e l l i t u s o n a n t i p y r i n e 25 m e t a b o l i s m a n d C Y P 1 A 2 a n d C Y P 2 D 6 a c t i v i t y . P h a r m a c o t h e r a p y 2 0 ( 2 ) : 1 8 2 - 1 9 0 . 2276 M a t s u m u r a , F . ( 2 0 0 3 ) O n t h e s i g n i f i c a n c e o f t h e r o l e o f c e l l u l a r s t r e s s r e s p o n s e r e a c t i o n s i n t h e t o x i c a c t i o n s o f 28 d i o x i n . B i o c h e m i c a l P h a r m a c o l . 6 6 : 5 2 7 - 5 4 0 . 3209 M a y , G . ( 1 9 8 2 ) T e t r a c h l o r o d i b e n z o d i o x i n : a s u r v e y o f s u b j e c t s t e n y e a r s a f t e r e x p o s u r e . B r J I n d M e d 3 9 : 1 2 8 - 1 3 5 . 3312 M a y a n i , A ; B a r e l , S ; S o b a c k , S ; e t a l . ( 1 9 9 7 ) D i o x i n c o n c e n t r a t i o n s i n w o m e n w i t h e n d o m e t r i o s i s . H u m R e p r o d 33 1 2 : 3 7 3 - 3 7 5 . 3354 M c C o n n e l l , E E ; M o o r e , J A ; H a s e m a n , J K ; e t a l . ( 1 9 7 8 ) T h e c o m p a r a t i v e t o x i c i t y o f c h l o r i n a t e d d i b e n z o - p - d i o x i n s 36 i n m i c e a n d g u i n e a p i g s . T o x i c o l A p p l P h a r m a c o l 4 4 : 3 3 5 - 3 5 6 . 3378 M c G r e g o r , D B , P a r t e n s k y , C , W i l b o u r n , J , e t a l . ( 1 9 9 8 ) A n I A R C E v a l u a t i o n o f P o l y c h l o r i n a t e d D i b e n z o - p - d i o x i n s 39 a n d P o l y c h l o r i n a t e d D i b e n z o f u r a n s a s R i s k F a c t o r s i n H u m a n C a r c i n o g e n e s i s . E n v i r o n H e a l t h . P e r s p e c t 1 0 6 ( 2 ) : 7 5 5 40 7 6 0 . 4412 M c N u l t y , W P . ( 1 9 7 7 ) T o x i c i t y o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n f o r r h e s u s m o n k e y s : b r i e f r e p o r t . B u l l E n v i r o n 43 C o n t a m T o x i c o l 1 8 : 1 0 8 - 1 0 9 . 4454 M e b u s , C A ; R e d d y , V R ; P i p e r , W N . ( 1 9 8 7 ) D e p r e s s i o n o f r a t t e s t i c u l a r 1 7 - h y d r o x y l a s e a n d 1 7 , 2 0 - l y a s e a f t e r 46 a d m i n i s t r a t i o n o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) . B i o c h e m P h a r m a c o l 3 6 ( 5 ) : 1 7 2 7 - 1 7 3 1 . 4478 M i c h a l e k , J E ; T r i p a t h i R C ( 1 9 9 9 ) P h a r m a k o t i n e t i c s o f T C D D i n v e t e r a n s o f o p e r a t i o n R a n c h H a n d : 1 5 - y e a r f o l l o w 49 u p . J T o x i c o l E n v i r o n H e a l t h 5 7 : 3 6 9 - 3 7 8 . 5510 M i c h a l e k , J ; P i r k l e , J ; C a u d i l l , S ; e t a l . ( 1 9 9 6 ) P h a r m a c o k i n e t i c s o f T C D D i n v e t e r a n s o f o p e r a t i o n R a n c h H a n d : 1 0 5523 y e a r f o l l o w - u p . J T o x E n v i r o n E p i 4 7 : 2 0 9 - 2 2 0 . 12/23/03 R-17 DRAFT--DO NOT CITE OR QUOTE 1 M ic h a le k , JE ; R a h e , A J ; K u lk a r n i, P M ; et al. ( 1 9 9 8 ) L e v e ls o f 2 ,3 ,7 ,8 - te tr a c h lo r o d ib e n z o -p -d io x in in 1 ,3 0 2 2 u n ex p o sed A ir F orce V ietnam -era veterans. J E xp osu re A n al E n viron E p id 8:59-64. 43 M i c h a l e k , J E ; A k h t a r , F Z ; K i e l , J L . ( 1 9 9 9 a ) S e r u m d i o x i n , i n s u l i n , f a s t i n g g l u c o s e , a n d s e x h o r m o n e - b i n d i n g 5 glob u lin in veteran s o f O p eration R a n ch H an d . J C lin E n d o crin ol M etab (5 ):1 5 4 0 -1 5 4 3 . 67 M i c h a l e k , J E ; K e t c h u m , N S ; C h e c k , I J . ( 1 9 9 9 b ) S e r u m d i o x i n a n d i m m u n o l o g i c r e s p o n s e i n v e t e r a n s o f O p e r a t i o n 8 R anch H and. A m J E p idem iol 1 4 9:10 3 8 -1 0 46 . 109 M i c h a l e k , J E ; P i r k l e . , J L ; N e e d h a m , L L ; e t a l . ( 2 0 0 2 ) . P h a r m a c o k i n e t i c s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n 11 S e v e s o a d u l t s a n d v e t e r a n s o f o p e r a t i o n R a n c h H a n d . J E x p o A n a l E n v i r o n E p i d e m i o l 1 2 ( 1 ) : 4 4 - 5 3 . E r r a t u m i n : J 12 E x p o A n a l E n v i r o n E p i d e m i o l 2 0 0 2 , 1 2 ( 2 ) : 1 6 5 . 1134 M i c h a l e k , J E ; K e t c h u m , N ; T r i p a t h i , R C . ( 2 0 0 3 ) D i a b e t e s m e l l i t u s a n d 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n 15 e l i m i n a t i o n i n v e t e r a n s o f O p e r a t i o n R a n c h H a n d . J T o x i c o l E n v i r o n H e a l t h 6 6 ( 3 ) : 2 1 1 - 2 1 . 1176 M o c a r e l l i , P ; N e e d h a m , L L ; M a r o c c h i , A ; e t a l . ( 1 9 9 1 ) S e r u m c o n c e n t r a t i o n s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n 18 a n d t e s t r e s u l t s f r o m s e l e c t e d r e s i d e n t s o f S e v e s o , I t a l y . J T o x i c o l E n v i r o n H e a l t h 3 2 : 3 5 7 - 3 6 6 . 2109 M o c a r e l l i P ; B r a m b i l l a P ; G e r t h o u x , P M ; e t a l . ( 1 9 9 6 ) C h a n g e i n s e x r a t i o w i t h e x p o s u r e t o d i o x i n [ l e t t e r ] . L a n c e t 21 3 4 8 : 4 0 9 . 2223 M o c a r e l l i , P ; G e r t h o u x , P M ; F e r r a r i , E ; e t a l . ( 2 0 0 0 ) P a t e r n a l c o n c e n t r a t i o n s o f d i o x i n a n d s e x r a t i o o f o f f s p r i n g . 24 L a n c e t 3 5 5 : 1 8 5 8 - 1 8 6 3 . 2256 M o c a r e l l i , P ; M a r o c c h i , A ; B r a m b i l l a , P ; e t a l . ( 1 9 8 6 ) C l i n i c a l l a b o r a t o r y m a n i f e s t a t i o n s o f e x p o s u r e t o d i o x i n i n 27 c h i l d r e n . A s i x y e a r s t u d y o f t h e e f f e c t s o f a n e n v i r o n m e n t a l d i s a s t e r n e a r S e v e s o , I t a l y . J A M A 2 5 6 : 2 6 8 7 - 2 6 9 5 . 2289 M o o r e , R W ; P e t e r s o n , R E . ( 1 9 8 8 ) A n d r o g e n c a t a b o l i s m a n d e x c r e t i o n i n 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n - t r e a t e d 30 r a t s . B i o c h e m P h a r m a c o l 3 7 : 5 6 0 - 5 6 2 . 3312 M o o r e , R W ; B o o k s t a f f , R C ; M a b l y , R A ; e t a l . ( 1 9 9 1 ) D i f f e r e n t i a l e f f e c t s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n o n 33 r e s p o n s i v e n e s s o f m a l e r a t s t o a n d r o g e n s , 1 7 B - e s t r a d i o l , l u t e i n i z i n g h o r m o n e , g o n a d o t r o p i n r e l e a s i n g h o r m o n e , a n d 34 p r o g e s t e r o n e . P r e s e n t e d a t: D i o x i n ` 9 1 , 1 1 t h i n t e r n a t i o n a l s y m p o s i u m o n c h l o r i n a t e d d i o x i n s a n d r e l a t e d c o m p o u n d s ; 35 R e s e a r c h T r i a n g l e P a r k , N C . 3376 M o o r e , R W ; P a r s o n s , J A ; B o o k s t a f f , R C ; e t a l . ( 1 9 8 9 ) P l a s m a c o n c e n t r a t i o n s o f p i t u i t a r y h o r m o n e s i n 2 , 3 , 7 , 8 38 t e t r a c h l o r o d i b e n z o - p - d i o x i n - t r e a t e d m a l e r a t s . J B i o c h e m T o x i c o l 4 : 1 6 5 - 1 7 2 . 4309 M o o r e , R W ; P o t t e r , C L ; T h e o b a l d , H M ; e t a l . ( 1 9 8 5 ) A n d r o g e n i c d e f i c i e n c y i n m a l e r a t s t r e a t e d w i t h 2 , 3 , 7 , 8 41 t e t r a c h l o r o d i b e n z o - p - d i o x i n . T o x i c o l A p p l P h a r m a c o l 7 9 : 9 9 - 1 1 1 . 4423 M o s e s , M ; L i l i s , R ; C r o w , K D ; e t a l . ( 1 9 8 4 ) H e a l t h s t a t u s o f w o r k e r s w i t h p a s t e x p o s u r e t o 44 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n t h e m a n u f a c t u r e o f 2 , 4 , 5 - t r i c h l o r o p h e n o x y a c e t i c a c i d . C o m p a r i s o n o f f i n d i n g s 45 w i t h a n d w i t h o u t c h l o r a c n e . A m J I n d M e d 5 : 1 6 1 - 1 8 2 . 4476 M u r r a y , F J ; S m i t h , F A ; N i t s c h k e , K D ; e t a l . ( 1 9 7 9 ) T h r e e - g e n e r a t i o n r e p r o d u c t i o n s t u d y o f r a t s g i v e n 2 , 3 , 7 , 8 48 t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) i n t h e d i e t . T o x i c o l A p p l P h a r m a c o l 5 0 : 2 4 1 - 2 5 2 . 4590 N a g a y a m a , J ; O k a m u r a , K ; I i d a , T ; e t a l . ( 1 9 9 8 ) P o s t n a t a l e x p o s u r e t o c h l o r i n a t e d d i o x i n s a n d r e l a t e d c h e m i c a l s o n 5512 t h y r o i d h o r m o n e s t a t u s i n J a p a n e s e b r e a s t - f e d i n f a n t s . C h e m o s p h e r e 3 7 ( 9 - 1 2 ) : 1 7 8 9 - 1 7 9 3 . 12/23/03 R-18 DRAFT--DO NOT CITE OR QUOTE 1 N a g e l, S; B e r g e r , J; F le s c h - J a n y s , D ; et al. ( 1 9 9 4 ) M o r ta lity a n d c a n c e r m o r ta lity in a c o h o r t o f f e m a le w o r k e r s o f a 2 h erb icid e p rod u cin g plant e x p o se d to p o ly ch lorin a ted d ib en zo -p -d io x in s and furans. In form B io m et E p id e m io l M ed 3 B iol25:32-38. 45 N a r a s i m h a n , T R ; C r a i g , A ; A r e l l a n o , L ; e t a l . ( 1 9 9 4 ) R e l a t i v e s e n s i t i v i t i e s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n 6 in d u ced C yp 1a-1 and C yp 1a-2 g en e exp ression and im m u n otoxicity in fem ale B 6 C 3 F 1 m ice. F u n d am A p p l T o x ico l 7 23:598-607. 89 N A S / I n s t i t u t e o f M e d i c i n e . ( 2 0 0 3 ) D i o x i n s a n d D i o x i n - L i k e C o m p o u n d s i n t h e F o o d S u p p l y . T h e N a t i o n a l 10 A c a d e m i e s P r e s s . W a s h i n g t o n , D C . 1112 N A S / N R C ( N a t i o n a l A c a d e m y o f S c i e n c e s / N a t i o n a l R e s e a r c h C o u n c i l ) . ( 1 9 8 3 ) R i s k a s s e s s m e n t i n t h e f e d e r a l 13 g o v e r n m e n t . W a s h i n g t o n , D C : N a t i o n a l A c a d e m y P r e s s . 1154 N A S / N R C . ( 1 9 9 4 ) S c i e n c e a n d j u d g m e n t i n r i s k a s s e s s m e n t . W a s h i n g t o n , D C : N a t i o n a l A c a d e m y P r e s s . 1176 N A S / N R C . ( 1 9 9 9 ) A r s e n i c i n d r i n k i n g w a t e r . W a s h i n g t o n , D C : N a t i o n a l A c a d e m y P r e s s . 1189 N e b e r t , D W ; P e t e r s e n , D D ; F o r n a c e , A J , J r . ( 1 9 9 0 ) C e l l u l a r r e s p o n s e s t o o x i d a t i v e s t r e s s : t h e [ A h ] g e n e b a t t e r y a s a 20 p a r a d i g m . E n v i r o n H e a l t h P e r s p e c t 8 8 : 1 3 - 2 5 . 2212 N e b e r t , D W ; M c K i n n o n , R A ; P u g a , A . ( 1 9 9 6 ) H u m a n d r u g - m e t a b o l i z i n g e n z y m e p o l y m o r p h i s m s : e f f e c t s o n r i s k o f 23 t o x i c i t y a n d c a n c e r . D N A C e l l B i o l 1 5 ( 4 ) : 2 7 3 - 2 8 0 . 2254 N e b e r t , D W ; R o e , A L ; D i e t e r , M Z ; e t a l . ( 2 0 0 0 ) R o l e o f t h e a r o m a t i c h y d r o c a r b o n r e c e p t o r a n d [ A h ] g e n e b a t t e r y i n 26 t h e o x i d a t i v e s t r e s s r e s p o n s e , c e l l c y c l e c o n t r o l , a n d a p o p t o s i s . B i o c h e m P h a r m a c o l 5 9 ( 1 ) : 6 5 - 8 5 . 2278 N e e d h a m , L L ; G e r t h o u x , P M ; P a t t e r s o n , D G ; e t a l . ( 1 9 9 9 ) E x p o s u r e a s s e s s m e n t : s e r u m l e v e l s o f T C D D i n S e v e s o , 29 I t a l y . E n v i r o n R e s ( A ) 8 0 : S 2 0 0 - S 2 0 6 . 3310 N e u b e r g e r , M ; L a n d v o i g t , W ; D e m t , F . ( 1 9 9 1 ) B l o o d l e v e l s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n c h e m i c a l 32 w o r k e r s a f t e r c h l o r a c n e a n d i n c o m p a r i s o n g r o u p s . I n t A r c h O c c u p E n v i r o n H e a l t h 6 3 : 3 2 5 - 3 2 7 . 3334 N e u b e r g e r , M ; R a p p e , C ; B e r g e k , S ; e t a l . ( 1 9 9 9 ) P e r s i s t e n t h e a l t h e f f e c t s o f d i o x i n c o n t a m i n a t i o n i n h e r b i c i d e 35 p r o d u c t i o n . E n v i r o n R e s 8 1 ( 3 ) : 2 0 6 - 2 1 4 . 3376 N e u b e r t , R ; G o l o r , G ; S t a h l m a n n , R ; e t a l . ( 1 9 9 2 ) P o l y h a l o g e n a t e d d i b e n z o - p - d i o x i n s a n d d i b e n z o f u r a n s a n d t h e 38 i m m u n e s y s t e m . 4 : e f f e c t s o f m u l t i p l e - d o s e t r e a t m e n t w i t h 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) o n 39 (C a llith rix ja c c h u s ).p e r i p h e r a l l y m p h o c y t e s u b p o p u l a t i o n s o f a n o n - h u m a n p r i m a t e A rch T oxicol 66:250-259. 4410 N i e , M ; B l a n k e n s h i p , A L ; G i e s y , J P . ( 2 0 0 1 ) I n t e r a c t i o n s b e t w e e n a r y l h y d r o c a r b o n r e c e p t o r ( A h R ) a n d h y p o x i a 42 s i g n a l i n g p a t h w a y s . E n v T o x i c o l P h a r m a c o l 1 0 : 1 7 - 2 7 . 4434 N i c k l a s , T A . ( 1 9 9 5 ) D i e t a r y s t u d i e s o f c h i l d r e n : t h e B o g a l u s a h e a r t s t u d y e x p e r i e n c e . J A m e r D i e t e t i c A s s c 45 9 5 : 1 1 2 7 - 1 1 3 3 . 4476 N i c k l a s , T A ; W e b b e r , L S ; S r i n i v a s a n , S R ; e t a l . ( 1 9 9 3 ) S e c u l a r t r e n d s i n d i e t a r y i n t a k e s a n d c a r d i o v a s c u l a r r i s k 48 f a c t o r s in 1 0 - y - o l d c h i l d r e n : t h e B o g a l u s a h e a r t s t u d y ( 1 9 7 3 - 1 9 8 8 ) . A m e r J C l i n N u t 5 7 : 9 3 0 - 9 3 7 . 4590 N i c k l a s , T A ; J o h n s o n , C C ; M e y e r s , L ; e t a l . ( 1 9 9 5 ) E a t i n g p a t t e r n s , n u t r i e n t i n t a k e s , a n d a l c o h o l c o n s u m p t i o n 5512 p a t t e r n s o f y o u n g a d u l t s : t h e B o g a l u s a h e a r t s t u d y . M e d E x e r c i s e N u t H e a l t h 4 : 3 1 6 - 3 2 4 . 12/23/03 R-19 DRAFT--DO NOT CITE OR QUOTE 1 N T P (N ation al T o x ic o lo g y Program ). (1 9 8 0 ) B io a ssa y o f a m ixture o f 1 ,2 ,3 ,6,7 ,8 -h ex ach lo ro d ib en zo -p -d io x in and 2 1 ,2 ,3 ,7,8 ,9 -h ex a ch lo ro d ib en zo -p -d io x in for p o ssib le ca rcin ogen icity (g a v a g e study). T ech . R ept. Ser. N o . 198. 3 D ep artm en t o f H ealth and H o m e S ervices, P ublic H ealth S ervices, R esearch T rian gle Park, N C . 45 N T P . ( 1 9 8 2 a ) B i o a s s a y o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n f o r p o s s i b l e c a r c i n o g e n i c i t y ( g a v a g e s t u d y ) . T e c h . 6 R ept. Ser. N o . 201. D H H S , P H S , R esearch T riangle Park, N C . 87 N T P . ( 1 9 8 2 b ) B i o a s s a y o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n f o r p o s s i b l e c a r c i n o g e n i c i t y ( d e r m a l s t u d y ) . T e c h . 9 R ept. Ser. N o . 201. D H H S , P H S , R esearch T riangle Park, N C . 1110 N T P . ( 2 0 0 0 ) R e p o r t o n c a r c i n o g e n s , 9 t h e d : C a r c i n o g e n p r o f i l e s 2 0 0 0 . D H H S , P H S , R e s e a r c h T r i a n g l e P a r k , N C . 1123 N T P . ( 2 0 0 1 ) . A d d e n d u m t o t h e n i n t h r e p o r t o n c a r c i n o g e n s . P u b l i c H e a l t h S e r v i c e , N a t i o n a l T o x i c o l o g y P r o g r a m . 14 J a n u a r y 2 0 0 1 A d d e n d u m . A v a i l a b l e a t h t t p : / / e h p . n i e h s . n i h . g o v / r o c / n i n t h / k n o w n / t c d d . p d f 1156 N T P . ( 2 0 0 3 a ) . T R - 5 2 0 : T o x i c o l o g y a n d C a r c i n o g e n e s i s S t u d i e s o f 3 , 3 ' , 4 , 4 ' , 5 - P e n t a c h l o r o b i p h e n y l ( P C B 1 2 6 ) 17 ( a b s t r a c t ) . A v a i l a b l e a t h t t p : / / n t p - s e r v e r . n i e h s . n i h . g o v / h t d o c s / L T - s t u d i e s / t r 5 2 0 . h t m l 1189 N T P . ( 2 0 0 3 b ) . T R - 5 2 1 : T o x i c o l o g y a n d C a r c i n o g e n e s i s S t u d i e s o f 2 , 3 , 7 , 8 - T e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) 20 ( a b s t r a c t ) . A v a i l a b l e a t h t t p : / / n t p - s e r v e r . n i e h s . n i h . g o v / h t d o c s / L T - s t u d i e s / t r 5 2 1 . h t m l 2212 N T P . ( 2 0 0 3 c ) . T R - 5 2 5 : T o x i c o l o g y a n d C a r c i n o g e n e s i s S t u d i e s o f 2 , 3 , 4 , 7 , 8 - P e n t a c h l o r o d i b e n z o - f u r a n ( P e C D F ) 23 ( a b s t r a c t ) . A v a i l a b l e a t h t t p : / / n t p - s e r v e r . n i e h s . n i h . g o v / h t d o c s / L T - s t u d i e s / t r 5 2 5 . h t m l 2254 N T P . ( 2 0 0 3 d ) . T R - 5 2 6 : T o x i c o l o g y a n d C a r c i n o g e n e s i s S t u d i e s o f A m i x t u r e o f P C B 1 2 6 , T C D D , a n d P e C D F 26 ( a b s t r a c t ) . A v a i l a b l e a t h t t p : / / n t p - s e r v e r . n i e h s . n i h . g o v / h t d o c s / L T - s t u d i e s / t r 5 2 6 . h t m l 2278 O h s a k o , S ; M i y a b a r a , Y ; N i s h i m u r a , N ; e t a l . ( 2 0 0 1 ) M a t e r n a l e x p o s u r e t o a l o w d o s e o f 29 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) s u p p r e s s e d t h e d e v e l o p m e n t o f r e p r o d u c t i v e o r g a n s o f m a l e r a t s : 30 d o s e - d e p e n d e n t i n c r e a s e o f m R N A l e v e l s o f 5 a l p h a - r e d u c t a s e t y p e 2 i n c o n t r a s t t o d e c r e a s e o f a n d r o g e n r e c e p t o r i n 31 t h e p u b e r t a l v e n t r a l p r o s t a t e . T o x i c o l S c i 6 0 ( 1 ) : 1 3 2 - 4 3 3323 O k e y , A B ; G i a n n o n e , J V ; S m a r t , W ; e t a l . ( 1 9 9 7 ) B i n d i n g o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n t o A H r e c e p t o r i n 34 p l a c e n t a s f r o m n o r m a l v e r s u s a b n o r m a l p r e g n a n c y o u t c o m e s . C h e m o s p h e r e 3 4 ( 5 - 7 ) : 1 5 3 5 - 1 5 4 7 . 3356 O l s e n , H ; E n a n , E ; M a t s u m u r a , F . ( 1 9 9 4 ) R e g u l a t i o n o f g l u c o s e t r a n s p o r t i n t h e N I H 3 T 3 L 1 p r e a d i p o c y t e c e l l l i n e 37 b y T C D D . E n v i r o n H e a l t h P e r s p e c t 1 0 2 ( 5 ) : 4 5 4 - 4 5 8 . 3389 O l s o n , J R ; M c G a r r i g l e , B P . ( 1 9 9 0 ) C h a r a c t e r i z a t i o n o f t h e d e v e l o p m e n t a l t o x i c i t y o f 2 , 3 , 7 , 8 - T C D D i n t h e G o l d e n 40 S y r i a n h a m s t e r . T o x i c o l o g i s t 1 0 : 3 1 3 . 4412 O l s o n , J R ; H o l s c h e r , M A ; N e a l , R A . ( 1 9 8 0 ) T o x i c i t y o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n t h e G o l d e n S y r i a n 43 h a m s t e r . T o x i c o l A p p l P h a r m a c o l 5 5 : 6 7 - 7 8 . 4454 O t t , M G ; Z o b e r , A . ( 1 9 9 6 a ) M o r b i d i t y s t u d y o f e x t r u d e r p e r s o n n e l w i t h p o t e n t i a l e x p o s u r e t o b r o m i n a t e d d i o x i n s 46 a n d f u r a n s . 2 : r e s u l t s o f c l i n i c a l l a b o r a t o r y s t u d i e s . O c c u p E n v i r o n M e d 5 3 : 8 4 4 - 8 4 6 . 4478 O t t , M G ; Z o b e r , A . ( 1 9 9 6 b ) C a u s e s p e c i f i c m o r t a l i t y a n d c a n c e r i n c i d e n c e a m o n g e m p l o y e e s e x p o s e d t o 2 , 3 , 7 , 8 49 T C D D a f t e r a 1 9 5 3 r e a c t o r a c c i d e n t . O c c u p E n v i r o n M e d 5 3 : 6 0 6 - 6 1 2 . 5510 O t t , M G ; M e s s e r e r , P ; Z o b e r , A . ( 1 9 9 3 ) A s s e s s m e n t o f p a s t o c c u p a t i o n a l e x p o s u r e t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p 52 d i o x i n u s i n g b l o o d l i p i d a n a l y s e s . I n t A r c h O c c u p E n v i r o n H e a l t h 6 5 : 1 - 8 . 5534 O t t , M G ; Z o b e r , A ; G e r m a n n , C . ( 1 9 9 4 ) L a b o r a t o r y r e s u l t s f o r s e l e c t e d t a r g e t o r g a n s i n 1 3 8 i n d i v i d u a l s 55 12/23/03 R-20 DRAFT--DO NOT CITE OR QUOTEo c c u p a t i o n a l l y e x p o s e d t o T C D D . C h e m o s p h e r e 2 9 : 2 4 2 3 - 2 4 3 7 . 1 O u id d ir , A ; P la n e s, C ; F e r n a n d e s , I; et al. ( 1 9 9 9 ) H y p o x ia u p r e g u la te s a c tiv ity a n d e x p r e s s io n o f th e g lu c o s e 2 transporter G L U T 1 in alveolar epithelial cells. A m J R esp ir C ell M o l B io l (6 ):7 1 0 -7 1 8. 43 P a r k , J - Y K ; S h i g e n a g a , M K ; A m e s , B N . ( 1 9 9 6 ) I n d u c t i o n o f c y t o c h r o m e P 4 5 0 1 A I b y 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p 5 d io x in or in d o lo (3 ,2 -b ) ca rb a zo le is asso cia ted w ith oxid a tiv e D N A d a m ag e. P roc N a t A ca d S ci 9 3 :2 3 2 2 -2 3 2 7 . 67 P a t a n d i n , S ; K o o p m a n - E s s e b o o m , C ; d e R i d d e r , M A ; e t a l . ( 1 9 9 8 ) P e d i a t r R e s 4 4 ( 4 ) : 5 3 8 - 5 4 5 . 89 P a t a n d i n , S ; L a n t i n g , C I ; M u l d e r , P G ; e t a l . ( 1 9 9 9 ) E f f e c t s o f e n v i r o n m e n t a l e x p o s u r e t o p o l y c h l o r i n a t e d b i p h e n y l s 10 a n d d i o x i n s o n c o g n i t i v e a b i l i t i e s i n D u t c h c h i l d r e n a t 4 2 m o n t h s o f a g e . J P e d i a t r 1 3 4 ( 1 ) : 3 3 - 4 1 . 1112 P a u w e l s , A ; C e n i j n , P ; C o v a c i , A ; e t a l . ( 1 9 9 9 ) A n a l y s i s o f P C B c o n g e n e r s ( b y G C - E C D ) a n d d i o x i n - l i k e t o x i c 13 e q u i v a l e n c e ( b y C A L U X a s s a y ) i n f e m a l e s w i t h e n d o m e t r i o s i s a n d o t h e r f e r t i l i t y p r o b l e m s . O r g a n o h a l o g e n 14 C o m p o u n d s 4 4 : 4 0 8 - 4 1 2 . 1156 P a v u k , M ; S c h e c t e r , A J ; A k h t a r , F Z ; M i c h a l e k . J E . ( 2 0 0 3 ) . S e r u m 2 , 3 , 7 , 8 - T e t r a c h l o r o r o d i b e n z o - p - d i o x i n ( T C D D ) 17 l e v e l s a n d t h r y o i d f u n c t i o n i n A i r F o r c e v e t e r a n s o f t h e V i e t n a m W a r . A E P 1 3 : 3 3 5 - 3 4 3 . 1189 P a z d e r o v a - V e j l u p k o v a , J ; N e m c o v a , M ; P i c k o v a , J ; e t a l . ( 1 9 8 1 ) T h e d e v e l o p m e n t a n d p r o g n o s i s o f c h r o n i c 20 i n t o x i c a t i o n b y t e t r a c h l o r o d i b e n z o - p - d i o x i n i n m a n . A r c h E n v i r o n H e a l t h 3 6 : 5 - 1 1 . 2212 P e s a t o r i , A C ; Z o c c h e t t i , C ; G u e r c i l e n a , S ; e t a l . ( 1 9 9 8 ) D i o x i n e x p o s u r e a n d n o n - m a l i g n a n t h e a l t h e f f e c t s : a 23 m o r t a l i t y s t u d y . O c c u p E n v i r o n M e d 5 5 ( 2 ) : 1 2 6 - 1 3 1 . 2254 P e s a t o r i , A C ; T i r o n i , A ; C o n s o n n i , A ; e t a l . ( 1 9 9 9 ) C a n c e r i n c i d e n c e i n t h e S e v e s o p o p u l a t i o n , 1 9 7 7 - 1 9 9 1 . 26 O r g a n o h a l o g e n C o m p o u n d s 4 4 : 4 1 1 - 4 1 2 . 2278 P e t e r s , J M ; N a r o t s k y , M G ; F e r n a n d e z - S a l g u e r o , P M ; e t a l . ( 1 9 9 9 ) A m e l i o r a t i o n o f T C D D - i n d u c e d t e r a t o g e n e s i s i n 29 a r y l h y d r o c a r b o n r e c e p t o r ( A h R ) - n u l l m i c e . T o x i c o l . S c i . 4 7 : 8 6 - 9 2 . 3310 P e t e r s o n , R E ; T h e o b a l d , H M ; K i m m e l , G L . ( 1 9 9 3 ) D e v e l o p m e n t a l a n d r e p r o d u c t i v e t o x i c i t y o f d i o x i n s a n d r e l a t e d 32 c o m p o u n d s : c r o s s - s p e c i e s c o m p a r i s o n s . C r i t R e v T o x i c o l 2 3 ( 3 ) : 2 8 3 - 3 3 5 . 3334 P i n s k y , P F ; L o r b e r , M N . ( 1 9 9 8 ) A m o d e l t o e v a l u a t e p a s t e x p o s u r e t o 2 , 3 , 7 , 8 - T C D D . J E x p o A n a l E n v i r o n 35 E p i d e m i o l 8 ( 2 ) : 1 8 7 - 2 0 6 . 3376 P l u i m , H J ; K o p p e , J G ; O l i e , K ; e t a l . ( 1 9 9 2 ) E f f e c t s o f d i o x i n s o n t h y r o i d f u n c t i o n i n n e w b o r n b a b i e s . L e t t e r t o t h e 38 e d i t o r . L a n c e t 3 3 9 : 1 3 0 3 . 4309 P l u i m , H J ; d e V i j l d e r , J J M ; O l i e , K ; e t a l . ( 1 9 9 3 ) E f f e c t s o f p r e - a n d p o s t n a t a l e x p o s u r e t o c h l o r i n a t e d d i o x i n s a n d 41 f u r a n s o n h u m a n n e o n a t a l t h y r o i d h o r m o n e c o n c e n t r a t i o n s . E n v i r o n H e a l t h P e r s p e c t 1 0 1 ( 6 ) : 5 0 4 - 5 0 8 . 4423 P l u i m , H J ; K o p p e , J G ; O l i e , K ; e t a l . ( 1 9 9 4 ) C l i n i c a l l a b o r a t o r y m a n i f e s t a t i o n s o f e x p o s u r e t o b a c k g r o u n d l e v e l s o f 44 d i o x i n s i n t h e p e r i n a t a l p e r i o d . A c t a P a e d i a t r 8 3 ( 6 ) : 5 8 3 - 5 8 7 . 4456 P o h j a n v i r t a , R ; T u o m i s t o , J . ( 1 9 9 4 ) S h o r t - t e r m t o x i c i t y o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n l a b o r a t o r y 47 a n i m a l s : e f f e c t s , m e c h a n i s m s , a n d a n i m a l m o d e l s . P h a r m a c o l R e v 4 6 ( 4 ) : 4 8 3 - 5 4 9 . 4489 P o h j a n v i r t a , R ; V i l u k s e l a , M ; T u o m i s t o , J T ; e t a l . ( 1 9 9 9 ) P h y s i c o c h e m i c a l d i f f e r e n c e s i n t h e A H r e c e p t o r s o f t h e 50 m o s t T C D D - s u s c e p t i b l e a n d t h e m o s t T C D D - r e s i s t a n t r a t s t r a i n s . T o x i c o l A p p l P h a r m a c o l 1 5 5 ( 1 ) : 8 2 - 9 5 . 5512 P o h j a n v i r t a , R ; K o r k a l a i n e n , M ; M c G u i r e , J ; e t a l . ( 2 0 0 2 ) T h e p o t e n t i n v i t r o A H r e c e p t o r a g o n i s t I n d o l e ( 3 , 2 53 b ) c a r b a z o l e ( I C Z ) * d o e s n o t e l i c i t a c u t e t o x i c i t y s y n d r o m e o f d i o x i n s i n r a t s i n v i v o . F o o d C h e m . T o x i c o l . 4 0 : 1 0 2 3 5554 1 0 3 2 . 12/23/03 R-21 DRAFT--DO NOT CITE OR QUOTE 1 P olan d , A D . (1 9 9 6 ) M eetin g report: recep tor-actin g x en o b io tics and their risk a ssessm en t. D ru g M etab D isp 2 24:1385-1388. 43 P o l a n d , A ; G l o v e r , E . ( 1 9 8 0 ) 2 , 3 , 7 , 8 , - T e t r a c h l o r o d i b e n z o - p - d i o x i n : s e g r e g a t i o n o f t o x i c i t y w i t h t h e A h l o c u s . M o l 5 Pharm acol 17(1):86-94. 67 P o l a n d , A D ; K n u t s o n , J C . ( 1 9 8 2 ) 2 , 3 , 7 , 8 - T e t r a c h l o r o d i b e n z o - p - d i o x i n a n d r e l a t e d h a l o g e n a t e d a r o m a t i c 8 h ydrocarbon s: exam in ation o f the m ech a n ism o f toxicity. A n n R ev P h arm acol T o x ico l 2 2 :5 1 7 -5 5 4 . 109 P o l a n d , A D ; P a l e n , D ; G l o v e r , E . ( 1 9 8 2 ) T u m o r p r o m o t i o n b y T C D D i n s k i n o f H R S / J m i c e . N a t u r e 11 3 0 0 ( 5 8 8 9 ) : 2 7 1 - 2 7 3 . 1123 P o r t i e r , C J ; K o h n , M C . ( 1 9 9 6 ) A b i o l o g i c a l l y - b a s e d m o d e l f o r t h e c a r c i n o g e n i c e f f e c t s o f 2 , 3 , 7 , 8 - T C D D i n f e m a l e 14 S p r a g u e - D a w l e y r a t s . O r g a n o h a l o g e n C o m p o u n d s 2 9 : 2 2 2 - 2 2 7 . 1156 P o r t i e r , C ; H o e l , D ; v a n R y z i n , J . ( 1 9 8 4 ) S t a t i s t i c a l a n a l y s i s o f t h e c a r c i n o g e n e s i s b i o a s s a y d a t a r e l a t i n g t o t h e r i s k s 17 f r o m e x p o s u r e t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n . I n : L o w r a n c e , W , e d . P u b l i c h e a l t h r i s k s o f t h e d i o x i n s . L o s 18 A l t o s , N M : W i l l i a m K a u f m a n n ; p p . 9 9 - 1 2 0 . 2109 P o r t i e r , C J ; S h e r m a n , C D ; K o h n , M ; e t a l . ( 1 9 9 6 ) M o d e l i n g t h e n u m b e r a n d s i z e o f h e p a t i c f o c a l l e s i o n s f o l l o w i n g 21 e x p o s u r e t o 2 , 3 , 7 , 8 - T C D D . T o x i c o l A p p l P h a r m a c o l 1 3 8 : 2 0 - 3 0 . 2223 P u g a , A ; M a i e r , A ; M e d v e d o v i c , M . ( 2 0 0 0 a ) T h e t r a n s c r i p t i o n a l s i g n a t u r e o f d i o x i n i n h u m a n h e m a t o m a H e p G 2 24 c e l l s . B i o c h e m P h a r m a c o l 6 0 : 1 1 2 9 - 1 1 4 2 . 2256 P u g a , A ; B a r n e s , S J ; D a l t o n , T P ; e t a l . ( 2 0 0 0 b ) A r o m a t i c h y d r o c a r b o n r e c e p t o r i n t e r a c t i o n w i t h t h e r e t i n o b l a s t o m a 27 p r o t e i n p o t e n t i a t e s r e p r e s s i o n o f E 2 F - d e p e n d e n t t r a n s c r i p t i o n a n d c e l l c y c l e a r r e s t . J B i o l C h e m 2 7 5 ( 4 ) : 2 9 4 3 - 2 9 5 0 . 2289 P u g a , A ; B a r n e s , S J ; C h a n g , C ; e t a l . ( 2 0 0 0 c ) A c t i v a t i o n o f t r a n s c r i p t i o n f a c t o r s a c t i v a t o r p r o t e i n - 1 a n d n u c l e a r 30 f a c t o r - k a p p a B b y 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n . B i o c h e m P h a r m a c o l 5 9 ( 8 ) : 9 9 7 - 1 0 0 5 . 3312 R a o , M S ; S u b b a r a o , V ; P r a s a d , J D ; e t a l . ( 1 9 8 8 ) C a r c i n o g e n i c i t y o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n t h e 33 S y r i a n g o l d e n h a m s t e r . C a r c i n o g e n e s i s 9 ( 9 ) : 1 6 7 7 - 1 6 7 9 . 3354 R a p p e , C . ( 1 9 9 1 ) S o u r c e s o f h u m a n e x p o s u r e t o C D D s a n d P C D F s . I n : G a l l o , M ; S c h e u p l e i n , R ; v a n d e r H e i d e n , 36 K , ( e d s ) . B i o l o g i c a l b a s i s f o r r i s k a s s e s s m e n t o f d i o x i n a n d r e l a t e d c o m p o u n d s , B a n b u r y R e p o r t N o . 3 5 . P l a i n v i e w , 37 N Y : C o l d S p r i n g H a r b o r L a b o r a t o r y P r e s s . 3389 R a y , S S a n d S w a n s o n , H I . ( 2 0 0 3 ) A l t e r a t i o n o f k e r a t i n o c y t e d i f f e r e n t i a t i o n a n d s e n e s c e n c e b y t h e t u m o r p r o m o t e r 40 d i o x i n . T o x i c o l . A p p l . P h a r m a c o l . 1 9 2 ( 2 ) : 1 3 1 - 4 5 . 4412 R e m i l l a r d , R B J ; B u n c e , N J . ( 2 0 0 2 ) . L i n k i n g d i o x i n s t o d i a b e t e s : E p i d e m i o l o g y a n d B i o l o g i c P l a u s i b i l i t y . E n v i r o n . 43 H e a l t h P e r s p e c t . 1 1 0 : 8 5 3 - 8 5 8 . 4454 R h i l e , M J ; N a g a r k a t t i , M ; N a g a r k a t t i , P S . ( 1 9 9 6 ) R o l e o f F a s a p o p t o s i s a n d M H C g e n e s i n 2 , 3 , 7 , 8 46 t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) - i n d u c e d i m m u n o t o x i c i t y o f T c e l l s . T o x i c o l o g y 1 1 0 : 1 5 3 - 1 6 7 . 4478 R i e r , S ; F o s t e r , W G . ( 2 0 0 2 ) E n v i r o n m e n t a l D i o x i n s a n d E n d o m e t r i o s i s . T o x i c o l . S c i 7 0 : 1 6 1 - 1 7 0 . 4590 R i e r , S E ; M a r t i n , D C ; B o w m a n , R E ; e t a l . ( 1 9 9 3 ) E n d o m e t r i o s i s i n r h e s u s m o n k e y s ( M a c a c a m u l a t t a ) f o l l o w i n g 51 c h r o n i c e x p o s u r e t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n . F u n d a m A p p l T o x i c o l 2 1 ( 4 ) : 4 3 3 - 4 4 1 . 5523 R o e g n e r , R H ; G r u b b s , W D ; L u s t i k , M B ; e t a l . ( 1 9 9 1 ) A i r F o r c e h e a l t h s t u d y : a n e p i d e m i o l o g i c i n v e s t i g a t i o n o f 54 h e a l t h e f f e c t s i n A i r F o r c e p e r s o n n e l f o l l o w i n g e x p o s u r e to h e r b i c i d e s . S e r u m d i o x i n a n a l y s i s o f 1 9 8 7 e x a m i n a t i o n 55 12/23/03 R-22 DRAFT--DO NOT CITE OR QUOTEr e s u l t s . N T I S # A D A - 2 3 7 - 5 1 6 t h r o u g h A D A - 2 3 7 - 5 2 4 . 1 R o g a n , W . (1 9 8 9 ) Y u -C h e n g . In: K im b r o u g h , R D ; Jen sen , A A , ed s. H a lo g e n a te d b ip h e n y ls, terp h en y ls, 2 n ap h th alen es, d ib en zo d io x in s and related prod u cts. 2n d ed. N e w Y ork: E lsevier; pp. 4 0 1 -4 1 5 . 43 R o g a n , W J ; G l a d e n , B C ; H u n g , K - L ; e t a l . ( 1 9 8 8 ) C o n g e n i t a l p o i s o n i n g b y p o l y c h l o r i n a t e d b i p h e n y l s a n d t h e i r 5 co n tam in an ts in T aiw an . S c ie n ce 2 4 1 :3 3 4 -3 3 8 . 67 R o m a n , B L ; S o m m e r , R J ; S h i n o m i y a , K ; e t a l . ( 1 9 9 5 ) . I n u t e r o a n d l a c t a t i o n a l e x p o s u r e o f t h e m a l e r a t t o 2 , 3 , 7 , 8 8 tetrach lorod ib en zo-p -d ioxin : Im paired p rostate grow th and d ev elo p m en t w ith ou t in h ib ited an d rogen p rod u ction . 9 T oxicol A p p l P harm acol 134:241 -250. 1110 R o m k e s , N ; S a f e , S . ( 1 9 8 8 ) C o m p a r a t i v e a c t i v i t i e s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n a n d p r o g e s t e r o n e a s 12 a n t i e s t r o g e n s i n t h e f e m a l e r a t u t e r u s . T o x i c o l A p p l P h a r m a c o l 9 2 : 3 6 8 - 3 8 0 . 1134 R o m k e s , N ; P i s k o r s k a - P l i s z y n s k a , J ; S a f e , S . ( 1 9 8 7 ) E f f e c t s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n o n h e p a t i c a n d 15 u t e r i n e e s t r o g e n r e c e p t o r l e v e l s i n r a t s . T o x i c o l A p p l P h a r m a c o l 8 7 : 3 0 6 - 3 1 4 . 1176 R o w l a n d s , J C ; G u s t a f s s o n , J - A . ( 1 9 9 7 ) A r y l h y d r o c a r b o n r e c e p t o r - m e d i a t e d s i g n a l t r a n s d u c t i o n . C r i t R e v T o x i c o l 18 2 7 : 1 0 9 - 1 3 4 . 2109 R o y , D ; B e r n h a r d t , A ; S t r o b e l , H W ; e t a l . ( 1 9 9 2 ) C a t a l y s i s o f t h e o x i d a t i o n o f s t e r o i d a n d s t i l b e n e e s t r o g e n s t o 21 e s t r o g e n q u i n o n e m e t a b o l i t e s b y t h e b e t a - n a p h t h o f l a v o n e - i n d u c i b l e c y t o c h r o m e P 4 5 0 I A f a m i l y . A r c h B i o c h e m 22 B i o p h y s 2 9 6 : 4 5 0 - 4 5 6 . 2234 R o z m a n , K K . ( 1 9 9 9 ) D e l a y e d a c u t e t o x i c i t y o f 1 , 2 , 3 , 4 , 6 , 7 , 8 - h e p t a c h l o r o d i b e n z o - p - d i o x i n ( H p C D D ) , a f t e r o r a l 25 a d m i n i s t r a t i o n , o b e y s H a b e r ' s r u l e o f i n h a l a t i o n t o x i c o l o g y . T o x i c o l S c i 4 9 : 1 0 2 - 1 0 9 . 2276 c x tR o z m a n , K K . ( 2 0 0 0 ) T h e r o l e o f t i m e i n t o x i c o l o g y o r H a b e r ' s product. T o x ico l 149:35-42. 2289 R o z m a n , K K ; L e b o f s k y , M ; P i n s o n , D M . ( 2 0 0 0 ) A n e m i a a n d l u n g c a n c e r i n 1 , 2 , 3 , 4 , 6 , 7 , 8 - h e p t a c h l o r o d i b e n z o - p 30 d i o x i n ( H P C D D ) - t r e a t e d f e m a l e S p r a g u e - D a w l e y r a t s a f t e r v a r i o u s s i n g l e a n d m u l t i p l e o r a l d o s e s . T o x i c o l S c i 31 5 4 ( 1 ) : 2 7 7 . 3323 R y a n , J J ; A m i r o v a , Z ; C a r r i e r , G . ( 2 0 0 2 ) S e x R a t i o s o f c h i l d r e n o f R u s s i a n P e s t i c i d e P r o d u c e r s E x p o s e d t o D i o x i n . 34 E n v i r o n . H e a l t h P e r s p e c t . 1 1 0 : A 6 9 9 - A 7 0 1 . 3356 R y a n , R P ; S u n a h a r a , G I ; L u c i e r , G W ; e t a l . ( 1 9 8 9 ) D e c r e a s e d l i g a n d b i n d i n g t o t h e h e p a t i c g l u c o c o r t i c o i d a n d 37 e p i d e r m a l g r o w t h f a c t o r r e c e p t o r s a f t e r 2 , 3 , 4 , 7 , 8 - p e n t a c h l o r o d i b e n z o f u r a n a n d 1 , 2 , 3 , 4 , 7 , 8 - h e x a c h l o r o d i b e n z o f u r a n 38 t r e a t m e n t o f p r e g n a n t m i c e . T o x i c o l A p p l P h a r m a c o l 9 8 ( 3 ) : 4 5 4 - 4 6 4 . 3490 S a f e , S . ( 1 9 9 5 a ) H u m a n d i e t a r y i n t a k e o f a r y l h y d r o c a r b o n ( A h ) r e c e p t o r a g o n i s t s : m a s s b a l a n c e e s t i m a t e s o f 41 e x o d i o x i n s a n d e n d o d i o x i n s a n d i m p l i c a t i o n s f o r h e a l t h a s s e s s m e n t . O r g a n o h a l o g e n C o m p o u n d s 2 6 : 7 - 1 3 . 4423 S a f e , S . ( 1 9 9 5 b ) M o d u l a t i o n o f g e n e e x p r e s s i o n a n d e n d o c r i n e r e s p o n s e p a t h w a y s b y 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p 44 d i o x i n a n d r e l a t e d c o m p o u n d s . P h a r m a c o l T h e r 6 7 ( 2 ) : 2 4 7 - 2 8 1 . 4456 S a l v a n , A ; T h o m a s e t h , K ; B o r t o t , P ; e t a l . ( 2 0 0 1 ) U s e o f a t o x i c o k i n e t i c m o d e l i n t h e a n a l y s i s o f c a n c e r m o r t a l i t y i n 47 r e l a t i o n t o t h e e s t i m a t e d a b s o r b e d d o s e o f d i o x i n ( 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n , T C D D ) . S c i T o t E n v 2 7 4 : 2 1 48 3 5 . 4590 S a r a c c i , R ; K o g e v i n a s , M ; B e r t a z z i , P ; e t a l . ( 1 9 9 1 ) C a n c e r m o r t a l i t y i n w o r k e r s e x p o s e d t o c h l o r o p h e n o x y 51 h e r b i c i d e s a n d c h l o r o p h e n o l s . L a n c e t 3 8 ( 3 7 7 4 ) : 1 0 2 7 - 1 0 3 2 . 5523 S C F 2 0 0 0 . O p i n i o n o f t h e S C F o n t h e R i s k A s s e s s m e n t o f D i o x i n - l i k e P C B s i n F o o d . E u r o p e a n C o m m i s s i o n , 54 H e a l t h & C o n s u m e r P r o t e c t i o n D i r e c t o r a t e - G e n e r a l . S c i e n t i f i c C o m m i t t e e o n F o o d . S C F / C S / C N T M / D I O X I N / 8 55 12/23/03 R-23 DRAFT--DO NOT CITE OR QUOTEF i n a l . 2 3 N o v e m b e r , 2 0 0 0 . B r u s s e l s . 1 S ch a n tz, S L ; B o w m a n , R E . (1 9 8 9 ) L ea rn in g in m o n k e y s e x p o s e d p erin atally to 2 ,3 ,7 ,8 -te tr a c h lo r o d ib e n z o -p -d io x in 2 (T C D D ). N eu rotoxicol T eratol 11:13-19. 43 S c h a n t z , S L ; B a r s o t t i , D A ; A l l e n , J R . ( 1 9 7 9 ) T o x i c o l o g i c a l e f f e c t s p r o d u c e d i n n o n h u m a n p r i m a t e s c h r o n i c a l l y 5 e x p o se d to fifty parts p er trillion 2 ,3 ,7 ,8 -tetra ch lo ro d ib en zo -p -d io x in (T C D D ). T o x ic o l A p p l P h a rm a co l 4 8 (Part 6 2):A 180. 87 S c h a n t z , S L ; F e r g u s o n , S A ; B o w m a n , R E . ( 1 9 9 2 ) E f f e c t s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n o n b e h a v i o r o f 9 m o n k e y s in p eer grou p s. N e u r o to x ic o l T eratol 1 4 :4 3 3 -4 4 6 . 1110 S c h a u m J , S c h u d a L , W u C , S e a r s R , F e r r a r i o J , A n d r e w s K . ( 2 0 0 3 ) A n a t i o n a l s u r v e y o f p e r s i s t e n t , 12 b i o a c c u m u l a t i v e , a n d t o x i c ( P B T ) p o l l u t a n t s i n t h e U n i t e d S t a t e s m i l k s u p p l y . J E x p o A n a l E n v i r o n E p i d e m i o l 1 3 : 13 1 7 7 - 1 8 6 . 1154 S c h e c t e r , A , e d . ( 1 9 9 4 ) D i o x i n s a n d h e a l t h . N e w Y o r k : P l e n u m P r e s s . 1167 S c h e c t e r , A ; G a s i e w i c z , T A . ( 2 0 0 3 ) D i o x i n s a n d H e a l t h , 2 nd E d i t i o n . H o b o k e n , N e w J e r s e y : W i l e y - I n t e r s c i e n c e . 1189 S c h m i d t , J V ; B r a d f i e l d , C A . ( 1 9 9 6 ) A h R s i g n a l i n g p a t h w a y s . A n n R e v C e l l D e v B i o l 1 2 : 5 5 - 8 9 . 2210 S c h r e n k , D ; B u c h m a n n , A ; D i e t z , K ; e t a l . ( 1 9 9 4 ) P r o m o t i o n o f p r e n e o p l a s t i c f o c i i n r a t l i v e r w i t h 22 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n , 1 , 2 , 3 , 4 , 6 , 7 , 8 - h e p t a c h l o r o d i b e n z o - p - d i o x i n a n d a d e f i n e d m i x t u r e o f 4 9 23 p o l y c h l o r i n a t e d d i b e n z o - p - d i o x i n s . C a r c i n o g e n e s i s 1 5 : 5 0 9 - 5 1 5 . 2254 S c h u d a , L ; S c h a u m , J ; L o r b e r M ; e t a l . ( 2 0 0 4 ) E v a l u a t i o n o f d i o x i n l e v e l s i n U . S . c o w ' s m i l k . 2 4 t h I n t e r n a t i o n a l 26 S y m p o s i u m o n H a l o g e n a t e d E n v i r o n m e n t a l O r g a n i c P o l l u t a n t s a n d P O P s . S e p t e m b e r 6 - 1 0 , 2 0 0 4 , B e r l i n , G e r m a n y . 27 (Reference added during Proof) 2289 S c h u u r , A G ; B o e k h o r s t , F M ; B r o u w e r , A ; e t a l . ( 1 9 9 7 ) E x t r a t h y r o i d a l e f f e c t s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n 30 o n t h y r o i d h o r m o n e t u r n o v e r i n m a l e S p r a g u e - D a w l e y r a t s . E n d o c r i n o l o g y 1 3 8 ( 9 ) : 3 7 2 7 - 3 7 3 4 . 3312 S e w a l l , C H ; L u c i e r , G W . ( 1 9 9 5 ) R e c e p t o r - m e d i a t e d e v e n t s a n d t h e e v a l u a t i o n o f t h e E n v i r o n m e n t a l P r o t e c t i o n 33 A g e n c y ( E P A ) o f d i o x i n r i s k s . M u t a t R e s 3 3 3 ( 1 - 2 ) : 1 1 1 - 1 2 2 . 3354 S e w a l l , C H ; L u c i e r , G W ; T r i t s c h e r , A M ; e t a l . ( 1 9 9 3 ) T C D D - m e d i a t e d c h a n g e s i n h e p a t i c e p i d e r m a l g r o w t h f a c t o r 36 r e c e p t o r m a y b e a c r i t i c a l e v e n t i n t h e h e p a t o c a r c i n o g e n i c a c t i o n o f T C D D . C a r c i n o g e n e s i s 1 4 : 1 8 8 5 - 1 8 9 3 . 3378 S h i m i z u , Y ; N a k a t s u r u , Y ; I c h i n o s e , M ; e t a l . ( 2 0 0 0 ) B e n z o [ a ] p y r e n e c a r c i n o g e n i c i t y i s l o s t i n m i c e l a c k i n g t h e a r y l 39 h y d r o c a r b o n r e c e p t o r . P r o c N a t l A c a d S c i U S A 9 7 : 7 7 9 - 7 8 2 . 4410 S l e z a k , B P ; H a t c h , G E ; D e V i t o , M J ; e t a l . ( 2 0 0 0 ) O x i d a t i v e s t r e s s i n f e m a l e B 6 C 3 F 1 m i c e f o l l o w i n g a c u t e a n d 42 s u b c h r o n i c e x p o s u r e t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) . T o x i c o l S c i , i n p r e s s . 4434 S m i a l o w i c z , R J ; R i d d l e , M M ; W i l l i a m s , W C ; e t a l . ( 1 9 9 4 ) E f f e c t s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) 45 o n h u m o r a l i m m u n i t y a n d l y m p h o c y t e s u b p o p u l a t i o n s : d i f f e r e n c e s b e t w e e n m i c e a n d r a t s . T o x i c o l A p p l P h a r m a c o l 46 1 2 4 : 2 4 8 - 2 5 6 . 4478 S m i a l o w i c z , R J ; D e V i t o , M J ; R i d d l e , M M : e t a l . ( 1 9 9 7 ) . C o m p a r a t i v e i m m u n o t o x i c p o t e n c y o f m i x t u r e s c o n t a i n i n g 49 p o l y c h l o r i n a t e d d i b e n z o - p - d i o x i n s , ( P C D D s ) , d i b e n z o f u r a n s ( P C D F s ) , a n d b i p h e n y l s ( P C B s ) . T o x i c o l o g i s t 3 6 : 1 3 5 0 . 5510 S m i t h , A H ; L o p i p e r o , P . ( 2 0 0 1 ) I n v i t e d C o m m e n t a r y : h o w d o t h e S e v e s o f i n d i n g s a f f e c t c o n c l u s i o n s c o n c e r n i n g 52 T C D D a s a h u m a n c a r c i n o g e n ? A m J E p i d e m i o l 1 5 3 ( 1 1 ) 1 0 4 5 - 1 0 4 7 . 5534 S m i t h , A G ; C l o t h i e r B ; C a r t h e w P ; e t a l . ( 2 0 0 1 ) P r o t e c t i o n o f t h e C y p 1 a 2 ( - / - ) n u l l m o u s e a g a i n s t u r o p o r p h y r i a a n d 55 12/23/03 R-24 DRAFT--DO NOT CITE OR QUOTEh e p a t i c i n j u r y f o l l o w i n g e x p o s u r e t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n . T o x i c o l A p p l P h a r m a c o l 1 7 3 ( 2 ) : 8 9 - 9 8 . 1 S p in k , D C ; L in c o ln , D W , II; D ic k e r m a n , H W ; et al. (1 9 9 0 ) 2 ,3 ,7 ,8 -T e tr a c h lo r o d ib e n z o -p -d io x in c a u s e s a n e x te n s iv e 2 a ltera tio n o f 1 7 $ -e s tr a d io l m e ta b o lis m in M C F -7 b reast tu m o r c e lls. P r o c N a tl A c a d S c i U S A 8 7 : 6 9 1 7 - 6 9 2 1 . 43 S q u i r e , R A . ( 1 9 8 0 ) P a t h o l o g i c e v a l u a t i o n s o f s e l e c t e d t i s s u e s f r o m t h e D o w C h e m i c a l T C D D a n d 2 , 4 , 5 - T r a t s t u d i e s . 5 S u bm itted to C arcin ogen A ssessm en t G roup, U .S . E n viron m en tal P rotection A g en cy , o n A u g u st 15 u nder contract 6 no. 68-01-5092. 87 S t a r r , T B . ( 2 0 0 1 ) S i g n i f i c a n t s h o r t c o m i n g s o f t h e U . S . E n v i r o n m e n t a l P r o t e c t i o n A g e n c y ' s l a t e s t d r a f t r i s k 9 characterization for d ioxin -lik e co m p o u n d s. T o x ic o l S ci 64(1 ):7 -1 3 . 1110 S t a r r , T B . ( 2 0 0 3 ) . S i g n i f i c a n t i s s u e s r a i s e d b y m e t a - a n a l y s e s o f c a n c e r m o r t a l i t y a n d d i o x i n e x p o s u r e . E n v i r o n 12 H e a l t h P e r s p e c t . 1 1 1 ( 1 2 ) : 1 4 4 3 - 7 . 1134 S t e e n l a n d , K ; P i a c i t e l l i , L ; D e d d e n s , J ; e t a l . ( 1 9 9 9 ) C a n c e r , h e a r t d i s e a s e , a n d d i a b e t e s i n w o r k e r s e x p o s e d t o 15 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n . J N a t l C a n c e r I n s t 9 1 ( 9 ) : 7 7 9 - 7 8 6 . 1176 S t e e n l a n d , K ; D e d d e n s , J ; P i a c i t e l l i , L . ( 2 0 0 1 ) C a n c e r , h e a r t d i s e a s e , a n d d i a b e t e s i n w o r k e r s e x p o s e d t o 2 , 3 , 7 , 8 18 t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) b a s e d o n a n e p i d e m i o l o g i c s t u d y . A m J E p i d e m i o l 1 5 4 : 4 5 1 - 4 5 8 . 2109 S t e e n l a n d , K ; D e d d e n s , J . ( 2 0 0 3 ) D i o x i n : e x p o s u r e - r e s p o n s e a n a l y s e s a n d r i s k a s s e s s m e n t . I n d . H e a l t h 4 1 : 1 7 5 - 1 8 0 . 2212 S t e p h e n s o n , R P . ( 1 9 5 6 ) A m o d i f i c a t i o n o f r e c e p t o r t h e o r y . B r J P h a r m a c o l 1 1 : 3 7 9 . 2234 S t o h s , S J . ( 1 9 9 0 ) O x i d a t i v e s t r e s s i n d u c e d b y 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) . F r e e R a d B i o l M e d 25 9 : 7 9 - 9 0 . 2276 S u s k i n d , R R . ( 1 9 8 5 ) C h l o r a c n e , t h e h a l l m a r k o f d i o x i n i n t o x i c a t i o n . S c a n d J W o r k E n v i r o n H e a l t h 1 1 : 1 6 5 - 1 7 1 . 2289 S u s k i n d , R R ; H e r t z b e r g , V S . ( 1 9 8 4 ) H u m a n h e a l t h e f f e c t s o f 2 , 4 , 5 - T a n d i t s t o x i c c o n t a m i n a n t s . J A M A 30 2 5 1 : 2 3 7 2 - 2 3 8 0 . 3312 S u t t e r , T R ; G r e e n l e e , W F . ( 1 9 9 2 ) C l a s s i f i c a t i o n o f m e m b e r s o f t h e A h g e n e b a t t e r y . C h e m o s p h e r e 2 5 : 2 2 3 - 2 2 6 . 3334 S w a n s o n , H I ; B r a d f i e l d , C A . ( 1 9 9 3 ) T h e A H - r e c e p t o r : g e n e t i c s , s t r u c t u r e a n d f u n c t i o n . P h a r m a c o g e n e t i c s 35 3 ( 5 ) : 2 1 3 - 3 0 3376 S w e e n e y , A . ( 1 9 9 4 ) R e p r o d u c t i v e e p i d e m i o l o g y o f d i o x i n s . I n : S c h e c t e r , A , e d . D i o x i n s a n d h e a l t h . N e w Y o r k : 38 P l e n u m P r e s s ; p p . 5 4 9 - 5 5 8 . 4309 S w e e n e y , M H ; F i n g e r h u t , M A ; C o n n a l l y , L B ; e t a l . ( 1 9 8 9 ) P r o g r e s s o f t h e N I O S H c r o s s - s e c t i o n a l m e d i c a l s t u d y o f 41 w o r k e r s o c c u p a t i o n a l l y e x p o s e d t o c h e m i c a l s c o n t a m i n a t e d w i t h 2 , 3 , 7 , 8 - T C D D . C h e m o s p h e r e 1 9 : 9 7 3 - 9 7 7 . 4423 S w e e n e y , M H ; C a l v e r t , G M ; E g e l a n d , G A ; e t a l . ( 1 9 9 7 - 9 8 ) R e v i e w a n d u p d a t e o f t h e r e s u l t s o f t h e N I O S H m e d i c a l 44 s t u d y o f w o r k e r s e x p o s e d to c h e m i c a l s c o n t a m i n a t e d w i t h 2 ,3 ,7 , 8 - t e t r a - c h l o r o d i b e n z o - p - d i o x i n . T e r a t o g C a r c in o g 45 M u t a g e n 1 7 ( 4 - 5 ) : 2 4 1 - 2 4 7 . 4476 T a y l o r , B L ; Z h u l i n , I B . ( 1 9 9 9 ) P A S d o m a i n s : i n t e r n a l s e n s o r s o f o x y g e n , r e d o x p o t e n t i a l , a n d l i g h t . M i c r o b i o l M o l 48 B i o l R e v 6 3 ( 2 ) : 4 7 9 - 5 0 6 . 4590 T e e g u a r d e n , J G ; D r a g a n , Y P ; S i n g h , J ; e t a l . ( 1 9 9 9 ) Q u a n t i t a t i v e a n a l y s i s o f d o s e - a n d t i m e - d e p e n d e n t p r o m o t i o n o f 51 f o u r p h e n o t y p e s o f a l t e r e d h e p a t i c f o c i b y 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n f e m a l e S p r a g u e - D a w l e y r a t s . 5523 T o x i c o l S c i 5 1 : 2 1 1 - 2 2 3 . 12/23/03 R-25 DRAFT--DO NOT CITE OR QUOTE 1 ten T u ssc h e r , G W ; S te eren b erg , P A , v a n L o v e r e n , H ; et al;. (2 0 0 3 ) P ersisten t H e m a to lo g ic an d Im m u n o lo g ic 2 D istu rb a n ces in 8 -y ear-old D u tch C h ild ren a sso cia ted w ith P erinatal D io x in E x p o su re. E n v iro n . H ea lth P ersp ect. 3 111: 1519-1523. 45 T h e o b a l d , H M ; P e t e r s o n , R E . ( 1 9 9 7 ) I n u t e r o a n d l a c t a t i o n a l e x p o s u r e t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - r h o - d i o x i n : 6 effects on d evelop m en t o f the m ale and fem a le rep rod u ctive system o f the m o u se. T o x ico l A p p l P h arm acol 7 145(1):124-35. 89 T h o m a s , V M ; S p i r o , T G ( 1 9 9 5 ) A n e s t i m a t i o n o f d i o x i n e m i s s i o n s i n t h e U n i t e d S t a t e s . T o x i c o l o g i c a l a n d E n v i r o n 10 C h e m 5 0 : 1 - 3 7 . 1112 T i a n , Y ; K e , S ; D e n i s o n , M S ; e t a l . ( 1 9 9 9 ) A h R a n d N F - k a p p a B i n t e r a c t i o n s , a p o t e n t i a l m e c h a n i s m f o r d i o x i n 13 t o x i c i t y . J B i o l C h e m 2 7 4 ( 1 ) : 5 1 0 - 5 1 5 . 1154 T o n n , T ; E s s e r , C ; S c h n e i d e r , E M ; e t a l . ( 1 9 9 6 ) P e r s i s t e n c e o f d e c r e a s e d T - h e l p e r c e l l f u n c t i o n i n i n d u s t r i a l w o r k e r s 16 2 0 y e a r s a f t e r e x p o s u r e t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n . E n v i r o n H e a l t h P e r s p e c t 1 0 4 : 4 2 2 - 4 2 6 . 1178 T o y o s h i b a , H ; W a l k e r , N J ; B a i l e r , A J ; e t a l . ( 2 0 0 4 ) E v a l u a t i o n o f t o x i c e q u i v a l e n c y f a c t o r s f o r i n d u c t i o n o f 19 c y t o c h r o m e s P 4 5 0 C Y P 1 A 1 a n d C Y P 1 A 2 e n z y m e a c t i v i t y b y d i o x i n - l i k e c o m p o u n d s . T o x i c o l A p p l P h a r m a c o l 20 (R eference added during P roof)1 9 4 ( 2 ) : 1 5 6 - 6 8 . 2212 T r i t s c h e r , A M ; G o l d s t e i n , J A ; P o r t i e r , C J ; e t a l . ( 1 9 9 2 ) D o s e - r e s p o n s e r e l a t i o n s h i p s f o r c h r o n i c e x p o s u r e t o 2 , 3 , 7 , 8 23 t e t r a c h l o r o d i b e n z o - p - d i o x i n i n a r a t - t u m o r p r o m o t i o n m o d e l : q u a n t i f i c a t i o n a n d i m m u n o l o c a l i z a t i o n o f C Y P 1 A 1 a n d 24 C Y P 1 A 2 i n t h e l i v e r . C a n c e r R e s 5 2 : 3 4 3 6 - 3 4 4 2 . 2256 T r i t s c h e r , A M ; C l a r k , G C ; S e w a l l , C ; e t a l . ( 1 9 9 5 ) P e r s i s t e n c e o f T C D D - i n d u c e d h e p a t i c c e l l p r o l i f e r a t i o n a n d 27 g r o w t h o f e n z y m e a l t e r e d f o c i a f t e r c h r o n i c e x p o s u r e f o l l o w e d b y c e s s a t i o n o f t r e a t m e n t i n D E N i n i t i a t e d f e m a l e 28 r a t s . C a r c i n o g e n e s i s 1 6 : 2 8 0 7 - 2 8 1 1 . 3209 T r i t s c h e r , A M ; S e a c a t , A M ; Y a g e r , J D ; e t a l . ( 1 9 9 6 ) I n c r e a s e d o x i d a t i v e D N A d a m a g e i n l i v e r s o f 2 , 3 , 7 , 8 31 t e t r a c h l o r o d i b e n z o - p - d i o x i n t r e a t e d i n t a c t b u t n o t o v a r i e c t o m i z e d r a t s . C a n c e r L e t t 9 8 : 2 1 9 - 2 2 5 . 3323 U . S . E P A ( E n v i r o n m e n t a l P r o t e c t i o n A g e n c y ) . ( 1 9 8 0 ) R i s k a s s e s s m e n t o n ( 2 , 4 , 5 - t e t r a c h l o r o p h e n o x y ) a c e t i c a c i d 34 [ 2 , 4 , 5 - T ] , ( 2 , 4 , 5 - t r i c h l o r o p h e n o x y ) p r o p i o n i c a c i d , a n d 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n [ T C D D ] . W a s h i n g t o n , 35 D C . 3376 U . S . E P A . ( 1 9 8 5 ) H e a l t h e f f e c t s a s s e s s m e n t d o c u m e n t f o r p o l y c h l o r i n a t e d d i b e n z o - p - d i o x i n s . P r e p a r e d b y t h e O f f i c e 38 o f H e a l t h a n d E n v i r o n m e n t a l A s s e s s m e n t , E n v i r o n m e n t a l C r i t e r i a a n d A s s e s s m e n t O f f i c e , C i n c i n n a t i , O H , f o r t h e 39 O f f i c e o f E m e r g e n c y a n d R e m e d i a l R e s p o n s e , W a s h i n g t o n , D C . E P A / 6 0 0 / 8 - 8 4 / 0 1 4 F . 4410 U . S . E P A . ( 1 9 8 7 ) I n t e r i m p r o c e d u r e s f o r e s t i m a t i n g r i s k s a s s o c i a t e d w i t h e x p o s u r e s t o m i x t u r e s o f c h l o r i n a t e d 42 d i b e n z o - p - d i o x i n s a n d - d i b e n z o f u r a n s ( C D D s a n d C D F s ) . E P A / 6 2 5 / 3 - 8 7 / 0 1 2 . 4434 U . S . E P A . ( 1 9 8 9 a ) I n t e r i m p r o c e d u r e s f o r e s t i m a t i n g r i s k s a s s o c i a t e d w i t h e x p o s u r e s t o m i x t u r e s o f c h l o r i n a t e d 45 d i b e n z o - p - d i o x i n s a n d - d i b e n z o f u r a n s ( C D D s a n d C D F s ) a n d 1 9 8 9 u p d a t e . R i s k A s s e s s m e n t F o r u m , W a s h i n g t o n , 46 D C . E P A / 6 2 5 / 3 - 8 9 . 0 1 6 . 4478 U . S . E P A . ( 1 9 8 9 b ) R e v i e w o f d r a f t d o c u m e n t s : a c a n c e r r i s k - s p e c i f i c d o s e e s t i m a t e f o r 2 , 3 , 7 , 8 - T C D D . E P A S c i e n c e 49 A d v i s o r y B o a r d A d H o c D i o x i n P a n e l , W a s h i n g t o n , D C . 5510 U . S . E P A . ( 1 9 9 1 a ) W o r k s h o p r e p o r t o n t o x i c i t y e q u i v a l e n c y f a c t o r s f o r p o l y c h l o r i n a t e d b i p h e n y l s c o n g e n e r s . 52 E P A / 6 2 5 / 3 - 9 1 / 0 2 0 . 5534 U . S . E P A . ( 1 9 9 1 b ) G u i d e l i n e s f o r d e v e l o p m e n t a l t o x i c i t y r i s k a s s e s s m e n t . F e d e r a l R e g i s t e r 5 7 : 2 2 8 8 8 - 2 2 9 3 8 . 12/23/03 R-26 DRAFT--DO NOT CITE OR QUOTE 1 U .S . E P A . (1 9 9 2 a ) D raft report: a cro ss sp ecies-sca lin g factor for ca rcin og en risk a ssessm en t b a sed o n e q u iv a len ce 2 o f m g/k g 3/4 /d a y. F ed eral R egister 5 7 (1 0 9 ):2 4 1 5 2 -2 4 1 7 3 . 43 U . S . E P A . ( 1 9 9 2 b ) N a t i o n a l s t u d y o f c h e m i c a l r e s i d u e s i n f i s h . O f f i c e o f S c i e n c e a n d T e c h n o l o g y , W a s h i n g t o n , D C . 5 E P A /823-R -02-008. 67 U . S . E P A . ( 1 9 9 4 ) H e a l t h a s s e s s m e n t d o c u m e n t f o r 2 , 3 , 7 , < 5 - t e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) a n d r e l a t e d 8 co m p o u n d s. E xtern al rev iew draft. P rep ared b y the O ffice o f H ealth and E n v iro n m en tal A ssessm en t, O ffice o f 9 R esearch and D ev elo p m en t, W ash in g to n , D C . E P A /6 0 0 /B P -9 2 /0 0 1 a , b, c. A v a ilab le from N T IS , S p ringfield , V A 10 P B 9 4 - 2 0 5 4 5 7 . 1112 U . S . E P A . ( 1 9 9 5 ) A n S A B R e p o r t : a s e c o n d l o o k a t d i o x i n . E P A - S A B - E C - 9 5 - 0 2 1 . 1134 U . S . E P A . ( 1 9 9 6 ) P r o p o s e d g u i d e l i n e s f o r c a r c i n o g e n r i s k a s s e s s m e n t . F e d e r a l R e g i s t e r 6 1 : 1 7 9 6 0 - 1 8 0 1 1 . 1156 U . S . E P A ( 1 9 9 8 ) D a t a b a s e o f s o u r c e s o f e n v i r o n m e n t a l r e l e a s e s o f d i o x i n - l i k e c o m p o u n d s i n t h e U n i t e d S t a t e s . 17 E P A / 6 0 0 / P - 9 8 / 0 0 2 A b ) . 1189 U . S . E P A . ( 1 9 9 9 ) R e v i s e d p r o p o s e d g u i d e l i n e s f o r c a r c i n o g e n r i s k a s s e s s m e n t . 2210 U . S . E P A . ( 2 0 0 1 a ) W o r k s h o p R e p o r t o n t h e A p p l i c a t i o n o f 2 , 3 , 7 , 8 - T C D D T o x i c i t y E q u i v a l e n c e F a c t o r s t o F i s h a n d 22 W i l d l i f e . D i o x i n R e a s s e s s m e n t . E P A / 6 3 0 / R - 0 1 / 0 0 2 , A u g u s t 2 0 0 1 . 2234 U . S . E P A . ( 2 0 0 1 b ) D i o x i n R e a s s e s s m e n t : a n S A B R e v i e w o f t h e O f f i c e o f R e s e a r c h a n d D e v e l o p m e n t ' s 25 R e a s s e s s m e n t o f D i o x i n . E P A - S A B - E C - 0 1 - 0 0 6 . 2276 U . S . E P A . ( 2 0 0 3 ) D r a f t F i n a l G u i d e l i n e s f o r C a r c i n o g e n R i s k A s s e s s m e n t . E P A / 6 3 0 / P - 0 3 / 0 0 1 A , F e b r u a r y 2 0 0 3 , 28 D r a f t F i n a l . w w w . e p a . g o v / n c e a / r a f / c a n c e r 2 0 0 3 . h t m 3209 v a n B i r g e l e n , A P ; V a n d e r K o l k , J; F a s e , K M : e t a l . ( 1 9 9 5 ) S u b c h r o n i c d o s e - r e s p o n s e s t u d y o f 2 , 3 , 7 , 8 31 t e t r a c h l o r o d i b e n z o - p - d i o x i n i n f e m a l e S p r a g u e - D a w l e y r a t s . T o x i c o l A p p l P h a r m a c o l 1 3 2 : 1 - 1 3 . 3332 v a n B i r g e l e n , A P J M ; D i l i b e r t o , J J ; D e V i t o , M J ; e t a l . ( 1 9 9 6 ) T i s s u e C Y P 1 A 1 a c t i v i t y r e f l e c t s t i s s u e 2 , 3 , 7 , 8 34 t e t r a c h l o r o d i b e n z o - p - d i o x i n c o n c e n t r a t i o n s . O r g a n o h a l o g e n C o m p o u n d s 2 9 : 4 3 9 - 4 4 2 . 3356 v a n B i r g e l e n , A P J M ; J o h n s o n , J D ; F u c i a r e l l i , A F ; e t a l . ( 1 9 9 9 ) D o s e a n d t i m e - r e s p o n s e o f T C D D i n T g . A C m i c e 37 a f t e r d e r m a l a n d o r a l e x p o s u r e . O r g a n o h a l o g e n C o m p o u n d s 4 2 : 2 3 5 - 2 3 9 . 3389 v a n d e n B e r g , M ; B i r n b a u m , L ; B o s v e l d , A T C ; e t a l . ( 1 9 9 8 ) T o x i c e q u i v a l e n c y f a c t o r s ( T E F s ) f o r P C B s , P C D D s , 40 P C D F s f o r h u m a n s a n d w i l d l i f e . E n v i r o n H e a l t h P e r s p e c t 1 0 6 ( 1 2 ) : 7 7 5 - 7 9 2 . 4412 v a n d e n B e r g , M ; P e t e r s o n , R E ; S c h r e n k , D . ( 2 0 0 0 ) H u m a n r i s k a s s e s s m e n t a n d T E F s . F o o d A d d i t C o n t a m 43 1 7 ( 4 ) : 3 4 7 - 3 5 8 . 4454 v a n d e n H e u v e l , J P ; C l a r k , G C ; K o h n , M C ; e t a l . ( 1 9 9 4 ) D i o x i n - r e s p o n s i v e g e n e s : e x a m i n a t i o n o f d o s e - r e s p o n s e 46 r e l a t i o n s h i p s u s i n g q u a n t i t a t i v e r e v e r s e t r a n s c r i p t a s e - p o l y m e r a s e c h a i n r e a c t i o n . C a n c e r R e s 5 4 : 6 2 - 6 8 . 4478 V a n d e r M o l e n , G W ; K o o i j m a n ; S A , M i c h a l e k , J E ; e t a l . ( 1 9 9 8 ) T h e e s t i m a t i o n o f e l i m i n a t i o n r a t e s o f p e r s i s t e n t 49 c o m p o u n d s : a r e - a n a l y s i s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n l e v e l s i n V i e t n a m v e t e r a n s . C h e m o s p h e r e 3 7 ( 9 50 1 2 ) : 1 8 3 3 - 4 4 . 5512 V a n d e r M o l e n , G W ; K o o i j m a n , B A ; W i t t s i e p e , J; e t a l . ( 2 0 0 0 ) E s t i m a t i o n o f d i o x i n a n d f u r a n e l i m i n a t i o n r a t e s w i t h 5534 a p h a r m a c o k i n e t i c m o d e l . J E x p o A n a l E n v i r o n E p i d e m i o l 1 0 : 5 7 9 - 5 8 5 . 12/23/03 R-27 DRAFT--DO NOT CITE OR QUOTE 1 v a n d er P las, S A ; H a a g -G ro n lu n d , M ; S ch eu , G ; et al. (1 9 9 9 ) In d u ctio n o f altered h ep atic fo c i b y a m ix tu re o f 2 d io x in -lik e c o m p o u n d s w ith a n d w ith o u t 2 ,2 ',4 ,4 ',5 ,5 '-h ex a ch lo ro b ip h en y l in fe m a le S p r a g u e -D a w le y rats. T o x ic o l 3 A ppl Pharm acol 156:30-39. 45 V e c c h i , A ; S i r o n i , M ; C a n e g r a t i , M A ; e t a l . ( 1 9 8 3 ) I m m u n o s u p p r e s s i v e e f f e c t s o f 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p 6 d io x in in strains o f m ic e w ith d ifferen t su scep tib ility to in d u ctio n o f aryl h y d ro ca rb o n h y d ro x y la se. T o x ic o l A p p l 7 Pharm acol 68:434-441. 89 V e n a , J ; B o f f e t t a , P ; B e c h e r , H ; e t a l . ( 1 9 9 8 ) E x p o s u r e t o d i o x i n a n d n o n n e o p l a s t i c m o r t a l i t y i n t h e e x p a n d e d I A R C 10 i n t e r n a t i o n a l c o h o r t s t u d y o f p h e n o x y h e r b i c i d e a n d c h l o r o p h e n o l p r o d u c t i o n w o r k e r s a n d s p r a y e r s . E n v i r o n H e a l t h 11 P e r s p e c t 1 0 6 ( S u p p l 2 ) : 6 4 5 - 6 5 3 . 1123 V i n e i s , P ; T e r r a c i n i , B ; C i c c o n e , G ; e t a l . ( 1 9 8 6 ) P h e n o x y h e r b i c i d e s a n d s o f t - t i s s u e s a r c o m a s i n f e m a l e r i c e 14 w e e d e r s : a p o p u l a t i o n - b a s e d c a s e - r e f e r e n t s t u d y . S c a n d J W o r k E n v i r o n H e a l t h 1 3 : 9 - 1 7 . 1156 V o g e l , C ; D o n a t , S ; D o h r , O ; e t a l . ( 1 9 9 7 ) E f f e c t o f s u b c h r o n i c 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n e x p o s u r e o n 17 i m m u n e s y s t e m a n d t a r g e t g e n e r e s p o n s e s i n m i c e : c a l c u l a t i o n o f b e n c h m a r k d o s e s f o r C Y P 1 A 1 a n d C Y P 1 A 2 18 r e l a t e d e n z y m e a c t i v i t i e s . A r c h T o x i c o l 7 1 : 3 7 2 - 3 8 2 . 2109 V o r d e r s t r a s s e , B A ; F e n t o n , S E ; B o h n , A A ; e t a l . ( 2 0 0 4 ) A n o v e l e f f e c t o f d i o x i n : e x p o s u r e d u r i n g p r e g n a n c y 21 in p ress. (R eference add ed du rin g P ro of)s e v e r e l y i m p a i r s m a m m a r y g l a n d d e v e l o p m e n t . T o x i c o l . S c i . 2223 V r e u g d e n h i l , H J I ; S l i j p e r , F M E ; M u l d e r , P G H ; W e i s g l a s - K u p e r u s , N . ( 2 0 0 2 ) E f f e c t s o f p e r i n a t a l e x p o s u r e t o P C B s 24 a n d d i o x i n s n o p l a y b e h a v i o r i n D u t c h c h i l d r e n a t S c h o o l A g e . E n v i r o n . H e a l t h P e r s p e c t . 1 1 0 : A 5 9 3 - A 5 9 8 . 2256 W a e r n , F ; F l o d s t r o m , S ; B u s k , L ; e t a l . ( 1 9 9 1 ) R e l a t i v e l i v e r t u m o u r p r o m o t i n g a c t i v i t y a n d t o x i c i t y o f s o m e 27 p o l y c h l o r i n a t e d d i b e n z o - p - d i o x i n - a n d d i b e n z o f u r a n - c o n g e n e r s i n f e m a l e S p r a g u e - D a w l e y r a t s . P h a r m a c o l T o x i c o l 28 6 9 : 4 5 0 - 4 5 8 . 3209 W a l k e r , N J ; K i m , A ; L u c i e r , G ; e t a l . ( 1 9 9 8 ) T h e u s e o f t i s s u e b u r d e n a s a d o s e m e t r i c f o r T C D D - i n d u c i b l e 31 r e s p o n s e s i n r a t l i v e r i s e n d p o i n t - s p e c i f i c . O r g a n o h a l o g e n C o m p o u n d s 3 8 : 3 3 7 - 3 4 0 . 3323 W a l k e r , N J ; P o r t i e r , C J ; L a x , S F ; e t a l . ( 1 9 9 9 ) C h a r a c t e r i z a t i o n o f t h e d o s e - r e s p o n s e o f C Y P 1 B 1 , C Y P 1 A 1 , a n d 34 C Y P 1 A 2 i n t h e l i v e r o f f e m a l e S p r a g u e - D a w l e y r a t s f o l l o w i n g c h r o n i c e x p o s u r e t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p 35 d i o x i n . T o x i c o l A p p l P h a r m a c o l 1 5 4 : 2 7 9 - 2 8 6 . 3376 W a l k e r , N J ; T r i t s c h e r , A M ; S i l l s , R C ; e t a l . ( 2 0 0 0 ) H e p a t o c a r c i n o g e n e s i s i n f e m a l e S p r a g u e - D a w l e y r a t s f o l l o w i n g 38 d i s c o n t i n u o u s t r e a t m e n t w i t h 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n . T o x i c o l S c i , i n p r e s s . 4309 W a n g , X , S a n t o s t e f a n o , M J , E v a n s , M V ; e t a l . ( 1 9 9 7 ) D e t e r m i n a t i o n o f p a r a m e t e r s r e s p o n s i b l e f o r p h a r m a c o k i n e t i c 41 b e h a v i o r o f T C D D i n f e m a l e S p r a g u e - D a w l e y r a t s . T o x i c o l A p p l P h a r m a c o l 1 4 7 ( 1 ) : 1 5 1 - 6 8 . 4423 W a n g , X ; S a n t o s t e f a n o ; M J , D e V i t o , M J ; e t a l . ( 2 0 0 0 ) E x t r a p o l a t i o n o f a P B P K m o d e l f o r d i o x i n s a c r o s s d o s a g e 44 r e g i m e n , g e n d e r , s t r a in , a n d s p e c i e s . T o x i c o l S c i 5 6 ( 1 ) : 4 9 - 6 0 . 4456 W a r n e r , M ; E s k e n a z i , B ; M o c a r e l l i , P , e t a l . ( 2 0 0 2 ) S e r u m D i o x i n C o n c e n t r a t i o n s a n d B r e a s t C a n c e r R i s k i n t h e 47 S e v e s o W o m e n ' s H e a l t h S t u d y . E n v i r o n H e a l t h P e r s p e c t 1 1 0 ( 7 ) : 6 2 5 - 8 . 4489 W e b b , K B ; E v a n s , R G ; K n u d s e n , D P ; e t a l . ( 1 9 8 9 ) M e d i c a l e v a l u a t i o n o f s u b j e c t s w i t h k n o w n b o d y l e v e l s o f 50 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n . J T o x i c o l E n v i r o n H e a l t h 2 8 : 1 8 3 - 1 9 3 . 5512 W e i s g l a s - K u p e r u s , N ; S a s , T C J ; K o o p m a n - E s s e b o o m , C ; e t a l . ( 1 9 9 5 ) I m m u n o l o g i c e f f e c t s o f b a c k g r o u n d p r e n a t a l 5534 a n d p o s t n a t a l e x p o s u r e t o d i o x i n s a n d p o l y c h l o r i n a t e d b i p h e n y l s i n D u t c h i n f a n t s . P e d i a t r R e s 3 8 : 4 0 4 - 4 1 0 . 12/23/03 R-28 DRAFT--DO NOT CITE OR QUOTE 1 W h itlo c k , JP, Jr; O k in o , S; D o n g , L; et al. (1 9 9 6 ) C y to c h r o m e s P 4 5 0 5: In d u c tio n o f c y to c h r o m e P 4 5 0 1 A 1 : a m o d e l 2 fo r a n a ly z in g m a m m a lia n g e n e tra n scrip tio n . F A S E B J. 1 0 (8 ):8 0 9 - 8 1 1 . 43 W H O ( W o r l d H e a l t h O r g a n i z a t i o n ) . ( 1 9 9 8 ) E x e c u t i v e s u m m a r y , a s s e s s m e n t o f h e a l t h r i s k o f d i o x i n s : R e - e v a l u a t i o n 5 o f the T olerab le D a ily Intake (T D I), W H O C on su ltation , M a y 2 5 -2 9 , 1 9 98 . 67 W H O ( 2 0 0 0 ) A s s e s s m e n t o f t h e h e a l t h r i s k o f d i o x i n s : r e - v a l u a t i o n o f t h e t o l e r a b l e d a i l y i n t a k e ( T D I ) . v a n 8 L eeu w en , F X R ; Y o u n es, M M eds. F o o d A d d . C on tam . V o l. 17(4), L on d on , U K : T aylor and F rancis. 109 W H O . ( 2 0 0 0 ) I n t e r n a t i o n a l P r o g r a m m e o n C h e m i c a l S a f e t y : h a r m o n i z a t i o n o f a p p r o a c h e s t o t h e a s s e s s m e n t o f 11 c h e m i c a l s . F a c t S h e e t N o . 8 . 1123 W i l s o n , C L ; S a f e , S . ( 1 9 9 8 ) M e c h a n i s m s o f l i g a n d - i n d u c e d a r y l h y d r o c a r b o n r e c e p t o r - m e d i a t e d b i o c h e m i c a l a n d 14 t o x i c r e s p o n s e s . T o x i c o l P a t h o l 2 6 : 6 5 7 - 6 7 1 . 1156 W i n t e r s , D L ; A n d e r s o n , S ; L o r b e r , M ; e t a l . ( 1 9 9 8 ) T r e n d s i n d i o x i n a n d P C B c o n c e n t r a t i o n s i n m e a t s a m p l e s f r o m 17 s e v e r a l d e c a d e s o f t h e 2 0 t h c e n t u r y . O r g a n o h a l o g e n C o m p o u n d s 3 8 : 7 5 - 7 8 . 1189 Y a g e r , J D ; L i e h r , J G . ( 1 9 9 6 ) M o l e c u l a r m e c h a n i s m s o f e s t r o g e n c a r c i n o g e n e s i s . A n n R e v P h a r m a c o l T o x i c o l 20 3 6 : 2 0 3 - 2 3 2 . 2212 Y a n g , J H ; V o g e l , C ; A b e l , J . ( 1 9 9 9 ) A m a l i g n a n t t r a n s f o r m a t i o n o f h u m a n c e l l s b y 23 2 . 3 . 7 . 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n e x h i b i t s a l t e r e d e x p r e s s i o n s o f g r o w t h r e g u l a t o r y f a c t o r s . 24 2 0 ( 1 ) : 1 3 - 8 C arcin ogen esis. 2256 Y a n g , J H ; T h r a v e s , P ; D r i t s c h i l o , A ; e t a l . ( 1 9 9 2 ) N e o p l a s t i c t r a n s f o r m a t i o n o f i m m o r t a l i z e d h u m a n k e r a t i n o c y t e s b y 27 2 . 3 . 7 . 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n . C a n c e r R e s 5 2 ( 1 2 ) : 3 4 7 8 - 8 2 . 2289 Y a n g , J Z ; F o s t e r , W G . ( 1 9 9 7 ) C o n t i n u o u s e x p o s u r e t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n i n h i b i t s t h e g r o w t h o f 30 s u r g i c a l l y i n d u c e d e n d o m e t r i o s i s i n t h e o v a r i e c t o m i z e d m o u s e t r e a t e d w i t h h i g h d o s e e s t r a d i o l . T o x i c o l I n d H e a l t h 31 1 3 ( 1 ) : 1 5 - 2 5 . 3323 Y a n g , J Z ; A g a r w a l , S ; F o s t e r , W G . ( 2 0 0 0 ) S u b c h r o n i c e x p o s u r e t o 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n m o d u l a t e s 34 t h e p a t h o p h y s i o l o g y o f e n d o m e t r i o s i s in t h e c y n o m o l g u s m o n k e y . T o x i c o l S c i . 5 6 : 3 7 4 - 3 8 1 . 3356 Z a h e r , H ; F e r n a n d e z - S a l g u e r o , P M ; L e t t e r i o , J ; e t a l . ( 1 9 9 8 ) T h e i n v o l v e m e n t o f a r y l h y d r o c a r b o n r e c e p t o r i n t h e 37 a c t i v a t i o n o f t r a n s f o r m i n g g r o w t h f a c t o r - b e t a a n d a p o p t o s i s . M o l P h a r m a c o l 5 4 ( 2 ) : 3 1 3 - 2 1 . 3389 Z a r e b a , G ; H o j o , R ; Z a r e b a , G M ; e t a l . ( 2 0 0 2 ) S e x u a l l y d i m o r p h i c a l t e r a t i o n s o f b r a i n c o r t i c a l d o m i n a n c e i n r a t s 40 p r e n a t a l l y e x p o s e d t o T C D D . J. A p p l . T o x i c o l . 2 2 : 1 2 9 - 1 3 7 . 4412 Z e i s e , L ; H u f f , J E ; S a l m o n , A G ; e t a l . ( 1 9 9 0 ) H u m a n r i s k s f r o m 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x i n a n d 43 h e x a c h l o r o d i b e n z o - p - d i o x i n s . I n : A d v a n c e s in m o d e r n e n v i r o n m e n t a l t o x i c o l o g y , v o l . 1 7 . P r i n c e t o n , N J : P r i n c e t o n 44 S c i e n t i f i c ; p p . 2 9 3 - 3 4 2 . 4456 Z h a n g , L ; S a v a s , U ; A l e x a n d e r , D L ; e t a l . ( 1 9 9 8 ) C h a r a c t e r i z a t i o n o f t h e m o u s e C y p 1 B 1 g e n e . I d e n t i f i c a t i o n o f a n 47 e n h a n c e r r e g i o n t h a t d i r e c t s a r y l h y d r o c a r b o n r e c e p t o r - m e d i a t e d c o n s t i t u t i v e a n d i n d u c e d e x p r e s s i o n . J B i o l C h e m 48 2 7 3 ( 9 ) : 5 1 7 4 - 8 3 . 4590 Z o b e r , A ; M e s s e r e r , P ; H u b e r , P . ( 1 9 9 0 ) T h i r t y - f o u r - y e a r m o r t a l i t y f o l l o w - u p o f B A S F e m p l o y e e s e x p o s e d t o 51 2 . 3 . 7 . 8 - T C D D a f t e r t h e 1 9 5 3 a c c i d e n t . I n t A r c h O c c u p E n v i r o n H e a l t h 6 2 : 1 3 8 - 1 5 7 . 5523 Z o b e r , M A ; O t t , M G ; P a p k e , O ; e t a l . ( 1 9 9 2 ) M o r b i d i t y s t u d y o f e x t r u d e r p e r s o n n e l w i t h p o t e n t i a l e x p o s u r e t o 5554 b r o m i n a t e d d i o x i n s a n d f u r a n s . I . r e s u l t s o f b l o o d m o n i t o r i n g a n d i m m u n o l o g i c a l t e s t s . B r J I n d M e d 4 9 : 5 3 2 - 5 4 4 . 12/23/03 R-29 DRAFT--DO NOT CITE OR QUOTE 21 Z o b e r , A ; O t t , M G ; M e s s e r e r , P . ( 1 9 9 4 ) M o r b i d i t y f o l l o w u p s t u d y o f B A S F e m p l o y e e s e x p o s e d t o 2 , 3 , 7 , 8 tetrach lorod ib en zo-p -d ioxin (T C D D ) after a 1953 ch em ical reactor incident. O ccu p E n viron M ed 5 1 :4 7 9 -4 8 6 . 12/23/03 R-30 DRAFT--DO NOT CITE OR QUOTE