Document wqnZkypM5rZ86rJ14gxmBqVRJ

A.; Reporfbn the Expert Panel on .Health Effects of Asbestos and SyntbetiCiYitreous Fibers: The Influence ofFiberLength -sm ,j . ; Ui'i C ' ' ; " :r 'r ' Preparedfor: Agency for Toxic. Substances and Disease Registry Division of Health Assessment and Consultation Atlanta, GA Prepared by: Eastern Research Group, Inc. 110 Hartwell Avenue Lexington. MA 02421 March 17,2003 HWBUI0009555 > This report was prepared by Eastern Research Group, Inc. (ERG), an ATSDR contractor, as a Synthetic Vitreous-Fibers: The lnJltieaieef*Fiberd^$$lrf^ the main points of scheduled presentations, highlights discussions among the panelists, and documents the public comments provided at the meeting. This report does not contain a verbatim transcript ofall issues discussed, and it does not embellish, interpret, or enlarge upon matters that were incomplete or unclear. ATSDR will use the information presented during the expert panel meeting to aid in developing scientifically sound public health evaluations for exposures to short fibers. Except af specifically noted, no statements til this report represent analyses by or positions ofATSDR or ERG. u HWBUI0009556 )) Table of Contents . Executive Summary ............ ............................ s.-................ i . .......................v 1.0 Introduction ...................................................... :.................................................... 1-1 ? ... A&r 1.1 Background .......................................................................................................1-1 1.2 Scope of the Expert Panel Review..................................................................... 1-2 1.2.1 Activities Prior to the Expert Panel Meeting................ . .. 1.2.2 Activities at the Expert Panel Meeting.............................................1-3 . 1.2.3 Activities Following the Expert Panel-Meeting .-.. A , ;-:y"l-6 f1 Re^rt Org^izatiiM A r.. :: .vA 1-6 ;-y \;ij V; :ig < 2.0 Comments on;Tdplc>lS:'EbysiolpgJcaliFatexf'Asb'estoS'aHt|.SVF Fibers Less; Than 5 Micrometers in Length . Ji': 5s JvV-'s.'i* .-Ji. r. vv- j - A AV^s-S-l 2.1 Deposirional Pattens in the Lung.........................................................................2-1 2.2 Lung Clearance and Biopersistence................................................................... 2-5 2.3 Migration ofFibers Deposited in the Lung................................ 2-8 2.4 Open Discussion Among Panelists ................................................................. 2-10 2.5 Observer Comments and Ensuing Discussions.............................................. 2-12 3.0 Comments on Topic 2: Health Effects of Asbestos and SVF Less Than 5 Micrometers in Length ................ :....................................................................................... 3-1 3.1 Cancer Effects ....................................................................................................3-2 3.1.1 Data from Cancer Mortality Studies...................................................3-2 3.1.2 Data from Human Studies of Lung-Retained Fibers (Cancer)........ 3-4 3.1.3 Data from Laboratory Animal Studies (Cancer)...... ......................... 3-6 3.2 Noncancer Effects ........ 3-7 3.2.1 Data from Occupational Studies-.......--------------- 3-8 3'2.2 Data from Human Studies of Lung-Retained Fibers (Noncancer) . 3-10 3.2.3 Data from Laboratory Animal Studies (Noncancer)........................3-12 3.3 Mechanisms ofToxicity............ ............................ 3-14 3.4 General Comments and Interpretations.................. 3-19 3.5 Research Needs .............. ..3-20 3.6 Observer Comments and Ensuing Discussions........ .....................................3-22 t ) HWBUI0009557 Table ofContents-CContinaed) 4.0 Conclusions and Recommendations................. .......... -> 1:- ' -'-i- 4-1 4.1 . . Panelists' Final Statements.................. ............................... -w.. - <... .4-1 4.2 Observer Comments and Ensuing Discussions............................................... 4-4 ' ................................. . - V. C S. References r. ....................................................................................... -.................... 5-1 *. ;........................... - -Appendices `-.w ^ v ; Appendix A List of ^pert^Panelisls C.:.; Appendix B .Premeeting Comments* Alphabetized by AntliorXiiMludes biQS ofpanelists and the charge to the reviewers) AppendrseG .L^dfR^stetMObsd^^Qflhe^pfettrPanelMeetSS'g: r ?*> ?..>;'> i>s Appendix D Agenda for fee Expert Panel Meeting A * ; t.-> ->j- : v. j Appendix E Panelists' Comments Submitted After the Meeting v:i'ie&Bftfc&L- 3ms.I . a-j o:v-eS*.-`;'r<A. -.....iO' 4 ;~.s'r~v>V;- ' *' ' \ a*;i F f-V X H M'.liiVO'.. i>.' . .virSS - ' ; t; :. . ;-#U ' rr ' ' 'C-'L-' V >7 . - . Si-':" : . . .,vHv;: ^.."c -of -J;:..: Ft. - v.ji:?.,. ' .V.rit' -fi.T f -'(&_-) ''ii.-.tK-' ... . . . . . ..... >ru. if.- r 's..*-. NV-V^rV^. . ,/ -;&& : F wc->: ;/..i ;C ;F.F;F ?.&. .. >..w: ~!r - .... .... ; fc-c:;; ^sta^Tiiriv 'V ."' L.-: tl HWBUI0009558 . .List of Abbreviations . ATSPRv Agency,foriToxic .Substances and Disease Registry RAL ;jDP?C broncboalveolar lavage ^pa!iimt6ylJp6tjphatldyi'choliine :EPA.. ; . ,.j... U.Si Eisyirpmeatal Prpteetic Agency , FEVl forced expiratory volume in 1 second FVC'''"1' ; forced ^incapacity ' ' " 1 ' Intanatfp^jyAgenty-fpr Resefttchpn Cancer ... NIOSH PCM*"' PM&:.,;; National Institute for Occupational Safety and Health plm'dfentraM'fficrcfec&py' ' pipppr^pn^ppit^li^ ratio, . rear admiral ROS SMR refiibttiryearanilH'fifjfcr' *" reactive oxygen species standardized mortality ratio " '"syiiihetiC'Viir^^ fiBeis-'lv: k -iti^SW^j^iSifectpr^alpha. um micrometers. ` J - ?. * :l* Vijj>'t -'} V .v r: Ci&\i -.v-c`: . .../'O; v.' ' . ;ti-;'y.; 'it,- f. Ui i"; . . ; .'Ar . . . 'H. ,, . . .. :: , :. -x'':. >:;< ' - . : :y-?:-5r. .v-i: . `' *r'Vv ' k--k:S:k" ...JAftT'ft-tejjtf;-h-----% ;fy?/ i - ``yX'-.ri:?- , i-1'.- -V'- y -Vi-:.- :.'v r--; sir. A:: j-1 " > 1-. `V1 '-v:d'- >- !? . / ` c' v:' .-s-v ' V . rv '.y'' HWBUI0009559 Executive Summary Pirate on-iiow' fiber lengtli relates to toxicity of asbestos and synthetic vitreous fibers (S^sjr^pi issue.reieyaqito the Agency for Toxic Substances and Disease Registry's (ATSDR*s)voihi^)iiig:;wdtt'''a`t'&vefal sites where-fifcer contamination is found in or near residential neighlrorhocKls. tbe expert panelists included .. epidemiologists, pathologists, physibi^;hygicbisfe/p!ilksc>HdIogiitsJ'affd`'tdXicologiste. During a 2-day meeting in October 2002 in New York City, thepanelists thpjgugHytfiscus^ the . , physiological fate of structures less than 5 micrometers (jfflr) indengtlt'hatlng aspect ratios ^ greater than 3:1, health effects ofasbestos and SVFs of.the;same.4liaieitslpns, and research needs. The panelists' main findings and recommendations areJijstod b^low. The,remainder of this report summarizes the discussions and observations that led-to^fiese findings^aHdTeviews tbe-pimelists' comments on many topics not listed in this executive sumngary,TJt^jepprt.pipvides irtsights.and advice on how to interpret exposures to asbestos and SVFs less than 5 pm in length based on panelist discussions; however, the contents of this report should not be considered ATSDR policy. Factors that Influence toxicity. Health effects from asbestos and SVFs ultimately are functions of fiber dose, fiber dimension (length and diameter), and fiber durability or persistence in the lung (as determined by the mineral type, the amorphous or crystalline structure, and the surface chemistry). Fibers or particles? Some panelists questioned why structures less than 5 pm long, regardless oftheir aspect ratio, were re ferred to as "fibers." This report refers to structures - less than 5 pm long as "fibers," while acknowledging that some expert panelists have reservations about this terminology. -i m Deposition and retention of short fibers. The lung depositiona! patterns of fibers less than 5 pm long have been well established and depend almost entirely on fiber width. For short fibers with diameters between 0.1 and l .6 pm, total lung deposition in healthy people will be between 10% and 20% of what is inhaled, with most of that deposition occurring in the deep lung; the fibers that do not deposit will be exhaled. For short fibers J HWBUI0009560 with diameters lqss thaaj). 1 pm, a greater proportion will deposit and there will be a somewhat greater proportion of deposition in the proximal airwayss . . The s!|Ott .fibers can be cleared frotBithe lung by varipus mechanisins> depending on where the fibers, deposit Fibers, depositing on the surface of conductive ahrways.(Le., the tracheobronchial region) are efficiently cleared by the mucociliary escalator, generally ; within. 24,hoprs.. Many-ofthe short fibers fisat reach the gas exchange region of the lung are cieared.by al^ooi^macTophages* anti.the,rate of clearance by phagocytosis has been ..founil to vary wito.fj|^.leng^und to differ acrpss maxnmalian species.. One panelist, for instance, citedstudies ofmice and rats suggesting that phagocytosis clears short fibers ... from.the alveolar regions ofihelung within a,few.jyeek|.following(exposure. On.the other . mediated c\eax$nccjnhtim?p lung? of 400 . . -:tp:10Q,day). pyerdlj -P^sibfts,nqte><j jjujt.rodents clear, short fibers;fipm. their lungs .. approximately. l|)i.toes.fasterfi!aH:<toh!nn.aiK. pepositioa.apdi:etmitiqi?patterns may foipigg materiaJfrpm their lungs. The ... which short ^|eis,prefereBBalIy.transipcate^om the gas exchange region to the .... ..ji,..- . . . ......v ... ' 'f.*- ' * *' ' *' ' '. ''* .i. .'.bSJ";!--:..- -v* .sh*t * Cancer effects of short fibers. Given findings from epidemiologic studies, laboratory t. stwfie^rombipqd %jjsjxs ability to clear ! short.ra^^e^anebste-agre^~that?ttere!is.a strong.wei^t p.fseyidenqe that asbestos and SVFs shorter dun 5 pm are unlikely to .cause cantor in .huBup. , ... ..Noncanirer .effects of,short fibers. The,laboratory apimal.studies,;epidemiologicstudles, , tayjfn vitro studiestg;en^liy sifgggs^ 'that asbestos and S'VF increases with fiber. lengii, .b^t fcere;|re ^eyhral:nqtehie .excepfio.ns. In iaborato^.anrinais, for example, \ shdjci asbestos. aniSVFs atjufficiently.higb doses have been shown,tp cause inflammation, pulmonary interstitial fibrosis, and pleural reactions; however, the doses jaepded-to. cause. Aesejffw.^>in>shurras< .may not be relevant,to, enidroupjental exposures. i^bbmaps,.fotoep.t.a..f.^..o..!.pgicstudie5.(Churg` et,.a..d.... 198. 9,lR90;bray..e..b..2..a. cleh etal. 2001; tial fibrosis is correlated with the aniount bfshortfibers in the lung at death; some researchers have ^hy^jfiiesize^^a^ijs.apgtoent^..association/is. exjrf^nediljy lopg^bers. breaking down into f^sh^|}er fibS.be^emiin^^^a^^c.MmeafwhichiJ^g^ii^pito/W^e collected. Finally, at least two^ih vitro studies (Ve ei al. 1999, 266't).havefcpnd that short fibers are at least as active as, ifnot more active than, long fibers on a surface area or mass basis for multiple endpoints (e.g. tumor necrosis factor-alpha [TNF-a) production, activation of TNF-ct gene promoter activity); however, the relevance ofthese in vitro findings to health effects in vivo is not known. Taken together, the findings from the laboratory animal, epidemiologic, and in vitro studies suggest that short fibers may be pathogenic for pulmonary fibrosis, and further research is needed to clarify this issue. HWBUI0009561 ) a Research aeec&atfcS reoa3is'eii{latloos. Thrdiighout the meeting, the panelists identified data gaps and imde reteonmi&d^iohs for'filling them: Some recommendations addressed issues specific to sites (e.g., Libby, Montana; Lower Manhattan) with concerns about short ; fi^;ihesSdehtid<mihtfttties::1hesfer^mm^datiofii'are listed in Scbtioii 4.1. The panelists* recommendations forgeneral research pfojects follow' in no particular order: :c 'r ` `1 . : ;ETO8iiM^biflCrtased;usebf%a^linghiimahlUfig-ttssueprotherfeiolbgical Utahanexposure situatiohs'toimprdVe'botliqualitative and qWahtitativee'xposare assessment V '.o:V: v ;: V 1:?::n -v.:;*.'.-- : ediid*yu' ct a*' laShri&ij; ich fibers of all ocaM fbr;fib6rs'of^ydinieiisibn Or type. Soiaepahelisti isoted tliat tt^Bslocafion -o8.-` 6fthesie :Ll Li 3d. refractory ceramic fibers; and a follow-up pot jet published, for amphibole fibers. but different pmjpitss:c^:lie cbiSiitL for S'V- Pe^rmpea^i^^ikjs^sSm^lHJg, dr aheqdivmos^td:q^!iia0Twlihi exposures :>n** i$s&.v- c; ar^contaMna^d'^idffaslwsSiMorS'Wiianalyze ' si&pels t^g&h^^b'oyi! f^fcQimtm^iaepjo^ipr^l^i^tm^bn^ 'fibers ' Ibhgeirth&B 5-fjai), Mi archive a subset'df -^|iafysis. ' ' i"' V' ' Fu^er'id^S^te dsf^os^ibld^ocianon be^eih'shoh^fibeii^ ahd pulmonary id&fsiiiisi iibrosis iQ hbrnans md the impact ofshort fibcni inmgditifo pleural conformed tn ahim: M :. - i-'idhi'. < '.-p; .r ' ry HWBUI0009562 1:0 . : Introduction The Agencj?:for Toxic Substances and; Ptsease. Registry (ATSE>R)..iny}td seven expert panelists to a meejtipg to discuss tbs* current understanding of health effects related tp asbestos and./ . .synthetic vitreous fibers (SV]^ less than 5 nucrpmetpiis (pm) in length^f-an issue that is related to the agency's ongoing work at many sites. The expert panel review took place in a meeting open to the public on October 29~30 2002, in New York City. Discussions at the meeting focused on three specific issues: the physiological fate of fibers less than-5 pm in length, health.eiTects of fibers less than 5 pm in length, and data gaps. ,v?;,^is reportvsunimamxs die technical.dis9ussipiK.aaspni,the.expprt panelists apt! documents comments provided by observers. The remainder of tMsjjtroductoiy section,reviews the.,.. background on ATSDR's concern about fibers less than 5 pm in length (Section 1.1), the scope ofthis expert panel review (Sectionand thf ^g^iz^tipn of.this report (Section 1.3). 1.1 Background , ,, ATSD^ppuductspubhc healthjm^esstn^pis;t0.,valuafe thepublic heaMi implicafionc?f i sites part#f.d>jse..eyg|pattonsis tmjdjijteading.the fpxipojpgic implications ofenvironmental ...^ .exposures..Recent events have highlighted a;nee4'for ATSDR to exjjlore .thejxitenfial of. .... .. ex^o,sm;^pJbjoi^rsistent ibereT^p^ifi.^!ly,asb^tps,mdjsgj3e.S.YF---to,cause health effects. .exposures to fibers;fi$gi past processing. plants ape^the country), contaminants at hazardous waste sites, and dust in Lower Manhattan geaemted frou! the collapse of the World Trade Center (WTC) buildings. These sites are distinct in that >,9<mtmniptmlS:b9vg^^iC^4-^^^p!^^.pf^t^.i^e^^;ta^resi()9pto'hoipps,..h|pieQver, - A1SPR has rfcejy9d.chetps .spec|^caSly; aboutdiapubfic health implications of.exposure to .shorter fibers, particularlyfor materials.found.in Lpiyerhdardiartan. . ... ] HWBUI0009563 ATSDR has therefore identified a need to understand the potential of fibers less than 5 pm in length to contribute to adverse health effects. As one part of addressing this need, ATSDR convened-air expert jpaiielto discuss arid review the current state-of the science rfegarding the influ^tfbffife len^ on h'ealtti effects ofasbristos arid SW. ATSEiRwill use the panel's" fMdligs iS help develop Scienfijffrially sound public h^th evaiuatidhs'foritiirisM exposrires to "sMaUTifes. r:':- ` : ; : '* ruyj :* , ij ' Sridpi of the-Expierit^aijel Review r ?u,ih j<.:: The expert panel review involved many activities before the meeting (see Section 1-2.1), at the tfe#h:i;2.'2)>':^:afterthd':meetint^ Sediotf1^23): ThWoM^gsuhsSiBoiJS describeTivhrit'each of ffirisb:trii:hs'eSfeiiSt: ' w ' '* ' fit'l- ' f ! v.r-br- ;re -n- :*ia. no * ' At^vklesltfritir tb'ileTSxjieWT'iriel Meeting' ATSDR selected seven experts in toxicology, epidemiology, pathology, pulHS6hM&gy?hygterie, and medicine to serve as panelists for the meeting. Every panelist is either a senior scientist, physician, of re^afcherwitifii rijiiyriVH^j^riteceih;ffie'aforem^ bypeer-fevifewdi puMiOatitihS/riwarti^' awdsehricS tb relevaritpfof^t0fiil>s6cieti&:'ATSDR agencies)M^iipe:'ll[at th'SbXpBrtpatoel w'otilS'ofrd: ab'alaribOd fesqpbfive dnWcfneetin^topics. its SfecBTofeiipe'rt piSc;lis&,''A'fSDRas:^ib cahdMSt^^6:!ilSiS.!^^'feal liSi#tii6hlin^Mdafifi!iatibrik'of th^S^hlexpert ' s 'V- 'C-H f /..':. -v.-: V;" 'J' * - }U?-t i;i ;> frt'l? `To' ffeis%eHdifeissi<>fij'afthS "clifge'TTbf ;quesTibiasxthat:th'e eJcpCTtpoia&listi discussed during the meeting.' T^Ssli'qfetibnS atldnKsedlhfeTbysiolbebal-'fele of fibers'IcSsrthan HWBUI0009564 5:Jim in lengthy the health effects associated with these fibers, .and data gaps. A copy of the charge is included in Appendix B. Several weeks prior to the expert'pdriei meetings every panelist 1 received a copy ofthe chargei ;iogistical information foj; the meeting, a preliminary, bibliography ofpublications on asbestos and SVF; arid copies ofsix publicationsrelevant to the meriting . 'topics.^o.tiides.etal; 2000,5 Churg et ah 2Q00j JDavis. Ig94; Khanula 1999; Morgan.J995; Qhyamarit'Ml 'ibol!).' "* -- ' ... ,.Sh lhe whefa ^cr&riparidisis r&ejyed|h^einitefiiisj;the panelists-wefe asked topfripare their initial responses to-.the charge questions^Booidets of tbe premeetiBg^comoeats .were distributed &e experfpifielistri, aiiil made aVailablefe ob&i'v^rs'i&iid'^^shaed iM;adyari5:tii"aftd6d the expdf,paiietemew^Thesri 88 . njpend&i&'lt'sihotiid lbe Some i-. :\ ' Ao'"-. ri-;-.-:_v-?;{? v.:/-; pane]ists?:.tfihmc?l findings.,tnay have, changed affgc.the ptej^Jx^g.jmp^mls wTeresubmitted. .-s -a -a, -tv. lari. v.'.-j.. .v v.1 1.2.2 Activities at the Expert Panel Review Meeting : r. -./imV-- - ^.ing, which W5ts;hd31#ttibc#ricbb fc^airitz Fedetril Btisldirig'm New:Voffc^etty/New-Y&rk;;on,fetober 29^3Qr?P02k>:Ehe,m5eting was. ppm tp_.the p1uW.id,.,and the meeting dates .a^gmeji wege aanbuhriedifflBe Federal Reipstrir. Appendix- 0 liSts the observers whd confirmed thefr- A-''r-.'.'V.o'-.'.-fi:' --o': V.-.'-o :& attendaac,e;atttiie.meethe schedule of theexpertpat|e| meetmg^generally :il"ioiiowai'fiiejage'tida,presented' heft'al^pprii^wti'Di Tlie remajiderof&is sri^bh'dristiribes the iotroductorypresentetiorisgiven^ : ...,. .' 'Intra^tory remarksfrom A1SQRi!fh&tp<scng, begao with : >. u-.; MteifeWilliilriSjiDirector of ATS^|^iyisipn.qf;Hmlth ^^SMntj|iijfonsuItation . .fiiv :ri si, hM-honvene^.theexperi.paneLfie;.|sis.t }^yie.w^^TSDiit'?:stte7spm!fic expertences with r :;asbrist9?*ontaminattons.inceri9fOf>assessing:fqn^3y,i'5Ci,sit^?^fwhich.asb^tos was a -coriianajpant- of compm, evaluating approxiniate|y.5Q,sites at whic:b completed, or potential j;i-. ^exposure pathways were fqurid for^sbes.tos. and. issuing p.ubtjc heal& for sites HWBUI0009565 where the public might come ihto contact'with- elevated levels of asbestos-contaminated . materiJs. RABM WilliaiBS indicated that the available epyir^mmental d^ta, for these previous evaluations were typically the percent of asbestos in i waste material, as' sites, detailed information op fiber size distributions is aptavailable. More rbcbnf work oa sites wth asbestobcohtaimaihoni-KADM'Willianis explaihedjbas led to a greater need to understand the role of fiber length on asbestqs toxicity. He , , reviewed ATSDR's activities at two sites with public health concerns regarding asbestos exposure. First, RADM Williams presented findings from medical testing that ATSDR : conducted on jesid(m^p|;U^hyl4MontmMi, where yeimicu^piuiflg.amd s^o!iatiQn f operations occurred fear more than 50 years. ATSDR fooiM't^i^'^me'lFesn^a^' tested '(which included Woiiceits afftefeteef mmO-and exfdliatiocipIaat)diad pleural isi jeople whp had lived inthe area longest T------------------------- vj**.-?;;/!,.<.,*/ rju . f\ > *(/'>; Hr !v'v-t*./4 9 and who had completed exposure pathways for asbestos. RADM Wifiliaims desenoed' ` etcposu^fesaie^ : SVF in dust generaiedduring die WTC collapse. Activities included feviewmg raiulis of whether buildings could be entered for occupational purposes, and assessing the need for maintaining the "exclusion zone" in Lower Manhattan. ' h&#$ J 'HW ;:i-.i. < . *' S..-L i RADM Williams indicated that ATSDR's experiences with the Libby, WTC, and other amounts ofshorter fibers (less than 5 jia) than were typicilly character^d previdusly. v<Sie Siegs in helpifig the agehc^rtK^hi'iib'ith'eSedlfallenges, RADM'Wiiita^visdliat^d, fOD^! their individual ppihibns and Were not askedto reach consetsstis da anyTSSute^aiid representatives from ATSDR were pres^FSlfifctly tobbse^ Jrtfroductary remarksfrom the meeting chair. Dr. Morton Ltppuaann, the clsahr.of the rTaiifiS WbgtiniK'itito\r?d& adtlsifon^l intim^ctbrv'remMSil,Aft*rftiVlew^E the 'rffetiti^gdW^, &.Tipprha&,ttidi<i!8tSfctteitdjfe. goal of ' tol'Mpeft'^^eiot^efihg'Whs'tb aSwfetStf-WStiff-isbi^toS'ahd'SVF, on fibers i^S &'ati-:5`|itoih6tgc^:rfefe^cphvbhtib1ns^r^biBty i^fcd^iWaluate asbestijsxpbsures; ,`S^feciily^^a^M'^ci^siciris%l.atha io'asbbstbs,;W.-Cippmann'Botfcd,i^ ^icattj^beSn bas^:difoptical meiisaremenfebf fibers5 longer thaift5 pia5-'i[ad;one goal of 1-4 A ) A .J HWBUI0009566 th^expeitpfJael was tff evaluate the toxicity of the. shorter fibers that are not counted by the optical analytical methods. Dr. Lippmanh also emphasized that the expert'panel's discussions should have a public heilthr focus, suehtMt ATSDR could apply the findings from the expert panel to sites where community members .are concerned about exposure to asbestos and SW. To illustrate recent coacerasabout.asbestos and S>V^, Jfr. I1ippmannjj|espribM..ongoing research being conducted to evaluate'contammatioii'by#iC dust in Lower Manhattan. He indicated, for example, that his research group and colleagues have collected and analyzed pumerous settled (fust samples and jpbient air samples following the: WTC collapse and are evaluating health effects among approximately 3Cto fuefighters and ' . imposed almost,entirelypfp^tticles..laii^rjth|p IQ only 1% offine particles less than 2.5 pin inaenxlynamicdiameter. Dr. Lippmanh afeo n;5' indicated that the purpose oifthe expert panel review1was to help ATSDK'ihSnpret the ptiblic healthsigEificance ofshOrt!fibere;fSike^0^;detectedin.tlte,WTC:dustiv; . . I . A' ,Vrty.j'V * ' - .aa :a<-i'~. 0Fd!i6SraHg'foesepetiin'gpresestefidrik Dn-Li|^maim<feedifoepkieHkts tointroducft themselves by stating their names, affiliations, areas of expertise, and past research experience. Eor the vTrti remainder of the meeting, the panelists gave individual presentations and engaged in free-flowing discussions when answering the charge questions and addressing additional;topics;apt specified noted that puhefaldgist^'gwjlogists, health scientists, arid individuals mother disciplines rosy other propeitie^ Sfection'2.4presortsmore detailed rirfotmatioit on tie panelists* oputtopk da- fo%'most ^piiJpr^fe teraamolo^; Tfiisi^tie is i^isSiPfferei to Mfi>raJrf^deisdiritfiit& eitfsre^ report uses the term `ffibers less than 5 pm," while acknowledging that some panelists had .reservations about suggesting that structures less than 5 pm are fibers. HWBUI0009567 engage in or direct the! jp&eliSts* <fis&issiot&' ^ ; okc.-.-. i4r'j-. - j>re|ja^g`:diis!siii&^!ir^ report. A teclmic?d.writer who thisjgpcrljTIbe expertpanelists wei asKdd to review^Md'tenQto&it te^f^Msuring'ffit itsfebriteats accurately : ' :' >!>**!'.*:-. ar }. ;,v. ?.fofrscs r,.- i'-vn-V: 1`"* .-------- J>-------- ' _ Jjri-----------'--._*------------------------ ---------------- 1 Tk* ,, revised Based on the paheUs^ iiSoniiiumen& iRb panelists wereifaea 'giv^l'the dppdrttiiiit; to. review to ATSDR. Some panelists submitted written comments after the meeting; these are included in thisregorfc ' >amw. .* Zvo;-^ ;. /;,,>T< ten';' 'd>r.-o \;-Hv -jw] >}-.; .vutffi ,-' ., The structure ofthis report follows the order of the panelists* discussions during the meeting. For HWBUI0009568 generated since the expert paneSmeetag (e.g., a final list ofattendees). Tbeappeadices contain the following information: h .c-.j.i- *. List:bfthe .expert panelists. (Appendix A). . .. ; . -expertpanelists..(AppendixS);...,:. to the reviewers, and brief bios of the >. s ' Listofrej^st^dofeetvefsofffie'ej^ertpraael'iiieetiiigCAppenahcC)^ . Agenda for the expert panel meeUng ,(Ap|^ndix D^. f rfnr;< t- - v.-rtf.-e-?'*. .V^avj /'.i ' k.n ... Js{t o* -nrv n iAiS-.-c \t:s :rrb-'-ioi k-.'jr.y.w->'' yiW'}: fi:"-' '>.< = Ji.'> sv` ` .; r-. ' ' -12 rt?V ; s.... ^K;V5'- '"'''i-' ' i:rr.-VS;;o ; J . ; rj M ISlty- '-/}-) *>' " -sir :fyj.' V-': i': .-'''dr ii-q 1-7 HWBUI0009569 2.0 Commerits on Toplc l: Physiological Fate of Asbestas'ahd SVF Fibers Less-Than 5 Micrometers In Length ." This section summarizes the panelists* discussions biithe physihlogicalfete of asbestos andSVF fibersJess than 5 ,fim tB..leBgth. ^p>.pa^dBtS7l^ Oppm^nn gpdpr, Dberddrete^---were designated discussion leaders for this part ofthe meeting;?diHTng ^hich this panelists responded to the three specific charge quesfions.regardmgphysiolo^cal fate of small fibers (Sections 2.1, 2.2, and 2.3) and addressed topics sot Identified in the charge (Section 2.4). Panelists also commented on the toxicity of asbestos anil S$F fibers; these comments are summarized in Section 3. This section&o stinffiaSize^^b'se^Ofconimetits mhde'aftfer the panefists completed their discussions (Section 2.5). Overall, this section presents a record of discussion of topics mentioned during the meeting, and it should not be viewed as a comprehensive literature review on the role of fiber length in the physiological fate of inhaled fibers. Dr. Lippmann's post meeting comments (see Appendix E) also summarize these discussions. Although the panelists focused their initial discussions on fiber length, several panelists stressed that length is not the only factor affecting fiber toxicity. These panelists noted.that toxicity is rather a complex function ofthe fiber dose, dimensions, and durability, as has been widely documented in the scientific literature. 2.1 Depositional Pattern in the Lung . : The first charge question asked the panelists: "What is the expected physiological depositional . pattern for less-than-5-pm fibers in the lung?" When responding, the panelists provided relevant background information on lung physiology, reviewed wbat researchers have established for depositional patterns ofparticles, and then addressed what is currently known about depositional patterns for fibers: 2-1 HWBUI0009570 Backgroundoh lungphysiology. Before addressing th.e specific charge questions on how fibers deposibra fee lung, onepanelist first reviewed. fundamentals of lung physiology, which largely dictate fiber dosimetry. He explained how air flows through fee respiratory systenr'inhaled air enters, fee-body at fee nose or month, passes ferough-fee larynx and `trachea, and eventually enters the lung in airways feat branch numerous times before teaching terminal bronchioles; These airways are all conductive, meaning featfeey move 4ir to fee deeper pbrtiobsfeftbefemgwhere ;gas;exchange occurs. The airHow velocity : decreases aSair moves ihto the inore.distantbronchij because the cross^sectioiia! area of ' ! ; fee branched bronclu is igreaterfean that of fee.pareht airways. 4Her.passing feroujgjr fee 'terinlrM'broacyoleSi'mhaled air. enters iatorespiratory broschioleg^thenalyeolar ducts, add eyentaaUy alveolar sads, whd^ mostgasexchangfeoccurs; Mpyementofah in the * respiratoiybronchioles and-alveolar sacs;fedonunate(|:by diffusioji, rafeer than by convective forces. . `Jxl -v .. ^ X\-A\ v.v._: > ... ^ fc '' ' y- . .'L Thisipanelist notedifeat clearance;processes- m^iCpndupfiye airwrays, diffejflrom those in c-v;. -fedaitways di^^ta-'ttte.termliidblRrcMKBluc^tes. jD^>@^is-siBegece(t- ntofee auwa^!!surfaces,-and.ciliated-c^ilsbhd4^rohPM'an4l?ipPy.9jieS;gradually feoyefee-mhcusaiptoHte throat, whereAemtteJts *s.sw.#0weA-:l^m^^ :; - ffiechahisii efiRcient!y;removes particles feAHe^ositedonfee ctondh^ve adways, . f^jically^thiH Aoutd'day follawingexj^uroxThe.cl^ag^aalfidbisusmSffdr particles - feabd^pdsit3iffefe;r^piratoiytbronchiole%.alveolarducts, anfehbwplicd^afi^operate on a much longer time scale (see discussion on "phagocytosis? in>!Sefctipn;2.2J;=;; yM. a >o\. D^sidamkpattemsfcnipariicl^OBs ^mclis^^mwnewpd^P^ts^ipithe science of how inhaled particles itenddo;depbsitAj;fee re^irato^ h^tliForbofe fibrcpij and non- fibrous particles* fee deposition pattern is dictated largely by fee particles' aerodynamic -: i'..diaDnieta'iiTh>aefo(fynaiiuc;diameteEj a4ofeer-pAfiliisfihQted;.is;equival.eht to the geometric ditoeier^ofaiiiinitdensify spherefeat has thesameitennioat settling velocity in still air as .'-*:fee;paiftiefe1ft;question;:--.'-' . atsV o v>4. k >-'i:`'t s>etd.r'?' ^ . i.:: ; - Tiie distAiSsionieader then noted-feat,researchers-have long.established that airborne and fee particles feat enter fee lungs deposit byope of three mechanisms---impaction, . ;. ^: d^limenfeticwf90i?feffiiMOQ{(%ow3ii.aaOTdtipn^^e.ielaJive importance of these vvbrohiM&hanismS is ^HuKdi^oi^h<^hftHde-^iz^^^ies^|i^jSleit<(hl^nter fee lung, for *,sS: auisample,Bavh!tIifcmost:mofeehtUm;- whjei;cah^.feefe.to,haye.ia.;greater tendency to a; .'-rdepdsitdti'airways by impactionias airflow. changes.directioii;at bronchial airway .SC ..i.JVV v -y i il:.-. . : A. 2-2 HWBUI0009571 branches. Smallerpartieles,1 on die other hand, are less -likely4o depositby impaction and therefore are typically carried by convective forces further into the lung. . ''; sCdimentationwStbwniao motion; impaction is: relatively unimportant iartgions where 1' the air flow veloc%is ltw; Sedimentation and difiEbsiod tendito be the morfcdominant :! mechanisms inthe sma8i;ton,g-airways for particles, whieh difluse in.air much slower than : gases. One ptolClist noted that Sedinientation is the dominant deposition .mechanism for -- 'ante itiereaSmgfy^ssibjectod'to'diffiistonal deposition'in themrwaySiPaitieles depositing in the re^iratoiy3)roiicMlesj:alVeolar ducts,: andalveolarsaCSiWill pttbjiMb^ regions ofthe luigtintilciehred-by odieicmediairisms (see'Sections'2i2 and2i3);; Depositionalpatternsforfibers. One panelist described depositional patterns of fibers, 1 ^iiib^g;bow;tKem:eloit|psd'shapfe's'camed fibemtodeposltaiflrerenflyln.d.eJupg titan . WpHtidteg' fiber ahttpaiticle dejK^tioiiis that fibers danbe ">' nntercjpted^b'y4tfway''Smfdcfeji.while'particles^generallycannoiriEor^instance;aslong. - airways; the end. of a fiber.mightcontact (and deposit on) an aiHtey.stiriai^'evea m-casesiwhdn the fitofeepterofm$ss$s.:am floifestp^ipliae in the ! when 6 cdmp'ared'to'pd^cte; aftdahteifception^b^dmes;an. mcre^in^yjnpMdaiit;dqiosition mechanisw'fb^efigirir'&bieikv'.H;:-- . ..$! u-***v,, swa-; u r... - rriig tbatmaajyiresearcheirshave evaluated the depositional, patterns of "`'..airri > -rsrtr-'o/r.i'-O'.i'eK :r-< a*-.; .-grrontiri ' Sto<fi^tismi|i|idlldrttatrwaytet-modelsfi:omrlliini.ai!ltiHgs-h3veleiadiistrated ' that tlte^tmt.of!fibteEmtereeptiQn variesj'W|th^fiber-length;Specifically, interception has been shown to be relatively unimportant.fijr-fih&Suk$g<than 10 pm in length (Sussman et al. 1991). This panelist indicated that these shorter - fibets;wiflii3tely!actliltepmnclesin:thelmg,:because:the:Oiie.depRsi^on WrMrS* 'vv-meciymtOT'ta!it|ne.to!fibterS ts;uaitti^irtaiiti>'v^t.';r-' *-rAv-,ur. ! OtherttufliS-'Kmg toi&^models have rej^i^Jdiat fibers.withasf^Ct'mtips 'Wi .#/1 i!i * -fpeafe&tfi&fttititefiratte^ ;v jv eralsilM0;>3'tmbrelT4922-).,Mtereepfioo -:v v- ivi'dCcodrife fotthe fact-diaplbnger'fibemhave.prppdrtionallyjgreatetdcpdsitioii in the conductive airways than shorter fibers. 1 Two panelists had different opinions on the panicle sizes that should be cited in this sentence. One panelist indicated at the meeting that particles with aerodynamic diameters tess than roughly 2 pm would he expected to be carried by convective forces further into the lung. Another panelist, when reviewing a draft of this report, recommended that the size cut-off for this sentence be 0.8 pm. : . 2-3 HWBUI0009572 Foif fibers less.tfran.5 iiprin length, DrrLippmann indicated, to inJformatiqn available on particle deposition and iopger.ffb|gs suggests that fiberdiameter likely has;the.greatest influence dn deposition patterns. Hgnqted tot.fibersjess than 5 pm in length.^yill have . di^ters.less ton 1,66 pip, assumrag the ^spept ratios are at least 3.: 1. This panelist estimated that T0% to 20% t>JFshort fibers with diameters between 0.1 pnd 1-6 fun will deposit in the lungs of healthy people. Another panelist reviewed findings from multiple publications to illustrate how the four deposition patterns. First, this panelist summarized results ofa lung modeling study (Asghariaa and Yu 1988), which predicted the relative importance of the four deposition - - - mechanisms as a'function' offibdridiameter. For all fiber dimensions consrdered/diffiiston ,r|B.rpwmanmQ^on) apcp^t^.for^an^hiCT^edMomit.of.d^sitapn as air.ttaveled^irther .... ' mtb to lung. Further, impacBoPt mtercepobh, arid srounentatibn were relatively -'f .iiotothpbitofitoto'thlMest fibers(thbsd%iflldiameters of 0.01 pm); yet ac'obuntddfbr mb|l. Of.^Pl^Pjed dqmsition,pa^in.^r.the larger, fiber? (those widi diameterof. 10. ........second^ he reviewed to extent to which fibers are filtered from rnhaied air in the filtering airborne fibers than is mouth breathing. In fact, appreciable filtration for mouth onljit to fibers'at Ibasflspm in diaifietCT-i'Ove^adhthesb;<iimaMts highlight tot researchers have already pr^c;^hp.w ^berdiooensipn ||toth lengdr a^l: diameter) affect depositions] patterns in the lung (see Dr. Obenlorster's premeeting comments in Appendix B for references to relevant peer-reviewed publications). i. ,,.jMole pf^c^rMojyjmima!deposi^ml.patte^.m.humqns._Th& pmefiste;ackaewledged thatJ^ratory:aoiEnal:Studies.liayeproxide.d.|dditional_iBsights ,." pp how ^bers^eppsit intite lung,-.hgj.to p^eiisfc uptpd-.that inter-species differences in lungaiiway indicated, for ipstetto* *ba* ' lafel^|oiy.`ainimal stupes have; 'lung.-fiber .^,bi^^^fenfttto1fe^y|^g:fi^^cpato^ed^pagficbpditra^Jbnthe- >}%!'"' ,;V ^uficu^B'pattcat& fiber v# -,i deposition behavior. Consequently, lung'deposition patterns in laboratory animali are ,. . expected .tO/ffiffer. from thosein huigans,. t this ex^e^to^Basedon prOTpfi,bhspfymajliempfic^jupg"dbsimet^mTOel develops* /.. 5 - ^gtoOTafioh^Qtnmissibhbn Radibio^caTRbtection, this panelist illustrated differences between rats and humans in estimated deposition fractions of fibexsjn alveolar repons. His figure indicated that the predicted deposition fraction in humans was greater 2-4 HWBUI0009573 than that in rats for all fiber lengths considered, and this difference was most striking for loiijger fibers.' Specifically;'the trihdel predicted that virtuallyno fibers'wi^^mxiynajiiic : diameters of3 phi aad^P&ctraidsof'iifcl depositin'thfealveolarregtbizofrate, while v'' ' fibe^'ar^]proMctecl'*t6':kSqposEkl|a t6e aj^edllrt^idn of biimahs- Such ptodictitjriSi'tMs p&elist iiolpd, raise' questions atoirt'&he&& rats are good ' mtodelsfor htimmSirr forms of'fiber deposition in the lung. 2.2 d^nace and Blopersisteiiee;: The. gecond charge questioaasked the.paii<$lists: t^What is kop^aboptclearancelblopersistence `' of f^s-thaniS-pm fiberslb the ling?"'Tfiie p^ieiiStsideiitifi'ed'sdVferal irii&iiahiioffi'Kj'which as|*dgtos. pad SVF are jesttpyed Sons ?upg issme.-AsiSectios explains, fAeis.-dgpqfSitmg rin the cSmSMive mrwaysPre fcfeiirfea, 'ty^s^lly1'witiSii \ 'day1; 5*U i /- netvjwt.Pioy ?v*fc,; ir.y.V .r i-,`s iif-'Ji-*** mgchanisig is.-nptidi?ptss^;fu|th^|ire5:^e;p^eSi^' cpnjmqn^j.fociisfd ptimaril^ps phagOcttdsis msd'!dissd!ii'Ubi^'tSit plahe|ists:pbhsidHfedseveral'aifiittijnallfecthSWiten discussing ar.i!*'. ;i?s. jptrpjf'-' ?. -T; -t stmnnariz^ holo^-Se(^pnf2i^addFesse$ . itmr ' lO .'.'r.-i'-T /.!? s-3: . ; v;:iiV37" ,,>. .,. : ,. . r.j a.^a^';'il*lfiMWduld:'^ai'^ly^'clear the iSa^a;&!t&':ike^haCor'fifey can ) ) The panelists noted that removal .of asbestos arid SVF fitim the alv^ti' b^pbsgo^tosis generally takes iniich longer than removal of these materials from the conductive airways _;l>y.m^fc^i!i^^n^^poil~an^h^^Mida tfiaris^^pqridd'hy.^din^s'df^^g'ilearance `SW^ds tn'ra^'^dih eCal: i$9)!fkpW!fically';ih'e sBjdy repdided how iteT^alf-life for lung 5; ; ` Noting that rat alveolar nmcrophdges have dimensions roughly between 10.5 and 13 pso, a panelist indicated that phagocytosis in rats is less effective than in humans at clearing fibers between S3 and 20 pm. X HWBUI0009574 ... clearance ill rats varied with,the. lepgth of chijrejolile asbestos fibers. For fibers .. ;v approximately 20 jm** long,,the estscaated haif^Mfe for cleamce i^y.aU.mechaaisins .ct^iD^Dj^gs 100 days.3. Qne.paijeUst.jilso.pr^eaitoi.data on: tune framesfoFjbng .. .clearance, of fibers in humaps, nptigg|bat thq.es^piated halfrlife for,iveoiar.iraCTophage p- clearance wag estimate^ to.be.befyfe.a 400 and t0O days; the panelist noted that these : ... estimates apply fopoorly soluble spheric^IparticJidfiow cyt^.tQjd.aty and to short fibers ;.?whiskcan1?.e pngulffd by alveolar macroplages. He,added tbailtgg fibers that cannot be ... .- ..,phagocytized;and tbatidp not,dissolveor breaJ^^witt npi t*e.;cleared from the lung. . - As ooe exception to the previous obrotyatioi^,,|5ne .panelsst,noted.tfiat phagocytosis is not .... anjefifctiyeplearappe mecbanisin m ."overload" .cpnditioa^,. orwhen exposure doses overwhelm, the lung's clcarance .m^hanisrasl.Jbe panelists questionpd whf&erdie environmental exposures that ATSIjR: typically evalyates would ever capserbyerload conditions, though they noted that overload conditions may be observed in some ... .i,pccuj^tional,rot^gS;^iu.twexpiected apcideptal c>r.emergency situations. ..r,.. ? lZii;V;:sXS: >' JC &K.V..`.`.r.'iy ;;lx!{ 't'i A..." via ; L'..? s .=:cPl9iPaW3? panelist . i^SSffiP^gn^AepH ofthe 5W#^^Si#S aPPear . A ,. : aw ffaSffiPbagg b^^pH^e?jppnsi#^bly,l!^^;foe;pl^pJ^iBp;^tiigialveolar macrophages (pH=4.5-5.0) and foe e5trapp||?|ar fluid ^K;T:;|*4)^f^S|||iers;aJready have documented the relative solubility of different fiber types (see Dr" Lockejds ;; ; - proPlPP^g cpSBm^ntsJn,^^A^pd|x^.|1jyhich.caa;bc usefol inpharacteri^ngtb? relative ;,bippejistfpce/p|differepter.^p^....... ... *v. b,ers pm fragment.in A^lujigafter being ... ,..: ;i^kgd;Fmgm^tatio|i is.t^|micalJy,Jnota cIeajapce process,.ljecanse;th^fiajmented : in &Jum^;lip:v!|pvw; ,&agpi.eB^iiQn can ,aAanpj;.cj^i^m^fthe nteforaed arej jmproe^silyplearg^by pjiaggcytosk.than ^jie..p'pgm^ffier. One --*! i --;-'J --- *=----L----'fY-,,&.be?t05 kfSF** for ae same fengta; therefore. the ...,-., ..... 1.^.-'. , .:<;.v,.,./ /-v"".-;---, y /j^gne^ejfcp-gxppsure. togfjfet; contaiginemls. A a mixed- ... wJ^dus^ exjm.sijjre'.study fora&|%yiset a).. 199 J^^iIIiist^t^j^p^CT^x^gsiir^i^bflier > ^jfzfjfc'I^Sniatetilcelyuridefstaies the ciearaiice half-life for araphibole fibers of the same length. :,c`lirte'jj&nfeiist nSfeil; iri6re'!(feentihidjei have shown that chtysotile' fibere ire cleared moth readily from the lung than are amosite fibers ofthe same dimension. > - ' HWBUI0009575 coQlatninants iffects fiber retention in the lung. M lie study, gro^s ofrate received differetif combinations ofexposures: chrysbiile ast&stbs'and titei&iM ffibxid^'chrysotile asbestos and qbartz, amosite ^bestos and filtemn dioxide, and ambsite ahbeStos and for the chrysbtilS aifeSos^aniosite ksb5Stbs,;:aiid titanium 43MvS<la nirari'^1l -1 A wi</in3- ltifit(<:#ftb `AVnAmha! vrinWd'dfl^raliAn ^rtr'Oni'arfo'-tM'ke' '0'mWr%5 Ykn y^x: 't^b %S^ foitatf tfiift co^eiposiare witK titaaiifia itioHde-Sfia quartz hM hd effect on Kiihg intention ofamosite fibm^dr chiysottle fibfers, on^dothefband, composure with titanium dioxide increased lung retention ofthe fibers (as compared to exposure to clr^6tlle'|ibnb) lungfetebtiontoffibers. This indlbated that this Sndy suggests that nbh-fibrbiis paffieltt ebuld' affectTsber t ,^`ietestibn Cliiratddmdt^^bKSfi^: be:acjaa()w^gl:thaf&ie expisure cOTiceiitiaiSons used ha " r ttie Studyaiief hbtrfefevaii) fo"^|cu:edvS!E>UifeirtaleqMgdres. !li' '- ~v \ * ' \ ", . V? ` i ;'J sorted* Influence 1 ' i^flus'fe^dby&mpatfogiM^s^riii}Ses'fir6iiiiafe'e3ipbd:1fof3 tdbitliii to'aSfidipbous silica **5i^atlSvar "M,y atm^liOTt SfficiiWasaear sti^esS-liSShe amorphous silica ') impaired capacity to clear fibers deposited in the lung. These populations included people "'a'; cdS^&DS-:<e.^|3risnary cfla^:^s&cdcaR^'ci^l(fc'fin5^ls^1ittiiiadi^\Ei^ affect can compared to cumulative exposure estimates, were more predicfrire dfradioTogica] changes in the |un^s .ofworkers ,%t vermiculite mines and mills (Sebastien et |). 1988); Though ' /MeseaiiA dt&'fi|di^^^^t il&ijgBfinto r 'asb&i<S etqp^fe'/fo^T^'elisdTndiCated thafH^lementing'S^uttM'siiSnple^study has a potential drawback. While smokers can produce voluntary sputam-sampfes relatively ., easily, np^smokfis offca.cannpt.lijduced sptrly^||roples,^nJhe.cjtllected.from non-' <?V ;:imokers,to chractenre past.exposure, and hr*------ *---------- -* for 2-7 HWBUI0009576 this purpose. Beth of these sampling techniques.are inyasiye andiquije,iiifojined consent, and have a consistently better yield than simple sputum collection. More than 50 such studies conducted in North America, Europe, and Japan hSve already been published. 23 . Migration of Fibers Deposited In the Lung The third charge question asked the panelists: "What types of migration are expected within die body for less-than-5-pm fibers?" Both in their premeeting comments and during & expert panel review meeting, the panelists offered various perspectives on how fibers of different lengths . jBigpateyrithm the. lung and from the lung to other organs. One panelist, for example, indicated t||kt^ters v^ith diameters less than 0.5 pm can penetrate through lung epithelia and be transported through lymph channels to lymph nodes, blood, and distent organs. However, most of -.v vY*-..,J. - ii-" the discussion focused on die extent to which small fibers translocate Into the pleura. Three reviewers' perspectives on this matter follow: ; f,j .... c ; tWi'.tV. . ji-'li s *r 5-5 iVsmo;:. ; fi%- "< - .Y: , ; ;v;'-..ciit-aoe C-. Fust, one panelist indicated that several researchers have attempted to characterize the IJ'v; -> ' - - Y c.~:> *y -hr L.&'it Y .0:; distribution of asbestos fibers in samples of human pleura. Although it has been reported that 3Vjr-V; ,v*(5i /!.?.?.? p . tr...-; I'yU, .-`wj "fi--s'ro-.-' 'S'r'H-''-'"'- onjlg short chr^sotile fibers (average length <0.2 pm) translocate to the pleura, this panelist found these studies to Be of questionable quality because they lacked matched controls or sampled .tissue (such as tumors) other than the pleura. This panelist then reviewed two preliminary studies offiber translocation, one in humans (Boutin et al. 1996) and the other in goats (Dumortier et al. 2002), which were based on more robust methods using controls. He noted that one study, found that 22.5,%.of fibers detected in the pleura were longer than 5 pm and that the pleural samples had iar greater amounts ofamphibole asbestos fibers than chiysotile asbdstos fibers (see Dr. Case's premeeting comments in Appendix B). The studies did hot examine how fibers > ..-j-ifb ~oJ -53?fis vih::-'.,x;f<:[. translocate to the pleura, though the ` ' J~i` ~ important role.4 ) in -.v o: zs-mos?!?' . r.<; .iJ.r-:wA,pahelistratsQ.noted ibat lymphatie.;UW}spoq .has been dappimiated to occur.iftlabqra.tOQf studies of it'dogs thatiwensi<lqsed.^ift:.ap05ite.asbtos by,.intabrqncfi!ai in^llati^ (pber^dfstqr et. of i.'pdst-jiqdali.lynjpb collectjsdjifcqrn, die right lymph duct found.fihets only.ofshorter f$fnen$iqqsrttM|iu9u^mtengdi offiterdetected was 9 iun> airfl the maximum diameter i**s 0.5 pm. :: .> 2-8 HWBUI0009577 The auffams atthse studies`'Hj^otfeesized that the translocated fibers might contribute to Second, another panelist summarized the findings from a study ofrats exposed via inhalation to kaolin-based refractory ceramic fibers with geometric mean length' of4.$ pm (Gelz&chter cfaL 1990). The study reported that the fete of the fibers depended on fiber length: fibers in the pleural tissue 32 days1 after exposure had a geometric mean length of 1.5 pm and geometric mean ' /.rv-.-r: : ik ,v~ ftpjo'.i :M./ '> diameter of0.09 pm, while fibers in the parenchymal tissue were much larger with geombtnc mean length of 5 pm and geometric mean diameter of 0.3 pm. Thus, the study indicates that very ihm fibers smaller than 5 pm-~fibers thtt would not be counted by codventidhai phase contrast `V-' 'r.r:<i r-;; :.i-. 'if-};- : / /iSiw .iiU microscopy (PCM) asbiStos sampling methods--are capable oftranslocating to me pleural tissue 1^. Lockey*s premeeting comments in Appendix B). Thind, a panelist reviewed findings ofa rat inhalation study that invesfigated vfcttief' co-exposure to non-fibrous particles affects translocation of fibers to die pleura (Davis et aL )K:` iJTpV feqa- a!;--. 1991). The study found more amosite asbestos fibers translocated to the pleura In. rats that were *! ,V:v .. *' ;>:r,'^ co-exposed to non-fibrous particles (quartz or titanium dioxide), as compared to rats that were /'& 0- .-.'kv-Cy /sssr l ' L yh,, sp&ig-r-i:..:'$$& sBva'nfoiKuk Vfcr exposed to amosite asbestos alone. The panelist noted, however, that the exposure doses of titanium dioxide (10 mg/m3) might have overloaded the rat lungs and Impaired alveolar 'f Jj.rpwy: .tr::V.q r.-syi i;i. ;u -..4!. macrophage clearance processes. If the observed fiber translocation to the pleura was caused by feitei <f- .-h* (&>' it JO tr r. v.d0 these overload conditions, the relevance of this study to environmental exposures is questionable. wfr- -- -Jotter <%A--s>nm v;r - d: 'r-A ' The panelists noted that the extent to which fibers translocate to the pleura is not fully understood, but is likely an kappitant consideration when evaluating pleural plaques, diffuse pleural thickening, and mesothelioma. For instance, if fibers must actually inter the pleura for .C':-i yi::]' -Jyk -fj-s ?->*; tyjfzuifiik these outeomes to occur (a hypothesis that has not been verified), then understanding fiber 'picurt,esp&ialiyifditm peiidimtioBisIwjilired Mifieiohg fibers:t transport for shorter fibeis). '-1 *' ' ' 'v 2-9 ffiepl&fia!(as'eoiripared'i j HWBUI0009578 translocation into .the pleura is critical, If, on.the other hand,iibers localized.toward.the lung periphery beneath the pleura ban cause disease, perhaps through Chemical mediators that cross into the pleural,space, then translocation of fiber? is less importamhjtherefore, without a more detailed i the significance offiber translocation into the pleura is not fully known. The panelists revisited fiber trarislocatiorfissues'When discussing the role of fiber length. Ifany*-in causing-pleura! : 5' - abnormalities. -- . ' ' _,v ... .... . ..... ^ t --.-sorr,V.. ...... . JL4 Open-Discussjion Among;Pa|ielistoi ,v .,* . h. . ;. T' 'f< ' s':..:; .-.a. /: "./ij H'v :`lj- - .'> : I O-.jll- .'jtTj'h: biW.vb-:- >; bT?*: , After.snnjimariziqg thepaaeKsts.' rjcgpqnsesjto the three charge ^ugstions, the.discussion leaders ihVjfed additional topics fel^ahfto phySiologiGilfate of :3drt-'-'!;--v. :-X l f.M.-. si:i f: uM.(^.'fib.era^ThejP^elists-rai|efijt|e/^ilqwjngissues:..-. .....u:.,., ^axu-.^id iiS-'v *U.; ' - i- .q sdT .ah: ':a: v:.1 :,T V'tOt: .7.-:7ye-ri'SSsiL;.: .li'siaori i'i ..-rdvAvohtti <;%> . Terminology:fibers orparticles? One panelist had reseraatipns^^u^gill|^s^iuctures ) with lengths less than 5 pm fibers. He explained that mineridogists, geologists, and health . scientists geggraljydp not fibers, |jgardless.qfJh^aspect. ;. ; ratio; sjich particies.,This ^w^Uirt.np^&at br the ., - ;:;0<xupatjional.Saie^ smaller . }_ . ..than 5 p^a^pairicl|s notfOtheryrise ^|^iate4 rathefAan'^ jB[!^^]fpr.%^n.kid other re^qn%(s^^.iCsis.e,spj^eeting^pnraente,inAB|^nc&^),.fiii|.pageitfi^aconceras ;;xu. * .ai^jjtjhe .ternunology/^^Ei^ less . -Jhan refers tostructufes less tbap,5pig,as fibers. h?-**..'-;; &-Sdh^m%rspq-:tsSrsid!"b: ,.: .Kio^'b" - ii&oSn:has n.n c . - :. * ii itypprmncetpfiltg . '.b.yKrh!'::v->/i:vel^yijny?lxS:i^!^tign^jr^.Mg^^i^^hti.on;pffii^.4iz^^^j^e^''q^e^oiiedtl!e' ' "'. utility of focusing exch||p^toD.^h^4e^ij^a^$;!^|Iin.')j^..^ct|^i^le:^ concern, be showed a graph depicting the fiber size distribution (in terins ofi^igth and diameter) in an ambient air sample collected at Libby. The graph showed that a dear majority offibeis i>A . \ :2-10 / ') HWBUI0009579 were less thha-5 pitL ks is ofteii bbserved in bccufiatibiial and environmental exposure situations*.?The saaiple alsq;mcluded jhough in considerably smaller amounts than the short fibers. In such cases, the panelist cautioned about focusingekeluslvely&ri fibers smaller ; more to overall toxicity. To illustrate this issue; furthers the paadistp^esented duta qn.fhe.disfributipn of fiber lengths measured in surgical lung tissue samples from six miners and four cement plant workers who were exposed to asbestos fibers (primarily chrysotile) and non-aSbesto^ fibers (Case et al. 2002a). The men were hospitalized with various lung diseases, which were mostly not related to their asbestos exposures. In these individuals, the majority (71 %, by fiber count) oflung-retained chrysotileasbestos fiijers:wOre shorterthan 5 -pm, with lesser amounts (25%) ofchrysotile asbestos fibers between 5 and 20 pm, and even lesser amounts (4%) ofchrysotile asbestos fibers longer than 20 pm (Case et al. 2002a). A - - ^s:grea^.npmber offib^s.shorter thmiS.pia (5^%).^d,apaejpjiger)tt^.:2_0..prBu:Based,pB these results^ this panelist reiterated drat chaiacterfztag how toxicity varies with fiber length is critical, because retainsiil ifcses;c;v^'SI>nillffi^bl^Ttotw^QdMei^f fibfef^ length intervals. The panelists revisited this topic when discussing whether a critical fiber length exists below which adverse health effects from environmental exposures would be A . -- ;in trends .. ; -X 9MK.ku6 (winfcKiteiaujd riclitSfiteySre^inclilied OTbngtte fiberSWtS^esMripleS.?E>r.MiUer noted feat some Libby rest&SlS^fiovfefe ri&P&%rfp&ti^alljr to'kSbiistok hM who: had of the - - 6 During this discussion, one panelist cautioned about distinguishing environmental exposures from occupational exposures and instead encouraged scientists to focus on the exposure dose, regardless of whether it was experienced in an occupational or environmental setting. To illustrate this concern, be noted that some ' "environmental exposures," such as those experienced by Libby residents, might exceed "occupational" exposures in well-regulated work places. 2-11 } HWBUI0009580 *i Dose metric issuesj The panelists briefly-discussed how the aivailabledose metrics--mass, number, and surface area of fibers^rcorrelate with toxicity. A panelist npteAthat one study V (TimbibU et aL 1988) reported that surfacerarea correlated best with.puhnpnary fibrosis sedfesaM therefore migfatbe.the best dose; metric for that endpoint; Thi&panelist said this vfiiiding iscpbSistentwith toxicologic studiesofjaon-fibrous particles, yrhjcbalsp indicate 'that stiiface`'area correlates better with pulmonary fibrosis .than do other,dose metrics. . Another panelist questioned whether,surfiice area ofretained.fibefSji&aa appropriate dose metric, noting that such a selection implies that shortfibers,(Le., fibers less than 5 pin in length), if inhaled in substantial quantities, can be equally toxic as very long fibers. This !issuewasnotresolved, but a panelistmoted-that surface area pfifihei$:might be more s v *' predictive ofcertain endpoints^e-g., lung fibrdsis);,whileptherdosemetrics may correlate . rbetter withcarcinogeeic-en(%)oinfe. . r. .... n >':. m : Research needs: While discussingdbe physiologicabfafc of fibers m^the lung, the panelists identified several research?needs:.C>ne pahelist;for..exai|}ple, suggested,that a laboratory study comparing dosimetry of fibers less than 5 pin to that ofnon-fibrous particles less a.' 'jdjan^|um'eoMd>proOTde insighteihtoimg.depQsiti0n.and.clea^ce,,of;Shpjtter';gf)ers. ! Anotbefepanelist advcated!researeh;thafeeharaptierizes dosimetry fpta series;Of;fiber U*3.:*.p -sfengfinlnterval^EaftiM v.v -i ,len^hv(i.e; 5ipm)iibecausejpeople.areiultiniately adii -? Jeagfiis. ^ae^anelisbsugge^edthatstudies o^tdet&eineJ.evaaoeIpf^^pMhle f.-tty >)Sjj^julalioaS,*'bid!flither panelists indicated thatijsseaich'pa sns^jtiblepopulatipns should ./`h-r;. >ybe!c0hdttEtedafterJceystadiesonhep3thyipfipM!htiotishave:be3|completed.;Jh.e:panelists n -discussed ad#tional research needsjatef inltie.nie^ting (see 5pption3-.5)- ' .-''Or;.; y.ic- : . .. a ; ' r; -p. 1- V-bjrvC-'. .'.,4, 2.5 Observer Comments and Ensuing Discussions i^pitsH finished'adidressihg the firstiopib ^a, ofeerve|S were invited to provide conirheh^'The.'p|fieIists:were not requi^ to re|pond;.idtho;0!bservaFooiTsinents. However, some continents ied to 1urtB'df'&sa&idn;an^ftg'.tfi^paiseii^tsj,'as dobtiniehted here; The observer ;s ...: .v**: -:hv Comment I: David Bernstein, consultant in toxicology Dr. Bernstein presented findings from a chronic inhalation study that investigated the ' .mfluericfe of fiberlength-'and bitjpersisteneeioiitbxiciiyiin' rats. Jbe^tudy was conducted, -.forithe European Gdntfiussibn, butfindingsifromitho stody^ hayepot-beeh reported in the ..peer*feviewed.Siterature,and.awritten summary;oftfie study,was notproyided.to the expert , .panelists. Df. Bernstein indicated that this study found that long fibers were ,more 2-12 HWBUI0009581 i biopersistent than short fibers: He further noted that exposure, to fibers tip to 2Q pm long -J wersfoundto be-uacorfelatedfimth toxicrespoose.and onlythosefiberslongerthan 20 j correlated^wfth toxicity, These findings were reportedly derivedjby<cpmparing a ' - *t63tlc;end^pbirit'at'24 monthsfoUowmg. exposure to the^istribution offibia^eiigtlis ' '`: vfetaified-ilt fife lats^lungsdThe toxicendpoint considered was eoHagendeppsition at '-bmnchoalv'eblaPjoiie'fiohj^a precursor toijjulmona^'fibrosis. Dr. Bernstein elaimed that ,v t &g:pau'elfstt^'iriw^offllhiSiStudy^siiadings to^^fisake definitive. statements;on the n ;Mxitify'6ffilSersshdrter--ffiah^S'pint:^'.' . A'-.- . . :ii v* oft : - -i,;iPanellstS'Dbcussln::When.disciissiagtiMsstudyj'onepapelist.askedif !]:i'prefefghtiai'd^posidon oflong fibers is .exported to ckxs atihebrohehiiaf-alveolar junctions, and Dr. Bernstein said yes. This panelist noted that.theappacgnt correlation between fibersize and toxicity might simply result from studying an :c^-? v- S;; ^. .v y. CTdpouit^wh& short fibers do .nbt prejferemtiaHy deposit-AnotMer-panelist 0 r, ..encdtKag^DriBerfisteih.ahdJMs.coUeagues'to^Mbfishthese^t^f>; br-',-Si'.-rLvt:w: :uf: 0/ ?;?. ~sS- j yyqwc-:- vsi.j; -i',' ":rPBerilsteiii a!s0:pt'es!mted'data fr6m an-animal study otrbiopersistence. ofiGhiysotile !'%b^mmed-m'BtaziL'He explainedtbatdhrysotilefibers-haveasoine'phatiiiiii'que atomsrare in (die fiber surfe^ih-amphibole f ;-`^Mfe,:bhfiifrGtfi#h'aiiidt~tir8se 4tote aifc more'-conq^tratediritona! to-thefibef, away tStMiique^striiotore# Dr.B^jteisarguedf4heolHytile .fibers He reitorted.:thatilpng'ClHysdfile^btSii(!?^20 pin) amfirit&fibersof similar length have a:J^4ife- OT468 daysKHe also showed a series ofimages depictingthe fate of different length fibers in the lung as a function ofdays following exposure.. Dr. Bernstein did not provide a reference for the data he presented. , 'UJK:/:Y.v' > --r:.-. w= '^o2= .>- V.',-. Panelists' Discussion: One panelist took exception to these studies, noting that his colleagues have published a study (Finkelstein and Dufiense 1999) indicating Sb; -. tfjatsc^sod|e fibers, lo^gfr than, 10.pm have ai^stiraated halfrlifi; of8.gearg in ibe lungs of Canadian ifiinfersrFur&f^ltS hdtba dSda study ofSouth Caroluri'an &:; .. ,;-sv texfiid^oikeis!fe<xpb^ito.c!ySotil!c!-fibersfCe:et^::200@..){a.ls.dj.St.ip.p0.rt.s.?3-gv? r tm.* 1 the : i' wddke^-cumulativ^k^ltififfkogg^trng-foat foe^%hgerifibeis'are-more ;c . ' .V persistent in the lungs of occupationally exposed individuals than Dr. Bernstein's data imply. 12: Jay Ttirim, Sciences International, Inc. ^^foe;|i^eKsts'to;cofisideKthe:fiiidihgspf two studies. First, he y'H ='^referifed thie^aneliStl'tdl'pubticatiOQ (Berman et aLrl99S)'tbat re-feyaluated data from iki*;*3' '?-'`;,pieVi6tis''ldbdiSit6ryatittoal experiiftebts in rato. TWs:studyreported:that 99.7%oftbe potency- for rotsddielidma 'waS due to asbestos fibers:longer 'than dO'jitii, with only 0.3% :i-i3 "t / s HWBUI0009582 of the potency attributed to fibers shorter than 40 pm. Mr.Turim suggested that the : ' ; panelists consider these findings whearcommenting on the carcinogewcity^ftfshort fibers. Sec^di^MriJTtsiim reviewedra recent study (Brown et aL 200P) jn; which two; groins of fc .rats inhaled formulations ofdifferent refractory ceramic fibstyj(RCFl. an^RQFla). The f' fiber formulations wore reported as:baying approximatelyfoe saine.numberof long fibers, -bhtfofe RGFI formulation containsrinuch more non-fibrous-particles thandoesfoe RCFla formulation. In the study, the rats were exposed for 3 weeks (6 hours per dayj-5 days per week), and were followed up for 1 year after exposure ceased. Mr. Turim noted that the 1 lutig retention of long fibers did not differ between the two'exposure groups, even though th&Stiidy authors reported that macrophage clearance processes were severely impaired in the hits exposed to R.CF1, dueio lung overload conditions. Mr. Tutim also indicated that l~- 'fob kuifyprovideseviitence.:tMatRGF (and SWs, in general) behave differently from ' ^a^^ds'fibers;inifrie.friag;;henause ftie short RCF fibers werqlmgelynmjoved despite the sn Fimpaired-macrophage .activity#Finallyi-feecause fo%study fbtmd more persistent ^inflammatory. response- as gauged.-by bipachoalyeplar layage (BAL), analysis, in the rats -iS''doed witfrfoe RCEI the presence of >.x npt-fibrous.particles must be considered whien-.eya!uafoigfoe toxicity ofSVFs. * .* _ v v.'* v\. ` Tv- ' ' : \U''`"i-,- os - - -' i: /.Panelists8 I>isissidns One panelist addressed this ifopnment, noting that some b.- `: -q; r?; . k aspects-.ofthe RCF-study-tyereinot entirely.olear to; hinx,Ffly;instaiice, be did not could be similarly effective in the two groups, when macrophage activity was - - . v severely impamed only in the.rats ifosedwifo'RCFJa.FffltiJ^ho noted that the i r v . .'diffdm^-tntoxicity!botw.!SenROFiandRCF4.a.'WCTeiag|uallyreiatiyelyminor, -). based on.Usiinterpratetionpfithe'BALdata and foeJn^op^glpgy results. ::Moi^ver,fotepaneli^indiqated;.tiiata:follo!W.-:tiP,stody;.l}y\fti,e;Samegrotqhas found the aon-fibrous FGF particles tp be .o.fhigh toxicity ^5eilmann et al. 2002; Brown et al. 2002). ff ' v. - -v *- Comment 3: Jenna Orkln, 911 Environmental Action Concern ".hz f'>^/(Xldn'ykeditBe!paafclistedo.;S9ijhiitedtbtt'ehyiranmental:cbBtamin!^pi|;|^fdtingfiom s WTG%oilapse Whifcfcble^cSnraminationdQ^^windtowaFdl^^dQ^mtoW(n,Biobklyo,. fMV-w^elrefshe-ihesi^bOc^mid abbui*rtgding:'ejj^sureitp:)^e.'dus^ ^r!^n;-indicated %at-sherbcfentiy;ihad a! ite^ebsartip.le from beneath ,a.window in^ her hQU&e.|inalyzsed for i - Vii - -'fitef contamination tisihg:'ultraspnication;: She liidi<^^^ed|^tis3Ea^lx|i^.te^D^quie can ;i.T>`iHfget^ab0Ut'lOO times Sirore^bestos.fibersthaiycanbe.fouhdby;ASTM;NficraVac J i Js.'ttfethbdsiMs.' Oddn'hoted.that;;ejfperts haye repotted that,..for ASTM Idtcrp^ac samples, if :d,O00.-sructi!ies persquare eeit?iroeipr;iscpnsidered typical forna^l homesand 10,000 structures per square centimeter typical for urban homes. However, she said that experts will not specify* safe leyel ofsttpefores pleasured,|>y ultrasonication. HWBUI0009583 Ms. Orion indicated that EMSL Analytical analyzed the carpet sample from, her home and found "80,000 structures per square centimeter of asbestos;" Seven chiysotile fibers were in the sample, including five long fibers. She indicated that the ultrasonication instrumentation eventually clogged, which she was told might mean that the, contamination levels in the sample could not be measured because they were higher than the measurement sensitivity. Ms. Orkin asked ifthe panelists would comment on the data she presented, sucfras the exposure levels she and her family members might have experienced. ; ' . -; Panelists' Discussion: Three panelists and anEPA observer-responded to the comment. One panelist noted that regulatory agencies have* not established "safe limits" for measurements ofasbestos fibers on fabrics. This, panelist acknowledged that be was unfamiliar with the measurement method identified in the comment, but be did question why any sampling or analytical instrument would clog when analjmng.a sample with only seven chiysotile fibers. Another panelist said the kejrissue for thii scenario is characterizing the inhalation exposure, but he notedthat noone has established howto estimate airborne exposure levels from asbestos levels in isolated carpet samples. Finally; noting that amphibole minerals make up 7% ofthe Earth's crust, a dun! reviewer suggested comparing the.sampfing results from.1the Brooklyn residence to measurements using identical methods in other locations that,were not impacted by-WTGdast Dr. Miller (EPA) indicated that EPA struggles with issues like those raised in the . : ; comment at many sites: Wbai levels can be considered safe in ternes? What fibers should oneeount when'establishing these levels?.When should regulatory : agencies recommend ahatemeot? He acknowledged that these decisions are beyond EPA's current regulatory guidelines. Comment 4: Bertram Price, Price Associates, Inc. Dr. Price's comment addressed asbestosis in Libby, Montana--a topic the panelists had ; questions! about during their earlier discussions. Dr.'Priee indicated thatATSDR's recent . . * ,/ stiidy ofM>byresidents: identified 12.-cases-of asbestosis: 1.1 among foraSermine workers, - TthafSiniiy meinberof a-former thine woricer. He said these'vfinditig? illustrate the - ''>impact ofdose on asbestosis,:andhe cautioned against attempting to distinguish =: ^ environmental exposures from occupational exposures, Commenting on .the. influence of -/ fiberlength; Dr: Price noted that researchers have established a dose-response gradient fits:- between exposures to long asbestos fibets-and asbestosis,-,thqugjb he acknowledged that. v.' the past studies used measurement techniques that did notcount fibers shorter than 5 pm. Panelists' Discussions:-No panelists addressed this comment. 2-15 ) ) ,.) HWBUI0009584 Comment 5: Suresh Mooigavkar, University of Washington Dr. Mooigavkar's comments also addressed asbestos-related disease among residents in Libby, Montana. Dr. Mooigavkar noted that ATSDR has conducted two epidemiologic studies on Libby residents--the second was necessary after the agency realized that some dehtfa certificate data were inadvertently omitted from the initial report He indicated that the second, study reported that lung cancer mortality in Libby was higher than expected when compared to the state of Montana and the United States, while the first study found no excess. Regarding asbestosis. Dr. Mooigavkar summarized the available data on asbestosis cases (see Dr. Price's comment, above), and noted that asbestosis is linked to the most highly exposed individuals, regardless of whether their exposures were environmental or occupational. Dr. Mooigavkar then commented on results from multiple mortality studies published on occupational cohorts ofLibby mine workers (Amandus and Wheeler 1987; McDonald et aL i986,; 2002). Hefound no indication that asbestos from the Libtty mines is more toxic than is predicted from cancer risk calculations using asbestos unit risk data fromEPA's IntegratedRisk lufonnatidn System. Dr. Mooigavkar mentioned this to question the suggestion among the panelists that Libby asbestos is more toxic than asbestos from;other sites (see Section 3). In fact. Dr. Mooigavkar noted, radiological examinations documented in the previous mortality studies found no evidence (based tin prevalence Of lung abnormalities) that Libby asbestos poses a greater health risk than asbestos from other sites. Panelists' Discussions: One panelist indicated that he agreed with the comment, in terms of lung cancer outcomes and lung parenchyma abnormalities, but he rioted that mesothelioma cancer risks may in fact be uniquely higher at LSBby; Specifically, the risk of developing mesothelioma' among asbestos miners in, Libby, as gauged by the proportional mortality ratio (PMR), is greater than that experienced by crocidolite asbestos miners in South Africa and Australia (see Section 3.1.1 fora more detailed summary of this argument). ' 'Dir; Mtibigavkar questioned this response, arg&ftig that the PMR is not a good metric to \ usey.Hein^ expect to see .an elevated;PMR tfthe Libby.eobort had a strong "healthy worker effect" Panelists' Discussions: The panelist who addressed this issue agreed with this response, but noted that there is no evidence of a "healthy worker effect" among Libby miners, as demonstrated by the large number ofaccidental deaths in the cohort This panelist defended use of the PMR for mesothelioma because it is a rare disease, and use of other cancer risk metrics (e.g., the standardized mortality ratio) might not be appropriate. 2-16 HWBUI0009585 3.0 Comments on Topic 2: Health Effects of Asbestos and SVF Less Than 5 Micrometers . in Length , This section summarizes the panelists' discussions on the role of fiber length in health effects from asbestos and SVF fibers; The sheeting agenda (see Appendix D) lists the specific topics that the panelists addressed and identifies the discussion leaders for these topics. This section organizes the panelists* comments as follows: carichr effects (Section 311), noncancer effects (Section 3.2), mechanisms of toxicity (Section 3.3), general comments and interpretations (Section 3.4), and recommended research (Section 3.5). Section 3.6 summarizes observer comments made after the panelists completed their discussions. Seine panelists: submitted post- meeting commeatsdo summarize their finding. These aie indudod'ih Appendix E fcir the following topics: review of epidennoiogic. data (see Dr. lock^'s comments), review of labbratoiy ahimal studies (see Dr. McConnell's comments), and review ofmechanistic studies (see Dr. Mossm^'s and Dr..Wallace's cpnuBepts), . , . . . ... : When evaluating health effects, panelists were asked to review findings from key studies that examuied the role of fiber length en toxicity, whether in'vivo or in vitro; Accordingly, this section should not be viewed a$. a literature reyiew ofalt toxicity studies fiijr asbestos and SVF; rather, it documents results from key studies that examined impacts, of fiber length. Although the panelists focused their initial discussions on fiber length, several panelists stressed that lengthis not the only factor a^tip^.(lber^^ity.ainhew.pap^i9>i%ct<^j^^4bxicity'is 'ihlhef: afeomplex function ofthfe fiberdosfc, dimensions; idd dufabiiity;-as has been widely documented in the scientific literature. 3-1 HWBUI0009586 3.1 Cancer Effects This section summarizes the panelists' comments on the role of fiber length on cancer effects. The section is organized into three different types of studies: human cancer mortality studies (Section 3.1.1), studies oflung-retained fibers in humans (Section 3.1.2), and laboratory animal studies (Section 3.1.3). Within each section, comments are organized by type of fiber (asbestos or SVF) and type of cancer (lung cancer and mesothelioma). 3.1.1 Data from Cancer Mortality Studies The panelists' comments on cancer mortality studies from occupational cohorts fptlow: Asbestos. Oae:paae\ist. indicated that no studies have.pyaluated cancer outcomes associated wife fibers.shorter than 5. pm,,because.no occupational cohort is exposed ; ^exclusively to such fibers. Fpr insights, into carcinogenicity of the shbri fibers, he reviewed findings reported for.two occupational cohorts that were exposed predominantly (though not exclusively) to .short asbestiform minerals: The panelist first reviewed' a study ofworkers at reserve mine,deposits, ib Minnesota (Higgins et al. 1983). The workers at this site were exposed to cummingtonlte-gruneritei a, mineral related to amosite, and toe vast majority of fibers were reportedly less-than 10. pur in length. The study found no increase in overall mortality or mortality from respiratory cancers, but the panelist indicated that toe average latency for the cohort was 14.7 years after initial exposure, with a maximum of 24.6.years, or & relatively short latency for development of cancer. . :: *.. ;;: yiSgcpad, mine workers in South Dakota who .: Mlsp.yiere^e^pp^/to^eyn^ii^.oni.te-grmente.gsbestifijmj material. He indicated 's-.-- .vis -.. . toat'an :initial;stody >f,Lhi cbhoi^ ((Qiilam.et.ai- 1976) found increased mortality firpm mahgnsmt respuatpry disease among wortcers with at least > years or - ffltposmftiA follow-up study of this same cohort (McDonald pt al. 1978), which considered wprkersjvhp,had worked fpr 21 years or longer, found no such increase, but did report increased risks of silicosis and tuberculosis. Average exposure concentrations for this site were 4.82 (0.68) fibers per cubic centimeter, with 94% of airborne fibers being less than 5 pm in length. 3-2 HWBUI0009587 This panelist indicated that these two studies were the closest approximation he could find to occupational cohorts exposed only to fibers shorter than 5 pm, and neither showed evidence of increased cancer mortality. He advocated follow-up studies of these cohorts in view of the passage of more than 20 years since the original publications to investigate carcinogenicity ofshort fibers more fully. During this discussion, one panelist reviewed cancer mortality data published in two studies for an occupational cohort ofLibby miners (McDonald et aL 1986,2002). These studies considered 406 men who worked in the mine for at least I month prior to 1963; the more recent study, therefore, considers an average latency ofperiod ofmore than 30 years from first exposure. This panelist noted that both studies reported elevated mortality rates for lung cancer, mesothelioma, and non-malignant respiratory disease (including asbestosis7). Ofparticular note, the panelist indicated that the more recent follow-up study (McDonald et al. 2002) suggests a PMR for mesothelioma of 6.7%--otherwise stated, 1 out ofevery 15 deaths identified in the follow-up study was from mesothelioma He found this PMR; significant be*&use:il is'hlgher than those observed among most othercohorts studied, including crocidolite miners in South Africa and Australia. SVF. One panelist reviewed cancermortality studies ofoccupational cohorts exposed to SVFs, ihciudihg glass fibers, mineral wool, and RCFs, The panelist first noted that no . staffiei havb heeh conducted oh p6cupatidhM*hohbrts expthied exclusively to' fibers less toah 5 hni lofigi agiin because ho hobbits appeal to be expo^J only to'Shortffibers. However, he noted that cancer mortality at fiber glassand mineral wool production facilities.has been extensively studied, both in the United States and Europe. He sum.m-"ac rizedthese studies fdfd:.i...rent, mact-erial^: . For fiber glass, thepatfeiist noted dial the studies did not find increases in respiratory cancer to ire related to fiber glass exposures. For rock wool and slag wool, the panelist indicated that studies ofproduction facilities in the United States found nb evidence of increased risk for respiratory cancer. At production facilities in Europe, on the other hand, initial studies have deihonsteted fnciras'&ih 'rhspiratbry.caaceh; but ribcleaHrifofeiatioa to indicate 'was^jtticTftchlly related to fiberexposure. A. siibsequoat Case4f6ntf6i ^ttidy itfdii^t^ rio' relatidnship beWeeri cumulative rock or slag wool exporiitoiancl lung caricrir pCjaerbeiiri etal. 2002); The Intejnational . Agency for Research ori Cancer (1ARC) aultlibfs'did not conclude that the increased cahcn was. related to the exporitfes to rock orstag wool.1 1 One panelist, when reviewing a draft ofthis report, indicated that death certificate data typically use a single code for alt non-malignant respiratory disease. He added that asbestosis probably accounts for a minority of these deaths when compared to chronic obstructive lung disease. 3-3 J HWBUI0009588  For RCF, which are more durable Fibers than the other SVFs, the panelist indicated that no cancer mortality data have been published for occupational cohorts exposed to RCF. This panelist noted that a recent study of a relatively small cohort ofplant production workers has not demonstrated increased respiratory cancer risk for RCF, nor any identified mesothelioma, but he acknowledged that the study had limited statistical power for detecting an increased risk. Results from this study have been accepted for publication in a peer-reviewed publication (Lemasters etal. 2002). The panelist who summarized these results also specifically noted that there is no indication ofa relationship between exposure to SVFs and mesothelioma. Though a small number 6fmesotheliomas have been reported for workers at SVF manufacturing plants, these cases have since been explained by other factors {e.g. probable prior exposure to asbestos, incdriect diagnoses). 3.1.2 Dafa from Human Studies of Lung-Retained Fibers (Cancer) Additional insights on the influence of fiber length on cancer outcomes was presented for studies that analyzed the amounts and sizes of fibers retained in the human Iung.In these studies, lung- retained fiber is used to characterize exposure. The panelists identified limitations associated with such studies, most notably that the measurements of lung-detained fibers (typically at autopsy) are static and do not characterize When exposure occurred or temporal variations in exposure. Moreover, because lung-retained fibers can break or partially dissolve after exposure, it is possible that.the length distribution of fibers observed after death is different from the length distribution offibers in the original exposures. The panelists proyided the following comments on available studies of lungr-rctained fibers: ->* ' ---V.-- ' - - - - t . ' .' . .. - -. r. HI General comments. One panelist provided general comments on fiber accumulation and human A'seise^ Eu^t, the panelist indicated ihat people are exposed to'fibers-ofvarying lea^h, .with shorter fibers, generally accounting for the majority of Exposure (by fiber count); % similar pattem^-a majority of in the . lung-retenti'oa^hidies. Second, because asbestos fi|bjs'wi& widely valuing lengths are detected in lung tissue samples from all populations,..this panelist concluded that the human lung, under continuing exposure conditions, is not Capable ofcompletely clearing fibers ofany length to background levels--a finding that is not replicated in inhalation 3-4 HWBUI0009589 studies conducted in rats.8 He demonstrated lung accumulation by displaying data from multiple studies (e.g., Sebastien et al. 1980; Case et aL 2000), which showed that all types of asbestos fibers (including long chrysotile fibers) accumulate in the lung with Cumulative exposure. m Meiolheiioma. The panelists then commented on three case-control studies that examined the distribution of fiber, lengths in people who died from mesothelioma (and most with matched controls). All three studies showed that risk of mesothelioma was considerably higher for individuals with larger amounts of long fibers retained in their lungs; * The first study (McDonald et al. 1989) examined lung tissues from 78 Canadian men and women who died of mesothelioma, as well as 78 lung tissues from age-, sex-; and hospital-matched controls. The lung samples were from pathologists* stock, without information on what parts ofthe lung the samples were collected from. Relative risk for developing mesothelioma was reported for different fiber types and lengths (<8 pm and >8 pm). "Hie study found that the risk of mesothelioma was significantly related to concentrations of amphibole fibers longer than 8 pin and that fibers shorter than 8 pra accounted for none of the : cancer risk. The scxabhd study (Rogers eta'i. 1991.) eximined lung tissues fibm Austmltans > Who.diedof best fitting adilwiidaifiwjgd;^. model/' the.stody reported that mesothelioma risk was greatest for crocidolite asbestos nbeis'lbhger than 1 6 pm,^ Followed bjt amosite asbestos fibersioager than 10 pm,-andthen by chrysotile fibeisless than 10 pnvThe authors suspected thpt the relative risk for chrysotile fibers less than 10 pm resulted from longer fibers brewing into shorter fibers. ..... :: The third.stpdy.(R6delsperger et al. 1999) evaluatetl lung tissue samples from 66 German individuals who died from mesotbeiioma and 66 matched controls. The study reported that ".,,a clear dose-response relationship up to an .odds ratio of 99% has been demonstrated for the lung tissue concentration oftotal amphibole fibers longer than 5 pm/* The study providSd ffew details on the Cancer risk r' associated with short fibers. ` ,* .^ungvapcjsr.'A panelist lodicafed that tip iuhg-iete'ntibn studies in hurpaiisliaye attalipted : to exai^e rektitMahips between the 'length distribution ofretain^ asbestos fibers and TM? panelist noted that mah| studies' have.pfejpprted the . tgti.i'whttenfratiqn or asbestos fibersTor. lungcanceirIn lung samples/biit boiae ofthese t... . evaiyated'.me rbi'ep| nbeilength: ' 8 When reviewing a draft ofthis report, another panelist indicated that animal studies have found that animals are also not capable of completely clearing fibers ofall lengths to background levels. 3-5 '"3 j HWBUI0009590 3.1,3 Data from Laboratory Animal Studies (Cancer) The panelists identified several laboratory animal studies that illustrate the influence of fiber length on carcinogenicity, and made general comments about the relevance of these studies to humans. Panelists specifically referred to the following three studies when discussing how fiber length has been shown to relate to lung cancer and mesothelioma in laboratory animals: fit the first study (Davis et al. 1986), no malignant cancers were observed in 42 rats exposed yia inhalation to a short-fiberaraosite mixture, white eight malignant cancers were reported in the 40 rats exposed to the long-fiber amosite mixture (30% of fibers longer thaim S pin and 5% of fibers longer than 10 pm). . . , .. . ....... ....................... In the second study (Davis and Jones 1988), seven malignant cancers were observed among rats exposed via ihtraperitoneal injection to a "`sKorf' clnysotile fiber mixture, while 22jnalignant.cancers were observed among those exposed to the "long" fiber mixture. Cancers in the former group, however, have since been attributed to contMnidatioh of tie "short" fiber samples with longer chiysotfie fibers-^ippmann 1994). In the third study (Wagner et al. 1985), rats exposed! to mixtures oferionite fibers that were mostly shorter than 5 pm did not develop mesothelioma, while every rat exposed to the longer erionite fiber mixtures developed the disease. One panelist found certain aspects of this study surprising, such as the fact that all ofthe rats exposed to long fibers died within 15 months, even -though mesothelioma .typically isnot lethal in rats, tmd that General strengths (^'weaknesses Oj The panelists provided Several general comments oathim for understanding toxicity'ofasbestos and SVFs; Behefite.efantmai-stnclies incluifc^ie ability tn /It rcnnrfiu'f Kiofihr'nriihnltM nnmmnih tvellwIefinRfl fTnitoimlevtelitand ' evaluate health, outcome? mid lung-retention sampling and pflier hi^i^jmTOsiy^i^te.in humans;oh the- . other autopsy. However, paheli^STdmitmSil key factors that mirst-be ctorisiderM when labttfatbry animal admimstratioameth^^ andfiaurafo'^ exposure"eonditions (e!g$-smoking). Overall, the paneifiKg?neiaE^'agreed.tl6t laboratory; : ; antmal stiidiesvcaiiifprovideusefiilihsights into foxici^tQ'hisijaaiiSi provided thestudies are: -fft nmnisf rtnnta#>t thmc yalsjrrf^fw'w jfit Wtmttnb: . * 3-6 HWBUI0009591 the histopathologjcal slides showed very intense pleural reactions. The panelists revisited this study (see Section 3.4) when discussing how chemical composition and surface properties might affect toxicity. One panelist synthesized the findings from these and other relevant laboratory animal studies. This panelist first noted that the rat is an adequate model for cancers in humans, because the rat has been shown to develop both mesothelioma and lung cancer, though he acknowledged that these cancers are not as aggressive in the rat as in humans.9 He added that the laboratory animal studies have allowed researchers to observe the progression ofdisease for both lung cancer and mesothelioma. Regarding the administration method,,this panelist indicated drat th inhalation . studies were more relevant to human exposures. He noted that fiber administration by intrapleural implantation and intraperitonea!.injection does not represent human exposures for several Seasons (e.g. extremely large doses are administered in Very short lime frames, alveolar Twacmphaga arifi mticociltary transport clearance mecfaanisijRS are bypassed, and ine fibers inserted into the pleura might not be capable ofreaching these tissues following inhalation expbstbe). . .-'C . Overall, shown that short fibers ofanylype are less potent than long fibers, both for mesothelioma mid cancer, but the relative potency has hot been quantified. 3.2 NdhibCer Effects tncancer effects ':?'jbe panelists htrteddsfferenees' iiraisbestos^rdated cancers in rats andhuspans-One panelist, said dial lung caniieri^niSstends'te'-be brbnchiaalveolar.anjl ^eyelppsin ibcdistal lung, whjlfi luisg.cancer in huinaiislargciy tendstooccarlnpraxt!il.areits.ofthej!nig..fie wondered ^differencesin fiberdepb$itK>npatterns(duets ' differing airway sizes and branching patterns) might explain differences'iti where lung cancers dervclbp itirails and humans. Another panelist Cautioned against expecting that limg cancer would develop in'the ssiirte parts Of the lung in rats and humans, primarily because of the confounding factor of cigarette smoking in humans. 3-7 HWBUI0009592 3.2.1), studies of lung-retained fibers in humans (Section 3.2.2), and laboratory animal studies (Section 3.2.3). Each section is further organized by noncancer endpoint; Although many different endpoints ware discussed (e.g., irritation, nephrosis), the majority of discussions focused on pulmonary interstitial fibrosis and pleural abnormalities (e.g., pleural plaques, pleural thickening, and calcification). 3.2.1 Data from Occupational Studies Overall, the discussion leader for this topic area indicated, there is limited evidence ofnoncancer toxicity being associated with fibers less than 5 pm in length, with two exceptions. First, he indicated that very high doses to short fibers, especially those that are durable in intracellular fluids, may have the propensity to cause interstitial fibrosis. Second, he noted that exposure to short, thin durable fibers may play a role iadevelopment of pleural plaques or diffuse pleural fibrosis ifthe dose is high, enough. The following paragraphs review the discussion that led to these suminary statements: ; ., ^ 5, :. Asbestos. One panelist noted that no. epidemiologic studies have examined populations exposed only to short asbestos.flbers, because actual exposures are inevitably to a broad distribution offiber lengths. To address this issue, the panelists commented on data reported among.Libby residents, particularly the prevalence of intense bilateral pleural fibrosis in commiinityrinembers-r-sorae ofwhom reportedly did not work in the local vermiculite mine or processing plant, anddid not live with mine or mill workers. One panelist was particularly concerned about the role of short fibers, noting that a very large portion.of fibersin the homes are too short op too thin |o be counted by conventional PCM ' sampling methods. Hd added, however^thatsdroe researchers have speculated that short particularly, fiemoltte asbestos, may ' preferentially depositon the pleural surface.;and<therefore be associated with pleural plaquesi,This panelist emphasized that the relevance ofshort,,thin fibers ?md the risk for pleural abnormalities has only been speculated,'and heeds to be further investigated. The panelists also wondered ifthe intense pleural effectsobserved in the Libby cohort might be associated with the unique mineralogy of the Libby asbestiform fibers. Pleural plaques - have been associated with environmental exposures jn;areas where tretnolite fibers naturally ocoir(e.g;, in certain regions of Greece, Cyprus. Turkey, Canada, the Czech Republic, Romania). Some discussion focused on the extent to which pleural effects are associated with occupational versus environmental exposures. Two panelists cautioned against attempting 3-8 HWBUI0009593 to classify exposures in this maimer, because some individual exposures were difficult to assess. For instance, some residents might not have worked at the mine or the mill or lived with mine or mill workers, but could have been highly exposed through routine contacts with these individuals in other settings. These panelists recommended that the discussion focus strictly on dose, regardless of the contributions from occupational and environmental exposures. SVF. One panelist indicated that the available epidemiologic studies provide no indication of increased mortality from nonmalignant respiratory disease among occupational cohorts exposed to SVF. He then summarized morbiditydata for several cohorts. The summary focused on SVF production workers. Although SVF "end users" (e.g., insulators, pipe fitters, heatingfyeadlatioB workers) have also been evaluated, these studies are commonly confounded by potential asbestos exposures.. Overall, this panelist concluded that the' available occupational studies indicate limited overalltoxicity associated with SVF exposure, with the exception of RCF exposure being associated mm pleura! plaques; This conclusion was based on the following observations: //; For exposures to SVFs (all types), one panelist notedthat multiple studies Have found that SVF exposure among current or former smokers Is associated with , small additional decrentents. in forcedyital capacity (fVC) and forced expiratory volume in 1 secbnd (FfiVl): He add&ti diat siinilar detrfements'in spironiefnc parameters are observed among other non-specific dust exposed industrial working populations, suggesting that the effect is not specific to SVFs. This panelist ^so reviewed studies, albeit limited! ones, ofskin irritation. These t^5:pm in diameter), with.inefejs^>imtation observed irt;hbt, hirtriid'climates. ;; Eye, upper respiratory, and lower respiratory irritatidn;has also'freen reported in case studies amongpeople accidentally exposed to'high fiber concentrations, and these irritation effects are generally tremsienL : . -iv v For fiber glass and mineral woof-this panelist;noted that the available studies (e&;-Hug&esret a!; iSSJ^though-limited in inimbw, provide a<p indication of chest-radi&graphic^iiiirastitial,onpleuritt changesj amoiigproduetioil workers. The ' pahdisff8ddedtbatstbd&s4bvsuggestMaB nohmalfgsant renal dlseasefe.g, n%Mti^uepbrosis)is;oJij'patioiial cohorts ;; exposed toniineral wobl, buirtot among thoreex^sed'fofibef glass; he questioned the biological plausibility ofthese outcomes: ;; V ; j. For the more durable RFs. thepanelisfindicated that occupational exposures f. .0-.1 : have been associated with pleural.cHanges.-.pri'mairily pleural plaques. The pleura! plaques were observed among approximately 3% ofthe production workers, but were found to be correlated with duration of RCF exposure, time since initial 3-9 i HWBUI0009594 exposure, and cumulative RCF exposure. The panelist added, however, that the available studies have not found RCF exposure to be associated with a statistically increased risk for pulmonary interstitial fibrosis. During this discussion. Dr. Ralph Zumwalde (NIOSH) informed the panel that, in the late 1970s, NIOSH studied the health implications among more than 2,000 miners who were exposed to an attapulgite clay that has fiber-like characteristics (V\(axweiler et al. 1988). The clay "fibers" were less than 5 pm long, with diameters of approximately 0.1 pm. Dr. Zumwalde noted that this study, which be . recalled found excess lung cancer among whites, might be useful in ATSDR's overall evaluation of short fibers. The increase in lung cancer deaths, however, was not associated with latency, duration of employment^ or attapulgite exposure, and there was no increase in mortality from nonmalignant respiratory disease. Overall,.the relevance ofshort asbestos and SVFs to noncancer disease in humans was not entirely known. For the SVFs, only the durable RCF was found to be associated with pleural places; exposures to ItCFs were not.associated with pulmonary fibrosis,andexposures to fiber glass and mineral wobls had no indication ofchest radiographic, interstitial, or pleurai changes. Given dita collected in Libby, Montana, however, some panelists questioned whether short fibers might play a role in the observed cases ofpleural plaques and diffuse pleural fibrosis; but others : Cautioned against inferring that the risk results from exjjosure to short fibers, given that the Libby samples contained significant numbers of long fibers as we?l. 3:2.2 Data from Human Stndies.ofLung-Retained Fibers (Noacancer) Two panelists reviewed publications (case-control studies, a study recently submitted for :di \.V- ; - ... .'v . i?.-: : publication, and a case report) that examine the influence offiber length reteieti lit the lung on the grade of pulmonary interstitial fibrosis, which is reported on a scale froih 0 to 12. A summary of these !, organized by fiber type, follows: Findingsfor tremolite asbestos. One panelist indicated that a study of tissues from chirysotiSe'aibestos itiineirs and ttiillers reported an inVeise relationship between fibrosis grade andjength of tremolite.fibers retained in the lung (Churg et al. 1989). Ia other 3-10 ) HWBUI0009595 words, the most severe fibrosis was observed among those with smaller (on average) tremolite fibers in their lungs. Another study (Nayebzadeh etal. 2001) and a study recently submitted for publication (Case et al. 2002b) examined fibrosis grades for different length intervals of tremolite fibers: 0-5 pm, 5-10 pm, and 10-20 pm. Both studies found the highest average fibrosis grade occurred among those with the lowest tremolite fiber length interval, or for those with average tremolite fiber length less than 5 pm. Findingsfor amosite asbestos. One study (Cbiirg et al. 1990) examined lung tissue samples from a small groupr(<20) of shipyard workers and insulators selected from litigation cases. This study" also' found ah inverse relationship between fibrosis grade and length of retained asbestos fibers (amositd fibers, in this case). Findingsfor total asbestosfibers. One panelist summarized a study (Timbrel! et ai. 1988) that evaluated lung tissue samples at autopsy from workers exposed in different asbestos mines. Data were collected both for retained asbestos fibers and fibrosis score. The ' fibrosis scores were then'consisted with lung-retained asbestos characterized by three different metrics: number of fibers, mass of fibers, and surface area of fibere. The : correlation was best When the surface area ofretained fibers was used as a dose metric. This panelist added that the'OTffade aha close metric has correlated well with piiffiibhaiy inflampaticm, including fibrosis, following exposure to particulate contaminants that are The panelists referred'to tins study,;Which did not examine the role of fiber, length, several times when discussing appropriate dose , metrics. Findingsfor aluminum oxfifefibers. One, panelist reviewed.data from a case report (Churg et al. 1993) on an individual with diffuse interstitial fibrosis who was occupationally exposed to aluminum oxide fibers. The lung-retained fibers in this case were ` predominantly 3-4 pm long and 0.0 ( pm in diameter. The panelist indicated that these findings raise questions about the significance of short, thin, durable fibers in the lung, though he aekribwledgeti that'cbnclusidns"sbiduid not bb drawn from a single case report. , Several panelists commented oa theTrehdgpmong the aforementioned studies. Two panelists, for instance, noted that the trend of shorter fibers possibly being more toxic, at least in terms of- interstitial fibrous, is counterintuitive. Two other panelists, on the other band, noted that these findings suggest that, for interstitial fibrosis, the surface area of retained fibers may be more important than the fiber length, because larger amounts of short fibers would have considerably greater surface area than smaller amounts of long,fibers. Finally, some panelists wondered ifthe apparent inverse relationship beiweeff fiberlength aihd fibrosis score might be explained by long 3-11 ) HWBUI0009596 fibers breaking down into shorter fibers between exposure and the time that lung samples were collected. 3.23 Data from Laboratory Animal Studies (Noncancer) This section reviews the panelists' discussions on noncancer outcomes from asbestos and SVF exposure identified in laboratory animal studies. Before addressing this topic, one panelist summarized how the mammalian lung responds to exposures to inert materials, whether fibrous or particulate: once an inert material deposits -in the lung beyond the conductive airways, it will either dissolve or be engulfed and'Oleafed by alveolar tnhcrophages; ifthe dose exceeds the lungs' capacity to clear the material, natural defense mechanisms may act, leading to fibrosis. Section 3.3 presents inore details oh die mechanisms involved ie these steps. Specific comments on noncancer effects in laboratory animajs,- organized by endpoint, follow: Inflammation, pulifionary;.interstitialfibrpsisr and'pleural reactions, Thp panelists presented several observations when summarizing findings from laboratory animal studies on noncancer effects in die lung and pleura. First; two panelists noted that many laboratory fibrous material and non-fibrous particles. The sequence ofevents leading to the fibrosis was described (see Dr. McConnell's premeetiag comments in Appendix B). When doses reach high enough levels, pleural reactions (e.g., localized acellylar fibrotic changes) were observed, but one panelist questioned ifthe dose levels needed to elicit the pleural responses, are relevant to environmental exposures in humans. Another panelist noted that the animal studies.suggesfcthat the plepral effects do not or&ur unless fibers are. present in the. pleura. When.dlscus^ingmterstitial fibrosis outcomes,;one-panelist said the long fibers _;,;.appear to be.raoiecfibrogefuc than, the, sbditTibers,.thon^jb%sfr`?^^ that short fibers .:a|pne are capgbfepfgeaeptting fibrpgenic responsesifthe dpse is sufficjentiy high. The . .panelists' premeeting comments include specific references to studies that reported ,relattveJojiadty,Ofshort and long fibers for tibpcjmcer.outcomes (see Dr. McKsman's .premeeting comments in.AppendixB).;. ; Reviewing specific studies, one panelist indicated that the intensity ofnoncancer responses in laboratory animats varies from one fiber type to the next. He noted, for example* that hamsters exposed to amosite asbestos had an increased incidence ofpleural .fibrosis,.while hamsters exposed to.comparable araouts.qf duysotile asbestos did not; pulmonary fibrosis was. evident, however, in both groups ofhamsters-The panelist suspected that the different outcomes resulted from either the amosite fibers being more 3-12 HWBUI0009597 durable (less soluble) in the lung or the amosite fibers being more likely to translocate to the pleura. One issue that generated significant discussion was the extent to which interstitial fibrosis progresses in laboratory animals and the relevance of disease progression to humans. One panelist noted that, in every animal study he has conducted and reviewed to date, interstitial fibrosis is progressive only when asbestos exposure is ongoing. After asbestos exposure ceases, he noted, no overt,^igns ofprogressive fibrosis are apparent, although this has not been quantified in a definitive way. The inflammatory responses, rriicrograriulomas, and bronchiolization also tend to decrease. This panelist added that fibrosis dpes not appear to progress and maqrpphage response tends to decrease when the exposure ceases, even though long asbestos fibers remain in the animals' lungs. He interpreted this trend as suggesting that short asbestos fibers in the original dose1 might; play a role in stimulatiijg.an initial inflammatory response in fee. rats,..Another panelist, suggested feat the lack of fibrosis progression, eve in fee presence oflong fibers, might inhaled fibers), possibly by being coated, wife, biological .fluids. .In, other words, he ... wondered if fee freshly inhaled fibers are more likely to elicit cellular responses than fibers feat have been in fee lung for ah extendedperiod ofdine. " Though not questioning fee comments on fibrosis progression in animals, two panelists ' etoplmized that fee trends discussed above are not observed in humans. Cituig'-their experiences evaluating shipyard workers and chrysotile miners, these panelists noted feat fibrosis'arid pleural changes have progressed in humans, even after asbestos exposures ceased. Reasons why fibrosis might progress difiTetehtly in rats and humans were not discusstedi' ': - " Commenting further on disease progression, one panelist indicated feat certain honcancer effects and hmg Cancer appear to have consistent patterns is allanimal studies he has reviewed, ihciiudingrsttidies ofasbestos exposure aridlhidies of exposure to riori-fibrous 'particulatel Specifically, this panelist said he had not found any study in which a rodent not-have interstitial-fib'rosfsfand he had never feCn rodents with .,::riBteKtififffibfoSii'in?feb;absCnc:e;d:fiiiflamm'atidh..Thiese observatiottsTed feeipanelist to ^Bfrirthaf-lurig'cariCe?- ^duid-fiot.be' expected t6; develop' at- doles feat do not induce stresSed feaf this infeireh'ce is bSsed'solely oft observations ;-dM;preVibus animal studies and'does riot many way suggest feaffibrosis'is a precursor to lung cancer--an issue feat came up during fee observer comments'(see'Section 3.6). He also added feat this relative sensitivity of noncancer endpoints may not necessarily be observed in hinriaitsi `.1 C ' ; *' - " ' Irrimiaii. Oriepahelist rioted feat laboratory anirftal studies have riot studied fee extent to. ; Which asbestos arid SVF irritate the skin and eye. He addedthat histopafeological studies of the nrisaPcavi^pharyrix, larynx; trachea, and conductive airways have not identified 3-13 HWBUI0009598 evidence of irritation, though be acknowledged that the histopathologicai techniques might not have detected-certain responses (e.g., increased mucus production). He cautioned that these results do not necessarily suggest that humans will not experience fiber-induced irritation in the nasal cavity, larynx, and upper respiratory tract, because the rat studies did not consider populations with impaired mucociliary clearance, as might be observed in smokers. Finally,! this panelist indicated that ingestion studies in rats and hamsters have shownno evidence of irritation in.the gastrointestinal tract. ; 33 Mechanisiqs.of Toxicity This section reviews .the panelists' comments on mechanisms of toxicity, primarily as presented by the two designated discussion leaders. Dr. Mossman and Dr. Wallace. After identifying several general advantages and disadvantages of in vitro studies, the discussion leaders reviewed current theories on rifechaiisms oftoxicity for a wide range of fibers and analogous non-fibrous particles. This section review^ key. points from those presentations. Emphasis is placed on what has been established or hypothesized regarding the relative toxicities of short and long fibers. For more detailed information on mechanisms of foxicify, refer to Dri Mossman's arid Dr. Wallace's post-meeting corameots in Appendix E. . Genera! comments onthe utility ofin vitro studies. To initiate discussions, one panelist listed several strengths and limitations associated with in vitro toxicity studies. First, she indicated that in vitro studies, when compared to laboratory animal studies, offer a far more cbntrriHed'sfetting for examiriing mechanians oftoxicity and dose-response behavior for specificrteU types. Shb acknowledged, however; that interpreting trends among studies -'using'^widely!'Wiyiag drills and multiple cell types' can be complicated. Moreover, the in '; ! vl/^^tudiris'^e.alilSlffediia darariori,`fypicrally'ltetiiig!a few, days, due to the limited life : " spatei? of is6latedS`efells`iii ihe\m:'v/tm erivirbrimehtfConsequently,; the in vitro studies , : eahhbt charaCferize^M>lutihri,; macrophage cle'arariCfc; and other processes that occur over vivtygg^-t||ag'sgHe>Fii&tly; tins pabelist noted that doses to in vitro samples: cannot readily :Ae extrapolated tohumaii utKalation exposttres. 1- Role ofreactive oxygen species (ROS). One panelist reviewed a widely accepted theory of hbw gdridrafioririf ROS might explain asbestos-related toxicity. She indicated that alveolar teacfopfiages^'Ss they attempt to digest foreign ftberaand particles, produce an "oxidative burst" iritfrelease'ROS; (Otitef cell types that contact asbestos fibers also release ROS.) 3-14 \ X HWBUI0009599 These ROS caa initiate sequences of events that have been shown in vitro to lead to outcomes such as genotoxicity, cytotoxicity, and cell proliferation. "i . This panelist highlighted two key observations regarding ROS. First, in vitro studies have shown that alveolar macrophages generate more ROS when attempting to digest longer fibers, while shorter fibers can be engulfed completely by macrophages (and other cell types) with no visible damage to the cells. Second; she noted that-ROS can form highly reactive hydroxyl radicals via a reaction that is facilitated by the presence of iron. Therefore, long, iron-containing fibers, like several amphibole asbestos fibers, are capable of generating an intense "oxidative burst," which might explain their greater potency, when compared to fibers that do not contain iron. Finally, this panelist noted thht researchers can prevent pulmonary fibrosis in animals by administering free radical scavengers or other substances that interfere with ROS formation and reactions--a finding that argues strongly for ROS having a Causative role in inducing asbestos-related fibrosis. Overall, this panelist noted that many aspects of the ROS theory help explain how fiber length and, to a lesser extent; mineral content relate to toxicity and why shorter fibers are substantially less toxic than longer ones. She presented results frojm several fn vitro studies (e.g_, Ohyama et al. 2001) that confirm that longer fibers generate a greater "oxidative bursts when they are not ingestedby alvdolar macrophages. ` ' ' '' Effects on cell.signaling events. The panelist then described current research that has characterised effects ofasbestos- and fibef-related cell sigaalmg evenfr. Sfie-ekpldned that these events originate when fibers interact with cell surfaces, softer which the cells activate transcription factors that mediate various outcomes which can be measured in vitro, such as cell proliferation, cell transformation, and cell death. She noted that cell proliferation is an important step in development in both malignant and noomalignant disease. .... Thepanelist then described studies examining bow selected signalingpathways are affected by asbestos and glass fibers ofdifferent lengths. She,summarized studies that ' demonstrated activation oftranscription factors and cell proliferation. Fhrst,1the panelist reviewed a study etalJ T95KI) in which mouse macppphhge-cell lines were challenged with two. tormulations of fiber glass mixtures; ooe.with average length of 6.5.;pra, the other 16.7 pm. These challenges caused-production, of (TNF- d), a cytokine involved in ittflammatipn and fibrosis, which in turn caused actiyation of; nuclear factor-xB. Gene promoter actiyation. induced.by.tbe short fibers was found to be between one-third and one-half what was observed for the long fibers. Second, file panelist reviewed w vitrostudies that examined Specific aspects,ofcell proliferation. Although celfproliferatiori relates to cancer outcomes, she emphasized that development ofmesothelioma and lung cancer is a multi-stage, process with a long latency period, which cannot be captured in the short time frame of an in vitro study. The panelist identified many studies (see Appendix E) demonstrating that longer fibers are more apt to 3-15 ^ ) -\ HWBUI0009600 cause cell proliferation than are short fibers, whether from tracheal explant studies (e.g., Sesko and Mossman 1989) or intratracheal models in rats (Adamson and Bowden 1990). Studies ofasbestos genotoxicity. The panelist indicated that researchers have been studying the genotoxicity of asbestos, both in vivo and in vitro, for more than 20 years. These studies examined a wide range ofendpoints (e.g., cell transformation, chromosomal aberrations, gene mutation) in various matrices. The panelist focused, however, on a series ofstudies conducted to.examine the role of fiber length on cell transformation and cytogenetic effects (Hesterberg and Barrett 1984, 1985; Uesterbergetal. 1986). These studies demonstrated that long, thin fibers are most potent for both types of effects, and the shortest fibers examined (less than 1.7 pm long) had no indication of tumorigenic potential:'These findings, she noted, indicate that longer fibers are again more toxic, with some suggestion that fibers below a certain length threshold may not be carcinogenic at 'all . Observations regarding mechanisms oftoxicityfrom non-fibrous particulates. One : panelist addressed mechanisms of action for non-fibrous particulates having compositions similar to thoserin asbestos and SVEs, First, he indicated that non-fibrous crystalline silica is'Strongty.pathpgenicTdr fibrotic lung disease, while two polymorphs ofcrystalline silica-^qtiartz and cristobalite--have recently been classified-as carcinogenic (IARC In contrast, amorphous silica (more akin to SVFs) hasnot been shown to cause .- luhg tancer or mesotoefioma in rodents (IARC 1987). Exposure to the crystalline silica polymorphic^directly damage cells, resulting in intracellular generation ofreactive oxygen species and a cascade of events;(e.g., synthesis and release ofcytokines, cell ; proUferatiom secretion fcpUagen into the extracefrular space) similar to the those evoked - by-asbestos fiber. In vitro studies have shown that silanols (hydroxyl groups on the xiystalline stirface) are. associated with the initial damage to .cells: loss of surface silanols caused the crystalline silica to exhibit less damaging activity, and subsequent formation of silanols restored the silica's toxicity (Pandurangi et al. 1990). These and other studies (see Appendix E)>suggest that surface chemistry plays a role in silica's toxicity; m but ggnerailyrignored component for physiologically " .: v representafi^i viP0:bioassays is that;particles and fsbeimdeposlting In the lung initially ;. -xbMtaet-theaquepi^;`'hypQpbase'` lining oh tbetenriinal,airway and airsac surfaces. The hypophase layer is rich with micellar dispersion of surfactant, composed largely of lipids : - and lipoproietnsi Ofparticular note, the hypophase can be simulated in vitro with dipalfrutoyl'phophatidyl choline (DPPC) dispersed in physiological saline. Silica particles . and other maiterials deposited in the lung have beett:shown_to adsorb the surfactant, which extiagtitsbesshbrt-term^cytotoxicity---another observation indticatirig that the toxicity of : particleS:iBsthe..lung is affected by surface chemistry.,.This panelist noted that the alveolar - .lihypdphase contains more than enough surfactant to coat and neutralize the entire surfaces r bfrespirable-particles, even in most high dust exposures (Wallace et al. 1975). 3-16 ) HWBUI0009601 Although the volume of surfactants in the alveolar hypophase is sufficient to coat respired particles completely (even in high dust exposures) and thus is theoretically capable of extinguishing the particles' toxicity, this panelist indicated that the toxicity can be restored when other cellular mechanisms remove the protective surfactant cover. Specifically, macrophages Can engulf surfactant-coated particles, where they are subject to-, pbagolysosoraal enzymatic digestion which can remove the surfactant film and thus restore toxicity. Some study has shown that the surfactant film is more readily removed from crystalline silica than it is from kaolin, which suggests ? mechanism by which quartz may be more toxic than kaolin; however, experimental study has hot demonstrated that particle dertoxicificadon and rertoxicification explains the relative toxicides of these materials. Thus, surfactant coating of foreign particles deposited in the alveolar space again appears to play an important role in toxicity. The. influence4>f surfacechemistry has also been observed in quartz particles having ahunino-silicate surface contamination; for such particles the surface contamination can delay for months or perhaps years the expression offibrogenic activity. Finally, this panelist noted that researchers raightglean greater understanding ofthe main site ofasbr^tbs fibrogenic activity from theories reported-dor crystalline silica. He explained that a series of studies (&gvBowden et aL1989) suggeststhat:fibrosis results froma sequence ofevents following interactions between crystalline si.Uca.ahd interstitial ' cells; ihtherttfah interactions with alveolar- macrophages. Specifically, it isbypothesi2ed thht interacfiohs with the interstitiai celk control the stiihiilatiottrof.exacerba,ted collagen Synthesis by pulmonary fibroblasts; whereas; interactions withmacrophagesare hypothesized as being responsible only for an inflammatory response:(not fibrosis) evoking neutrophil influx to the alveolus. This paneEst suggested tirat fiirtiier research on interstitial Cells, rather than focusing largely on responses initiated by interactions with alveolar macrophages. Comparisons betweenfibrous minerals andCrystalline.silicaparticles: This panelist noted that the available in vitro studies do not explain comprehensively bow asbestos fibers and crystalline silica particles differ ih.indticing fibrosis.-:AItliojiifi they identify.several endpoints that asbcstos and crystaSline^siStcahave ihobmbton, the studies cannot predict .-wB'y asbestosis-appeafs.'as.a diffuse;fibrosis,.-while silicosis appearsin locafeodnodules. However, some research provides insights on differences between how long fibers, short fibers, and particles contribute to cytotoxicity. Specifically, an vitro. stody:.(t4U 1994) examined?whether surfactant coating inhibits the cytotoxicity ofasbestos.; (Asthe previous bulleied item indicates,'similar studies found that surfactant coatihg;virtually<.extinguished the shortterm toxicity ofcrystalline silica particles.) In the study.Chinese hamster lung ceils were tested for micronucleus ihductionafter being challenged with surfactant-coated chrysotile asbestos. The study considered how induction differs between long fibers (average fiber length of 101 pm) and shorter fibers (average fiber length of 11.6 pm). It 3-1? ) HWBUI0009602 found a slight, but not significant, decrement in cytotoxic endpoints for the long fibers and a considerable, statistically significant decrement for the shorter fibers. The findings . suggest that surfactant coating is less effective at impairing toxicity for longer fibers. Although the studies on crystalline silica underscored the role ofsurface chemistry in eliciting toxic responses, changes in the surface composition in chrysotile asbestos were found to have no significant effect on in vitro genotoxic activity (Keane et al. 1999). Specifically, fibers that bad been mildly leached to remove near-surface magnesium atoms exhibited comparable genotoxicity to fibers that were not treated with the leaching solution. Based on his revieur of.these and other studies, one panelist suggested that .more than one mechanism^of toxicity may operate for asbestos and.SVF, and the roles ofthe individual mechanisms might depend on fiber length. He explained that "frustrated phagocytosis" and its ensuing events clearly appear more relevant to long fibers (i.e., long fibers are much more likely to be only partially engulfed by alveolar macrophages), while a toxicity mechanism mediated by surface properties ofphagocytized material (e.g., restoration of fiber toxicity in the intracellular matrix) would beforerelevant to short'fibers. In otherwords, part of the short fiber toxicity might be related to mechanisms involving surface chemistry, which were described in the previous bulleted item. This.panelist added, hoWevdr, that additional mechanisms could contribute to toxicity. AS orieTexarripIe, lie . r .indicated that asb^stps fibers penetrating the cell orcell nucleus may exercise.niCKles of direct genetic or epigenetic damage. Whatever the mechanisms of direct fiber damage or sdmuMioirof the cell surface, he noted, several components ofthe consequent intracellular response have.been well defined. Appendix.E provides additional detail.on . the responses that have been characterized, and die influence of fiber length on these responses. Recent advances infiberpreparation methods. One panelist noted that researchers at NIOSH have been developing a fiber size classifier (separator) that permits in vitro or perhaps limited in vivo experiments wish sets of fibers of fairly well-defined length (Baron ei al. 1994): The dieiectrophoreric classifier rejmrt^y can separate an aiHheam Mndproduce about i mg/day pfa giyen st& interval. The panelistindicated that this prepmi^'oE method recently was ussdfd^erierate the following categories! Of fiber rize'thtervais:''- : 1 '.V; '' fiber Length ' "' h'"' Average (urn)?- ' Standard Deviation fiinrt 1 32.7 23.5 ...........: . 10.6 = - "p~ I 5. 6.5 4.3 3:0 2.7 1.0 1.0 >''' ' Fiber Dhpeii!d^: | Average (um)- Standu^DeHation fpa) 1 """61$"' " 6.56" j 0.49 0.27 . 0.22 0.40 0.15 6.35 0.14 3-18 I .* HWBUI0009603 This panelist noted that the preparation technique may now allow researchers to investigate the influences of fiber length more rigorously. Some panelists noted that the distribution of fiber lengths in: the first "cut" is quite broad, but other panelists indicated that the subsequent "cuts" were more narrowly distributed. One panelist illustrated the utility ofthe fiber preparation technique by reviewing findings from a recent publication.'In initial studies with these size-classified'materials, NIOSH research compared fibers from "Cut 2" and "Cut 3" (see table above) for their induction of the cytokine cascade cellular responses (Ye et al. 1999); The'longer fiber sample was more active wben dose was measured as fibers per cell, but the shorter fiber sample was equally or more active when dose was characterized on a surface area or mass hams. One panel member noted that this whs of interest in the contextofthe previously presented "counter- / intuitive" histopathology reports (see Section 3.2.2) associating fibrosis with short fiber exposures.' ' v ' " ':V ' ' ' 3.4 General Comments and luterpretofioas v . .. , While discussing the influence offibar length on asbestos aqd SyFtbxieity, the.paneliste made sevef^l'generalcotniBentsand iuterpretMobservarioasfromthe Saboratoiyanimal, human, and in vitro studies. This section suipmanzes there general .comments and interpretations, while Section 4.Treviews the panelists* fedrodua! summary stefemerifs provided at the end ofthe meeting. . ... ... . Evaluating toxicity based We- "reasonable certainty of.po harnL " Wjhem discussing . asbestos and SVF Joxicity^the panelists discussed theterminology tifey:slipuldtise to ..dewing from^e ** '. dose-response data for humans or animals Uniquely exposed to fifem 5 pm is largely not available, most panelists agreed that die terminology proposed was appropriate * - `A s * -.I-'..' . ... .. differenteiidpbtats,-using'aweight-qfevide?ice approach.that drawsfiom-ail-^y^.bf 4 0`- y.0: Tuh:!u<fin]|di&unetne;t&id<i&I^ - -r.;$ * Dofibers shorter than adertain length have a ''reasonable certqinty'f>fho harm "fjTKji panelists debated, whether summary statements could be made regardingwhether fibers of certain length intervals hive a "reasonable certainty ofno harm." Two panelists, suggested that environmental exposures to fibers shorter than 5 pm would likelybe free of 3-19 ) .. s HWBUI0009604 carcinogenic effects. Other panelists, however, felt uncomfortable making such judgments for noncancer effects (e.g., pleural abnormalities), especially considering the evidence summarized in Section 3.2. Refer to Section 4.1 for the panelists' individual summary statements regarding the influence of fiber length. Why arbitrarily establish criticalfiber lengths? Because humans are always exposed to fibers with a wride distribution of fiber lengths, one panelist wondered ifATSDR or environmental agencies could.develop a universal algorithm that quantifies health risks associated with different types of fiber rnlxtures. For instance, an algorithm ought include different relative toxicity factors fox different fiber length intervals (e.g; 6^-5 pm, 5-10 pm, 10^*20 pm, and so on). Such data could,then % applied to the distribution of fiber lengths measured in the environment to assess site-specific risks. This panelist acknowledged that the relative toxicity data do not appear to be available to support this approach, but he noted such a universal algorithm would be far less arbitrary than completely ruling out fibers having dimensions below a certain level. He added that such an.^gprithm can eventaally account for other factors (e.g.,`btqparsisten<ie) that are also known:to affecttoxicity. In short, this panelist mdioated that it'is thepretically possible to express health risk as a function of fiber dose, dimessipfi,.ani durability, though he noted that one would need additional research into dose-response and extensive inputs from biostatisticians to develop such an algorithm. Other influences on toxicity. While recognizing that theIgM^isdfihemeeting was on how fiberlengths affect toxicity, the panelists.noted dui'the toxicity ofa fiber mixture- Examples ofother factors include dose, fiber composition (mineral type), physical state (amorphous or crystalline), suffice area, and surface . .predict toxicity. First, the pan.eltsts.noted .that die cheers observed m.'tbe sttidy ofrats exposed to. erionite (Wagner et ah 1985) could not be explained by fiber lengfii alone; they suggested that the unique.findings of this study might be best explained by unique surface chemistry or the mineral's relatively large internal surface area (2.5 H?/gram). Second, the .panelists, noted that fiber durability likely explains why asbestos fibers and SVFs of the saijje length are not equallytoxic. .Ejue to these and other dbrervddpns, a .panelist noted, . 4iJ^pR.inighiipv.erloqk;other important factor? thafinfiuepce toxicity.if it..focuses . ;;ex^lusivelyjpn;.fiberlengdir... * 1 3:5 Research Needs The panelists identified several research needs when discussing the influence of fiber length on health effects. In general, the panelists encouraged thorough planning of any future study, emphasized the need for having well characterized exposures, and advocated involving 3-20 HWBUI0009605 researchers from multiple disciplines (e.g., epidemiologists, physicians, toxicologists, mineralogists). All research needs mentioned dining this session of the meeting are documented here: Several panelists indicated that further study should be conducted'among'the residents of Libby, Montana, to understand the effect offiber length on toidfcity. Otie' suggestion was, through the cooperation ofdie community and consent ofresidents, establishing a protocol to analyze lung and pleural tissue from community members who die; regardless of the cause of death. Another suggestion was to track the progression ofthe observed pleural disease. ' . " !V" * Giyen the !ifeal& outcomes `observed in Libby, onepanelist encouraged focusing future re|^cJi in.l^ra|oiy animals on.undhrst^dmg fiber ddse-re^?onse Behavior for the viS&ral Md pmb^ plei&h Such stodife could iise fibers from tib%' fb:6xaiiiine how , doses to the pleim'a&ffprogrfessibii of.toxic responses vary with fiber length and between fibers afrd iioii-fibrbils particles. Another panelist added that a Well-cbiistmcted study can For added insights on toxicity of short fibers, possibly those from Libby or Lower Ma^qtqijy, ccSi&ctEu^t'Stt'Jw vint sttiwyfuslrigsevefai'fcell types (eig., rat pleural mesotiefiai cells, trabheial'^pjtheHai cells) fri'ddfrufriaidtipie endpoints that can be coDUfiini^'tn`a^aafmd4l^lsii^ as cell prolifaiitibn and cytbtbxicity. ; One on residdntisd.development in arm with ihci^ecl levels ofnitofMlyfreoirihg tremolite asbestos (eig;, the Siena foothills in Calffoniia); but be addedihat a WgfrTevel-of = / i:iv,-;, To assess'.human he|ltb effects associatedwith exposures to short fibersi;'one panelist recpmxneqdm foliowfug shidy oftwb cphbfe dfriiineis, one iii South.-DSkp^aad one to Minneso^ who weffc'ej^^pr^dmin^tiyfosbbrtcuinii^^b^te^gmfrOTfe fibers. Further study would take into account a longer latencyp^od'amd^trMj^'rb^'eal insights on tbe role of fiber length in toxicity. Several panelists encouraged NIOSH to continue to re-analyzep^spnal ^ppspre samples collected on membrane filters in the 1960s and 1970s from textile workers in Charleston, South Carolina. This suggestion followed an observer comment that informed the panel of 'NIOSH'ts;'pIannedwdrk.ort;this-prqject ,vv'.: ... v p , - o I HWBUI0009606 3.6 Observer Comments and Ensuing Discussions Observers were given two opportunities to provide comments on the second day of the meeting. The panelists were hot required to respond to the observer comments. However, some comments led to further discussion among the panelists, as documented here. The. observer..comments are summarized in the order they were presented: Comment 1: John Hadley, representing the North American Industrial Manufacturers Mir. Hadley summarized selected IARC publications regarding the toxicity of SVFs. First, he noted that IARC lias accounted for the influence of fiber length in one ofits 1997 monographs (iARfc 1997)- Specifically, IARC classified palygorskitetattapulgite) fibers longer th^S pm ifi "Group 2B," or "possibly carcinogenic to humans (limited human * evidence* le^'ftari sufficient evidence in animals)." On the other hand; IARC classified palygoisloie (aftepujpte) fibers less than 5 pm in "Group 3," of "not classifiable." Mr. Hadley added' that 1AJR.C researchers recently published an article bn tock and slag wool production workers (Kjacrheim et a!. 2002) indicating "no evidence 6fcarcinogenic effect on the lung ofrock and slag wool under exposure circumstances in the production industry during the last four to five decades." Panelists' Discussions: No panelists addressed this comment Comment 2: David Bernstein,.consultant in toxicology Dr. Bernstein asked the panelists to provide more information on the lung-retention studidS (e.g., how much of the lung was sampled;' What parts ofthe rung were sampled, how representffiVe'afe the sampies of fiber loading in the entire lung). Panelists* Discussions: One panelist summarized details of the lung-retention sampling performed in studies he authored, and be suggested that observers refer to t^e.diri^li|^pubtidatidii foradditional details: hi ode stddy,!.ihis panelist indicated; samples Iranithe periphery ahd lhe &ntrai parenchyma were collected SystematiGaily fromtongitudirial sectiohs of the'entire iung. He noted that 'prefefeatiSJ sampling (e g-, diseased locations) (Ud hot d^alf.'aad he added that thWstud^'ato&ed cbhCenis about sampling bias by collecting larger amounts of Saihplesfiomd'gi'veiiIiing;-' ; ' 3-22 HWBUI0009607 Comment 3: Aubrey Miller, EPA Dr. Miller asked the panelists to comment on research opportunities to examine why certain health outcomes (e.g., pleural abnormalities) are being observed in Libby, but have not been repotted (and perhaps not examined) in other mining communities with generally similar doses as gauged by conventional fiber sampling methods (PCM). He wondered if research should be conducted in other mining communities to search for pleural abnormalities or ifit should focus on understanding what makes the Libby experience unique. Panelists* Discussion: One panelist indicated that extensive research has already been conducted to characterize mining communities in Quebec He noted mat the fibers have been well,characterized and health effects thoroughly studied and identified key differences;hetween these; sites. For Instance, there are far more .fsbestosis, cases in Quebec.miners, but the psmelist noted that this might result simply, from the larger size.ofthe work- force in Quebec. The proportional numbers of, anil SMR for, lung cancers among -workers are in fact twice as high . among the vermiculite,miners in Libby than among chrysotile miners and millers in Quet^. Additionally,,there is more evidenceofpleural dis&ase in the Libby cohort... .. Comment 4: Mark Maddaloni, EPA Region 2 Mr. Maddaloni asked the panelists to disfcuss residential cleanup issues associated with .WTC dusts in Lower Manhattan,,where.fibers in dust samples are largely (80% to 90%) shorter than $ pm and *e,asb^.tp.s,fibers found arej.aimost eh^fely ductile. He was specifically. interested in &se-rc,spdnse data'for short asbestos-fibers aiid whether the panelists could establish a dose level for short fibers that constitute "a reasonable certainty ,-;.;-;ofnofaarini" ........ - commented on this matter. One panelist, on fibets' lessmm 5 gin is an arbitrary decision'. He arcultipateiy exp^^ tq a.complex mixture of . fiber? ofmMy iengfe,. Further,; this panelist, ^^tra.'raai'amtually all dust and afc.s^piescontain large.amounts'/peihaps,90ySj) b]fshort fibers, and the ihet that WTC dust is composed lar^iyofshort fibers is;not .unusual. He radicated that, at most sites, concentrations oflong fibas and concentrations of short fibers are correlated Due to this correlation, this panelist argued, when measurements suggest that low levels of long fibers are present, one can have a "reasonable certainty ofno harm" not only from the long fibers but also from the short fibers, because they are found in proportional amounts. Some panelists suggested that EPA consider using threshold limit values to evaluate the exposure levels. 3-23 '"A1 HWBUI0009608 Panelists expressed differing opinions on how to evaluate exposures. One panelist suggested that exposures to WTC have decreased considerably from the large amounts found immediately after September 11,2001. One panelist, however, noted that the presence of fibers in household dusts presents an opportunity for ongoing exposure; he added that this exposure scenario differs from what has been evaluated in the literature among occupational cohorts of adults. Comment 5: David Bernstein, consultant in toxicology Dr. Bernstein commented on laboratory animal studies conducted for the European Commission, hr these studies, rats were administered fibers both by inhalation and by inteiperitoneal injection. Though he agreed with the panelists' comments that inhalation v administration is most relevant to human exposure. Dr. Bernstein cautioned against . disregarding the data from inteiperitoneal injection studies, which have addressed the issue offiber length For example, be said recent data from the inteiperitoneal injection studies, has showmthat fiber length coirelatesbetter with, cancer risk inxats than does the dose. Dr. Bernstein added th|t these studies foundlhat the dose for short fibers had to be increased by orders of magnitude,to elicit the same carcinogenic responses as observed for long-fibers.... ,: - Panefiste5 Discussions:^ No panelists addressbd this comment Comment 6: Joel Kupferman, New York Environmental Law Project Mr. Kupferman urged the panelists, when discussing the WTC site, to not assume that exposures have ceased because much of the dust has settled. He noted that asbestos still remains thr-pughout.Lower Manhattan: in hpmes, in fire trucks, and in ventilation systems. He mentioned that dusts from some fire trucks have contained as much as 5% (by weight) . ; asbestos. Mr. Kupferman asked the panelists, to consider the fret that asbestos exposure is still occurring.. - .PaneHsfs'Dls?BSsioss: One panelist poled diat ,^[e pj>servef raised an important ,;:pointi He add^dithat researchers;clap.-ks^tiga^ foe exposure potential of these . . setdedduststhtongh dujmg\which time surfaces h . are dtsturbedtosimulate.actual work orfiome exposure situations: The panelists revisited'this issue when roayngthefrfinalr.ec^nimeiidation.s. (see Section 4)- Comment 7: Ralph Zumwalde, NIOSH Dr. Zumwalde suggested that, when recommending research needs, the panelists not only consider long-term projects that would help characterize dose-response, but also projects that might help ATSDR make prudent public health decisions in the short term. Regarding the short fibers, he asked the panelists to discuss research needs to characterize possible links between short fibers and inflammation and fibrosis (e.g., how do fibrosis grades in animals compare to those in humans? are rats an appropriate model for these endpoint?). 3-24 HWBUI0009609 Panelists* Discussions: One panelist noted that several human studies have examined relationships between asbestos exposure (as gauged by lung-retained fibers) and fibrosis grade, but two panelists noted thait comparable studies in which the length distribution of fibers was known have not been performed in animals. Comment 8: Suresh Moolgavkar, University of Washington Regarding the panelists' comments on progression of fibrosis. Dr. Moolgavkar cautioned the panelists about assuming that fibrosis is an intermediate endpoint for lung cancer, because these two endpoints result from very different pathogenicprocesses; Noting that toxicologists have loig assumed linear dose-response relationships for cancer and threshold dose-respoatse behavior fomoncancer effects, he argued that low exposures levels might pose arisk{albeit small)'for lung cancer and perhaps noriskfor fibrosis. Panelists* Discussions: One panelist agreed that fibrosis and lung ciancer develop conducted and reviewed involving fibrous and particulate materials all suggest that lung cancers are not observed in the absence of fibrosis. He emphasized that this does not mean that fibrosis is on a causal pathway for lung cancer, but rather deinofiitiates difeitnt'dose-res|MMte behavior forthelwO outcomes, namely that fibrosis outcomes in animals appear to occur at lower doses than do cancer outcomes. ' ` Comment 9: Jay Tutim,'Sciences filternational, Inc. Mr. Turim asked thh panelists to clarify comments made on disease progression. Paueiists* Dlsciss$rosis: One panelist responded, explaining that he has not observed overt progression of interstitial fibrosis in animals after asbestos exposures cease. He added that inflammatory response, microgranulomas, and ; ; >:bronchioli&tiOa fend t@;'decrease after fiber exposures ceases; even for amosite. dn rats and^bSmstexs-Thisipanelist ate : releV&tit tWopaheliSisindicated that progFessidn tiffibrosis has -absolutely?' been Observed m'hutnans after cessation of exposure. v-". HWBUI0009610 4.0 Conclusions and Recommendations This section reviews the panelists' individual conclusions (Section 4.1) and summarizes remarks from the final observer, comment period (Section 4.2). 4.1 Panelists* Final Statements After addressing ail agenda items, each panelist was asked to make a final statement with his or her individual conclusions and recommendations. These summary statements wereused to draft the executive summary ofthis report A review of the summary statements, in the order in which they were presented; follows: ......... .. Dr. Case 'ssurrimary statement. Dr. Case said than is a strong weightpf.evidence that ' asbestos and SVFs shorter than 5 pm donot cause cancerin humans and no further reseiaroli ismeedbd on this matter. For lung fibrosis ot asbcStosis, on the other hand, he noted tlmt'the role'of fiberb shorter than 5 pm is not as; clear and might iequireTurther study. Dr; Case suggested designing a laboratory animal study to characterize the extent to which fibers translocate into the pleura,,and to determine whether translocation preferentially occitts.for any fiber dimensions or types. To prevent health effeetsifrora occurring in the ftataej Dr. Cassmoted that scientists need a better understaadffiag.of exposure levels;.he.advocated characterizing the fiber length fdistribationin expbsure;samples at;sites with residential exposures. For the. Libby site. Dr. Case indicated that furthefcresearcfa is needed to understand the,unusuai pleural pathology among residents. He suggested conducting systematic farther study ofavailable data, including teftjfe blinded reading ofx-rays and examination.ofpleural histppathology data, if also.trecpnunendgd.coopeiiatiiig with-cpnaraunities believed to have -. .elfcyaisd ^^tsiapbsure.^e:g.^Libby) to esteblish protocols to obtain humahJung v speoihens'aftcfedeathj ithese protocols must.ensufe iliat.blinded analysis of samples occurs andraatched controls arePelected, . . . :.. : ; `Dr. toelteyJs stmtiiary statemenLDs. Lpckey first said he:.concurred with-the conclusions 1 ;:of Dr. Case; He then identified several research opportunities for Lower Manhattan and Libby^twO sites where contamination with short fibers has been observed in residential cbihmuhities;; 4-1 HWBUI0009611 > Regarding the WTC site. Dr. Lockey recommended that health agencies characterize exposure in residential settings using proper industrial hygiene measuring techniques, such that the samples collected reflect personal exposures while individuals perform their normal activities ofdaily living. He suggested that samples be analyzed for asbestos-fiber contest using conventional analytical methods (i.e., those that count fibers longer than 5 pm) and that particulate samples be collected to characterize the amount ofmaterial shorter titan 5 pm. Dr. Lockey indicated that health agencies could then compare the measured level of fibers longer than 5 pm to occupational exposure limits with, appropriate adjustment factors to account for the fact that potential sensitive stibpopulations, such as children, are being potentially exposal To evaluate particulate levels. Dr. Lockey.iecommesded, health agendas should compare the measured levels of particulate; to current recommended occupational arid environment exposure levels and trvsampling results from similar non-WTC urban areas to determine ifelevated particulate . . exposures are occurring. He added that the available human and animal data suggest that "asbestos' paftfciilafe" 0a, asbestos fibers shdrter than 5 pm) dd&'m4''pres(ttiit'a'&izard for cancer or, in the case of the relative short term exposure from WTC, pulmonary asbestosis. S'- > Regardihg the Libby site. Dr; Lockey identified several data gaps and research needs.*. First; he again suggested that future exposure assessment work involve collecting air shmpl& ffiafebest reflect personal exposure levels during typical activities oLdaily living, ^including personal air-sampling forpopulations-rsuch as childrent^^hafchaye potentially 'r high' orpdsures because ofenvironmental activities, Lockey.recOhsnjeoded.that health ageaeiesrefer to the existing literature to-detenninethe implications ofexposures to fibers longer than 5 pm. Dr. Lockey was not sure how;to-evaluate risks ofpleural abnormalities associated with exposures to short, thin, durable tremolite fibers, because these fibers typicafUy have not been quantified in previously pabiiShed'Scientific articles; He did ' recoofinend,-however, thatATSDR study ehest x-ray results from the Libby population to - qiiamtifytbe nuinher ofresidents with pleUralsplaquesanddiffuse pleural fibrosis. This " : "ictistectiqivhe riottdis important because the medical literature reports that diffuse pleUraifibforis cart impair pulmonary function and can be a very progressive disease, vfrHle^plettral plaqpes have, in;ihemselvS,imore limited clinical significance. Dr. Lockey : ' i^iso^ecdniiae^ed'that ATSDR-'investigate -whether- correlations exist betweea.the ;rfe^|iMmofiai^:fiihction.tests (e.g:, spirometric resiilts)'.and the types ofpleurad:,abBOnnalities Sl^e^A-f^iSl^^^iKiial^iDfiliodkey supported ^recommendation made.prevjotJsiydoinitiate a protocol to conduct lung tissue analysis among residents. - t . Dr. McConnell's summary statement. Dr. McConnell first said he supported most of the ; &'> 1 onclusionsrand recdoimendations identified by Dr. Oase.and Dr. Lockey. His main > !-"r. ; finding for the meeting was a revtew of tbe^ends-among the taboratoiy animal studies. Dr. McConnell indicated that these animal studies consistently demonstrate that fiber pathogenicity increases with fiber length. However, he noted that short fibers, if administered in high enough doses, can also produce disease. 4-2 HWBUI0009612 Regarding future research directions in animal studies. Dr. McConnell encouraged health and environmental agencies to specify exactly what questions must be answered in order to address health issues at sites of concern. Once agencies indicate the fiber type, dose, . fiber length distribution, and health endpoint of concern (e.g., pleural changes), then toxicologists can design and conduct animal studies to address these specific issues. Dr. Lippmann's summary statement. Dr. Lippmann supported the other panelists' recommendations for characterizing personal exposures at sites where asbestos and SVF contamination is in residents' homes. Sampling of indoor environments during simulated extreme activity was also recommended. Dr.,Lippmann suggested that sampling from these sites continue to use the conventional fiber counting methods {i.e., counting those longer thanS pm), blit recommended that environmental and health agencies archive the sampling filters for further analysis in the future, should the need for examining shorter fibers become necessary. He added that fiber sampling and analytical protocols should be v standardizedand.adopted to ensure that^samples collected from different sites for different purposes can be comparedL /- Dr. Lippmann encouraged further research into site-specific issues, such as pleural disease in Libby, but he also recommended that future laboratory animal studies, quantify fiber closed-response behavior.as.a function offiber composition and fiber.dimension. He screening studies or intermediate studies. Dr. Mossman's summary statement. Dr. Mossman agreed with other panelists' suggestions and recommendations. She supported initiating further human studies at sites such ab Libby, but she added that additional studies of laboratory animals are needed to quantify bow dose-response varies with fiber dimension and durability. Dr. Mossman also indicated that in vitro studies can (a) provide insights. Within a short time frame, into important questions about relative toxicity Of various materials (e.g., fibers,ofdifferent lengths, fibers with different mineral content), (b) further examine theories ofmechanisms oftoxicity, and (c) direct future research in^laboratory animals. She recommended that such studies challenge target cells.witb welbcharacterized fiber samples to study, bqw. fiber length relates to cel! proliferation, DNA damage, and cytotoxicity. Dr. Mossman emphasized that such short-term studies should use appropriate positive and negative coiiftols and should select egdpoirits that can be later confirmed inanimal studies. m Dr. Oberddrster's summary statement. Dt. OberdSrster-concluded.that most of the available data suggest that fibersdessihaa 5 gni`ia length behave Idee non-fibrous ..A--i\partieles;;b6wever,he noted thatra tew recent publications (e.g.. Brown et al. 2000) have - raised sotrie'questionsrabout this..TodeteniuBe more conclusively whether short fibers . trulybehave like particles and .to asSess howfiher dimension relates to toxicity. Dr. Obefdorster recommended conducting asimple intertracheaUnstiilatson study in rats with different fiber length categories using lung lavage, pleural lavage, and histopathology to , 4-3 HWBUI0009613 characterize toxic endpoints. For each asbestos and SVF material tested,.he suggested evaluating dose-response for different size-selected fiber samples, as well as for an analogous non-fibrous material; ifneeded, this could be followed by a more expensive inhalation study with different well-defined fiber size categories. Second, Dr. Oberddrster recommended that future public health evaluations consider susceptible populations for asbestos and SVF exposure. Dr: Wallace's summary statement. Dr. Wallace recommended that firture research take advantage of the emerging capability ofgenerating samples of well-classified fibers, particularly those in the range ofsmall fiber lengths. He believed this new capability can support very meaningful rn vitro studies, such as those described in Br. Mossman's summary statement, which can then lead into nasabinhalation studies In rats. Recalling the experience ofconducting in Pitrd studies for crystalline silica. Dr. .Wallace urged very thorough planning of future in vitro studies ofshort asbestos and SVEs'to ensure that the assays selected model tise surface conditioning ofdeposited materials which occurs in vfvo, especially for short fiber studies, to avoid false positive resulted Dr. Wallace recommended that priority be placed on investigating the correlation betweenshort ` ' asbestos fibers in the lurtg and pulmonary mferstitial fibrosis (see Section 3.2^2), given the toxicologic findings of in vitro activities ofshoit glass-fibers (Ye et all 1999)' and the inverse-cortelations between fiber length andhing fibrosis score in some studies ofhuman luhg4tissue'('Ghuargcf al.1989,1990; NayobzadelfetaL2001).'. .. 4.2 ObseryM'f^omateuts and Easnysg Dfaeassloiis. ..... Observers were given the opportunity to provide, comments before the meeting adjourned. The panelists were not required to respond to the observer comments; However, some comments led to further discussion among the panelist, as ddcumpnled here. The observer cqmimSnts are summairfeedia^thebrdertiieywrat;preSeDted: . r*v . 1 . A. ` r. ... Comme'dit 1: Windiia Russet toca! 829 findustrtaliheatrical stage employed* ' MsJRossel commented that the role of industrial hygiene for the residences in Lower . Manhattan is to getriddf.tbe WTG dusL'Shemfgedrembval of the dust because scientists ' - truly,do notknow the health implications efithe Complex mixture ofchemieais in the dust. \:Ms. Rb&e! said officials should take precautions when addressing tWs site and remediate and clean' homes, rather than' continue'tostudy the dust sampIes.vAs an example ofher coriccith, Ms. RossCl said, a local high schodl that had already been abated had to be cleaned further recently, when carpets were found to contain WTC dusts. She also 4-4 .j HWBUI0009614 recommended that a registry be formed to track health effects among the community members. Panelists' Discussions: The panelists discussed, the concerns expressed by.community members after all three comments in this section were presented. Refer to the summary following "Comment 3" for the panelists' remarks. Comment 2: Katherine Ewe$ resident of Lower Manhattan Ms. Ewes, a resident ofLower Manhattan,, informed the. panel that asbestos, pulverized glass, and iron have been detected in samples from ventilation systems in residential buildings. Ms. Ewes said it would be helpful ifthe panelists would suggest research on : these materials, particularly interactions between asbestos and iron. Panelists' Discussions: The panelists discussed the concerns expressed by community members after all three comments in this section were presented. Refer to the summary following "Comment 3" for the panelists' remarks. Comment 3: Kimberly Flynn, 911 Environmental Action Ms. Flynn indicated that she is a member of 911 Environmental Action, a coalition of residents and community groups in Lower Manhattan. Ms. Flynn indicated that her group's priority is to stop all continuing exposures to WTC dusts. Ms. Flynn noted that the people who were exposed to dusts on September 11 should definitely be followed up on for health effects, but she emphasized that exposures in residential areas must stop. Ms. Flynn challenged use ofoccupational exposure limits to evaluate exposures to WTC dusts, . because residents in the area are potentially exposed to WTC dusts 24 hours per day and some populations (e.g., housekeepers) might be receiving unusually high exposures. Ms. Flynn said she was pleased that the panelists advocated air sampling to characterize "real world" residential exposure scenarios, like children playing on carpets. Ms. Flynn acknowledged that there are many uncertainties regarding the health effects associated with WTC dust, such as possible synergistic effects, but she was disappointed with how some agencies have responded to public concerns. She was particularly : frustrated that agencies have acknowledged the complexities and uncertainties ofthe WTC dust issue, without taking precautionary measures to cease exposure or provide risk . communication messages to the public. Ms. Flynn asked the panelists, to all of their thinking and research design, to be as protective as possible. Panelists' Discussions: The panelists acknowledged the public concern about WTC dusts, and offered several insights in response. One panelist encouraged residents to participate in research projects that have already been funded, such as one being conducted by faculty at New York University. Another panelist made two comments. First, this panelist noted 4-5 HWBUI0009615 that WTC dust has unique features (e.g., extreme alkalinity) that need to be considered in future sits evaluations. Second, agreeing with the observers, he noted that eliminating exposures to WTC dusts is as important factor. Finally, a different panelist addressed a comment regarding exposures to short chrysolite fibers. He noted that the medical and scientific literature offer iso evidence of exposure tb:short'chiysbtile fibers being of significant health concern, except in cases of prolonged exposures at extremely high doses; he added that the presence of long chiysotile fibers in residences would clearly be ofgreater concern. This panelist also acknowledged thafodier components ofWTC dust (e.g^, metals, polycyclic aromatic hydrocarbons) might be of health concern, but he indicated.that the experts at Ibis meeting were convened to discuss their knowledge of fiber-toxicity.- '>' ' " During this discussion, a representative from ATSDR added that the agency has initiated a registry to track health effects that might be associated with the collapse ofthe World `Trade Center buildings. ` ; , < W f,: /c. y:-w ` r - ' ; 4-6 J HWBUI0009616 5.0 References Adamson IYR, Bowden DH. 1990. Pulmonary reaction to long and short asbestos fibers is independent of fibroblast growth factor production by alveolar macrophages. Am J Pathol 137:523-529. . .. Amandus HE, Wheeler R. 1987. The morbidity and mortality of venniculite miners and millers exposed to tremolite-actinplite: Part tt Mortality. Am J had Med Il :15r-26. Asgharian B, Yu CP. 1988. 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V: 5-6 HWBUI0009622 Appendix A List of Expert Panelists HWBUI0009623 Atsdr Agency for Toxic Substances & Disease Registry Division of Health Assessment & Consultation Expert Panel on Health Effects of Asbestos and Synthetic Vitreous Fibers (SVF): The Influence of Fiber Length Panelists Brace Case Associate Professor of Pathology Director, Environmental Pathology McGill University, Room 203 3775 University Street Montreal, Quebec H3A 2B4 Canada Phone: 514-396-7192 (ext 00521) Fax:514-931-6417 Email: brura.case@fncaiil.ea Morton Uppmann Department of Environmental Median New York University School of Medicine 57 Old Forge Road Tuxedo, NY 10987 Phone: 845-731-3558 Fax: 845-351-5472 Email: lippmann@env.med.nvu.edu James Lockey Professor of Occupational and Environmental Medicine University of Cincinnati College of Medicine 3223 Eden Avenue Kettering Laboratory - Suite G12A Cincinnati, OH 45267-0056 Phone: 513-558-0030 Fax: 513-558-6272 Email.- lames.iockey@uc.edu Ernest McConnell President ToxPath Inc. 3028 Ethan Lane Raleigh. NC 27613 Phone:919-848-1576 Fax. 919-848-1576 Email: 1 Brooke Messman Department of Pathology University of Vermont College of Medicine Health Science Research Facility 218 142 Beaumont Avenue Burlington, VT 05405 Phone: 802-425-3909 Fare 802-656-8892 Email: brooke.mossman@uvro.edu GGnter Oberdtirster University of Rochester Department of Environmental Medicine 5FS Elmwood Avenue Annex - Room A-225 Rochester, NY 14627 Phone: 585-275-3804 Fax:585-275-3709 Email: punter oberdorsteriai.urmc.rochester.edu William Wallace Leader Molecular Biophysics Team NIOSH-CDC 1095 Wfllowdate Road Morgantown, WV 26505-2888 Phone: 304-2556096 Fax: 304-285-6041 Email: wwailac8@cdc.gov HWBUI0009624 Appendix B Premeeting Comments, Alphabetized by Author (includes bios of panelists and the charge to the reviewers) Note: This appendix is a copy of the booklet of the premeeting comments that ERG distributed at the expert panel review meeting. The references for Dr. Lippmann's comments were inadvertently omitted from the booklets available at the meeting. Full citations for the references cited in Dr. Lippmann's premetting comments are included in Appendix E (see pages E-4 through E-6). J\ HWBUI0009625 Atsdr AGENCY FOB TOXIC SUBSTANCES AND DISEASE REGISTRY Ql 'SJ. T? ^ *T Division of Health Assessment & Consultation Expert Panel on Health Effects of Asbestos and Synthetic Vitreous Fibers (SVF): The influence of Fiber Length Premeeting Comments t New York, NY October 29-30, 2002 HWBUI0009626 Notice This booklet includes the panelists' pre-meeting responses to the charge questions. It should be noted that the pre-meeting comments are preliminary in nature. The purpose of these comments is to stimulate meeting discussions. Some panelists' technical findings might change based on discussions during the meeting; therefore, pre-meeting comments should not necessarily be considered the panelists' final opinions. Any mention of trade names or commercial products does not constitute endorsement or recommendation for use. HWBUI0009627 TABLE OF CONTENTS Charge to the Panel.................................................................................................................................... 1 Morton Lippman.................................................................................................................................-..... 15 Ernest McConnell.................... ................................................................................................. -...............35 Brooke Mossman........................ ............................................................................................................ -45 GOnter OberdSrster............. ............................................................................................. -......................55 William Wallace.................................................... ........................................................................... -...............71 ) HWBUI0009628 Health Effects of Asbestos and Synthetic Vitreous Fibers: The Influence of Fiber Length Charge to the Panel The Agency for Toxic Substances and Disease Registry (ATSDR) is holding a panel discussion to review and discuss health effects associated with asbestos and synthetic (man-made) vitreous fibers (SVFs), especially those of less than 5 microns in length. ATSDR has invited a cross-section of scientific experts in the fields of toxicology, epidemiology, pulmonology/pathology, and medicine to participate in 12 days of discussions on a variety of topics, including deposiUonat patterns of fibers in the lung and mechanisms of toxic action, the relationship of fiber size to toxicity, irritant effects of fibers, relationships between measured fiber levels and observed adverse health outcomes, and recommendations for future research. The meeting will have a public health focus, specifically related to evaluating environmental exposures and drawing public health conclusions associated with sites at which fibers and fibrous materials may be an issue. The agency will use input received during discussions to aid in developing scientifically defensible public health evaluations for human exposures to smaller-than-5-micron fibers. Background ATSDR conducts public health assessments to evaluate possible public health implications of contaminants associated with hazardous waste sites and other environmental releases. A crucial part of this evaluation is the understanding of toxicological implications of exposure to substances that may be present Recent events have highlighted a need to further explore the potential for health effects from exposure to biopersistent fibers, specifically asbestos and some SVFs. ATSDR is currently involved in several site assessments that address the potential for residential and community exposures to persistent fibers from past industrial operations (e.g., vermiculite processing plants across the country), hazardous waste sites, and dust generated from the World Trade Center (WTC) collapses in lower Manhattan. These sites are unique in that contaminant materials are/may be present in people's homes and communities. Additionally, there are potential concerns surrounding smaller length fibers which may have been generated by each of these past activities, especially in relation to the materials found in lower Manhattan. Smaller fibers and non-fibrous particles may be generated as fibrous materials are processed, disposed of, or damaged, as in the case of the WTC collapses. In these situations, traditional fiber counting techniques may not quantify all of the materials present Standard assessment methodology addresses fibers greater than 5 microns in length, based on the relative risk of longer fibers being greater than that of shorter fibers. Significant toxicology and occupational health research has focused on asbestos fibers and SVF greater than five microns in length, however, it seems that much less is known about the potential health effects of smaller fibers. ATSDR has identified a need to understand the potential for fibers less than 5 microns in length to contribute to adverse health effects. A TSOR is convening this panel to gain a greater understanding ofasbestos and SVF toxicity, especially as it relates to fibers less than 5 microns in length. Charge to Panel Members . -; The purpose of the panel is to discuss and summarize the best known science for each question. Consensus or specific advice on each question is not requested. ) HWBUI0009629 Specific Charge Questions Discussions on the first day of the meeting will focus on answering questions that pertain to Topic #1, below. In asking these questions, ATSDR seeks a discerning review of the fate of inhaled asbestos and vitreous fibers less than 5 microns In length. The second day of the meeting will be devoted to critical assessment of the health effects that can be justifiably attributed to asbestos and vitreous libers and to identifying critical data gaps and research needs that would further enlighten this subject (Topics #2 and #3). Topic #1: Physiological Fate of Asbestos and Vitreous Fibers less than 5 Microns In Length. Discuss/review current knowledge about the physiological fate of small fibers when they enter the body. > What is the expected physiological depositional pattern for fess-than-5-micron fibers in the lung? What is known about ctearance/biopersistence of less-than-5-micron fibers once deposited in the lungs? What type(s) of migration are expected within tee body for tess-tean-5-micron fibers? Topic #2; Health Effects of Asbestos and Vitreous Fibers less than 5 Microns in Length. Discuss/review health effects that may be due to less-than-5-micron asbestos and vitreous fibers present in air or settled dust How robust are the animal and human cancer data for these fibers/particles? Do the data adequately address exposures where the majority of materials are tess-than-5-microns in length? What is the state of the art understanding of the potential for SVFs to induce cancer in humans? Is there any direct evidence that less-than-5-micron fibers contribute to adverse health effects? Is there Indirect evidence for tess-than-5-micron fiber induced adverse health effects? Do the mechanisms of action of other materials (e.g., longer asbestos fibers, silicates, mineral dusts, amorphous silica) with potentially similar compositions aid in understanding small-fiber mechanisms ofaction? At what length does a material no longer exhibit fiber-like toxicity and can be considered particulate matter regardless of aspect ratio? Can any thresholds be defined for the mechanisms of action that may influence the toxicity of less-than-6-micron materials? Can an exposure threshold be developed for the irritant effects of SVFs for skin contact or eye irritation, based on either fiber loading or fiber content of handled materials? (What are fiberglass levels seen in housing and office areas where SVF insulation has been used, expressed as either* fiber loading or fiber content of settled dust? Have irritant effects been associated with these levels?) .. .. Topic #3: Data Gaps. What data gaps are evident when addressing the above questions? What research is needed to fill these data gaps? HWBUI0009630 Bruce Case McGill University y> HWBUI0009631 Bruce Case Associate Professor of Pathology Director, Environmental Pathology McGill University, Room 203 3775 University Street Montreal, Quebec H3A 2B4 Canada Phone: 514-398-7192 {ext. 00521) Fax: 514-931-6417 Email: bruce.case@iricgiil.ca Dr. Case is a pathologist and epidemiologist at McGill University in Montreal, Canada. Following his residency in pathology at McGill University he obtained the Diploma in Occupational Hygiene at McGill, and worked as a post-doctoral fellow and instructor at the Mount Sinai School of Medicine, New York, from 1980B1983. While there, he performed some of the first studies on asbestos-mediated free radical release, with the help of the Young Investigator's Award of She American Lung Association. On his return to McGill he joined the Dust Disease Research UniL The focus of this group was the epidemiological study of diseases related to mineral fiber exposure using lung-retained fiber in exposure assessment In 1986, he received the National Health Scholarship of NHRDP (Canada) for his work in the field. In 1988, he moved to the University of Pittsburgh, where he succeeded Dr. Philip Enteriine as Director of the U.S. EPA Center for Environmental Epidemiology, through their cooperative agreement with the University of Pittsburgh School of Public Health, where he was also associate professor of epidemiology. He returned to McGill in 1992 and continues research, teaching, and clinical work there In pathology, epidemiology, occupational health and In the McGill School of Environment Dr. Case has participated in workshops, given lectures, and provided peer reviews and advice for many national and international agencies and professional societies on the subject of the exposure assessment and health affects of mineral fibers, including: EPA, CDC (through ATSDR and NIOSH), the U.S. Consumer Product Safety Commission (CPSC), the International Agency for Research on Cancer (IARC). the International Commission on Occupational Health (ICOH), the British Occupational Hygiene Society (BOHS), the American Thoracic Society (ATS), the Geological Society of America (GSA), and the Collegium Ramazzini. His research on asbestos and other mineral fiber and particle exposures and related diseases has been funded by American and Canadian public agencies including EPA, MRC (Canada) and NHRDP (Canada). Dr. Case has published over 100 papers on these subjects. HWBUI0009632 HEALTH EFFECTS OF ASBESTOS AND SYNTHETIC VITREOUS FIBRES: The influence of fibre length. Comments on the Charge to the Panel For the meeting scheduled for New York City October 29/30,2002-10-17 Bruce W. Case, M.D., M.Sc., Dipl. Occupational Hygiene, F.RX.P.(C.) School ofEnvironment Department of Pathology Combined Departments of Epidemiology, Biostatistics and Occupational Health McGill University, Montreal, Canada. First of all, there are some inaccuracies in the charge to the panel as stated. It is in fact not true that "much less is known" about the potential effects of "smaller" (sic) fibers. The effects offiber length are well known for all ofthe asbestos-related diseases (except as noted below) and there is a general consensus that "Fibre dose, dimension, and durability are currently accepted as importantparameters...relevant to potential bioactivity" (1); emphasis added). This statement refers to both diameter (in the sense of respirability) and length (in the sense ofpathogenicity). What is unknown is the means by which these parameters, including fiber length, operate at a mechanistic level, although a great deal ofwork has in fact been done in animals. In fact, although the choice of fibre length (usually 5 pm) by regulatory and other agencies such as NIOSH, OSHA, and WHO was originally practical, being based in part on the resolution of the light microscope, there has been for some time increasing consensus thatfibrogenicity andcarcinogenicity are infact not only related to, but proportional to, fiber length, and many scientists believe that the use of a length of 5 pm as a lower-limit cut-offis not overly liberal (that is, not "too long") but overly conservative (that is, too short, what is lacking in research is not enough research on short fibres but on long fibres (where long refers to fibres longer than 10 pm, 20 pm, or even greater lengths). As some will know, EPA is currently considering a new risk assessment which will take this into consideration, at least for asbestos. There is a considerable paucity of such work on long fibres; see for example our own paper on intrapulmonafy "long" (defined as > 18 pm) fibres in relation to asbestos textile and mining work (2)), which is being used in cument risk assessment revisions by EPA contractors (Berman W., personal communication). To the best ofmy'knowledge this is the only published paper in the so-called "lung burden" (lung-retained fibre) literature which separately assesses long lung-retained fibres, whereas the majority ofsuch papers assess "short" (< 5 pm) fibres; sometimes by default by counting "all" fibres (which overemphasizes the shortfibres and virtually eliminates evaluation of longer fibres due to the log-normal distribution of fiber lengths coupled with counting rules that "stop" after a given number offibers or transmission electron microscopic "fields" are counted) and sometimes through categorizing this fibre interval (between the limits of resolution for length - usually around 0.2 pm in most published work -- and 5 pm). ) HWBUI0009633 HEALTH EFFECTS OF ASBESTOS AND SYNTHETIC VITREOUS FIBRES: The influence of fibre length. (Bruce W. Case; McGill University; October 21,2002) page 2 Before a meaningful discussion of "short fibers" can in fact be held, a strict definition ofterms must be performed. Most mineralogists and geologists and many health scientists do not regard structures having length "less than 5 pm" as fibers at all, regardless of their aspect ratio. Those who believe this would categorize such structures as particles of length less than 5 pm and aspect ratio greater than a given ratio (usually 3:1 or 5:1, although here too, there is debate about what aspect ratio is acceptable in order to "define a fiber"). This is not a mere academic distinction, because the behaviour of these short particles in terms of deposition and lung retention is quite different than that of "true fibers", and the biological effects are likely to (indeed have been demonstrated to) vary from those of "true fibers" as well. In "short"... concentration on so-called "short" fibres (which are not fibres) is a scientific sense worse than a waste of time, it is a diversion from truly pathogenic fibres: fibres which are "long". It remains ofvalue to look at the question of fibre length per se, but not as defined in this Charge: The title is fine ("Theinfluence ofFibre Length") as is part one ofthe principal charge ("ATSDR seeks a discerning review ofthe fate of inhaled asbestos and vitreous fibres...") but the end of the latter sentence less than five microns in length") precludes useful discussion ofthe effects of fibre length on any ofthe parameters presented. Length cannot be arbitrarily divided in this way, although fibres "this short" are almost certainly not pathogenic except in their role as (not necessarily "fibrous" particles; see below) at sufficient bio-persistent dose, some ofthe underlying questions (especially the main heading of Topics # 1 and # 2, which in fact makes.up most of the charge) appear to be limited to the influence of "short" (< 5 pm) length; a length range that is not in the range of fibres at alL The remainder of this discussion will focus on fibre length, not on "short fibres", the term itself being an oxymoron. The sole exception, in my view -and one worth some discussion - is the potential role ofasbestos structures having aspect ratio greater than 3:1 and length less than 5 pm in the pathogenesis of interstitial lung fibrosis ("asbestosis'O- The publication of four articles (two from our laboratory and two from Dr. Churg's) demonstrating an inverse relationship between fibre length and fibrosis in human lung-retained fibre studies is important in this regard (see below), although it may represent an epiphenomenon rather than a true picture ofdecreasing length as a factor in increasing fibrogenesis. In the remainder ofthis document I will concentrate on studies ofhuman exposure, often as demonstrated by tissue retambd-fibre dose (so-called "fibre burden") studies, as other members of the panel are likely to concentrate ihbre on the animal and mechanistic data.. . Briefcomments on the printed charge "questions": Topic 1: What is the expected physiological depositional pattern for less-than-five pm fibres once deposited in the lung? J HWBUI0009634 HEALTH EFFECTS OF ASBESTOS AND SYNTHETIC VITREOUS FIBRES: The influence of fibre length. (Bruce W. Case; McGill University; October 21, 2002) page 3 This is well established in terms of the depositional mechanisms of impaction, settling, sedimentation. Brownian motion and (for fibres) interception. Particles larger than 2 mm. in diameter tend to be deposited directly on the respiratory mucosa (particularly in the nose, nasopharynx and bifurcation of bronchi) by inertial impaction of the particle on the wall as the air in which it is carried changes direction. Particles 0.5 mm. and less tend to remain suspended in gas and exhaled out ofthe lung (Brownian motion). Particles between 0.5 mm. and 2 mm. in diameter tend to be deposited on the mucosa ofdistal bronchi and membranous bronchioles through settling from the force of gravity (sedimentation-, this is the most important deposition mechanism in humans). Fibre length is only important in the sense of interception, which is dependent on length; the longer the fibre the greater the degree of interception in a tube of fixed length. What is known about clearance/ biopersistence of less-than-5... etc. Essentially, outside ofoverloadconditions (which Dr. Oberdorster will be most familiar with), the particles tend to be removed from the lung by a variety of physiological mechanisms the most important ofwhich are macrophage ingestion, dissolution (where chemically possible), and the muco-ciliaiy escalator. Absent abnormalities in phagocyte Enaction these particles should be removed even if they are chemically resistant if(a) the dose is not too great to overwhelm these normal mechanisms and (b) the mechanisms themselves are intact There are medical conditions which affect these mechanisms, however, so there are likely to be vulnerable populations (such as those withprimary ciliary disorders; these tend to be genetic and very rare such as primary ciliary dyskinesia (incidence 1:20,000 to 1:60,000)). Of greater frequency is the lesser effect on muco-ciliaiy clearance in asthma. In addition environmental influences, including smoking and nitrogen dioxide (3), can affect these normal mechanisms through direct ciliary damage or disrupted function. Some common pharmaceuticals slow muco-ciliaiy transport (for example some general anaesthetics and atropine), while others accelerate it (for example theophyllines and sympathomimetics). Bronchial secretion is also an important contributor to clearance or impaired clearance, as can be seen most dramatically in cystic fibrosis. Overall, then, there are a number of possible factors which may interfere with particle clearance, but none have been associated with "fibre length" parameters with the possible exception ofsmoking (4). ... What type of migration are expected within the body for ("short fibres")? This may be an important subject, at least for the parietal pleura, ifit is necessary for fibres to reach the pleura to cause lesions (plaques and mesothelioma). It remains possible that fibres still within the peripheral lung may be capable ofcontributing to the mechanisms ofthese diseases. Mechanisms remain speculative, but long amphibole fibres may tend to localize toward the lung periphery, and it remains possible (but unproven and indeed untested) that chemical mediators may cross the visceral pleura into the pleural space. Churg, among others, has observed that "accumulation of long fibers immediately under the upper lobe pleura may be important in the genesis of mesothelioma" (5). The idea that it is biologically necessary that fibres "reach the HWBUI0009635 HEALTH EFFECTS OF ASBESTOS AND SYNTHETIC VITREOUS FIBRES: The influence of fibre length. (Bruce W. Case; McGill University; October 21,2002) page 4 parietal pleura" to cause mesothelioma is not scientifically tenable, although intellectually appealing. Unfortunately, less is known about this than what has been published, due to the exceptionally poor quality ofwhat has been published, with two exceptions from a group based in Brussels and Marseilles (6,7). The few additional papers that have been published (in relation to human disease) have been for the most part based on static "fiber burdens" that purport to be in "the pleura" but which on careful reading are in fact in mesotheliomatous tissues and/ or pleural plaques; the false assumptions are then made that "short fibres" - usually very short chrysotile fibres, averaging less than 0.2 pm in length - have "translocated" to the "pleura" from the lung. In fact the "pleura" was not studied, tumor and plaquew which by definition could not contain fibres except via specimen contamination or incorporation, most likely from adjacent lung. Both Rogers et al. 1994 (8) and Case et at 1994 (9) have also reported contamination by short crocidolite fibers ofNuclepore filter materials and in uncontrolled studies ofthis nature any material from air, fluids, and paraffin in the pathology laboratory from which the specimens originally were referred to specimen preparation materials are suspect. All of the studies lacked matched controls, and in the American cases all were selected for litigation and subjected to a non-standard digestion technique. Examples of this are provided by all papers having Y. Suzuki as co-author on this topic (10-12) and some early papers by Sebastien (13,14); the topic has been fully reviewed elsewhere (15). It remains possible to do good studies of translocation of fibres, but for lung-topleura in humans at least only the two preliminary studies mentioned above have proved useful, and their results have been quite different: Boutin et al. and Dumortier et al. (6,7) have found that "the distribution ofasbestos fibers in the pleura was heterogeneous and that they might concentrate in.. ."black spots" ofthe parietal pleura". Using thoracoscopy in living patients from "normal areas of the parietal pleura" rather than plaques and tumor, and using controls, they showed that "amphibofes outnumbered chrysotile in all samples" and that of all fibres 22.5% were in fact greater than or equal to 5 microns in length; a proportion at least as great as that .usually seen in lung tissue. The means of translocation remains unknown, although these findings strongly suggest lymphatic drainage paths; The pathogenic significance also remains unknown, although the authors emphasized their hypothesis that these fibres might contribute to plaque and mesothelioma genesis. Topic # 2; Health effects... How robust are the animal and human cancer data...do the data adequately address...less-tban-5... As noted above, regrettably, this is the wrong question. The correct question would be, either "Do the data adequately address the effects of dimension" (the answer to which is a qualified yes) and "do the data adequately address MORE THAN 5 N. -J HWBUI0009636 HEALTH EFFECTS OF ASBESTOS AND SYNTHETIC VITREOUS FIBRES: The influence of fibre length. (Bruce W. Case; McGill University; October 21,2002) page 5 (substitute more-than-10, more-than-20... etc.). Here the answer Is that the data clearly do not adequately access the effects of long fibres, the fibres of greatest concern for disease, or more properly they do not address the longestfibres, as a result of too much concentration on published studies on fibres under 5 micrometres in length. This has been essentially "by default" in the lung-retained fibre field, since studies which take as their starting point "all fibres from 1 micrometre up", or less, will be definition inadequately address the most pathogenic fibres, known to be the longest fibres. What is the state of the art understanding of the potential for SVFs to induce cancer in humans? Thanks to the excellent studies of the European Group, of Enterline, and most recently of Gary Marsh et at. at the University ofPittsburgh, it has now been established that SVFs do not induce cancer in humans. Original concern arose when Saracci and the European group noted in a very large cohort of 13 plants an SMR for lung cancer of 192 (17 observed, 8.9 expected; 95% confidence interval 117-307). Although an initial dose-response relationship was believed present, subsequent study showed that the excess appeared in an anomalous group of workers; first, those limited to the "early technological phase" ofthe industry, but perhaps even more important workers having different lifestyles (and dehth-style; a high suicide rate), and in many cases short-term workers. No such excess was ever seen in the American workers except in some rock-wool plants, and lung-retained fibre studies demonstrated no excess of MVF but an excess ofamosite asbestos in the lungs of workers compared with controls dying in the same hospital in one of the "higher lung cancer" areas. Enteriine and colleagues demonstrated "no consistent evidence of a respiratory disease hazard related to exposure to man-made mineral fibers among the workers who produce these fibers" in the largest study of these workers (16); although lung cancer and non-malignant respiratory disease were increased in some rock- and slag- wool plants there was no evidence ofa dose-response relationship. Complete follow-up ofthe study has recently been completed (17-24) and the lack ofany relationship, to disease confirmed, including for mesothelioma; of ten cases originally reported most were not mesothelioma and in any case almost all were asbestos-exposed. Overall, Marsh and colleagues noted -The excess in respiratory system cancer is largely a reflection of elevated lung cancer risks that we attributed mainly to confounding by smoking, to exposures outside the MMVF industry to agents such as asbestos, or to one or ritore of the several co-exposures present in many ofthe study plants (including asbestos)" (23), '' Is there any direct evidence that (short) "fibres" contribute to adverse health effects? No, with the possible exception of asbestosis. For mesothelioma, at least three wellconducted case-control studies have now established that lung-retained.fibre "risk" is entirely accounted for by long amphibole lung-retainedfibre content and that any initial apparent effect of shorter fibres was a statistical artefact (15,25-27). An initial observation by Rogers et at. of an increased risk associated with the intrapulmonary size HWBUI0009637 HEALTH EFFECTS OF ASBESTOS AND SYNTHETIC VITREOUS FIBRES: The Influence f fibre length. (Broce W. Case; McGill University; October 21,2002) page 6 category "shorter than 10 pm" (26) was later thought by the authors to lack biological plausibility, and ifanything the "short" (< 10, not < 5) fibres represented broken down "longer" fibres (8). Lung cancer, due to its overwhelming relationship to smoking, as proved difficult to investigate in this way. Animal studies and theoretical data are consistent with the overwhelming importance of fibres longer than 5 (indeed longer than 10, or longer than 20) micrometres (28-32). Recent observations that the half-life of chrysolite fibres longer than 10 micrometres may be more than eight years, at least in long-term chrysotile miners and millers (33), and that in mixed-exposure asbestos textile workers lung content of fibres longer than 18 micrometres was proportional to cumulative exposure (2) has shown that even for chrysotile, any effect appears to be related to long, not shorter, fibres. At what length does a material no longer exhibit fiber-like toxicity and can be considered particulate matter... This is one of the most important issues to be addressed; the most recent science from the point ofview ofrisk assessment would imply that this figure is much higher than previous believed; certainly higher than 10 micrometres, much less 5. Modem risk assessments will take fiber length into account, possibly by the application of algorithms which assign increasing risk with increasing length. It is difficult to imagine setting one number below which a structure is a "particle" and not a "fibre"; it is much easier to say that structures less than five micrometres do not - ever - behave as fibres with respect to lung cancer and mesothelioma. As alluded to several times above, there are a series ofhuman studies which show an inverse relationship between fibre length and asbestosis severity. Studies by Churg and colleagues first of long term chrysotile asbestos miners and millers, in which "tremolite mean fiber length, aspect ratio, and surface area were, surprisingly, negatively correlated with fibrosis grade" (34). A similar study found a similar result for amosite in unselected litigation cases, mainly in shipyard workers and insulators, prompting the authors to conclude that "these observations again raise the possibility that short fibers maybe more important than is commonly believed in the genesis of fibrosis in'man" (35). However, there were some serious problems with these papers in that groups were small (no more than 21) and (as is always the case).fibre lengths Were very strongly inter-correlated. Contradictory data initially came from our own laboratory (15), but more recent unpublished work with a much larger data base of workers selected across a more homogeneous base and divided into fiber length "strata" has once again demonstrated an apparent inverse association between interstitital fibrosis grade and (in this experiment) fiber length interval. Results, which are about to be published, will be discussed, as they and the previous human work contradict some animal work on fibrosis and fiber length. The latter however appears somewhat speculative with respect to postulated mechanisms of fibrosis. Is it reasonable to believe, for example, that "frustrated phagocytosis" results in much more chemical mediation than "simple" phagocytosis of muchlarger quantities of shorter fibre? If "short" fibres do have an effect which has not been adequately ) HWBUI0009638 HEALTH EFFECTS OF ASBESTOS AND SYNTHETIC VITREOUS FIBRES: The influence of Fibre length. (Bruce W. Case; McGill University; October 21,2002) page 7 explored - as fibres, rather than particles--then it surely the production of interstitial fibrosis. REFERENCE LIST 1. Kane AB, Boffelta, P., Saracci, R.. Wilbourn, J.D., editor. Mechanisms ofFibre Carcinogenesis. Lyon:International AgencyforResearch on Cancer; WHO; 1996. 2. Case BW, Dufresne A, McDonaldAD, McDonaldJC, Sebastien P. Asbestosfiber type andlength in lungs ofchrysotile textile andproduction workers: Fibers longer than 18 mu m. Inhalation Toxicology 2000;12:411-418. 3. Case BW, Gordon RE, Kleinerman J. Acute bronchiolar injuryfollowing nitrogen dioxide exposure: Afreezefracture study. Environ Res I982;29(2):399-413. 4. Takahashi K, Case BW, Dufresne A, Fraser R, Higashi T, Siemiatycki J. Relation between lung asbestosfibre burden and exposure indices based onjob history. Occup Environ Med 1994;51(7):461-9. 5. Churg A, Wiggs B. Accumulation oflong asbestosfibers in theperipheral upper lobe in cases ofmalignant mesothelioma. Am J Ind Med 1987;11(5):563-9. 6. Boutin C, Dumortier P, Rey F, Viallat JR, De Vuyst P. Black spots concentrate oncogenic asbestosfibers in the parietalpleura. Thoracoscopic and mineralogic study. Am J Respir Crit Care Med1996;153(1):444-9. 7. Dumortier P, Rey F, Viallat JR, Broucke I, Boutin C, De Vuyst P. Chrysotile and tremolite asbestosfibres in the lungs andparietalpleura ofCorsican goats. Occup Environ Med2002;59(9):643-6. 8. Rogers AL, J. Berry G. et al. Dose-response relationship between airborne and lung asbestosfibre type, length, and concentration, and the relative risk ofmesothelioma. Ann Occup Hyg 1994;38(Sl):631-638. 9. Case BW KM, Harrigan M, Dufresne A. Lungfibre content ofAmerican children aged 8-15years. Ann Occup Hyg 1994;38(S1). 639-645. 10. Kohyama N, Suzuki 7. Analysis ofasbestosfibers in lungparenchyma, pleural plaques, and mesothelioma tissues ofNorth American insulation workers. Ann NYAcad Sci 1991;643:27-52. 11. Suzuki Y, Kohyama N. Translocation ofinhaled asbestosfibersfrom the lung to other tissues. Am JInd Med 1991;19(5): 701-4. 12: } Suzuki Y, Yuen SR. Asbestos tissue burden study on human malignant mesothelioma: Ind Health 2001;39(2):150-60:. 13. Sebastien P, Fondimare A, Bignon J, Monchaux G, Desbordes J. Bonnaud G. Topographic distribution ofasbestosfibres in human lung in relation to.occupational and non-occupational exposure. InhaledPart 1975;4(Pt 2):435-46. 14. Sebastien P. Janson X, Gaudichet A, ffirsch A, Bignon J. Asbestos retention in. human respiratory,tissues: comparative measurements in lungparenchyma and in parietalpleura.MRCSei Publ 1980(30):237r46. 15. Case BW. Biological indicators ofchrysotile exposure. Ann Occup Hyg 1994;38(4):503-J8. 410-1. 16. Enterline PE, Marsh GM. Esmen NA. Respiratory disease among workers exposedto man-made mineralfibers. Am Rev Respir Dis 1983; 128(l):l-7. HWBUI0009639 HEALTH EFFECTS OF ASBESTOS AND SYNTHETIC VITREOUS FIBRES: The influence of fibre length. (Brace W. Case; McGill University; October 21,2602) page 8 17. Quinn MM, Smith TJ, YoukAO, Marsh GM, Stone RA, Buchanich JM. et al. Historical cohort study of US man-made vitreousfiber production workers: VIII. Exposure-specificjob analysis. J Occup Environ Med 2001;43(9):824-34. 18. Smith TJ, Quinn MM Marsh GM, YoukAO. Stone RA. Buchanich JM, et al. Historical cohort study ofUS man-made vitreousfiber production workers: VII. Overview ofthe exposure assessment J Occup Environ Med2001;43(9):809-23. 19. Marsh GM, Buchanich JM, YoukAO. Historical cohort study of US man-made vitreousfiberproduction workers: VI. Respiratory system cancerstandardizedmortality ratios adjustedfor the confounding effect ofcigarette smoking. J Occup Environ Med 2001;43(9):803-8. 20. Buchanich JM, Marsh GM, YoukAO. Historicalcohort study ofUS man-made vitreousfiberproduction workers: V. Tobacco-smoking habits. J Occup Environ Med 2001:43(9):793-802. 21. Stone RA, YoukAO, Marsh GM Buchanich JM, McHenry MB, Smith TJ. Historical cohort study of US man-made vitreousfiberproduction workers: IV. Quantitative exposure-response analysis ofthe nested case-control study ofrespiratory system cancer. J Occup Environ Med2001;43(9):779-92. 22. YoukAO, Marsh GM, Stone RA, Buchanich JM, Smith TJ. Historical cohort study ofUS man-made vitreousfiberproduction workers: HI. Analysis ofexposure-weighted measures ofrespirablefibers andformaldehyde in the nested case-control study of respiratory system cancer. J Occup Environ Med2001;43(9):767-78. 23. Marsh GM, Guta Ml, Youk AO, Buchanich JM, Churg A, Colby TV. Historical cohort study ofUS man-made vitreousfiberproduction workers: II. Mortalityfrom mesothelioma. J Occup Environ Med 200l;43(9):757-66. 24. Marsh GM, YoukAO, Stone RA, Buchanich JM, Gula MJ, Smith TJ, et al. Historical cohort study ofUS man-made vitreousfiberproduction workers: I. 1992 fiberglass cohortfollow-up: initialfindings. J Occup Environ Med2001;43(9):741-56. 25. Rodelsperger K, Woitowitz HJ, Bruckel B, Arhelger R, Pohlabeln H, Jockel KH. Dose-response relationship between amphibolefiber lung burden and mesothelioma. Cancer Detect Prev 1999:23(3):183-93: 26. Rogers AJ, Leigh J, Berry G, Ferguson DA, MulderHB, Ackad M Relationship between lung asbestosfiber type and concentration and relative risk ofmesothelioma. A case-control study. Cancer 1991;67(7):1912-20. 27. McDonaldJC, Armstrong B, Case B.Ddetl D, McCaUghey WT, McDonaldAD, et al. Mesothelioma and asbestosfiber type. Evidencefrom lung tissue analyses. Cancer 1989;63(8):1544-7: : 28. Miller BG, Jones AD, Sear1 A, Buchanan D, Cullen RT, Soutar CA, et al. Influence ofcharacteristics ofinhaledfibres on development oftumours in the rat lung. Annals ofOccupational Hygiene 1999:43(3):167-179. ' 29. Miller BG, SearlA, Davis JMG, Donaldson K, Cullen RT, Bolton RE, etal. Influence offibre length, dissolution and biopersistence on theproduction of mesothelioma in the rat peritoneal cavity. Annals ofOccupational Hygiene 1999:43(3):155-166. 30. Miller BG, Jones AD, Sear! A, Buchanan D, Cullen RT, Soutar CA, et al. Influence ofcharacteristics ofinhaledfibres on development oftumours in the rat lung. Ann OccupHyg 1999;43(3):167-79. ') HWBUI0009640 HEALTH EFFECTS OF ASBESTOS AND SYNTHETIC VITREOUS FIBRES: The Influence of fibre length. (Bruce W. Case; McGill University; October 21,2002) page 9 3 1. Lippmann M Deposition and retention ofinhaledfibres: effects on incidence of lung cancer andmesothelioma. Occup Environ Med 1994;51(12):793-8. 32. Lippmann M Effects offiber characteristics on lung deposition, retention, and disease. Environ Health Perspect 1990;88:311-7. 33. Finkelstein MM, Dufresne A. Inferences on the kinetics ofasbestos deposition and clearance among chrysotile miners and millers. Am JIndMed 1999;35(4):401-12. 34. Churg A, WrightJL, DePaoliL, Wiggs B. Mineralogic correlates offibrosis in chrysotile miners and millers. Am Rev Respir Dis 1989;139(4):89l-6. 35. Churg A, Wright J, Wiggs B, Depaoli L. Mineralogic parameters related to amosite asbestos-inducedfibrosis in humans. Am Rev Respir Dis 1990;142(6 Pt 1}:1331- HWBUI0009641 Morton Lippmann New York University School of Medicine i 0 ) HWBUI0009642 Morton Lippmann Department of Environmental Medicine New York University School of Medicine 57 Old Forge Road Tuxedo, NY 10987 Phone: 845-731-3558 Fax: 845-351-5472 Email: lippmann@env.med.nyu.edu Dr. Lippmann is a Professor of Environmental Medicine at the New York University (NYU) School of Medicine. He holds a Ph.D. (NYU, 1967) in Environmental Health Science, an S.M. (Harvard University. 1955) in Industrial Hygiene, and a B.Ch.E. (The Cooper Union, 1954) in Chemical Engineering. At NYU, he directs a research program cm Human Exposure and Health Effects, and the EPA-supported Particulate Matter Health Effects Research Center. He has been the recipient of numerous awards for his research and contributions in aerosol science and pulmonary physiology, human exposure assessment and dosimetry, chemical transformations in the atmosphere, population studies of exposure-response relationships in occupational and community cohorts, and factors affecting the toxicity of airborne fibers. Much of this research has been focused on specific chemical agents, notably ozone, sulfuric acid, and asbestos. Dr. Lippmann is a past President of the International Society of Exposure Analysis (19941995), past Chairman of: the ACGIH (1982-1983); the EPA Science Advisory Board's Executive Committee (20.00-2001); EPA's Advisory Committee on Indoor Air Quality and Total Human Exposure (1987-1993); and EPA's Clean Air Scientific Advisory Committee (1983-1987). He has also chaired and been a member of numerous National Research Council committees, including committees on the airliner cabin environment and the health of passengers and crew, synthetic vitreous fibers, measurement and control of respirable dust in mines, indoor pollutants, toxicity data elements, and in-vivo toxicity testing of complex mixtures. His publications include 270 research and review papers in the scientific literature and two reference texts on environmental health science. HWBUI0009643 RESPONSES TO ATSRR FIBERS PANEL CHARGE QUESTIONS M. Lippmann Specific Charge Questions Topic # 1. Physiological Fate of Asbestos and Vitreous Fibers less than 5 Microns in Length. Discuss/review current knowledge about the physiological fate of small fibers when they enter the body. A. What is the expected physiological depositional pattern for less-than-5-micron fibers in the lung? Fibers with aspect ratios >10 behave aerodynamically like unit density spheres with diameters one-third their fiber width (Stdber et al., 1970; Timbrell, 1972). The only exception, in terms ofbeing influential in deposition in lung airways is for fibers longer than about 10 pm, where the mechanism of interception becomes influential (Sussman et at, 1991). Thus, for fibers <5 pm in length, deposition patterns and efficiencies will be determined almost entirely according to the fiber width, which for fibers <5 pm long will be less than about 1.6 pm. For fiber widths between about 0.1 and 1.6 mm, total lung deposition in healthy people will be between 10 and 20%, with almost all of it in the deep lung. For fibers thinner than 0.1 pm, deposition will increase with decreasing width, and there will be a somewhat greater proportion of the deposition in the more proximal airways. B. What is known about clearance/biopersistence of less-than-5-micron fibers once deposited in the lungs? For these short fibers, which can be fully engulfed by lung cells and do not dissolve in airway fluids in less than a few weeks, their clearance will be similar to other mineral and vitreous particles. Those depositing in lung conductive airways will be largely removed to the G.I. tract by mucociliary clearance within about one day. Most of those depositing in the gasexchange region will be phagocytized by alveolar macrophages and cleared to and through the HWBUI0009644 mucociliary escalator within a few weeks. Other particles may be engulfed by epithelial cells, primarily in the respiratory acinus, and retained for much longer periods, with gradual removal to lymph nodes. C. What type(s) of migration are expected within the body for less-than-5-micron fibers? Fibers with diameters less than -0.1 pm, which could be a significant fraction of fibers <5 pm in length, can penetrate through the respiratory epithelia and be transported through lymph channels to hilar and peripheral (mesothelial) lymph nodes and through blood to more distant body organs. However, quantitative aspects of these pathways have not been described. Topic # 2. Health Effects of Asbestos and Vitreous Fibers less than 5 Microns in Length. Discuss/review health effects that may be due to less-than-5-micron asbestos and vitreous fibers present in air or settled dust. A. How robust are the animal and human cancer data for these fibers/particles? Do the data adequately address exposures where the majority of materials are Iess-than-5-microns in length? Animal Toxicology Cancer Data: The most definitive studies for short fibers (<5 pm in length) was carried out by Davis et al. (1986, 1987) in Edinburgh using inhalation' exposures and length classified amosite and chrysolite asbestos fibers. The short-fiber amosite (1.7% <5 pm in length) produced no malignant cancers in 42 rats,, whereas the long-fiber amosite (30% >5 pm in length, 10% >10 pm), with the same diameter distribution, produced 8 cancers in 40 animals (Davis et al., 1986). In the corresponding study using chrysotile (Davis et al., 1987), the short-fiber material was less successfully depleted in long fibers. There were 330 0'mL longer than 10 pm in the "short" chrysotile, versus 12 FmL in the "short" amosite, and the "short" chrysotile produced seven HWBUI0009645 cancers (while the "long" chiysotile produced 22 cancers). These results suggest that the cancers produced by the "short" chiysotile preparation were, in fact, due to its contamination by longer chrysotile fibers. This conclusion is supported by the analysis of Lippmann (1994) using the fiber length distribution data for rat inhalation studies of unclassified fibers of amosite, brucite, chiysotile, crocidolite, erionite, and tremolite. He concluded that the tumor yield was better predicted by the concentration of fibers longer than either 10 or 20 pm than by the concentration of fibers longer than 5 pm. The animat cancer data for injected fiber suspensions and the human epidemiologic data where fiber length distributions are available are consistent with carcinogenicity being attributable solely to fibers longer than 5 pm, but are not by themselves definitive. B. What is the state of the art understanding of the potential for SVFs to induce cancer in humans? The state-of-the-art on this issue was summarized in a recent National Research Council report (NRC, 2000), as follows: "In a review of the published epidemiologic literature with respect to respiratory system cancer, Lee et at. (1995) concluded that 'available data indicate that among those occupationally exposed, glass fibers do not appear to increase the risk of respiratory system cancer. Exposure to rock or slag wool may increase the risk of such cancers; however, the data do not convincingly' prove that this association is causal.' Recent studies, including case-control studies, make it clear that any lung-cancer SMKs based on national data must take into account the potential confounding effect of smoking.. Evidence from the case-control studies demonstrates that there is no significant association between fiber exposure and lung cancer or nonmalignant respiratory disease in the MVF manufacturing environment It is clear, for example, that of the Newark, Ohio, plant workers (who made up some 35% of the U.S.' Cohbrt) exposure to MVF, including respirable glass fibers, was not responsible for any increase in lung cancer risk (Chiazze el a!., 1993)." ) ) HWBUI0009646 C. Is there any direct evidence that less-than-5-microa fibers contribute to adverse health effects? In the absence of data that SVF fibers of all lengths cause respiratory disease, it is highly unlikely that the SVF fibers <5 pm in length cause any. D. Is there indirect evidence for less-tban-5-micron fiber induced adverse health effects? Do the mechanisms of action of other materials (e.g., longer asbestos fibers, silicates, mineral dusts, amorphous silica) with potentially similar compositions aid in understanding smalt-fiber mechanisms ofaction? There is no such evidence, and the greater rate of SVF fiber dissolution than of other materials cited in the question makes it very unlikely that short-fiber SVF causes health effects. E. At what length does a material no longer exhibit fiber-like toxicity and can be considered particulate matter regardless ofaspect ratio? The length limit is clearly not less than 5 pm and, for humans, probably closer to 10 pm. F. Can any thresholds be defined for the mechanisms of action that may influence the toxicity of less-than-5-.micron materials? Possibly, but if they exist, they would be much higher than any reasonably anticipated exposures in modem society. G. Can an exposure threshold be developed for the irritant effects of SVFs for skin contact or eye irritation, based on either fiber loading or fiber content of handled materials? (What are fiberglass levels seen in housing and office areas where SVF insulation has been used, expressed as either fiber loading or fiber content of settled dust? Have irritant effects been associated with these levels?) HWBUI0009647 Possibly, but not likely for airborne concentrations as measured in fibers/mL. Topic #3: Data Gaps. A. What data gaps are evident when addressing the above questions? The rat inhalation studies with size-classified amosite and chrysotile show how a well conceived study can help to resolve critical questions about lung cancer. More studies with better classified chrysotile, and with other well-classified asbestos and vitreous fibers of varying lengths and biopersistence properties, would be very informative. A major data gap is the influence of fiber length on mesothelioma, which could be addressed in the hamster model. B. What research is needed to fill these data gaps? Inhalation studies in rats with size-classified fibers for lung cancer, and inhalation studies in hamsters with size-classified fibers for mesothelioma. 1 HWBUI0009648 Janies Lockey University of Cincinnati College of Medicine HWBUI0009649 Jamas Lockey Professor of Occupational and Environmental Medicine University of Cincinnati College of Medicine 3223 Eden Avenue Kettering Laboratory - Suite G12A Cincinnati, OH 45267-0056 Phone: 513-558-0030 Fax: 513-558-6272 ____________ Email: jatnes.lockey@uc.edu Dr. Lockey has been associate director of the Department of Environmental Health, director of the Division of Occupational and Environmental Medicine, and a professor of environmental medicine at the University of Cincinnati College of Medicine since 1986. In addition, he is a consultant in employee health to the Children's Hospital Medical Center. Dr. Lockey completed his M.D. in 1972 (Temple University School of Medicine), and an additional M.S. in 1985 (University of Cincinnati College of Medicine). He was instrumental in developing the Center for Occupational Health (COH) at Holmes Hospital in the University of Cincinnati Medical Center white serving as director (1990B1998). Dr. Lockey continues to work in the COH through the Occupational Pulmonary Clinic where specialized services are provided in occupational medicine, occupational pulmonary services, disability management, and medical surveillance. In addition to his clinical activities. Dr. Lockey is a prolific researcher. The focus of his research has been on the health effects of exposure to man-made vitreous fibers (MMVF). He initiated, and currently directs, an industry-wide study of the health effects of refractory ceramic fibers. This study will continue until at least 2005 and has been the first to identify that exposure to certain types of MMVF is associated with scarring along the chest wall (pleural plaques). Dr. Lockey has developed a national, as well as international reputation, in regard to the health effects of MMVF and has written over 100 articles and book chapters on this topic. y HWBUI0009650 James E. Lockey, MD, MS Topic #1: Physiological Fate ofAsbestos and Vitreous Fibers less than 5 Microns in Length. What is the expectedphysiological'deposUionaUratJem forless-than-5-micron fibers in the lung? What is known about clearance/biopersistence ofless-than-5-micron fibers once deposited in the lunss? Hazards associated with man-made vitreous fiber (MMVF) appears to be most strongly associated with the ability to persist within lung tissue. This is in part dependent upon chemical composition of the MMVF in that increased concentrations ofstabilizers such as aluminum impact a greater degree of chemical durability. In vitro tests to measure fiber solubility should be performed to reflect an acid pH of 4.5 to 5.0 such as found in phagolysomes within alveolar macrophages as well as pH of7.4 reflecting extra-cellular fluid. Short fibers that are ingested by macrophages will encounter the lower pH that overall could affect their biopersistence. In general, solubility tests identified the following rank order from lowest to greatest solubility ofMMVF in comparison to asbestos fibers: crocidolite <amosite <RCF <special purpose glass fibere <rock wool <slag wool <conventional glass fibers. [IJ In rodent exposure to mixed dust resulted in an increased transport of fibers across the visceral pleura and increase production of lung tumors and mesothelioma. [2] Fibers may act as carcinogens or carriers of chemical carcinogens to the target organ. [2] What typefs) ofmigration are exoeclsd within the body for less-than-5-micron fibers? Gelzleichteret al, in 1996 exposedrats to nose only inhalation ofkaolin-basedrefractory ceramic fiber. It was identified that fibers rapidly translocate to the pleural tissue with a difference between those in the pleural tissue, and the parenchymal tissue. Within the pleural tissue the geometric mean length 1.5 pun (GSD -- 2.0 pm) and geometric mean diameter 0.09pm (GSD ~1.5 pm). For comparison parenchymal tissue GML=5.0 pm (GSD --2.3) arid GMD 0.3 pm (GSD --1.9.) This would indicate the short thin fibers are capable of translocating to the pleural tissue. [3] HWBUI0009651 James E. Lockey, MD, MS Tbe efficiency ofclearance by macrophages is greatest with fibers less than 5 microns in length and becomes less efficient with increasing length offibers. Certain fibers may stimulate macrophages to move to the pleura rather than to be cleared from the lung which may be the case with crocidolite and erionite. [4] Topic Mil Health Effects ofAsbestos and Vitreous Fibers less than 5 Microns in Length. How robust are the animal andhuman cancer data for these fibers/particles? Do the data adequately address exposures where the majority ofmaterials are less-than-5-microns in length? Conventional glass fiber has only a very small fraction that would be small enough from an aerodynamic diameter perspective to be able to penetrate into the lungs. Those conventional glass fibers that actually do penetrate into the lungs would rapidly break into shorter segments and rapidly dissolve. Therefore, the risk for lung cancer and mesothelioma from exposure to conventional glass fiber is extremely small unless there was an ongoing continuous exposure to high levels of long fibers. [5J. Probability of pleural sarcomas was best correlated with fibers 0.25 microns or less in diameter and >8 microns in length, but there was a high correlation with fibers up to 1.5 microns in diameter and length >4 microns. [6] Further analysis of the Stanton hypothesis indicated that the type of mineral fiber was significant in relationship to predicted tumor incidence as was the number of index particles rather than log mean aspect ratio, [7] What is the state ofthe art understanding ofthe potential for SVFs to induce cancer in humans? Mortality studies of MMVF have not demonstrated a cancer risk regarding glass fiber and mineral wool production workers. There is no current published human mortality data available regarding refractory ceramic fibers. James E. Lockey, MD, MS Is (here any direct evidence that less-Shan-5-micron fibers contribute to adverse health effects? There is some indication that fibers with diameters of<0.1 - 0.4 fjm in lengths <10 fim may have a greater propensity for inducing pleural plaques as reviewed in an article by Lentz et al.[8] In regard to pleural plaques, Churg et al, identified that fiber size is significantly related to plaque formation with a geometric length of3.0 fim and aspect ratio of 19.4 in patients with plaques versus 2.5 fan and aspect ratio 14.5 with no plaques. [9] Some studies have suggested that short asbestos fiber may be carcinogenic when injected, but these results are difficult to interpret as the short fibers are only reported as a proportion of the total. With the ability of the fibers to cleave longitudinally as well as transversely, it is quite possible that the mean fiber length of the sample is reduced while actually increasing the number of long fibers per unit mass. A study of amosite fibers by an inhalations! studies in rats with almost ail fibers less than 5 microns in length was compared to normal amosite dust and the short fibers produced neither fibrosis nor neoplasm in comparison to the long fibers. [10,11] Intrapleural inoculation studies and inhalation studies ofshort (<5fim) and long crocidolite and erionite fibers demonstrated tumors and fibrosis, with long fiber exposure and tissue reaction only with the short fibers. [18] Studies of asbestiform versus nonasbestiform tremolite by in vivo intrapleural injection demonstrated production ofmesotheliomas with the asbestiform fiber exposure as well as markedly increased cytotoxicity. [12] HWBUI0009653  <Sa>5r ,a ,, Jl i 0 1 IS* 11111 JL> t> u u u Jg s E 'E 6 ft-. tu a63 o Ji ss TO < JkQD> SgoM5 a<P?. *s 5 -S -3 o(*UA 3aE> E Sa S_> B(JO ,, - n. M S e* aM sK> Qs *S s t* .2 &s 2-1 o V Q VO o ? p Ail>f 3 ui Il^s I ovi *--Vo<|<PJL? 1PJL? "ov qiiaJ?ks ol I A, I|9/a .a a J-cj _ s ft a> ? *~4 ; If I oC>l ssIX,, PQ exposed to fibers by noseonly inhalation ) HWBUI0009654 James E. Lockey, MD, MS SUMMARY OF RECOMMENDATIONS ON ASBESTOS EXPOSURE INDICES Disease Relevant exposure index Asbestosis Surface area of fibers with: Length >2 pm; diameter >QA5pm Mesothelioma Number of fibers with: Length >5/m; diameter <0.1 pm Lung cancer Number of fibers with: Length > 10um; diameter >0.1 Stmt [Lippmann M. Asbestos exposure indices, Environ Res 46:86-106,1988] [13] > HWBUI0009655 James E. Lockey, MD, MS Tremolite asbestos is an atnphibole that can cleave resulting in short squatty cleavage fragments depending on crystalline plain or tong thin asbestifonn fibers with high aspect ratios. As tremolite can contaminate chrysolite deposits, it has been postulated that mesothelioma cases identified in chiysotile workers may in part be related to the tremolite ampbibole content identified within the lungs. This has to be interpreted with caution in that even though tremolite only constitutes a few percent ofthe parent ore source, chrysolite tends to disappear from lung tissue over time and tremolite is much more durable and persist within lung tissue. If all fibers are counted in the lungs ofQuebec chrysotile workers, the tremolite fibers are relativelyshort with low aspect ratio (geometric mean length 2 microns, geometric mean aspect ratio 8:1 to 10:1). Ifone were to count those fibers greater than 5 microns, the geometric mean aspect ratio oftremolite fibers is greater than 20:1. [14] Tremolite is the most commonly encountered ampbibole fiber in lungs ofurban dwellers in North America, and apparently they are short with low aspect ratios and actually shorter than those seen in the chrysotile miners. Lung burdens have been associated with pleural plaques particularly in individuals who would encounter dust from soil such as farmers. At these levels there is no evidence that chrysotile or tremolite produce an excess of lung cancer or mesothelioma. [14] The ATS statement indicates that long high aspect tremolite fibers behave like other amphiboles with a high propensity for inducingmesothelioma, but the lower aspect tremolite fibers are capable most likely ofcausing pleural plaques in low concentrations but only are a risk factor for mesothelioma and asbestosis in high concentrations. This statementwas made with caution because ofthe confounding factor ofchrysotile versus tremolite and that the population had a high chiysotile exposure which was not reflected in lung tissue analysis because of the propensity of chiysotile to dissolve over time. [ 14] HWBUI0009656 James E. Lockey, MD, MS Is there indirect evidence for less-than-5-micron fiber inducedadverse health effects? Do the mechanisms ofaction ofother materials fe.tr.. longer asbestos libers, silicates, mineral dusts, amorphous silica) with potentially similar compositions aid in understanding small-fiber mechanisms ofaction? An interesting case report regarding aluminum oxide fibers was reported by GiUcs and Ctaurg. Electron optical techniques identified 1.3 billion fiber particles ofaluminum oxide per gram of dried lung tissue with a geometric mean aluminum fiber length of 1.0 micron and width 0.06 micron with an aspect ratio of 16. Ninety-eight percent ofthe fibers were shorter than.2.5 microns and no fibers were longer than 5 microns. There was also extremely high non-fibrous particulate content at 15 billion non-fibrous particles per gram ofdry lung tissue. The authors raised the possibility ofaa association ofthe presence of the large number offibers with diffuse interstitial fibrosis, and that a significant number of short fibers may be as dangerous as a smaller number of long fibers. 15] Recent results of the ATSDR medical testing program of residents in Libby, Montana indicated chest radiographic changes consistent with pleural plaques or diffuse fibrosis in 17.8% ofthose screened (994of 5590) using PA and bilateral oblique chest radiographs. On PA views alone 780 or 14% had pleural changes and 49 or 0.9% had interstitial changes. Pleural changes were associated with increasing age at 5% for those individual 18 to 44,22.2% in those individuals 45 to 64; and 37.8% in those individuals 65 years or older. There was also a gradient seen with years of residency in Libby, Montana as well as in regard to exposure pathway gradient [Year 2000 Medical Testing ofIndividuals Potentially Exposed to Asbestiform Minerals Associated with Vermiculite in Libby, Montana. A Report to the Community, August 23,2001. Agency for Toxic Substances and Disease Registry, US Department ofHealth and Human Services, Atlanta, Georgia]. There is. adequate documentation, within the medical literature that local deposits of tremolite in various populations has been associated with the various types ofasbestos related abnormalities and the threshold to which these do not occur has not been established. Plaques can occur with minimal exposures to asbestos HWBUI0009657 James E. Lockey, MD, MS and can occur within a wide range of tissue burdens of asbestos fibers which overlap with control popuIations.[16) At what length does a material no longer exhibit fiber-like toxicity and can be considered particulate matter regardless ofaspect ratio? Within this particular reference by Schneider, Dr. Potts from an article in 1987 is quoted as suggesting "All mineral fibers having an aspect ratio of>5 can be classified as carcinogenic irrespective of their mineralogical composition if: (hamster of fiber <1 pm or can split into such lengths of fibers >3 pm and durability in vivo longer than 3 years.) Schneider reported that from a transitional electron microscopy perspective only fibers longer than 3 pm need to be counted. It is Interesting to note that for short tremolite fibers there was a relative low lung cancer risk and a higher relative mesothelioma risk, based on a study by Dement and Harris in 1979 involving talc mining and milling. Size distribution of man made fibers and asbestos fibers is best described as bivariate log-normal size distribution. [17] Can am thresholds be defined for the mechanisms ofaction that may influence the toxicity ofless-than-5micron materials? Available data from asbestos fiber exposure is inadequate to establish thresholds other than for pulmonary asbestosis. Can an exposure threshold be developed for the irritant effects ofSVFs for skin contact or eve irritation, based on either fiber loading or fiber content ofhandled materials? Glass fiber >5 pm in diameter appear to be most irritating to the skin based on limited available data. Topic #3: Data Gaps. What data traps are evident when addressing the above questions? From evaluating araphiboles such as tremolite, anthophyllite, and actinolite, the difficulty is differentiating the ashestiform from the non-asbestiform analogs that are chemically identical but have different crystalline planes resulting in cleavage fragments rather than long thin fibers. Presently the data in regard to these minerals both from an animal as well as a human epidemiology perspective is not sufficient to determine ") HWBUI0009658 James B. Lockey, MD, MS whether the nonasbestifonn varieties are as hazardous as are the asbestiform counterparts. [Reference 11, chapter 16: Bignoa & BrochardJ What research is needed to fillthese data saps? Animal studies oa different types of tremoiite indicate that the asbestos form of tremolite has a high propensity toproduce both mesothelioma and carcinomas in experimental animals. Dataregarding tremolite cleavage fragments compared to asbestos form tremolite are really inconclusive in that the fibers are usually composed of a mix containing both relatively and broad fibers as well as long fibers. ATS indicated that more definitive work is needed to determine whether cleavage fragments that are short and squatty are biologically different than the asbestiform type fragments.[14] References: 1) National Research Council. Review of the U.S. Navy's Exposure Standards for Manufactured Vitreous Fibers, in: National Academy Press. Washington DC, 2000. 2) Mechanisms ofFibre Carcinogenesis, eds: Kane AB, Bofetta P, Saracci R, Wilboum ID. in: 1ARC Scientific Publications No. 140. International Agency for Research on Cancer, Lyon, 1996. 3) Gelzleichter TR, Bermudez E, Mangum JB, Wong BA, Everitt Jl, Moss OR- Pulmonary and pleural responses in Fischer 344 rats following short-term inhalation ofa synthetic vitreous fiber. I. Quantitation of lung and pleural fiber burdens. II. Pathobiologic responses. Fundam Appl Toxicol 30:31-46,1996. 4) Davis JMG. The role-ofclearance and.dissolution in determining the durabilityofbiopersistence of mineral fibers. Environmental Health Perspectives 102(5) October 1994. 5) Lippmann M: Man-made mineral fibers (MMMF); human exposures and health risk assessment, Toxicol Ind Health 1990;6:225-246. 6) Stanton MF, Layard M, Tegeris A, et aL Relation of particle dimension to carcinogenicity in ampbibole asbestoses and. other fibrous minerals. JNCI198fil-.965-915. 7) Oehlert GW. A reanalysis of the Stanton et al, pleural sarcoma data. Environ Res 1991;54:194-205. 8) Lentz TJ, Rice CH, Lockey JE, Succop PA, Lemasters GK- Potential significance of airborne fiber dimensions measured in the U.S. refractory ceramic fiber manufacturing industry. Am JInd Med 1999;36:286-198. HWBUI0009659 James E. Lockey, MD, MS 9) Chuig A, Wright JL, Vedal S. Fiber burden and patterns ofasbestos-related disease in chrysotile miners and millets. Am Rev Respir Dis. 1993;148:25-31. 10) Davis JM, Addison J, Bolton RF, Donaldson K, Jones AD, Smith T. The pathogenicity of long versus short fibre samples ofamosite asbestos administered to rats by inhalation and intreaperitoneal injection. Br Exp Pathol 67:417,1986. 11) MineralFibers andHealth, eds: Liddell D, Miller K. CRC Press 1991, Boca Raton, Florida. 12) Wagner JC, Chamberlain M, Brown RC, Berry G, Pooiey FD, Davies R, Griffiths DM. Biological effects oftremolite. BrJ Cancer 45:52,1982. 13) Lippmann M. Asbestos exposure indices. Environ Res 46:86-106, 1988. 14) American Thoracic Society. Medical Section ofthe American Lung Association. Health effects of tremolite. Am Rev Respir Dis 1990;142:1453-1458. 15) Gilks B and Churg A. Aluminum-induced pulmonaty fibrosis: do fibers play a role? Am Rev Respir Disl36:176-179,1987. 16) Hillerdal G. Pleural plaques: incidence and epidemiology, exposed workers and the general population; a review. Indoor Built Environ. 1997;6:86-95. 17) Schneider T, Skotte J. Fiber exposure reassessed with the new indices. Environ Res 1990;51:108-116. 18) Wagner JC. Biological effects of short fibers, in - Proceedings of the VUth International Pneumoconiosis Conference Part If, November 1990. DHHS (NIOSH) Publication No. 90-108 Part II. Animal Models-Pneumoconiosis L Additional Critical Studies/Papers 1) McDonald JC, Case BW, Enteriine PE, Henderson V, McDonald AD, Plourde M, Sebastien S. Lung dust analysis in the assessment of past exposure ofman-made mineral fibre workers. Ann Occvp Hyg. 34:427,1990. .T 2) McDonald JC, Armstrong B, Base B. Dpell D, McGaughey WT, McDonald AD, and Sebastient P. Mesothelioma and asbestos fiber type. Cancer, 63:1544,1989. 3) Case BW, Sebastien P. Fibre levels in lung and correlation with air samples, in N6n-Occupationdl Exposure to Mineral Fibres, Bigrion J, Peto J, and Saracci R- International Agency for Research on Cancer Scientific Publications, No. 90, Lyon, 1989,207. 4) Wright RS, Abraham JL, Harber P, Burnett BR, Morris P, West P. Fatal asbestosis 50 years after brief high intensity exposure in vermicuiite expansion plant Am JRespir Crit Care Med 2002;165:1145-1149. "\ } HWBUI0009660 Ernest McConnell ToxPath Inc. HWBUI0009661 Ernest McConnell President ToxPath Inc. 3028 Ethan Lane Raleigh, NC 27613 Phone:919-848-1576 Fax: 919-848-1576 Email: toxpathmcc@aol.com Dr. McConnell is an experimental pathologist He holds a D.V.M. from Ohio State University (1961) and an M.S. in pathology from Michigan State University (1966). He was Veterinary Director in the National institute of Environmental Health Sciences' Research and Testing Program, Research Triangle Park, NC, from 1978-1988, where he received broad recognition for his research on the pathological responses of animals to inhaled toxicants. Dr. McConnell has been a panel member on numerous national and international government and scientific committees including: Refractory Ceramic Fiber Animal Studies, TIMA (1986); IARC Working Group on the Evaluation of the Carcinogenic Risk of Chemicals to Humans-- Silica and Some Silicates (1986); DHHS Committee to Coordinate Environmental and Related Prcgrams "Report on Cancer Risks Associated with the Ingestion of Asbestos" (1987); Health Consequences of Occupational Exposure to Man-Made Mineral Fibers, TIMA (1987). He lias been on the editorial board of the journal Inhalation Toxicology since 1995. Dr. McConnell has written more than 125 journal articles, the most recent of which have been related to toxicity and carcinogenicity of inhaled stone woof fibers, asbestos, synthetic vitreous fibers, and refractory ceramic fibers. He is especially recognized for his expertise in the comparative responses of laboratory animals to inhaled man-made and natural fibers. In addition to the 125 journal articles, I have aulhored/co-authored additional 43 book chapters, published symposia or reviews. He has also served as a panel member for IPCS Task Group Meeting on Synthetic Organic Fibers, London. England, September 1992; WHO European Programme for Occupational Health, "Validity of Methods for Assessing the Carcinogenicity of Man-Made Fibers", Copenhagen, Denmark. 1992; IPCS Task Group Meeting on Synthetic Organic Fibers, London, England, September 1992; WHO European Programme for Occupational Health, "Validity of Methods for Assessing the Carcinogenicity of Man-Made Fibers", Copenhagen, Denmark, 1992; National Research Council, Commission on Life Sciences, Subcommittee on "Review of the US Navy's Exposure Limits for Manufactured Vitreous Fibers', 19992000. He is also a member of Lovelace Respiratory Research Institute's `Research Programs Oversight Committee, 2002-present HWBUI0009662 Ernest E. McConnell, D.V.M., MS. (Path), DACVP, DABT President, ToxPath, Inc. Office Telephone/FAX 919-848-1576 21 October 2002 3028 Ethan Lane Laurdane Est. Raleigh, NC 27613 To: Kate Schalk Conference Management Group Subj: Health Effects of Asbestos and Synthetic Vitreous Fibers (SVF): Influence of Fiber Length Following are some comments regarding the subject "How do animal/experimental data augment our understanding of human health effects?" I have not included the reference citations at this point, but can do this in the future. Let me know ifyou want me to include Dr. Case's comments after you receive them. Background; There have been numerous studies of the effects of various types of asbestos and SVFs in animals. Both fibrous and nonfibrous particulates have been used. Most studies have been conducted in rats and hamsters, but others, including nonhuman primates have been used. Routes of exposure have included inhalation (whole-body and nose-only), intratracheal instillation, intrapleural implantation/injection, intraperitoneal injection and ingestion. All of the routes of administration have their strengths and weaknesses (advantages and disadvantages) for use for assessing potential health effects in humans. However, the inhalation route appears to produce the most relevant data because it is the only route that duplicates all aspects of human fiber exposure and disease (inflammation, fibrosis, lung cancer and mesothelioma) resulting from the exposure. Also, the neoplastic changes typically occur late in the rodents' life, similar to what occurs in humans exposed to asbestos. Other routes of exposure are also useful for comparing the toxic potential of various types of fibers and understanding the mode of action and many of the mechanisms of fiber toxicity and carcinogenicity. Additionally, the oral route (ingestion) appears to be the most appropriate route of exposure for studying the potential hazard of ingested asbestos. Cancer Effects: Rats and hamsters are the'raost frequently used species for assessing the potential carcinogenic effects as asbestos and SVFs and have been used with various routes of exposure. Of the two species, the rat appears to be the most appropriate one because it exhibits both lung cancer and mesothelioma in response to inhalation of known human carcinogenic fibers, e.g. asbestos. The hamster can be a useful model if one is only interested in the inflammatory, Fibrogenic and mesotheliogenic effects of particulates. However, the hamster does not develop lung cancer after exposure to high levels of either chiysotile or. amosite asbestos. Other species have been used but have significant limitations that preclude their general use for carcinogenic bioassays. For example, the mouse is not as useful as the rat 'or hamster because its terminal airways are smaller and therefore, particulates of a mean mass HWBUI0009663 > aerodynamic diameter (MMAD) of greater than >0.5 um cannot reach the deep lung (alveolar region) which is the site of primary disease. Non-human primates would be an ideal animal model but are precluded because of their long life-span (would require at least 20-30 years to demonstrate a noncarcinogenic effect), availability (a cancer bioassay requires >200 animals/sex), and expense (such a study would cost >$20 million. Most chronic rodent inhalation bioassays of asbestos have been conducted in rats, have not shown significant strain differences and males and females are equally sensitive to its carcinogenic effects. The only large series of studies of various types of asbestos showed that if there is a gender difference, males might be slightly more responsive. Therefore, either sex is appropriate with males slightly more preferable. Just as importantly, both sexes are probably not necessary. However, these same studies have shown that while life-time exposure to asbestos may. not be necessary, it is important to observe the animals for most of their life-span (see below). The types of cancer induced by asbestos and SVFs in rodents are comparable to those observed in humans, although the preponderance of a given type and its biologic behavior appears to be species specific. In inhalation studies in rats the preponderant form of lung cancer is bronchoalveolar in origin, arising from type IT alveolar cells. They occur late in the animal's life, usually after 21 months of age. This is why lifetime studies may be necessary to fully exonerate a fiber from being .considered carcinogenic. The tumors are slow growing and only occasionally are the cause of death. The biological sequence of growth is typically from bronchoalveolar hyperplasia to bronchoalveolar adenoma to bronchoalveolar carcinoma, although all aspects of the sequence of progression may not be found in a given lesion. Squamous cell metaplasia is not unusual and typically is found as part of the morphology of larger tumors. Squamous cell carcinoma may predominate in a small percentage of rodent tumors, but has rarely been observed to occur de novo. Squamous cell types may be more common with intratracheal instillation of the fibers. The malignant tumors are locally invasive and can metastasize but it is an unusual event for them to do so. When this occurs it is usually within the lung, but distant metastases have been observed. The presence of mitotic figures is in direct relation to the degree of malignant transformation. Tumors of the upper respiratory tract and airways have not been observed in response to inhalation exposure of asbestos or SVFs in rodents. : ' Mesothelioma has also been found in rodent carcinogenic bioassays of asbestos and SVFs. In inhalation studies in rats they are usually found at a lower incidence than lung cancer. Again, there does not appear to be a gender predisposition and the mesotheliomas in rodents typically occur late in life (after 21 months of age). They rarely are the cause of death. They grow by expansion, growing over the pleural surface. They: typically do not invade the lung or other adjacent structures, although this has been observed; They usually present as multiple lesions on both sides of the lung and involve both the visceral and parietal pleura. "Rarely, distant metastases have been observed. . In inhalation studies, all of the major morphological types (tubulopapillary, sarcomatous and mixed) have been observed, although the tubulopapiiliary response is the predominate form. There is one exception to this and that is found in the inhalation study of erionite, where the sarcomatous type predominated, was highly invasive and the tumors were exceptionally lethal causing death in most of the rats by 15 months. In contrast HWBUI0009664 %. to inhalation, direct instillation into the pleural or peritoneal cavities results in a preponderance of sarcomatous neoplasms, and in fact, it may be difficult to find mesothetial cells in many of the tumors, particularly after peritoneal injection. However, even in these studies, the mesotheliomas seldom invade local tissues or metastasize to other areas of the body. The biological sequence ofevents in the development ofmesothelioma in rodents also appears to have a series ofprogressive steps. In inhalation studies, the first event that is observed is fibrosis . in the pleura immediately subjacent to the mesothelial lining. This is multifocal in nature, possibly occurring more frequently in the interlobular pleura. In the few studies where the parietal pleura has been investigated, the initial change was found in the nonmuscular portion of the diaphragm and over the ribs (as compared to intercostal). The first indication of mesothelial ^change is found in these areas of pleural fibrosis. The mesothelial cells become ciiboidal (as compared to a normal squamous morphology) and progress to focal hyperplasia of one to three cell layers thickness. The next step is the formation of papillary forms of growth and overgrowth of adjacent pleurp. It is at this stage that mesothelioma is diagnosed. Pseudovacuolated tumor cells may be noted at this stage. Finally, the tumor evolves into the classical forms noted above. The course of events is somewhat different for instillation and injection studies. The initial response in the latter studies is inflammation, followed by a fibrogranulomatous reaction (assumed to be an attempt to wall off the fibers). A similar sequence of progression is assumed but results in a higher proportion ofsarcomatous types ofmesothelioma. Pulmonary interstitial fibrosis (see below for description) is invariably found in studies where either asbestos or SVFs have caused either lung cancer or mesothelioma. However, there have been fiber studies where pulmonary fibrosis was observed without the development of fiber related neoplasms. In vitro studies may not be of value for predicting the carcinogenic potential of a given type of fiber. There are several reasons for this. First, the fiber used is not subjected to physiological processes such as clearance and dissolution that are found in the lung. Also, the in vitro test systems use "fresh" fibers, so do not typically take into account pathology attenuating changes in fibers that occur over time in the lung. Finally, the in vitro "dose" may have no relevance to the lung fiber burden. However, not withstanding this, in vitro methods are highly powerful tools for understanding fiber/cell interactions and mechanisms oftoxicity (see Mossman for details). jNqn^cancer Effects: Animal models have also demonstrated many of the same pathological ^responses that are found in humans exposed to particulates. The major noncancer endpoints that have been described in animals in experimental studies are phagocytosis, inflammation ancf pulmonary, fibrosis. In regard to these endpoints, the rodent lung (and presumably other species) reacts to asbestos and SVFs as it would to any inhaled nonorganic. foreign body that is not chemically toxic, e.g. beryllium. The lung can only react to such materials in a limited number .ofways. In animals, if the particulate were deposited in the upper respiratory tract, one would assume that it would be possible for it to cause local irritation. However; this has not been observed in inhalation studies, even at high exposure levels. It is assumed that the resident time for such particles is brief, not allowing for a pathologic response. The mucous layer in these tissues is relatively thick compared to the size of the particulate and the methods of removal are quite efficient. The same is true for the major airways. In experimental animals the airways are HWBUI0009665 intact and have not been compromised by other toxicants as in humans, e.g. smoking. Therefore, particulates deposited on these surfaces are again efficiently removed via the mucociliary escalator and are either swallowed or expectorated. In either case, the resident time in the body is relatively brief. For a particulate to cause pathology after inhalation, it must reach the alveolar region of the lung. Particulate size dictates whether this happens or not. If the particle reaches terminal bronchiole it causes a foreign body reaction which is dictated by dose, particle (fiber) size and to some extent physical chemistry. The lungs' initial response is an attempt to remove the offending substance. This is accomplished by resident macrophages. If the particle is of a size that the macrophage can engulf (phagocytize), it will be "captured) and removed from the lung either by translocation to the airways or draining lymphatics. As the dose (number of particulates) increases, more macrophages are recruited. However, if the dose is too large for the number of available macrophages to remove, an "overload" situation develops which results in other pathologic events. Such events have been documented in animals both by histopathology and physiological tests (see Oberdorster for details). If the fiber is too large to be phagocytized and removed, i.e. longer than the size of the macrophage (~13 run diameter in rats and hamsters; ~2I um diameter in humans), the fiber cannot be removed unless it is broken into shorter lengths or dissolves. Both of the latter two phenomenons have been observed with several SVFs (see below). If the dose overwhelms the physiological pulmonary defenses or the fiber is too large to be removed, the initial series of events in animals occur at the junction of the terminal bronchioles and proximal alveolar duct (this is where most ofthe fibers are initially deposited. In addition to a stimulating the local macrophages, an influx of additional macrophages is recruited to the area. At this point, the local type II alveolar cells (in the proximal alveoli) undergo metaplasia to a cuboidal appearance and become hyperplastic. The resulting lesion has been termed "bronchiolization" because the change mimics the appearance of the terminal airways. Increased amounts of mucous production and sometimes inspissation of the material often accompany this. Coincident to the bronchiolization, microgranulomas are observed. These appear to form from a coalition of macrophages and fibroblasts. At this time the microgranulomas are restricted to the proximal portion of the alveolar duct, particularly along the alveolar duct ridge. With time and continued insult the process proceeds peripherally and becomes more apparent If the offending fiber persists, collagen is laid down in the adjacent interstitrom (presumably by direct invasion of the: fiber into the epithelium hnd interslitiutaj. At this time the lesion is referred to as interstitial fibrosis. In rodent studies, the fibrotic areas are initially focal and widely disseminated. But, if the Insult persists or the dose is high enough, fibrosis Becomes more widespread. Various schemes have been developed to describe these events and grade them as to their severity for comparative puiposes. There is one notable difference between the qualitative appearance of the lesions produced by asbestos and SVFs in animals. Neutiophils are often a prominent part ofthe inflammatory reaction with asbestos, especially with amphiboles, while they are rarely found in studies of SVFs, even at doses that produce fibrosis. The inflammatory reaction can also be documented and quantified by conducting pulmonary lavage studies (see Oberdorster). Stop studies (exposure is stopped and is followed by a nonexposed recovery period) have proved useful for determining the reversibility of the above lesions. Such studies have clearly shown HWBUI0009666 ) that the initial changes (macrophage response and bronchiolization) are totally reversible with most SVFs and to some degree with asbestos. Early fibrosis also is to some degree resolvable, at least with SVFs. Rodent studies have demonstrated that fibrosis, even with asbestos, is not progressive, once the exposure ceases. While there is no exact correlate for pleural plaques in animals, localized acellular fibrotic changes reminiscent of this lesion have been observed, albeit on a much smaller scale. The qualitative changes in the pleura are somewhat different than in the lung. Macrophages and inflammatory cells are almost totally absent in the pleural response. Lavage studies have not been conducted with instillation or injection studies so it is not known if the same events occur with these routes of exposure. In addition, animal inhalation studies also suggest that fibers need to be present in the pleura for pathologic events to occur: In vitro studies of mesothelial cells have been conducted using both human and animal cells. These have been primarily designed to study the mechanisms ofcarcinogenicity (see Mossman). Irritant Effects: While there is evidence ofdermal and ocular irritation of humans as a response to exposure to asbestos and SVFs, no such evidence has been observed in animals. Histopathological studies of the nasal cavity in rodents exposed vja inhalation have not shown any evidence of pathology, although an increased mucous response could be missed with standard histopathology techniques. Similarly, ingestion studies in rats and hamsters ofasbestos did not reveal any irritation of the alimentary tract We are unaware of in vitro studies on the irritant effects ofeitherasbestos or SVFs. Association Between Fiber Length and Fiber-like Toxicity: There are numerous animal studies that demonstrate the influence of fiber length and pathogenicity/carcinogenicity. The early studies using intrapleural implantation/instillation and intraperitoneal injection in rats clearly show a direct relationship between fiber size and carcinogenic activity. The longer the fiber, the more carcinogenic it was in these studies. These same studies provided the basis for the hypothesis that short fibers, i.e. shorter than 8 um in length may not represent a significant carcinogenic risk. However, the same investigations, particularly the intraperitoneal studies.also demonstrated that. if. the dose was high enough even so-called "innocuous" particulates, e.g. titanium dioxide, caused the induction of peritoneal mesotheliomas, albeit at a lower incidence than long fibers. Additionally, the latter studies also Remonstrated that if even long fibers, e.g. woilastonite and some SVFs, were not carcinogenic if they were not biopersistent in the ` peritoneal cavityt While few inhalation studies have been conducted to study the influence :of the fiber length on the pathology of asbestos, there is one persuasive study ofcrocidolite asbestos in rats. In that study, short crocidolite (<2.0 um length) did not cause either pulmonary cancer or mesotheliomas in . rats, even at relatively high, exposure levels, while longer crocidolite was highly carcinogenic;; Other circumstantial evidence for considering fiber length as being critical to the carcinogenic potential of fibers is provided by the observation that amorphous silica has been shown to be noncarcinogenic in several inhalation studies in rats, while some types of glass fibers of similar chemistry have shown to have carcinogenic activity. In fact, amorphous silica has been used as a "negative control" in rodent inhalation studies. HWBUI0009667 jggt^ A final piece of evidence for the importance of fiber length for the carcinogenic of asbestos and SVFs is found in the hilar lymph nodes that drain the lungs of animals exposed via inhalation to both asbestos and SVFs. These lymph nodes are literally filled with macrophages containing short fibers and fiber fragments with no evidence of pathology or neoplastic change in either the lymph nodes or adjacent tissues. To summarize studies in animals ofshort fibers and nonfibrous particulates have shown that both are potentially carcinogenic if they are introduced into a confined cavity, e.g. pleural or peritoneal, at sufficiently high doses. But the same studies clearly show that the carcinogenic potential is definitely less than fibers of the same type that are longer. However, inhalation studies (although limited in number) suggest that short fibers have not caused cancer in animals. The other part of the equation that needs to be considered is the influence of pulmonaiy clearance and biopersistence on the carcinogenic potential of particulates. As noted above, even long fibers are not carcinogenic.in animals unless they are biopersistent in the animal. There are only a few in vitro studies that address this subject. In a study of Chinese hamster ovary cells (CHO) short amosite failed did not cause chromosomal aberrations while long fiber amosite did. Thresholds of Toxic Action: There have been very few inhalation studies in animals of either asbestos or SVFs to assess a carcinogenic dose response. It needs to be remembered that to assess a carcinogenic dose response, one must have a multidose study that shows a carcinogenic response. Most asbestos and SVF studies were designed to address the carcinogenic potential of the fiber, not dose response. The only multi-dose inhalation study of asbestos used amosite in hamsters. In that study, there was a definite dose-related response with regard to both nonneoplastic (macrophage response, pulmonary fibrosis, etc.) and carcinogenic activity (mesotheliomas). Unfortunately, the potential lung cancer response could not be assessed because hamsters do not develop pulmonary tumors with particulates. There are a few inhalation studies of SVFs that address dose response. The only one that was positive for cancer involved .refractory ceramic, fibers in rats. In that study there was a clear dose response for both cancer and noncancer endpoints and a no-effect level. There are a few other multidose studies in rats using .various types of SVFs, but since none showed carcinogenic activity, one can only evaluate the dose response for noncancer endpoints. Again, there was'evidence in these studies ofa doserelated change in the endpoints showing recognizable change. The "stop-studies" in many of these' inhalation studies (both asbestos and SVFs) provide evidence for a dose response for noncancer endpoints. However, the number of animals evaluated in the "stop studies" is too small to address a cancer dose response. The only study in primates that addresses a potential threshold of action was with chrysofile asbestos. In this study, monkeys were exposed to chrysotile asbestos at an exposure level of 1 Fee for two years. Teh months following the last exposure, lung biopsies were taken and evaluated for fiber burden and tiistopathology. There was no evidence of pathology although a few asbestos bodies were observed in the lung. The monkeys were then held unexposed for an additional 10 years at which time they were subjected to necropsy examination and the lungs for histopathology examination. Again, there was no evidence of pulmonary pathology and the number of asbestos bodies had decreased. HWBUI0009668 In summary, the totality of available data suggests that there is a dose-response for both neoplastic and nonneoplastic endpoints in animals and there is a no effect level for both asbestos and SVFs. One attempt at deciding if a given exposure in animals is potentially carcinogenic involves the use of noncancer endpoints. In this scheme it was assumed that a dose that caused pulmonary fibrosis could also represent an exposure that was potentially carcinogenic in animals. This was because no animal study has ever produced cancer in the absence of fibrosis. The next assumption was that since no inhalation study had ever shown fibrosis in the absence of inflammation, one could assume that an exposure that didn't result in inflammation would not reasonably be expected to be carcinogenic. The endpoint chosen for assessing inflammation was the presence of inflammatory cells over background in bronchoalveolar lavage (BAL) fluid after a 90-day inhalation exposure. Therefore, ifone did not find an increase in inflammatory cells in BAL fluid, one could chose this exposure as a no-effect threshold. It is reasonable to expect that in vitro studies could shed light on the dose response of both asbestos and SVFs. While these types of studies are primarily designed to capture and elucidate specific mechanisms of toxicity and carcinogenicity, there may be insights into dose response that could help in establishing thresholds of effect One such study showed that short fiber amosite did not cause inflammation, while long amosite did. The only draw backs to and in vitro approach is that these techniques do no take lung clearance phenomena into consideration and fibers that are not biopersistent in the lung might not be differentiated from biopersistent ones because of the short time flame of the in vitro studies. Ernest E. McConnell ... ' HWBUI0009669 Brooke Mossman University of Vermont, College of Medicine HWBUI0009670 Brooke Mossman Department of Pathology University of Vermont, College of Medicine Health Science Research Facility 218 142 Beaumont Avenue Burlington, VT 05405 Phone: 802-425-3909 Fax: 802-656-8892 Email: brooke.mo3sman@uvm.edu Or. Mossman has been studying the mechanisms of environmental lung disease for over 20 years and has generated over 200 publications. Her interest in the field began with graduate training in the lab of Andrew Sivak, Ph.D., at the NY University Institute of Environmental Medicine where she worked on the effects of phorbol esters in skin carcinogenesis. She completed her Ph.D. degree in the lab of John E. Craighead, M.D. in the Department of Pathology at the University of Vermont (UVM). She then pursued postdoctoral research on interactions of asbestos and cigarette smoke in lung tumors with Edward Bnesnick, Ph.D., Department of Biochemistry, UVM. She Is a past director of the Cell & Molecular Biology Program at UVM and is now a professor in the Dept of Pathology and Director of the Environmental Pathology Program. Her current research, which focuses on cell signaling by asbestos, silica, and oxidant stress in cells of the respiratory tract, is funded by grants from the National Institute of Environmental Health Sciences and the National Heart. Lung and Blood Institute. :) HWBUI0009671 Mossman 1 Topic# 1: Physiological Fate ofAsbestos and Vitreous Fibers less than 5 Microns in Length: Short fibers (<5 microns in length) may be less pathogenic because oftheir decreased deposition or penetration into the airways, and increased clearance by macrophages and other cell types (reviewed in Health Effects Institute-Asbestos Research, 1991). For example, fiber length governs fiber penetration into.and along the airways, and as the length increases, there is more interception which can enhance deposition (Sussman et aL, 1991) This also accounts for the fact that longer fibers have proportionately more deposition in the airways as opposed to peripheral alveoli. The fact that lung retention also increases more markedly with fibers greater than 10 microns is supported by theoretical calculations (Yu et aL, 1990), analysis of lung dust content in humans (Timbrell, 1982; Churg andWiggs, 1987; Pooley and Wagner, 1998) and studies using experimental animals (Morgan 1979,1995). Aerodynamic diameter also is a feature offibers governing their initial deposition, and it is unlikely that fibers with a diameter exceeding 3 microns reach the alveolar regions of the deep lung (Morgan, 1995). Since most commercial fibrous glass preparations exhibit fiber diameters of approximately 73 microns (equivalent to mean aerodynamic diameters of 22 microns), airborne fibers for the most part may not penetrate into the lung (Lippman, 1990). The increased clearance ofshort fibers from the lung has been demonstrated in a number ofstudies (reviewed in Health Effects Institute-Asbestos Research, 1991; Davis, 1994; Oberdorster et al., 1988; Morgan, 1995). These can be: 1) readily transported through tracheobronchial and other lymph nodes to more distal lymphatics, the pleura, or other organs, 2) cleared via the mucociliary escalator and alveolar macrophages, and 3) effectively phagocytized by a number ofcell types in the lung including epithelial cells (Churg et al., 2000). Once within a phagolysosome or in general in lung fluids, shorter fibers ofcluysotile asbestos (Hume and Rimstidt, 1992) or glass (reviewed in Lippman, 1990) arc more prone to dissolution and fragmentation than longer fibers and amphibole types ofasbestos. Tonic #2: Health Effects of Asbestos and Vitreous Fibers less than S Microns in Length: Human Studies: Epidemiologic data indicate that there is no increased evidence ofchronic neoplastic or nonneoplastic lung or pleural disease with occupational exposures to Man-Made Mineral Fibers (MMMF) (reviewed in Lippman, 1990; Health Effects Institute-Asbestos Research, 1991). Limited evidence suggests an increase of lung carcinomas among workers using rock or slag wool, but whether or not trace metals or other contaminants in the workplace setting play a contributing role is unclear. A difficulty in HWBUI0009672 #} Mossman 2 assessing the role of fiber size in disease causation in man is that historical measurements ofsize dimensions f fibers in past workplace settings do not exist Moreover, size dimensions of fibers in human lungs at autopsy may not reflect the actual sizes that individuals were exposed to in the 20 or 40 year periods prior to death. Animal Studies: Data from a number of experiments overwhelmingly support the concept that the risks of lung cancer, mesothelioma, and fibrosis increase with increasing fiber length (reviewed in Churg et at, 2000; Lippmann, 1900; Mossman and Churg, 1998; Health Effects Institute-Asbestos Research, 1991). Short fibers in these studies have much less carcinogenic activity than long fibers. Chronic inhalation of short chrysolite fibers (less than 5 microns in length) for lifetime exposures (2 years) in rats or 28 months in baboons yielded no fibrosis nor pulmonary tumors despite the presence ofasbestos bodies (Platek et aL, 1985). Moreover, a lifetime inhalation study in Fischer 344 rats exposed to Jeffrey mine cbrysotile fibers, UICC/B cbrysotile fibers or short (< 5 microns) Coalinga mine fibers showed no fibrosis nor lung tumors with the short fiber preparation, although significant tumor induction and fibrosis were noted with both long fiber preparations (Ilgren and Chatfield, 1997,1998a) The lack ofpathogenesis of the Coalinga fibers was attributed to their increased lung clearance (Ilgren and Chatfield, 1998b). Several experiments show,that asbestos and erionite fibers less than 5 microns in length have less toxicity, inflammatory potential, and disease potential after inhalation or intratracheal/intrapleritoneal/ intrapleural injections (Davis et al., 1986; Donaldson et at., 1989; Wagner et al., 1985; Wagner et ai., 1990) . Injection studies using MMMF also reveal that they are carcinogenic or fibrogenic (Wright and Kuschner, 1977) if they contaui large numbers oflong thin fibers, but carcinogenicity and pulmonary . fibrosis in rodents is only achieved after inhalation of ceramic fibers (Davis et al., 1984;) and Araraid fibers (Lee et al., 1988) as opposed to vitreous fibers (reviewed in Health Effects-Asbestos Research, 1991) . The importance of fiber length in pulmonary fibrosis has been shown in studies using asbestos by Vorwald et al. (1951), King et al. (1946), Scymczykiewicz and Wiecek (1960), and Klosterkottcr '(1968). Classical studies by the Stanton (Stanton and Wrench, 1972; Stanton et al., 1977; Stanton and Layard, 1978) and Pott laboratories (Pott and Friedrichs 1972; Pott, 1978) have indicated that the induction of mesothelioma by any asbestos or nonasbestos fiber is directly related to the presence of fibers > 8 microns HWBUI0009673 Mossman 3 ia length and diameters less than .25 microns. Although some studies have suggested that short fiber asbestos preparations may be carcinogenic after injection (Kolev, 1982; Le Bouffant et al., 1985), these preparations also contained a small percentage of long fibers, making results difficult to interpret Inhalation studies have more convincingly demonstrated the importance of fiber length in mesothelioma, lung cancers, and pulmonary fibrosis. In studies by Wagner using eriionite (Wagner et ai 1985; Wagner 1990), an almost 100% rate ofmesotheliomas was induced with long fiber material, which was reduced to zero when short fiber preparations were used. This is evidence ofa threshold for short fibers in tumorigencity. Studies by Davis et al., (1986) also show that short fiber (< 5 microns) preparations ofamosite prodnced neither fibrosis nor lung tumors, and only a single mesothelioma after injection Into rats as opposed to highly pathogenic long fibers. Results with chrysotile asbestos were similar (Davis and Jones, 1988), but the short-fiber chrysotile was contaminated with some longer fibers. An intratracheal model in rats using long (> 2.5 microns) and short crocidolite asbestos has yielded some mechanistic information on the differentia! effects oflong vs. short fibers (Adamson and Bowden, 1987a,b; 1990). These studies suggest that the increased fibrogenic response to long fibers may be due to selective increases in cell proliferation. In addition, both long and short asbestos fibers cause alveolar macrophages to secrete fibrogenic cytokines, but interstitial fibroblasts exposed to short asbestos fibers do not respond to these cytokines. Mechanistic studies on cells in culture or tracheal explants have also supported the increased toxicity,. mutagenicity, and proliferative potential of long vs. short fibers (Brown et al., 1986; Wright et al., 1-986; Donaldson etal., 1986; Marsh and Mbssman, 1988; Woodworth etal., 1983; Sesko and Mossman, 1989). These studies also show that hdnfibroiis, chemically similar analogs ofboth chrysotile and crocidolite asbestos are without effects on cell proliferation or cell survival. Studies on cell transformation and cytogenetic effects in Syrian hamster embryo (SHE) fibroblasts also denlonstrate that long.thin fibers are most potent, regardless of composition (Hesterberg and Barrett, 1984,1985; Hesterberg et aL, 1986). After milling of fibers to reduce the length from 10 to 16 microns to less than 1.7 microns, morphologic transformation, an indication oftumorigenic potential, is completely inhibited (Hesterberg and Barrett, 1984). Thus, a threshold for fiber length in carcinogenesis may exist ) s.7 HWBUI0009674 Mossman 4 One theory advanced by these studies is that toog fibers can penetrate the nuclear membrane during division ofcells and interfere with the genetic apparatus. The increased potential of long fibers in elicitation oftoxicity (broadly defined as injury to cells), proliferation, inflammation, transformation, fibrosis and carcinogenesis may be related to their ability to generate reactive oxygen or nitrogen species (ROS/RNS) after frustrated or incomplete phagocytosis by cells (Hansen and Mossman, 1987; Goodglick and Kane, 1990; Kinnula, 1999; Ohyama et aL, 2001). Studies show that even short fibers at massive concentrations may elicit ROS from elicited macrophages when clearance is impaired (Goodglick and Kane, 1990). Recent studies suggest that the release of oxidants from macrophages depends on fiber length as opposed to composition- there is a strong correlation between geometric mean length and the ability to induce an oxidative response ini fiber samples > 6 microns in length (Ohyama et at., 2001). Topic #3: Data Gaps The major data gap in demonstrating whether thresholds exist for the effects ofshort (or for that matter, long fibers) ofany composition is the fact that standardized preparations ofsized fibers are unavailable for experimental studies, especially inhalation studies which are expensive and require vast quantities of material. This has severely hampered experimental research. The information on airborne fiberglass levels and size dimensions in environmental settings in the US is another limitation in attempting to define risks. HWBUI0009675 BIBLIOGRAPHY Adamson IYR, DH Bowden. (1990) Pulmonary reaction to long and short asbestos fibers is independent of fibroblast growth factor production by alveolar macrophages. American Journal of Pathology 137:523-529. Brown GM, H Cowie, JMG Davis, K Donaldson. (1986) In vitro assays for detecting carcinogenic mineral fibres: A comparison of two assays and the role of fibre size. Carcinogenesis 7(12):1971-1974. Churg A, J Wright, B Gilks, J Dai. (2000) Pathogenesis of fibrosis produced by asbestos and man-made mineral fibers: what makes a fiber fibrogenic? Inhalation Toxicology 12(Suppl 3): 15-26. Davis JMG, J Addison, RE Bolton, K Donaldson, AD Jones, T Smith.' (1986) The pathogenicity of long versus short fibre samples ofamosito asbestos administered to rats by inhalation and intraperitoneal injection. British Journal ofExperimental Pathology 67:415-430. Davis JMG, ST Beckett, RE Bolton, P Codings, AP Middleton. (1978) Mass and number of fibres in the pathogenesis of asbestos-related lung disease in rats. British Journal of Cancer 37:673-688. Davis JMG, J Addison, RE Bolton, K Donaldson, AD Jones, A Wright (1984) The pathogenic effects offibrous ceramic aluminum silicate glass administered to rats by inhalation or peritoneal injection. In: Biological Effects of Man-Made Mineral Fibres. Proceedings of a WHO/IARC Conference, Copenhagen 301-322. Geneva: World Health Organization. Davis JMG, AD Jones. (1988) Comparisons of the pathogenicity of long and short fibres of chiysotile asbestos in rats. British Journal of Experimental Pathology 69:717-737. Davis JMG. (1994) The role ofclearance and dissolution in determining the durability of biopersistence of mineral fibers. Environmental Health Perspectives I02(Suppl 5): 113-117. Donaldson K, GM Brown, DM Brown, RE Bolton, JMG Davis. (1989) Inflammation generating potential of long and short fibre amosite asbestos samples. British Journal of Industrial Medicine 46:271-276. Goodglick LA, AB Kane. (1990) Cytotoxicity of long and short crocidolite asbestos fibers in vitro and in vivo. Cancer Research 50:5153-5163. Hansen K, BT Mossman. (1987) Generation of superoxide from alveolar macrophages exposed to ashestiform and nonfibrous particles. Cancer Research 47:1681-1686. Health Effects Institute - Asbestos Research (1991) Asbestos in public and commercial buildings: A literature review and synthesis of current knowledge. > HWBUI0009676 Hesterberg TW, JC Barrett (1984) Dependence of asbestos and mineral dust-induced transformation of mammalian cells in culture on fiber dimension. Cancer Research 44:21702180. Hesterberg TW, JC Barrett (1985) Induction ofasbestos fibers of anaphase abnormalities: mechanism for aneuploidy induction and possibly carcinogenesis. Carcinogenesis 6:473-475. Hesterberg TW, CJ Butterick, M Oshimura, AR Brody, JC Barrett (1986) Role of phagocytosis in Syrian hamster cell transformation and cytogenetic effects induced by asbestos and short and long glass fibers. Cancer Research 46:5795-5802. Hume LA, JD Rimstidt (1992) The biodurability of chrysotile asbestos. American Mineral 77:1125-1128. . Ilgren E, E Chatfield. (1997) Coalinga Fibre - A short amphibole-free chrysotile. Part 1: Evidence for a lack of fibrogenic activity. Indoor Built Environment 6:264-276. Ilgren E, E Chatfield. (1998) Coalinga Fibre - A short amphibole-free chrysotile. Part 2: Evidence for lack of tumourigenic activity. Indoor Built Environment 7:18-31. Ilgren E, E Chatfield. (1998) Coalinga Fibre: A short, amphibole-free chrysotile. Part 3: Lack of biopersistence. Indoor Built Environment 7:98-109. King EJ, JW Glegg, VM Rae. (1946) Effect of asbestos and asbestos and aluminum on the lungs ofrabbits. Thorax 1:188. Kinnula VL. (1999) Oxidant and antioxidant mechanisms of lung disease caused by asbestos fibres. European Respiratory Journal 14:706-716.. Klosterkotter W. (1968) Experimentelle Untersuchunger liber die Bedeutung der Faserlange fur die Asbest-Fibrose sowie Untersuchungen fiber die Beeinflussung der Fibrose durch Polyvinylridin-n-oxid. In: Biologische Wirkungen des Asbestos, p. 47. Proceedings of the International Conference^ Dresden, Germany. . Deutches Zenralinstitute ffir Arbeitsmedizin, Berlin, Germany. Kolev_ EL: (1.982) Experimentally-induced mesothelioma in white rats in response to intraperitoneal administration of amorphous crocidolite asbestos. Environmental Research 29:123. Le Bouffant L, H Daniel, JP Heflin, JC Martin. (1985) Carcinogenic potency of chrysotile fibers of the length <5m- Cahiers de Notes Dociunentaires 118:83-90. Lee KP, DP Kelly, FO O'Neal, JC Sjader, GL Kennedy. (1988) Lung response to ultrafine kevlar aramid synthetic fibrils following 2-year inhalation exposure in rats. Fundamental and Applied Toxicology 11:1. HWBUI0009677 Lippmann M. (1990) Effects of fiber characteristics on lung deposition, retention, and disease. Environmental Health Perspectives 88:311-317. Marsh JP, BT Mossman. (1988) Mechanisms of induction of ornithine decarboxylase activity in tracheal epithelial cells by asbestiform minerals. Cancer Research 48:709-714. Morgan A. (1995) Deposition of inhaled asbestos and man-made mineral fibres in the respiratory tract Annals of Occupational Hygiene 39:747-758. Mossman BT, A Churg. (1998) State-of-the-ArL Mechanisms in the pathogenesis of asbestosis and silicosis. American Journal ofRespiratory and Critical Care Medicine 157:1666-1680 Oberdorster G, J Ferin, J Finkelstein, S Soderholm, R Gelein. (1990) Mechanistic studies on particle-induced acute and chronic lung injury. In: Aerosols: Science, Industry, Health and Environment, Vol. 2 (Masuda S, Takahashi K; eds.) pp. 1229-1233. Pergamon Press, New York, NY. Ohyama M; T Otake, K Morinaga. (2001) Effect ofsize ofman-made and natural mineral fibers on chemiluminescent response in human monocyte-derived macrophages. Environmental Health Perspectives 109:1033-1038. Piatek SF, DH Groth, CE Ulrich, LE Stettler, MS Finnell, M Stoll. (1985) Chronic inhalation of short asbestos fibers. Fundamental and Applied Toxicology 5:327-340. Pott F. (1978) Some aspects on the dosimetry of the carcinogenic potency of asbestos and other fibrous dusts. Staub-Reinholt Luff 38:486-490. Pott F, KH Friedrichs. (1972) Tumours in rats after intraperitoneal injection of asbestos dusts. Naturwissenschaften 59:318. Scymczykiewicz K, E Wiecek. (1960) The effect of fibrous and amorphous asbestos on the collagen content in the lungs of guinea pigs. In: Proceedings of the 13th International Congress on Occupational Hygiene, New York, NY. Excerpta Medica Foundation, New York, NY Stanton MF, M Layard. (1978) The carcinogenicity of fibrous minerals. Proceedings of the Workshop on Asbestos; Gaithersburg, MD. NBS special publication 506 (National Bureau of Standards) National Institute ofStandards and Teehnology, Gaithersburg, MD. : Stanton MF, M Layard, A Tegeris, M Miller, E Kent. (1977) Carcinogenicity of fibrous glass: Pleural response in the rat in relation to fiber dimension. Journal of the National Cancer Institute 58:587. Stanton MF, C Wrench. (i 972) Mechanisms of mesothelioma induction with dsbestos and fibrous glass. Journal of the National Cancer Institute 48:797. ) HWBUI0009678 Sussman RG, BS Cohen, M Lippmann. (1991) Asbestos fiber deposition in a human tracheobronchial cast. Part I: Experimental. Inhalation Toxicology 3:145-160. Vorwald AJ, TM Durkan, PC Pratt (1951) Experimental studies ofasbestosis. AMA Archives of Industrial Hygiene and Occupational Medicine 3:1. Wagner JC. (1990) Biological effects of short fibers. Proceedings of the VII International Pneumoconiosis Conference, Pittsburgh, PA, August 1988. NIOSH 90-108, Vol. 2, pp. 835-840. National Institute of Occupational Safety and Health, Washington, DC. Wagner JC, DM Griffiths, Rl Hill. (1984) The effect of fibre size on the in vivo activity ofUICC crocidolite. British Journal of Cancer 49:455-458. Wagner JC, JW Skidmore, RJ Hill, DM Griffiths. (1985) Erionite exposure and malignant mesothelioma in rats. British Journal of Cancer 51:727-730. Woodworth CD, BT Mossman, JE Craighead. (1983) Induction of squamous metaplasia in organ cultures of hamster trachea by naturally occurring and synthetic fibers. Cancer Research 43:4906-4912. Wright GW, M Kuschner. (1977) The influence of varying lengths of glass and asbestos fibres on tissue response in guinea pigs. In: Inhaled Particles, Vol. IV (Walton WH, ed.) pp. 455-474. Pergamon Press, Oxford, England. Wright A, H Cowie, IP Gormley, JMG Davis. (1986) The in vitro cytotoxicity of asbestos fibers. I. P388D1 cells. American Journal of Industrial Medicine 9(4):371-384. Yu CP, B Asgharian, JL Abraham. (1990) Mathematical modeling of alveolar clearance of chrysotile asbestos fibers from rat lungs. Journal ofAerosol Science 21:587-594. / HWBUI0009679 Gunter Oberddrster University of Rochester HWBUI0009680 Gunter Oberdorster University of Rochester Department of Environmental Medicine 575 Elmwood Avenue Annex - Room A-225 Rochester, NY 14627 Phone: 585-275-3804 Fax; 585-275-3709 Email: gunter_oberdorster@unnc.rochester.edu Dr. OberdSrster holds a D.V.M. (1964) and a Ph.D. in pharmacology (1966) from the University of Giessen, Germany. He is a professor of toxicology in environmental medicine and head of the Division of Respiratory Biology and Toxicology at the University of Rochester School of Medicine. Since 1999, he has also served as Director at the U.S. EPA-funded Particulate Matter Center on ultrafine particles in the Department of Environmental Medicine at University of Rochester. Dr. Oberdorster has served as chairperson or session chairperson at many national and international conferences related to aerosols, inhalation and pulmonary toxicology, and natural and man-made fibrous and non-fibrous particles. He has served as a peer reviewer for over 30 scientific journals. Dr. OberdSrster has been investigating the effects and toxicokinetics of occupational and environmental particles for more than 25 years, more recently focusing on ultrafine particles. His current research includes studies related to mechanisms of acute and chronic lung injury by inhaled particulate pollutants, including ultrafine particles (Inflammatory responses, fibrosis); toxicological evaluation of air pollutants measured by the response of iavagable lung celts; mechanisms of pulmonary carcinogenesis of. different inorganic compounds in rats and mice; inflammation, cell proliferation, and carcinogenesis of the lung; alveolar macrophage induced cytokines, chemotactic factors and growth factors; deposition and retention modeling of inhaled non-fibrotrs and fibrous particulate compounds (lung-dosimetry); species differences in pulmonary responses and extrapolation to man for risk assessment; pulmonary effects of air contaminants during space flights; preventive and therapeutic measures of polymer-fume induced lung Injury: and relationships of age and disease for pulmonary responses of inhaled particles. He has published --200 journal articles on these topics. HWBUI0009681 % G. Oberdorster ______________________ ATSPR Panel Meeting The term "fiber" should be defined first (WHO definition is different from the NIOSH definition). The selection of a 5 pm cut for a short fiber as a limit should also be discussed. I assume that both cancer and non-cancer endpoints are to be included in the discussion and it might be useful to list the different endpoints such as: Cancer Lung tumor (bronchogenic); mesothelioma (pleura; abdominal) Non-cancer. Chronic inflammation (bronchial, alveolar), cell proliferation, interstitial fibrosis, pleural fibrosis, others. Topic 1: Physiological fate of asbestos and, vitreous fibers < 5 pm in length PfeysMogisai dgposition.pattem.for shprt fibers: At present the references do not include publications by Yu et aL, oh the deposition and clearance of fibrous and non-fibrohs particles in humans and rodents. (A list of those publications is attached.) The nose is an efficient filter for long fibers, and less for shorter ones, depending on their aerodynamic properties as will be discussed at the meeting. The aspect ratio of the fibers is an important factor for their deposition, and several figures from Dr. Yu's work are attached. There are significant differences between humans and rats with respect to deposition efficiencies of long as well as short fibers; respirability is very differe.nt and the deposition fractions. are significantly different as well between the two species (see attached figures). For very short fibers, their aerodynamic properties approach those of spherical particles. Material density also has to be considered. \ J HWBUI0009682 Clearance/Biopersistence ofShort Fibers: Biopersistence is the sum ofphysiological clearance processes and physicochemical processes which together account for the retention halftime of the fibrous or non-fibrous material in the lung. Physicochemical processes include dissolution, leaching, breaking and splitting, depending on the fibrous material, that can occur intra- as well as extra-cellularly, and differences in pH in both locations are of importance here. Clearance rates of fibers of different length categories have been determined from short and long term inhalation studies ( refs, to be provided). Generally, short fibers are cleared rapidly if biosoluble (pH differs intracellularly vs extracellularly), or at rates similar to non fibrous particles. Breakage of long fibers will give input into short fiber category. Most important physiological clearance mechanism in alveolar region is clearance by alveolar macrophages (AM). Of importance is fiber length with respect to phagocytosis and removal by alveolar macrophages. Short fibers are easily phagocytized, fibers longer than 20 pm are not Species differences in AM size. Thus, clearance for long fibers is prolonged, as is that for short fibers when high lung burdens are reached (particle overload). Also, intrinsic toxicity of short fibers has to be considered which influences clearance. Inflammatory conditions in the lung (for example, smokers) also contribute to impairment of alveolar macrophage-mediated mechanical clearance and need to be considered. Typjes of migration: Among physiological clearance processes are translocation along the mucociliary escalator from the conducting airways; translocation to interstitial sites, depending on fiber length and fiber load. Especially at higher lung burdens, short fibers are more likely to penetrate into the interstitium and translocate to pleural sites, lymph nodes, and short fibers can even enter the blood circulation. HWBUI0009683 Animal studies found preferentially translocation of short fibers to the pleural space in rodents when high lung burdens after inhalation exposure were achieved (Gelzleichter et al. 1996). They found a geometric median length of 1.5 pm for fibers recovered at the pleural site after RCF exposure, whereas the inhaled RCF fibers had a geometric median length of 4.5 pm with the longest fibers being longer than 100 pm. Very few fibers longer than 5 pm were found at the pleural site, whereas longer fibers were found in the pulmonary tissues but did not appear to migrate to the pleura. Migration of the short fibers in the animat studies resulted in a pleural inflammatory response which was lower than in the lung and was also delayed compared to the response in pulmonary tissue. In general, many studies with fibers have used fiber preparations with so-called "non-fibrous particles" which contain significant numbers of short fibers (if the WHO definition is Followed). Such short fibers are of importance since they contribute to the overall lung burden and may actually amplify the effects of long fibers as has been shown in animal studies with mixed fibrous/non-fibrous particle exposures (both cancer and non-cancer endpoints). In this context, inhalation studies by Beflmann et al (2001; 2002) using RCF with and without non fibrous particles are of interest Reduction of the non fibrous particles restored impaired clearance of test particles, although other endpoints of toxicity (lung lavage data, histopathology) did not seem to be significantly different, and fiber clearance per se was not different between the 2 groups. (Belimann, 2001). (Need to consider also total lung burden differences between the 2 grpups!) Non fibrous particles of the same chemical composition induced high inflammatory responses in a subchronic inhalation study ( Belimann et al, 2002,a,b: Arm. Occup. Hyg. 46, Stippl.l, 102-104; and 1664 69,2002) HWBUI0009684 Topic 2: Health effects of asbestos and vitreous fibers <5 microns in length. Robustness of animat and human cancer data for short fibers: Animal inhalation and i.p. injection studies consistently show that short fibers are clearly less tumorigenic than long fibers (eg., Davis et al. studies, example attached). An important factor in many studies is the existence of "a non-fibrous fraction" in fiber samples which contribute to both cancer and non-cancer effects of the fibers. Contamination of a fiber sample with other fibrous materials (for example, tremolite [moe toxic] in chrysotile [less toxic]) is also important. With respect to cancer induction, the intrinsic toxicity ofshort fibers -- like that of non-fibrous particles-- is of high importance, both arc readily phagocytized by alveolar macrophages and subjected to AMmediated clearance unless they have significant cytotoxicity (e.g., crystalline silica vs. TiO* for nonfibrous particles). Biopersistence is a most important factor as pointed out and discussed under Topic 1. Potential for SVF to induce cancer: Biopersistence is a most important factor (see emphasis in new European regulations for testing of SVFs for biopersistence, in order for SVF's to be exonerated from a carcinogen label). Other important factors are exposure, concentration (dose to the lung), length (long fibers most carcinogenic) and surface properties (crystalline vs. amorphous). Evidence ofshort fibers causing health effects: Contribution of short fibers to effects caused by long fibers is probably similar to non-fibrous particles (mixed dust exposure studies). For rats a pathogenic mechanism due to lung overload from short fibers/non-fibrous particles becomes important for high doses, overload conditions in humans are not likely to be achieved (relevance of discussion on particle overload?). However, low doses HWBUI0009685 also result in AM activation. To be considered as well: compromised hosts (respiratory; cardiovascular); and pre-exposure history (e.g., development of tolerance). Indirect evidence for short fibers to induce health effects: Evidence exists from combination studies, e.g., asbestos fibers TiO, or Si02; need to discuss effects of non-fibrous particles ofdifferent compositions, animal studies (usually very high doses) vs. human exposures. Length ofmaterial to no longer induce fiber-like toxicity: There is an no systematic study which would allow to define a specific fiber length to answer this question. There are a number of studies showing that short fibers (<5 pm) are less biologically active than long fibers. The discussion here needs to focus also on what is "fiber-like toxicity": A clear difference obviously exists when fibers are phagocytizable vs. non-phagocytizable, as well as their propensity to be translocated into and across epithelium. There are data for tangential vs. perpendicular uptake of fibers by AM, resulting in different responses (Okyama et al., 2001), but not conclusive. There is also the issue of nanofibers (e.g., nanotubes). These fibers are so small that they very likely behave very differently with respect to interactions with cells, e.g., translocation to interstitial and extrapulmonary tissues. Thresholds for mechanisms of toxicity for short fibers: Existence for threshold for pulmonary kinetics (accumulation and retention, can we extrapolate from non-fibrous studies? General threshold when exceeding physiological defense mechanisms (e.g., clearance mechanism, antioxidant - anti-inflammatory defenses). LN accumulation as indicators of toxicity? HWBUI0009686 Topic 3: Data gaps. Data on toxic effects of fibers of one specific length only, without contamination with longer fibers (in vitro, i.t instillation; inhalation) of materials of different compositions. Side by side comparison of different effects of different length fibers with non fibrous particles of the same material. Research needed to fill gaps: Short-term studies, it combination studies, long fibers alone; long combined with short i fibers, different fiber length and non fibrous particles, dosed by different dosemetrics, e.g., mass, number, surface area. Toxicokinetic studies (accumulation, retention) HWBUI0009687 Asgharian, B. and C. P. Yu (1988). "Deposition of inhaled fibrous particles in the human lung." Journal of Aerosol Medicine l(No. 1): 37-50. Asgharian, B. and C. P. Yu (1989). "Deposition of fibers in the rat lung." Journal of Aerosol Science 20: 355-366. Asgharian, B. and S. Anjilvel (1998). "A Multiple-Path Model ofFiber Deposition in the Rat Lung." Toxicological Sciences 44: 80-86. Dai, Y. T. and C. P. Yu (1998). "Alveolar deposition of fibers in rodents and humans." U(No. 4): 247-258. Ding, J. Y., C. P. Yu, et al. (1997). "Deposition modeling of fibrous particles in rats: Comparisons with available experimental data." Aerosol Science & Technology 26:403414. Griffis, L. C., J. A. Pickrell, et al. (1983). "Deposition ofcrocidolite asbestos and glass microfibers inhaled by the beagle dog." 44:216-222. Hashish, A. H. and A. G. Bailey (1991). "The importance of electrostatic charge on the deposition of fibrous particles in human and rat lungs. Presented at Electrostatics '91, Oxford." InstPhvs-Conf.Series No. 118, Section 1: 51-56. Jones, A. D., J. H. Vincent, et al. (1988). "Effects of electrostatic charge on the pulmonary deposition of mineral dust aerosols inhaled by rats.; J. Aerosol Sci., Vol. 19, no. 5, pp. 565-575." <None Soecified>. Lentz, T. J., C. H. Rice, et al. (2001). Pulmonary deposition modeling with airborne fiber exposure data: A study ofworkers manufacturing refractory ceramic fibers: 38 pages. Lippmann, M. (1994). "Deposition and retention of inhaled fibres: effects on incidence of lung cancer and mesothelioma." Occupational and Environmental Medicine 51: 793-798. Morgan, A., J. C. Evans, et al. (1977). "Deposition and clearance of inhaled fibrous minerals in the rat. Studies using radioactive tracer techniques.; Inhaled Particles IV, pp. 259-272 Ed. W.H. Walton, Pergamon Press Oxford and N.Y." <None Specified>. Okabe, K., G. G. K. Murihy, et al. (1997). "Deposition efficiency of inhaled fibers in the hamster lung." Inhalation Toxicology 9: 85-98. Strom, K. A. and C. P. Yu (1994). "Mathematical modeling of silicon carbide whisker deposition in the lung: Comparison between rats and humans." Aerosol Science and Technology 21: 193-209. Sussman, R. G., B. S. Cohen, et al. (1991). "Asbestos fiber deposition in a human tracheobronchial cast 1. Experimental." Inhalation Toxicology 3: 145-160. o \ - .J HWBUI0009688 Sussman, R. G., B. S. Cohen, et at. (1991). "Asbestos fiber deposition in a human tracheobronchial cast II. Empirical model" Inhalation Toxicology 3: 161-179. Timbrel!, V. (1982). "Depositon and retention of fibres in the human lung." 26: 347-369. Yu, C. P., B. Asgharian, et at. (1986). "Impaction and sedimentation deposition of fibers in airways.; Am. Ind. Hyg. Assoc. J., VoL 47, no. 2, pp. 72-77." Yu, C. P., B. Asgharian, et al. (1991). "Intrapulmonary deposition and retention modeling of chiysotile asbestos fibers in rats." 22:757-763. Yu, C. P., L. Zhang, et al. (1994). "Deposition modeling ofrefractory ceramic fibers in the rat lung." 25 (No.2): 407-417. Yu, C. P., Y. J. Ding, etal. (1995). "Deposition' and clearance modeling of inhaled kaolin refractory ceramic fibers (RCF) in hamsters - comparison between species." Inhalation Toxicology 7: 165-177. Yu, C. P., L. Zhang, et al. (1995). "Deposition of refractory, ceramic fibers (RCF) in the human respiratory tract and comparison with rodent studies." Aerosol Science and Technology. HWBUI0009689 fran: Gtkkkfrer&ttt. I9& Wf BO. 3. Sejjftfc .Sferamoin (a txa&um# nomas bOawiat * a*. feta&te'K&p&s'isjr iMtas-ra <n$ ffesttj Wjwejst*. ^faiegna *. fMw> i Sirtdl <bto, By 1* (#*( mfia Ml WWW. ^.Wyai^^lpj|^.Wka&4-far^t. *<S*6*S*a*a**&(h*aq*^em^AfeoU} w=toBg*>><feM^tf>iB. SB^i!^-^aaijSaBi^- wwi or*w Cehjeicklerti at, 1996 <WVft<U %*4i i H.j* H HWBUI0009690 > HWBUI0009691 o '\ HWBUI0009692 ).) From: TmbreUetoI.. dParticles W. HWBUI0009693 HWBUI0009694 William Wallace NIOSH - CDC HWBUI0009695 William Wallace Leader Molecular Biophysics Team NIOSH-CDC 1095WiHowdale Road Morgantown. WV 26505-2888 Phone: 304-258-6096 Fax: 304-285-6041 Email: wwaltace@cdc.gov Dr. Wallace holds a Ph.D.. M.S., and B.S. in physics from West Virginia University. He is currently serving as a molecular biophysics team leader and research physical scientist in the Exposure Assessment Branch, Health Effects Laboratory Division of NIOSH, in addition to acting as a National Research Council Postdoctoral Research Advisor. Dr. Wallace has been an adjunct professor in the Department of Chemical Engineering, Genetics and Developmental Biology Program, and a member of the graduate faculty. College of Engineering and Mineral Resources at West Virginia University since 1985. His current research at NIOSH centers around respirable particle surface properties and toxicity, explored through directing projects examining elemental surface composition of respirable dusts, surface chemistry characterization of particulate exposures, computational studies of biomolecular adsorption on mineral surfaces, and toxic respirable particle biological surface interactions. He has contributed articles to many books and journals including, papers related to the effect of chrysolite fiber surface composition on genotoxicity in vitro, particulate surface-phospholipid surfactant interactions affecting expressions of toxicity, in vitro genotoxic activities of diesel exhaust particulate soot and of quartz dust, intracellular surfactant removal from phagocytized minerals, the structure of silica surfaces in relation to cytotoxicity, and modulation of silica pathogenicity by surface processes. / HWBUI0009696 ATSDR FIBERS PANEL William E Wallace 1 Health Effects of Asbestos and Synthetic Vitreous Fibers: The Influence of Fiber Length Topic #2: Health Effects of Asbestos and Vitreous Fibers less than 5 micrometers in length Question: Is there indirect evidence for less-than-5 micron fiber induced adverse health effects? Do the mechanisms of action of other materials (e.g., larger asbestos fibers, silicates, mineral dusts, amorphous silica) with potentially similar compositions aid in understanding small-fiber mechanisms of action? Discussion: There appears tobea significant difference in the pathogenic activity of respirable fibers with fiber length, with fibers below approximately 5 um (micrometers) in length being significantly less hazardous for cancer or pulmonary fibrosis. This prompts the questions: What are the mechanisms of observed long fiber toxicity? Are compositionaUy similar non-fibrous dusts pathogenic? If so, what are the mechanisms of their toxicity? Do short fibers express either or both or combinations of those toxic mechanisms. There is a profound literature on the topic of long fiber mechanisms of toxicity and fibrogenesis. The report by V Kinnula "Oxidant and antioxidant mechanisms of lung disease caused by asbestos fibers" European Respiratory Journal 14(3):706-716,1999, reviews the possible roles of reactive oxygen species (ROS) and reactive nitrogen species (RNS) generated by asbestos fiber in cell-free and cellular and tissue systems. A primary step in response to asbestos fiber challenge, of cells is agreed to be superoxide anion release is cells which have attempted to phagocytize fiber.. This superoxide can further be dismutated to hydrogen peroxide, which can generate hydroxyl radical, catalyzed by iron via the Fenton reaction. That hydroxyl radical is extremely toxic and reactive, but therefore short-lived. There is some contention that fibers stimulate the release of ROS from inflammatory cells and not target cells. However, asbestos fiber can generate ROS spontaneously in cell-free systems. HWBUI0009697 ATSDR FIBERS PANEL William E Wallace 2 Another pertinent review is by C Manning, V Vallyathan, and B Mossman: 'Diseases caused by asbestos: mechanisms of injury and disease development" International Immunopharmacology 2:191-200,2002. This explicates the central dogma that asbestos fibers activate transcription factors and early response genes involved in cell proliferation by generating ROS on ironcontaining fiber surfaces, and that "frustrated* phagocytosis may be involved. The paper by M Ohyama, T Otake, and K Morinaga presents a difficult argument against frustrated phagocytosis: "Effect of size of man-made and natural mineral fibers on chemiluminescent response in human monocyte-derived macrophages.* Environ Hlth Perspec 109:10331039,2001. This study of luciginen-dependent chemiluminescence (CL) induced in vitro over a 2 h period found a strong correlation of response indicative of superoxide release with fiber length 6 to.20 urn. All samples except wollastonite induced CL response in a dosedependent manner. Superoxide release was non-specific for compositional type of fiber. The four fibers with lengths below 7 um :KT whisker, at 6 urn, microglass at 3 um, TO whisker at 2 um, and SiC whisker at 6.4 um were only weakly active. Longer fiber activity correlated with length. This is consistent with the extensive literature indicating long, thin, durable fibers are tumorogenic. Some other studies suggest and support a "frustrated* phaghocytosis mechanism. This includes some recent NIOSH research results: T Blake, et al. "Effect of fiber length on glass microfiber cytotoxicity* J Toxicol Environm Hlth 54:243-259,1998. CL induction after zymosan stimulation and LDH release were measured for Manville Code 100 (JM-100) fiber challenged rat AM in vitro.in EMEM Tor 18h. A novel feature of this study was the use of fibers carefully sized to average lengths of 33,17, 7,4, arid.3 um: The greatest toxicity was seen with the longer fibers. And multiple macrophages were seen attached along the length of the long fibers., suggesting "frustrated* or incomplete phagocytosis as a factor in increased toxicity with length. . This was also seen in J Ye et al. "Critical role of glass fiber length in TNF-alpha production arid transcription factor activation in macrophages." Am J Physiol276 (Lung Cell Mo) Physiol 20):L426-L434,1999. Glass fibers with lengths of 6.5 +/- 2.7 um and 16.7 +/-10.6 um were used to challenge a mouse macrophage cell line in fetal calf serum (FCS)-containing culture HWBUI0009698 medium., for 3,6, and 16 h. Glass fibers stimulated TNF-afpha production and caused NF-kB activation. Reactive oxygen species (ROS) were involved in the activation and production. Long fibers were more potent than short fibers. Short fibers but not long fibers were effectively engulfed by macrophages. However, short fiber induced TNF-a and TNF-a gene promoter activation was on the order of one-third to one-half that of the long fiber. In a subsequent study by Ye et al. "Activation of mitogen-activated protein kinase p38 and extracellular signal-regulated kinase is involved in glass fiber-induced tumor necrosis factoralpha production in macrophages' J Biological Chem 276:5360-5367,2001., it was found that the long fibers were more potent than short fibers in activating MAP kinases which activates transcription factor c-Jun which acts on the TNF-a gene promoter through the cyclic AMP response element and the AP-1 binding site. In a study by Cheng et al. "Role of transcription factro NF-kB in asbestos-induced TNF-alpha response from Macrophages* ExpL And Mol Pathology 66:201-210,1999, Crocidolite with a median, fiber length of 11.5 um challenged lavaged rat AM in F8S-conta?ning medium for 1 to 24 h.. Crocidolite caused parallel increases in TNF-a production and NF-kB activation.in a dosedependent manner. Interestingly, at the optimun stimulating condition the asbestos did not cause a significant cytotoxic effect A titanium oxide control dust had no stimulatory effect on TNF-a secretion. One aspect of fiber production of toxic hydroxyl radical is that fibers long enough to be not fully phagocytized by a cell are involved in "frustrated" phagocytosis. One possible consequence is that the partially invaginated fiber stimulates the cell to release superoxide in a manner related to the respiratory burst upon normal phagocytosis, or that superoxide is produced by the cell in response to an autolytic effect of enzymes or other lysosomal or cytosolic agents released into the annularInvagination of the fiber. The superoxide is then in close approximation with reactive iron species on the fiber surface in or. extending beyond the partially invaginated fiber to create hydroxyl radical for strongly toxic effects at the cell or neighboring cells. Mechanisms of toxicity for fibrous and non-fibrous materials are discussed by A Chung et al. In "Pathogenesis of fibrosis produced by asbestos and man-made mineral fibers: what makes a fiber fibrogenic?", Inhalation Toxicology 12(S3):15-26 2000. The review highlights caveats to the general models of asbestos activity. Some fibers can evoke the responses from ROS HWBUI0009699 generation through the cascade to and including expression of TNF-alpha, but have not been shown to induce fibrosis. And asbestos produces fibrosis in some systems without increasing TNF-alpha expression. Chrysolite contains little iron but is fibrogenic, albeit not a potent as amphibole. Churg et al. Suggest a comparison of asbestos and silica-induced fibrosis data. Table 3 of the paper compares the generation of ROS, RNS, and activation of NF-kB and AP-1 . and increased production of TNF-atpha and other factors and find the dusts to be indistinguishable. In the face of this, asbestosis and silicosis differ in histopathological appearance: asbestosis is a diffuse fibrosis and sificosis is in localized nodules.. The conclusion is that the tabulated responses fail to explain comprehensively how asbestosis or silicosis develop. Crystalline silica dust is a well established eb'ologic agent for pulmonary fibrosis, i.e.i silicosis. However (a) the mechanism of the disease is still not fully known, and (2) the effect of silica in mixed dust exposures frequently Is not proportional to the silica content of the dust, and (3) short-term in vitro investigations of toxicity fail to distinguish crystalline silica from somei nonfibrogenic dusts. Crystalline silica can directly cause membranolysfs and induce the release of cytosolic and lysosomal enzymes from lavaged lung macrophages or other cell lines in vitro. Experiments with thermally treated crystalline quartz and cristobalite have shown the the membranolytic activity is associated with silica surface silanol hydroxyl (not hydroxyl radical) groups. From a compositional standpoint, crystalline quartz is not a good non-fibrous analog of asbestos. Riebeckite is onfe such choice, and is not fibrogenic. A partially analogous'set of non-fibrous minerals are layered alumino-sllicate minerals, days. 'Our research has been ' comparing in vitro cytotoxicities and physico-chemical surface properties of reSpirPble quartz in comparison with the structurally-simplest day; kaotinite. Those comparisons may povide some limited guidance in assessing the potential toxicrties of short fiber asbestos which are distinct from fiber size and "frustrated1' phagocytosis-associated mechanisms. r-~-\ HWBUI0009700 Respirable quartz is strongly fibrogenic, while respirable kaolin is not Nevertheless, in vitro short term tests do not distinguish between then. On a surface area basis they are comparably active for membranoiysis, lactate dehydrogenase (LDH) release, beta-glucuronidase release, beta-n-acetyl giucosaminidase release, and cytotoxicity as measured by trypan blue dye exclusion. It is important to note that these are short-term (one to a few hour) in vitro challenges in the absence of serum in the medium, or with the challenge managed such that serum is excluded from contact with the dusts during the challenge period. It appears that silica and silicate surfaces are comparably innately active for direct prompt cell membranolytic damage. When a respired particle deposits in the terminal lung airways or the pulmonary alveoli, its first contact is not with the epithelium surface or with free macrophages on the lung surface, but with a thin hypophase environmental interface which is coated by and saturated with a dispersion of lung surfactants. This surfactant coating is know to function to reduce the surface tension of the air - aqueous layer interface. However, it appears to also function to suppress the otherwise prompt cytotoxicity of many non-fibrous mineral dusts, e.g., silica and silicates. Brief incubation of silica or day dust in a dispersion of diacyl phosphatidyl choline (DPPC), the primary constituent of lung surfactant, in physiologic saline results in the immediate attenuation of dust cytotoxicity. That passivation is total if adequate surfactant-to-dust surface area is available. That is always the case for a normal lung under other than suffocating dust exposure conditions. That surfactant adsorption and passivation occurs for quartz dust as well as kaolin dust. So the question becomes not why both dusts are not strongly fibrogenic, but rather why either is active. Research indicates that multi-layers of DPPC surfactant will loosely adsorb to the partides, but a residual bilayer which cannot is not water rinsed from the particle surface is fully prophylactic. Surfactant coated dusts are phagocytized by lavaged rat macrophages in vitro and do not express otherwise prompt cytotoxicity, e.g., damage measurable in a one or two hour time after challenge. However, over a several day period there is a restoration of toxidty seen in the lavaged macrophage system or in vitro systems using several different cell lines. Radio-tracer studies show that the. surfactant coating on the dusts is digested in parallel with the restoration of toxicity. Cell-free system studies show that phospholipase A2 hydrolyzes the particle bound DPPC surfactant. The lysolecithin product is partially water soluble. The restoration of membranolytic activity maps with the digestive removal of the adsorbed surfactant. HWBUI0009701 That is, adsorption of components of pulmonary surfactant promptly adsorb and passivate silica and silicate surfaces by prophylactically masking the membranolyiic dust surface silanol hydroxyl groups. But following phagocytosis the particles are stripped of the protective coating by phagotysosomal enzymatic digestion. Research has indicated that the kinetics of the first half of the digestion process are rapid compared to the second half, and that toxicity restoration follows with removal of that second half of the surfactant. That is, the outer side of the adsorbed bilayer is readily digested and the surface-contacted layer more slowly. Using extracellular pHneutral PLA2 in a cell-free system, the rate of digestive removal of DPPC is significantly greater for quartz-adsorbed in comparison to kaolin-adsorbed DPPC. However, for phagocytic cell in vitro systems, quartz and kaolin rates of surfactant loss and toxicity restoration are comparable. Churg et al. Briefly discuss the principal site of asbestos activity, noting the alveolar macrophage is commonly regarded as the crucial effector cell. This is the background assumption also for most experiments on the cytotoxic and fibrosis-associated activity of crystalline silica dusts. However, Adamson, referenced by Churg et al in a different context, has published a suite of studies which make a case that it is interactions of silica particles with interstitial cells which control the stimulation of exacerbated collagen synthesis by pulmonary fibroblasts, and that the macrophage is responsible for only an inflammatory response evoking neutrophil influx to the alveolus but not tied to explicit fibrosis. Thus that model suggests that it may be the removal of surfactant under conditions of interstitial ceil phagolysosomal or extracellular digestion which initiates cell response leading to fibroblast stimulation and fibrosis. While the mechanism of initial cell damage or stimulation may differ between silica or silicates and fibers, e.g., ROS from a "frustrated* phagocytosis mechanism for asbestos and surface silanol hydroxyl membranoiysis by quartz or clay, a parallel analysis to Adamson's silica study and findings should be considered for localization of the effective site of asbestos action for fibrosis.. We have briefly researched'the question of the effect of surfactant adsorption on chrysolite in vitro genotoxicity, using an assay for micronudeus induction in cultured Chinese hamster lung cells (V79 cells). J Lu et al. "In vitro genotoxicity studies of chrysotile asbestos fibers dispersed in simulated pulmonary surfactant" Mutation Res 320:253-259,1994.Two lengths of chrysotile asbestos were used: NIEHS intermediate length (101 urn mean with 65% > lOum), and short length (11.6 um with 98% of fibers < 10 um) chrysotile fibers. Fibers were pre-treated with DPPC and used to challenge V79 cells in FBS-supplemented medium for a total of 72 h. Four o !) HWBUI0009702 types of fiber preparetions: imterroediate length +/- DPPC treatment, short length +/- DPPC, gave dose dependent micronucleus induction activity. The longer fiber samples were most active and DPPC treatment diminished the activity approximately 15%, the maximum activity of the short fiber sample was 70% of the activity of the non-treated intermediate; and the DPPC treated short fibers expressed about 45% of the activity of the untreated. That is, DPPC did not fully suppress the activity of the fibers, but had a much more pronounced partial passivation effect on the short fibers.. One possibility is that the partial suppression of the activity may reflect surfactant suppression of a component of toxicity due to mineral surface rather than frustrated' phagocytosis mechanism. We also attempted to see if a significant surface modification of chrysotile without a significant modification of fiber size would affect in vitro genotoxic activity. M Keane et al. `A study of the effect of chrysotile fiber surface composition on genotoxicity in vitro*. J Tox & Environm Hlth:57:529-541,1999. NIEHS intermediate length chrysotile again was used in the V79 system, with parallel samples of the fiber which had been subjected to mild add teaching to remove near-surface magnesium. Fiber modification was demonstrated and measured by X-ray photoelectron spectroscopy, scanning electron microscopy - X-ray spectroscopy, and zetapotentiaf measurement No significant differences in genotoxic activity were found between the treated and untreated fibers. Small fiber toxicity may be a combination of mineral surface functional group direct membranolytic activity as modulated by interactions with components of the pulmonary surfactant system, and some limited "frustrated' phagoctyosis-associated ROS induced damage, the latter dependent on the possible spread of fiber length values which permit or hinder phagocytosis with variations in cell siza. In assaying for the first mechanism, the non-fiber mechanism, there is one additional caveat to be considered in experimental design. While the use of components of pulmonary surfactant or of surrogate surfactant, e.g., Survanta, may partially model a physiological prophylaxis in the lung, cell test systems may inadvertently introduce a non-representative prophylactic effect through the use of serum in the in vitro system media. Dr. Oberdorster and colleagues published an observation of such partial passivation of silica by lipoproteins in a serum medium seen in an in vitro test; and we have seen apparent similar phenomena in the pasivation of kaolin in such a system. HWBUI0009703 This is a peripheral matter to the question posed, but of possible interest with regard to the overall question of health protection for anomalously high environmental or occupational exposures to respirable and potentially fibrogenic particles or fibers. Some of the provided literature and the body of medical experience indicate that pulmonary fibrosis resulting from asbestos or non-extreme silica dust exposures may be slow to progress, but detection can be subject to even greater delay: Early pulmonary fibrosis seen in tissue section histopathoiogy frequently is not discemable on chest X-ray. Some of the new imaging modalities may provide an alternative to conventional radiological detection or grading of pulmonary fibrosis. Tritiated proline amino acid has been used for decades for autoradiographic analysis of collagen formation in lung necropsy sections of animal models of silicosis. Positron emission tomography using a: positron-emitter labeled analog of the amino acid proline, which is used in great fractional quantity in collagen synthesis, may permit a relatively non-irivasive method to detect and localize heightened collagen synthesis activity, i.e., localized fibrosis; in the lungs after exposure to asbestos or crystalline silica respirable dusts. Initial testing with a rabbit model of silicosis' suggests the approach has the efficacyter detection of fibrosis as an early active metabolic event. Wallace et a(. "Cis-4:{F-18]fluorb-L-proline PET imaging of pulmonary fibrosis in a rabbit model'. J Nuc Med 43:413-420,2002. .Specificity of the method, e.g., for response to fibroblast collagen synthesis versus to a generally heightened metabolism associated with non-specific and transient inflammatory response by macrophages or neutrophils. The latter is seen with conventional fluoro-deoxy-glucose PET imaging. A noninvasive method for active fibrosis might also aid In surveillance of special populations for early indications of lung fibrosis or in evaluating medical management of advancing disease. ) HWBUI0009704 i Appendix C List of Registered Observers of the Expert Panel Meeting \ J HWBUI0009705 A ^tsdri Agency for Toxic Substances & Disease Registry Division of Health Assessment & Consultation ''i Expert Panel on Health Effects of Asbestos and Synthetic Vitreous Fibers (SVF): The Influence of Fiber Length Observers Bill Baughman Office of Standards, Regulations, and Variances Mine Safety and Health Administration 1100 Wilson Boulevard - Room 2309 Arlington, VA 22209 202-693-9458 E-maif: baughman-william@msha.gov David Bernstein Consultant in Toxicology 40 ch. De la Petite-Boissiere CH-1208 Geneva Switzerland 41-22-735-00-43 Fax: 41-22-735-14-63 E-mail: davidb@ipro1ink.ch Arthur Block Senior Regional Representative Agency for Toxic Substances & Disease Registry 290 Broadway - 23rd Roor New York, NY 10003 212-637-4307 Fax: 212-637-3253 . E-mail: axb9@cdc.gov David Bowen Wilcox & Savage 1800 Bank of America Center Norfolk, VA 23510 757-628-5507 Fax: 757-628-5566 E-mail: dbowen@wilsav.com David Brase Health Scientist Office of Occupational Medicine Occupational Safety & Health Administration U.S. Department of Labor 200 Constitution Avenue, NW - Room N3457 Washington, DC 20210 202-693-2323 Fax: 202-693-1647 E-maii: davkJ.brase@osha.gov Daniel Crane Occupational Safety & Health Administration U.S. Department of Labor Salt Lake Technical Center 1781 South 300 West Salt Lake City, UT 84115-1802 801-524-7961 Fax: 801-524-6660 E-mail: dan.crane@osha.gov Michael Dellarco Environmental Health Scientist Office of Research & Development National Center for Environmental Assessment U.S. Environmental Protection Agency 1200 Pennsylvania Avenue (8623D) Washington, DC 20007 202-564-3239 Fax: 202-565-0079 E-mail: dellarco.mike@epa.gov Danielle Devoney Division of Health Assessment and Consultation Agency for Toxic Substances and Disease Registry 1600 Clifton Road, NE (MS-E-32) Atlanta, GA 30333 HWBUI0009706 > ) > Morton Dubin do Orrick Herrington & Sutcliffe 666 Fifth Avenue - 20th Floor New York, NY 10103 212-506-3752 Fax: 212-506-5151 E-mail: mdubin@omck.com Richard Finke Senior Litigation Counsel W.R. Grace & Company 5400 Broken Sound Boulevard, NW - Suite 300 Boca Raton, FL 33487 561-362-1533 Fax: 561-362-1583 E-mail: richard.finke@grace.com Jay Flynn Medical Director Health Network America 187 Monmouth Parkway. West Long Branch. NJ 07764 732-232-9696 E-mail: pynn@healthnetworkamerica.com Kenneth Fradkin Air Programs Branch U.S. Environmental Protection Agency 290 Broadway New York. NY 10007 212-637-3702 E-mail: fradkin.kenneth@epa.gov Debra Gable Division of Health Assessment and Consultation Agency for Toxic Substances & Disease Registry 1825 Century Boulevard Atlanta, GA 30345 404-498-0423 E-mail: dfg0@cdc.gov John Hadley do North American Insulation Manufacturers Association - 44 Canal Center Plaza - Suite 310 Alexandria, VA 22314 703-684-0084 . Fax: 703-684-0427 E-mail: john.hadley@owenscoming.com Ed llgren Consultant 830 Montgomery Avenue - #503 Brynmauss, VA 19010 610-525-5960 Debra Janes Office of Standards, Regulations, and Variances Mine Safety and Health Administration 1100 Wilson Boulevard - Room 2307 Arlington, VA 22209 202- 693-9450 E-mail: janes-debra@msha.gov Nancy Jeffery New York City Department of Health & Mental Hygiene 125 Worth Street New York, NY 10013 212-676-6323 E-mail: njeffery@health.nyc.gov Antoinette Jones Agency for Toxic Substances & Disease Registry 290 Broadway - 28th Floor New York, NY 10007-1866 212-637-4305 Fax: 212-637-3253 E-mail: amj3@cdc.gov John Kelse Corporate Industrial Hygienist R.T. Vanderbilt Company, Inc. 30 Winfield Street Norwalk. CT. 06856 203- 853-1400 Fax: 203-831-0648 E-mail: jkelse@rtvanderbilt.com Dori Kuchinsky Senior Council W.R. Grace & Company 44084 Riverside Parkway - Suite 300 Leesburg, VA 20176 703-729-8543 Fax: 703-729-8587 E-mail: dori.kuchinsky@grace.com Joel Kupferman Executive Director - Senior Attorney New York Environmental Law & Justic Project 351, Broadway - Suite 400 New York, NHY 10013 212-334-5551 Fax: 212-202-6388 E-mail: envjoel@ix.netcom.com HWBUI0009707 #3 Burton Arthur Kushner Senior Environmental Employee Air Compliance Branch U.S. Environmental Protection Agency 290 Broadway New York, NY 10007-1866 212-637-3491 E-mail: kushner.burton@epa.gov Nancy LaVerda Exponent 1730 Rhode Island Avenue, NW - Suite 1100 Washington, DC 20036 202-293-5374 Fax:202-293-5377 E-mail: nlaverda@exponent.com Jessica Leighton New York City Department of Health & Mental Hygiene 125 Worth Street New York, NY 10013 212-6766323 E-mail: jleighto@health.nyc.gov Katie Lynch Environmental Scientist Agency for Toxic Substances & Disease Registry 290 Broadway -28th Floor New York, NY 10007 212-637-4304 E-mail: lynch.katie@epa.gov Mark Maddaloni U.S. Environmental Protection Agency 290 Broadway New York, NY 10007 212-637-3590 Fax: 212-637-5045 E-mail: maddaloni.mark@epa.gov L. Daniel Maxim Everest Consulting Associates ' 15 North Main Street Cranbury, NJ 08512 609-655-7426 Fax: 609655-5637 E-mail: postsf@aol.com; ecasharon@aol.com '4 Catherine McVay * Hughes World Trade Center Community Outreach New York University 176 Broadway - 14th Floor New York, NY 10038 212-732-9234 E-mail: catherine@asthmamoms.com Aubrey Miller Senior Medical Advisor/Toxicologist U.S. Environmental Protection Agency 303-312-7023 Fax: 303-844-7857 E-mail: miller.aubrey@epa.gov Suresh Mootgavkar 9005 Northeast 21st Place Bellevue, WA 98004 E-mail: moolgavkar@earthlink.net Chuck Nace Environmental Toxicologist/Risk Assessor ERRD/PSB/TST U.S. Environmental Protection Agency 290 Broadway - 18th Floor New York, NY 10007-1866 212-637-3459 Fax: 212-637-4360 E-mail: nace.charies@epa.gov Jenna Orkin 9/11 Environmental Action Steering Committee 96 Schermerhous Street - #7H New York 11201 718-246-1577 E-mail: jenna.kilt@aol.com Bertram Price Price Associates, Inc. 1 North Broadway - Suite 406 White Plains, NY 10601 914-686-7975 Fax: 914-686-7977 E-mail: bprice@priceassociatesinc.com Monona Rossoi Safety Director Local 829 - IATSE 181 Thompson Street - Suite 23 New York, NY 10012 212-777-0062 E-mail: actsnyc@cs.cbm Tom Simons Environmental Protection Specialist Fibers and Organics Branch/NPCD U.S. Environmental Protection Agency 1201 Pennsylvania Avenue (7404T) Washington, DC 20460 202-566-0517 Fax: 202-566-0473 E-mail: simons.tom@epa.gov ) j HWBUI0009708 David Speziali Attorney 1081 Winslow Road Wittiamstown, NJ 08094 856-728-3600 Fax; 856-728-3996 E-mail; dspeziali@comcast.net Jan Storm Bureau of Toxic Substance Assessment Center for Environmental Health New York State Department of Health Flanigan Square - 547 River Street Troy. NY 12180-2216 516402-7820 Fax: 518-402-7819 E-mail: jes19@health.state.ny.us Laurie Strauch Dix do Onick Herrington & Sutcliffe 666 Fifth Avenue - 19th Floor New York, NY 10103 212-506-3749 Fax:212-506-5151 E-mail: lstrauchweiss@orrick.com Ethan Streli Pillsbury Winthrop 1 Battery Park Plaza New York, NY 10004 212-8561270 E-mail: estrell@pillsburywinthrop.com Allan Susten Division of Health Assessment and Consultation Agency for Toxic Substances & Disease Registry 1600 Clifton Road, NE (E-32) Atlanta, GA 30333 E-mail: ass1@cdc.gov Brian Toal Director Toxic Hazards Program Connecticut Department of Health 410 Capitol Avenue Hartford, CT 06134 866509-7741 Fax: 866509-7785 E-mail: brian.toal@po.state.ctus ' Jay Turim Executive Vice President Sciences International, Inc. 1800 Diagonal Road - Suite 500 Alexandria, VA 22314 703-684-0123 Fax: 703-684-2223 E-mail: jturim@sciences.com Drew Van Orden RJ Lee Group, Inc. 350 Hochberg Road Monroeville, PA 15146 724-3261776 Fax: 724-733-1799 E-mail: drew@rjlg.com Rand! Walker Research Scientist Bureau of Toxic.Substance Assessment New York State Department of Health Flanigan Square - Room 330 547 River Street Troy. NY 121862216 516402-7820 Fax: 518-402-7819 E-mail: rjw03@health.state.ny.us Robert Williams Assistant Surgeon General U.S. Public Health Service and Director Division of Health Assessment and Consultation Agency for Toxic Substances and Disease Registry 1600 Clifton Road. NE (MS-E-32) Atlanta, GA 30333 Malcolm Williams Senior Environmental Health Scientist Toxicology Information Branch Division of Toxicology Agency foe Toxic Substances & Disease Registry 1600 Clifton Road, NE (E-29) Atlanta, GA 30333 404-498-0731 E-mail: mxw7@cdc.gov Katherine Yagerman Assistant General Counsel Minerals Technologies, Inc. 405 Lexington Avenue - 20th Floor New York. NY 10174 212-878-1858 Fax: 212-8761804 E-mail: katie.yagerman@mineralstech.com HWBUI0009709 Ralph Zumwalde Senior Scientist National Institute for Occupational Safety & Health 4676 Columbia Parkway Cincinnati, OH 45226 513-533-8320 Fax: 513-533-8230 E-mail: rdz1@cdc.gov .'1 J ) HWBUI0009710 Appendix D Agenda for the Expert Panel Meeting HWBUI0009711 r Agency for Toxic Substances & Disease Registry Division of Health Assessment & Consultation Expert Panel on Health Effects of Asbestos and Synthetic Vitreous Fibers (SVF): The Influence of Fiber Length Agenda Day #1, Tuesday, October 29, 2002 (afternoon only) 1:00 PM 1:30 PM Registration Welcome and Introductory remarks........................................ .................. Dr. Henry Falk Assistant Administrator, ATSDR 1:45 PM Purpose of meeting ............................................................... RADM Robert C. Williams Director, Division of Health Assessment and Consultation, ATSDR 2:00 PM Review of meeting charge and agenda ............................. . Morton Lippmann, Ph.D. Panel Chair 2:15 PM 2:25 PM introduction of panelists ............................................................ Meeting logistics......................................................................... ........................... Panelists ....................................ERG Topic #1: Physiological Fate of Asbestos and SVF less than 5 Microns in Length 2:30 PM What happens to small fibers when inhaled? Discussion Leaders: Dr. Lippmann and Dr. Oberdorster - Depositions! patterns in the lung - Clearance * Biopersistence * Migration from the lung - Fiber-iike vs. particle-like activity patterns - Asbestos vs. MMVF 3:30 PM Break 3:45 PM Topic #1 (continued) 5:30 PM Observer comments/questions 6:00 PM Adjourn HWBUI0009712 Day #2, Wednesday, October 30,2002 ) 8:00 AM Review of Day #1 issues Morton Lippmann, Ph.D. Panel Chair Topic #2: Health Effects ofAsbestos and SVF less than 5 NScrons in Length 8:15 AM What do human/epidemiological data tell us about small fibers? Discussion Leaders: Dr. Lockey and Dr. Case Cancer effects Non-cancer effects Irritant effects * Association between fiberlength and fiber-like toxicity - Thresholds of toxic action Asbestos vs. MMVF 9:45 AM Break 10:00 AM How do animal/experimental data augment our understanding of human health effects? Discussion Leaders: Dr. McConnell and Dr. Case * Cancereffects * Non-cancer effects *- Irritant effects - Association between fiberlength and fiber-like toxicity - Thresholds of toxic action Asbestos vs. MMVF ") 12:00 PM Lunch 1:00 PM What are the mechanisms of action of small fibers? Can the more robust knowledge base about other fiber or particle materials supplement this understanding? Discussion Leaders: Dr. Mossman and Dr. Wallace Immune system responses * Cell signaling Role ofreactive oxygen/nitrogen species Function ofgrowth factors * Othermechanisms - Asbestos vs. MMVF 3:30 PM Break 4 4 Topic #3: Data Gaps 3:45 PM Data gaps and research needs........................................................ Panelists 4:30 PM Observer comments/questions 5:00 PM Conclusions/recommendations.............................................................................................. Panelists 5:30 PM Adjourn ) HWBUI0009713 Appendix D Agenda for the Expert Panel Meeting i my HWBUI0009714 Atsdr V Agency for Toxic Substances & Disease Registry Division of Health Assessment & Consultation 3 Expert Panel on Health Effects of Asbestos and Synthetic Vitreous Fibers (SVF): The Influence of Fiber Length Agenda Day #1, Tuesday, October 29, 2002 (afternoon only) 1.00 PM 1:30 PM Registration Welcome and Introductory remarks ..................................................................... Dr. Henry Falk Assistant Administrator, ATSDR . 1:45 PM Purpose of meeting ............................................................................RADM Robert C. Williams Director, Division ofHealth Assessment and Consultation, ATSDR 2:00 PM Review of meeting charge and agenda ................................................ Morton Uppmann. Ph.O. Pane! Chair 2:15 PM Introduction of panelists ................................................................................................ Panelists 2:25 PM Meeting logistics................................................................................................................... Topic #1: Physiological Fate of Asbestos and SVF less than 5 Microns In Length 2:30 PM What happens to small fibers when inhaled? Discussion Leaders: Dr. Uppmann and Dr. Oberdorster Depositionai patterns in the lung Clearance - Biopersistence f Migration from the lung * Fiber-like vs. particle-tike activity patterns - Asbestos vs. MMVF 3:30 PM Break 3:45 PM Topic #1 (continued) 5:30 PM Observer comments/questions 6:00 PM Adjourn ... HWBUI0009715 Day #2, Wednesday, October 30, 2002 8:00 AM Review of Day #1 issues...................................................................... Morton Lippmann, Ph.D. Panel Chair Topic #2: Health Effects ofAsbestos and SVF less than 5 Microns in Length 8:15 AM What do human/epidemiological data tell us about small fibers? Discussion Leaders: Dr. Lockey and Dr. Case * Cancer effects - Non-cancer effects Irritant effects - Association between liber length and fiber-like toxidty Thresholds oftoxic action - Asbestos vs. MMVF 9:45 AM Break 10:00 AM How do animat/axperimentat data augment our understanding ofhuman health effects? Discussion Leaders: Dr. McConnell and Dr. Case * Cancer effects * Non-cancer effects * Irritant effects Association between fiber length and fiber-tike toxicity Thresholds oftoxic action - Asbestos vs. MMVF 12:00 PM Lunch 1:00 PM What are the mechanisms of action ofsmall fibers? Can the more robust knowledge base about other fiber orparticle materials supplement this understanding? Discussion Leaders: Dr. Mossman and Dr. Wallace . * Immune system responses Cell signaling < Role ofreactive oxygen/nilrogen species - Function of growth factors - Other mechanisms * Asbestos vs. MMVF 3:30 PM Break Topic #3: Data Gaps 3:45 PM Data gaps and research needs . Panelists 4:30 PM 5:00 PM Observer comments/questions Condusiohs/recommendations . Panelists 5:30 PM Adjourn HWBUI0009716 Appendix E Panelists' Comments Submitted After the Meeting Note: The expert panelists were asked to provide premeeting comments and to participate in the discussions at the expert panel review meeting, fn addition, several panelists chose to submit additional written comments after the expert panel review meeting. Some panelists submitted updated versions of their premeeting comments (see Appendix B), while others wrote summaries of the discussions they led at the expert panel review meeting. All post meeting comments are presented here, regardless of their content. Panelists were not required to submit post-meeting comments. This section presents the post-meeting comments exactly as they were submitted to ERG, with only minor changes to format and references. The expert panel was not asked to comment on the content of these post-meeting comments. Contents: Dr. Lippmann's Post-Meeting Comments ................................................................. E-l Dr. Lockey's Post-Meeting Comments......................... .................................... ......... E-7 Dr. McConnell's Post-Meeting Comments....................................... ......................- E-17 Dr. Mossman's Post-Meeting Comments............................................. .................. E-27 Dr. Oberddrster's Post-Meeting Comments............................................................. E-33 Dr. Wallace's Post-Meeting Comments................................. ................................. E-57 Note: Dr. Case submitted post-meeting comments as a list of suggested revisions to an earlier draft of this report. Dr. Case's comments have been incorporated directly into the text of this report and are not replicated here. HWBUI0009717 Dr. Lippmann's Post-Meeting Comments ATSDR Fiber Panel Review Topic # 1. Physiological Fate of Asbestos and Vitreous Fibers less than S Microns in Length. Discuss/review current knowledge about the physiological fate ofsmall fibers when they enter the body. A. What is the expectedphysiological depositionalpatternfor less-than-5-micronfibers in the lung? This is well established in terms of the depositional mechanisms of impaction, sedimentation. Brownian motion and (for fibers) interception. Fibers with aspect ratios >10 behave aerodynamically like unit density spheres with diameters three times their fiber width (Stdber et al. 1970; Timbrell, 1972). The only exception, in terms of being influential in deposition in lung airways is.for fibers longer than about 10 pm, where the mechanism of interception becomes influential (Sussman et a!, 1991). This also accounts for the fact that longer fibers have proportionately more deposition in the airways as opposed to peripheral alveoli. The fact that lung retention also increases more markedly with fibers greater than 10 microns is supported by theoretical calculations (Yu et al., 1990), analysis of lung dust content in humans (Timbrell, 1982; Churg and Wiggs, 1987; Pooley and Wagner, 1998) and studies using experimental animals (Morgan 1979, 1995). Thus, for fibers <5 pm in length, deposition patterns and efficiencies will be determined almost entirely according to the fiber width, which for fibers <5 pm long will be less than about 1.6 pm. For fiber widths between about 0.1 and 1.6 mm, total lung deposition in healthy people will be between 10 and 20%, with almost all of it in the deep lung. For fibers thinner than 0.1 pm, deposition will increase with decreasing width, and there will be a somewhat greater proportion of the deposition in the more proximal airways. Particles that are not deposited remain suspended in the tidal air and are exhaled. There are significant differences between humans and rats with respect to deposition efficiencies of long as well as short fibers; respirability is very different and the deposition fractions are significantly different as well between the two species; B. What is known about clearance/biopersistence ofless-than-5-micronfibers once-deposited in the lungs? * For these short fibers, which can be fully engulfed by lung ceils and do not dissolve in airway fluids in less than a few weeks, their clearance, will be similar to other mineral and vitreous . particles. Those depositing in lung conductive airways will be largely removed to the G.I. tract by mucociliary clearance within about one day. Most of those depositing in the gas-exchange region will be phagocytized by alveolar macrophages and cleared to and through the mucociliary escalator within a few weeks. Other particles may be engulfed by epithelial cells, primarily in the E-l HWBUI0009718 0 vicinity of the bronchial-alveolar duct junctions, and retained for much longer periods, with gradual removal to lymph nodes. The relatively rapid clearance of short fibers and compact particles from the lung has been demonstrated in a number ofstudies (reviewed in Health Effects Institute-Asbestos Research, 1991; Davis, 1994; Oberddrsteret a!., 1990; Morgan, 1995). Such particles can be: 1) readily transported through tracheobronchial and other lymph nodes to more distal lymphatics, the pleura, or other organs; 2) cleared via the mucociliary escalator and alveolar macrophages; and 3) effectively phagocytized by a number of cell types in the lung including epithelial cells (Churg et ai., 2000). Once within a phagolysosome or in general in lung fluids, shorter fibers of chrysotile asbestos (Hume and Rimstidt, 1992) or glass (reviewed in Lippmann, 1990) are more prone to dissolution and fragmentation than longer fibers and amphiboie types of asbestos. Absent abnormalities in phagocyte function ofthese particles shoutd be removed even ifthey are chemically resistant if: (a) the dose is not too great to overwhelm these normal mechanisms; and (b) the mechanisms themselves are intact There are medical conditions which affect these mechanisms, however, so there are likely to be vulnerable populations (such as those with primary ciliary disorders; these tend to be genetic and very rare such as primary ciliary dyskinesia (incidence 1:20,000 to 1:60,000)). Of greater frequency is the lesser effect on mucociliary clearance in asthma. In addition environmental influences, including smoking and nitrogen dioxide (Case et al., 1982), can affect these normal mechanisms through direct ciliary damage or disrupted function. Some common pharmaceuticals slow mucociliary transport (for example, some general anaesthetics and atropine), while others accelerate it (for example, theophyllines and sympathomimetics). Bronchial secretion is also an important contributor to clearance or impaired clearance, as can be seen most dramatically in cystic fibrosis. Overall, then, there are a number of possible factors that may interfere with particle clearance, but none have been associated with "fiber length" parameters with the possible exception of smoking (Takahashi etal., 1994). The most important physiological clearance mechanism in alveolar region is clearance by alveolar macrophages (AM). Of importance is fiber length with respect to phagocytosis and removal by alveolar macrophages! Short fibers are easily' phagocytized, fibers longer than 20 pm are not. There are species differences in AM size. ' Thus, Clearance for long fibers is prolonged, as is that for short fibers when high lung burdens arc reached (particle overload). Also, intrinsic toxicity- which influences clearance, has to be considered. Inflammatory conditions in the lung (for example, smokers) also contribute to impairment of alveolar macrophage-mediated mechanical clearance and need to be considered. Biopersistence is the sum ofphysiological clearance processes and physicochemical processes, which together account for the retention halftime of the fibrous or non-fibrous material in the lung. Physicochemical processes include dissolution, leaching; breaking and splitting, depending on the fibrous material, that can occur ihtra- as well as cxtfa-cellularly, and differences in pH in both locations are of importance heire. Clearance rates of fibers ofdifferent length categories have been determined from short- and long-term inhalation studies (Davis et al., 1986, 1987; E-2 HWBUI0009719 Wagner, 1990). Generally, short fibers are cleared rapidly if biosoluble (pH differs intracellularly vs. extracellularly), or at rates similar to nonfibrous particles. Breakage of long fibers will give input into short fiber category. The hazards associated with man-made vitreous fiber (MMW) appear to be most strongly associated with the ability to persist within lung tissue. This is, in part, dependent upon chemical composition of the MMVF, in that increased concentrations of stabilizers such as aluminum impact a greater degree of chemical durability. In vitro tests to measure fiber solubility should be performed to reflect an acid pH of4.5 to 5.0 such as found in phagolysomes within alveolar macrophages as well as pH of7.4 reflecting extra-cellular fluid. Short fibers that are ingested by macrophages will encounter the lower pH that overall could affect their biopersistence. In general, solubility tests identified the following rank order from lowest to greatest solubility of MMVF is comparison to asbestos fibers: crocidolite <amosite <RCF <special purpose glass fibers <rock wool <s!ag wool <conventional glass fibers (NRC, 2000). In rodent exposure to mixed dust resulted in an increased transport of fibers across the visceral pleura and increase production of lung tumors and mesothelioma (IARC# 140,1996). C. . What typefs) ofmigration are expected within the bodyfor less-than-5-micronfibers? Fibers with diameters less than -0.1 pm, which could be a significant fraction of fibers <5 pm in length, can penetrate through the respiratory epithelia and be transported through lymph channels to hilar and peripheral (mesothelial) lymph nodes and through blood to more distant body organs. Gelzleichter et al. (1996) exposed rats to nose only inhalation of kaolin-based refractory ceramic fiber. It. was identified that fibers rapidly translocate to the pleural tissue with a difference between those in the pleural tissue and the parenchymal tissue. Within the pleural tissue the geometric mean length ! .5 pm (GSD - 2.0) and geometric mean diameter 0.09 pm (GSD -1.5). For comparison parenchymal tissue GML = 5.0 pm (GSD --2.3) and GMD 0.3 pm (GSD-1.9.) This would indicate the short thin fibers are capable of translocating to the pleural tissue. This may be an important subject, at least for the parietal pleura, ifil is necessary for fibers to reach the pleura to cause lesions (plaques and mesothelioma). It remains possible that fibers still within the peripheral lung may be capable of contributing to the mechanisms of thesS diseases. Mechanisms remain speculative, but long amphibole fibers may tend tp localize.toward the lung periphery, and it remains possible (but unproven ind indeed untested) that chemical mediators may cross the visceral pleura into the pleural space. Churg and Wiggs (1987), amopg others, have observed that "accumulation of long fibers immediately under the upper lobe; pleura may be important in the genesis of mesothelioma.'' Two recent studies are informative (Boutin et al., 1996; Dumortier et at., 2002). They found that "the distribution of asbestos fibers in the pleura was heterogeneous and that they might concentrate in...'black spots' of the parietal pleura," Using thoracoscopy in living patients from "normal areas of the parietal pleura" rather than plaques and tumor, and using controls, they showed that "amphiboles outnumbered chrysotilc in all samples" arid that of all fibers 22.5% were in fact greater than or equal to 5 pm in length; a proportion at least as great as that usually seen in lung tissue. The means of translocation remains unknown, although these findings E-3 HWBUI0009720 % strongly suggest lymphatic drainage paths. The pathogenic significance also remains unknown, although the authors emphasized their hypothesis that these fibers might contribute to plaque and mesothelioma genesis. Other papers that have been published (in relation to human disease) have been for the most part based on static "fiber burdens*' that purport to be in "the pleura" but which on careful reading are in fact in mesotheliomatous tissues and/or pleural plaques; the false assumptions are then made that "short fibers" - usually very short chrysotile fibers, averaging less than 0.2 pm in length have "translocated" to the "pleura" from the lung. In fact the "pleura" was not studied, tumor and plaque, which by definition could not contain fibers except via specimen contamination or incorporation, most likely from adjacent lung. Both Rogers et al. (1994) and Case et al. (1994) have also reported contamination by short crocidolite fibers of Nuclepore filter materials and in uncontrolled studies of this nature any material from air, fluids, and paraffin in the pathology laboratory from which the specimens originally were referred to specimen preparation materials are suspect References Boutin, C., P. Dumortier, F. Rey, J.R. Viallat, and P. De Vuyst. 1996. Black spots concentrate oncogenic asbestos fibers in the parietal pleura. Thoracoscopic and mineraiogjc study. Am. J. Respir. Crit. Care Med. 153:444-449. Case, B.W., R.E. Gordon, and J. Kleinerman. 1982. Acute bronchiolar injury following nitrogen dioxide exposure: A freeze fracture study. Environ. Res. 29:399-413. Case, B.W.K., M. Hairigan, and A. Dufresne. 1994. Lung fibre content ofAmerican children aged 8-15 years. Ann. Occup. Hyg. 38:639-645. Churg, A. and B. Wiggs. 1987. Accumulation of long asbestos fibers in the peripheral upper lobe in cases of malignant mesothelioma. Am. J. Ind. Med. 11:563-569. Churg, A., J. Wright, B. Gilks, and J Dai. 2000. Pathogenesis of fibrosis produced by asbestos and man-made mineral fibers: What makes a fiber Fibrogenic? Inhal. Toxicol. 12:15-26. I)^is;;iM.G. 1987. .Experimental data relating to die importance of fibre type, size, deposition, dissoitifipii'and migration, in:; Proceedings of i 987 Mineral Fiber Symposium. Lyons: internaiiohaVAgency for Research on Cancer. Davis, J.M.G. 1994. The role of clearance and dissolution in determining the durability of biopersistence of mineral fibers. Environ. Health Pcrspect 102:113-117. Davis, J.M.G., j. Addison, R.E, Bolton. K. Donaldson, A.D. Jones, and T. Smith. 1986. The pathogenicity of long versus short fiber samples of amosite asbestos administered to rats by inhalation.and.intraperitoneal injection. Br. J. Exp. Pathol. 67:415-430. F.~t J HWBUI0009721 Dumortier, P., F. Rey, J.R. Viallat, I. Broucke, C. Boutin, P. De Vuyst. 2002. Chrysotile and tremoiite asbestos Fibres in the lungs and parietal pleura of Corsican goats. Occup. Environ. Med 59:643-646. Gelzleichter T.R., E. Bermudez, J.B. Mangum, B.A. Wong, J.I. Everitt, and O.R. Moss. 1996. Pulmonary and.pleurat responses in Fischer 344 rats following short-term inhalation of a synthetic vitreous fiber. I. Quantitation of lung and pleural fiber burdens. II. Pathobiologic responses. Fundam. Appl. Toxicol. 30:31-46. HEI-AR Asbestos Literature Review Panel. 1991. Asbestos in public and commercial buildings: A literature review and synthesis ofcurrent knowledge. Cambridge, MA: Health Effects Institute - Asbestos Research. Hume, LA. and J.D. Rimstidt. .1992. The biodurability of chrysotile asbestos. Am. Mineral 77:1125-1128. IARC. 1996. Mechanisms of Fibre Carcinogenesis. In: IARC Scientific Publications No. 140, eds. A.B. Kane, P. Bofetta, R. Saracci, and J.D. Wilboum. Lyon: International Agency for Research on Cancer. Lippmann, M. 1990. Effects of Fiber characteristics on lung deposition, retention, and disease. Environ. Health PerspecL 88:311-317. Morgan, A. 1995. Deposition ofinhaled asbestos and man-made mineral fibres in the respiratory tract. Ann. Occup. Hyg. 39:747-758. NRC. 2000. Review of the U.S. Navy's Exposure Standard for Manufactured Vitreous Fibers. Washington, DC: National Academy Press. Oberdfirster, G., J. Ferin, J. Finkelstein, S. Soderholm, and R. Gelein. 1990. Mechanistic studies on particle-induced acute and chronic lung injury. In: Aerosols: Science, Industry, Health and Environment, Vol. 2, eds. S. Masuda and K. Takahashi, pp. 1229-1233. New York, NY: Pergamon Press. Rogers A.L, J. Berry, et al. 1994. Dose-response relationship between airborne and lung asbestos fibre type, length, and concentration, and the relative risk of mesothelioma. Ann. Occup. Hyg. 38:631-638. Stober, W., H. Flachsbait, and D. Hochraincr. 1970. Der aerodynamische Durchmesser von Latexaggregaten and Asbestfasem. Staub-Rcinhalt. Luft. 30:277-285. Sussman, R.G., B.S. Cohen, and M. Lippmann 1991a. Asbestos fiber deposition in a human tracheobronchial cast. I. Experimental. Inhal. Toxicol. 3:145-160. Sussman, R.G., B.S. Cohen, and M. Lippmann 1991b. Asbestos fiber deposition in a human tracheobronchial cast. II. Empirical model. Inhal. Toxicol. 3:161-179. E-5 HWBUI0009722 % Takabashi, K., B.W. Case, A. Dufresne, R. Fraser, T. Higashi, and I. Siemiatycki. 1994. Relation between lung asbestos fibre burden and exposure indices based on job history. Occup. Environ. Med. 51:461-469. Timbrell, V. 1972. An aerosol spectrometer and its applications. In: Assessment of Airborne Particles, eds. T.T. Mercer, P.E. Morrow, and W. Stober, pp. 290-330. Springfield, EL: Charles C. Thomas. Timbrell, V. 1982. Deposition and retention of fibres in the human lung. Ann. Occup. Hyg. 26:347-369. Wagner, J.C. 1990. Biological effects ofshort fibers. In: Proceedings of the VII International Pneumoconiosis Conference (Pittsburgh, PA, August 1988). NIOSH 90-108, Vol. 2, pp. 835840. Washington, DC: National Institute ofOccupational Safety and Health. ) ) E-6 HWBUI0009723 ) -)' Dr. Lockey's Post-Meeting Comments What do human/epidemiological data tell us about small fibers? Discussion Leaders: Dr. Lockey and Dr. Case Cancer Effects Short natural occurring fibers. A study by Higgins, et al. {!] in 1983 reviewed the mortality of workers employed at the Reserve Mining Company at Babbit, Minnesota. These workers were involved with mining taconife- which is a dense hard rock composed of silica, silicates and iron. Taconite mined in the eastern tip of the Mesabi range contained amphiboles in the cummingtonite-grunerite series. These fibers are short in length with reportedly the vast majority being <10 pm and are related to amosite asbestos. Of the 9,065 men employed by the company as of July 1,1976,5,751 had worked one year or more. The investigators established the vital status of 96% ofthose who worked for five years or longer and 75% of former workers who worked one to four years. The total respirable dust ranged from 0.02 mg/m1 to 2.52 mg/m1 and as high as 2.75 mg/m* with the modal range from 0.2 mg/m1 to 0.6 mg/m1. There were relatively few measurements of fibers and those that were available demonstrated concentrations usually low with a few at or above 0.5 Ftbers/ml in the crushing department Reportedly none approached the OSHA threshold limit value which at that time was 2 fibers/ml. Results of the study indicated that there was no excess death in this population including those men with cumulative exposure of 1,000 to 3,000 total dust years or 500 to 1,000 silica dust years. The conclusions of the study indicated the death rates for all causes were significantly below expectations including selected respiratory disease and death from malignant disease was marginally below that expected for the State of Minnesota. There was no relationship between lifetime'dust exposure and increased mortality, nor was there any indication that malignant neoplasm was increased after 15 lo 20 years latency. The authors identified a weakness of the study in that the average latency of the cohort was 14.7 years with a maximum of 24.6 years, or a relatively short latency for development of cancer. A study by McDonald, et al. (2) regarding the mortality from long-term exposure to cummingtonite-grunerite from a gold extraction process at the Homestake Mine, Lead, South Dakota was-reviewed. Those workers who had worked 21 years or longer were traced.attd of 660 men who had died.the Cause of death was ascertained for 657. Results of the study indicated pneumoconiosis, which was mainly silicosis along with tuberculosis, and heart disease were causes ofexcess death. There was a dust exposure relationship for both pneumoconiosis and respiratory tuberculosis, but reportedly no convincing increase in respiratory cancer. It was noted that more than 75% of the 660 men who had died started to work before 1925. TKe interval between first employment and death and the 76 fatalities from tuberculosis or pneumoconiosis ranged from 22 to..6l years with a median of 35 years. Average silica dust concentrations ranged from 11.0 to 24.6 mppef before 1952. A study by Dement, et al. [3] reported that 80% to 90% of fibers in the mine had an amphibole diffraction pattern by transrnission/scannipg electron microscope equipped with an energy-dispersive X-ray spectrometer. The mean total fiber concentration was 4.82 + 0.68 free (range 0.66-11.79) with 0.36 + 0.08 free (range 0.07-1.29) greater than 5 pm in length. There was one potential mediastinal mesothelioma which could not be confirmed in the 17 respiratory malignancies (16.5 expected based on South Dakota rates). n-7 - HWBUI0009724 o The results of the study were in conflict with an earlier study by Gillani, et a! of the same mine of 440 males who worked at least five years underground by 1960. Reportedly there were 10 deaths from neoplasm of the respiratory system between 1960 and 1973 where as 2.7 were expected based on the male population of South Dakota [4]. Conclusions There is no data regarding human exposure to asbestos fiber uniformity less than 5 pm in length. Studies ofworkers exposed to cummingtonite-gmnerite, a type of amphibote related to amosite, demonstrated no consistent increase in overall mortality, mortality related to selected respiratory disease, or respiratory cancer. The vast majority ofairborne fibers were reported to be less than 10 pm in length. .. Studies ofworkers of a gold mine in Lead, South Dakota exposed to cummingtonitegrunerite initially demonstrated an increased mortality from malignant respiratory disease. A subsequent study did not confirm the initial finding but demonstrated an increase in silicosis and tuberculosis. Mean total fiber concentration was 4.82 f/cc with 0.36 ffcc greater than 5 pm in length. Consideration should be given for performing a feasibility study regarding an updated mortality analysis of these two cohorts. MMYF Mortality Studies. Mortality studies of glass fiber and mineral wool production workers have been ongoing in the U.S. most recently under the direction of Marsh, et al at the University of Pittsburgh, and within the European Union under the direction of the International Agency for Research on Cancer (LARC). The most recent follow up study by Marsh, et al. [5,6,7] of 10 U.S. glass fiber manufacturing plants demonstrate no excess mortality from all causes, all cancers combined, or non-malignant respiratory disease. For respiratory system cancer, there was an observed 6% excess that was statistically significant for the total cohort but not found in workers who bad five or more years of employment. An association was seen with calendar time and time since first employment, but no relationship was found with duration of employment, or increase in exposure to respirable glass fiber. A case-control study of respiratory system cancer did not identify increased risk with duration of exposure, cumulative exposure, or time since first employment. An association with non-baseline levels ofaverage intensity of exposure to respiratory fibers washot present when adjusted for smoking. A previous case-control study ofa glass fiber manufacturing facility included in the U.S. glass fiber study demonstrated that differences in local versus national smoking rates may have been a contributing factor in theexcess respiratory cancer seen in that manufacturing facility: [8] The potential confouhding'impact ofcigarette smoking in the U.S. glass fiber and rock/slag wool studies was further explored by Buchanich. cl al. [9] and Marsh, et al. [10] and identified as the potential unaccounted for factor regarding the small excess respiratory system cancer not related to exposure indices. Previous analysis of five rock and slag wool plants in the U.S. demonstrated increased lung E-8 ) 'i J HWBUI0009725 cancer mortality using U.S. but not local rates, and this was confined to short-term workers or those workers with less than five years duration ofemployment. There was no association with measures of respirable fiber exposure. [11] Within the U.S. a case-control study of 9 slag wool plants demonstrated an association with smoking but not MMVF exposure. [12] Most recent analysis of the U.S. rock and slag wool workers as well as glass fiber production workers identified ten death certificates that mentioned the term mesothelioma. [13] Of the ten cases of mesothelioma, two on pathology review were definitely not felt to be mesotheliomas, one had a 50% chance of mesothelioma, and two others had less than 50% chance of mesothelioma. Medical records or pathology specimens were not available on the remaining five. Using a timeframe when specific malignant mesothelioma coding rubrics were available, the expected mesothelioma rate (local county comparison) was 2.19 versus 1 observed. Overall the authors felt there was no increased risk from the malignant mesothelioma in the U.S. MMVF cohort The IARC have followed the mortality of workers among 13 MMVF manufacturing facilities in Europe. [14] The most recent update demonstrated a significant increase in lung cancer mortality in rock and slag wool workers as well as glass wool workers, using national mortality rates which disappeared for the glass wool workers when using local adjustment factors to the national mortality rates. Ia addition, there was no association in the glass wool workers with time since initial employment or duration of employment, and with removal of glass wool workers with less than one-year employment no excess Sung cancer was noted. Within the rock and slag wool cohort there was an increase in lung cancer risk but the authors felt there was no clear information to indicate that the increased cancer risk was specifically related to fiber exposure. [14] A subsequent cohort study demonstrated similar results. [15] A case-control study nested in this latter cohort indicated no relationship between cumulative rock or slag wool exposure and lung cancer. [16,17] Within the IARC study there were five cases of mesothelioma, two which occurred in workers with less than one-year employment and two in workers with most likely prior asbestos exposure. [14] Preliminary results of a mortality study of U.S. RCF manufacturing workers demonstrate no significant increase in malignant or non-malignant respiratory mortality and no malignant mesothelioma. The power ofthe study, was limited as the cohort was .relatively young and small in number. [18] Conclusions There are no data regardingliuman exposure to MMVF uniformity less than 5 pm in length. There is no persuasive evidence that exposure to glass fiber, rock wool, slag wool, or refractory ceramic fiber has been associated with increased lung cancer risks based on ongoing U.S. and European mortality studies. There is no indication of an increased risk for mesothelioma. F.-9 HWBUI0009726 Non-Cancer Effects MMVF Morbidity and Mortality Studies. Non-malignant respiratory effects: Studies of five fiberglass and two mineral wool manufacturing facilities identified smalt opacities in 1.6% of the population studied that were predominantly irregular in shape. [19} These workers were involved with working in facility manufacturing fibers over 3 pm in diameter and fibers averaging 1 pm to 3 pm in diameter. The overall rate of chest X-ray changes was no different in comparison to a non-MMVF exposed comparison group, and any relationship between exposure indices was seen at profusion level I/O but not 1/1. There was no increase in upper or lower respiratory tract symptoms. Similar results were seen in a study in Australia ofglass and rock wool production workers with no findings of asthma, pulmonary fibrosis or pleural disease. [20] A similar study of rock wool workers also did not demonstrate increased respiratory symptoms or abnormalities with DLCO or DL/Va. A potential additive or synergistic effect, however, was seen regarding the FEV1/FVC ratio, fiber exposure, and those with greater than 40-pack year histoiy ofcigarette smoking. [21] The IARC [22] study demonstrated no increased mortality from asthma, bronchitis or emphysema, which is similar to the most recent analysis of the glass fiber wotkers in the United States which did hot identify increased mortality from non-malignant respiratory disease. [5] Of interest in the IARC study was the suggestion of an increased risk from non-malignant renal , disease (SMR0.97,95% Cl 0.36 to2.il) in regard to duration ofemployment or employment at an early phase within the rock and slag wool industry. Within the U.S. mineral wool study a similar trend was noted (p < .05) with a SMR of 204 (observed 12) in regard to nephritis and nephrosis. [II] Similar type patterns have not been demonstrated in relationship to nephritis and nephrosis deaths in U.S. glass wool manufacturing facilities. [23] There are very limited studies on end users ofman-made vitreous fibers. One study identified increased prevalence of chest radiograph evidence of irregular opacities in workers using rotary spun fiberglass, but there was a question of airborne asbestos fibers within the plant site. [24,25] In insulators a decrease in FEVI was identified in comparison to a non-exposed control group after adjusting for smoking habits and self-assessed former asbestos exposure. [26] On-going morbidity studies ofworkers involved with refractory ceramic fiber (RCF) manufacturing have identified a relationship between pleural plaques and time from initial employment, duration of employment, and cumulative refractory ceramic fiber exposure. Pleural changes were seen 2.7% or 27 workers out of 1,008 of which 22 were pleura! plaques. Of those with greater than 20 years latency from initial production job or 20 years duration in a production job, 16 workers or 8.0% and 5 workers or 8.1% had pleural changes, respectively. Interstitial changes were noted in 1.0% at profusion category >1/0, similar to other non-specified dust exposed worker populations and showed a non-significant elevated OR in regard to cumulative ' fiber exposure of 4.7 (95% Cl, 0.97 to 23.5). In regard to cumulative fiber exposure, 5.4% (8 of 148) with greater than 45 to 135 fiber-month/'cc exposure had pleural changes (OR 5.6,95% Cl, 1.5 - 28.1). For those with >135 fiber-months/cc exposure, 9.8% (6 of 61) had pleural changes (OR 6.0; Cl 1.4 - 31.0). [27] European studies concurred that there was some evidence of a relationship between RCF latency and pleural changes including pleural plaques but not duration or intensity of RCF exposure, but it was difficult to separate the effects asbestos and RCF exposure and any relationship between RCF exposure and small opacities was at best ambiguous. [28] E-I0 HWBUI0009727 Previous studies ofthe RCF workers demonstrated a relationship between 10 years of employment in productionjob tasks prior to 1987 and small decrements in FVC for current (165.4 ml) and past (i 55.5 ml) male smokers, but not never-smokers, and small decrements in FEVI for current male smokers only (134.9 ml). For never-smoker women there was also a decrement in FVC (350.3 ml) per 10-years employment in production job tasks. [29] A longitudinal analysis in those mate workers able to provide five tests or more did not demonstrate any further decrement of the FEVI or FVC between initial and final tests. [30] Conclusions Regading Non-Cancer Effects of MMVF There are no available morbidity studies of workers exposed to MMVF uniformly less than 5 pm in length. No increased mortality from nan-malignant respiratory disease. No indication ofchest radiograph interstitial or pleural changes in regard to glass and mineral wool production workers but data is limited. Refractory ceramic fiber (RCF) exposure appears to be associated with the occurrence of pleura! plaques that most likely are related to increased exposure levels in the RCF manufacturing facilities prior to 1985. Potential additive of synergistic effect with MMVF exposure and small decrement in FVC and/or FEVI involving current or former smokers. Within mineral wool cohort, question of potential increased mortality from non-malignant renal disease such as nephritis and nephrosis. ' End user studies ofMMVF users are limited and are confounded by potential previous asbestos exposure. Irritant Effects MMVF can cause skin irritation particularly in an area where clothing comes in close contact to the skin such as around the neck or forearms. Essentially this occurs in 5% of new workers involved with MMVF production. [31] Residential contamination ofman-made vitreous fibers in high concentration can also cause irritation to the upper as well as lower respiratory tract. [32] 'Glass fibers with diameters greater than 5:3 pm have been reported to be more likelyJo cause skin irritation than the smaller diameter fibers, mainly due to mechanical irritation. [33,34] There has been documentation of eye irritation associated with MMVF as well as nasal and pharyngeal irritation with unusual MMVF dust exposure situations. [35,36] 'Conclusions Skin irritation appears to be related to the mechanical effects of fiber --5 pm in diameter and appears to be worse in hot, humid weather. F.-ll HWBUI0009728 Accidental exposure to increased concentrations of MMVF can result in upper and lower respiratory tract irritation as well as eye irritation. Association Between Fiber Length and Fiber-like Toxicity There have been no published studies that address whether asbestos fibers uniformly <5 pm in length have been associated with pleural or parenchymal disease in human. Any potential risk associated with fiber exposure <5 pm in length most likely would be related to an increased risk for pulmonary asbestosis, and most likely would occur at a substantially higher dose in comparison to exposures to asbestiform fibers (long fibers with high aspect ratios). [37] There is some indication that fibers with diameters with <0.1 pm to 0.4 pm and lengths <10 pm may have a propensity for inducing pleural plaques. [38] Methodologies used to analyze pleural and/or parenchymal tissue for the presence of fibers and association ofpleural changes differ markedly between investigators, however. Human studies of individual exposed to asbestos fibers are difficult to interpret in regard to toxicity solely related to fibers <5 pm in length because exposure situations almost uniformly contain a broad distribution of fiber diameters and length. Preliminary results of residents of Libby, Montana that, were exposed to asbestiform tremolite indicate a high propensity for pleural changes in comparison to interstitial changes. [39] There is some indication that exposure to tremolite fibers with relatively low aspect ratios in comparison to the asbestiform type tremolite may be capable ofcausing pleura! plaques. [40] Pleural plaques can occur with minimal exposure to asbestos and can occur within a wide range of tissue burdens ofasbestos fibers which overlap with control populations. [41] Conclusions Even though there are no human studies solely ofMMVF <5 pm in length, the available morbidity and mortality studies ofMMVF production workers indicate limited overall toxicity from MMVF exposure. There are no human studies regarding exposures solely to asbestos fiber <5 pm in length but there has been some speculation that durable fibers <10 pm in length and <0.1 to 0.4 pm in diameter maybe associated with pleural plaques in relatively low concentration, in particular the amphiboie tremoHtei: - ; ' For asbestos fibers <5 pm in length, it would appear that very high doses may have the propensity to cause interstitial fibrosis, particularly ifthe fibers are durable within intracellular fluids. * . Thresholds for Toxic Action .- For asbestos and MMVF less than 5 pm in length, thresholds for toxic action in humans have not been established but most likely is substantially higher than the thresholds for long durable fibers with increased aspect ratios of respirable size. J E-f 2 j HWBUI0009729 Asbestos Versus MMVF Based on animal and human studies, natural occurring asbestos fibers that are of respiratory size, long and thin with high aspect ratios, and durable within physiologic fluids represent the highest risk for malignant (lung cancer and mesothelioma) and non-malignant (interstitial fibers) respiratory disease. These abnormalities have not been demonstrated in MMVF manufacturing workers. References 1) Higgins ITT, Gtassman JH, Ob MS, Cornell RG. Mortality of reserve mining company employees in relation to taconite dust exposure. Am JEpidemiol I983;l 18(5);710-719. 2) McDonald JC, Gibbs GW, Liddell FDK, McDonald AD. Mortality after long exposure to cununingtonite-grunerite. Am Rev Respir Dis 1978; 118:271-277. 3) GiUam JD, Dement JD, Lemen JM, Wagoner JK, Archer VE, Blejer HP. Mortality patterns among hard rock gold miners exposed to an asbestiform mineral. NYAcadSci 1976:271-336. 4) Dement JM, Zumwalde RD, Wallingford KM. Discussion paper Asbestos fiber exposure in a hard rock gold mine. Ann NY AcadSci. 1976:271-345. 5) Marsh GM, Youk AO, Stone RA, Buchanich JM, Guta MJ, Smith TJ, Quinn MM. Historical cohort studyofUS man-made vitreous fiber production workers: L 1992 fiberglass cohort follow-up: Initial finding. J0A/2OOl;43(9):741-756. 6) Youk, AO, Marsh GM, Stone RA, Buchanich JM, Smith TJ. Historical cohort study of U.S. man-made vitreous fiber production workers: ID. Analysis of exposure-weighted measures of respirable fibers and formaldehyde in the nested case-control study of respiratory system cancer. JOEM 2001;43(9):767-778. 7) Stone RA, Youk AO, Marsh GM, Buchanich JM, McHenry MB, Smith TJ. Historical cohort study of U.S. man-made quantitative exposure-response analysis of the nested case-control study .of respiratory system cancer.,/0M2OOl;43(9):779-792. 8) Chiazze L, Watkins DK, Fryan C. A casc-control study of malignant and non-malignant respiratory disease among employees of a fiberglass manufacturing facility. BrJlnd Med 1992,49:326-331. - . .. 9) Buchanich JM, Marsh GM, Youk AO. Historical cohort of U.S. man-made vitreous fiber production workers: V. Tobacco-smoking habits. JOEM 2001 ;43(?):?93-8G2. SO) Marsh GM, Buchanich JM, Youk AO. Historical cohort study of U.S. man-made vitreous fiber production workers: VI. Respiratory system cancer standardized mortality ratios adjusted for the confounding effects of cigarette smoking. JOEM 2001 ;43(9):803-808. 11)Marsh G, Stone R, Youk A, et al. Mortality among United States rock wool and slag wool workers: 1989 update. JOccup Health 5<;/efr-Anst NZ 1996;12:297-312. E-I3 HWBUI0009730 12) Wong O, Foliart D, Trent LS. A case-control study of lung cancer in a cohort of workers potentially exposed to slag wool fibres. Br J Ind Med 1991 ;48:818-824. 13) Marsh GM, Gula MJ, Youk AO, Buchanich JM, Churg A, Colby TV. Historical cohort study of U.S. man-made vitreous fiber production workers: 0. Mortality from mesothelioma. JOEM2001 ;43(9):757-766. 14) Boffetta P, Saracci R, Andersen A, et al. Cancer mortality among man-made vitreous fiber production workers. Epidemiology 1997;8:259-268. 15) Boffetta P, Anderson A, Hansen J, et al. Cancer incidence among European man-made vitreous fiber production workers. Scan J Work Environ Heallhl999;2S:222-226. 16) Kjaerheim K, Boffetta P, Hansen J, Cherrie I, Chang-Claude J, Either U, Ferro G, Gufdner K, Olsen JH, Plato N, Proud L, Saracci R, Westerholm P, Andersen A. Lung cancer among rock and slag wool production workers. Epidemiology 2002 Jul; 13(4):445-453. 17) IARC monographs on the evaluation ofcarcinogenic risks to humans. Volume 81, Man made Vitreous Fibres 2002. 18) Lemasters G, Lockey J, Levin L, Yiin I, Reutman S, Papes D, Rice C. A longitudinal study of chest radiographic changes and mortality ofworkers in the refractory ceramic fiber industry. k 2001 Congress ofEpidemiology Abstracts Am J Epidemiology 2001 ;153(l 1):S264. J 19) Hughes JM, Jones RN, Glindmeyer HW, et al. Follow up study ofworkers exposed to man made mineral fibres. BrJIndMed 1993;50:658-666. 20) Woodcock AJ, Mettis CM. Respiratory health of workers in the Australian glasswool and rockwool manufacturing industry. Final report prepared for Insulation Wools Research Advisory Board by Institute of Respiratory Medicine. Royal Prince Alfred Hospitals. Sydney, Australia. 1994. 21) Hansen EF, Rasmussen FV. Hard! F. KamstrupO. Lung function and respiratory health of long-term fiber-exposed stonewodl factory workers. Am JRespir Crit Care Med 1999;160:466472. ' 71 22) Salt D, Boffetta P, Anderson A, et al. Non-ncoplastic mortality of European workers who produce man made vitreous fibres. Occup Environ Med 1999;56:612-617. 23) Chiazze L, Watfcihs DK; Fryari G. Faycrweathcr W, Bender JR, Chiazze M. Mortality from nephritis and nephrosis in the fiberglass manufacturing industry. Occup Environ Med 1999;56:164-166. ; 24) Kitbum KH, Powers D, Warshaw RH. Pulmonary effects of exposure to fine fiberglass: Irregular opacities and small airways obstruction. BrJInd Med 1992;49:714-720. F.-14 \ ) s HWBUI0009731 25) Bender JR. Pulmonary effects ofexposure to fine fiberglass: Irregular opacities and small airways obstruction. BrJIndMed 1993;50:381-382. 26) Clausen J, Netterstrom B, Wolff C. Lung function ia insulation workers. BrJ Ind Med 1993;50:252-256. 27) Lockey JE, LeMasters GK, Levin L, Rice C, Yiin J, Reutman S, Papes D. A longitudinal study of chest radiographic changes of workers in the refractory ceramic fiber industry. Chest 2002;121:2044-2051. 28) Cowie HA, Wild P, Beck J, Auburtin G, Piekarski C, Massin N, Cherrie JW, Hurley JF, Miller BG, Groat S, Soutar CA. An epidemiological study of the respiratory health ofworkers in the European refractory ceramic fibre industry. Occup Environ Med 2001;58:800-810. 29) Lemasters G, Lockey J, Rice C, et al. Radiographic changes among workers manufacturing refractory ceramic fibre and products. Ann Occup Hyg 1994;38(1 ):745-751. 30) Lockey JE, Levin LS, Lemasters GK, et al. Longitudinal estimates ofpulmonary function in refractory ceramic fiber manufacturing workers. Am J Respir Crit Care Med 1998; 157:12261233. 31) Bjomberg A. Glass fiber dermatitis. Am J Ind Med 1985;8:395-400. 32) Newhall HH, Brahim SA. Respiratory response to domestic fibrous glass exposure. Environ Res 1976;12:201-207. 33) Possick PA, Gellin GA, Key MM. Fibrous glass dermatitis. Am Ind Hyg Assoc J 1970;31:12-15. 34) Heisel EB, Mitchell JH. Cutaneous reaction to fiberglass. Ind MedSurg 1957;26:547-550. 35) Stokholm J, Nom M, Schneider T. Ophthalmologic effects of man made mineral fibers. ScandJ Work Environ Health 1982;8:185-190. 36) Milby TH, WolfCR. Respiratory tract irritation from fibrous glass inhalation. J Occup Med 1969;11:409-410. 37) Lippmann M. Asbestos exposure indices. Environ Res 46:86-108, 1988. 38) Lentz TJ, Rice CH, Lockey JE, Succop PA, Lemasters GK. Potential significance of airborne fiber dimensions measured in the U.S. refractory ceramic fiber manufacturing industry. Am J Ind Med 1999;36:286-298. 39) Year 2000 Medical testing of individuals potentially exposed to asbestoform minerals associated with vermiculite in Libby, Montana. A report to the community. August 23,2001. ATSDR E-15 HWBUI0009732 40) American Thoracic Society. Medical Section of the American Lung Association. Health effects of tremolite. Am Rev Respir Dis 1990; 142:1453-1458. 41) Hillerdal G. Pleural plaques: incidence and epidemiology, exposed workers and the general population; a review. Indoor Built Environ 1997;6:86-95. n-i6 ;... HWBUI0009733 Dr. McConnell's Post-Meeting Comments How Do Animal/Experimental Data Augment Our Understanding of Human Health Effects Background: There have been numerous studies of the effects of various types of asbestos (ATSDR, in press) and SVFs (ATSDR, in press) in animals. Both fibrous and nonfibrous particulates have been used. Most studies have been conducted in rats and hamsters, but others, including nonhuman primates have been used. Routes ofexposure have included inhalation (whole-body and nose-only), intratracheal instillation, intrapleural implantation/injection, intraperitoneal injection and ingestion. All of the routes of administration have their strengths and weaknesses (advantages, disadvantages and limitations) for use for assessing potential health effects in humans (McConnell, 1995). However, the inhalation route appears to produce the most relevant data because it is the only route that duplicates all aspects of human fiber exposure and disease (inflammation, fibrosis, lung cancer and mesothelioma) resulting from the exposure (McClellan et af., 1992). Also, the neoplastic changes typically occur late in the rodents' life, similar to what occurs in humans exposed to asbestos. Other routes of exposure are also useful for comparing the toxic potential of various types of fibers and understanding the mode of action and many of the mechanisms of fiber toxicity and carcinogenicity. Additionally, the oral route (ingestion) appears to be the most appropriate route ofexposure for studying the potential hazard of ingested asbestos. Cancer effects: Rats and hamsters are the most frequently used species for assessing the potential carcinogenic effects as asbestos (IARC, 1987) and SVFs (IARC, 2002) and have been used with various routes ofexposure. Of the two species, the rat appears to be the most appropriate one because it exhibits both lung cancer and mesothelioma in response to inhalation of known human carcinogenic fibers, e.g. asbestos. The hamster can be a useful mode! ifone is only interested in the inflammatoiy, fibrogenic and mesotheliogenic effects of particulates. However, the hamster does not develop lung cancer after exposure to high levels of either chrysotile (McConnell et al., 1995) or amositc asbestos (McConnell et a!., 1999). Otherspecies have been used but have significant limitations that preclude their general use for carcinogenic btoassaysi' For example, the mouse is not as useful as the rat or hamster because its terminal airways are smaller and therefore, particulates of a mean mass aerodynamic diameter (MMAD) of greater than >0.5 um cannot reach the'deep lung (alveolar region) which is the site of primary disease. Non-human primates would be an idea! animal model but are precluded because of their long life-span (would require at least 20-30 years to demonstrate a noncarcinogenic effect), availability (a cancer bioassay requires >200 animals/sex), and expense (such a study would cost >520 million. Most chronic rodent inhalation bioassays ofasbestos have been conducted in rats, have not shown significant strain differences and males and females are equally sensitive to its carcinogenic effects (ATSDR, in press). The only large series of studies of various types of IT-17 HWBUI0009734 "A asbestos showed that if there is a gender difference, mates might be slightly more responsive (Wagner, et a!., 1974). Therefore, either sex is appropriate with males slightly more preferable. Just as importantly, both sexes are probably not necessary. However, these same studies have shown that while life-time exposure to asbestos may not be necessary, it is important to observe the animats for most of theirtife-span (see below). O The types of cancer induced by asbestos and SVFs in rodents are comparable to those observed in humans, although the preponderance ofa given type and its biologic behavior appears to be species specific. In inhalation studies in rats the preponderant form of lung cancer is bronchoalveolar in origin, arising from type Q alveolar cells. They occur late in the animal's life, usually after 21 months ofage. This is why lifetime studies may be necessary to fully exonerate a fiber from being considered carcinogenic. The tumors are slow growing and only occasionally are the cause ofdeath. The biological sequence of growth is typically from bronchoalveolar hyperplasia to bronchoalveolar adenoma to bronchoalveolar carcinoma, although all aspects of the sequence ofprogression may not be found in a given lesion (Boorman and Eustis, 1990). Squamous cell metaplasia is not unusual and typically is found as part of the morphology,of larger tumors. Squamous cell carcinoma may predominate in a small percentage of rodent tumors, but has rarely been observed to occur de novo. Squamous cell types may be more common with intratracheal instillation of the fibers (Pott et ah, 1994). The malignant tumors are locally invasive and can metastasize but it is an unusual event for them to do so. When this occurs it is usually within the lung, but distant metastases have been observed. The presence of mitotic figures is in direct relation to the degree of malignant transformation. Tumors ofthe upper respiratory tract and airways have not been observed in response to inhalation exposure of asbestos or SVFs in rodents (1ARC, 1987; 2002). Mesothelioma has also been found in rodent carcinogenic bioassays of asbestos and SVFs (IARC, 1987; 2002. In inhalation studies in rats they are usually found at a lower incidence than lung cancer. Again, there does not appear to be a gender predisposition and the mesotheliomas in rodents typically occur late in life (after 21 months of age). They rarely are the cause ofdeath. They grow by expansion, growing over the.pleural surface. They typically do not invade the lung or other adjacent structures, although this has been observed. They usually present as multiple lesions on both sides of the luxlg and involve- both the visceral and parietal pleura. Rarely, distant metastases have been observed. ; hi inhalation studies, all of the major morphological types. (tubulo|SpiHafy, sarcomatous arid mixed) have been observed, although the tubulopapillary response is the predominate form. There is one exception to this and that is found in the inhalation study oferionite, where the sarcomatous type predominated, was highly.invasive and the tumois were exceptionally lethal causing death in most of the rats by 15 months (Wagner ct a!., 1988). In contrast to inhalation, direct instillation into the pleural (Stanton et al. 1981) or peritoneal cavities (Pott et at, 1987) results in a preponderance of Sarcomatous, neoplasms, and in fact, it may be difficult to find mesothclial cells in many of the tumors, particularly after peritoneal injection. However, even in these studies, the mesotheliomas seldom invade local tissues or metastasize to other areas of the body. '- E-18 HWBUI0009735