Document Ddm3RpR06xjMqEqoxdDEoa3XO

Interoffice Communication TO: FROM: DATE: SUBJ: Distribution T. G. Grumbles July 21, 1990 TGG: JCL; FPT- MJH: AJO; RF XF:_ _ ACGIH RECOMMENDED CHANGE FOR BENZENE TLV The ACGIH TLV committee is proposing to revise the Benzene TLV from 10 ppm to 0.1 ppra, 8-hour TWA, with no STEL recommended.. This change is recommended based on revised risk assessments of the available animal and epidemiological data. It is an unprecedented recommendation for ACGIH in that they are recommending a "no residual risk" exposure limit. Also, ACGIH generally does not consider feasibility issues in their determinations. The TLV process will put this 0.1 ppm limit on a "notice of intended changes" list for 2 years, during which interested parties can comment. No final decision will be made until then. The impact of this recommendation is undefinable at this time. TLV's have some regulatory significance but are not binding in occupational settings per se. Some states use them as air toxics guidelines, and plantiff's lawyers certainly will utilize the recommendation. The documentation for the recommended change is attached. dlj .132 Attachment Distribution: R. Gantz-LCLAB, K. Fogg, Mike Hayes-LCCP, J. Harris, D. Mahler-Balt J. R. Drumwright, W, L. McClain cc: w/o attachment R. Bauer-Balt, J. Ware-LCLAB, J. Friend-LCCP J. A. DeBernardi vvv 000013383 Notice of Intended Changes-Benzene Editor's Note: In anticipation of significant interest and to ensure reader awareness of the proposed revision of the Threshold Limit Value (TLV) for benzene, publication of this revised documentation is issued at this time and in advance of the pubJication of the Threshold Limit Values and Biological Exposure Indices for 1990-1991 booklet. The recommendation of the Chemical Substances TLV Committee received approval from the ACGIH Board of Directors and members in attendance at the annual ACGIH business meeting on May 16, 1990, The recommendation is that benzene be listed on the Chemical Substances TLV Notice of Intended Changes for 1990-91 at 0.1 ppm as a time-weighted average (TWA) with a Skin notation and designation as an A1 carcinogen (confirmed human carcinogen). This proposed reduction for the adopted benzene TLV-TVCA of 10 ppm and A2 carcinogen designation (sus pected human carcinogen) will undoubtedly prompt spec ulation as to the basis for the proposed revision. An esti mated exposure to benzene of 238,000 LLS. workers and usage of more than 11 billion gallons of benzene per year are added incentives to publish the rev ised documentation at this time. The proposed revision will remain on the Notice of Intended Changes for a period of at least two years during which comment and substantive evidence for or against the appropriateness of the revised TLV is solic ited by the TLV Committee. This publication of the documentation in Applied pro vides an additional opportunity for comment. Benzene CAS: 71-43-2 Benzol; phenyl hydride; cyclohexatriene; coal naptha C6H6 Skin TLV-TWA, 0,1 ppm (0.3 mg/m) A1--Confirmed Human Carcinogen tration grade, or refined. Physicochemical properties of reagent grade benzene include: Molecular weight: 78.11 Specific gravin': 0.87865 at 20C Melting point: 5-5C Boiling point: 80.tC Vapor pressure: 75 torr at 20C Closed cup flash point: - 11.1C Autoignition temperature: 562C Flammability limit in air: 1.5-8 0 vol% Odor threshold: 12 ppm Saturated air at 25*C contains 120,000 ppm Solubility: 0.180 g/100 ml water at 25C; miscible in all proportions with carbon tetrachloride, ethanol, chlo roform, diethyl ether, carbon disulfide, acetone, gla cial acetic acid, and oils. Major Uses and Sources of Occupational Exposure At one time, benzene was an important solvent, espe cially for inks, rubber, lacquers, and paint removers. At present, such uses are minimal; most benzene is consumed in the chemical industry' as a raw material for numerous organic chemicals and in plastics manufacture. It is found in gasoline from trace amounts to as much as 30 percent in some countries (US. average, 1-3%). Total benzene usage exceeds 11 billion gallons per year/11 and it is es timated that 238,000 employees in LLS. petrochemical plants, petroleum refineries, coke and coal operations, tire man ufacturers, bulk terminals and plants, and in truck transport are exposed to benzene/21 Benzene is a myelnioxicant, known to suppress bone marrow cell proliferation and to* induce hematologic dis orders in humans and in animals. Signs of benzeneinduced aplastic anemia include suppression of leukocytes (leukopenia), red cells (anemia), platelets (thrombocyto penia), or all three cell types (pancytopenia). Classic symp toms include weakness, purpura, hemorrhage, pancyto penia, and aplastic anemia. TLV-TWt, 100 ppm. 1946 TIV-TW. 50 ppm, 1947 TIV-TYA 35 ppm, 1948-1956 71V-TW, 25 ppm, 1957-1962 TLV-Ceiling. 25 ppm. Skin, 1963-1976 TLV-TVA, 10 ppm,A2, Skin, 1977-present; Skin notation deleted 1978 TLV-Sia. 25 ppm, A2,1980-1987 TLV-1W4, 0.1 ppm, A1, Skin, proposed 1990 Documental ion revised, 1990 Chemical and Physical Properties Benzene is a colorless, highly flammable, nonpolar liq uid with an odor that is characteristic of aromatic hydro carbons. Benzene can be supplied as industrial grade, ni Animal Studies Subchronic yyV 0oQOl3384 When Sprague-Dawley rats and CD-I mice of either sex were exposed by inhalation to benzene at 1, 10, 30, or 300 ppm, 6 hours per day, 5 days per week for 13 weeks, treatment-related pathology was observed in the high dose (300 ppm) groups of both species/31 In mice, hematologic changes included decreased hematocrit, total hemoglobin, erythrocyte/leukocyte count, platelet count, and mye!oid:erythroid ratio. In rats, decreased lymphocyte count and a relative increase in neutrophil count were the only exposure-related clinical change. Histopathologicnl chances were observed in the rcstes and ovaries at concentrations below 300 ppm. and lesions were observed in the thymus, bone marrow, lymph nixies, spleen, ovaries, and testes in mice inhaling 300 ppm. The alterations were more severe in the males than in the females. In rats, the only exposurerelated pathology was a slight reduction in femoral marrow cellularity at 300ppni/-M Studies to identify the target cells for benzene hema topoietic toxicity indicated that benzene exposure dam aged mouse pluripotent stent cells, the colony-forming cell units in the spleen, and the progenitor cells for granulo cytes and macrophages.u-<') Hematopoietic depression in rodents was observed at benzene concentrations as low as 103 ppm after a 5-day exposure/7' Cronkite et d//H9> reported a series of studies where CBA/CA mice were ex posed to benzene at 10, 25, 100, 300, or 400 ppm, 6 hours per day, 5 days per week for 2,4,8, and 16 weeks. Exposure to 100 ppm or greater for two weeks reduced bone mar row cellularity.lH) When C57BL/6J mice inhaled 300 ppm benzene 6 hours per day, 5 days per week for a total of 115 exposures, the numlxT.s of B-lyntphocytes in bone marrow and spleen and the numbers of T-lymphoeytes in thymus and spleen were reduced.*101 When BALB/C mice were exposed at 50 or 200 ppm benzene 6 hours per day for ? or 14 days, the ratios and the absolute numbers of T- and B-lymphixytes in blood and spleen were de pressed.111 ' Depression of B-lvniphocytes was dosedependent. and it was more severe than that of die T-ce!ls.( *'1 When male C5-BL mice inhaled 10 ppm. 6 hours per dav for 6 days, a significant depression in colony-forming units in B-lympbocytes was observed; similar inhalation of 31 ppm resulted in depressed blastogenesis of T-lymph<xytes/1 - ' Chronic/Carcinogenicity 'X'hen groups of 40 CD-1 mice were exposed to benzene in air at 100 or 300 ppm. 6 hours per day, 5 days per week for life, two mice in the high dose group developed mye logenous leukemia. No leukemia was observed in the 100-ppm dose group/^ Snyder et found that after groups of 40 C5"BI. mice inhaled 300 ppm benzene for 6 hours per day, 5 days per week for 2 years, eight cases of lymphoreticular neoplasia (six thymic lymphocytic lym phomas, one plasmocytoma, and one hcmocNtoblastic leu kemia ) occurred; two mice in the control group developed lymphocytic lymphomas. The incidence of tumors in the benzene-treated mice was significantly greater (p = 0.005) than that in the control.1 ,H) In a lifetime carcinogenicity bioassay in which oral doses of benzene w<jre adminis tered at 50 and 250 mg/kg-day, 4-5 days per week for 52 weeks, there was a dose-dependent increase in total can- cers.{,,', The most prominent rat tumors observed were Zymbal gland carcinomas, mammary carcinomas, and leu kemia. When Wistar rats and Swiss mice were given ben zene at 500 mg/kg-day, 4 or 5 days per week for 104 or 78 weeks, respectively, the numbers of Zymbal gland car cinomas, hemolymphoreticular neoplasias, and total ma lignant tumors were increased in the rats; increases in mouse Zymbal gland dysplasia and carcinomas, mammary carcinomas, pulmonary tumors, and total malignant tumor were observed.'Ul' In the National Toxicology Program lifetime bioassay,'r 50 F344/N rats of each sex per dose group were treatec w ith benzene by oral gavage at doses of 50. 100, or 20C mg/kg-day for the males and at 25, 50, or 100 mg/kg-da\ for the females for two years. Similar groups of B6C3F1 mice of both sexes were treated with 25, 50, or 100 mg/kgday. For the male and female rats, increases of Zymbal gland carcinoma, squamous cell papilloma, and squamous cell carcinoma of the mouth were observed. In the male rats, squamous papilloma and squamous cell carcinoma of the skin were also increased. For male mice, increased numbers of animals with Zymbal gland carcinoma, malig nant lymphoma, alveolar/bronchiolar carcinoma, and alveolarhronchiolar adenoma or carcinoma (combined), Harderian gland adenoma, and squamous carcinoma of the preputial gland were observed. For female mice, in creased numbers of animals compared to the control were afflicted with malignant lymphoma, ovarian granular cell carcinoma, carcinosarcoma of the mammary gland, alveo lar bronchiolar adenoma, and alveolar/bronchiolar carci noma were reported/ Cronkite'lK> conducted a carcinogenicity bioassay wherein male and female CS'Biyfi and CBA/Ca mice inhaled 100300 ppm benzene, 6 hours per day, 5 days per week for 16 weeks and found benzene-induced leukemia in the males. NXlien mice inhaled 25 ppm benzene for as few as ten such exposures, lymphopenia resulted/,K> Reproductive/Developmental Studies on the potential developmental toxicity of ben zene administered by subcutaneous injections, ingestion, or inhalation have generally failed to show significant ad verse effects in mice, rats, or rabbits (for review, see Schwctz1 m). Adverse developmental effects have been de scribed in an unpublished rat bioassay performed by Litton Bionciics'-0> wherein Sprague-Dawley rats inhaled 10-40 ppm benzene, 6 hours per day on days 6-15 of gestation. Embryonic death increased from the control (6.2%) to 8,1 and 9.5 percent for rats exposed to 10 and -tO ppm ben zene. respectively. However, the Litton study*Jl" was con founded by the high ambient temperature in one of the exposure chambers during the study; maternal hyper thermia is a known rodent teratogen. Kuna and Kapp'conducted an inhalation study in which pregnant Sprague-Dawlev rats were exposed to benzene at 10, 50, or 500 ppm 7 hours per day on days 6-15 of gestation. Significant reductions in mean maternal body weight gain occurred. Mean fetal body weight was reduced. Fetal crown-rump distance was decreased significantly at 500 ppm, and developmental delay was evident upon ex amination of the fetal skeletons. Benzene was judged by these authors'-211 to be fetotoxic in rats at 50 and 500 ppm and to manifest teratogenicity at 500 ppm. Coate et <*/.<"> found that when pregnant Sprague-Dawley rats inhaled 1, 10, 40, or 100 ppm benzene 6 hours per day on days 6-15 of gestation, no maternal toxicity was noted; however, 454 VVV 000013385 APPL OCCUR ENVIRON. HYG. 5(71 - JULY 1990 a reduction in mean fetal 1-xxjy weight at 100 ppm was observed. No teratogenic effects were found.'--1 When pregnant Swiss-Vt'elsster mice were exposed to 5, 10, or 20 ppm benzene in air on days 6-15 of gestation for 6 hours per day, alterations in the numbers of hematopoietic colony-forming cells in the progeny were recorded/231 Marked reductions in erythroid colony-forming cells were observed at all benzene concentrations studied, and in halation of 10 or 20 ppm also decreased the numbers of granulocytic coionv-forming cells. 'When mice, previously exposed in utero to 10 ppm benzene, were re-exposed to 10 ppm for 6 hours per day for 2 weeks, a marked reduc tion in the numbers of bone marrow differentiated erythroid colony-forming cells occurred/231 Keller and Snyder1231 interpreted these data as an indication that alterations of the murine hematopoietic system induced by neonatal Isenzene exposure could persist into adulthood. rngvarv and Tatrai'241 exposed CFLP mice and NZ rab bits to benzene at 154 or 308 ppm, 24 hours per day, throughout days 6-15 of gestation. Benzene was detected in fetal bkx>d and in amniotic fluid. At 308 ppm, retarded skeletal development and reduced feta! body weight were observed in mouse fetuses, and spontaneous abortions were reported in rabbits.1 241 Genotoxicity Studies Benzene exposure can cause chromosomal aberrations in animals and in humans. Benzene exposure induces clastogenosis, sister chromatid exchange, and micronuclei both in rux) and in nVro/251 Benzene exposure has been shown to induce aneuploidy in dividing cells, presumably through inhibition of tubulin assembly during mitosis. However, benzene exposure has failed consistently to induce point mutations in genotoxicity test systems. Point Mutation In the Salmonella typhimurium gene mutation assay, benzene proved consistently negative for mutagenesis in plate-incorporation assays with or without microsomal en zyme activation/20'24' McCarroll et ctl}-M>) published the only positive result using a microsuspension assay with hepatic microsomal activation such that an increase in the numbers of revenants in Salmonella strain TA100 was observed. Benzene exposure inhibited the growth of DNA repair deficient Escherichia coli strain WP1Q0 (uvra~, recA", but no such effect was observed in repair proficient strains/311 Growth inhibition was also observed in DNA repair defi cient Bacillus subtilis strain M45 (rec~)<32) but benzene was considered without mutagenic activity in the E. coli PolA assay, an indication that the DNA polvmerase activity was not critical for repair of benzene-induced damage to nucleic acid/331 Benzene was reported negative in Saccharomyces cereiisiae gene conversion and mitotic cross ing-over assays/341 however, it was considered mutagenic for 5. cereiisiae strains D61-M and D6.<35) When benzene was fed to Drosophila melanogaster at up to 2.5 percent in the diet, no evidence for a mutagenic response using the eve pigmentation as a genetic market was found/361 When Drosophila were placed in air con taining 27,000 ppm for 60 minutes (20% survival), a sig nificant increase in spermatogonia! crossing-over was ob served and mutation frequency and translocation frequency were increased. These data were considered indicative of the stage-specific nature of benzene-induced spermatogonial mutagenesis in Drosophila} Benzene exposure altered gene expression as measured in the Drosophila wing morphology assay/3H1 but results using the Droso phila eye spot assay were judged negative139' or at most equivocal/401 In grasshopper embryos, benzene exposure was associated with mitotic arrest, multipolar division, and chromosome lags/4'1 Benzene was tested in a colloborative study of 12 lab oratories using a variety of cell lines and genetic mark ers/421 Benzene was mutagenic without hepatic enzyme (S9) activation in the mouse lymphoma L5178Y (TK + /+ ) assay in one laboratory , it was mutagenic in the Chinese hamster V79 cell assay at the oubain-resistant locus (NaKATPase defective) in one laboratory, and it was mutagenic at the 6-thioguanine resistance locus (HGPRT-) in one laboratory Mutagenic activity was observed with S9 acti vation in the mouse lymphoma L5178Y (TK +/+ ) assay for trilluorothymine resistance (TK-) in two of the laborato ries, and mutagenicity was observed in the mouse lym phoma L5178Y (TK + /4-) assay for ouhain-resistance in one of the laboratories. Benzene was considered muta genic without exogenous activation for 6-thk>guanine re sistance in human AHH-l lymphoblasts. Except for the human Kmphoblast and Chinese hamster V79 studies (which were not repeated in other laboratories), the findings for benzene point mutation could not be confirmed by other laboratories involved in the collaborative study/421 There fore, potential point mutation associated with benzene ex posure in cultured mammalian cells is considered incon clusive based on the studies published to date. Chromosomal Aberration VVV 000013386 Benzene treatment induces chromosomal structural changes and aneuploidy in cultured mammalian cells. In cultured human lymphocytes, chromosomal aberrations were observed after three hours of incubation with 9-88 p,g benzene/mi with or without S9 activation/431 Aberrations were also observed in Chinese hamster lung fibroblasts after treatment with 1100|xg benzene/ml and in Chinese hamster ovary (CHO) cells at 100 p.g benzene/ml with S9 activation. Aneupoloidv was reported in Chinese hamster primary hepatocvies treated with benzene at 62.5 gg/ml/441 Benzene itself failed to induce sister chromatid ex change (SCE) in cultured human lymphocytes without ex ogenous metabolic activation (S9), but benzene metabo lites increased SCE in a dose-dependent fashion/431 The primary benzene metabolites (phenol, catechol, hydroquinone) are transformed to benzo(semi)quinones1 which presumably act as the ultimate genotoxic agents/451 Ca- APPL 0CCUP. HV1R0H. HYG. 5171 JULY 1990 techol and hvdn>qvHnone were potent SCE inducers at after inhalation of 100 or \000ppm benzene/'*' 'Xh *a ftj* ml/'*"' Glutathione (GSU) inhibited benzene-induced male DIW2 mice inhaled benzene at 0, 10, 100, or 1000 pf SCE formation. and it was hypothesized that GSM conju or male Sprague-Dawley rats inhaled benzene at 0, 0 gation to benzene metaltolites prevented DNA damage.14"1 0.3, 1, 3, 10, or 30 ppm for 6 hours, significant (das Benzene and its metalsolites were reported to decrease dependent) increases in SCE and micronuclei were o mitotic index, to inhibit ceil cycle transverse, and to in served in mice at s* 10 ppm, and increased SCE and rr crease SCE frequency in cultured human T-!ymphocytes. cronuclei were observed in rats inhaling ^ 3 ppm and The relative potency of benzene metabolites for SCE in 1 ppm, respectively/**' The Erexson data'v'> are the lowe duction were catechol > 1,4-benzoquinone > hydroqui concentrations of inhaled benzene that have been reporte none > l ,2,-t-benzenetriol > phenol > benzene/48' to induce genotoxicity. Tice et al.1 '91 found a concentration-dependent increase in DBA/2 mouse bone marrow lymphocytes after a single, Neoplastic Transformation I 4-hour inhalation study of benzene at 28-3000 ppm; an Using morphologically transformed colonies as a marker 5 increase in SCE was detected at 28 ppm. This response was benzene was considered mutagenic in Syrian hamster em strain-dependent as DBA/2 mice were more sensitive than bryo (SHE) cells, but it was not considered mutagenic ir C57BL/6 mice, young DBA/2 mice (three months) were cultured Balb/C 3T3 mouse fibroblasts, in Simian adeno more sensitive than older mice (10 months), and male virus-transformed SHE cells, and in Chinese hamster ovary mice were more sensitive than female mice. Following (CHO) cells/58' Benzene, hydroquinone, and para-ben- intraperitonea! injection, a linear dose-dependent increase zoquinone were reponed to alter gene expression in cul in SCE was observed in DBA/2 mice.1495 tured Swiss mouse spleen lymphocytes, where hydroqui DNA Damage none and para-benzoquinone at 10-20 jaM inhibited RNA synthesis 50 percent/59' Inhibition of T-cell proliferation Benzene failed repeatedly to exhibit genotoxicity in tests for unscheduled DNA systhesis (UDS) in cultured primary rat hepatoeyies. Benzene is consistently negative in Hela and reduced produaion of interleukin-2 (a T-cell growth factor) by 5 p-M para-benzoquinone was suggested to ac count, in part, for benzene-induced aplastic anemia/591 cells w ith or without metabolic activation. Glauert et a/.'50' published the single positive report for increased CDS in Human Cytogenictty cultured primary rat hepatocvtes associated with benzene Forni el al.um found a significant increase in lymphocyte exposure. chromosome aberrations in two groups of workers with In a study of in litro DNA damage, mouse L5H8 YS oven benzene intoxication as compared to age-matched Ivmphoma cells failed to show single strand breaks after controls. One group consisted of 25 individuals recovered exposure to 1.0 mM benzene, phenol, or catechol or to from benzene hemopathy 1-18 years previous along with 0.1 mM hydroquinone; however, a dose-dependent in 4 additional workers currently suffering from acute ben crease in DNA damage was observed after treatment with zene poisoning. The second group consisted of 34 workers paru-hesv/A>qumone or l,2,4-benzenetriol/51! Para-benzo- in a rotogravure plant exposed at 125-532 ppm benzene quinone at 6 gM induced T'O percent single strand DNA in air from 1952 to 1953 Tough et a/.'616-' found an in breaks w ithin 3 minutes of exposure; the same damage creased incidence of chromosome aberrations in 38 work was achieved by benzenetriol within 60 minutes/511 ers inhaling 25-150 ppm benzene for 1-25 years com A concentration-dependent increase in mouse periph pared to the incidence in the general human population eral bhxxJ micronuclei was observed after C57BIV6 mice These individuals had been exposed to benzene until two inhaled 10. 23. 100, or -tOO ppm, 6 hours per day, for 9 to four years prior to the study."1'h-' Watanabe el ?//6,) days/ 5i 1 When C5_rBU6 mice inhaled 300 ppm benzene for found an increase in the frequency of SCE among nine 16 weeks under a similar protocol and the patterns for females at six months after cessation of benzene exposure micronucleus induction monitored, the initial increase was at 1-9 ppm for 1-20 years and among seven females ex followed by a gradual decrease/53' When the peripheral posed to benzene at 3-50 ppm for 2-12 years. Killian and hkxxi of B6C3F1 mice given oral benzene'171 w-as studied, Daniel"*1 found a significant increase in chromosomal a dose-dependent increase in the numbers of circulating aberrations among workers exposed to average benzene erythnxyie micronuclei occurred. A significant increase levels below 10 ppm. Workers exposed to benzene (av was observed in male mice given a dose as low as 25 mg/kg- erage, 56.6 months) had a doubling of chromosomal breaks dav for 120 days/54 ` Pretreatment of male and female CD-1 and a threefold increase in rings and dicentric chromo mice with metabolic enzyme-inducing agents (phenobar- somes. Almost twice as many benzene-exposed workers bital, SKF-525A, Arochlor 1254) failed to protect against as controls exhibited both chromosome breaks and rings the clastogenic effect of benzene exposure, but pretreat and dicentric chromosomes."*' ment with 3-methylcholanthrene potentiated benzene Picciano'65*6' examined the Killian and Daniel**4' data myekxrlastogenidty/55' Male mice were more sensitive than and reponed that 38 (73.1%) of 52 workers exposed to female mice and chromosomal damage was greater after mean ambient benzene at less than 10 ppm had chromo oral than after intraperitoneal administration/'''*1 some breaks as compared with 18 (40.9%) of 44 matched Chromosome aberrations w'ere induced in Wistar rats (unexposed) controls. When individuals with both chro- 458 I ooooi-^81 APPL 0CCUP. ENVIRON. HY6. NT) JULY tWO mosonte breaks and chromosome markers (rings, dicen tric chromosomes) were compared, less than 3 percent of the nonexposed group showed genetic damage where 27 percent of the exposed workers were afflicted with chro mosome aberrations (p < 0.001). A number of reports suggests that benzene-induced hu man chromosome damage is site-specific. Ding et al{('r) reported a cytogenetic study of 21 patients (8 male and 13 female) with chronic benzene poisoning who had been exposed to unspecified benzene concentrations for 1-28 years (average, 6 years). At the time of cytogenetic analyses, all individuals had not been exposed for 5-20 years (av erage, 10 years), and all but one had recovered from clin ical signs of benzene poisoning. Hypodiploid and hyperdipioid cells were increased significantly in the benzeneexposed patients, and chromosome deletions in the hy podiploid cells involved groups C, E, and G chromosomes and chromosome gains in the hyperdiploid cells involved groups C and E. Similar findings were also reported by Sasiadek and Jagielski(6M) where chromosomal aberrations were detected more frequently in chromosomes 2 (Group A), 4 (Group B), and 6 and 9 (both are Group C). Sarto and associates*69* found an increase in chromosome ab errations among 22 workers inhaling 0.2-12.4 ppm ben zene for 11.4 7.0 years; a control population was matched for sex, age. smoking habits, and site of residence. Pharmacokinetic/Metabolism Studies Rusch et alPs concluded that humans absorb approxi mately 46 percent of the benzene that is inhaled. Assuming a respiratory rate of 16 per minute and a tidal volume of 0.5 liters, approximately 7.5 pL benzene can be expected to be absorbed each hour through the lungs of a person inhaling air containing 10 ppm benzene/"' Benzene derma! absorption was 0.05 percent when neat liquid benzene was applied directly to a human forearm at 0.0022 mg/cm2 and allowed to dry/"0' and the flux of benzene through cultured human abdominal skin from air saturated with benzene at 31C wax 1.0 pLcm-^hr-1/71' Susten et it//"21 found that after dermal application of 5 pL,4C-labeled benzene to intact skin of hairless mice, maximal skin radioactivity occurred at 1.5 min, and it re mained "essentially unchanged for at least 2.5 hr." Perme ability is, however, dependent upon presence of solvents. Blank and McAuliffe'71' found the constants to be 111, 3.73, 2.4, and 1.4 x 10-3 p.Lcm-2,hr_l, respectively, for water, hexadecane, isooctane, hexane, and gasoline. Based on in vitro percutaneous absorption and in tivo inhalation data, one example of calculated total benzene exposure used an adult working in ambient air containing 10 ppm ben zene with 100 cm2 skin surface in direct contact with gas oline containing 5 percent benzene. It was estimated that if the worker's entire skin surface was in contact with ambient air, the individual would absorb 7.5 pL benzene via inhalation in one hour, 7.0 pL from direct dermal con tact with gasoline, and 1.5 pi from body surface exposure to ambient air/"11 Sabourin et investigated the absorption and elim ination of benzene in F344/N rats, Sprague-Dawlev rats, and B6C3F1 mice after an oral or imraperitoneai dose of 0.5-150 mg/kg. They reported that gastrointestinal absorp tion was essentially complete. The toxicity of benzene has been attributed to its me tabolites/"'4' A major metabolite is phenol (Figure 1). gen erated by oxidation of benzene by the liver cytochrome microsomal system'*'5' via the reactive epoxide interme diate, benzene oxide. Results of physiologically based pharmacokinetic modeling of benzene metabolism found that mice metabolized a greater proportion of absorbed benzene to the hydroquinone conjugates and muconic acid than did rats/''6' Rats metabolized benzene primarily to the phenyl conjugates and to the phenyl mercapturic a S-M-Actyi-Cy RGUAE1. Major pathways of benzene metabolism. (Reproduced with permission from reference 76.) APPL 0CCUP ENVIRON. HYG. SW - JULY 1990 acids.' ~* AJthough bone marrow enzymes arc not efficient for benzene metabolism, phenol can he meialxtlized in marrow via myeloix'roMdase.'"' Iienzene metalsolism to phenol, formation of water soluble phenyl glucuronide atid sulfate conjugates, and conjugation with glutathione and urinary elimination of benzene its the phcnylmercapturic acid are considered detoxication pathways. Microsome ringopening reactions giving rise to the reactive mucondialdehvde yield muconic acid, a pathway consid ered responsible for at least some aspects of benzene tox icity. Hvdroxylation of phenol generates hydroquinone; dehydrogenation of benzene dihydrcxJiol generates ca techol.' ~H'9) Hydroquinone and catechol can accumulate in bone marrow and lymphoid tissues;180* hydroquinone can oxidize spontaneously m vitro to para-benzoquinone under physiologic conditions.185 825 Catechol does not ox idize spontaneously under these conditions; however, it can be metabolized (presumably the cytochrome P-450 system) to CZA-benzenetrioI.*83* The toxicity of hydro quinone and 1,2,-i-henzenetriol involves free radical for mation via superoxides; covalent binding of the semiquinones to DNA, RNA, and other cellular components, and direct alkylation of sulfhydryl groups by para-lsen/oquinone or its derivatives. Hvdroquinone and benzoquinone were the most toxic metabolites to cultured bone marrow stromal cells, where catechol and benzeneiriol inhibited colony growth only at very high benzene doses to male B6C3F1 mice.*801 Injury to bone marrow stromal cells has been implicated as a precursor step to benzene hematotoxicity.1805 A recent symposium on benzene metabolism, toxicity, and carcinogenesis*84* provides an authoritative summary on benzene biotransformation and the implica tion for human health risk assessment Human Studies As an acute poison, benzene produces narcotic effects comparable to those of toluene. Benzene is considered verv toxic; probable human oral lethal dose would be between SO-SOO mgltg (1 t.sp to 1 oz).*8<'> Human inha lation of approximately 20,000 ppm (2% in air) was fatal in 3-10 minutes.180* Aksoye//.,8"-K9>.studied 28,300 Turkish shoe and hand bag production workers who inhaled an average of 150210 ppm when benzene-containing adhesives were used and 13-30 ppm at other times. Peak benzene exposures varied between 210 and 640 ppm, and the duration of exposure was estimated to average 9.7 years. Of the 44 cases of pancytopenia, 23 (32%) experienced remission of the aplastic anemia, 14 (32%) died from complications of aplastic anemia or pancytopenia, and 6 (14%) later died from leukemia. Of 42 leukemia cases, 26 percent were preceded by a 6-monih to 6-year period of pancytopenia prior to the onset of leukemia. Aksoy*90-95 * reported an update to the above cohort to the year 1983, wherein a total of 73 patients chronically exposed to benzene were examined. Fifty-one of the 73 had leukemia, 12 had ma lignant lymphoma, 4 had multiple myeloma, and 6 had lung cancer. Among the 31 leukemic patients, 20 were afflicted with acute myeloblastic leukemia, 7 were consid ered preleukemic. 20 were diagnosed with acute erythroleukemia, 5 had acute myelomonooiic leukemia, and 1 was diagnosed as an acute undifferentiated leukemia. Thir teen of the 31 leukemic patients had suffered pancyto penia; the average duration of benzene exposure was 9 93 years. Vigliani,92) studied groups of workers employed in ro togravure plants, shoe factories, and oilier industries where benzene was used as a solvent. Benzene concentrations in air near the rotogravure machines were 200-400 ppm, with peak values as high as 1300 ppm. Sixty-six cases of benzene hemopathv were observed, and of the 18 deaths in this group, 7 died of aplastic anemia and 11 died of leukemia. In a second group of workers where ambient benzene ranged from 25-600 ppm, 135 workers with ben zene hemopathv were studied. Of the 135, 16 died (3 from aplastic anemia and 13 from leukemia). Infante et alrev iewed death certificates for a cohort of 748 white male workers who had been ixcupationally exposed to benzene from 1940-1949; exposures are not known precisely but ranged up to 100 ppm.(t>4' Othersl0s> cite reports that peak exposures may have been as high as 200-3^0 ppm. Vital status was followed up to 1973. A fivefold excess risk of all leukemias was reported, and a tenfold excess of deaths from myelogenous and monocytic leukemias was observed. In a follow-up through June 30. 1975. Rinsky et tf/J90* reported 7 deaths from leukemia versus 1.25 expected (standardized mortality ratit) fSMRj = observed no. deaths/expected no. deaths = 560). When compared by length of employment, there was a significant excess of leukemia observed among workers employed five or more years, but not among those employed less than five years. Two workers died from leukemia among the group employed less than five years compared to 1.02 expected (not statistically significant). Among those em ployed for five or more years, five died from leukemia compared to0.2.3 expected (SMR = 2100). Short-term area samples measured between 19-6 and 1976 indicated that most benzene levels were below 100 ppm and some were above 100 ppm.l9syo1 Rinsky et tf/.,9o> cite documents in dicating that these workers were required to wear respi rators (efficiency' not stated) when exposed (even mo mentarily) to concentrations greater than the TWA (ranging to a maximum allowable concentration of 100 ppm in 1941 to an 8-hour TWA of 10 ppm from 1969 on). For those individuals with more than ten years of employment, three leukemia deaths were observed as compared to 0.09 ex pected (SMR = 3300). Cumulative benzene exposure was calculated for each member of the benzene cohort in ppmvears, and the cohort follow-up was extended to 1982.<97> A total of 1165 white males with at least one ppm-day of cumulative benzene exposure (to December 31, 1965) were included in the cohort for a total of 31,612 person-years at risk. Fifteen deaths in this cohort were observed from lymphatic and hemopoietic cancers versus 6.6 expected (SMR = 227). Nine cases of leukemia were observed com- VVV) ooooi^4 458 A PPL OCCUP ENVIRON HYG. 5(7) JULY 1990 pared to 27 expected (SMR = 337), and four cases of multiple myeloma were observed compared to one ex pected (SMR = 409) [all cases statistically significant]. Rinsky et at}*-' determined that cumulative exposure to ben zene (measured a.s ppm-vears) was the most reliable predictor of death from benzene-induced leukemia. In creases in cumulative exposure were associated with marked progressive increases in the SMR for leukemia: among workers with less than 40 ppm-vears cumulative exposure, the SMR = 109; with 40 to 199.99 ppm-vears cumulative exposure, the SMR = 322; with 200 to 399 99 ppm-vears cumulative exposure, the SMR = 1186: and with 400 or more ppm-vears, the SMR = 6637. (The ppm-vears were calculated as 40 years at lOppm average exposure/year = 400 ppm-vears.) Seven of the nine leukemia deaths with multiple mveloma had less than 40 ppm-years of benzene exposure. Rimsky el al{9') concluded that protection from benzene-induced leukemia increased exponentially with reductions in exposure time. Yin et conducted a retrospective cohort study of 28,460 workers exposed to 3-308 ppm benzene (with the majority exposed to 15-150 ppm) compared to a control cohort of 28,257 workers not known to be exposed to benzene. Thirty cases of leukemia were found in the ex posed population compared to four such cases in die con trol. The benzene cohort experienced a leukemia mortality rate of 14 per 100,000 person-years, and the control pop ulation experienced a leukemia mortality rate of 2 per 100.000 person veurs (SMR = 5.74). In an additional study authored by Yin and associates,<99) ambient benzene con centrations for 508,818 workers averaged 5.6 ppm with 65 percent of the workplaces having less than 12 ppm and 1.3 percent having benzene levels greater than 308 ppm. Aplastic anemia occurred at 12.1 per 100,000 persons in this cohort and represented a 5.8-fold increase over that of the general population. Ott tv at}l(XM carried out a mortality study of 594 white male workers exposed to benzene from 1940-1970. The Occupational Safety and Health Administration (OSHAfl,m concluded that the On cohort was exposed to an average of 5 ppm for an average of nine years. Three cases of myelocytic leukemia (2 classified as acute) were found compared to 0.8 cases expected (p < 0.047). Bond et at} l0-> extended the cohort definition for the Ott study to include those employees who worked for at least one month (19381978) and increased the observation follow-up to 1982, bringing the total persons studied to 956. Four deaths due to myelogenous leukemia were observed with 0.9 ex pected (SMR = 444). Decoufle et at}l0-4' found a fourfold excess risk for lym phatic and hematopoietic cancers among oil refinery and chemical plant workers exposed to benzene. The expo sures were very poorly documented, but they resulted primarily from plant fugitive emissions and perhaps ac companied by gross exposures from cleaning tools, hands, and clothing with liquid benzene. The historical cohort mortiality study of 259 male employees found four deaths from lymphoreticular cancers compared to 1.1 expected (SMR = 364), and three deaths due to leukemia where 0.4 were expected. The multiple myelomas observed here, taken together with previous reports of benzene-associated myeloma, prompted the suggestion that the pathogenesis of human multiple myeloma and chronic lymphatic leu kemia may arise front damage to B-cell lineage/ Wong4 divided the benzene exposure for 4602 work ers (minimum lime of 6 months) into four categories: < 1 ppm; 1-10 ppm; 11-50 ppm; and 50 ppm, with peak exposures of < 25 ppm, 25-100 ppm, and > 100 ppm. He compared their mortality with that of 3074 employees from the same or similar plants who had no known occupational benzene exposure. When all lymphatic and hemotopoietic cancers were considered, there was a significantly elevated risk (p = 0 03) for benzene-exposed white males when compared to unexposed workers. There was a significant concentration-dependent increase for all lymphohemato- poietic cancers (p = 0.02), for leukemia (p = 0,01), with borderline significance (p = 0.057) for non-Hodgkin s lymphopoietic cancers. Prolonged cumulative exposures were judged more important for human benzene carcin ogenicity than maximum peak exposure.s, and the au- thorsn(K,t'> concluded that there was a significant asso ciation between occupational benzene exposure and the occurrence of leukemia, all lymphopoietic cancers, and non-Hodgkin's lymphopoietic cancers. A number of epidemiologic studies4 t4X,u"J have consid ered the mortality and cancer incidence among petroleum and rubber workers. Most of these studies, however, failed to quantify the benzene exposures adequately, failed to determine whether the toxicity reported was indeed as sociated with benzene exposures, and were confounded by difficulties in confirming the validity' of the diagnoses upon which the SMR and other risk estimates were made. Tlie latency period for benzene induction of human leukemia varies from 2 to 50 years. Aksoye/tf/.187-911 found that the induction period ranged from 6 to 14 years (me dian, 11 years). Vigliani1921 reported an induction period of 3 to 23 years (median. 9 years), and Rinskv4965 indicated a median latency of 12 years (2-22 years). The Shell Oil study411/41 indicated a latency of 17-54 years between the date of hire and date of death from leukemia. Yin1981 es timated the average latency time for benzene-induced leu kemia as 11.4 years. The 1985 OSHA report41015 concluded that 11 years was a reasonable estimate for the average duration of leukemia induction associated with occupa tional benzene exposure. Basis of the TLV VVV 000013390 Although benzene has long been recognized as a mye- lotoxicant (e,g., more than 140 fatalities due to benzene poisoning were recorded in the open scientific literature prior to 1959), the carcinogenic activity of chronic expo sure to relatively low ambient concentrations of benzene in workplace air was not recognized until the last ten years. Benzene is a human and rodent clastogen and carcinogen. Adverse health effects in animals exposed to benzene mir- APPl OCCUP ENVIRON. HYG 5(7) JULY 1990 459 ror [hose* reported in humans, with exposure at 1 ppm benzene and alxtve inducing measurable cytogenetic dam* age/<r) Women inhaling 1-9 ppm exhibited increased lym phocyte chromosome aberrations/'1-''' and significant ele vations in chromosom;tl aberrations have Ixren corrol'xjrated among workers inhaling benzene at mean concentrations less than 10 ppm/(H-661 Several quantitative human health risk assessments have been carried out in an attempt to define the concentrations of benzene in air that are associated with lifetime excess cancer risk/-' but these methods are problematic, partic ularly when attempting to extrapolate quantitative animal data to the human. Notable has been their failure to in corporate the differential metabolic disposition and known pharmacokinetic parameters for rodents1'61 compared to human beings. The rodent carcinogenicity data support the designation of benzene as a known human carcinogen. Theoretical estimates of excess cancer risk can be cal culated using any of a variety of statistical models, including the linearized ` multistage " (which does not describe bio logic initiatioiVprornotion phenomena), the one-hit, Weibull. logit, or probit models; however, there is no current understanding of the biochemical mechanisms involved in benzene-induced leukemia and other cancers to show that any one of these methtxis is any more accurate than an other. Because of the different assumptions that must be made for use of the different models, the theoretical es timates of excess cancer risk that result can differ by orders of magnitude. White e//.n,M) used a linear, nonthreshold model to describe the benzene dose-response human carcinogenicity data and calculated that at 10 ppm benzene, 44-152 excess cases of leukemia per 1000 exposed work ers would occur, and that at 1 ppm benzene, 5-16 such excess case would occur. The International Agency for Research on Cancer (lARC)(llS) used a similar approach and published theoretical excess cancer risk estimates of 14-140 excess cases per 1000 individuals exposed at 10 ppm. and 1.4-14 excess cases among 1000 individuals ex posed at 1 ppm. Crump and Allen12119' carried out quan titative analyses of the epidemiologic data gathered by Rjn- skv et Ott el a/./,om and Wong et Ajt<>r 45 years (working lifetime) exposure at 10ppm benzene, Crump and Allen11191 calculated 95 theoretical excess leu kemia deaths per 1000 workers. Exposure at 1 ppm was calculated as associated with 10 theoretical excess leuke mia deaths per 1000 workers. Although such estimates have been preferred in the legal arena/21 these methods remain the subjects of severe criticism/21201211 Because of the acknowledged high quality of the epi demiologic data/21 direct inspection of these data can pro vide the basis for the benzene TLV. The Dow Chemical Company study*1001 "demonstrates a significant fourfold increase in myelogenous leukemia for workers who had been exposed to average benzene concentrations of about 5 ppm for an average of about nine years'' and "two out of the four individuals in the study who died from leukemia were characterized as having been exposed to average benzene levels below 2 ppm.',(2) The risk assessment for benzene and leukemia is has on the human data. Rinsky et a//9'1 provided the ni< authoritative examination of the known odds of death fre benzene-induced leukemia. For a worker exposed at i erage daily benzene concentrations of 10 ppm for 45 yeai the odds of death front leukemia were 290 times that an unexposed worker. For an individual inhaling 1 ppi for 45 years, the odds of benzene-induced leukemic deal were 1.7 times that of an unexposed worker. For an if dividual inhaling 0.5 ppm for 45 years, the odds of her zene-induced leukemic death were 1.3 times that of ai unexposed worker. Using these data, the odds of benzene induced leukemic death at 0.1 ppm approach very nearl' the odds of leukemic death for a worker who is not ex posed to benzene. Accordingly, a TT-V-TOCA of 0.1 pprr benzene is recommended. A STEL is not recommended. The reader is encouraged to review the sea ion on Ex cursion Limits in the "Imrixluaion to the Chemical Sub stances" of the current TLV/BEI Booklet for guidance and control of excursions above the TLV-TVCA even w'hen the 8-hour TWA is within recommended limits. The recom mended TLV of 0.1 ppm is less than the concentration associated with genetic damage in animals/ `r ' and it is less than the concentrations associated with genetic damage in human beings/611 As calculations show that benzene der mal absorption can contribute substantially to the total absorbed benzene dose/'11 the skin designation is appropriate. BEI Indication Biological monitoring for human benzene exposure at ambient concentrations less than 1 ppm can be most readilv documented by determination of urinary S-phenvlmercapturic acid (Figure l)/122' The mercapturic acid conju gate is formed and excreted together with phenol, catechol, hydroquinone, and hydroxy hydroquinone. It is a urinary metabolite of high specificity for occupational benzene exposure giving reliable indication of exposures ut the 0.1-0.15 ppm range, w hereas urinary phenol is not reliable unless gross benzene exposure has occurred/122' The lowest practical deteaion limit, in the absence of interfering substances, has been reported at concentra tions at least as low as 0.1 ppm. In the presence of inter fering vapors, the accuracy and reliability of workplace air monitoring at ambient benzene concentrations even above 1.0 ppm can be questioned. References 1. Svnder. R.: The Benzene Problem in Historical Perspective. Fundam. Appl. Toxicol. 4.692-699 (1984). 2. Occupational Safety and Health Administration: 29 CFR Part 1910, Occupational Exposure to Benzene: Final Rule. Pan II, Department of labor. Fed. Reg. 52< 176):34460-345?H (September 11. 1987). 3. Ward, C O.: Kuna. RA; Snyder, N.K.; et at.: .Subchronic Inhalation Toxicity of Benzene in Rats and Mice. Am- J. Ind. Med 7.457-473 (1985). 4. Uveki, E.M., Ashkar, AE., Shoeman, D.W.; Uisel, T.V.-. Acute Toxicity of Benzene inhalation in Hemopoietic Precursor Cells. Toxicol. Appl. Pharmacol. 40:49-57 (1977). 5. Gill, D.D.; Jenkins, V.J.; Kempen, R.E.; Ellis, S.; The importance of 460 VVV 000013391 APPL 0CCUP. ENVIRON. HY6. 5(7) JULY 1990 Fluripotenr Stem Ceils m Ikmzene Toxicity Toxic*ilogy 16:165-PI <19H0). 6. Green, I D ; Nmder. C A. HiHue.. .. et al.. Acute and Chrome f>ose Response Effects of Inhaled Benzene on Muliipoiemini Hemato poietic Si cm (CFt1 S) and Granul<Kyto/Macroph;ige Progenitor (GM- CFV-C) Cells in CD-I Mice. Toxicol Appl. Pharmacol. 58 492-503 (19H1) 7. Rusch, G M.. Leorij*. H K.. Ltskin, S.: Benzene Metabolism J. Toxicol. Environ Health 2:23-36 U9T'). 8 Cronkite, E.P; L>rew, R.T. Inove, T.. Bullis. J E : Benzene Memato toxicity and Leukemogenesis Am. J. Ind. Med. 4S6 11985) 9. Cronkite, E P. Chemical l.eukemogeneM.s: Benzene as a Model Sem inar Hematol. 24:2-11 11987). 10 Rozen. M G; Snyder, CA. Protracted Exposure of C5'?BL6J Mice to 300 ppm [benzene Depresses B- and Tl.ymphocyte Numbers and Mitogen Responses. Evidence for Thymic and B*>ne Marrow Prolif eration in Respon.se to the Exposures. Toxicology 37:13-26 (1985). U. Aoyama. K_ Effects of Benzene Inhalation on lymphocyte Subpop ulations and Immune Response in Mice Toxicol Appi. Pharmacol 85:92-101 (1986) 12. Rozen, M.G.; Snvder, C.A; Albert, R.E.. Depression in B- and T-I.ym- pbocyte Mitogen-induced Blastogenest.s in Mice Exposed to Lov. Concentrations of Benzene. Toxicol, l-ett. 20 343-3*19 ( 1984 ). 13 Snyder, CA; Goldstein, B.D ; Sellakumar. 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