Abstract  Ethylbenzene is commonly used as a solvent and chemical intermediate and as an additive in some motor fuel formulations. Inhalation toxicology studies of ethylbenzene (99% pure) were conducted by exposing groups of F344/N rats and B6C3F1 mice of each sex to ethylbenzene vapor at chamber concentrations of 0, 100, 250, 500, 750, or 1000 ppm, 6 hours per day, 5 days per week for 13 weeks. No rats or mice died during the 13-week exposure. Body weight gains were slightly lower in the high dose groups of male and female rats, but the differences were not statistically significant. Absolute and relative kidney, liver, and lung weights were increased in the exposed rats, while weight increases occurred only in the livers of exposed mice. Chemically related histopathologic changes were not observed in any tissues of rats or mice. No changes were observed in the evaluation of sperm or vaginal cytology in rats or mice. Ethylbenzene was not mutagenic in Salmonella and did not induce chromosomal aberrations or sister chromatid exchanges in Chinese hamster ovary (CHO) cells in vitro, though it did induce trifluorothymidine resistance in mouse lymphoma cells at the highest concentration tested. Micronuclei assays in peripheral blood of mice were negative. Thus, there appears to be only minimal evidence of toxicity in F344/N rats and B6C3F1 mice exposed to ethylbenzene by inhalation at concentrations as high as to 1000 ppm for 13 weeks.

Abstract  It is proposed that metabolism of several structurally-related chemicals by CYP2F isoforms of the cytochromes P450 family results in a cytotoxicity-driven mode of action in organs high in CYP2F; namely, CYP2F2 in nasal and lung tissue in mice and CYP2F4 in nasal tissues in rats. Importantly, the CYP2F1 isozyme expressed in humans appears to have a low capacity to metabolize these compounds. In mice, the resultant cytotoxicity and subsequent regenerative hyperplasia is hypothesized drive an increase in lung tumors that are mostly benign and are not life shortening. Although a complete picture of the mode of action has not been developed in any one model compound, data from the individual compounds can be combined to synthesize and reinforce confidence in the CYP2F toxicity hypothesis. For coumarin, naphthalene, and styrene, inhibition of toxicity with inhibition of CYP2F2 has been demonstrated. Rat CYP2F4 appears to be equally active in metabolizing these chemicals; however, CYP2F4 occurs to a much lower extent in rat Clara cells and levels of metabolites produced are not sufficient to cause lung cytotoxicity. Human lungs contain far fewer of Clara cells than rats or mice, and human lung microsomes failed to, or only marginally, metabolize these compounds. In addition, the human lung differs markedly from the mouse lung in the morphology of its Clara cells, which make humans much less sensitive than mice to toxicity due to reactive metabolites. The absence of a role for CYP2E1-generated metabolites (primarily alkyl oxidation vs. ring-oxidation) in mouse pulmonary effects was demonstrated by the lack of protection from styrene toxicity by CYP2E1 inhibitor, or reduction of toxicity in CYP2E1-knockout mice, and lack of lung toxicity of the primary metabolite of ethylbenzene. The chemicals used as examples of this mode of action generally are negative in standard genotoxicity assays. Apart from increased SCE, no consistent pattern in genotoxicity results was found among these chemicals. Thus, while lung tumors from bronchiolar cell cytotoxicity are theoretically possible in humans, it is unlikely that metabolism by CYP2F1 would produce levels of cytotoxic metabolites in human lungs sufficient to result in lung cytotoxic responses and thus tumors. Therefore, it is unlikely several chemicals that cause mouse lung tumors via CYP2F2 metabolism will cause lung tumors in humans.

Abstract  Methylene chloride has been the subject of recent toxicological and carcinogenesis studies because of significant human exposure and widespread use in industrial processing, food preparation and agriculture. In this study, liver and lung tumors, induced in female B6C3F1 mice by inhalation of 2000 p.p.m. methylene chloride (6 h/day, 5 days/week continuous exposure), were examined for the presence of activated ras proto-oncogenes. DNA was isolated from 49 spontaneous and 50 methylene chloride-induced liver tumors and screened by oligonucleotide hybridization of PCR amplified H-ras gene fragments for codon 61 mutations. In the chemically induced tumors, 38 mutations were detected, 16 C to A transversions in base 1, 16 A to G transitions in base 2 and 6 A to T transversions in base 2. This mutation profile was similar to that identified for the H-ras gene in the spontaneous liver tumors and suggests that methylene chloride acts in liver by promoting cells with spontaneous lesions. Tumors in which H-ras codon 61 mutations were not detected were examined for the presence of transforming genes by the nude mouse tumorigenicity assay. Except for activated K-ras genes detected in DNA from two methylene chloride induced tumors and one spontaneous tumor, no other transforming genes were identified. DNA from 54 lung tumors was screened by direct sequencing of PCR amplified DNA fragments of the K-ras gene for first and second exon mutations, and 12 mutations were identified, 5 in exon one and 7 in exon 2. The low number of spontaneous tumors available in this study limits the interpretation of the data, and thus the frequency and spectrum of K-ras activation in the methylene chloride induced tumors was not significantly different from that in the seven spontaneous tumors analyzed. Since K-ras activation was not detected in 80% of the tumors, the nude mouse tumorigenicity assay was used to examine the lung tumors for the presence of other transforming genes. At present no transforming genes other than ras genes were identified in either liver or lung tumors.

Abstract  To investigate its carcinogenic potential, dichloromethane (DCM) was administered at levels of 0, 0, 60, 125, 185 and 250 mg/kg body weight/day to a total of 1000 B6C3F1 mice in deionized drinking-water for 104 wk. The high-dose male and female mice showed a transitory increase in mean leucocyte counts. Treatment-related toxic changes were noted in both male and female livers at the highest dose. There was a slight elevation of proliferative hepatocellular lesions in the treated males but no dose-related trend was apparent and the effect was absent in the females. Neoplastic lesions observed in the study were homogeneous among all groups and were within the range of incidence in historical controls. The results of this study demonstrated a toxicological no-observable-effect level (NOEL) for DCM of 185 mg/kg body weight/day in both sexes.

Abstract  Tenax-TA adsorbent tubes were used to collect 54 volatile hydrocarbon compounds in the workplace air and detected by thermal desorption-gas chromatography. The results showed that the correlation coefficients of 1,1-dichloroethylene, dichloromethane, 1,2-dichloroethylene (trans), 1,2-dichloroethylene (cis), 2,2-dichloropropane, bromochloromethane, 1,1,1-trichloroethane, 1,2-dichloroethane, and 1,1-dichloropropene were between 0.9941 and 0.9986, and the detection limits of bromochloromethane, dibromomethane, trichloromethane, bromodichloromethane, 2,2-dichloropropane, dibromochloromethane, and bromoform were 5.4 to 10.3 ng, and the minimum detection concentration was 0.01 to 0.1 mg/m³ (sampling volume 0.5 L). The correlation coefficients of the remaining 38 volatile hydrocarbons were all greater than 0.999, and the minimum detection concentration was 0.001-0.01 mg/m³; the detection limits of olefins were 0.4-2.7 ng, alkanes were 1.4-3.7 ng, aromatic hydrocarbons were 0.2-1.0 ng, and naphthalene was 2.2 ng; the thermal desorption efficiencies of 54 volatile hydrocarbons were 92.1%-113.1%, and the RSDs were 0.6%-17.4%. The RSD values ​​of -trichloroethane, 1,1-dichloroethylene, 2,2-dichloropropane, trichloromethane, 1,2-dichloroethylene (trans), dichloromethane, and bromochloromethane were between 5.1% and 17.4%, while the RSDs of the other 45 volatile hydrocarbons were all less than 5%; the penetration capacity of 9 compounds was 400-4000 ng, and the penetration capacity of the other compounds was greater than 10000 ng; in the stability experiment, except for 2,2-dichloropropane and bromodichloromethane, the loss rate within 15 days was 10%-15%, and the loss rate of the other 52 compounds was less than 5%. This method can be used for the detection of volatile hydrocarbons in the workplace air, and it is fast and accurate.

Abstract  Styrene is a widely used chemical that has been shown to cause lung tumors in mice but not in rats. Styrene toxicity appears to be related to its bioactivation to styrene oxide, and this occurs almost exclusively in Clara cells. An important pathway in the detoxification of styrene oxide is via epoxide hydrolase to yield styrene glycol. When mouse Clara cells were incubated with racemic styrene oxide, R-styrene glycol was the predominant metabolite, giving an R/S ratio of 3.6. When the pure styrene oxide enantiomers were used as substrates, the corresponding styrene glycols were the predominant but not exclusive metabolites. Activity was slightly higher with the S-styrene oxide than with the R-styrene oxide. Addition of reduced glutathione to the incubation medium resulted in an increase in epoxide hydrolase activity, perhaps by decreasing oxidative stress. Mouse Clara cells thus show the capacity for detoxifying styrene oxide.

Abstract  The health effects of styrene have been extensively investigated during the past 40 years. Acute exposure to styrene is lethal only at high concentrations (inhalation LC50s range from 2,700 to 6,000 ppm; oral LD50s from 316 to 5,000 mg/kg). Styrene is no more than moderately irritating to skin on a single exposure, but repeated exposures can cause defatting and dermatitis. Eye irritation is produced by contact with liquid styrene or by prolonged exposure to styrene vapour concentrations of approximately 100 ppm. Similarly, styrene vapours produce nasal irritation. A styrene vapour concentration of 160 ppm caused a 50% decrease in the respiratory rate in mice, an indication of sensory irritation. Because of the irritant nature of styrene vapour this must be included in any criteria for establishing the occupational exposure limit. Styrene is well absorbed by all routes of exposure and once absorbed is distributed throughout the body, especially concentrating in the fat. Styrene is cleared relatively rapidly from the body, and at low doses there is no tendency towards bioaccumulation in any organ or tissue. Studies examining the potential for specific organic toxicities in humans were negative for the haematopoietic system, immune system, kidney, urinary tract, gastrointestinal tract, liver, cardiovacscular and respiratory systems and the endocrine organs (WHO, 1983). Slight effects on the respiratory tract have been noted in some studies although the major responses have been noted on the central nervous system. High styrene exposure concentrations can cause acute, transient effects on the central nervous system. Pre-narcotic symptoms (headache, dizziness, nausea) and feelings such as fatigue and tiredness occur at exposure concentrations of 100 ppm or greater. Exposure to 1 00 ppm or greater may result in mild sensory impairment (5-10%) in the peripheral nerves, measured by nerve conduction velocity or sensory amplitude. Some reduction may be observed already between 50 and 100 ppm. There is no evidence of any permanent or irreversible effects that persist after exposures have been discontinued and styrene and its metabolites have been cleared. Based on the available data the effect of styrene on the CNS is an important factor in establishing an occupational exposure limit. Styrene is metabolised mostly through epoxidation of the vinyl side chain, forming styrene-7,8- epoxide (SO). Once formed, SO is either conjugated with glutathione or converted to styrene glycol, which is further metabolised to mandelic acid, phenylglyoxylic acid, benzoic acid, and/or hippuric acid which are excreted in the urine. Formation and excretion of styrene metabolises is species specific and influenced by many environmental and lifestyle factors; therefore, measurement of urinary metabolises gives an unreliable estimation of styrene exposure. Recent studies show that mice have the greatest capacity and humans the least to form SO from styrene. In addition, human liver is more effective at hydrolysing low levels of SO formed from styrene. Consequently, at any given styrene exposure concentration, SO levels in humans will be lower than in rodents. Studies indicate that styrene is not a teratogen. Some studies report embryotoxic or foetotoxic effects, but only at doses toxic to the parents. Initial human studies suggested an association between styrene exposure, congenital CNS malformation and spontaneous abortion. These assertions have been disproved by the same authors in more complete follow-up studies. Overall, there is no evidence that styrene exerts specific developmental or reproductive toxicity. Scott and Preston (1994) reported that 18 of 52 cytogenetic studies (chromosomal aberrations, micronuclei, sister chromatid exchanges) on peripheral blood lymphocytes of workers in industries in which there is exposure to styrene have reported significant increases in chromosome damage compared with non-exposed controls. The remaining investigations reported negative results. The data suggesting a positive association of clastogenic effects with styrene exposure are however very far from demonstrating convincingly that styrene produces chromosomal damage in exposed individuals. Reason for this include: (i) many of the studies are based on extremely small numbers of cases; (ii) the only two reports involving relatively large numbers have shown no association between styrene exposure and clastogenic effects e.g. the most recent data from an extensive EEC supported biomonitoring program showed that styrene exposure concentrations in the range of 5 to 182 ppm did not result in chromosome damage; (iii) a number of studies report relatively high levels of clastogenic effects which are implausibly high bearing in mind the rest of the published data; (iv) notwithstanding the large number of studies there is no quantitative relationship between styrene exposure and chromosomal damage; the lack of a dose-effect relationship in such a large group of data is a major confounder for accepting causality between styrene exposure and clastogenic effects. Support for the proposition that styrene is not responsible for the clastogenic effects reported in workers can be found in the in vivo animal data. An examination of the results show that studies in which exposures have been much higher than those encountered in the workplace the results have been overwhelmingly negative. A recent study conducted under the auspices of the US-EPA (Kligerman et al, 1992 and 1993) and CIIT (Preston 1993) showed that mice and rats exposed to styrene concentrations up to 500 ppm for two wk and rats exposed to 1,000 ppm for 4 wk showed no evidence of an increase in micronuclei or chromosomal aberrations. It is well possible that styrene exposure is not responsible for the observed chromosomal changes. Other factors which could be responsible for the results including co-exposure to other chemicals, cigarette smoking, life style etc; confounding factors that could not be excluded in the studies reported (Scott, 1993). Styrene is not a direct-acting mutagen in in vitro bacterial and eukaryotic cell assay systems. With activation, styrene is either non-mutagenic or very weakly mutagenic. Macromoiecular binding studies have shown that styrene and styrene oxide have very low potential to react with haemoglobin or DNA. Because of the many inconsistencies and imponderables associated with the available mutagenic and cytogenetic data it is probably inappropriate to use such information to reach a health based decision on a suitable occupational exposure limit. The available animal and human data do not indicate that styrene is a carcinogen and it should not be classified as such. A total of nine long-term bioassays have been conducted on styrene, and two additional studies have been performed using a mixture of styrene and beta-nitrostyrene. Some of these studies have specific deficiencies and limitations that preclude definitive conclusions. The available data provide no evidence of a carcinogenic response related to styrene exposure. Additional long-term animal studies are currently in progress. Although there have been some epidemiological studies which suggest there may be an association between styrene exposure and an increased risk of leukaemia and lymphoma the evidence is generally weak. The majority of the studies show no evidence for a causal relationship between styrene exposure and leukaemia and any other form of cancer. The combined weight of evidence of these epidemiological studies, including nearly 50,000 workers in the time period 1940 to 1986, argues against a carcinogenic role for styrene. This conclusion is supported by a study conducted by the International Agency for Research on Cancer (Kogevinas et al, 1993) involving over 40,000 workers from the European reinforced plastics industry and an update of the American reinforced plastics industry which included approximately 16,000 workers (Wong, 1994). While the body of evidence from both of these large studies is quite complex the overall result is not supporting the causal link between styrene and cancer, including the occurrence of tumours of the lymphatic and haematopoietic tissues.

Abstract  Styrene is a widely used compound in the manufacturing industry. In mice and rats, it is both hepatotoxic and pneumotoxic. It causes lung tumors in mice, but not in rats. The Clara cell is the main target for the toxicity of styrene and its metabolites, and it also has the greatest activity for styrene metabolism. Therefore, Clara cells isolated from CD-1 mice and Sprague?Dawley rats were used to compare the cytotoxicities induced by styrene and its metabolites. The cytotoxicity of styrene was greater in vitro than that of its metabolites styrene oxide (racemic, R- and S-) and 4-vinylphenol in contrast with what has been observed in vivo in previous studies on hepatotoxicity and pneumotoxicity. Susceptibility of rats to styrene and its metabolites are 4-fold less than that observed with mice. Glutathione levels were also measured in mice following addition of the chemicals in vitro and treatment of the CD-1 mice in vivo. Decreases in glutathione concentrations were seen even at doses which did not cause the death of mouse Clara cells. Significant decreases in glutathione were observed 3 h after treatment with racemic SO and R-SO. At 12 h, rebound effects were seen for all compounds, with all but R-SO rebounding above controls. These studies suggest that in vitro cytotoxicity of styrene and its metabolites does not strictly follow in vivo effects and that decreases in mouse glutathione levels may be related to oxidative stress.

Abstract  Styrene (ST) is an important industrial chemical. In long-term inhalation studies, ST-induced lung tumors in mice but not in rats. To test the hypothesis that the lung burden by the reactive metabolite styrene-7,8-oxide (SO) would be most relevant for the species-specific tumorigenicity, we investigated the SO burden in isolated lungs of male Sprague-Dawley rats and in-situ prepared lungs of male B6C3F1 mice ventilated with air containing vaporous ST and perfused with a modified Krebs-Henseleit buffer (37°C). Styrene vapor concentrations were determined in air samples collected in the immediate vicinity of the trachea. They were almost constant during each experiment. Styrene exposures ranged from 50 to 980 ppm (rats) and from 40 to 410 ppm (mice). SO was quantified from the effluent perfusate. Lungs of both species metabolized ST to SO. After a mathematical translation of the ex-vivo data to ventilation and perfusion conditions as they are occurring in vivo, a species comparison was carried out. At ST concentrations of up to 410 ppm, mean SO levels in mouse lungs ranged up to 0.45 nmol/g lung, about 2 times higher than in rat lungs at equal conditions of ST exposure. We conclude that the species difference in the SO lung burden is too small to consider the genotoxicity of SO as sufficient for explaining the fact that only mice developed lung tumors when exposed to ST. Another cause is considered as driving force for lung tumor development in the mouse.

Abstract  Styrene and styrene oxide mutagenicity was tested in cultured human lymphocytes treated in vitro with various concentrations of test agents. Styrene alone was found mutagenic at the highest concentration used (5 X 10(-4) mol. l-1, combined with the alkylating agent THIO-TEPA it did not affect the chromosome aberration yield. Exposure to styrene oxide gave a positive result showing a clear-cut dose-effect relationship within the concentration range 5 X 10(-6) to 1 X 10(-3) mol. l-1. In combination with THIO-TEPA its effect on chromosome aberration yields was additive. Styrene oxide proved also to be a very potent inducer of sister chromatid exchanges (SCE) within the concentration range 5 X 10(-6) to 1 X 10(-3) mol. l-1 tested. Combined with THIO-TEPA it exhibited a distinct additive effect in the production of SCEs.

Abstract  Pulmonary Clara cells are selectively damaged in mice given 1, 1-dichloroethylene (DCE), a chemical used in the plastics industry. The cytotoxicity is attributed to formation of a reactive metabolite believed to be the DCE-epoxide, which was detected in vitro. We have undertaken in vivo studies to test the hypothesis that in situ formation of the DCE-epoxide within Clara cells mediates the cell-specific injury manifested after DCE exposure. Formation of the epoxide was estimated by trapping of the metabolite with glutathione (GSH) and identifying the conjugated products as 2-(S-glutathionyl) acetyl glutathione ([B]) and 2-S-glutathionyl acetate ([C]). High-pressure liquid chromatographic analyses showed that conjugates [B] and [C] were both detected in lung cytosol isolated from mice treated in vivo with [14C]DCE. Epoxide levels in the cytosol, as estimated by the total amount of conjugates formed, were dose-dependent at DCE doses ranging from 25 to 225 mg/kg. Pretreatment of mice with buthionine sulfoximine (BSO) decreased sulfhydryl levels and significantly inhibited the formation of the GSH conjugates. Epoxide levels were also reduced by pretreatment with diallyl sulfone (DASO2), an inhibitor of the P450 isozyme CYP2E1. A polyclonal antibody was developed that is specific for conjugate [C] and that recognizes an antigen consisting of the conjugate epoxide-GSH-glutaraldehyde-bovine serum albumin. Immunohistochemical studies with this antibody revealed staining in Clara cells of mice treated with DCE. Staining was also present in Clara cells of mice treated with both BSO and DCE, but at slightly reduced levels. Reduction of this staining was more pronounced in Clara cells of mice treated with both DASO2 and DCE. These results show that the DCE-epoxide is formed in vivo, is localized in Clara cells, and correlates with the cytotoxicity manifested in this cell type.

Abstract  This paper presents formaldehyde and volatile organic compounds (VOC) concentrations, potential sources and impact factors in 100 homes. The 24-h average formaldehyde concentration in 37 homes exceeded the good class of the Hong Kong Indoor Air Quality Objectives (HKIAQO), whereas the total VOCs concentration in all homes was lower than the HKIAQO. Compared to other East Asian cities, indoor formaldehyde and styrene in Hong Kong was the highest, reflecting that the homes in Hong Kong were more affected by household products and materials. The formaldehyde concentration in newly built apartments was significantly higher than that in old buildings, whereas no relationship between the concentration and the building age was found for VOCs. There was no difference for formaldehyde and toluene between smoking and non-smoking homes, suggesting that cigarette smoking was not the major source of these two species. Homes of a couple with a child had higher formaldehyde and acetic acid concentrations, while homes with more than three people had higher concentrations of 1-butanol, heptane and d-limonene. When shoes were inside the homes, heptane, acetic acid, nonane and styrene concentrations were statistically higher than that when shoes were out of the homes. Furthermore, higher levels of 1,2,4-trimethylbenzene, styrene, nonane and heptane were found in gas-use families rather than in electricity-use homes. PRACTICAL IMPLICATIONS: Long-term exposure to formaldehyde and volatile organic compounds (VOC) in indoor environments may cause a number of adverse health effects such as asthma, dizziness, respiratory and lung diseases, and even cancers. Therefore, it is critical to minimize indoor air pollution caused by formaldehyde and VOCs. The findings obtained in this study would significantly enhance our understanding on the levels, emission sources and factors which affect indoor concentrations of formaldehyde and VOCs. The results can help housing designers, builders, home residents, and housing department of the government to improve indoor air quality (IAQ) by means of appropriate building materials, clean household products and proper life styles. It can also help policy makers reconcile the IAQ objectives and guidelines.

Abstract  Exposure to arsenic through domestic burning arsenic-containing coal causes various tumors in a population of Guizhou, China. The glycophorin A (GPA) assay is a human mutation assay detecting somatic variation in erythrocytes expressing the MN blood type, and was used to assess genotoxicity of arsenic-exposed patients. Peripheral blood was collected from 18 adult healthy subjects and 40 arsenic-exposed patients in heparin-treated tubes. Erythrocytes were isolated, fixed in formalin and immuno-labeled with fluorescent antibodies against GPA, followed by flow cytometry analysis. Arsenic exposure increased the variant frequency (expressed as the number of variant red cells per 10(6) erythrocytes): NN, 3.7 in healthy subjects versus 21.2 in arsenic-exposed patients; N phi, 12.6 versus 33.1; MM, 13.1 versus 110; and M phi, 5.2 versus 20.3. The total GPA variant frequency was increased about five-fold (34.7 in healthy subjects versus 185 in arsenosis patients). Furthermore, the variant frequency was significantly higher in skin tumor-bearing patients: NN, 19.4 in arsenic-exposed non-tumor patients versus 31.5 in tumor-bearing patients; N phi, 29.5 versus 54.5; MM, 102 versus 159; M phi, 15.9 versus 45.1. Total GPA variant frequency in arsenic-exposed patients bearing skin tumors was significantly increased compared to patients without skin tumors (167 versus 290). The relationship between arsenic exposure history and GPA variant frequency was less evident. These data demonstrate that arsenic exposure is associated with mutations at the GPA locus, an effect exaggerated in patients bearing arsenic-induced skin tumors. The variant frequency of GPA could be a useful biomarker for arsenic exposure and arsenic carcinogenesis.

Abstract  The aim of this study was to investigate the cytogenetic changes induced in humans exposed to styrene in a reinforced plastics plant. Blood and urine samples were collected from 18 styrene exposed workers and 18 age and sex matched control subjects from the administrative department of the same factory. Chromosome aberrations (CAs) and micronuclei (MN) (cytokinesis block method) were analyzed in blood lymphocytes. All of the subjects included in the study were male non-smokers. The duration of employment ranged from 10 to 22 years (14.3 ± 4.4). In order to monitor exposure to styrene, urinary mandelic acid (MA) levels were measured using a standard colorimetric method. The level of thioethers in the urine was also determined colorimetrically. The mean level of mandelic acid was significantly higher in the exposed workers (328.44 ± 266.21 mg/g creatinine) compared with that of the controls (50.09 ± 16.84 mg/g creatinine) (p < 0.05). The level of urinary thioethers was found to be higher among the exposed workers. The number of cells with chromosomal aberrations was significantly higher in the workers (6.06 ± 4.41) compared with the controls (3.44 ± 2.28) (p < 0.05). There was no significant increase in the frequency of micronuclei in the exposed workers compared to controls. Our results support earlier findings on increased rates of chromosomal aberrations in reinforced plastics workers.

Abstract  Fifty-nine chemicals that had completed National Cancer Institute rat and mouse 2-year carcinogenicity tests were tested in the strain A mouse pulmonary tumor assay. Without knowledge of chemical identity, 53 chemicals were tested in strain A mice in one laboratory and 30 were tested in a second independent laboratory. Strain A tests on 24 of these chemicals were conducted in both laboratories. The strain A results were generally not predictive of the 2-year rat and mouse carcinogenicity test results. Furthermore, there was poor agreement of strain A results between the two laboratories. Although a variety of explanations may be invoked to explain the lack of concordance between the strain A tests and the 2-year rat and mouse tests, no one factor is sufficient to rationalize the poor concordance between strain A and 2-year carcinogenicity bioassay results.

Abstract  This 1986 to 1992 update and expansion of an earlier historical cohort study examined the 1946 to 1992 mortality experience of 32,110 workers employed for 1 year or more during 1945 to 1978 at any of 10 US fiberglass (FG) manufacturing plants. Included are (1) a new historical exposure reconstruction for respirable glass fibers and several co-exposures (arsenic, asbestos, asphalt, epoxy, formaldehyde, polycyclic aromatic hydrocarbons, phenolics, silica, styrene, and urea); and (2) a nested, matched case-control study of 631 respiratory system cancer (RSC) deaths in male workers during 1970 to 1992 with interview data on tobacco smoking history. Our findings to date from external comparisons based on standardized mortality ratios (SMRs) in the cohort study provide no evidence of excess mortality risk from all causes combined, all cancers combined, and non-malignant respiratory disease. Also, excluding RSC, we observed no evidence of excess mortality risk from any of the other cause-of-death categories considered. For RSC among the total cohort, we observed a 6% excess (P = 0.05) based on 874 deaths. Among long-term workers (5 or more years of employment) we observed a not statistically significant 3% excess based on 496 deaths. Among the total cohort, we observed increases in RSC SMRs with calendar time and time since first employment, but these were less pronounced among long-term workers. RSC SMRs were not related to duration of employment among the total cohort or long-term workers. In an externally controlled analysis of male workers at risk between 1970 and 1992, we observed no association between RSC SMRs and increasing exposure to respirable FG. Our findings to date from internal comparisons based on rate ratios in the case-control study of RSC were limited to analyses of categorized study variables with and without adjustment for smoking. On the basis of these analyses, the duration of exposure and cumulative exposure to respirable FG at the levels encountered at the study plants did not appear to be associated with an increased risk of RSC. RSC risk also did not seem to increase with time since first employment. There is some evidence of elevated RSC risk associated with non-baseline levels of average intensity of exposure to respirable glass, but when adjusted for smoking this was not statistically significant, and there was no apparent trend with increasing exposure. This same pattern of findings was observed for duration of exposure, cumulative exposure, and average intensity of exposure to formaldehyde. None of the other individual co-exposures encountered in the study plants appeared to be associated with an increased risk of RSC. The primary focus of ongoing analyses is to determine the extent to which our present findings are robust to alternative characterizations of exposure.

Abstract  Many epoxides and their precursors are high production volume chemicals that have major uses in the polymer industry and as intermediates in the manufacture of other chemicals. Several of these chemicals were demonstrated to be carcinogenic in laboratory animal studies conducted by the Ramazzini Foundation (e.g., vinyl chloride, acrylonitrile, styrene, styrene oxide, and benzene) and by the National Toxicology Program (e.g., ethylene oxide, 1,3-butadiene, isoprene, chloroprene, acrylonitrile, glycidol, and benzene). The most common sites of tumor induction were lung, liver, harderian gland, and circulatory system in mice; Zymbal's gland and brain in rats; and mammary gland and forestomach in both species. Differences in cancer outcome among studies of epoxide chemicals may be related to differences in study design (e.g., dose, duration, and route of exposure; observation period; animal strains), as well as biological factors affecting target organ dosimetry of the DNA-reactive epoxide (toxicokinetics) and tissue response (toxicodynamics). N7-Alkylguanine, N1-alkyladenine, and cyclic etheno adducts, as well as K-ras and p53 mutations, have been detected in animals and/or workers exposed to several of these chemicals. The classifications of these chemical carcinogens by IARC and NTP are based on animal and human data and results of mechanistic studies. Reducing occupational and environmental exposures to these chemicals will certainly reduce human cancer risks.

Abstract  To assess whether occupational exposure to aromatic hydrocarbons increases carcinogenic risk.

We followed cancer incidence among 3,922 male and 1,379 female workers monitored for exposure to styrene, toluene, or xylene. The follow-up after the first personal measurement comprised 66,500 person-years at risk over the period 1973-1992. We computed the indirectly standardized incidence ratios (SIR) with 95% confidence interval (CI) with regard to age-, gender-, and period-specific incidence rates of cancer in the Finnish general population.

The overall rate of cancer incidence for the total cohort was fairly similar to that of the general population. The risk for nervous system tumors was increased at 10 years after the first personal measurement (SIR 2.80, CI 1.03-6.08). For styrene there was an excess risk for rectal cancer (SIR 3.11, CI 1.14-6.77), and risks for pancreatic and nervous system tumors were increased nonsignificantly. For toluene and xylene, no clear increase in cancer risk was found.

The data are not supportive of an overall increase in the cancer risk for these solvents, even though we cannot rule out site-specific associations with the rectum, pancreas, and nervous system. There is supporting evidence in the epidemiology literature for pancreatic cancer risk and heavy exposure to styrene. More studies are warranted on solvents, with detailed information on lifetime exposures and habits being collected whenever possible.

Abstract  Earlier studies have produced evidence for an association between work-related styrene exposure and cytogenetic damage, while more recent studies have failed to show such an association. In the present study, chromosome aberrations (CA) and sister chromatid exchanges (SCE) were measured in peripheral blood lymphocytes of 46 male workers employed in a fiber-reinforced plastic boat building factory and exposed to styrene. Two groups of 23 workers each, characterized by different exposure levels (ranges: 2-120 mg/rn3 and 86-1389 mg/m3 ambient air) were studied, fifty-one controls matched by sex, age and smoking habits were included. Randomized blood samples were analyzed for cytogenetic damage separately in two laboratories. Interlaboratory differences in the scoring of CA and SCE were noted. However, increases of the considered cytogenetic endpoints in exposed vs control groups were consistently observed in both laboratories. Multivariate statistical analysis of pooled data revealed increases of CA ranging between 19% (RR = 1.19; 95% C.I., 0.80-I .78; chromatid-type aberrations, low exposure group) and 144% (RR = 2.44; 95% C.I., 1.26-4.70; chromosome-type aberrations, high exposure group). Parallel excess of SCE in styrene exposed workers was also observed, although at a lesser extent (RR = 1.22; 95% C.I., 1.05-1.43, low exposure group; RR = 1.26; 95% C.I.,1.07-1.47, high exposure group). These findings suggest the presence of a causal association between occupational exposure to styrene and cytogenetic damage in the plastic boat building factory that was the object of the study.

Abstract  Concern about the carcinogenic potential of styrene (ST) is due to its reactive metabolite, styrene-7,8-oxide (SO). To estimate the body burden of SO resulting from various scenarios, a physiologically based pharmacokinetic (PBPK) model for ST and its metabolite SO was developed. This PBPK model describes the distribution and metabolism of ST and SO in the rat, mouse and man following inhalation, intravenous (i. v.), oral (p. o.) and intraperitoneal (i. p.) administration of ST or i. v., p.o. and i. p .administration of SO. Its structure includes the oxidation of ST to SO, the intracellular first-pass hydrolysis of SO catalyzed by epoxide hydrolase and the conjugation of SO with glutathione. This conjugation is described by an ordered sequential ping-pong mechanism between glutathione, SO and glutathione S-transferase. The model was based on a PBPK model constructed previously to describe the pharmacokinetics of butadiene with its metabolite butadiene monoxide. The equations of the original model were revised to refer to the actual tissue concentration of chemicals instead of their air equivalents used originally. Blood: air and tissue: blood partition coefficients for ST and SO were determined experimentally and have been published previously. Metabolic parameters were taken from in vitro or in vivo measurements. The model was validated using various data sets of different laboratories describing pharmacokinetics of ST and SO in rodents and man. In addition, the influences of the biochemical parameters, alveolar ventilation and blood: air partition coefficient for ST on the pharmacokinetics of ST and SO were investigated by sensitivity analysis. The PBPK model presented can be used to predict concentration-time curves of ST or SO in blood and different tissues.

Abstract  1,3-Butadiene and styrene are suspected carcinogens and common chemicals used in the synthesis of rubber. To investigate any potential human hazards from exposure to these chemicals, a case-control study of 59 lymphohematopoietic cancers was conducted within a cohort of male workers employed between 1943 and 1982 in eight North American styrene-butadiene rubber polymer-producing plants. A total of 193 controls were matched to the cases by plant, age, year of hire, duration worked, and survival to time of death of the case. Each job was assigned an estimated exposure rank, and each worker's cumulated rank score was calculated on the basis of the tim espent in each job throughout his employment. "Exposure" as a dichotomous variable was defined as a log rank score above the mean of the log scores for the total population of cases and controls within a subtype of cancer. Matched-pair analysis identified a strong association between leukemia and butadiene, with an odds ratio of 9.36 (95% confidence interval 2.05-22.9) and an association between styrene and leukemia (odds ratio = 3.13, 95% confidence interval 0.84-11.2) that did not achieve statistical significance. When exposure to both styrene and butadiene was included in a conditional logistic regression model, the odds ratio for butadiene remained high (odds ratio =7.39), but the estimated association of leukemia with styrene was small. The results of this study support the hypothesis that exposure to butadiene is associated with the risk of leukemia. There also appears to be an additional risk from work in specific subdivisions of the industry.

Abstract  Styrene (100-500 mg/kg b.wt.) and styrene oxide (50-200 mg/kg b.wt.) were given as a single intraperitoneal injection to female mice (C57BL/6) at various time intervals before sacrifice. Primary DNA damage in various organs was studied using alkaline single cell gel electrophoresis (comet) assay. Both substances induced significant DNA damage in lymphocytes, liver, bone marrow and kidney after 4 hr. The lymphocytes and liver cells were found to be the most sensitive cells to the DNA damaging effects of both agents. With the exception of bone marrow cells, the degree of DNA damage in all other cell types was decreased from 4 hr to 16 hr after the administration of both compounds. A strong sublinear dose-response relationship was observed in the lymphocytes, liver and bone marrow cells, possibly indicating a saturation of the detoxifying enzyme systems in these organs. The present work suggests that the comet assay can be used for detection of primary DNA damage induced by styrene and styrene oxide in vivo and for comparing the sensitivity of various target organs.

Abstract  We have used monoclonal antibodies that were prepared against and specifically recognize human hepatic cytochromes P450 as probes for solid phase radioimmunoassay and Western immunoblotting to directly demonstrate the presence in human lung microsomes of cytochromes P450 immunochemically related to human liver cytochromes P450IIE1 (CYP2E1) and P450IIIA (CYP3A).The detected levels of these cytochromes are much lower than levels in human liver microsomes, but similar to the levels seen in microsomes from untreated baboon lung. Proteins immunochemically related to two other constitutive hepatic cytochromes P450, cytochrome P450IIC8 (CYP2C8) andcytochrome P450IIC9 (CYP2C9), were not detectable in lung microsomes.

Abstract  ABSTRACT. The effect of potential risk factors for acute myeloid leukemia was evaluated in a case-referent study encompassing 59 cases and 354 referents, all of whom were alive. Information on exposure was obtained through a questionnaire mailed to the subjects. The possible effect of background radiation was evaluated by means of a gamma radiation index, which accounted for the differences between cases and referents in this respect, i.e.,in time spent in concrete buildings both at home and at work places. In the 20-54 yr old age group, there was an association between leukemia morbidity and index of background radiation. X-ray treatment and electrical work were also associated with increased rate ratios. With regard to solvents, only styrene appeared as a risk factor, but the number of exposed subjects was small. Other exposures were less clearly associated with increased risks.

Abstract  Jet Propellant 8 (JP-8) is a kerosene-based jet fuel used in the military and is composed of hundreds of hydrocarbons. A PBPK model was developed to assess the metabolic interactions of JP-8 vapor on two prominent constituents of JP-8 vapor, m-xylene (XYL) and ethylbenzene (EBZ). A limited number of rats were exposed to JP-8 vapor in a Leach chamber for 4 h to 380, 1100, or 2700 mg/m3 (total hydrocarbon). Several individual hydrocarbons were monitored in the chamber atmosphere, including XYL, EBZ, and the total hydrocarbon concentration. Blood and liver were harvested and analyzed by a novel headspace SPME/GC-MS method that allowed for identification of individual hydrocarbons and low limits of detection. The PBPK model was able to describe the metabolic interactions between XYL, EBZ, and a lumped aromatic fraction of JP-8 vapor estimated to be 18 to 25% of the fuel vapor. Competitive inhibition of XYL and EBZ metabolism was observed for JP-8 vapor inhalation exposures of 1100 and 2700 mg/m3. Future inhalation studies with jet fuel include aerosol exposures and expansion of the PBPK models to include other hydrocarbons such as n-alkanes and upper respiratory tract dosimetry of aerosol droplets.