Benzene exposure in the United States 1978-1983: an overview

Combined analysis of job and task benzene air exposures among workers at four US refinery operations

Workplace air samples analyzed for benzene at four US refineries from 1976 to 2007 were pooled into a single dataset to characterize similarities and differences between job titles, tasks and refineries, and to provide a robust dataset for exposure reconstruction. Approximately 12,000 non-task (>180 min) personal samples associated with 50 job titles and 4000 task (<180 min) samples characterizing 24 tasks were evaluated. Personal air sample data from four individual refineries were pooled based on a number of factors including (1) the consistent sampling approach used by refinery industrial hygienists over time, (2) the use of similar exposure controls, (3) the comparability of benzene content of process streams and end products, (4) the ability to assign uniform job titles and task codes across all four refineries, and (5) our analysis of variance (ANOVA) of the distribution of benzene air concentrations for select jobs/tasks across all four refineries. The jobs and tasks most frequently sampled included those with highest potential contact with refinery product streams containing benzene, which reflected the targeted sampling approach utilized by the facility industrial hygienists. Task and non-task data were analyzed to identify and account for significant differences within job-area, task-job, and task-area categories. This analysis demonstrated that in general, areas with benzene containing process streams were associated with greater benzene air concentrations compared to areas with process streams containing little to no benzene. For several job titles and tasks analyzed, there was a statistically significant decrease in benzene air concentration after 1990. This study provides a job and task-focused analysis of occupational exposure to benzene during refinery operations, and it should be useful for reconstructing refinery workers' exposures to benzene over the past 30 years.

Frequent p53 and H-ras Mutations in Benzene- and Ethylene Oxide-Induced Mammary Gland Carcinomas from B6C3F1 Mice

Benzene and ethylene oxide are multisite carcinogens in rodents and classified as human carcinogens by the National Toxicology Program. In 2-year mouse studies, both chemicals induced mammary carcinomas. We examined spontaneous, benzene-, and ethylene oxide-induced mouse mammary carcinomas for p53 protein expression, using immunohistochemistry, and p53 (exons 5–8) and H -ras (codon 61) mutations using cycle sequencing techniques. p53 protein expression was detected in 42% (8/19) of spontaneous, 43% (6/14) of benzene-, and 67% (8/12) of ethylene oxide-induced carcinomas. However, semiquantitative evaluation of p53 protein expression revealed that benzene- and ethylene oxide-induced carcinomas exhibited expression levels five- to six-fold higher than spontaneous carcinomas. p53 mutations were found in 58% (7/12) of spontaneous, 57% (8/14) of benzene-, and 67% (8/12) of ethylene oxide-induced carcinomas. H -ras mutations were identified in 26% (5/19) of spontaneous, 50% (7/14) of benzene-, and 33% (4/12) of ethylene oxide-induced carcinomas. When H- ras mutations were present, concurrent p53 mutations were identified in 40% (2/5) of spontaneous, 71% (5/7) of benzene-, and 75% (3/4) of ethylene oxide-induced carcinomas. Our results demonstrate that p53 and H -ras mutations are relatively common in control and chemically induced mouse mammary carcinomas although both chemicals can alter the mutational spectra and more commonly induce concurrent mutations.

An analysis of violations of Osha's (1987) occupational exposure to benzene standard

The Occupational Safety and Health Administration (OSHA), which was formed by the Occupational Safety and Health Act of 1970 (OSH Act), establishes enforceable health and safety standards in the workplace and issues violations and penalties for non-compliance with these standards. The purpose of the current study was to evaluate the number and type of violations of the OSHA (1987) Occupational Exposure to Benzene Standard. Violations of the OSHA Hazard Communication Standard (HCS), particularly those that may pertain to specific provisions of the benzene standard, were also assessed. All analyses were based on OSHA inspection data that have been collected since the early 1970s and that are publicly available from the U.S. Department of Labor enforcement website. Analysis of these data shows that fewer than a thousand OSHA violations of the benzene standard have been issued over the last 25+ years. The results for benzene are in contrast to those for some other toxic and hazardous substances that are regulated by OSHA, such as blood-borne pathogens, lead, and asbestos, for which there have been issued tens of thousands of OSHA violations. The number of benzene standard violations also varies by time period, standard provision, industry sector, and other factors. In particular, the greatest number of benzene standard violations occurred during the late 1980s to early/mid 1990s, soon after the 1987 final benzene rule was promulgated. The majority of benzene standard violations also pertain to noncompliance with specific provisions and subprovisions of the standard dealing with initial exposure monitoring requirements, the communication of hazards to employees, and medical surveillance programs. Only a small fraction of HCS violations are attributed, at least in part, to potential benzene hazards in the workplace. In addition, most benzene standard violations are associated with specific industries within the manufacturing sector where benzene or benzene-containing products may be used or produced during production processes, such as petroleum refineries, metal industries, and chemical companies. Not surprisingly, the greatest number of benzene standard violations have been issued to private facility owners (rather than government entities), given that the OSH Act primarily covers private sector employers. More violations have also been issued during inspections where union representation was present and from complaint-driven (vs. planned or other) inspections, which is consistent with OSHA inspection priorities. Violations of the benzene standard have typically involved a single instance per facility and 10 or fewer exposed employees. Because the OSH Act prescribes penalty caps for citations, initial penalties issued for noncompliance with the benzene standard have generally been less than $5,000 per violation. Despite some potential limitations, the OSHA inspection database contains the best available data for assessing historical and current violations of the benzene standard. These data, which have not been previously analyzed or published for benzene, may be of interest to professionals and practitioners involved in benzene risk assessment, risk management, and/or public policy issues.

An analysis of workplace exposures to benzene over four decades at a petrochemical processing and manufacturing facility (1962-1999)

Benzene, a known carcinogen, can be generated as a by-product during the use of petroleum-based raw materials in chemical manufacturing. The aim of this study was to analyze a large data set of benzene air concentration measurements collected over nearly 40 years during routine employee exposure monitoring at a petrochemical manufacturing facility. The facility used ethane, propane, and natural gas as raw materials in the production of common commercial materials such as polyethylene, polypropylene, waxes, adhesives, alcohols, and aldehydes. In total, 3607 benzene air samples were collected at the facility from 1962 to 1999. Of these, in total 2359 long-term (>1 h) personal exposure samples for benzene were collected during routine operations at the facility between 1974 and 1999. These samples were analyzed by division, department, and job title to establish employee benzene exposures in different areas of the facility over time. Sampling data were also analyzed by key events over time, including changes in the occupational exposure limits (OELs) for benzene and key equipment process changes at the facility. Although mean benzene concentrations varied according to operation, in nearly all cases measured benzene quantities were below the OEL in place at the time for benzene (10 ppm for 1974-1986 and 1 ppm for 1987-1999). Decreases in mean benzene air concentrations were also found when data were evaluated according to 7- to 10-yr periods following key equipment process changes. Further, an evaluation of mortality rates for a retrospective employee cohort (n = 3938) demonstrated that the average personal benzene exposures at this facility (0.89 ppm for the period 1974-1986 and 0.125 ppm for the period 1987-1999) did not result in increased standardized mortality ratio (SMRs) for diseases or malignancies of the lymphatic system. The robust nature of this data set provides comprehensive exposure information that may be useful for assessing human benzene exposures at similar facilities. The data also provide a basis for comparable measured exposure levels and the potential for adverse health effects. These data may also prove beneficial for comparing relative exposure potential for production versus nonproduction operations and the relationship between area and personal breathing zone samples.

Occupational exposure to benzene at the ExxonMobil refinery in Baytown, TX (1978-2006)

Although occupational benzene exposure of refinery workers has been studied for decades, no extensive analysis of historical industrial hygiene data has been performed focusing on airborne concentrations at specific refineries and tasks. This study characterizes benzene exposures at the ExxonMobil Baytown, TX, refinery from 1978 to 2006 to understand the variability in workers' exposures over time and during different job tasks. Exposures were grouped by operational status, job title, and tasks. More than 9000 industrial hygiene air samples were evaluated; approximately 4000 non-task (> 3 h) and 1000 task-related (< 3 h) personal samples were considered. Each sample was assigned to one of 27 job titles, 29 work areas, and 16 task bins (when applicable). Process technicians were sampled most frequently, resulting in the following mean benzene concentrations by area: hydrofiner (n=245, mean=1.3 p.p.m.), oil movements (n=286, mean=0.23 p.p.m.), reformer (n=575, mean=0.10 p.p.m.), tank farm (n=9, mean=0.65 p.p.m.), waste treatment (n=446, mean=0.13 p.p.m.), and other areas (n=460, mean=0.062 p.p.m.). The most frequently sampled task was sample collection (n=218, mean=0.40 p.p.m.). Job title and area did not significantly impact task-related exposures. Airborne concentrations were significantly lower after 1990 than before 1990. Results of this task-focused study may be useful when analyzing benzene exposures at other refineries.

Benzene exposure in refinery workers: ExxonMobil Joliet, Illinois, USA (1977-2006)

While petroleum industry studies have indicated low benzene exposure potential for refinery workers, most provide limited data for assessing job or task-related benzene exposures. This study characterizes job and task-specific airborne benzene concentrations and variability over time for the ExxonMobil refinery in Joliet, Illinois from 1977 to 2006. A database of 2289 industrial hygiene air samples, including 1145 non-task (≥180 min) personal samples and 480 task-related (<180 min) personal samples, were analyzed. Samples were grouped by operational status, job, and task. Benzene concentrations were determined for each job category and task bin, with additional analyses conducted to determine whether benzene concentrations changed over time. The results indicate that the benzene concentrations for non-task and task samples were relatively low. For all non-task samples, the arithmetic mean benzene concentration was 0.12 part per million (ppm). The most frequently sampled workers (process technicians during routine operations) had an arithmetic mean benzene concentration of 0.038 ppm. The most frequently sampled task bin (blinding and breaking) had an arithmetic mean benzene concentration of 1.0 ppm. This study provides benzene air concentration data that can be used in combination with job histories to reconstruct historical benzene exposures for workers at the Joliet Refinery over the past 30 years.

Occupational exposure to benzene at the ExxonMobil refinery at Baton Rouge, Louisiana (1977-2005)

Because crude oil contains up to 3% benzene and there is an association between high chronic exposure to appreciable concentrations of benzene and acute myelogenous leukemia, exposure of refinery workers has been studied for many years. To date, no extensive industrial hygiene exposure analyses for historical benzene exposure have been performed, and none have focused on the airborne concentrations in the workplace at specific refineries or for specific tasks. In this study, the authors evaluated the airborne concentrations of benzene and their variability over time at the ExxonMobil refinery in Baton Rouge between 1977 and 2005. Refinery workers were categorized into 117 worker groups using company job descriptions. These 117 groups were further collapsed into 25 job categories based on similarity of measured exposure results. Results of 5289 personal air samples are included in this analysis; 3403 were considered nontask (>or= 180 min) personal samples, and 830 were considered task-related (< 180 min) personal samples; the remainder did not fit in either category. In general, nontask personal air samples indicated that exposures of the past 30 years were generally below the occupational exposure limit of 1 ppm, but there was only a small, decreasing temporal trend in the concentrations. The job sampled most frequently during routine operations was process technician and, as broken down by area, resulted in the following mean benzene concentrations: analyzers (mean = 0.12 ppm), coker (mean = 0.013 ppm), hydrofiner (mean = 0.0054 ppm), lube blending and storage (mean = 0.010 ppm), waste treatment (mean = 0.092 ppm), and all other areas (mean = 0.055 ppm). Task-based samples indicated that the highest exposures resulted from the sampling tasks, specifically from those performed on process materials; in general, though, even these tasks had concentrations well below the STEL of 5 ppm. The most frequently sampled task was gauging (mean = 0.12 ppm). Task-related exposures were also similar across job categories for a given task, with a few exceptions. This study thus provides a task-focused analysis for occupational exposure to benzene during refinery operations, which can be insightful for understanding exposures at this refinery and perhaps others operated since about 1975.

Occupational exposures associated with petroleum-derived products containing trace levels of benzene

Benzene may be present as a trace impurity or residual component of mixed petroleum products due to refining processes. In this article, the authors review the historical benzene content of various petroleum-derived products and characterize the airborne concentrations of benzene associated with the typical handling or use of these products in the United States, based on indoor exposure modeling and industrial hygiene air monitoring data collected since the late 1970s. Analysis showed that products that normally contained less than 0.1% v/v benzene, such as paints and paint solvents, printing solvents and inks, cutting and honing oils, adhesives, mineral spirits and degreasers, and jet fuel typically have yielded time-weighted average (TWA) airborne concentrations of benzene in the breathing zone and surrounding air ranging on average from <0.01 to 0.3 ppm. Except for a limited number of studies where the benzene content of the product was not confirmed to be <0.1% v/v, airborne benzene concentrations were also less than current occupational exposure limits (e.g., threshold limit value of 0.5 ppm and permissible exposure limit of 1.0 ppm) based on exceedance fraction calculations. Exposure modeling using Monte Carlo techniques also predicted 8-hr TWA near field airborne benzene concentrations ranging from 0.002 to 0.4 ppm under three hypothetical solvent use scenarios involving mineral spirits. The overall weight-of-evidence indicates that the vast majority of products manufactured in the United States after about 1978 contained <0.1% v/v benzene, and 8-hr TWA airborne concentrations of benzene in the workplace during the use of these products would not have been expected to exceed 0.5 ppm under most product use scenarios. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: a document containing exposure modeling scenarios and results, historical benzene content of petroleum-derived products, and air monitoring results.].

Physiologically-based pharmacokinetic modeling of benzene in humans: a Bayesian approach

Benzene is myelotoxic and leukemogenic in humans exposed at high doses (>1 ppm, more definitely above 10 ppm) for extended periods. However, leukemia risks at lower exposures are uncertain. Benzene occurs widely in the work environment and also indoor air, but mostly below 1 ppm, so assessing the leukemia risks at these low concentrations is important. Here, we describe a human physiologically-based pharmacokinetic (PBPK) model that quantifies tissue doses of benzene and its key metabolites, benzene oxide, phenol, and hydroquinone after inhalation and oral exposures. The model was integrated into a statistical framework that acknowledges sources of variation due to inherent intra- and interindividual variation, measurement error, and other data collection issues. A primary contribution of this work is the estimation of population distributions of key PBPK model parameters. We hypothesized that observed interindividual variability in the dosimetry of benzene and its metabolites resulted primarily from known or estimated variability in key metabolic parameters and that a statistical PBPK model that explicitly included variability in only those metabolic parameters would sufficiently describe the observed variability. We then identified parameter distributions for the PBPK model to characterize observed variability through the use of Markov chain Monte Carlo analysis applied to two data sets. The identified parameter distributions described most of the observed variability, but variability in physiological parameters such as organ weights may also be helpful to faithfully predict the observed human-population variability in benzene dosimetry.

Genetic Polymorphisms in XRCC1, APE1, ADPRT, XRCC2, and XRCC3 and Risk of Chronic Benzene Poisoning in a Chinese Occupational Population

DNA damage induced by benzene is an important mechanism of its genotoxicity that leads to chronic benzene poisoning (CBP). Therefore, genetic variation in DNA repair genes may contribute to susceptibility to CBP in the exposed population. Because benzene-induced DNA damage includes single- and double-strand breaks, we hypothesized that single-nucleotide polymorphisms in X-ray repair cross-complementing group 1 (XRCC1), apurinic/apyrimidinic endonuclease (APE1), ADP ribosyltransferase (ADPRT), X-ray repair cross-complementing group 2 (XRCC2), and X-ray repair cross-complementing group 3 (XRCC3) are associated with risk of CBP. We genotyped single-nucleotide polymorphisms at codons 194, 280, and 399 of XRCC1, codon 148 of APE1, codon 762 of ADPRT, codon 188 of XRCC2, and codon 241 of XRCC3 in 152 CBP patients and 152 healthy workers frequency matched on age and sex among those who were occupationally exposed to benzene. The genotypes were determined by PCR-RFLP technique with genomic DNA. We found that no individuals had the XRCC2 codon 188 variant alleles or Met/Met genotype of XRCC3 codon 241 in this study population. However, individuals carrying the XRCC1 194Trp allele (i.e., Arg/Trp+Trp/Trp genotypes) had a decreased risk of CBP [adjusted odds ratio (OR(adj)), 0.60; 95% confidence interval (95% CI), 0.37-0.98; P = 0.041] compared with subjects with the Arg/Arg genotype whereas individuals carrying the XRCC1 280His allele (i.e., Arg/His+His/His genotypes) had an increased risk of CBP compared with those with the Arg/Arg genotype (OR(adj), 1.91; 95% CI, 1.17-3.10; P = 0.009). The analysis of haplotypes of polymorphisms in XRCC1 showed that there was a 2.96-fold (OR, 2.96; 95% CI, 1.60-5.49; chi(2) = 12.39, P = 0.001) increased risk of CBP for subjects with alleles of XRCC1 194Arg, XRCC1 280His, and XRCC1 399Arg compared with those carrying alleles of XRCC1 194Arg, XRCC1 280Arg, and XRCC1 399Arg. Therefore, our results suggest that polymorphisms at codons 194 and 280 of XRCC1 may contribute to CBP in a Chinese occupational population.

Benzene exposures associated with tasks performed on marine vessels (circa 1975 to 2000)

In this article, we assemble and synthesize the available industrial hygiene data that describe exposure during the marine transport of benzene-containing products in the United States and abroad. A total of 25 studies were identified and summarized. The measured airborne concentrations of benzene on marine vessels were found to vary depending on several key factors, including the job task, vessel characteristics, cargo type, and sample type and duration. Despite the differences in sampling strategies and benzene content of the liquids being transported, personal time-weighted-average benzene air concentrations typically ranged from 0.2-2.0 ppm during closed loading and 2-10 ppm during open loading operations. Benzene exposures during these activities are likely due to specific short-term tasks, such as connecting and disconnecting hoses and tank gauging and sampling. Similar concentrations of benzene have been reported in the pump room during marine loading operations and during tank cleaning activities in various settings. When compared with contemporaneous occupational health standards, our review indicates that most activities performed on marine vessels from the 1970s to 1990s usually did not result in benzene exposures that exceeded these standards. The information and data presented here may be useful for quantitatively estimating or reconstructing historical exposures during the marine transport of benzene-containing cargo if details about individual's work histories in the maritime industry are available.

An overview of occupational benzene exposures and occupational exposure limits in Europe and North America

Benzene has become one of the most intensely regulated substances in the world. Its ubiquitous use as a solvent has led to many working populations being exposed; in the early days often in uncontrolled conditions, leading to high exposures. Current occupational exposures are tightly controlled and are largely confined to workers in the petrochemical industry, vehicle mechanics, firefighters, workers exposed to automobile emissions, and some other occupational groups. Typically, occupational exposure levels are currently at or below 3.25 mg/m3 (1 ppm), and environmental exposures are typically below 50 microg/m3 (15 ppb). Smoking remains a significant source of exposure in both occupationally and non-occupationally exposed individuals. The early experiences of high occupational exposures led to the identification of haematopoietic effects of benzene and the need for improved control and regulation. As with most occupational standards, there has been a reduction in exposure limits as effects have been identified at ever-lower levels, accompanied by a societal concern for improved standards of occupational health. In 1946, the United States occupational exposure limit for benzene, promulgated by the American Conference of Governmental Industrial Hygienists, was 325 mg/m3 (100 ppm), but nowadays most European and North American countries have harmonised at 1.63-3.25mg/m3 (0.5-1 ppm). This latter figure was agreed within the European Union in 1997 and was adopted within national legislation by all Member States. The data on which this limit is set are essentially the same as those used by other standard-setting committees; this is an excellent example of how standards are set using science, pragmatism and societal values in the absence of complete information.

Gene expression profile in bone marrow and hematopoietic stem cells in mice exposed to inhaled benzene

Acute myeloid leukemia and chronic lymphocytic leukemia are associated with benzene exposure. In mice, benzene induces chromosomal breaks as a primary mode of genotoxicity in the bone marrow (BM). Benzene-induced DNA lesions can lead to changes in hematopoietic stem cells (HSC) that give rise to leukemic clones. To gain insight into the mechanism of benzene-induced leukemia, we investigated the DNA damage repair and response pathways in total bone marrow and bone marrow fractions enriched for HSC from male 129/SvJ mice exposed to benzene by inhalation. Mice exposed to 100 ppm benzene for 6h per day, 5 days per week for 2 week showed significant hematotoxicity and genotoxicity compared to air-exposed control mice. Benzene exposure did not alter the level of apoptosis in BM or the percentage of HSC in BM. RNA isolated from total BM cells and the enriched HSC fractions from benzene-exposed and air-exposed mice was used for microarray analysis and quantitative real-time RT-PCR. Interestingly, mRNA levels of DNA repair genes representing distinct repair pathways were largely unaffected by benzene exposure, whereas altered mRNA expression of various apoptosis, cell cycle, and growth control genes was observed in samples from benzene-exposed mice. Differences in gene expression profiles were observed between total BM and HSC. Notably, p21 mRNA was highly induced in BM but was not altered in HSC following benzene exposure. The gene expression pattern suggests that HSC isolated immediately following a 2 weeks exposure to 100 ppm benzene were not actively proliferating. Understanding the toxicogenomic profile of the specific target cell population involved in the development of benzene-associated diseases may lead to a better understanding of the mechanism of benzene-induced leukemia and may identify important interindividual and tissue susceptibility factors.

Kinetic factors involved in the metabolism of benzene in mouse lung and liver

Benzene is an occupational and environmental toxicant. The main human health concern associated with benzene exposure is acute myelogenous leukemia. Benzene produces lung tumors in mice, while its effects on human lung are not clear. The adverse effects of benzene are dependent on its metabolism by the cytochrome P-450 enzyme system. The isozymes CYP2E1 and CYP2F2 play roles in the metabolism of benzene at low, environmentally relevant concentrations. Previous studies indicate that the mouse lung readily metabolizes benzene and that CYP2F2 plays a role in this biotransformation. The significance of CYP2E1 and CYP2F2 in benzene metabolism was determined by measuring their apparent kinetic parameters K(m) and V(max). Use of wild-type and CYP2E1 knockout mice and selective inhibitors allowed the determination of the individual importance of both CYP2E1 and CYP2F2 in mouse liver and lung. A simple Michaelis-Menten relationship involving Lineweaver-Burk plots for the microsomal metabolism of benzene shows the apparent kinetic factors are different between the wild-type (K(m): 30.4 microM, V(max): 25.3 pmol/mg protein/min) and knockout (K(m): 1.9 microM, V(max): 0.5 pmol/mg protein/min) mouse livers. Wild-type lung has a K(m) of 2.3 microM and V(max) of 0.9 pmol/mg protein/min. CYP2E1 knockout lung has similar affinity and metabolic activity with a K(m) of 3.7 microM and V(max) of 1.2 pmol/mg protein/min. These data suggest CYP2E1 is less important in the lung than liver, and that it has a lower affinity for benzene but higher rate of hydroxylated metabolite production than does CYP2F2, which plays the predominant role in metabolizing benzene in mouse lung.

Critical literature review of determinants and levels of occupational benzene exposure for United States community-based case-control studies

This article presents the results of an extensive literature review identifying the uses or occurrences of, and exposures to, benzene in a variety of industries for a community-based case-control study of childhood brain cancer in the United States and Canada. We focused on industries for which quantitative exposure data were identified in studies conducted in North America in the 1980s. Each industry was coded according to the 1987 Standard Industrial Classification (SIC) system. For each industry, information relevant to exposure assessment, including process descriptions, job titles, tasks, and work practices, was summarized when available. Estimates of probability and intensity of exposure, and our confidence in these estimates are presented. Arithmetic means (AMs), weighted for the number of measurements for each industry, were calculated based on measurement data from long-term (i.e., 60+ minutes) personal sampling; short-term or area samples were only used when no other data were available for a given industry. Industries for which no quantitative exposure levels were identified in the North American literature but for which information was found on benzene use are briefly described. Published exposure data indicate that workers in most industries in the 1980s experienced exposure levels below the current standard of 1 part per million (ppm), with a weighted AM of 0.33 ppm across all industries. Despite the longtime recognition of the hematological effects of benzene, little information was available on exposure levels and determinants for many industries with potential exposure. Nevertheless, this review may clarify some of the procedures involved in assessing occupational exposures in community-based studies and may aid in the interpretation of previous occupational studies that relied on job title or industry.

Validation of exposure estimation for benzene in the Australian petroleum industry

A nested case-control study was undertaken to investigate whether an excess of lympho-haematopoietic cancers in the Australian petroleum industry was associated with benzene exposure. The benzene exposures of the cases and controls were estimated using a quantitative algorithm based largely on exposures measured in the Australian petroleum industry. The algorithm was used to estimate, for each subject, the benzene exposure in parts per million (ppm) for each job held in the industry, and the cumulative exposure in ppm years. Because of the critical importance of the exposure assessment in this design of epidemiological study, particular attention was paid to the reliability of the inputs to the algorithm. The inputs [base estimates (BEs) of exposure and technology-specific exposure modifiers (EMs)] were compared to data from other sources including the occupational hygiene literature. Where such comparison data were available, they were generally found to confirm the values used in the algorithm, although four input values were changed as a result of the validation exercise. The integrity of the task-based algorithm was validated by employing it to calculate the exposures of the tanker drivers in the study and comparing these with measured daily exposure for tanker drivers in the Australian petroleum industry and exposure values found in the occupational hygiene literature. After adjustment for the mix of products carried by the Australian tanker drivers, the estimates from the algorithm were found to be comparable to the measured and literature values. This exercise provided evidence that the exposure assessment for the epidemiological study was reliable and that the results of the study can be used as the basis for evaluating the relationship between exposure to benzene and the risk of lympho-haematopoietic cancer.

Investigation of a cluster of leukaemia in the Illawarra region of New South Wales, 1989-1996

OBJECTIVES

To investigate a cluster of leukaemia among young people and assess the plausibility of a disease-exposure relationship.

DESIGN

Descriptive analysis of population-based leukaemia incidence data, review of evidence related to the causation of leukaemia, assessment of environmental exposures to known leukaemogens, and resulting risks of leukaemia.

SETTING

Illawarra region of New South Wales, Australia, focusing on suburbs between the Port Kembla industrial complex and Lake Illawarra (the Warrawong area).

MAIN OUTCOME MEASURES

Standardised incidence ratios (SIRs) for leukaemia; current measured and past estimated ambient air benzene concentrations; and expected leukaemia cases attributable to estimates of ambient air benzene concentrations.

RESULTS

In 1989-1996, 12 leukaemia cases among Warrawong residents aged less than 50 years were observed, more than the 3.49 cases expected from the rate in the rest of the Illawarra region (SIR, 343.8; 99% CI, 141.6-691.7). These people lived in suburbs immediately to the south-southwest of a coke byproducts plant (a major industrial source of benzene, one of the few known leukaemogens). The greatest excess was among 15-24-year-olds (SIR, 1085.6; 99% CI, 234.1-3072.4). In 1996, ambient air concentrations of benzene averaged less than 1 part per billion (ppb). Since 1970, ambient air concentrations of benzene were estimated to have averaged up to 3 ppb, about one-thousandth of the level at which leukaemia risk has been identified in occupational epidemiological studies. Using the risk assessment model developed by the US Environmental Protection Agency, we estimate that past benzene levels in the Warrawong area could have resulted in 0.4 additional cases of leukaemia in 1989-1996.

CONCLUSIONS

The excess occurrence of leukaemia in the Warrawong area in 1989-1996 is highly unusual. Current environmental benzene exposure and the reconstructed past environmental benzene exposure level are too low to explain the large excess of leukaemia. The cause of the cluster is uncertain.

Hematopoietic and lymphatic malignancies in vehicle mechanics

Although it is generally acknowledged that benzene causes leukemia, especially acute myeloid leukemia, considerable divergences persist in the assessment of the leukemia risk due to occupational low-level benzene exposure. Specifically, the risk for vehicle mechanics is considered by some authors as being nondetectable with epidemiologic methods, whereas others calculated that the incidence rate of leukemia (all types) in vehicle mechanics is increased more than 60 times. The purpose of this review is to examine the publications on this topic in light of criteria for causal inference and to discuss the possible role of bias, confounding factors, and chance. The results of this analysis reveal that there are surprisingly few epidemiologic observations supporting an increased incidence of leukemia in vehicle mechanics. Apparently, publications suggesting a leukemogenic effect of low-level benzene exposure in garage mechanics are more often quoted than their negative counterparts, although they are not better designed.

Benzene-induced genotoxicity in mice in vivo detected by the alkaline comet assay: reduction by CYP2E1 inhibition

The myelotoxic and genotoxic effects of benzene have been related to oxidative DNA damage after metabolism by CYP2E1. Single cell gel electrophoresis (alkaline comet assay) detects DNA damage and may thus be a convenient method for the study of benzene genotoxicity. Benzene exposure to NMRI mice as a single oral gavage at 40, 200 or 450 mg/kg resulted in dose-related DNA damage indicated by an increased comet tail length of peripheral blood lymphocytes and bone marrow nucleated cells sampled 6 h after exposure. After a dose of 40 mg/kg, there was a 1.6-fold increase of 'tail length' in bone marrow nucleated cells in comparison with the control (p < 0.01). There was no significant increase in DNA damage in peripheral blood lymphocytes in the same animals. At 200 mg/kg, the tail length was 4.8-fold and 4.0-fold increased in the two cell types, respectively (p < 0.01). At 450 mg/kg, the tail length was further increased to 5.4-fold and 6.6-fold of the control values, respectively (p < 0.01). Pretreatment with propylene glycol (5 microliters/g b.wt., twice with a 60-min interval), a selective CYP2E1 inhibitor, reduced the increase in the tail length by about half at all doses in both cell types (p < 0.01). By comparing our data with those from genotoxicity studies on benzene using other methods, we conclude that the 'alkaline comet assay' is a sensitive method to detect DNA damage induced by benzene. We also infer that CYP2E1 contributes, at least partly, to the formation of the 'comet'-inducing metabolites in the chosen cell types.

Benzene: a case study in parent chemical and metabolite interactions

Benzene, an important industrial solvent, is also present in unleaded gasoline and cigarette smoke. The hematotoxic effects of benzene in humans are well documented and include aplastic anemia and pancytopenia, and acute myelogenous leukemia. A combination of metabolites (hydroquinone and phenol for example) is apparently necessary to duplicate the hematotoxic effect of benzene, perhaps due in part to the synergistic effect of phenol on myeloperoxidase-mediated oxidation of hydroquinone to the reactive metabolite benzoquinone. Since benzene and its hydroxylated metabolites (phenol, hydroquinone and catechol) are substrates for the same cytochrome P450 enzymes, competitive interactions among the metabolites are possible. In vivo data on metabolite formation by mice exposed to various benzene concentrations are consistent with competitive inhibition of phenol oxidation by benzene. In vitro studies of the metabolic oxidation of benzene, phenol and hydroquinone are consistent with the mechanism of competitive interaction among the metabolites. The dosimetry of benzene and its metabolites in the target tissue, bone marrow, depends on the balance of activation processes such as enzymatic oxidation and deactivation processes such as conjugation and excretion. Phenol, the primary benzene metabolite, can undergo both oxidation and conjugation. Thus, the potential exists for competition among various enzymes for phenol. However, zonal localization of Phase I and Phase II enzymes in various regions of the liver acinus regulates this competition. Biologically-based dosimetry models that incorporate the important determinants of benzene flux, including interactions with other chemicals, will enable prediction of target tissue doses of benzene and metabolites at low exposure concentrations relevant for humans.

Critical issues in benzene toxicity and metabolism: the effect of interactions with other organic chemicals on risk assessment

Benzene, an important industrial solvent, is also present in unleaded gasoline and cigarette smoke. The hematotoxic effects of benzene are well documented and include aplastic anemia and pancytopenia. Some individuals exposed repeatedly to cytotoxic concentrations of benzene develop acute myeloblastic anemia. It has been hypothesized that metabolism of benzene is required for its toxicity, although administration of no single benzene metabolite duplicates the toxicity of benzene. Several investigators have demonstrated that a combination of metabolites (hydroquinone and phenol, for example) is necessary to duplicate the hematotoxic effect of benzene. Enzymes implicated in the metabolic activation of benzene and its metabolites include the cytochrome P450 monooxygenases and myeloperoxidase. Since benzene and its hydroxylated metabolites (phenol, hydroquinone, and catechol) are substrates for the same cytochrome P450 enzymes, competitive interactions among the metabolites are possible. In vivo data on metabolite formation by mice exposed to various benzene concentrations are consistent with competitive inhibition of phenol oxidation by benzene. Other organic molecules that are substrates for cytochrome P450 can inhibit the metabolism of benzene. For example, toluene has been shown to inhibit the oxidation of benzene in a noncompetitive manner. Enzyme inducers, such as ethanol, can alter the target tissue dosimetry of benzene metabolites by inducing enzymes responsible for oxidation reactions involved in benzene metabolism. The dosimetry of benzene and its metabolites in the target tissue, bone marrow, depends on the balance of activation processes, such as enzymatic oxidation, and deactivation processes, like conjugation and excretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Concentrations of benzene in blood and S-phenylmercapturic and t,t-muconic acid in urine in car mechanics

Different parameters of biological monitoring were applied to 26 benzene-exposed car mechanics. Twenty car mechanics worked in a work environment with probably high benzene exposures (exposed workers); six car mechanics primarily involved in work organization were classified as non-exposed. The maximum air benzene concentration at the work places of exposed mechanics was 13 mg/m3 (mean 2.6 mg/m3). Elevated benzene exposure was associated with job tasks involving work on fuel injections, petrol tanks, cylinder blocks, gasoline pipes, fuel filters, fuel pumps and valves. The mean blood benzene level in the exposed workers was 3.3 micrograms/l (range 0.7-13.6 micrograms/l). Phenol proved to be an inadequate monitoring parameter within the exposure ranges investigated. The muconic and S-phenylmercapturic acid concentrations in urine showed a marked increase during the work shift. Both also showed significant correlations with benzene concentrations in air or in blood. The best correlations between the benzene air level and the mercapturic and muconic acid concentrations in urine were found at the end of the work shift (phenylmercapturic acid concentration: r = 0.81, P < 0.0001; muconic acid concentration: r = 0.54, P < 0.05). In conclusion, the concentrations of benzene in blood and mercapturic and muconic acid in urine proved to be good parameters for monitoring benzene exposure at the workplace even at benzene air levels below the current exposure limits. Today working as a car mechanic seems to be one of the occupations typically associated with benzene exposure.

Chromosome aberration, sister-chromatid exchange, proliferative rate index, and serum thiocyanate concentration in smokers exposed to low-dose benzene

Cytogenetical endpoints, i.e., chromosome aberration (CA), sister-chromatid exchange (SCE), and proliferative rate indexes (PRI), were measured in peripheral blood lymphocytes (PBL) of 42 workers exposed occupationally to low-dose benzene, and of 42 controls. The role of smoking habit as a confounding factor of genotoxic effects caused by occupational low-dose benzene exposure was also studied. The benzene concentrations in the ambient air samples varied from 3 to 20 mg/m3 (mean: 7 mg/m3). The continuous low-dose benzene exposure significantly increased the CA and SCE frequencies, but did not influence PRI. Smoking levels were characterized by subjective accounts and by serum thiocyanate concentrations (SCN). CA and SCE were not significantly increased in smokers compared to nonsmokers, but the differences were expressed to a greater extent in the case of measurement of SCN concentrations. Determination of SCN proved to be more objective in the assessment of genotoxic effects of smoking as a confounding factor of occupational low-dose benzene exposure.

Benzene exposure in a Japanese petroleum refinery

Time-weighted average (TWA) intensity of exposure of workers to benzene vapor during a shift was monitored by diffusive sampling technique in a Japanese petroleum refinery. The subjects monitored (83 in total) included refinery operators, laboratory personnel and tanker-loading workers. The results showed that the time-weighted average exposures are well below 1 ppm in most cases. The highest exposure was recorded in 1 case involved in bulk loading of tanker ships, in which exposure of over 1 ppm might take place depending on operational conditions. The observation was generally in agreement with levels previously reported.

Effect of dose on the absorption and excretion of [14C]benzene administered orally or by inhalation in rats and mice

The effect of dose on the absorption and excretion of [14C]benzene was studied using 13-week old male F344/N rats, Sprague-Dawley rats, and B6C3F1 mice. Gastrointestinal absorption of benzene administered by gavage was greater than 97% in these species for doses between 0.5 and 150 mg benzene/kg body wt. At oral doses below 15 mg/kg, greater than 90% of the 14C excreted was in the urine as nonethylacetate extractable material. Above 15 mg/kg, in both rats and mice, an increasing percentage of the administered benzene was exhaled unmetabolized, suggesting saturation of metabolic pathways. Above 50 mg/kg, total metabolites (as determined by 14C in the urine, feces, and carcass after 2 days) were not linearly related to administered dose. Total metabolites per unit body weight was equal in F344/N rats and B6C3F1 mice at gavage doses up to 50 mg/kg; however, total metabolites in mice did not increase at higher doses. For inhalation exposures, the percentage of inhaled benzene that was absorbed and retained during a 6-hr exposure decreased from 33 +/- 6% (mean +/- standard deviation) to 15 +/- 9% in rats, and from 50 +/- 15 to 10 +/- 2% in mice as the exposure concentration was increased from approximately 26 to 2600 micrograms/liter (10 to 1000 ppm at 615 Torr, 23 degrees C). Total metabolite formation was exponentially related to the benzene exposure concentration with one-half the maximal amount of metabolite formation occurring at 220 micrograms/liter (84 ppm) for B6C3F1 mice and 650 micrograms/liter (250 ppm) for F344/N rats. Total metabolites were higher in mice than in rats at any of the vapor concentrations used due mainly to the higher amount inhaled by mice. Saturation of overall metabolism in mice but not in rats at high doses by both routes of administration indicates species differences in metabolism of benzene.