A hematology survey of workers at a styrene-butadiene synthetic rubber manufacturing plant

Industry-wide review of potential worker exposure to 1,3-butadiene during chemical manufacturing and processing as a reactant

Among the first 20 high-priority chemical substances selected by USEPA to undergo risk evaluation as part of the Toxic Substances Control Act, as amended by the Frank R. Lautenberg Chemical Safety for the 21st Century Act of 2016 is 1,3-butadiene (1,3-BD). Because much of the literature related to occupational exposure to 1,3-BD is associated with the use of the substance in synthetic rubber production and few data have been published for exposures to 1,3-BD manufacturing workers, existing industrial hygiene data collected at facilities where the substance is manufactured or processed as a reactant were compiled and analyzed. The dataset was comprised of personal air samples collected between 2010 and 2019 at facilities located throughout the United States and was compiled into a single database using a uniform data collection template. Data designated by the companies as full-shift were stratified by job group and one of three operational conditions of the workplace: routine, turnaround, and non-routine. Data designated by the companies as short-term and task-level were stratified by task description, sample duration, and operational condition. The final aggregated database contained a total of 5,676 full-shift personal samples. Mean concentrations of 1,3-BD for the job groups ranged from 0.012 ppm to 0.16 ppm. High-end estimates of 1,3-BD air concentrations for the job groups under routine operations ranged from 0.014 ppm to 0.23 ppm. The aggregated database also included 1,063 short-term and task-level personal samples. For short-term samples (< =15 min), mean concentrations ranged from 0.49 ppm to 3.9 ppm, with the highest concentrations observed for the cleaning and maintaining equipment tasks. For task samples with durations greater than 15 min, mean concentrations ranged from 0.49 to 3.6 ppm, with the highest concentrations observed for the unloading and loading task. In addition to the personal air sampling records, information on the use of PPE during various tasks was compiled and analyzed. This data set provides robust quantitative air concentration data and exposure control information for which occupational exposures to 1,3-BD in the Manufacturing and Processing as a Reactant condition of use can be assessed.

Diepoxybutane-induced apoptosis is mediated through the ERK1/2 pathway

Diepoxybutane (DEB) is the most potent active metabolite of butadiene, a regulated air pollutant. We previously reported the occurrence of DEB-induced, p53-dependent, mitochondrial-mediated apoptosis in human lymphoblasts. The present study investigated the role of the extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) pathway in DEB-induced apoptotic signaling in exposed human lymphoblasts. Activated ERK1/2 and mitogen-activated protein (MAP) kinase/ERK1/2 kinase (MEK) levels were significantly upregulated in DEB-exposed human lymphoblasts. The MEK inhibitor PD98059 and ERK1/2 siRNA significantly inhibited apoptosis, ERK1/2 activation, as well as p53 and phospho-p53 (serine-15) levels in human lymphoblasts undergoing DEB-induced apoptosis. Collectively, these results demonstrate that DEB induces apoptotic signaling through the MEK-ERK1/2-p53 pathway in human lymphoblasts. This is the first report implicating the activation of the ERK1/2 pathway and its subsequent role in mediating DEB-induced apoptotic signaling in human lymphoblasts. These findings contribute towards the understanding of DEB toxicity, as well as the signaling pathways mediating DEB-induced apoptosis in human lymphoblasts.

1,3-Butadiene: III. Assessing carcinogenic modes of action

1,3-Butadiene (BD) is a multisite carcinogen in laboratory rodents following lifetime exposure, with greater potency in the mouse than the rat, and is associated with an increase in leukemia mortality in highly exposed workers. Species differences in the formation of reactive metabolites underlie observed species differences in sensitivity to the carcinogenic effects of BD. The modes of action (MOAs) for human leukemia and rodent tumors are both likely related to mutagenic potencies of one or more of these metabolites. However, differences in the nature of genotoxic lesions associated with human leukemia and rodent tumors, along with their implications for risk assessment, require that they be discussed separately. The MOAs for BD are assessed in this review using the modified Hill criteria and human relevance framework. Key events in MOAs for human and rodent cancers are identified, along with important species differences and sources of nonlinearity for each event that can affect extrapolations made from high- to low-dose exposures. Because occupational exposures to BD have also included co-exposures to styrene and dimethyldithiocarbamide (DMDTC), potential interactions with BD carcinogenicity are also discussed. The MOAs for BD carcinogenesis will be used to guide key decisions made in the quantitative cancer dose-response assessment.

A hematology surveillance study of petrochemical workers exposed to 1,3 butadiene

Complete blood counts (CBC) have been recognized as an easy and readily available screen for hematotoxicity following occupational exposure to 1,3-butadiene. This study evaluated hematology data from employees who have ever participated in the Shell Butadiene Medical Surveillance Program (BMSP), compared with employees who have not participated. This study examined potential hematopoietic toxicity in relation to the occupational exposures at two Shell facilities. This study included 404 employees who participated in the BMSP, with mean butadiene exposure (TWA-8, TWA-10, and TWA-12 together) of 4.55 ppm from 1979-1996 and 0.25 ppm from 1997-2003, and 773 comparison employees. The comparison group included employees not participating in either the benzene or butadiene surveillance programs. Abnormality of six CBC parameters, including white blood cell count, red blood cell count, lymphocyte count, hemoglobin concentration, mean corpuscular volume and platelet count, and the adjusted mean values of these parameters in the exposed group were compared with those of the comparison group. We found no significantly increased abnormality for any hematology parameter among exposed employees. The adjusted mean values (adjusted for age, sex, race, length of time between first and last exam, current smoking status, and first exam value) of the exposed employees were similar to those in the comparison group. At current occupational exposure levels for 1,3-butadiene, there is no evidence of adverse hematological effects observed in this study. These findings are consistent with results of three similar studies in the literature.

Hematological changes due to chronic exposure to natural gas leakage in polluted areas of Masjid-i-Sulaiman (Khozestan province, Iran)

An overwhelming number of studies have given consistent findings that environmental or occupational exposure to oil products results in a significant decrease in circulating erythrocytes, hemoglobin, platelets, total white blood cells, and absolute numbers of lymphocytes and neutrophils. Some parts of Masjid-i-Sulaiman (located in the southwest of Iran) are contaminated by subsurface leakage of natural gas, which contains a high level of hydrogen sulfide. The amount of all reactive sulfur compounds in air of contaminated areas of MIS was estimated as equal to 0.023+/-0.002 ppm of SO(2). In the present report the hematological findings of 99 persons from polluted areas of MIS were compared with those of 396 individuals from the general population of MIS matched by age (+/-3 years) and sex. The CBC test and the WBC differential were analyzed in one central laboratory according to standard hematological methods, by Coulter S (Biomedical). The multiple linear regression method was applied in order to detect differences among exposed and unexposed groups for hematological markers. The absolute mean number of red blood cells, percentages of hematocrit, level of hemoglobin, and absolute number of platelets were significantly higher among the exposed subjects compared with the control group. However, the absolute mean numbers of white blood cells, lymphocytes, and neutrophils were significantly decreased in the exposed group compared with the control.

Diepoxybutane induces caspase and p53-mediated apoptosis in human lymphoblasts

Diepoxybutane (DEB) is the most potent metabolite of the environmental chemical 1,3-butadiene (BD), which is prevalent in petrochemical industrial areas. BD is a known mutagen and human carcinogen, and possesses multiorgan systems toxicity that includes bone marrow depletion, spleen, and thymus atrophy. Toxic effects of BD are mediated through its epoxy metabolites. In working towards elucidating the cellular and molecular mechanisms of BD toxicity, we investigated the ability of DEB to induce apoptosis in human lymphoblasts. DEB induced a concentration and exposure time-dependent apoptosis, which accounted for the DEB-induced loss of cell viability observed in TK6 lymphoblasts. The DEB-induced apoptosis was inhibited by inhibitors of caspases 3 and 9. The role of p53 in mediating the DEB-induced apoptosis was also investigated. DEB induced elevated p53 levels in direct correlation to the extent of DEB-induced apoptosis, as the concentration of DEB increased up to 5 microM. The extent of DEB-induced apoptosis was dramatically higher in TK6 lymphoblasts as compared to the genetically paired p53-deficient NH32 lymphoblasts under the same experimental conditions. Our results confirm and extend observations on the occurrence of apoptosis in DEB exposed cells, and demonstrate for the first time the elevation of p53 levels in human lymphoblasts in response to DEB exposure. In addition, our results demonstrate for the first time that DEB-induced apoptosis is mediated by caspases 3 and 9, as well as the p53 protein. It is possible that DEB-induced apoptosis may explain BD-induced bone marrow depletion, spleen and thymus atrophy in BD-exposed animals.

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.

Markers for carcinogenicity among butadiene-polymer workers in China

We examined a spectrum of genotoxic and other outcomes in 41 butadiene-polymer production workers and 38 nonexposed controls, in China, to explore the role of butadiene in human carcinogenesis. Among butadiene-exposed workers, median air exposure was 2 ppm (6-h TWA), due largely to intermittent high-level exposures. Compared to unexposed subjects, butadiene-exposed workers had greater levels of hemoglobin N-(2,3,4-trihydroxybutyl)valine (THBVal) adducts (P<0.0001), and adduct levels tended to correlate, among butadiene-exposed workers, with air measures (P=0.03). Butadiene-exposed workers did not differ, however, from unexposed workers with respect to frequency of uninduced or diepoxybutane-induced sister chromatid exchanges, aneuploidy as measured by fluorescence in situ hybridization of chromosomes 1, 7, 8 and 12, glycophorin A variants or lymphocyte hprt somatic mutation. Also among the exposed, greater THBVal levels were not associated with increases in uninduced sister chromatid exchanges, aneuploidy, glycophorin A, or hprt mutations. Butadiene-exposed workers had greater lymphocyte (P=0.002) and platelet counts (P=0.07) and lymphocytes as a percent of white blood cells were moderately correlated with greater THBVal levels (Spearman's rho=0.32, P=0.07). Among butadiene-exposed workers, several serum cytokines correlated with THBVal adduct levels. Overall, the study demonstrated exposure to butadiene in these workers, by a variety of short-term and long-term measures, but did not show specific genotoxic effects, at the chromosomal or gene levels, related to that exposure.

A mortality, morbidity, and hematology study of petrochemical employees potentially exposed to 1,3-butadiene monomer

This three-part study is an update of a previous report that examined the mortality, morbidity, and hematological data of employees from a petrochemical facility in Texas who had potential exposure to 1,3-butadiene monomer. The first part describes the updated cause-specific mortality of 614 workers. Vital status for each cohort member was ascertained through 1998, a 9-year extension of the previous study. The second part is an examination of the morbidity experience of cohort members who were still working during 1992-1998, including 289 of the 614 mortality cohort members. The third part is an evaluation of the hematological results from routine health surveillance and/or medical examinations. Approximately 430 of the 614 employees who had complete blood count (CBC) data as of December 1999 were included in the hematological evaluations. The most recent examination containing CBC data was used and compared with similar data for over 2600 other employees from this facility. Overall mortality during the follow-up period, 1948-1998, was significantly lower than for the local comparison population (standardized mortality ratio (SMR) of 0.55 with a 95% confidence interval (CI) of 0.42-0.70). Mortality for all cancer was also significantly lower (SMR, 0.57; 95% CI, 0.32-0.92). Mortality for all lymphohematopoietic cancer was about the same as the comparison population (SMR, 1.06; 95% CI, 0.22-3.11). None of the cause-specific morbidity was in excess compared with an internal comparison group. There were no differences in the distribution or mean values of hematological variables (e.g. white blood cells, red blood cells, hemoglobin, platelets, mean corpuscular volume) between the butadiene cohort and the comparison group, or between a subgroup of workers in jobs with the highest potential for butadiene exposure (i.e. shipping) and the rest of the butadiene cohort. The findings of this study suggest that the butadiene exposure at this facility in the last 20 years does not pose a health hazard to employees.

Mortality, morbidity, and haematological results from a cohort of long-term workers involved in 1,3-butadiene monomer production

A retrospective mortality analysis and prospective morbidity and haematological analyses were performed for Shell Deer Park Manufacturing Complex (DPMC) male employees who worked in jobs with potential exposure to 1,3-butadiene from 1948 to 1989. 614 employees qualified for the mortality study (1948-89), 438 of those were still employed during the period of the morbidity study (1982-9), and 429 of those had haematological data available for analysis. Industrial hygiene data from 1979 to 1992 showed that most butadiene exposures did not exceed 10 ppm (eight-hour time weighted average (8 hour TWA)), and most were below 1 ppm, with an arithmetic mean of 3.5 ppm. 24 deaths occurred during the mortality study period. For all causes of death, the standardised mortality ratio (SMR) was 48 (95% confidence interval (95% CI) = 31-72), and the all cancer SMR was 34 (95% CI = 9-87). There were only two deaths due to lung cancer (SMR 42, 95% CI = 5-151) and none due to lymphohaematopoietic cancer (expected = 1.2). Morbidity (illness absence) events of six days or more for the 438 butadiene employees were compared with the rest of the complex. No cause of morbidity was in excess for this group; the all cause standardised morbidity ratio (SMbR) was 85 (95% CI = 77-93) and the all neoplasms SMbR was 51 (95% CI = 22-100). Haematological results for the 429 with laboratory data were compared with results for the rest of the complex. No significant differences occurred between the two groups and the distributions of results between butadiene and non-butadiene groups were virtually identical. These results suggest that butadiene exposures at concentrations common at DPMC in the past 10-20 years do not pose a health hazard to employees.

Assessment of the potential risk to workers from exposure to 1,3-butadiene

The available epidemiologic data provide equivocal evidence that 1,3-butadiene is carcinogenic in humans; some available studies suggest that the lymphopoietic system is a target, but there are inconsistencies among studies in the types of tumors associated with 1,3-butadiene exposure, and there is no evidence of a relationship between length of exposure and cancer risk, as one might expect if there was a true causal relationship between 1,3-butadiene exposure and cancer risk. The available chronic animal studies, however, show an increase in tumor incidence associated with exposure to high concentrations of 1,3-butadiene. In addition to the general uncertainty of the relevance of animal data to humans, there are several additional reasons why the National Toxicology Program's mouse study may not be appropriate for assessing possible human risks. These include: a) the possible involvement of a species-specific tumor virus (MuLV) in the response in mice; b) apparent differences between mice and humans in the rate of metabolism of 1,3-butadiene to reactive epoxides that may be proximate carcinogens; c) use of high dose levels that caused excess early mortality; and d) exposure of animals to 1,3-butadiene for only about half their lifetime. While recognizing the uncertainty in using the available animal data for risk assessment, we have performed low-dose extrapolation of the data to examine the implications of the data if humans were as sensitive as rats or mice to 1,3-butadiene, and to examine how the predictions of the animal data compare to that observed in the epidemiologic studies. With the mouse data, because the study was of less than lifetime duration, we have used the Hartley-Sielken time-to-tumor model to permit estimation of lifetime risk from the less than lifetime exposure of the study. With the rat data, we have used three plausible models for assessing low-dose risk: the multistage model, the Weibull model, and the Mantel-Bryan probit model. With both the rat and mouse data, we used information on how much 1,3-butadiene is retained by animals exposed to various concentrations of the chemical. This improves the accuracy of the low-dose extrapolation. When extrapolated to low-dose levels, mice appear to be at greater risk (by a factor of 5-fold to 40-fold) than rats. Some of this difference (a factor 3-fold to 5-fold) may be due to the faster rate of metabolism of 1,3-butadiene to, and higher blood levels of, epoxide derivatives in mice than in rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Hematological findings among styrene-exposed workers in the reinforced plastics industry

A cross-sectional survey of hematological parameters was carried out among 221 workers exposed to styrene in the reinforced plastics industry and 104 controls. Styrene exposure was assessed in both groups by monitoring urinary excretion of styrene metabolites (i.e. mandelic and phenylglyoxylic acids) in post-shift urinary samples collected over five consecutive days. Blood tests were performed with the same counter for all subjects. Information on factors liable to affect hematological parameters was collected from personal questionnaires completed by the workers. Urinary excretion of styrene metabolites varied from 15 to 3740 mg/g creatinine. Exposed subjects exhibited significantly lower mean values of neutrophils and mean corpuscular hemoglobin concentration (MCHC) than controls, and significantly higher mean values for monocytes and mean corpuscular volume. A dose-effect relationship was found for MCHC which decreased with urinary metabolite concentrations. These results remained statistically significant for all parameters after adjustment for age, sex, tobacco and alcohol consumption, place of residence (rural or urban) and time of blood sampling (morning or afternoon) with the exception of neutrophils whose relationship with exposure was essentially explained by smoking. These results are suggestive of a direct effect of styrene-exposure--in the range considered--on the statistical distribution of some hematological parameters.