Mortality Among Men and Women in the North American Synthetic Rubber Industry, 1943 to 2009

Human health risk assessment for exposures to 1,3-butadiene in the United States with input from an independent science advisory panel

A human health risk assessment was conducted for potential cancer and noncancer effects of 1,3-butadiene (BD) using best available science, data, and methodologies. An independent panel of experts was engaged to provide input and guidance on key decisions made in the quantitative assessment. BD biomarker data played an important role in quantifying species differences, human variation, and quantifying smoking exposures. The assessment included consideration of nineteen scenarios for potential worker exposures, each of which include characterization of the impact of respirator use, and seven scenarios for aggregate exposures to BD across pathways. Monte Carlo methods were used to characterize uncertainty and variation risks and hazards from exposures to BD. The results of this assessment support three general conclusions: (1) ambient air is generally not an important source of BD exposure to the U.S. population when compared to other sources; (2) exposures to BD in the US are not expected to pose an unreasonable risk of cancer or noncancer effects; and (3) the existing OSHA PEL of 1 ppm is considered to be protective of the potential cancer risks and noncancer hazards from BD exposures.

Exposure to volatile organic compounds and chronic respiratory disease mortality, a case-cohort study

BACKGROUND

Chronic respiratory diseases (CRDs) are the third leading cause of death worldwide. Data of the associations between specific volatile organic compounds (VOCs), a major component of air pollution and tobacco smoke, and subsequent CRD mortality in the general population are scarce.

METHODS

In a case-cohort analysis within the population-based Golestan cohort study (n = 50045, aged 40-75 years, 58% women, enrollment: 2004-2008, northeastern Iran), we included all participants who died from CRD during follow-up through 2018 (n = 242) as cases and stratified them into 16 strata defined by age, sex, residence, and tobacco smoking. Subcohort participants (n = 610) were randomly selected from all eligible cohort participants in each stratum, and sampling fractions were calculated. Baseline urine samples were used to measure 20 VOCs using ultra high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry. After excluding participants with previous history of CRDs, we used stratified Cox regression models weighted by the inverse sampling fractions (i.e. inverse probability weighting) adjusted for potential confounders, including urinary cotinine and pack-years of smoking, to calculate hazard ratios (HR) for the associations between biomarker tertiles and CRD mortality.

RESULTS

Data from 545 non-case, sub-cohort participants and 149 cases (69.1% chronic obstructive pulmonary disease, 13.4% asthma, 17.5% other CRDs) were assessed in this study. During a follow-up of 10.5 years, associations [2nd and 3rd vs. 1st tertiles, HR (95% confidence interval), p for trend] were observed between metabolites of acrolein [1.56 (0.64,3.79), 3.53 (1.53,8.16), 0.002] and styrene/ethylbenzene [1.17 (0.53,2.60), 3.24 (1.37,7.66), 0.005] and CRD mortality, which persisted after excluding the first four years of follow-up.

CONCLUSION

Our findings support prior research suggesting respiratory toxicity of VOCs. Further investigation and monitoring of these compounds, especially acrolein and styrene/ethylbenzene, as CRD risk factors, are recommended.

Styrene lung cancer risk assessment: an alternative evaluation of human lung cancer risk assuming mouse lung tumors are potentially human relevant and operating by a threshold-based non-genotoxic mode of action

Rodent inhalation studies indicate styrene is a mouse lung-specific carcinogen. Mode-of-action (MOA) analyses indicate that the lung tumors cannot be excluded as weakly quantitatively relevant to humans due to shared oxidative metabolites detected in rodents and humans. However, styrene also is not genotoxic following in vivo dosing. The objective of this review was to characterize occupational and general population cancer risks by conservatively assuming mouse lung tumors were relevant to humans but operating by a non-genotoxic MOA. Inhalation cancer values reference concentrations for respective occupational and general population exposures (RfCcar-occup and RfCcar-genpop) were derived from initial benchmark dose (BMD) modeling of mouse inhalation tumor dose-response data. An overall lowest BMDL10 of 4.7 ppm was modeled for lung tumors, which was further duration- and dose-adjusted by physiologically based pharmacokinetic (PBPK) modeling to derive RfCcar-occup/genpop values of 6.2 ppm and 0.8 ppm, respectively. With the exception of open-mold fiber reinforced composite workers not using personal protective equipment (PPE), the RfCcar-occup/genpop values are greater than typical occupational and general population human exposures, thus indicating styrene exposures represent a low potential for human lung cancer risk. Consistent with this conclusion, a review of styrene occupational epidemiology did not support a conclusion of an association between styrene exposure and lung cancer occurrence, and further supports a conclusion that the conservatively derived RfCcar-occup is lung cancer protective.

Exposure to polycyclic aromatic hydrocarbons, volatile organic compounds, and tobacco-specific nitrosamines and incidence of esophageal cancer

BACKGROUND

Studying carcinogens in tobacco and nontobacco sources may be key to understanding the pathogenesis and geographic distribution of esophageal cancer.

METHODS

The Golestan Cohort Study has been conducted since 2004 in a region with high rates of esophageal squamous cell carcinoma. For this nested study, the cases comprised of all incident cases by January 1, 2018; controls were matched to the case by age, sex, residence, time in cohort, and tobacco use. We measured urinary concentrations of 33 exposure biomarkers of nicotine, polycyclic aromatic hydrocarbons, volatile organic compounds, and tobacco-specific nitrosamines. We used conditional logistic regression to calculate odds ratios (ORs) and 95% confidence intervals for associations between the 90th vs the 10th percentiles of the biomarker concentrations and incident esophageal squamous cell carcinoma.

RESULTS

Among individuals who did not currently use tobacco (148 cases and 163 controls), 2 acrolein metabolites, 2 acrylonitrile metabolites, 1 propylene oxide metabolite, and one 1,3-butadiene metabolite were significantly associated with incident esophageal squamous cell carcinoma (adjusted odds ratios between 1.8 and 4.3). Among tobacco users (57 cases and 63 controls), metabolites of 2 other volatile organic compounds (styrene and xylene) were associated with esophageal squamous cell carcinoma (OR = 6.2 and 9.0, respectively). In tobacco users, 2 tobacco-specific nitrosamines (NNN and N'-Nitrosoanatabine) were also associated with esophageal squamous cell carcinoma. Suggestive associations were seen with some polycyclic aromatic hydrocarbons (especially 2-hydroxynaphthalene) in nonusers of tobacco products and other tobacco-specific nitrosamines in tobacco users.

CONCLUSION

These novel associations based on individual-level data and samples collected many years before cancer diagnosis, from a population without occupational exposure, have important public health implications.

An updated lymphohematopoietic and bladder cancers risk evaluation for occupational and environmental exposures to 1,3-butadiene

EPA designated 1,3-butadiene (BD) as a high priority chemical in December 2019 and is presently performing an evaluation under the Toxic Substances Control Act (TSCA). EPA's cancer dose-response assessment for BD was published in 2002 and was primarily based on a study on workers exposed to BD in the North American synthetic Styrene-Butadiene Rubber (SBR) Industry developed by the University of Alabama at Birmingham (UAB). EPA relied upon a Poisson regression of leukemia mortality data from this cohort (hereinafter referred to as the SBR study) to estimate the cancer potency of BD. At the time, the SBR cohort included more than 15,000 male workers that were followed up through 1991. The SBR cohort has undergone multiple updates over the past two decades. Most recently, Sathiakumar et al. (2021a, b) published an update, with 18 more years of follow up in addition to approximately 5,000 female workers and updated exposure concentration estimates. Recent EPA assessments (e.g., for ethylene oxide, USEPA 2016) based on epidemiological studies use Cox proportional hazards models because they offer better control of the effect of age in cancer development and are less restrictive than Poisson regression models. Here, we develop exposure-response models using standard Cox proportional hazards regression. We explore the relationship between six endpoints (all leukemia, lymphoid leukemia, myeloid leukemia, multiple myeloma, non-Hodgkin's lymphoma, and bladder cancer) and exposures to BD using the most recent exposure metrics and the most recent update of the SBR study. After adjusting for statistically significant covariates, an upper 95% confidence level on the cancer potency based on leukemia derived herein is 0.000086 per ppm, which is approximately 1,000-fold less than EPA's (2002) estimate of 0.08 per ppm and about 10-fold less than TCEQ's (2008) estimate of 0.0011 per ppm.

1,3-Butadiene: a ubiquitous environmental mutagen and its associations with diseases

1,3-Butadiene (BD) is a petrochemical manufactured in high volumes. It is a human carcinogen and can induce lymphohematopoietic cancers, particularly leukemia, in occupationally-exposed workers. BD is an air pollutant with the major environmental sources being automobile exhaust and tobacco smoke. It is one of the major constituents and is considered the most carcinogenic compound in cigarette smoke. The BD concentrations in urban areas usually vary between 0.01 and 3.3 μg/m³ but can be significantly higher in some microenvironments. For BD exposure of the general population, microenvironments, particularly indoor microenvironments, are the primary determinant and environmental tobacco smoke is the main contributor. BD has high cancer risk and has been ranked the second or the third in the environmental pollutants monitored in most urban areas, with the cancer risks exceeding 10^-5. Mutagenicity/carcinogenicity of BD is mediated by its genotoxic metabolites but the specific metabolite(s) responsible for the effects in humans have not been determined. BD can be bioactivated to yield three mutagenic epoxide metabolites by cytochrome P450 enzymes, or potentially be biotransformed into a mutagenic chlorohydrin by myeloperoxidase, a peroxidase almost specifically present in neutrophils and monocytes. Several urinary BD biomarkers have been developed, among which N-acetyl-S-(4-hydroxy-2-buten-1-yl)-L-cysteine is the most sensitive and is suitable for biomonitoring BD exposure in the general population. Exposure to BD has been associated with leukemia, cardiovascular disease, and possibly reproductive effects, and may be associated with several cancers, autism, and asthma in children. Collectively, BD is a ubiquitous pollutant that has been associated with a range of adverse health effects and diseases with children being a subpopulation with potentially greater susceptibility. Its adverse effects on human health may have been underestimated and more studies are needed.

1,3-Butadiene, styrene and lymphohaematopoietic cancers among North American synthetic rubber polymer workers: exposure-response analyses

OBJECTIVE

To evaluate exposure-response between 1,3-butadiene, styrene and lymphohaematopoietic cancers in an updated cohort of workers at six North American plants that made synthetic rubber polymers.

METHODS

Employees were followed from 1943 through 2009 to determine mortality outcomes. Cox regression analyses estimated rate ratios (RRs) and 95% CIs by quartile of cumulative exposure to butadiene or styrene, measured in parts per million-years (ppm-years), and exposure-response trends for all leukaemia, lymphoid leukaemia, myeloid leukaemia, acute myeloid leukaemia, non-Hodgkin's lymphoma (NHL), multiple myeloma and all B-cell malignancies.

RESULTS

Among 21 087 workers, adjusted RRs for butadiene and all leukaemia (132 deaths) rose with increasing exposure, with an RR of 2.53 (95% CI 1.37 to 4.67) in the highest exposure quartile (≥363.64 ppm-years), and the exposure-response trend was statistically significant for all leukaemia (p=0.014) and for lymphoid leukaemia (52 deaths, p=0.007). Styrene exposure-response trends for all leukaemia and lymphoid leukaemia were less consistent than those for butadiene. Cumulative exposures to butadiene and styrene were not associated consistently with myeloid leukaemias or the B-cell malignancies, NHL and multiple myeloma.

CONCLUSIONS

We confirmed a positive exposure-response relationship between butadiene and all leukaemia among workers, most of whom had coexposure to styrene. Results supported an association between butadiene and lymphoid leukaemia, but not myeloid leukaemia, and provided little evidence of any association of butadiene or styrene exposures with major subtypes of B-cell malignancies other than lymphoid leukaemia, including NHL and multiple myeloma.

A reproductive and developmental toxicity screening study of 1,3-butadiene in Sprague-Dawley rats

1,3 Butadiene (BD) is an industrial intermediate used primarily in product manufacturing with the greatest exposure potential via inhalation. BD was evaluated for reproductive and developmental effects in a Good Laboratory Practice (GLP)-compliant, extended OECD 421 guideline study (completed 2003). Twelve-week old rats (12/sex/dose) were exposed via whole-body inhalation to BD vapor (0, 300, 1500, 6000 ppm) for 6 h/day, 7 days/week, starting 14 days prior to mating through the day prior to euthanasia (total exposures: 83-84 days for F0 males 60-70 days for F0 females). Select F1 offspring (1/sex/litter) were dosed 7 days (postnatal days 21-27 or 28-34), then necropsied. At 1500 and 6000 ppm, treatment-related facial soiling was seen in F0 males and females with decreased body weights/gains in F0 males. F1 males and females exhibited similar effects at 1500 and 6000 ppm. Importantly, the F0 generation had no evidence of altered sperm production, testicular effects, or ovarian atrophy, which were sensitive responses in mice. The no-observed-adverse-effect-level (NOAEL) is 300 ppm due to decreased body weight/gain and facial soiling at 1500 ppm, whereas 6000 ppm serves as a NOAEL for reproductive and developmental endpoints. This study contributes to the weight-of-evidence of differential BD reproductive toxicity in rats and mice.

1,3-Butadiene, styrene and selected outcomes among synthetic rubber polymer workers: Updated exposure-response analyses

OBJECTIVE

- To evaluate exposure-response relationships between 1,3-butadiene and styrene and selected diseases among synthetic rubber polymer workers.

METHODS

- 21,087 workers (16,579 men; 4508 women) were followed from 1943 through 2009 to determine mortality outcomes. Cox regression models estimated rate ratios (RRs) and 95% confidence intervals (CIs) by quartile of cumulative exposure to butadiene or styrene and exposure-response trends for cancers of the bladder, lung, kidney, esophagus and pancreas, and for all nonmalignant respiratory disease (NMRD), chronic obstructive pulmonary disease (COPD) and pneumonia.

RESULTS

- Bladder cancer RRs were 2.13 (95% CI = 1.03 to 4.41) and 1.64 (95% CI = 0.76 to 3.54) in the highest quartiles of cumulative exposure to butadiene and styrene, respectively, and exposure-response trends were positive for both monomers (butadiene, trend p = 0.001; styrene, trend p = 0.004). Further analyses indicated that the exposure-response effect of each monomer on bladder cancer was demonstrated clearly only in the subgroup with high cumulative exposure (at or above the median) to the other monomer. Lung cancer was not associated with either monomer among men. Among women, lung cancer RRs were above 1.0 in each quartile of cumulative exposure to each monomer, but exposure-response was not seen for either monomer. Male workers had COPD RRs slightly above 1.0 in each quartile of cumulative exposure to each monomer, but there was no evidence of exposure-response among the exposed. Monomer exposure was not consistently associated with COPD in women or with the other cancer outcomes.

CONCLUSIONS

- This study found a positive exposure-response relationship between monomer exposures and bladder cancer. The independent effects of butadiene and styrene on this cancer could not be delineated. In some analyses, monomer exposure was associated with lung cancer in women and with COPD in men, but inconsistent exposure-response trends and divergent results by sex do not support a causal interpretation of the isolated positive associations.

Development of a Questionnaire for the Search for Occupational Causes in Patients with Non-Hodgkin Lymphoma: The RHELYPRO Study

Non-Hodgkin lymphoma (NHL), multiple myeloma and chronic lymphocytic leukemia are possibly related to environmental and/or occupational exposure. The primary objective of this study was to develop a questionnaire for screening patients with these blood disorders who might benefit from a specialized consultation for possible recognition of the disease as an occupational disease. The study included 205 subjects (male gender, 67.3%; mean age, 60 years; NHL, 78.5%). The questionnaire performed very satisfactorily in identifying the exposures most frequently retained by experts for their potential involvement in the occurrence of NHL. Its sensitivity and specificity in relation to the final expertise were 96% and 96% for trichloroethylene, 85% and 82% for benzene, 78% and 87% for solvents other than trichloroethylene and dichloromethane, 87% and 95% for pesticides, respectively. Overall, 15% of the subjects were invited to ask National Social Insurance for compensation as occupational disease. These declarations concerned exposure to pesticides (64%), solvents (trichloroethylene: 29%; benzene: 18%; other than chlorinated solvents: 18%) and sometimes multiple exposures. In conclusion, this questionnaire appears as a useful tool to identify NHL patients for a specialized consultation, in order to ask for compensation for occupational disease.

Cancer surveillance among workers in plastics and rubber manufacturing in Ontario, Canada

OBJECTIVE

Occupational exposure to agents in plastics and rubber manufacturing has been associated with elevated risk of certain cancers. We sought to evaluate cancer risk among workers employed in occupations and industries with these exposures as part of an ongoing surveillance programme in Ontario, Canada.

METHODS

The Occupational Disease Surveillance System (ODSS) cohort was established using workers' compensation claims data and includes 2.18 million workers employed from 1983 to 2014. Workers were followed for site-specific cancer diagnoses in the Ontario Cancer Registry through 2016. Cox proportional hazard models were used to estimate adjusted HR and 95% CI.

RESULTS

We identified 81 127 workers employed in plastics and rubber manufacturing industries or materials processing and product fabricating occupations. Compared with all other women in the ODSS, those in materials processing occupations had an elevated rate of lung cancer (HR 1.38, 95% CI 1.20 to 1.58) that was not observed among men. An elevated rate of breast cancer was observed among female labourers (HR 1.36, 95% CI 1.01 to 1.82) and moulders (HR 1.47, 95% CI 0.91 to 2.37) in plastics and rubber product fabricating occupations. Overall, elevated rates were observed for oesophageal, liver, stomach, prostate and kidney cancer in job-specific subgroups, including mixing and blending, bonding and cementing, and labouring. There was little evidence of association for lymphatic or haematopoietic cancers.

CONCLUSIONS

Findings for lung and breast cancer in women are consistent with other studies and warrant further attention in Ontario. Given the relatively young age at end of follow-up, surveillance in these workers should continue as the cohort ages.

Exposure-response assessment of cancer mortality in styrene-exposed boatbuilders

OBJECTIVES

To improve exposure estimates and reexamine exposure-response relationships between cumulative styrene exposure and cancer mortality in a previously studied cohort of US boatbuilders exposed between 1959 and 1978 and followed through 2016.

METHODS

Cumulative styrene exposure was estimated from work assignments and air-sampling data. Exposure-response relationships between styrene and select cancers were examined in Cox proportional hazards models matched on attained age, sex, race, birth cohort and employment duration. Models adjusted for socioeconomic status (SES). Exposures were lagged 10 years or by a period maximising the likelihood. HRs included 95% profile-likelihood CIs. Actuarial methods were used to estimate the styrene exposure corresponding to 10^-4 extra lifetime risk.

RESULTS

The cohort (n= 5163) contributed 201 951 person-years. Exposures were right-skewed, with mean and median of 31 and 5.7 ppm-years, respectively. Positive, monotonic exposure-response associations were evident for leukaemia (HR at 50 ppm-years styrene = 1.46; 95% CI 1.04 to 1.97) and bladder cancer (HR at 50 ppm-years styrene =1.64; 95% CI 1.14 to 2.33). There was no evidence of confounding by SES. A working lifetime exposure to 0.05 ppm styrene corresponded to one extra leukaemia death per 10 000 workers.

CONCLUSIONS

The study contributes evidence of exposure-response associations between cumulative styrene exposure and cancer. Simple risk projections at current exposure levels indicate a need for formal risk assessment. Future recommendations on worker protection would benefit from additional research clarifying cancer risks from styrene exposure.