Exposure to styrene and mortality from nonmalignant respiratory diseases

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.

Lung disease associated with occupational styrene exposure

Despite reports of pulmonary toxicity due to styrene, guidelines on acceptable styrene exposure levels have been based on risk of cancer and central nervous system and liver toxicity and not on respiratory effects. Many reports have linked exposure to styrene vapor in occupational settings to various forms of non-malignant pulmonary disorders including bronchiolitis, hypersensitivity pneumonitis, and occupational asthma. We report two cases in which the same tasks performed in a single workplace resulted in exposure to styrene vapor with subsequent development of acute respiratory symptoms associated with impaired gas exchange and imaging and histopathologic findings consistent with bronchiolitis and organizing pneumonia. Both patients gradually recovered once their workplace exposure to styrene was terminated. Clinicians, employers, and insurers should be aware of the potential for pulmonary toxicity from exposure to styrene.

Non-malignant respiratory disease among workers in industries using styrene-A review of the evidence

BACKGROUND

Asthma and obliterative bronchiolitis (OB) cases have occurred among styrene-exposed workers. We aimed to investigate styrene as a risk factor for non-malignant respiratory disease (NMRD).

METHODS

From a literature review, we identified case reports and assessed cross-sectional and mortality studies for strength of evidence of positive association (i.e., strong, intermediate, suggestive, none) between styrene exposure and NMRD-related morbidity and mortality.

RESULTS

We analyzed 55 articles and two unpublished case reports. Ten OB cases and eight asthma cases were identified. Six (75%) asthma cases had abnormal styrene inhalation challenges. Thirteen (87%) of 15 cross-sectional studies and 12 (50%) of 24 mortality studies provided at least suggestive evidence that styrene was associated with NMRD-related morbidity or mortality. Six (66%) of nine mortality studies assessing chronic obstructive pulmonary disease-related mortality indicated excess mortality.

CONCLUSIONS

Available evidence suggests styrene exposure is a potential risk factor for NMRD. Additional studies of styrene-exposed workers are warranted. Am. J. Ind. Med. 60:163-180, 2017. © 2016 Wiley Periodicals, Inc.

Mortality among styrene-exposed workers in the reinforced plastic boatbuilding industry

BACKGROUND

We updated mortality through 2011 for 5203 boat-building workers potentially exposed to styrene, and analysed mortality among 1678 employed a year or more between 1959 and 1978. The a priori hypotheses: excess leukaemia and lymphoma would be found.

METHODS

Standardised mortality ratios (SMRs) and 95% CIs and standardised rate ratios (SRRs) used Washington State rates and a person-years analysis programme, LTAS.NET. The SRR analysis compared outcomes among tertiles of estimated cumulative potential styrene exposure.

RESULTS

Overall, 598 deaths (SMR=0.96, CI 0.89 to 1.04) included excess lung (SMR=1.23, CI 0.95 to 1.56) and ovarian cancer (SMR 3.08, CI 1.00 to 7.19), and chronic obstructive pulmonary disease (COPD) (SMR=1.15, CI 0.81 to 1.58). Among 580 workers with potential high-styrene exposure, COPD mortality increased 2-fold (SMR=2.02, CI 1.08 to 3.46).

CONCLUSIONS

COPD was more pronounced among those with potential high-styrene exposure. However, no outcome was related to estimated cumulative styrene exposure, and there was no change when latency was taken into account. We found no excess leukaemia or lymphoma mortality. As in most occupational cohort studies, lack of information on lifestyle factors or other employment was a substantial limitation although we excluded from the analyses those (n=3525) who worked <1 year. Unanticipated excess ovarian cancer mortality could be a chance finding. Comparing subcohorts with potential high-styrene and low-styrene exposure, COPD mortality SRR was elevated while lung cancer SRR was not, suggesting that smoking was not the only cause for excess COPD mortality.

Mortality patterns among workers exposed to styrene in the reinforced plastic boatbuilding industry: an update

BACKGROUND

Mortality was updated through 1998 for 5,204 workers exposed to styrene between 1959 and 1978 at two reinforced plastic boatbuilding plants. The a priori hypothesis: leukemia and lymphoma excesses would be found.

METHODS

Standardized mortality ratios (SMR) and 95% confidence intervals (CI) used Washington State and U.S. rates.

RESULTS

Overall, 860 deaths occurred (SMR 1.09, CI 1.02-1.17), with excess mortality for esophageal cancer (n = 12, SMR 2.30, CI 1.19-4.02), prostate cancer (n = 24, SMR 1.71, CI 1.09-2.54), and accidents (n = 99, SMR 1.26, CI 1.02-1.53). Among 2,062 highly exposed workers, urinary tract cancer (n = 6, SMR 3.44, CI 1.26-7.50) and respiratory disease (n = 12, SMR 2.54, CI 1.31-4.44) rates were elevated. Urinary tract cancer SMR increased with duration of employment.

CONCLUSIONS

We found no excess leukemia or lymphoma mortality. Unanticipated excess urinary tract cancer and respiratory disease mortality, possibly associated with styrene exposure, are difficult to interpret and could be chance findings.

A meta-analysis of cohort studies describing mortality and cancer incidence among chemical workers in the United States and western Europe

We evaluated the mortality and cancer experience of employees of the chemical industry in the United States and western Europe, as reported in the peer-reviewed literature between 1966 and 1997 (>1 million workers and >15 million person-years). Cohort studies (N = 461) were grouped (N = 181) so that specific populations could be traced from the earliest to the most recently published report, and we extracted observed and expected numbers of cases for each of 35 mortality and 23 cancer incidence endpoints. We then generated standardized mortality ratios or standardized incidence ratios and 95% confidence intervals, and undertook meta-analyses of subcohorts (for example, gender, latency, or duration of employment), as well as the entire cohort. With few exceptions, the observed cause-specific mortality and site-specific cancer incidences were reassuring: overall, 10% fewer deaths were observed than expected. Fewer than expected deaths from all causes, cardiovascular disease, noncancer respiratory disease, cirrhosis of the liver, and external causes were observed, some or all of which may be attributed to a "healthy worker effect." Meta-analyses revealed weak to moderate excesses of lung and bladder cancers likely caused by occupational exposure to known human carcinogens. We also observed a 10-15% increase in lymphatic and hematopoietic cancers. Additional research is required to gain a more complete understanding of the potential role that methodology and environmental or occupational influences may play in these associations.

An application of the challenge assay in boat builders exposed to low levels of styrene--a feasibility study of a possible biomarker for acquired susceptibility

Sensitivity to carcinogens and susceptibility for malignant diseases may be related to genetic predisposition, e.g. polymorphisms in toxicant-metabolizing enzymes or DNA repair deficiencies. The latter may also be acquired by exposure to substances that interfere with DNA repair processes. Application of the challenge assay to an exposed population may allow scientists to study the interference of DNA repair as an acquired susceptibility phenomenon. The assay was therefore used in a feasibility study to evaluate its application. A group of 14 workers exposed to low levels of styrene (mean < 100 mg/m3 styrene in air; 35 micrograms/l styrene in blood) and a reference of seven controls were investigated for structural chromosomal aberrations using FISH. The rate of exchange-type aberrations per 100 metaphases was 0.14 (95% CI, 0.05-0.31) in controls and 0.22 (95% CI, 0.13-0.36) in exposed workers. The difference is not statistically significant. Interaction with DNA repair was measured in the 14 workers and 2 historical controls using the challenge assay. Exchange-type aberrations per 100 metaphases after X-ray challenge of 1.66 Gy were 13.26 (10.53-16.50) and 16.19 (15.00-17.40) for the controls and exposed, respectively. The difference is statistically significant (p < 0.038). Among the exposed group, the challenge response was also significantly correlated with the cumulative lifetime exposure to styrene (R2 = 0.3996; p < 0.015) but not with the current exposure as measured in blood (R2 = 0.0226; p = 0.700). The challenge responses in the short-term and long-term exposed subgroups were 15.55 (14.23-16.96) and 17.90 (15.64-20.39), respectively, based on sample sizes of 5 and 9, respectively. The difference was not significant. Hence, data from our study are consistent with the hypothesis that long-term exposure to styrene can interfere with DNA repair activities. The lack of statistically significant differences in some of the data may be due to the small sample size and a possible confounding by age in our investigation. Additional data from our ongoing study should clarify this uncertainty.