Occupational epidemiological study of workers in an acrylonitrile using factory with particular attention to cancers and birth defects

Epidemiology of lung cancer among acrylonitrile-exposed study populations: A meta-analysis

PURPOSE

To conduct a systematic review and meta-analysis of lung cancer among acrylonitrile-exposed workers.

METHODS

A literature search through April 2020 was performed to identify relevant cohort and case-control studies. Data from these studies were meta-analyzed to generate summary relative risk estimates (SRREs). Heterogeneity was examined in sub-group and sensitivity analyses, and by meta-regression.

RESULTS

Twenty-two studies were reviewed systematically, and 10 cohort studies and one case-control study were meta-analyzed. Individual relative risk estimates reported across studies were heterogeneous, with most being relatively weak in statistical strength and non-statistically significant on both sides of the null value. Meta-analysis of these data resulted in an SRRE of 1.04 (95% CI: 0.89-1.21; overall model, largely consisting of all workers exposed to acrylonitrile). Sub-group analyses and meta-regression did not support patterns of positive dose-response relationships by duration of exposure/employment or cumulative exposure.

CONCLUSIONS

Although some positive associations have been reported in internal comparison analyses based on increasing exposure categories, few associations are statistically significant, there are no apparent or consistent patterns of dose-response, and the confounding influence of cigarette smoking was not adequately controlled. Thus, findings from this review and meta-analysis do not support an increased risk of lung cancer among acrylonitrile workers.

Weight-of-the-evidence review of acrylonitrile reproductive and developmental toxicity studies

Risk assessment of acrylonitrile (AN) toxicity to humans has focused on potential carcinogenicity and acute toxicity. Epidemiological studies from China reported reproductive and developmental effects in AN workers, including infertility, birth defects, and spontaneous abortions. A weight-of-the-evidence (WoE) evaluation of the AN database assessed study strength, characterized toxicity, and identified no-observed-adverse-effect levels (NOAELs). The epidemiological studies do not demonstrate causality and are not sufficiently robust to be used for risk assessment. Rodent developmental studies showed fetotoxicity and malformations at maternally toxic levels; there was no unique developmental susceptibility. NOAELs for oral and inhalation exposures were 10 mg/kg/day and 12 ppm (6 h/day), respectively. Drinking-water and inhalation reproductive toxicity studies showed no clear effects on reproductive performance or fertility. Maternally toxic concentrations caused decreased pup growth. The drinking-water reproductive NOAEL was 100 ppm (moderate confidence due to study limitations). The inhalation exposure reproductive and neonatal toxicity high confidence NOAEL was 45 ppm (first generation 90 ppm) (6 h/day). The inhalation reproductive toxicity study provides the most robust data for risk assessment. Based on the WoE evaluation, AN is not expected to be a developmental or reproductive toxicant in the absence of significant maternal toxicity.

Acrylonitrile and cancer: a review of the epidemiology

Several retrospective cohort epidemiology studies evaluated a number of health outcomes in workers exposed to acrylonitrile (AN). The epidemiology studies included in this review have been published since 1970 and were identified through Ovid and MEDLINE retrieval services using search words "acrylonitrile and cancer". We identified 26 studies which examined mortality and/or incidence rates among persons with AN exposure. Where cohorts have been updated the most recent data were relied upon but descriptions of the earlier publications are provided for background and rationale. Results are provided for all causes of death and all cancers. Detailed results and discussions are provided for the cancers which have received the most attention and for which some positive results have been reported. These include lung, bladder, prostate, and central nervous system cancers. In this review the four most informative cohort studies are evaluated and it is apparent that the results do not support a causal relationship between AN and all cancers or any specific type of cancer. IARC actually downgraded acrylonitrile from "probably carcinogenic" to "possibly carcinogenic to humans" finding that "the earlier indications of an increased risk among workers exposed to acrylonitrile were not confirmed by the recent, more informative studies". This was one of few downgrades of classification by IARC. Our review of the epidemiology data is consistent with the conclusions of the earlier IARC review which found no consistent findings of increased cancer risk across studies.

Analysis of geographical clustering of birth defects in Heshun county, Shanxi province

Birth defects remain the leading cause of stillbirth and infant mortality in China, especially in rural areas. The objective of this research is to seek evidence of clustering of cases of birth defects within a highly endemic area and to identify the environmental and landscape characteristics associated with increased risk for birth defects in Heshun county. This study uses four years of data, 1998-2001, to identify clusters of birth defects in Heshun county. A spatial scan statistic was employed to examine the spatial and spatio-temporal clustering of birth defects in the study area. Statistically significant clusters with high relative risk (RR = 2.981, p = 0.008) were identified using a spatial scan statistic. The spatial cluster located in southeast Heshun county has a radius of 7.52 km and includes 27 villages and 27 cases, accounting for 21.25% of the total cases during the study period. The methodology applied in this study was useful for evaluating the spatial distribution of birth defects in Heshun county from 1998-2001. The identified areas may be critical to control birth defects and may provide important direction for further study and targeted interventions.

Occupational acrylonitrile exposure and lung cancer: a meta-analysis

The present work summarizes the currently available published studies on lung cancer and occupational acrylonitrile exposure. Meta-analytic methods were used to estimate the overall risk. To adjust for the healthy worker effect, rate ratio estimates based on regression analyses and ratios of standard mortality ratios were aggregated. Overall effect estimates were 0.95 (95% CI 0.86 to 1.06) and 1.25 (95% CI 1.10 to 1.43) before and after adjustment for the healthy worker effect, respectively. Therefore, a 25% increase in lung cancer risk attributable to occupational acrylonitrile exposure is suggested. Possible contribution of smoking confounding the increased risk cannot be fully excluded.