Organophosphate and Organohalogen Flame-Retardant Exposure and Thyroid Hormone Disruption in a Cross-Sectional Study of Female Firefighters and Office Workers from San Francisco

Abstract

Occupational exposures to flame retardants (FRs), a class of suspected endocrine-disrupting compounds, are of health concern for firefighters. We sought to characterize exposure to FR compounds and evaluate their association with thyroid hormone levels, a biomarker of early effect, in female firefighters and office workers in San Francisco. In a cross-sectional study, we measured replacement organophosphate and organohalogen FRs in spot urine samples from firefighters (N = 86) and office workers (N = 84), as well as total thyroxine (T₄) and thyroid-stimulating hormone in plasma for 84 firefighters and 81 office workers. Median bis(1,3-dichloro-2-propyl)phosphate (BDCPP) levels were 5 times higher in firefighters than office workers. Among firefighters, a doubling of BDCPP was associated with a 2.88% decrease (95% confidence interval -5.28, -0.42) in T₄. We did not observe significant associations between FRs and T₄ among office workers. In the full group, intermediate body mass index and a college education were associated with higher FR levels. The inverse association observed between FRs and T₄ coupled with the lack of studies on women workers and evidence of adverse health effects from FR exposure─including endocrine disruption and breast cancer risk─warrant further research on occupational exposures and identification of opportunities for exposure reduction.

Keywords: bis(1,3-dichloro-2-propyl)phosphate; endocrine disruption; firefighters; flame retardants; thyroid hormone.

Figure 1

Distribution (median, IQR, and 95th percentile) of FRs (μg/g-creatinine) in urine from 86 firefighters and 84 office workers of the Women Firefighters Biomonitoring Collaborative (WFBC) (2014–15). We substituted values below the LOD with . Significance stars represent the p-value from the permutation test of the difference in the average chemical level between firefighters and office workers: *** <0.001; ** <0.05; and * <0.1.