Prenatal exposure to mixtures of persistent environmental chemicals and fetal growth outcomes in Western Australia

Abstract

Background: Environmental chemicals have been implicated in the etiology of impaired fetal growth; however, few studies have assessed the effects of chemical mixtures or considered the possibility of non-monotonic exposure–response relationships for chemicals that act through the endocrine system. Methods: We assessed exposure to polybrominated diphenyl ethers, organochlorine pesticides, metals, and perfluoroalkyl substances in blood and urine samples collected two weeks prior to delivery in 166 non-smoking pregnant women, and subsequent birth weight, length, and head circumference of neonates who were part of the Australian Maternal Exposures to Toxic Substances (AMETS) study. We used Bayesian structured additive regression models with spike–slab priors to estimate mixture effects, identify important exposures, and model non-linearity in exposure–response relationships. Results: An increase in cesium exposure measured in whole blood from the 10th to 90th percentile was associated with a reduction in both birth weight (-236.5 g, 90% credible interval: -458.1 to -6.5 g) and the proportion of optimal birth weight (-8.6%, 90% credible interval: -14.8 to -0.4%), after adjusting for potential confounders. We identified several other chemicals and mixtures that may be associated with fetal growth, some non-linearly; however, 90% credible intervals contained the null. Conclusions: Using a Bayesian penalised regression method that is robust to multicollinearity, we assessed the shapes of exposure–response relationships, controlled for confounding by co-exposure, and estimated the single and combined effects of a large mixture of correlated environmental chemicals on fetal growth. While exposure concentrations in the AMETS study were generally low, our findings suggest that cesium exposure is associated with a reduction in birth weight. The potential for non-monotonic relationships between environmental chemicals and fetal growth outcomes warrants further study.