Variability of urinary organophosphate esters (OPEs) during childhood: The HOME Study

Abstract

BACKGROUND AND AIM: Organophosphate esters (OPEs) are widely used as flame retardants and plasticizers. Previous research has shown that gestational exposure to OPEs is variable, but no studies have examined the patterns and variability of postnatal exposure to our best knowledge. METHODS: In a prospective birth cohort (HOME Study, Cincinnati, OH, USA), we measured urinary OPE metabolite concentrations three times (16 and 26 weeks of gestation, at delivery) during pregnancy and five times (ages 1, 2, 3, 5, 8 years) during childhood. We log10-transformed creatinine-standardized OPE metabolite concentrations. We calculated Spearman correlation coefficients between postnatal OPE metabolites at each time point. We then used linear mixed models to calculate intraclass correlation coefficients (ICCs) for metabolite concentrations across the five postnatal time points. We further examined the association between three prenatal measures and early childhood (ages 1, 2, 3 years) exposure and subsequent metabolite concentrations at ages 5 and 8 years, including the main effect and the interaction term with the subsequent time points of metabolite measurement using linear mixed models. RESULTS:We detected (2-chloroethyl) phosphate (BCEP), bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), and diphenyl phosphate (DPHP) in 79 to 100% of children. The median concentrations (µg/g creatinine) were 0.78-4.76 for BCEP, 4.02-7.42 for BDCIPP, and 2.57-11.48 for DPHP. We found moderate correlations between BCEP and BDCIPP (rs: 0.28-0.49, p 0.001) at all time points. ICCs for metabolites across five postnatal time points, however, indicated poor within-person correlation (0.09–0.25). Prenatal urinary DPHP concentrations were positively associated with postnatal DPHP concentrations at some time points. Positive associations between early (1-3 years) and late childhood concentrations (age 8 years) were found for BCEP and BDCIPP. CONCLUSIONS:We found high within-person variability of OPE exposure within children across the first 8 years of life, suggesting that multiple urine samples are needed to characterize children’s exposures to OPEs. KEYWORDS: Chemical exposures, Endocrine disrupting chemicals, Children's environmental health, Environmental epidemiology