Organophosphate Ester (OPE) Exposures and Asthma Morbidity Among Urban School-Aged Children in Baltimore City, Maryland

Abstract

BACKGROUND AND AIM: OPEs are used as flame retardants and plasticizers in many consumer products. Studies suggest OPEs may be linked with respiratory outcomes among children. We aimed to examine associations between OPEs and asthma morbidity among 179 mostly Black children (93%), aged 5-12 years with asthma enrolled in a panel study between 2009-2013¬ in Baltimore City. METHODS: The panel study included up to four seasonal, week-long in-home visits. We collected urine samples on visit-days 4 and 7 (n = 618 samples). We quantified concentrations of 9 OPE metabolites: bis(2-chloroethyl)phosphate(BCEtp), bis(1-chloro-2-propyl)phosphate(BCPP), bis(1-chloro-2-propyl)phosphate(BDCPP), di-benzylphosphate(DBuP), di-benzylphosphate(DBzP), di-o-cresylphosphate(DOCP), di-p-cresylphosphate(DPCP), diphenyl-phosphate(DPHP), and 2,3,4,5-tetrabromobenzoic acid(TBBA). At each visit, participants self-reported asthma symptoms. We calculated Spearman’s rank (continuous) and tetrachoric (binary) correlation coefficients to assess variability of concentrations on days 4 and 7 and intraclass correlation coefficients (ICCs) to assess variability by visit. We assessed associations between metabolite concentrations and asthma symptoms using logistic regression models with generalized estimating equations. We examined BDCPP and DPHP as continuous variables; dichotomized BCEtP, DBuP, and DPCP; and excluded others not frequently detected. We adjusted models for season, visit-day, age, race, sex, BMI, caregiver education, and household income. RESULTS:Detection frequencies were 95% for BDCPP and DPHP, 4.6-31.1% for BCEtP, DBuP and DPCP, respectively and 3% for all other metabolites. OPE concentrations on days 4 and 7 were moderately correlated (rho=0.3-0.6) with low reproducibility across visits (ICC=0.2-0.4). In adjusted models, higher DPHP concentrations were associated with greater odds of self-reported difficulty breathing (odds ratio [OR]: 2.0; 95%CI:1.1-3.6), activity limitation due to asthma (OR:1.6; 95%CI:1.0-2.8), and being bothered by asthma (OR:1.9; 95%CI:1.2-3.2). No associations were observed with other OPEs. CONCLUSIONS:In this predominantly pediatric Black cohort, higher DPHP concentrations were consistently associated with asthma symptoms. We did not observe consistent patterns of association between other OPE metabolites and asthma morbidity. KEYWORDS: Biomarkers of exposure, Respiratory outcomes, Children's environmental health, Environmental disparities, Environmental epidemiology