Does Early Life Phthalate Exposure Mediate Racial Disparities in Children’s Cognitive Abilities?

Abstract

BACKGROUND AND AIM: Early life exposure to phthalates is associated with diminished childhood cognitive abilities. However, it is unclear if disproportionate exposure to some phthalates among non-Hispanic Black individuals contributes to racial disparities in children’s intellectual abilities (e.g., IQ). Here, we assess the extent that phthalates mediate racial disparities in child IQ. METHODS: We used data from 253 mother-child pairs in Cincinnati, OH (HOME Study). We quantified urinary concentrations of eleven phthalate metabolites twice during pregnancy and up to six times in childhood (ages 1,2,3,4,5 and 8 years). We evaluated children’s cognitive abilities using the Wechsler Preschool and Primary Scale of Intelligence and Wechsler Intelligence Scale for Children at ages 5 and 8 years, respectively. Using causal mediation models, we quantified covariate-adjusted direct and indirect effects of race/ethnicity on child IQ through individual measurement-error corrected phthalate metabolite concentrations during gestation and childhood. RESULTS:Average IQ scores among non-Hispanic Black children (n=90) were 7.0-points lower (95% CI: -12.1, -1.8) than non-Hispanic White children (n=145) after adjustment for socioeconomic factors. Urinary monobenzyl phthalate (MBzP) and monoethyl phthalate (MEP) concentrations during childhood were 33-100% higher in non-Hispanic Black children than non-Hispanic White children. We found evidence that childhood MEP concentrations mediated the race-IQ association. For instance, the disparities in IQ scores between non-Hispanic Black and non-Hispanic White children would have been reduced by 1.9 points (95% CI: -4.7, 0.7), in the absence of childhood diethyl phthalate exposure, the parent metabolite of MEP, at age 2. Other phthalate metabolite concentrations during pregnancy or childhood did not mediate the race-IQ association. CONCLUSIONS:Children’s urinary concentrations of MEP partly mediated racial disparities in IQ scores among these children. While phthalate exposures do not fully explain racial disparities in IQ, reducing exposure to some phthalates might reduce IQ differences among non-Hispanic Black and non-Hispanic White children. KEYWORDS: Phthalates, children’s environmental health, Neurodevelopmental outcomes