Temporal Trends in Phthalate Metabolite Exposure of Girls in the United States Across Sociodemographic Factors and Intersectional Social Identities: National Health and Nutrition Examination Survey 2001-2018

Exposure to phthalates during the pubertal window impacts chronic disease risk and temporal trends in exposure can inform public health initiatives. Characterize temporal trends in phthalate metabolite exposure for adolescent girls overall and by sociodemographic characteristics. We used the cross-sectional data from each cycle of the National Health and Nutrition Examination Survey from years 2001 to 2018. We restricted participants to ages of 8-14 with at least one urinary measurement of the selected 12 phthalate metabolites within the study period (n=2,063). We used multivariable linear regression to assess temporal trends for selected individual phthalate metabolite concentrations (ng/ml) and source groupings of parent metabolites (sum low and high molecular weight phthalates; ∑LMW and ∑HMW) overall and individually by sociodemographic characteristics (race/ethnicity), nativity, socioeconomic status (SES), intersection of race/ethnicity-SES) to assess for modification. Overall ∑HMW and ∑LMW concentrations declined between 2001 and 2018; however, only ∑LMW consistently differed by all sociodemographic characteristics. Trends in ∑LMW concentration were significantly higher across all racial/ethnic groups, ranging from an average of 35% (Other Hispanic) to 65% (Mexican American and non-Hispanic Black) higher than non-Hispanic White (all p-values<0.0001). Compared to non-Hispanic White, we observed an average decrease of 15% in MiBP for non-Hispanic Black (βSpline=-0.16, p<0.0001) and 28% for Other Hispanic (βSpline=-0.33, p=0.01) in 2011-2018 vs. 2001-2010. Summary and individual LMW metabolite phthalate concentrations were 11%-49% higher among low vs. high SES girls. LMW metabolites MBP and MiBP were on average 22% and 35% higher; respectively, among foreign born vs. U.S. born. Compared to non-Hispanic Whites, all racial/ethnic groups had statistically significant higher trends in ∑LMW concentration irrespective of SES status. Girls identifying with a historically disadvantaged racial/ethnic group have elevated ∑LMW concentrations irrespective of SES class; suggesting the need for interventions to mitigate exposure among the most historically disadvantaged strata.