Environmental chemical exposures and attention-deficit/hyperactivity disorder in U.S. children and adolescents: A non-targeted exposomic and mixture-based analysis

• ADHD prevalence was 7.4% among U.S. youth aged 6-15 years in NHANES 1999-2004. • ExWAS identified 9 chemical biomarkers linked to ADHD prevalence. • Five biomarkers remained significant after multiple comparison correction. • PFHxS, PFOS and three DEHP metabolites showed the strongest associations with ADHD. • The 5-biomarker mixture showed significant associations across all subgroups. The prevalence of attention-deficit/hyperactivity disorder (ADHD) among children and adolescents has increased in recent decades, with environmental chemical exposures increasingly recognized as potential risk factors. However, most prior studies have focused on individual chemicals, limiting the ability to detect complex exposure-outcome relationship. This study aimed to identify chemical biomarkers associated with ADHD, characterize potential exposure-response relationships, and evaluate joint effects of chemical mixtures using a multi-tiered exposomic framework. We analyzed data from 5,176 U.S. children and adolescents aged 6-15 years in the National Health and Nutrition Examination Survey (1999-2004). Survey-weighted Poisson regression models with robust standard error were used to examine associations between ADHD and 76 biomarkers with detection rates ≥50%. Among nine biomarkers associated with ADHD prevalence (unadjusted p <0.05), five met the FDR-corrected significance threshold, including perfluorohexane sulfonate (PFHxS), perfluorooctane sulfonate (PFOS), three metabolites of di-(2-ethylhexyl) phthalate (DEHP) metabolites: mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), and mono-(2-ethylhexyl) phthalate (MEHP). Exposure-response analyses showed monotonic positive associations for PFHxS, PFOS, and the sum of DEHP metabolites. In quantile g-computation mixture analyses, the mixture of the five biomarkers showed consistent and statistically significant associations in the overall sample (prevalence ratio = 2.28, 95% confidence interval: 1.67-3.11) and across all subgroups. In this nationally representative sample, we identified two PFAS and DEHP metabolites that were associated with ADHD prevalence, and their combined effects were more apparent. These findings highlight the importance of assessing environmental exposures as mixtures.