Effects of urinary organophosphate flame retardants in susceptibility to attention-deficit/hyperactivity disorder in school-age children

Our previous studies have revealed a correlation between urinary phthalates (PAE) metabolites and parabens and PM_2.5 exposure and susceptibility to attention-deficit/hyperactivity disorder (ADHD) in school-age children. Our goal was to examine the relationships between urinary organophosphate flame retardants (OPFRs) and their metabolites and the susceptibility to ADHD in the same cohort of children. We recruited 186 school children, including 132 with ADHD and 54 normal controls, living in southern Taiwan to investigate five OPFRs (1,3-dichloro-2-propyl phosphate (TDCPP), tri-n-butyl phosphate (TnBP), tris (2-chloroethyl) phosphate (TCEP), tris(2-butoxyethyl) phosphate (TBEP), and triphenyl phosphate (TPHP)) and five OPFR metabolites (bis(1,3-dichloro-2-propyl) phosphate (BDCPP), di-n-butyl phosphate (DNBP), bis(2-chloroethyl) hydrogen phosphate (BCEP), di-(2-butoxyethyl) phosphate (DBEP), and diphenyl phosphate (DPHP)) in urine. ADHD patients' behavioral symptoms and neuropsychological function were assessed using the Swanson, Nolan, and Pelham Version IV Scale (SNAP-IV) and the Conners' Continuous Performance Test 3rd Edition (Conners CPT3), respectively. BCEP was predominant among urinary OPFRs and the metabolites in both the ADHD and control groups. ADHD children had significantly higher levels of urinary BDCPP, BCEP, DBEP, DPHP, TCEP, TBEP, TNBP, TPHP, and Σ₁₀OPFR compared to the controls. After controlling for age, gender, body mass index, PM_2.5 exposure scenarios, and urinary phthalate metabolites, parabens, bisphenol-A and creatinine, levels of urinary BDCPP, TDCPP, and TBEP in ADHD children showed significant and dose-dependent effects on core behavioral symptoms of inattention. DNBP levels were positively correlated with neuropsychological deficits (CPT detectability, omission, and commission), while urinary DPHP in ADHD children were negatively related to CPT detectability and commission. Hyperactivity and impulsivity were not correlated with urinary OPFRs and their metabolites in ADHD children. In conclusion, the ADHD symptom of inattention and CPT performance may be closely associated with certain urinary OPFRs and their metabolites, independent of urinary PAE metabolites, parabens, and bisphenol-A in school-age-ADHD children.