Exposure to chlorpyrifos and pyrethroid insecticides and symptoms of Attention Deficit Hyperactivity Disorder (ADHD) in preschool children from the Odense Child Cohort [Epub ahead of print]

BACKGROUND: Attention Deficit Hyperactivity Disorder (ADHD) is a common childhood psychiatric disorder with severe and lifelong impact on mental health and socioeconomic achievements. Environmental factors may play a role in the increasing incidens rates. Previous studies on associations between prenatal and childhood exposure to organophosphate and pyrethroid insecticides and ADHD symptoms have yielded mixed findings.

OBJECTIVES: To investigate associations between prenatal and childhood exposure to chlorpyrifos and pyrethroids and ADHD symptoms in 5-year-old children from the Odense Child Cohort.

METHODS: Spot urine samples from pregnant women in gestational week 28 (n = 614) and offspring at 5 years of age (n = 814) were collected and analyzed for the specific metabolite of chlorpyrifos, TCPY (3,5,6-trichloro-2-pyridinol), as well as the generic pyrethroid metabolite, 3-PBA (3-phenoxybenzoic acid). Offspring ADHD symptoms were assessed at age 5 years using the parent reported "ADHD scale" from the "Child Behavior Checklist 1½-5" (n = 1114). Associations between insecticide exposure variables and an ADHD score ≥90th percentile were analyzed using logistic regression for all children and stratified by sex.

RESULTS: Most pregnant women had detectable concentrations of 3-PBA (93%) and TCPY (91%) with median concentrations of 0.20 μg/L and 1.62 μg/L, respectively. In children, 3-PBA and TCPY concentrations were detectable in 88% and 82% of the samples, and the median concentrations were 0.17 and 1.16 μg/L. No statistically significant associations were observed between insecticide metabolites and an ADHD score ≥90th percentile at age 5.

CONCLUSION: In this relatively large Danish birth cohort study with mainly low dietary insecticide exposure, we found no statistically significant associations between prenatal or childhood exposure to chlorpyrifos or pyrethroids, and excess ADHD-symptom load, in 5-year-old children. Prospective studies with multiple urine samples across vulnerable windows of neurodevelopment is warranted to improve assessment of safe exposure levels, which is particularly relevant for pyrethroids, since their use is increasing.