Association between exposure to pyrethroids and chlorpyrifos at age 5 years and IQ at age 7 years among children from the Odense Child Cohort, a prospective birth cohort study

Background: Over the past decade, the use of organophosphate insecticides including chlorpyrifos has faced increasing restrictions due to health concerns, leading to a rise in use of pyrethroids. Concerns about neurodevelopmental insults following pyrethroids exposure exist, but few studies have examined the long-term effects of childhood exposure to chlorpyrifos and pyrethroids on IQ. Objective: To investigate the prospective associations between pyrethroids and chlorpyrifos exposure at age 5 years and IQ scores assessed at age 7. Materials and methods: A total of 1083 children from the Odense Child Cohort (OCC), born between 2010 and 2012, were included. Chlorpyrifos metabolite chlorpyrifos-methyl, 3,5,6-trichloro-2-pyridinol (TCPy) and pyrethroid metabolite 3-phenoxy-benzoic acid (3-PBA) were measured in urine at age 5. An abbreviated version of the Danish Wechsler Intelligence Scale for Children fifth edition (WISC-V) was administered at age 7 years. Results: Median urine concentrations of 3-PBA and TCPy at age 5 were 0.18 mu g/L and 1.15 mu g/L, respectively. Higher childhood urine TCPy concentration was associated with a reduction in IQ at 7 years (-0.80 (95%CI:-1.29,-0.31)) for each doubling of TCPy. The association was more pronounced in girls (-1.09 (95%CI:-1.80,-0.38)) than in boys. (-0.54 (95%CI:-1.21,-0.14)). No association was observed for 3-PBA. Conclusions: Even in this low exposed cohort, early childhood exposure to chlorpyrifos was associated with lower IQ at age 7. Our results align with previous reports in both animals and humans suggesting that chlorpyrifos exposure may adversely affect neurodevelopment. No association between pyrethroid exposure (3-PBA) and IQ scores was found. The lack of association for 3-PBA is likely due to the low and uniform exposure levels among the participants. To establish a definitive exposure- response relationship, studies or combined datasets with greater variability in exposure levels are required. Continued monitoring and regulation of insecticide use are recommended to protect the health of children.