Association between urinary 3, 5, 6-trichloro-2-pyridinol, a metabolite of chlorpyrifos and chlorpyrifos-methyl, and serum T4 and TSH in NHANES 1999-2002

► Urinary TCPY is a biomarker of the common organophosphate insecticide chlorpyrifos. ► TCPY was associated with higher T4 among males aged 12-< 18 and 18-< 40 years of age. ► TCPY also associated with a suggestive decrease in TSH among men 18-< 40 years old. ► Contradicting associations were found for TSH among men and women > 60 years old.