Thyroid hormones in relation to urinary metabolites of non-persistent insecticides in men of reproductive age

Human exposure to contemporary-use insecticides is widespread, but effects of exposure on human endocrine function have gone largely untested to date. Samples of urine and blood were collected concurrently from 322 adult men between the years 2000 and 2003. Urine samples were analyzed for 3,5,6-trichloro-2-pyridinol (TCPY), a metabolite of chlorpyrifos and chlorpyrifos-methyl, and 1-napththol (1N), a metabolite of carbaryl and naphthalene. Serum samples were analyzed for free T4, total T3, and thyroid stimulating hormone (TSH). There was an association between TCPY and TSH, where an interquartile range (IQR) increase in TCPY was associated with a 9% (95% confidence interval 0–18%) increase in TSH. There was also a suggestive inverse association between TCPY and free T4. There were no associations between 1N and thyroid hormones. Environmental exposure to chlorpyrifos, chlorpyrifos-methyl, or its metabolite TCPY may be associated with altered thyroid function in human males.