Chlorpyrifos Weight of the Evidence Shows No Potential for Endocrine-Mediated Effects

06/13/2013 -

Chlorpyrifos has “no potential to interact with the endocrine system,” particularly in light of current authorized uses, according to a recently published, peer-reviewed, weight of the evidence evaluation of all relevant studies. The report considers an 11-assay battery of tests designed by EPA as a high volume screen to identify potential endocrine disruptors in context with other research findings, including results of previous short-term studies with animal tissues and one- and two-generation reproductive studies, developmental and lifetime chronic toxicity studies.

EPA began requiring use of new high volume screening tests to evaluate commonly used products for potential endocrine interactions in 2007. This was done to address concerns that, while existing studies provided many insights on endocrine-related outcomes these androgen, estrogen and thyroid endpoints may not have been specifically examined in previous regulatory health and safety evaluations. Chlorpyrifos was selected for screening by EPA along with about 70 other compounds not because of evidence of interactions but because potential exposures from everyday use made these materials priorities for regulatory evaluation.

Extensive research had previously demonstrated that chlorpyrifos exposures from authorized uses fall well within protective, independent health-based standards established by EPA and other regulatory authorities as safeguards against reproductive, developmental and other long and short-term adverse effects. This new battery of EPA-required screening studies extends these observations, demonstrating that at exposures from authorized use chlorpyrifos does not interact with androgen, estrogen or thyroid systems in fish, amphibian and mammalian test organisms.

The weight of the evidence evaluation notes that numerous guideline studies previously conducted on chlorpyrifos for registration purposes “have not identified the endocrine system as a primary toxicological target.” This recently completed new battery of EPA-mandated studies further documents, the report further notes, that EPA’s regulatory endpoint for establishing chlorpyrifos restrictions (i.e. prevention of inhibition of the cholinesterase enzyme in red blood cells) also ensures protection against any other higher-dose toxicological effects.

Link to the full report: “Chlorpyrifos: Weight of the Evidence Evaluation of Potential Interaction With Estrogen, Androgen or Thyroid Pathways,” Regulatory Toxicology and Pharmacology 66 (2013) 249-263. 

Related: Human Health » Protecting People » Toxicology

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