Chlorpyrifos Under Review

Chlorpyrifos is an organophosphate insecticide, acaricide, and miticide used to control foliage growth and soil-borne insects.The use of chlorpyrifos as a pesticide began in 1965. It has been predominately used on corn crops, but it has also been used on numerous row crops and fruit and nut trees. Studies show chlorpyrifos is relatively hydrophobic and binds strongly to soil particles. The major metabolite, 3,5,6-trichloro-2-pyridinol (TCPy), is moderately persistent and mobile in soil as a result of weak binding to soil particles.¹

Chlorpyrifos functions as a cholinesterase inhibitor in the nervous system of insects. It has become a cause for concern for neurotoxicity in humans for single exposure at high doses or repeated long-term exposure at lower doses. In an initial effort to minimize human exposure to chlorpyrifos, the US Environmental Protection Agency (EPA) banned most home use in the US in 2000. Additional measures were taken in 2012 when the EPA created chlorpyrifos “no spray” buffer zones around public spaces.²

In October 2015, the EPA responded to a 2007 petition filed by environmental groups to ban chlorpyrifos by proposing to revoke all food residue tolerances for the pesticide.³ The EPA released a revised human health risk assessment for chlorpyrifos on November 10, 2016, and again proposed to revoke all food residue tolerances for the pesticide.⁴ The 9th Circuit Court of Appeals had given the EPA a deadline of March 31, 2017, to make a final decision on the potential ban of chlorpyrifos on food. The EPA has provisionally declined to ban chlorpyrifos on the basis that further evaluation is necessary. A new deadline of October 1, 2022, has been set for the EPA to finalize their evaluation of chlorpyrifos and make a decision if a ban will be enacted.⁵

CIL offers stable isotope labeled and native chlorpyrifos and TCPy standards to assist researchers with their analytical testing needs.