The Environmental Protection Agency will not revoke tolerances for chlorpyrifos, an insecticide environmental and farmworker groups say is a dangerous neurotoxin and should be banned.

In a decision signed Wednesday by Alexandra Dunn, assistant administrator for the agency’s Office of Chemical Safety and Pollution Prevention, EPA said it did not have enough evidence of neurodevelopmental effects “that is sufficiently valid, complete, and reliable at this time” to justify revoking tolerances.

The Ninth Circuit Court of Appeals had ordered the agency to make a decision by July 18 on the chemical marketed as Lorsban by Corteva Agriscience. The Natural Resources Defense Council and Pesticide Action Network North America had petitioned EPA in 2007 to revoke food tolerances and cancel registrations for the substance, which was banned for household use in 2001.

After years of litigation, EPA was forced by the Ninth Circuit Court of Appeals to respond to the petition, which it did in March 2017, early in the tenure of then-Administrator Scott Pruitt. The agency denied it, but 12 public interest groups, the North Coast Rivers Alliance, and the states of New York, Washington, California, Massachusetts, Maine, Maryland, and Vermont all objected.

The decision Thursday denied those objections.

“In sum, the objections are focused on EPA’s ongoing work in FIFRA registration review to evaluate more recent information addressing the risk of adverse neurodevelopmental effects,” EPA said in its decision. FIFRA, the Federal Insecticide, Fungicide, and Rodenticide Act, is the nation's pesticide law.

"With respect to these claims, EPA has concluded, after many years of attempting to obtain information necessary to validate this information, that the objections and the underlying petition fail to provide evidence of neurodevelopmental effects that is sufficiently valid, complete, and reliable at this time to meet the burden petitioners for revocation bear in presenting a case that tolerances are unsafe.”

The decision prompted immediate criticism from environmental groups and some politicians. Sen. Tom Udall, D-N.M., said “there is no excuse for the Trump administration keeping a toxic nerve agent like chlorpyrifos on the shelves and in our fields. The science on chlorpyrifos is clear and unambiguous: it damages the developing brains of children and causes serious health problems in those who have been exposed to it.”

Farm groups have consistently argued in favor of continued use of chlorpyrifos, saying it is a valuable and versatile crop protection tool that is safe if used according to the label. 

"Chlorpyrifos is a critical pest management tool used by growers around the world to manage a large number of pests, and regulatory bodies in 79 countries have looked at the science, carefully evaluated the product and its significant benefits and continued to approve its use," chlorpyrifos manufacturer Corteva Agriscience said last year after the Ninth Circuit ordered EPA to revoke tolerances for the chemical. The court backed off in a later decision, giving EPA the discretion to make its own decision.

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