Studies have not settled whether the pesticide chlorpyrifos poses a risk to young brains, according to a new assessment by the Environmental Protection Agency.

The assessment challenges some evidence cited by advocates of banning chlorpyrifos. “Despite several years of study, the science addressing neurodevelopmental effects remains unresolved,” the EPA stated.

The report, released this week by the EPA, precedes a decision on the pesticide’s future uses. The EPA says it will make an interim decision in October, but a final rule won’t be due for two more years.

Environmental and labor groups are pushing in court for an immediate ban. Farm groups have defended chlorpyrifos, saying the pesticide has been a safe, versatile and an effective crop protector since 1965.

The EPA has resisted a ban, but is required by law to review a pesticide’s uses at least every 15 years. In a case pending in the U.S. 9th Circuit of Appeals, the EPA has asked judges to not intervene and let the review continue.

The EPA assessment looked at various ways pesticide handlers, rural residents and consumers could come into contact with chlorpyrifos. The risk of residential exposure to chlorpyrifos is “negligible,” according to the EPA.

Children should not be in danger if roach-bait packages are properly handled, the EPA stated. Only licensed applicators can use chlorpyrifos on ant mounds around homes. Other residential uses are banned.

The assessment, however, did identify concerns about dietary exposure to chlorpyrifos and to pesticide handlers. The EPA identified the same concerns in 2016, while continuing to seek more information. The EPA says it will subject the new assessment to scientific review and open it up to public comment next month.

Ban advocates claim that exposing pregnant women to chlorpyrifos harms unborn children, lowering birth weights and IQs and causing other problems.

Earthjustice attorney Patti Goldman, who has presented arguments to the circuit court on behalf of ban advocates, criticized the assessment.

“Ignoring the demonstrated harm to children doesn’t make chlorpyrifos safe. It shows a commitment to keep a toxic pesticide in the market and in our food at all cost,” she said in a statement.

Studies cited by ban advocates include one by Columbia University in an urban setting. The EPA says researchers have declined to turn over the study’s raw data, preventing the agency from doing its own analysis.

“With respect to effects on the developing brain, very little is known about the duration of chlorpyrifos exposure needed to precipitate adverse effects in the developing brain,” according to the EPA’s assessment.

The assessment also discussed some crops particularly reliant on chlorpyrifos, including Oregon strawberries. Growers depend on chlorpyrifos to control garden symphylans, a pest that feeds on plant roots, according to the EPA.

The assessment affirms chlorpyrifos is risky, but farmers should have confidence in the EPA’s registered uses, Washington State University entomologist Allan Felsot said.

The use of chlorpyrifos is declining, he said. “The market tends to take care of a lot of this.” 

A few states have banned or limited the pesticide’s use. The California Department of Registration in 2019 announced a ban on nearly all products that contain chlorpyrifos.

The Washington Senate this year voted to restrict the use of chlorpyrifos, over the objections of farm groups. The bill was blocked by House Agriculture and Natural Resources Committee chairman Brian Blake, D-Aberdeen.