Chlorpyrifos is an organophosphate insecticide. It has been almost entirely banned for residential use since 2000 because of the heath risks it presents for children. But the pesticide's residue is still persistent in the environment. In addition, it is still sprayed commercially on some agricultural crops, including fruit trees and vegetables, and is also used on golf courses and for mosquito control.

There has been a back-and-forth through the years as the government has struggled whether to keep the pesticide legal. Most recently, California announced that it will ban the sale of the pesticide beginning in early 2020, NPR reports. Sales will end in early February and growers will not be able to use it after Dec. 31, 2020.

The Environmental Protection Agency (EPA) banned the pesticide in 2015, but it reversed that decision in 2017 under the Trump administration.

Since then, a dozen environmental groups petitioned the EPA to ban the pesticide and a federal judge ordered the agency in August 2018 "to revoke all tolerances and cancel all registrations for chlorpyrifos within 60 days." But the EPA announced in July 2019 that it would not institute a federal ban on chlorpyrifos, CNN reports.

"EPA has determined that their objections must be denied because the data available are not sufficiently valid, complete or reliable to meet petitioners' burden to present evidence demonstrating that the tolerances are not safe," the agency said in a statement.

Environmental groups have argued that studies show that exposures to the pesticide is liked to low birth weight, reduced IQ, attention disorders and other issues in infants and children.

Earlier worries

boy struggling with homework Prenatal exposure to chlorpyrifos can affect a boy's short term memory later in life. (Photo: mike mols/Shutterstock)

This is not the first time the insecticide has come under scrutiny. A 2012 study regarding chlorpyrifos shows a link between exposure and its effect on kids' brains — particularly for boys.

The study, published in the journal Neurotoxicology and Teratology and reported on by Environmental Health News followed 335 pairs of mothers and children that were part of a large group of families living in low-income neighborhoods in New York City that have been tracked by Columbia University scientists since the kids were born. Several years ago, researchers were able to test each child's umbilical cord blood after birth to determine exposure level to various chemicals — including chlorpyrifos. Now, as many of the children are reaching school age, researchers are able to link the effect of various levels of chlorpyrifos exposure with each child's short-term memory.

For the boys, prenatal exposure to chlorpyrifos was associated with lower scores on short-term memory tests than girls who were exposed to similar levels of the pesticide. Scores were an average of three-points lower for boys than girls. These findings suggest that chlorpyrifos may harm boys’ developing brains more than girls’.

Editor's note: This article has been updated since it was originally published in August 2012.

What you need to know about chlorpyrifos
This pesticide used in farming is linked to health issues in children.