Giving Compass' Take:

· Writing for The Conversation, Gina Solomon takes a look at the reasons behind California's decision to ban chlorpyrifos, a widely-used pesticide.

· What health issues have been linked to this popular pesticide? What alternative are available?

· To learn more about this topic, check out this article about the problem of wind-blown pesticides.

1. What is chlorpyrifos and how is it used?
Chlorpyrifos is an inexpensive and effective pesticide that has been on the market since 1965. Farmers across the U.S. use millions of pounds of it each year on a wide range of crops, including many different vegetables, corn, soybeans, cotton and fruit and nut trees.

Like other organophosphate insecticides, chlorpyrifos is designed to kill insects by blocking an enzyme called acetylcholinesterase. This enzyme normally breaks down acetylcholine, a chemical that the body uses to transmit nerve impulses. Blocking the enzyme causes insects to have convulsions and die. All organophosphate insecticides are also toxic and potentially lethal to humans.

2. What’s the evidence that chlorpyrifos is harmful?
Researchers published the first study linking chlorpyrifos to potential developmental harm in children in 2003. They found that higher levels of a chlorpyrifos metabolite – a substance that’s produced when the body breaks down the pesticide – in umbilical cord blood were significantly associated with smaller infant birth weight and length.

Subsequent studies published between 2006 and 2014 showed that those same infants had developmental delays that persisted into childhood, with lower scores on standard tests of development and changes that researchers could see on MRI scans of the children’s brains. Scientists also discovered that a genetic subtype of a common metabolic enzyme in pregnant women increased the likelihood that their children would experience neurodevelopmental delays.

3. Why did it take so long to reach a conclusion?
As evidence accumulated that low levels of chlorpyrifos were probably toxic in humans, regulatory scientists at the U.S. EPA and in California reviewed it – but they took very different paths.

At first, both groups focused on the established toxicity mechanism: acetylcholinesterase inhibition. They reasoned that preventing significant disruption of this key enzyme would protect people from other neurological effects.

4. What convinced California to impose a ban?
Three new papers on prenatal exposures to chlorpyrifos, published in 2017 and 2018, broke the logjam. These were independent studies, conducted in rats, that evaluated subtle effects on learning and development.

The results were consistent and clear: Chlorpyrifos caused decreased learning, hyperactivity and anxiety in rat pups at doses lower than those that affected acetylcholinesterase. And these studies clearly quantified doses to the rats, so there was no uncertainty about their exposure levels during pregnancy. The results were eerily similar to effects seen in human epidemiological studies, vindicating health concerns about chlorpyrifos.

5. What’s the U.S. EPA’s view?
In a July 2019 statement, the EPA asserted that “claims regarding neurodevelopmental toxicity must be denied because they are not supported by valid, complete, and reliable evidence.” The agency indicated that it would continue to review the evidence and planned to make a decision by 2021.

EPA did not mention the animal studies published in 2017 and 2018, but it legally must include them in its new assessment. When it does so, I believe EPA leaders will have great difficulty making a case that chlorpyrifos is safe.

Read the full article about banning chlorpyrifos by Gina Solomon at The Conversation.