The EPA is banning chlorpyrifos, a pesticide widely used on food crops, after 14 years of pressure from environmental and labor groups
On Aug. 18, 2021, the U.S. Environmental Protection Agency announced that it will end use of chlorpyrifos – a pesticide associated with neurodevelopmental problems and impaired brain function in children – on all food products nationwide. Gina Solomon, a principal investigator at the Public Health Institute, clinical professor at the University of California, San Francisco and former deputy secretary at the California Environmental Protection Agency, explains the scientific evidence that led California to ban chlorpyrifos in 2020 and why the EPA is now following suit.
1. What is chlorpyrifos, and how is it used?
Chlorpyrifos is an inexpensive and effective pesticide that has been on the market since 1965. According to the EPA, approximately 5.1 million pounds of chlorpyrifos have been used annually in recent years (2014-2018) 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.
Until 2000, chlorpyrifos was also used in homes for pest control. It was banned for indoor use after passage of the 1996 Food Quality Protection Act, which required additional protection of children’s health. Residues left after indoor use were quite high, and toddlers who crawled on the floor and put their hands in their mouth were found to be at risk of poisoning.
Despite the ban on household use and the fact that chlorpyrifos doesn’t linger in the body, over 75% of people in the U.S. still have traces of chlorpyrifos in their bodies, mostly due to residues on food. Higher exposures have been documented in farm workers and people who live or work near agricultural fields.
The Environmental Protection Agency has concluded that less-toxic alternatives to chlorpyrifos are available.
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 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 from 2006 to 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.
These findings touched off a battle to protect children from chlorpyrifos. Some scientists were skeptical of results from epidemiological studies that followed the children of pregnant women with greater or lesser levels of chlorpyrifos in their urine or cord blood and looked for adverse effects.
Epidemiological studies can provide powerful evidence that something is harmful to humans, but results can also be muddled by gaps in information about the timing and level of exposures. They also can be complicated by exposures to other harmful substances through diet, personal habits, homes, communities and workplaces.
