Pregnant women who live near agricultural land where pesticides are applied have a 60 percent higher risk of giving birth to children with autism or other developmental delays, a new study from the University of California Davis found.
The study, which was conducted in California, looked at three classes of common pesticides: organophosphates, pyrethroids and carbamates. All three of them were found to have an association with autism spectrum disorders or developmental delays.
Organophosphates applied to nearby fields during various stages of the mothers' pregnancy were associated with a heightened risk of autism spectrum disorder, while Pyrethroids were associated with autism spectrum disorder when the mothers were exposed immediately prior to conception and in the third trimester. Carbamates applied during pregnancy were associated with developmental delay.
"While we still must investigate whether certain sub-groups are more vulnerable to exposures to these compounds than others, the message is very clear: Women who are pregnant should take special care to avoid contact with agricultural chemicals whenever possible," lead study author Janie F. Shelton said in a press release.
Yet in certain parts of California, exposure may be hard to avoid. It produces more agricultural products than anywhere in the country, and statewide approximately 200 million pounds of active pesticides are used each year. The greatest portion of pesticides are applied in the large Central Valley. In Sacramento County, just south of the Central Valley, the autistic population in the county has risen sevenfold since 2000, according to the California Department of Education. In 2001, fewer than 500 students in Sacramento County public schools were enrolled in special education classes due to a diagnosis of autism. A decade later, the number increased to 2,275—roughly one of every 105 pupils, according to the Sacramento Bee.
Links between geography and autism has become more apparent in recent years. An info graphic from the LA Times shows, for example, that a child born in California is several times more likely to be diagnosed with autism than a child in, say, Alabama. Those numbers imply that local environmental factors may contribute to autism, a hypothesis which the most recent UC Davis study supports. "This is actually the third study that shows some link with the organophosphates and autism risks," Dr. Irva Hertz-Picciotto, an author of the study said.
Researchers were able to conduct the study because in California, pesticide applicators are required to report where they spray, and what they are spraying. The researchers mapped their homes from where they lived at the time of the pregnancy and around the time of birth, and then linked those addresses to the database of commercial applications of pesticides in California.
"I think it’s an area that people do need to think about, both at the individual level…if they can make some choices, it may be worth it to them," Hertz-Picciotto said. She also suggested individuals avoid the types of exposure that they can easily control, such as what pesticides they apply within their own homes and gardens. "I don’t use chemical pesticides that are toxic. I know it takes sometimes a little longer. I’m willing to live with those extra couple days when there might be creepy crawly things," she said.