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Pesticide Exposure in Pregnancy Tied to Autism Risk

But it doesn't prove pesticides cause autism, and didn't directly measure women's chemical exposure, expert notes

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Parents were asked extensive lists of questions about lifestyle and environmental exposures, and mothers listed the addresses where they lived shortly before and during their pregnancies.

Researchers then compared those addresses to a California database of pesticide applications. The database collects information about the kind of chemical that is used, how much is used, and when it is applied.

Most of the women in the study had not lived near any pesticide applications during their pregnancies. Only about a third had been within a mile of where the chemicals were sprayed.

The researchers found that children with autism were more likely to have lived within a mile of a pesticide exposure before birth than typically developing kids. The risk was 60 percent to about 200 percent higher, depending on the kind of chemicals that were sprayed, how close the family had been to the treated area, and when, during pregnancy, a woman had been exposed.

In general, exposure during the third trimester appeared to be riskiest, and odds of having a child with autism went up the closer the family had been living to the pesticide application, suggesting that doses got higher the nearer women were to the chemicals.

Despite some concerns about the study design, Grandjean says this study -- along with previous studies that were able to measure exposure more directly -- provides further support for the notion that pesticides may be a contributing factor in the autism story.

The authors agree that their study represents only a small piece of the puzzle.

"These neurodevelopment disabilities are not the function of a single factor," said Hertz-Picciotto. "I would suspect that there's a number of different factors at play that have to do with maternal health, maternal nutrition, as well as chemicals that are used around the home as well as other factors like air pollution. It's going to be an accumulation of factors for any one woman," she said.

But based on her study, she said pregnant women should be aware that some of the chemicals found in commercial pesticides, like pyrethroids, are also sold for use around the home.

Even worse, they're sometimes labeled as "all natural" products, because they're based on a chemical that comes from chrysanthemum flowers. But Hertz-Picciotto says there's nothing natural about them.

"It's a synthetic product that's been designed to be more toxic than the natural product it's imitating," she said.

Hertz-Picciotto recommends that pregnant women with insect problems play it safe by looking for less toxic alternatives, like a powder called diatomaceous earth, which kills insects by dehydrating them.

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