A new study suggests that pregnant women who live within a mile of spaces where certain commercial pesticides are applied appear to have an increased risk of having a child with autism.
Proximity to agricultural pesticides in pregnancy was also linked to other types of developmental delays in children.
The risk appeared to be highest for women who lived near farms, golf courses and other public spaces that were treated with pesticides during the last three months of their pregnancies.
This isn’t the first study to make this connection, as lead author Janie F. Shelton, from the University of California, Davis, pointed out:
“Ours is the third study to specifically link autism spectrum disorders to pesticide exposure, whereas more papers have demonstrated links with developmental delay.”
The new study does not prove a link between pesticides and autism, but pesticides all affect signaling between cells in the nervous system, so a direct link is plausible, said Shelton in an email to Reuters Health.
California is one of the few states that reports and maps agricultural pesticide use. Those maps were used to track exposures during pregnancy for the mothers of 970 children.
The children included 486 with an autism spectrum disorder (ASD), 168 with a developmental delay and 316 with typical development.
Developmental delay, in which children take extra time to reach communication, social or motor skills milestones, affects about four percent of kids in the United States. The Centers for Disease Control and Prevention estimates that one in 68 children has an ASD, which are marked by deficits in social interaction and language.
In the new study, about a third of mothers had lived within a mile of fields treated with pesticides, most commonly organophosphates.
Children of mothers exposed to organophosphates were 60 percent more likely to have an ASD than children of non-exposed mothers, the authors reported.
Organophosphates are a group of chemicals that have many domestic and industrial uses, though they are most commonly used as insecticides and are responsible for a number of poisonings. They were originally developed for chemical warfare.
The main mechanism involves blocking the enzyme acetylcholinesterase, which causes nervous and respiratory damages that result in the insect’s death. They are also hazardous to humans, and are one of the most commonly used pesticides in the United States. There are about 40 organophosphate pesticides registered in the US.
Dr. Philip J. Landrigan, director of the Children’s Environmental Health Center at the Icahn School of Medicine at Mount Sinai in New York, was not involved in this study, but he told Reuters Health that similar studies support these findings:
“We already knew from animal studies as well as from epidemiologic studies of women and children that prenatal exposure (to pesticides) is associated with lower IQ. This study builds on that, uses the population of a whole state, looks at multiple different pesticides and finds a pattern of wide association between pesticide exposure and developmental disability.”
Dr. Landrigan also said that this study almost certainly underestimates the true strength of the association between pesticides and neurological problems since it did not precisely measure each individual woman’s exposure.
Dr. Irva Hertz-Picciotto, senior author of the report and professor and vice chair of the Department of Public Health Services at UC Davis, said that families living close to agricultural fields may want “to leave town or keep their children away or close the windows” on days when pesticides are being applied.
A 2007 study by the California Department of Public Health also showed a possible link between organochlorine pesticides and autism. That study found that children born to mothers who had been exposed to two of the pesticides during their first trimester of pregnancy were six times more likely to develop autism than a control group whose mothers did not live near fields.
State health officials are saying that more research is needed, but the UC Davis researchers cited the state study and said their evidence supports findings that link autism spectrum disorder to agricultural pesticide exposure.
The researchers agreed that more research needs to be done to learn how pesticides might influence brain development, but said it is clear that most are neurotoxic. Hertz-Piccotto said, “A number of pesticides impact the balance of neuro-excitation and neuro-inhibition” that control mood, learning, social interactions and behavior.
She also pointed out that the process that pesticides use to kill insects “is also a process that is shared with mammals and with human beings, and I think that makes them something we should think twice about exposing ourselves to.”