The long-suspected role of pesticides in the development of autism has been reinforced by a new study. The findings suggest that mothers’ exposure to pesticides during pregnancy puts their unborn children at higher risk of developing the condition.

Billed as the largest study into the issue to date, the University of California Davis research involved almost 1,000 children born in farm-rich areas of Northern California.

It is the third study to link prenatal insecticide exposure to autism and draws further attention to the way the developing fetal brain may be vulnerable to pesticides.

The study reports that children whose mothers live less than one mile from fields treated with organophosphate pesticides during pregnancy were 60 per cent more likely to have autism than children whose mothers did not live close to treated fields. The majority of women resided in the Sacramento Valley area.

Several pesticides in the frame

Irva Hertz-Picciotto, vice chair of the Department of Public Health Sciences at the University, said the study involved mapping where the participants lived during pregnancy and around the time of birth.  She said: “What we saw were several classes of pesticides more commonly applied near residences of mothers whose children developed autism or had delayed cognitive or other skills.”

The research will look further at whether sub groups are more vulnerable, but until then it highlights the need for women who are pregnant to take special care to avoid contact with agricultural chemicals.

The university’s research looked at Chlorpyrifos, an insecticide once widely used to kill insects in homes and gardens that was banned for residential use in 2001 after being linked to neurological problems in children. However, it is still widely used on crops, including vegetables, fruits and nut trees.

First link of autism with pyrethroid insecticides and autism

The new study is also the first to draw a link between pyrethroid insecticides and autism. Researchers found that exposure to pyrethroids prior to conception increased the risk of a baby developing autism by 82 per cent. During the third trimester the risk was 87 per cent higher.

This finding has raised particular concern because pyrethroids were considered a safer alternative to organophosphates and have increased in use in recent years at home and on farms.

Published: 23 June 2014