Pregnant women who lived near fields and farms that used chemical pesticides were found to have a 60 percent increased risk for having a child with autism or other developmental delays, a new study found. The research, which was published today in the Environmental Health Perspectives journal, revealed the relationship between specific classes of pesticides and the different stages of pregnancy in a large, multisite study by UC Davis MIND Institute.

"This study validates the results of earlier research that has reported associations between having a child with autism and prenatal exposure to agricultural chemicals in California," said the study's lead author Janie F. Shelton, a UC Davis graduate student who now consults with the United Nations.

The study, titled "Neurodevelopmental Disorders and Prenatal Residential Proximity to Agricultural Pesticides: Childhood Autism Risks from Genetics and Environment (CHARGE)," evaluated 970 pregnant participants who were exposed to common pesticides listed in the California Pesticide Use Report and lived 1.25 to 1.75 kilometers (.77 to 1.08 mile) away from an agricultural pesticide application. "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," Shelton said.

The women filled out a questionnaire in order to see where they lived in proximity to the pesticides and at what point of their pregnancy. Those who lived near farms, golf courses, and other public places that were treated with pesticides during the last three months of their pregnancy were at the highest risk for autism development. In California alone there are approximately 200 million pounds of pesticides applied every year.

"We mapped where our study participants' lived during pregnancy and around the time of birth. In California, pesticide applicators must report what they're applying, where they're applying it, dates when the applications were made and how much was applied," said Irva Hertz-Picciotto, the lead researcher at MIND Institute and professor of the Department of Public Health Sciences at UC Davis.

One in 68 children have been diagnosed with autism spectrum disorder (ASD) according to the Centers for Disease Control and Prevention (CDC). ASD is an umbrella diagnosis that encompasses autism’s varying degrees of difficulties with social interaction, verbal and nonverbal communication, and repetitive behaviors. There is currently no cure or definitive cause of autism, however according to Autism Speaks, an advocacy and fundraising organization for those with ASD, autism appears to have its roots in early childhood brain development. Signs become identifiable between two and three years of age and recent statistics have found a 10 to 17 percent increase in autism diagnoses in more recent years.

"In that early developmental gestational period, the brain is developing synapses, the spaces between neurons, where electrical impulses are turned into neurotransmitting chemicals that leap from one neuron to another to pass messages along” Hertz-Picciotto explained. The formation of these junctions is really important and may well be where these pesticides are operating and affecting neurotransmission."

The study looked back at time, so researchers weren’t able to gather blood or urine samples, which would’ve allowed them to identify the specific chemicals associated with risk and at what levels. Not being able to pinpoint the chemicals and levels out of the 21 found in the pesticides that cause each risk means that further research will need to be conducted. Although identifying the dangerous link may encourage women to be more careful to exposure during pregnancy.

"We need to open up a dialogue about how this can be done, at both a societal and individual level," Hertz-Picciotto said. "If it were my family, I wouldn't want to live close to where heavy pesticides are being applied."

Source: Hertz-Picciotto I, Shelton JF, Geraghty EM, et al. Neurodevelopmental Disorders and Prenatal Residential Proximity to Agricultural Pesticides: The CHARGE Study. Environmental Health Perspectives. 2014.