Pregnant women who live near fields and farms where chemical pesticides are used may face a potentially increased risk of having a child with autism spectrum disorder (ASD), a study released Monday indicated.
The report, "Childhood Autism Risks from Genes and Environment," was carried out by researchers at the University of California at Davis and published in the online scientific journal Environmental Health Perspectives. It’s release comes as scientists probe whether environmental factors, as opposed to or in conjunction with genetic ones, may play a role in causing the disorder.
“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 Janie F. Shelton, the study's lead author, in a press release.
“While we still must investigate whether certain subgroups 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,” she said.
Autism is characterized by deficits in social interaction, language and repetitive behaviors — symptoms that usually appear by age 3. A diagnosis of ASD can represent a lower severity of those symptoms.
California is the top agricultural producing state in the United States — each year over 200 million pounds of active pesticides are applied across its territory. Most pesticides used in the United States are neurotoxins, and since a developing fetal brain is more vulnerable to environmental toxins than an adult's, in utero exposures can have a dramatic effect on mental development.
“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,” said Irva Hertz-Picciotto, an environmental epidemiologist at UC-Davis who was the principal investigator of the study.
Metabolic disturbances, a universal symptom of autism, occur when cells are threatened or damaged by viruses, bacteria or chemicals. The cells react by hardening their walls — cutting off communication and damaging cellular function, often resulting in delayed neurodevelopment in children.
“The formation of these junctions is really important and may well be where these pesticides are operating and affecting neurotransmission,” she added.
Researchers behind the study mapped where participants lived during pregnancy and around the time of birth. Then, they contrasted that data with dates and quantity of nearby pesticide applications — which must be reported in the state of California.
They found that specific classes of pesticides — such as organophosphates, pyrethroids and carbamates — were more commonly applied near the residences of mothers whose children had ASD or other forms of developmental disorders.
Proximity to pesticides at some point during gestation was associated with a 60 percent increased risk for autism, the report said, adding the association was stronger when exposure occurred during the second or third trimester.
There has been a 78 percent increase in diagnoses of ASD since 2007, the report said, and scientists say there is still no smoking gun as to what environmental or genetic influence may lead to the disorder.
Some recent research has suggested that less than half of the known factors that lead to autism are genetic, with the majority being environmental. It has been suggested that exposure to viruses, bacteria or toxic chemicals found around the home or in agricultural uses could be a factor.
While it would be impossible to eliminate all risks from environmental factors, Hertz-Picciotto said, “We need to open up a dialogue about how this can be done at both a societal and individual level.”
“If it were my family," she said, "I wouldn’t want to live close to where heavy pesticides are being applied.”