Exposure to certain pesticides while in the mother's womb can increase the risk of autism spectrum disorder (ASD) or autism in children, a new study says.
Autism is a developmental disorder that leads to significant social, communication and behavioural changes.
In the study, pregnant women who lived near fields sprayed with pesticides like organophosphates, pyrethroids and carbamates had two-thirds greater risk of giving birth to a child with autism or other developmental delays than others. Exposure to the chemical during the second and third trimester posed the greatest risk.
For the study, Irva Hertz-Picciotto and colleagues from the University of California - Davis Health System in US looked at nearly 1,000 women and their children enrolled in the Northern California-based Childhood Risk of Autism from Genetics and the Environment (CHARGE) Study. Through questionnaires, mothers provided their residential details before and after conceiving the child.
Researchers used the California Pesticide Use Report to collect information on pesticide application. It provided details about the exact place, date and doses of particular pesticides applied in California.
Based on the information, they later calculated each participant's proximity to the pesticide applied sites and noted down the particular chemical each person was exposed to while expecting their child.
Living within 1.25 to 1.75 kilometres of a commercial pesticide application site during pregnancy was directly linked to the disorder in children.
"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," principal investigator of the study, Hertz-Picciotto, a MIND Institute researcher and professor and vice chair of the Department of Public Health Sciences at UC Davis, said in a news release.
Exposure to organophosphates class of chemical compounds, mainly chlorpyrifos in the second trimester, posed the greatest risk. Exposure to pyrethroids just before pregnancy and in the third trimester moderately increased risk of autism in children, while carbamates exposure in pregnancy increased risk of developmental delays in children.
Exposure to the "neurotoxic" chemicals during the early stages of development interferes with the complex procedures involved in brain development, researchers said. "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. The formation of these junctions is really important and may well be where these pesticides are operating and affecting neurotransmission," Hertz-Picciotto said.
Exposure to toxic pesticide in pregnancy has long been associated with abnormalities in children. A study published in the Proceedings of the National Academy of Sciences in April, 2012 found that high exposure to chlorpyrifos (CPF) decreased IQ and memory in children.
Similarly, in September 2012, a study in The Journal of Pediatrics found that a widely used weed-killer atrazine escalated the risk of a congenital disorder called choanal atresia in children.