Many of today's insecticides work by scrambling insects' brains. And new research suggests they are having a similar effect on the brains of unborn humans, contributing to autism and development disorders—right up until the final trimester.
A team of researchers combined data from the Childhood Autism Risks From Genetics and the Environment (CHARGE) study with data from the California Pesticide Use Report, which is produced through one of the world's most comprehensive pesticide application reporting programs. They wanted to assess how exposure to pesticides drifting over sprayed nearby fields could contribute to autism spectral disorders and developmental difficulties among mothers' soon-to-be-born children.
The results of the analysis—which compared insecticide exposure from 1997 to 2008 with mental health metrics of the children of nearly 1,000 mothers in a state where 200 million pounds of insecticides are sprayed every year—were mind-boggling.
"They basically make it so that the neurons are firing more consistently and faster than they normally would. During development, these effects would be very catastrophic. The developing brain is working on a balancing act."
"We were expecting to see some association, only because it's previouslybeen reported," says Janie Shelton, an epidemiologist working as a United Nations consultant and an author of the study. "But we didn’t expect to see it in the second and third trimesters."
About a third of the mothers who took part in the study lived, during their pregnancy, within 5,000 feet of a farm where one of the four pesticide lasses being studied were sprayed. These mothers were more likely to have kids with autism, or kids who suffer difficulties developing communication, social, and motor skills (problems that affect one out of every 25 American children).
Children with autism spectral disorders were found to have had a 60 percent greater chance of having had organophosphates sprayed near their mothers' homes while they were still in the womb. Children with development disorders were nearly 150 percent more likely to have had carbamate pesticides applied near the home during their mothers' pregnancy. Both of the associations grew stronger as the pesticide applications encroached more closely upon their mothers' homes.
"Applications of two of the most common agricultural pesticides (organophosphates and pyrethroids) nearby the home may increase the prevalence of [autism spectrum disorders]," the researchers write in their paper, published Monday in Environmental Health Perspectives. "Our findings relating agricultural pesticides to [development disorders] were less robust, but were suggestive of an [association] with applications of carbamates during pregnancy nearby the home."
A large part of the problem is believed to be that the pesticides are neurotoxic—and tender neuron networks are particularly vulnerable to disruption.
"The way they function is to hyperexcite the neuronal synapses," Shelton says. "They basically make it so that the neurons are firing more consistently and faster than they normally would. During development, these effects would be very catastrophic. The developing brain is working on a balancing act."
Public health advocates said the findings were yet another reminder of the need for increasing no-spray buffer zones and reducing pesticide applications on farms.