Much of the concern about agricultural pesticides has centered on runoff, when chemicals are washed into our waterways.  But what about the pesticides that stay on the plants? What happens when humans ingest them?

Mark Zylka, PhD, and his research colleagues at the UNC School of Medicine have started to answer that question, finding that a class of common pesticides sprayed on crops causes changes in cultured neurons of mice that mirror the genetic changes in people with autism and Alzheimer’s disease.

“Virtually nothing is known about how these chemicals impact the developing or adult brain,” says Dr. Zylka, director of the UNC Neuroscience Center. “Yet these chemicals are being used at increasing levels on many of the foods we eat.”

In 2013, as part of his research into possible environmental links to autism, Dr. Zylka found drugs that inhibited a particular enzyme had profound effects on genes linked to autism. He wanted to investigate if other chemicals might produce similar cellular effects and decided to test pesticides.

Dr. Zylka and colleagues exposed mouse neurons, which have cellular similarities to human neurons, to about 300 chemicals used on crops. His lab found six groups of chemicals that altered gene expression; one group in particular had a substantial effect on genes related to neurological disorders.

These chemicals reduced the expression of genes that are important for communication between neurons. The chemicals also caused elevated expression of genes associated with neuroinflammation, commonly seen in people with autism and neurodegenerative diseases. Chemicals in this group included commonly used pesticides, such as the fungicides pyraclostrobin and trifloxystrobin. These have surged in popularity over the past 15 years and are used on leafy greens, grapes and tomatoes.

While the research findings have generated considerable interest, Dr. Zylka is quick to caution that this link does not prove causation and that further autism research should be conducted. His research was published last year in the journal Nature Communications.

“We cannot say that these chemicals cause these conditions in people,” says Dr. Zylka. “Many additional studies will be needed to determine if any of these chemicals represent real risks to the human brain.”

Proving a clear link to autism in humans would require lengthy epidemiological studies of exposed populations, like farm workers, to answer questions such as: What are the impacts on their long-term health? Do their children develop autism? Are they developing Alzheimer’s at higher rates?

Dr. Zylka hopes his work will prompt researchers and regulators to take a critical look at the chemicals being used on our food. In the meantime, he’ll continue researching potential environmental factors that contribute to autism.

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