UNC Health Care
Macro view of test tubes

Is There a Connection Between Pesticides and Autism?

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.

Read more about cutting-edge research at the UNC School of Medicine.

Mark Zylka, PhD, is professor and director of the UNC Neuroscience Center.