Following a study that showed that the banned chemical DDT was linked to a higher risk of developing Alzheimer’s disease, new research out this week shows that pesticides are associated with the development of Parkinson’s disease.

It’s not the first time the chemicals have been linked to the brain disease, but the latest study from UCLA researchers shows that the effect is exacerbated by genetics. Since Parkinson’s is known to be determined by a variety of factors, including family genetics, this new study shows how the two factors could be intimately involved.

In the study, published in the journal Neurology, researchers looked at 360 people with Parkinson’s from three California farming communities that used pesticides. They compared these people with 816 from the same regions who did not have the disease.

Prior research has shown that the pesticide benomyl (which has been banned in the U.S.) interferes with processes in the brain and contributes to the development of Parkinson’s. In this new study, the scientists developed a test targeting other chemicals that could contribute to Parkinson’s, and found that 11 other pesticides contribute to the disease in the same way as benomyl.

(MORE: Study Links DDT to Development of Alzheimer’s Disease)

Here’s how it works: the pesticides inhibit an enzyme called aldehyde dehydrogenase (ALDH), which is supposed to keep a naturally occurring toxin in the brain called DOPAL in check. When ALDH is inhibited, the detoxifying doesn’t happen, and this causes DOPAL to build up and contribute to Parkinson’s development.

Mostly interesting was that the population from the farming communities who had the gene variant ALDH2 were six times more likely to develop the disease, indicating that the gene variant made them especially vulnerable.

“We were very surprised that so many pesticides inhibited ALDH and at quite low concentrations, concentrations that were way below what was needed for the pesticides to do their job,” study author Dr. Jeff Bronstein, a professor of neurology and director of the Movement Disorders Program at UCLA, said in a statement. “These pesticides are pretty ubiquitous, and can be found on our food supply and are used in parks and golf courses and in pest control inside our buildings and homes.”

Building evidence of pesticide-related brain disorders is supporting the case for the dangers of pesticides, and giving researchers more insight into what treatments may be best for people who develop the disease from these chemicals.

MORE: Promising First Test to Detect Parkinson’s Disease

Contact us at letters@time.com.