US researchers said they have found that people who used two specific varieties of pesticide were 2.5 times as likely to develop Parkinson’s disease.

The pesticides, paraquat and rotenone, are not approved for house and garden use. Previous research on animals has linked paraquat to Parkinson’s disease, so it is restricted to use by certified applicators.

Rotenone is approved only for use in killing invasive fish species.

“Rotenone directly inhibits the function of the mitochondria, the structure responsible for making energy in the cell,” said study co-author Freya Kamel, a researcher at the National Institute of Environmental Health Sciences.

“Paraquat increases production of certain oxygen derivatives that may harm cellular structures. People who used these pesticides or others with a similar mechanism of action were more likely to develop Parkinson’s disease.”

The study examined 110 people with Parkinson’s disease and 358 people who served as a control group from the Farming and Movement Evaluation Study.

FAME is part of a larger Agricultural Health Study looking at the health of approximately 90,000 licensed pesticide applicators and their spouses.