US researchers say they have found people who used two specific varieties of pesticide were more likely to develop Parkinson's disease.
The study, which appears in the journal Environmental Health Perspectives, shows people who used either rotenone or paraquat are about two-and-a-half times more likely to develop Parkinson's than people who never used either pesticide.
"Rotenone directly inhibits the function of the mitochondria, the structure responsible for making energy in the cell," says study co-author Dr Freya Kamel, a researcher at the US 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," says Kamel.
The study examined 110 people with Parkinson's disease and 358 people who served as a control group from the Farming and Movement Evaluation (FAME) Study. FAME is part of the larger Agricultural Health Study looking at the health of approximately 90,000 licensed pesticide applicators and their spouses.
Link suspected for a while
Associate Professor Kay Double of Neuroscience Research Australia, say the study backs earlier studies implicating pesticides in the development of Parkinson's disease.
"We've known for a long time that there is an increased risk of Parkinson's disease of people who live in rural environments compared to people who live in cities," says Double. "It's been expected that would come down to some sort of environmental influences."
Double, whose research includes studying how and why brain cells die due to Parkinson's disease, says studies such as these will benefit research.
"Some of the biochemical mechanisms that we know occur in the Parkinson's disease brain ... are things that are affected by these pesticides," she says.
"[This study] is giving us more of a handle on what might be happening in the brain to cause someone to develop Parkinson's disease."
Pesticides under review
Jo Immig of the National Toxics Network says the findings are concerning, as both chemicals are used in Australia.
"This latest study is a very credible study that raises significant concerns about several pesticides that are used in Australia that may be contributing to Parkinson's disease," says Immig.
She says paraquat and rotenone are registered pesticides in Australia, despite being banned in the European Union.
"Paraquat, for instance, is a herbicide widely used in sugar cane and vegetable production, and it's used in making fire breaks and other general weed management," says Immig. "It's used in a lot of different contexts and by many people."
The Australia Pesticides and Veterinary Medicines Authority website lists rotenone as a chemical nominated for review, because "of human health concerns". Paraquat has been under review since 1997.