Long-term exposure to a pesticide commonly used around the house and garden makes rats develop symptoms eerily similar to Parkinson鈥檚 disease. The findings bolster the idea that pesticides could be causing the disease in humans.
It鈥檚 the first solid proof that long-term exposure to a toxin can cause this disease, says Abraham Lieberman, medical director of the National Parkinson Foundation in Miami, Florida. 鈥淚t鈥檚 a very provocative study, and you can鈥檛 just throw it away.鈥� But he says the study needs to be repeated in primates.
The pesticide the researchers investigated is called rotenone and is extracted from the derris plant. It is widely used as an insecticide in gardens and to kill pests on pets. It is also a favourite of organic farmers and gardeners.
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Michelle Burton is a pesticides advisor for the Soil Association, which promotes organic agriculture. She says: 鈥淥rganic farmers can鈥檛 use rotenone routinely 鈥� they have to apply and have a good reason. But in the light of this research, we will be looking into this product, and perhaps look into phasing it out.鈥�
Nature or nurture
Studies of twins suggest that genetic factors are to blame for Parkinson鈥檚 in people under 50 years of age. But this isn鈥檛 true for late-onset Parkinson鈥檚, the most common form of the disease. This affects one per cent of people over 65.
So researchers have searched for environmental risk factors. Earlier this year, a study of 1000 people found that those who often used pesticides at home had a 70 per cent increased risk of getting Parkinson鈥檚. Another study done earlier this year revealed that California counties with the most pesticide use also had the most deaths from the disease.
But these studies couldn鈥檛 show that the pesticide actually caused the disease. So Tim Greenamyre of Emory University in Atlanta, Georgia, and his colleagues gave rats low levels of a pesticide called rotenone over several weeks.
The rats gradually lost their dopamine neurons, and developed tremors and cellular protein deposits just like those seen in people with Parkinson鈥檚. Greenamyre鈥檚 work will be published in December in Nature Neuroscience.
Partial proof
鈥淚t clearly shows that environmental factors can be sufficient to produce all the features of Parkinson鈥檚 disease,鈥� says Greenamyre. He doesn鈥檛 think this is proof that pesticides cause Parkinson鈥檚 in humans.
But he believes the study suggests that we need to look again at the way we assess the safety of pesticides. 鈥淭here are a large number of pesticides that act by the same mechanism of action,鈥� he says.
Lieberman fears that the study will create 鈥渁 tremendous flurry of worried people鈥� wanting to know if pesticides have doomed them to Parkinson鈥檚. He also thinks that lawyers will use the study to seek damages on behalf of Parkinson鈥檚 patients exposed to pesticides.