LONG-TERM exposure to pesticides and toxins might cause Parkinson鈥檚 disease
in old age. Rats given small amounts of a common pesticide used around the house
have developed symptoms eerily similar to Parkinson鈥檚.
It is 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,鈥� he says.
Studies of twins suggest that genetic factors are to blame for Parkinson鈥檚 in
people under 50 years of age. This isn鈥檛 true, however, for late-onset
Parkinson鈥檚, the most common form of the disease, which affects 1 per cent of
people over 65.
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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 higher risk of getting Parkinson鈥檚. Another study earlier this
year, by Beate Ritz of the University of California at Los Angeles, revealed
that California counties with the most pesticide use also had the most deaths
from the disease.
But these studies could not show that pesticides 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. Just
like people with Parkinson鈥檚, the rats gradually lost their dopamine neurons and
developed tremors and cellular protein deposits. Greenamyre鈥檚 work will be
published in Nature Neuroscience in December.
鈥淚t clearly shows that environmental factors can be sufficient to produce all
the features of Parkinson鈥檚,鈥� says Greenamyre. He doesn鈥檛 think this is proof
that pesticides cause Parkinson鈥檚. But he believes the study suggests that we
need to look again at the way we assess the safety of pesticides. 鈥淎 large
number of pesticides act by the same mechanism,鈥� he says.
Lieberman thinks that lawyers will use the study to seek damages on behalf of
Parkinson鈥檚 patients exposed to pesticides. He 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.
Rotenone inhibits an enzyme in the tiny energy-producing organelles inside
cells called mitochondria. This enzyme is also inhibited by a chemical called
MPTP that was linked to Parkinson鈥檚 in the early 1980s, when some heroin addicts
developed sudden and irreversible symptoms of Parkinson鈥檚 after injecting drugs
contaminated by MPTP. However, MPTP only had an effect at high doses.
A natural insecticide extracted from the roots of the derris plant, rotenone
is found in various household and garden products. It is also used by some
organic farmers.
鈥淚n the light of this research, we will be looking into this product and
perhaps phasing it out,鈥� says Michelle Burton of Britain鈥檚 Soil Association,
which certifies organic produce.