A study into links between pesticides and Parkinson's disease is to be commissioned to examine fears that chemicals used by gardeners and farmers can bring on the degenerative neurological illness.
The Government's advisers on pesticides are so concerned about a possible link that they plan to pay experts to review the evidence on whether herbicides and fertilisers can lead to the condition.
Scientists say commonly-used products such as paraquat, which is used to clear garden paths of weeds, can act as a nerve toxin which may lead to the onset of Parkinson's if the exposure is prolonged or of a high enough concentration.
The disease is caused by the failure of cells in the brain to produce sufficient dopamine, a chemical used to transmit signals inside the brain. Too little leads to the uncontrolled shaking and freezing of the body that is typical of the disease.
Studies of rural populations have shown they have a higher chance of developing the disease. However, it is not only farmers who mix the chemicals who have shown symptoms, but also people who drink from wells or are exposed to pesticides sprayed on fields.
The decision to commission a study followed a recent meeting of the Government's Advisory Committee on Pesticides. Scientists studied a report by the Pesticides Safety Directorate, a government agency with powers to approve new chemicals and advise ministers on policy, and said it raised fresh questions about whether commonly used chemicals could be damaging the health of people who handled them regularly.
The chairman of the committee said yesterday that the only responsible option was to draw up an authoritative study by outside scientists. He said that since the BSE crisis, experts and officials had learnt to take heed of early warning signals over health scares and to take all possible precautions.
The study is expected to take at least six months and is likely to lead to further scientific investigation and even a ban on some chemicals.
Professor David Coggon, the professor of occupational and environmental medicine at the Medical Research Council, said his committee wanted to commission a team of expert epidemiologists. "If we were confident that there was nothing in it at all, we wouldn't be paying taxpayers' money to carry out a review. It's about being responsible about these things and looking if it's appropriate," he said. "If new evidence suggests there might be a problem we have to look at it."
News of the study was obtained by Norman Baker, the Liberal Democrat MP for Lewes, who has written a report on pesticides and is worried about their affects. Jacqui Smith, the health minister, told Mr Baker that officials were considering how to proceed.
Dr Ronald Pearce, a consultant neurologist who is in charge of studying the brains' of victims collected by the Parkinson's Disease Society, said it was time the Government looked at the issue. He said there was a proven link between pesticide exposure and the onset of Parkinson's.
"Over the last half century in many epidemiological studies there's a link between rural living exposure to pesticides and even well water," he said. "There have been a few cases of toxic exposure of pesticides and herbicides where people have developed clinical signs. There's a well known epidemiological link between agrochemicals, rural living and well water."
Professor Timothy Greenamyre, who specialises in Parkinson'sand is on the scientific board of the Michael J Fox Foundation, which aims to find cures, has pointed to the growing body of scientific research since 1993 in which the two seem to be linked. In 2000, he carried out research which backed up experiments on rats showing that exposure to pesticide doses gradually knocked out the cells in the brain which produce dopamine.
The mechanism of the action seemed to involve two stages. First, the pesticide works on the mitochondria – the "engines" of every cell – to make them produce highly reactive chemicals called free radicals. These react with "anything they can", as Professor Greenamyre put it. "Our findings are consistent with the idea that chronic exposure to low levels of toxin may cause cumulative damage to the brain's dopamine system, eventually leading to clinical symptoms."
He said that overall, the results "support the idea" that exposure to pesticides increases the chance of getting Parkinson's. His study came out in November 2000. However, a far more damning one was published earlier that year by a team at Stanford University in California who had studied more than 1,000 people, half of whom had Parkinson's. They found that those who had been frequently exposed to pesticides were twice as likely to develop the disease.A study of children under five in Mexico in 1998 showed a dramatic difference between those with high and low pesticide exposure.
The Government sets a "maximum residue level" for each pesticide, detailing how much is allowed to enter the food chain. In September 1999 a report by the Working Party on Pesticides found them in many supermarket foods. In some cases, there were potentially dangerous levels in food imported from abroad that contained pesticides not approved for use in the UK.
The fear is that children are at most risk from pesticide use, because they would take in more pesticides proportional to their body weight than adults, and because the residue level is set for adults, not children.
"There are more pesticides in food now, so they are growing up accumulating those chemicals," said a representative of the Pesticides Action Network.
News of the study was welcomed by the Soil Association which represents organic farmers and has been warning about the dangers of pesticides for decades.
Patrick Holden, the association's director, said the inquiry should look at the effects of being exposed to a number of pesticides.
"The cocktail effect is the most worrying thing of all," he said. "There are links between multiple accumulation and a whole range of diseases."
Friends of the Earth said pesticides, such as paraquat, with question marks over their safety should be banned until the study is complete.
Health risks case against chemicals
Pesticides have been linked to:
Parkinson's disease – by research using laboratory animals and large-scale statistical studies of humans. There is still a question whether it can be triggered by low-level exposure over a long period
Male infertility – a study in Argentina last year found a 'significant' statistical link between higher occupational exposure to pesticides and low sperm count
Potentially dangerous bacteria – salmonella, listeria and E.coli thrive on plants such as strawberries doused in some of the chemicals used, a team from the University of Minnesota found
Brain damage – research in the Netherlands in 2000, examined the health of 830 people. Of these, 629 had been exposed to pesticides in the course of their work. Many had 'mild cognitive dysfunction', which meant they had problems identifying words, colours or numbers and speaking fluently
Miscarriages and stillbirths – women living near farms were more likely to have miscarriages in the first three months of pregnancy, according to a study published in March 2001. The link was strongest for women living within a mile of pesticide spraying
Case study Emma Bennion, 51, former farmer
Emma Bennion was diagnosed with Parkinson's disease at the age of 37. Having grown up on her parents' fruit orchard in Suffolk she was no stranger to working with pesticides, which were sprayed regularly on the family's fruit trees.
She went on to marry a farmer, William Bennion, in 1974, living and working on dairy and arable farms in Leicestershire and Norfolk, where once again pesticides were used.
After experiencing baffling signs such as internal tremors and a frozen shoulder, Parkinson's was eventually diagnosed in November 1987. Since then the disease has taken an insidious grip and leaves her deeply frustrated and unable to do even the simplest tasks, such as placing a letter in an envelope or putting on her own tights.
Now 51, she is anxious to learn more and establish any possible link between the use of pesticides and the disease, not least because her husband and son still work on their 600-acre arable farm near King's Lynn, Norfolk.
"I have done a lot of manual work on our farms with my husband. We have also used chemical sprays on arable farmland.
"I personally think that there may possibly be a link between Parkinson's and something environmental. I would be very interested to see if a link between the two can be proved.
"Having said that I believe there may be a link, I also find myself asking the question, why me and not my husband?
While I grew up in a farm growing area, he was born into farming.
I think that Parkinson's is multi-factorial. It could have something to do with pesticides but for someone with a genetic predisposition perhaps."
The mother of three grown-up children, who now takes medicine every three and a half hours for severe rigidity and slowness in movement, said: "I have known plenty of people who have worked in farming whose children do not have Parkinson's so I am not going to spend my life getting overly worried about what might happen.
"My husband has not expressed worry about getting Parkinson's. He buries his head in the sand and thinks lightning doesn't strike twice in the same family. But then again farmers now use equipment that protects them from harmful exposure, which wasn't used in farming while I was involved."
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