Scientists have begun a three-year study aimed at establishing whether pesticides can cause Parkinson's disease as part of an attempt to assess the extent of long-term health risks from the chemicals. The project, funded by the environment department, Defra, provoked praise and scepticism among anti-pesticide campaigners, while the Parkinson's Disease Society said it could mark a significant step towards understanding the nervous condition, which affects about 150,000 Britons.

There has been much dispute about the long-term hazards for those involved in manufacturing the chemicals or spraying them on crops as well as for the public living near fields or eating fruit and vegetables. Studies have suggested increased risk of Parkinson's for pesticide users but no particular compounds have been consistently linked to the disorder, nor any causal mechanism confirmed.

The £906,000 project, with partners in Britain, the rest of Europe and the United States, aims to build on research at Rutgers University, New Jersey, which suggests mice injected with high doses of the pesticide paraquat and a fungicide called maneb lose nerve cells in the region of the brain that degenerates in people with Parkinson's. The new study will attempt to mimic more closely the levels and forms of exposure that people are likely to experience, such as inhalation of droplets, chemicals on the skin or swallowing of residues on food.

Some Parkinson's cases are linked to genetic mutations, although inherited disease is rare, but most are still unexplained.

Kieran Breen, director of research and development at the Parkinson's Disease Society, said: "It will go a long way to helping our understanding." If exposure to pesticides was shown to be a significant factor in the development of Parkinson's, "that will have serious implications for farming practice throughout the country". Elizabeth Sigmund, of the Organophosphates Information Network, said: "This is a very, very important piece of research. There has been a change of attitude [within Defra]."

Barbara Dinham, director of Pesticides Action Network, conceded that "a huge amount of money" was being spent on the study but asked whether it was being set up to undermine work already done at Rutgers. The results could benefit the agrochemical industry, she warned.

Defra maintains there has so far been "little conclusive evidence" that Parkinson's is caused by paraquat, recently banned for amateur gardeners but still used in farming and horticulture.