Exposure to pesticides could lead to an increased risk of contracting Parkinson's disease, a study has found.
Some pesticides may be bad for human health
Researchers discovered that high levels of exposure increased the risk by 39%, while even low levels raised it by 9%.
However, the Aberdeen University researchers stressed that the overall risk of developing the disease remained small.
In the UK, one person in 500 develops the incurable degenerative brain disease, or a similar illness.
Symptoms often include unsteadiness and tremor in the hands or arms, often alongside difficulties with speech or movement.
Other studies have pointed strongly towards exposure to pesticides being involved in some cases, with agricultural workers showing higher rates of the illness.
The Aberdeen study, reported in the journal Occupational and Environmental Medicine, involved 959 cases of parkinsonism, a term used to describe people with diagnoses of Parkinson's Disease, and other, similar conditions.
They all answered questioned about their lifetime occupational and recreational exposure to a variety of chemicals, including solvents, pesticides, iron, copper and manganese.
Some have suggested that the head injuries involved in boxing could be linked to Parkinson's, so the patients were also asked whether they had ever been knocked unconscious.
The study included more general questions about family health history and tobacco use.
All the replies were then compared to those from a group of people of similar age and sex who had not been diagnosed with Parkinson's.
They revealed that while having a family history of Parkinson's was the clearest risk factor for developing the disease, exposure to pesticides also gave a clear increase.
People who had been knocked out once were 35% more at risk, while being knocked out on more than one occasion appeared to increase the risk by two-and-a-half times.
However, the researchers acknowledged that it was impossible to tell from the results whether the patients had been knocked out after falling as a result of their Parkinson's.
Dr Finlay Dick, the lead researcher, said: "What we have shown in the study is that with increasing risk to exposure to pesticides, the risk of Parkinson's Disease increases.
"This doesn't prove that pesticides cause Parkinson's Disease - but does add to the weight of evidence of an association."
A spokesman for the Parkinson's Disease Society echoed this: "The important finding from this study is confirmation that Parkinson's is not caused by any one factor, but instead a combination of genetic susceptibility and environmental factors."
Georgina Downs, from the UK Pesticides Campaign, which represents people in rural communities, said: "Considering many pesticides are neurotoxic, then it isn't surprising that study after study has found associations with various chronic neurological and neurodegenerative diseases such as Parkinson's.
"This is highly significant in relation to the long-term exposure of rural residents and communities living near sprayed fields."