Peejay. Epidemiological studies of a complex condition like Parkinson's is notoriously difficult. To establish a causal link with any degree of certainty typically involves hundreds, if not thousands of individuals and take many years. Studies seem to suggest that people working with industrial solvents and pesticides may be more prone to the condition but this is by no means conclusive. There was an article about this in the Parkinsons UK research magazine a while back. You might be able to request a copy.