Very interesting. There was an article in the British newspaper, The Independent, a couple of weeks ago on how people in rural communities are more susceptible to Parkinson's. They believe it's because of the high amount of pesticides/herbacides they are exposed to. Not everyone succumbs, but some are more susceptible than others. It may be on the paper's web site (sorry don't have the address, but should be easy to find).
Good luck with your studies.