Long-term exposure to a chemical used in metal degreasing and dry cleaning might increase the risk of Parkinson 's disease , a new study says. Seniors living in places with the highest airborne levels of trichloroethylene showed a 10% higher risk for Parkinson's than those in areas with the lowest levels, researchers report in the journal Neurology . Further, risk of Parkinson's increased fourfold for people living one to five miles downwind of an Oregon factory that used the chemical,