A novel study in twins found that exposure to trichloroethylene (TCE) -- a hazardous organic contaminant found in soil, groundwater, and air -- is significantly associated with increased risk of Parkinson\'s disease (PD). Possibility of developing this neurodegenerative disease is also linked to perchloroethylene (PERC) and carbon tetrachloride (CCI4) exposure, according to the study appearing in Annals of Neurology on Monday. The National Institute of Neurological Disorders and Stroke estimates that as many as 500,000 Americans have PD and more than 50,000 new cases are diagnosed annually. While there is much debate regarding cause of PD, studies suggest that genetic and environmental factors likely trigger the disease. Several studies have reported that exposure to solvents may increase risk of PD, but research assessing specific agents is limited. The current epidemiological study, led by Samuel Goldman and Caroline Tanner with The Parkinson\'s Institute in Sunnyvale, California, investigated exposure to TCE, PERC and CCI4 and risk of developing PD. The team interviewed 99 twin pairs in which one twin had PD and one didn\'t, inquiring about lifetime occupations and hobbies. Lifetime exposures to six specific solvents previously linked to PD in medical literature -- n-hexane, xylene, toluene, CCI4, TCE and PERC -- were inferred for each job or hobby. The findings are the first to report a significant association between TCE exposure and PD -- a more than six-fold increased risk. Researchers also found that exposure to PERC and CCI4 tended toward significant risk of developing the disease. \"Our study confirms that common environmental contaminants may increase the risk of developing PD, which has considerable public health implications,\" commented Goldman in a statement. TCE, PERC and CCI4 have been used extensively worldwide, with TCE noted as a common agent in dry-cleaning solutions, adhesives, paints, and carpet cleaners. Despite the U.S. Food and Drug Administration (FDA) banning the use of TCE as a general anesthetic, skin disinfectant, and coffee decaffeinating agent in 1977, it is still widely used today as a degreasing agent. In the U.S., millions of pounds of TCE are still released into the environment each year and it is the most common organic contaminant found in ground water, detected in up to 30 percent of drinking water supplies in the country. In a release issued on Sept. 28, 2011, the Environmental Protection Agency announced that TCE is carcinogenic to humans.