Parkinson's disease risk greater in those exposed to trichloroethylene

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 today in Annals of Neurology, a journal published by Wiley-Blackwell on behalf of the American Neurological Association and Child Neurology Society.

The National Institute of Neurological Disorders and Stroke (NINDS) 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 which is characterized by symptoms such as limb tremors, slowed movement, muscle stiffness, and speech impairment. 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 Drs. 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 from the National Academy of Sciences/National Research Council World War II Veteran Twins Cohort 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, CCl4, 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 6-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 Dr. Goldman.

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 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% of drinking water supplies in the country.

While this study focused on occupational exposures, the solvents investigated are pervasive in the environment. The authors suggest that replication of well-characterized exposures in other populations is necessary. Dr. Goldman concluded, "Our findings, as well as prior case reports, suggest a lag time of up to 40 years between TCE exposure and onset of PD, providing a critical window of opportunity to potentially slow the disease process before clinical symptoms appear."