Industrial Cleaner Linked to Parkinson's Disease

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Trichloroethylene (TCE), a once-popular industrial solvent used in dry cleaning and as a grease-cleaner for metal, has been linked to an increased risk of Parkinson’s disease, according to a new study that will be presented at the American Academy of Neurology’s annual meeting in April.

Study author Dr. Samuel Goldman of the Parkinson’s Institute in Sunnyvale, CA and colleagues analyzed the job histories of 99 pairs of male twins from the World War II Veteran Twins Cohort in which only one had Parkinson’s disease. The men exposed to trichloroethylene (TCE) on the job were 5.5 times more likely to have Parkinson’s than those who had no exposure to the chemical.

Parkinson’s disease is a degenerative disorder of the central nervous system caused by the death of cells in the brain that secrete the neurotransmitter dopamine. It is characterized by impaired motor skills, severe tremors, rigidity in the limbs, and postural instability. While it is not considered fatal on its own, the average life expectancy for someone afflicted with Parkinson’s is generally lower than for those who do have the disease. It affects approximately 60,000 Americans each year, according to the National Parkinson Foundation.

Trichloroethylene has been shown in animal experiments to be selectively toxic to dopamine-producing cells in the substantia nigra portion of the brain. It also impairs the mitochondria of certain brain cells.

TCE is no longer widely used, according to Dr. Goldman. Industries that used the solvent included dry cleaners, electricians, machinists, and mechanics. In 2001 the EPA attempted to set more rigorous standards to limit public exposure to the chemical due to concern that it had been linked to cancer in humans. The International Agency for Research on Cancer considers TCE a Group 2A carcinogen.

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Other environmental chemicals that have been linked to Parkinson’s disease have included tetrachloroethylene or PERC, which is also used in dry cleaning. Those exposed to either TCE or PERC had eight times the risk of developing Parkinson’s.

According to Dr. Goldman, “Part of the problem is that the usage of the substances overlaps quite a bit. Nonetheless, the very high odds ratio for TCE is impressive, and certainly mandates that large population-based studies follow this up.” The team will begin to look at larger databases to find cohorts of people with high exposures to chemicals such as TCE to see how many have developed Parkinson’s disease.

Update: November 14, 2011
This study, previously presented at the American Academy of Neurology’s annual meeting in April 2010, has now been published in the peer-reviewed journal Annals of Neurology. The new paper expands on the preliminary findings and quantifies the individuals' exposures to the chemicals in terms of successive years and cumulative exposure over their lifetime.

Drs. Goldman and Tanner find that TCE exposure increases risk of Parkinson’s disease by 6-fold. They also suggest a lag time of up to 40 years between TCE exposure and onset of disease symptoms.

The Environmental Protection Agency has also recently announced that TCE is carcinogenic to humans.

Reference: Goldman SM et al. "Solvent Exposures and Parkinson Disease Risk in Twins" Annals of Neurology, published online Nov. 14, 2011

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