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Science News

Exposure to Chemical Solvents Linked to Parkinsonís

Exposure at work to the industrial solvent trichloroethylene (TCE) significantly increases a person’s risk of developing Parkinson’s disease (PD) according to research published in the November 14 online edition of Annals of Neurology.  The finding raises public health concerns because historically, TCE was an ingredient in household products such as spot removers, glues, carpet cleaners and paints and is now the most common organic contaminant in groundwater.

Based on scattered individual cases of people with high exposures, scientists have long suspected that solvents used in manufacturing to de-grease metals contribute to Parkinson’s.  The new research is the first to systematically assess solvent exposure in a group of people with Parkinson’s.

Led by Samuel M. Goldman, M.D., M.P.H. and Caroline M. Tanner, M.D., Ph.D., scientists at the Parkinson’s Institute in Sunnyvale, California studied 99 pairs of male twins in which one twin had Parkinson’s and the other did not.  Because twins have similar or identical genes, focusing on this group allowed the researchers to assess the relationship between Parkinson’s and environmental exposures, in particular to solvents, in each pair of twins.  The researchers hypothesized that differential solvent exposure may explain the phenomenon of discordant twin: that one twin developed Parkinson’s when the twin brother did not.

Study participants were identified through a registry of World War II veterans who are male twins.  A movement disorders specialist (a doctor specializing in Parkinson’s) confirmed the diagnosis of Parkinson’s in those affected.  The researchers then interviewed participants about jobs and hobbies, including tasks performed and materials used, to assess their lifetime exposure to six solvents anecdotally associated with Parkinson’s:  1) trichloroethylene (TCE), 2) tetrachloroethylene or perchloroethylene (PERC) 3) carbon tetrachloride (CCl4) 4) toluene 5) xylene and 6) n-hexane.

Results

  • Twins who worked with the solvent TCE had a six times higher risk of developing Parkinson’s than those who did not.
  • Workplace exposure to the solvents PERC (a chemical commonly used in dry-cleaning) and to CCl4 also were associated with higher risk of developing Parkinson’s.
  • Study participants developed Parkinson’s 30 to 40 years after exposure to solvents.

What Does It Mean?

The new report is the first epidemiology study to associate Parkinson’s with exposure to TCE in a group of people, corroborating previous anecdotal findings. 

Environmental risk factors play a major role in PD.  For example, a recent Swedish study estimated that only 11 percent of identical twins whose twin sibling developed Parkinson’s will develop the disease.  However, assessing for environmental risk factors is exceptionally difficult.

Estimating environmental exposures that occurred decades in the past is notoriously difficult and imprecise; but with the assistance of an industrial hygienist, the researchers made an effort to depend less on the ability of twins to recall solvent exposure and instead assigned solvent exposure based upon job task.  Their findings are also are supported by laboratory studies demonstrating that TCE exposure can replicate many of the key effects of Parkinson’s disease.  Nevertheless, additional research is needed with larger numbers of study participants to confirm the results.
 
Although the research focused on workplace exposure to TCE and PERC, virtually everyone is exposed to these solvents at low levels.  Millions of pounds of the chemicals are released into the environment each year, and they can be detected as contaminants in blood, breast milk, water and food.  Given the wide public exposure to these solvents and the link to Parkinson’s, the study authors conclude that though “[their] findings require replication … the potential public health implications are substantial.”

Source Date: Nov 18 2011