Researchers studying twins found that exposure to the industrial solvent trichloroethylene (TCE), a hazardous organic contaminant used as a degreaser, is linked to a significant increase in the risk of developing Parkinson’s disease. Led by Drs Samuel Goldman and Caroline M. Tanner, of The Parkinson’s Institute (PI) and Clinical Center in Sunnyvale, California, the international team write about their findings in the 14 November online issue of Annals of Neurology.

The team also found links between raised Parkinson’s risk and exposure to perchloroethylene (PERC, also known as tetrachloroethylene), a leading solvent used in dry-cleaning, and carbon tetrachloride (CCl4), formerly used in fire extinguishers, as a cleaning agent, and in making refrigerants.

TCE is used in industry to degrease metals and other materials, and PERC is the leading solvent used in the dry-cleaning industry and in degreasers and spot removers. As well as the exposure that occurs from working with these chemicals, you can also be exposed through using the dozens of household products like glues, carpet cleaners, spot removers and paints that contain them.

Apart from this, millions of pounds of these solvents are released into the environment every year, where they persist. For example, TCE is the most common organic contaminant in groundwater.

The chances are the vast majority of us have some level of exposure to some of these chemicals, either through work or otherwise.

For the study the team investigated 99 pairs of twins where one had Parkinson’s disease and the other did not.

They asked the twins detailed questions about their jobs and their hobbies, focusing on tasks and the materials involved, so they could assess lifelong exposure to 6 commonly-used solvents, comparing exposures in the participants who developed Parkinson’s with that of their twins who did not.

They found that:

  • There was a 6-fold increase in risk of Parkinson’s disease in people who worked with TCE.
  • There was a 10-fold increase in risk of Parkinson’s disease in people who worked with PERC.
  • Parkinson’s onset followed exposure by 30 to 40 years.

The researchers conclude that:

“Exposure to specific solvents may increase risk of PD. TCE is the most common organic contaminant in groundwater, and PERC and CCl4 are also ubiquitous in the environment. Our findings require replication in other populations with well-characterized exposures, but the potential public health implications are substantial.”

Although animal studies have suggested there is a link between TCE and Parkinson’s disease, and there have been some case reports of people who worked with TCE developing Parkinson’s disease, this is the first epidemiological analysis to link TCE or PERC exposure to the disease.

Thus more studies should now be done to prove or otherwise, that TCE and PERC actually cause Parkinson’s disease, and if not, then how do they influence the development of the disease.

The researchers commented that further lab studies could help explain the toxic effects of TCE and PERC on the brain and hopefully find new targets for drugs.

They also noted that because the study shows exposure can precede disease onset by several decades, this offers a chance that we may be able to intervene, once we understand the underlying biological mechanisms.

Funds from the National Institute of Neurological Disorders and Stroke in the US, the Michael J. Fox Foundation, Parkinson’s Unity Walk, The Valley Foundation, and James and Sharron Clark helped pay for the study.

Written by Catharine Paddock PhD