After 22 years of study, and intense political maneuvering, the US Environmental Protection Agency has formally classified TCE (trichloroethene, also called trichloroethylene) as a carcinogen, as well as a non-cancer hazard to human health. The assessment is now a formal part of the the Integrated Risk Information System (IRIS) database, a human health assessment program that evaluates the latest science on chemicals in the environment, and which has drawn considerable fire from industry. The new assessment may make it harder to cleanup TCE contaminated sites to acceptable levels, and may require changes in Canadian air, soil and water standards.

TCE is one of the most common man-made chemicals found in the environment. It is a volatile chemical and a widely used chlorinated solvent, especially from the 1930s to the 1970s. Frequently found at contaminated sites, TCE migrates easily from contaminated ground water and soil into the indoor air of overlying buildings. Since 1987, it has been classed as a "probable human carcinogen", but it now turns out to have been dangerous at levels previously believed to be safe. In 2001, EPA calculated that the chemical was 5 to 65 times more toxic than previously estimated, and classified it as "highly likely" to cause human cancer, especially in children.This assessment has undergone several levels of peer review including, agency review, interagency review, public comment, external peer review by EPA's Science Advisory Board in January 2011, and a scientific consultation review in 2006 by the National Academy of Sciences.

The new assessment may require regulators across Canada and the US to reassess generic criteria (for air, water and soil), risk assessments for sites contaminated with TCE, and limits on current industrial emissions. For example, until recently, Ontario allowed 50 ug/L of TCE in drinking water. According to the new assessment, that level was likely to cause cancer in about 1 in 10,000 people, possibly more in small children. Co-exposure to other chemicals can make TCE more dangerous to health.

The EPA plans to use the new TCE toxicity values in:

  • Establishing cleanup methods at the 761 Superfund sites where TCE has been identified as a contaminant
  • Understanding the risk from vapor intrusion as TCE vapors move from contaminated groundwater and soil into the indoor air of overlying buildings
  • Revising EPA's Maximum Contaminant Level for TCE as part of the carcinogenic volatile organic compounds group in drinking water
  • Developing appropriate regulatory standards limiting the atmospheric emissions of TCE.

All of these changes will likely affect Canadian standards as well, since we typically follow the US lead.

Thank you to Dr. Ron Brecher for alerting us to the change.

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