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
Revising EPA's Maximum Contaminant Level for TCE as part of
the carcinogenic volatile organic compounds group in drinking
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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