Dry Cleaning Chemical 'Likely' Causes Cancer
National Academy of Sciences Panel Agrees With EPA Analysis of the Risks of PERC
WebMD News Archive
Feb. 9, 2010 - PERC really is a "likely human carcinogen," the National
Academy of Sciences says.
PERC is a chemical known as perchloroethylene or tetrachloroethylene. It's
the solvent used by about 85% of U.S. dry cleaners, but is also used as a metal
degreaser and in the production of many other chemicals.
PERC is found in the air, in drinking water, and in soil. It can be detected
in most people's blood, as well as in breast milk. What's the risk?
In 2008, the Environmental Protection Agency (EPA) suggested that PERC be
classified as a "likely human carcinogen." Moreover, the EPA found that PERC's
most dangerous noncancer toxicity is brain and nervous system damage -- and set
safe exposure levels well below levels that cause such damage.
But rather than finalize the ruling, the EPA asked the prestigious National
Academy of Sciences to review it's PERC risk analysis and to tell the EPA if
it's system for analyzing chemical risk was correct.
Now the expert panel appointed by the National Academy of Sciences says
the EPA was basically correct. The panel agreed that:
- PERC is a "likely human carcinogen." This means that while there's no
definitive proof that the chemical causes cancer in humans, there's strong
evidence it does -- and there's proof that the chemical causes various cancers
- PERC's most dangerous noncancer effect is nerve and brain damage. Safe
exposure levels for drinking water and air quality should be set well above
levels that can cause such damage.
- The EPA's system for evaluating chemical risk is basically sound, although
procedures for evaluating the strength of relevant studies need to be
"We praised the EPA for doing a very thorough job," panel member Ivan Rusyn,
MD, PhD, a toxicologist at the University of North Carolina, tells WebMD. "The
overwhelming opinion of the committee was that the EPA was correct."
The major complaint the committee had with the EPA was that it put too much
emphasis on a single study in setting the safe concentration level. That level
is calculated by finding the highest dose that does no harm and dividing that
dose by 1,000 or more to err on the side of safety.
The EPA suggested that a safe PERC concentration would be 2 parts per
billion. The National Academy of Sciences committee used several different
studies to calculate a slightly higher safe level, between 6 and 50 parts per
"This is an immaterial difference," Rusyn says.
The National Academy of Sciences panel ruled only on the science used
by the EPA and did not offer any policy advice on the use of PERC by dry
cleaners or other industries. Such policies are for the EPA, Congress, and the
states to decide.
California, for example, in December 2007 passed a law that will outlaw the
use of PERC in that state by the year 2023. The California law also requires
removal of all dry cleaning machines 15 years old or older by July 1, 2010. As
of July, no PERC machines may be used in buildings shared with California
PERC is not the same chemical as perchlorate, a different environmental
contaminant used in products such as rocket fuel and fireworks.
The Halogenated Solvents Industry Alliance Inc., a chemical industry group
that has criticized the EPA's draft assessment of PERC, was unable to respond
to WebMD's request for an interview in time for publication.