|From:||Lenny Siegel <firstname.lastname@example.org>|
|Date:||Fri, 18 Jul 2008 11:15:44 -0700 (PDT)|
|Subject:||[CPEO-BIF] Perc screening level|
Tetrachloroethylene - also known as perchloroethylene, perc, or PCE - is
the dry-cleaning chemical and solvent found at thousands, perhaps
hundreds of thousands of sites across the country, often in conjunction
with TCE, which is a PCE breakdown product. People are exposed to PCE
through drinking water and household water vapors, emissions from dry
cleaners and other users of the chemicals, vapor intrusion from PCE
groundwater plumes, and from off-gases from dry-cleaned clothes. PCE is
one of the most common contaminants at small brownfields sites.
In May 2008 three EPA Regions published a harmonized set of Regional Risk Screening Levels (RSLs), formerly known as Preliminary Remediation Goals. See http://epa-prgs.ornl.gov/chemicals/index.shtml. They listed a inhalation screening level for PCE (in a residential scenario) of .41 micrograms per cubic meter, corresponding to a excess lifetime cancer risk of 10^-6 (one in a million).
On June 26, 2008 U.S. EPA announced the availability of a draft toxicological review for PCE. To download the draft, go to
Recognition of PCE's true risks should lead to an accelerated phase-out of the compound in dry-cleaning, but even if its use were to stop tomorrow there would be a vast number of sites, in strip malls and under residences, schools, day-care centers, and other workplaces with shallow groundwater plumes of PCE. Even if adjusted for occupational exposures - because people spend less time at work than at home - the new risk findings suggest that any structure with proven, or even likely vapor intrusion from PCE should be mitigated - with subslab depressurization systems, other forms of ventilation, and/or vapor barriers - to bring levels down to concentrations in the outdoor air.
And even that is not enough. At the Information Technology High School in Queens, New York, sampling found that concentrations of PCE in the school were 1.2 micrograms per cubic meter, but that the chemical was not coming from below. Instead, it was entering the school from the outdoor air. As dry cleaners are required to switch to other cleaning chemicals, outdoor concentrations should drop. (Since PCE breaks down in air, there must be continuing releases to maintain such concentrations.) Any building mitigated to today's outdoor levels will need to be revisited to match the safer outdoor levels that I anticipate.
Perhaps I'm being too optimistic. California is slowly phasing out PCE in dry-cleaning, but the rest of the country is only requiring that it be phased out in buildings where cleaners are collocated with residences. It seems that political/socio-economic factors - the difficulty in applying stringent environmental regulation to financially fragile mom-and-pop businesses - have held back risk-based regulation.
However, the solution to that socio-economic quandary is not to ignore the toxicological evidence, but to supplement regulation with technical and financial assistance. Years ago, a coalition of environmental groups here in Silicon Valley did something similar. Instead of forcing the sewage plants to pay fines for releasing heavy metals into the San Francisco Bay, we asked them to use the money to help small printed-circuit board manufacturers to switch over to environmentally responsible production processes. Something similar should be done to clear the air of PCE.
As I stated above, people are exposed to PCE through multiple pathways. The toxicological evidence demands that we address all those pathways at once, and soon.
-- Lenny Siegel Executive Director, Center for Public Environmental Oversight a project of the Pacific Studies Center 278-A Hope St., Mountain View, CA 94041 Voice: 650/961-8918 or 650/969-1545 Fax: 650/961-8918 <email@example.com> http://www.cpeo.org _______________________________________________ Brownfields mailing list Brownfields@lists.cpeo.org http://lists.cpeo.org/listinfo.cgi/brownfields-cpeo.org
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