[CPEO-BIF] Perc screening level

[Lenny Siegel <lennysiegel@gmail.com>]

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
http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=192423
and scroll down to Downloads. This document has a long way to go before 
it's finalized, but if the final risk factor remains the same, it will 
drive down the residential inhalation risk screening level to .1 
micrograms per cubic meter. This is below outdoor background 
concentrations in much of the country.

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
<lsiegel@cpeo.org>
http://www.cpeo.org



_______________________________________________
Brownfields mailing list
Brownfields@lists.cpeo.org
http://lists.cpeo.org/listinfo.cgi/brownfields-cpeo.org