Earlier this week, EPA announced the results of a new risk assessment that categorizes perchloroethylene (PCE) as a likely human carcinogen. This affirmed a conclusion by the National Research Council in a 2010 report.
So what does this mean for site cleanups?
Surprisingly, the new status of PCE as a suspected human carcinogen may not have as big an impact on site cleanups as many had thought (or feared depending on your perspective). The effect will depend on the current state standards which serve as the ARAR.
The assessment sets a safe daily dose of 0.006 mg of PCE per kg of body weight, on the basis of studies that found neurotoxic effects in workers exposed to the chemical. This replaces a safe dose that EPA set in 1988 of 0.01 mg/kg/day, on the basis of laboratory studies in rats.
The EPA Office of Solid Waste and Emergency Response (OSWER) indicated on the webpage discussing the regulatory developments that it will continue to use the Maximum Contaminant Level (MCL) of 5 ppb for PCE established by the EPA Office of Water, as the remediation goal for ground water that may be used as a drinking water supply. However, for superfund sites in states that have more stringent standard for PCE, the state standard will be considered the ARAR for setting the cleanup goal. But the office of water plans to revise the MCL (see below)
Impact on Vapor Intrusion
The new IRIS toxicity values will be used to derive cleanup levels for indoor air contaminated by vapor intrusion. Previously, the superfund program derived cleanup levels for indoor air based on the California EPA toxicity values. The new IRIS values for PCE will be used by the Superfund program to derive cleanup levels for any new sites with indoor air contaminated from vapor intrusion. It appears that EPA's residential indoor air screening level associated with a one in million (10^-6) excess lifetime cancer risk will RISE from 0.41 micrograms per cubic meter (ug/m3) to 4 ug/m3. The non-cancer screening level would drop from 280 ug/m3 to 40 ug/m3, but that would only make a difference where the cancer goal is 10^-4.
Because the cleanup levels based on the new IRIS values will be less stringent than the ones based on the California EPA values, no additional cleanup will need to be done at any previously cleaned Superfund sites. On the othehand, in states like NY that have higher action levels than California, the new standard may result in stricter cleanups since NY’s current action level s 100 ug/m3. EPA has also stated that “no additional cleanup will need to be done at any superfund sites that were remediated under the old standard.
Impact on MCLs
EPA’s Office of Water has decided to revise the federal Maximum Contaminant Level for perc in 2010 and intends to address the PCE MCL as part of a category of carcinogenic volatile organic compounds (VOCs). The agency expects to initiate regulatory efforts to begin addressing carcinogenic VOCs by the end of March 2011. Typically, it takes about 2 to 2.5 years to develop a proposed rule and about 2 years to promulgate a final rule. The final IRIS assessment for PCE will be considered in EPA’s review of the best available science and the agency’s responsibilities under the law.
For more information about the changes are available from the EPA website at: http://www.epa.gov/iris/subst/0106.htm