For many years, MassDEP has derived and updated cancer risk values for PCE due to the absence of formal toxicological guidance from the U.S. Environmental Protection Agency (EPA). What has currently made PCE an emerging contaminant is EPA’s recent cancer risk assessment for PCE which differs to greatly from MassDEP’s interpretation of the literature.

Tetrachloroethylene is a synthetic chemical that is widely used for dry cleaning of fabrics and for metal-degreasing operations. It is also used as a starting material for making other chemicals and is used in some consumer products. Another name for tetrachloroethylene is perchloroethylene (PCE or PERC).

In February 2012, EPA published its first cancer toxicity values (or unit risk ) for tetrachloroethylene (PCE) on the Integrated Risk Information System (IRIS). Using well established methods, EPA calculated two values based on cancers observed in animals treated with PCE under controlled experimental conditions. One value was based on liver tumors and the second on a type of leukemia. The liver tumor-based value results in a human cancer risk value that is about 33 times lower (less risky) than the leukemia-based value. EPA selected to adopt the cancer toxicity value based on liver tumors. While the majority of the National Research Council (NRC) recommended use of the liver tumor data, council members did not reach a full consensus on this matter.  

MassDEP considers PCE an emerging contaminant due to the new cancer risk information and a lack of consensus about which tumor type should be used to protect public health. It is also a common contaminant at hazardous waste sites found in groundwater and indoor air of buildings via vapor intrusion. In addition, the new EPA value is much less stringent (less protective) than the current MassDEP value. As a result, MassDEP conducted an in-depth assessment on this issue.

MassDEP Workplan:

  • Update the MassDEP Cancer Risk Value for deriving health based standards. Take into account the EPA 2012 new toxicity values published in the Integrated Risk Information System (IRIS). MassDEP will initially propose toxicity values and cleanup standards which will be published for review and comments. Submitted comments will be considered as part of MassDEP’s work to promulgate cleanup standards for groundwater and soil.  
  • Update existing tetrachloroethylene standards based on the outcome of this work. These include waste site cleanup standards and Allowable Ambient Air Limits.   

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