PCE Toxicity Value Review


On February 10, 2012, U.S. EPA published a final Health Assessment for Tetrachloroethylene (Perchloroethylene, or “Perc” or PCE) on the IRIS database (http://cfpub.epa.gov/ncea/iris/index.cfm?fuseaction=iris.showQuickView&substance_nmbr=0106). In the new Health Assessment, EPA provides revised toxicity values for oral exposures (a reference dose [RfD] for non-cancer and a cancer slope factor [CSF] for cancer risk) and for inhalation exposures (a reference concentration [RfC]for non-cancer and an inhalation unit risk factor [URF] for cancer).

Several years ago, while EPA’s Health Assessment was still in progress, assessment of tetracholorethylene in indoor air arose as a critical issue for a number of MCP sites.  The Bureau of Waste Site Cleanup (BWSC) requested that the Office of Research and Standards (ORS) review the inhalation unit risk factor (URF, for evaluating cancer risk from exposure to air contaminants) in use at the time.  ORS toxicologists conducted the review of the scientific literature available at the time, obtained a peer-review of the ORS assessment, and published a revised inhalation unit risk value in 2008 (http://www.mass.gov/dep/toxics/chemrs.htm).

In addition to the URF published in 2008, ORS has recently reviewed and updated the RfC used to calculate MassDEP’s Threshold Effects Limits (non-cancer) for tetrachloroethylene (http://www.mass.gov/dep/toxics/stypes/telaal.htm).  This review considered all of the toxicological data currently available.

Some of the toxicity values published in EPA’s Health Assessment differ significantly from those developed by MassDEP.  ORS plans to review the basis for the values provided by EPA before adopting final values.  MassDEP expects to complete the review by the end of March. Until then, MassDEP recommends the continued use of the MassDEP cancer slope factor of 5 x 10-2 (mg/kg/day)-1 and the inhalation unit risk of 1 x 10-5 (µg/m3)-1 for site-specific risk assessments conducted under the Massachusetts Contingency Plan (310 CMR 40.0000).

Any questions may be directed to BWSC.Information@state.ma.us.

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