US Environmental Protection Agency Issues New Toxicity Criteria for Dry Cleaning and Degreasing Solvents
The EPA recently released updated toxicity information for two chlorinated solvents prevalent at contaminated sites, tetrachloroethylene and trichloroethylene. These solvents are frequently the driver for site cleanups at a variety of properties, including dry cleaners, industrial sites, and brownfield properties undergoing development. In addition, they are common drinking water contaminants. This client alert presents a brief summary of the updated toxicity information and its probable effect on site cleanups and drinking water standards in the future.
On February 10, 2012, the U.S. Environmental Protection Agency (“EPA”) issued new toxicity information for the most prevalent dry cleaning compound –tetrachloroethylene, which is commonly called perchloroethylene or “PCE.” This publication follows on the heels of the release of new toxicity factors on September 28, 2011 for another common degreasing solvent, trichloroeythlene (“TCE”).
The new toxicity information affects how remediation professionals, regulators, the industrial community, and other stakeholders approach site assessments and cleanups, as PCE and TCE are two of the most prevalent and difficult to remediate contaminants affecting soil, groundwater, and, in particular, indoor air. In addition, the EPA intends to use the new toxicity factors in considering revisions to federal drinking water standards, maximum contaminant levels or “MCLs,” established under the Safe Drinking Water Act.
PCE is the most commonly used dry cleaning solvent and a common contaminant that adversely affects soil and groundwater quality. TCE has had similar impacts on soil and groundwater and was also used historically as an industrial solvent throughout the world, although its prevalence has decreased over the last decade. Both chemicals tend to volatilize and, thus, pose a concern because vapors seeping from contaminant sources into buildings can potentially affect indoor air quality adversely. TCE and PCE are present at over 50 percent of the Superfund sites in the U.S.
EPA’s New Toxicity Information
The EPA derives its toxicity values from an intensive literature review of toxicity studies. The PCE and TCE reviews each took longer than 20 years to complete. The EPA’s recent review lowered the carcinogenic values previously used as screening levels for TCE (i.e., TCE is now considered a more potent carcinogen). However, the EPA’s new toxicity factors consider that PCE is now slightly less toxic from a carcinogenic perspective, but more toxic for non-carcinogenic effects than previously used toxicity factors (which were based on California EPA guidance).
The new toxicity criteria led the EPA to adjust the Regional Screening Levels (“RSLs”) it uses for evaluating environmental data for TCE in November 2011. These changes resulted in lowering the TCE RSLs for soil, indoor air, and tap water (which is not the formal drinking water standard), as shown in the table below.
The EPA updates RSLs biannually with revised levels for PCE expected in May 2012. Based on the new toxicity criteria it is likely that the screening levels for PCE will increase for all exposure routes; however, as described below, the MCL may still be lowered.
Potential MCL Revisions
From a drinking water perspective, the new toxicity data are impacting the EPA’s review of its MCLs for both chemicals. In 2011, the EPA conducted its required six-year review for 71 regulated drinking water contaminants and retained only four for further consideration pending the release of updated toxicity information. Two of the four were PCE and TCE. It is clear that the Agency intends to focus on the MCLs for these chemicals now that the toxicity information is finalized.
Historically, MCLs for both chemicals were based on quantitation limits the EPA believed drinking water laboratories throughout the U.S. could consistently achieve. Analytical precision has improved significantly since the MCLs were last promulgated and are presently a fraction of historical levels. Now, the EPA’s consideration of MCLs will be based on health-based levels, ultra-low detection levels, or economic considerations. Clearly, the MCL for TCE is expected to decrease, perhaps by a factor of 10, or possibly even more, because it is considered to be carcinogenic by all routes of exposure (the EPA’s highest carcinogenicity classification). The PCE MCL is also likely to decrease because the new toxicity criteria designated the chemical as a likely human carcinogen, a designation that factors strongly into the EPA’s MCL setting process. This could occur despite the revision to the degree of carcinogenicity posed by the chemical.
According to the EPA, proposed MCL revisions are likely to be issued in two years with a final rule promulgated in another two or more years. Thus, the MCLs for both chemicals could be revised in the next five years. A change in MCLs would affect drinking water systems across the country and impact the values used as site cleanup levels at many sites as well as change the default cleanup levels used as a basis for site cleanups.
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