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GeoInsighter Spring 2003 Newsletter

TCE Alert!

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Those folks at the United States Environmental Protection Agency (USEPA) are at it again, and who knows when we’ll have a final word. However, the draft version of the Trichloroethylene (TCE) Health Risk Assessment includes changes to TCE toxicity that could have a significant impact to the regulated community and, more importantly, remedial cleanup standards.

In August 2001, the USEPA’s National Center for Environmental Assessment (NCEA), as part of the Office of Research and Development (ORD), prepared a draft report titled “TCE Health Risk Assessment: Synthesis and Characterization, External Review Draft (EPA/600/P-01/002A).” The report provided a reassessment of TCE with regard to current information regarding toxicity and heath effects. In addition to a general public comment period, the USEPA’s Science Advisory Panel convened an external (i.e., non USEPA) peer-review panel to review and comment on the draft assessment. Based upon the panel’s comments and input from the public, NCEA will finalize the assessment and the information will be included on the USEPA’s Integrated Risk Information System (IRIS). IRIS is the toxicological database that the USEPA relies upon when completing human health risk assessments.

The USEPA’s draft assessment indicated that TCE toxicity is complex and includes multiple modes of action. Under the USEPA’s proposed cancer guidelines, TCE is characterized as “highly likely to produce cancer in humans.” Information obtained during the current assessment suggested that TCE could affect children and adults differently and that how TCE behaves in the body can be altered by the presence of other chemicals. The USEPA also concluded that health risk assessments regarding TCE should consider the cumulative effect of TCE along with other environmental contaminants. Consequently, the USEPA reached the conclusion that TCE is more toxic than previously believed and has proposed lower factors for certain toxicities. The independent review panel recently completed its review of the August 2001 draft assessment and provided its comments to the USEPA’s Science Advisory Panel. The independent review panel generally agreed with the conclusions provided in the August 2001 draft assessment.

Based upon the toxicity factors included in the draft assessment, TCE risk standards are likely to be reduced significantly for water and air exposures. The current water standard of 5 parts per billion (ppb) could be reduced to a value of approximately 0.26 ppb. The current inhalation standard of 1 microgram per cubic meter (ug/m3) could be reduced to approximately 0.016 ug/m3. The possible new standards represent reductions in the risk limits of approximately 20 times the current water standard and 60 times the current air standard.

Obviously, the revised water standard of less than 1 ppb would present a formidable cleanup goal for many ground water remedial systems. The likely standard is only about two times greater than most laboratories’ ability to detect TCE using standard techniques! The revised air standard would refocus characterization on possible impacts to indoor air from plumes of ground water that contain TCE, even at lower concentrations. At many industrial sites, very low concentrations of TCE in indoor air can be just as likely associated with spills and releases to building surfaces as “off-gassing” from ground water. Differentiating between the two possible sources for very low levels of TCE in indoor air could be very difficult (and costly!).

In addition to comments from the independent review panel, the USEPA received over 800 additional pages of comments. It is uncertain how these comments and the independent panel’s comments will be incorporated into the final document. The USEPA has not committed to a schedule for finalizing the draft TCE assessment. It will be best to keep your “ear to the street” regarding TCE, and for active sites, consider achieving closure as soon as practicable, before possible new standards are developed.



Michael J. Webster, P.G., L.S.P.
mjwebster@geoinc.com


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