WASHINGTON, D.C. Feb. 9, 2010 - The U.S. Environmental Protection Agency's classification of the environmental contaminant tetrachloroethylene as "likely to be a human carcinogen" is appropriately supported in EPA's draft assessment of adverse human health effects for the chemical, says a new National Research Council report, which also recommends improvements for EPA's final assessment. The report suggests using better designed studies than those EPA had chosen in estimating the adverse health effects of tetrachloroethylene. In addition, the report proposes ways to strengthen the scientific basis for estimating the potential to cause cancer, as well as safe inhalation and oral exposures to tetrachloroethylene.
Tetrachloroethylene -- also known as perchloroethylene, PCE, or PERC -- is a dry-cleaning solvent that is found as a contaminant in the air, groundwater, surface waters, and soil. In humans it can damage the nervous and reproductive systems, liver, and kidneys and is a likely carcinogen. People are mostly exposed to PERC by breathing it in the air, but exposure can also occur by ingestion or skin contact. EPA's assessment aims to provide estimates of potential noncancerous and cancerous health effects following exposure to PERC and will be used to establish air- and water-quality standards and set cleanup standards for hazardous-waste sites. EPA asked the National Research Council to review the draft health assessment for PERC independently before EPA finalizes it.
For the cancer assessment, EPA's classification of PERC as "likely to be a human carcinogen" is supported by data that meets the relevant criteria in EPA's 2005 Guidelines for Carcinogen Risk Assessment, concluded the committee that wrote the report. The scientific community agrees in general that PERC is carcinogenic in laboratory animals, but debate continues about how to interpret and use those findings to predict human cancer risks, the report states. This debate is reflected in the committee's examination of which possible PERC-related cancer -- leukemia, liver tumors, or kidney cancer -- provides the strongest data for EPA to estimate its cancer potential.
The majority of the committee members judged that the leukemia data EPA chose to estimate cancer potential contained too many uncertainties to make the data useful. These members said that a more scientifically defensible approach would be to employ the dataset that has the least uncertainty rather than the cancer dataset that yields the highest estimates of adverse health effects. Following this approach, the committee members suggested EPA use the liver-cancer data, followed by the data based upon kidney cancer and leukemia.
However, other committee members judged that the leukemia dataset should be used for estimating cancer potential. Their opinions were based on the observation that reproducible, statistically significant increases in leukemia were found in male and female rats above the background incidence of leukemia and that leukemia was the type of cancer with the highest sensitivity to PERC exposure.
For the potential noncancerous health effects attributed to PERC, such as impairments to the nervous system, EPA estimated the inhalation and oral exposures allowed per day that will likely not cause harm. As the basis for its inhalation "reference concentration" calculation, EPA selected one study that observed adverse neurotoxic effects in people who lived near dry-cleaning facilities. Based on this study, EPA derived a value of 2 parts per billion (ppb) per day. The committee recommended instead that EPA use four other human studies and one animal study that applied stronger methods and provided more reliable findings. When the committee used these five studies and applied EPA's same estimation methods, it produced a range of daily allowable inhalation of 6 to 50 ppb.
The report was sponsored by the U.S. Environmental Protection Agency. The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council make up the National Academies. They are independent, nonprofit institutions that provide science, technology, and health policy advice under an 1863 congressional charter. Committee members, who serve pro bono as volunteers, are chosen by the Academies for each study based on their expertise and experience and must satisfy the Academies' conflict-of-interest standards. The resulting consensus reports undergo external peer review before completion. For more information, visit http://national-academies.org/studycommitteprocess.pdf. A committee roster follows.
Copies of Review of EPA's Draft IRIS Assessment of Tetrachloroethylene are available from the National Academies Press on the Internet at http://www.nap.edu
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