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Assessing the Human Health Risks of Trichloroethylene: Key Scientific Issues
THE COMMITTEE’S TASK AND APPROACH
The committee was asked to examine issues critical to developing an objective, realistic, scientifically based health risk assessment for trichloroethylene. It was asked to focus on hazard characterization and mode of action for trichloroethylene toxicity; possible approaches to synthesize epidemiologic data for characterization of hazard; human susceptibility in different subpopulations or life stages; evidence for effects from exposure to trichloroethylene alone compared with that for effects from mixtures of chemicals that include trichloroethylene; physiologically based pharmacokinetic (PBPK) modeling; dose-response assessment; and issues related to quantitative assessment of cancer and noncancer risks. Special attention was given to the availability of appropriate data and methods to implement the committee’s recommendations as well as the distinction between data analysis and data generation. The committee was asked to distinguish between issues that can be addressed through short-term analyses and issues that are more appropriately addressed through medium- or long-term research projects. The committee was not asked to perform a risk assessment or to address risk management issues.
To accomplish its task, the committee held public data-gathering sessions to hear from the sponsoring agencies, other invited speakers, representatives from citizens’ groups, and the public. The committee reviewed a large body of technical material on trichloroethylene, including relevant scientific literature, a draft risk assessment by EPA released in 2001, scientific and technical review comments on that draft assessment, and additional information provided by the sponsoring agencies and other interested parties. Because of the extent of the scientific literature on trichloroethylene, the committee took advantage of recent compilations of information as starting points and evaluated new literature to assess how the state of knowledge has advanced.
In this report, the committee provides guidance in three major categories: hazard characterization, PBPK modeling, and dose-response assessment. The section on hazard characterization provides guidance for identifying and characterizing risks to human health. Intrinsic and extrinsic factors that could modify those risks are discussed, and attention is given to issues related to susceptibility and to mixtures containing trichloroethylene. PBPK models are reviewed, and dose-response issues related to the database on trichloroethylene are considered.
THE COMMITTEE’S EVALUATION
The committee found that the evidence on carcinogenic risk and other health hazards from exposure to trichloroethylene has strengthened since