Key Scientific Issues in the Health Risk Assessment of Trichloroethylene
Chiu, Weihsueh A., Caldwell, Jane C., Keshava, Nagalakshmi, Scott, Cheryl Siegel, Environmental Health Perspectives
Trichloroethylene (TCE) is a common environmental contaminant at hazardous waste sites and in ambient and indoor air. Assessing the human health risks of TCE is challenging because of its inherently complex metabolism and toxicity and the widely varying perspectives on a number of critical scientific issues. Because of this complexity, the U.S. Environmental Protection Agency (EPA) drew upon scientific input and expertise from a wide range of groups and individuals in developing its 2001 draft health risk assessment of TCE. This scientific outreach, which was aimed at engaging a diversity of perspectives rather than developing consensus, culminated in 2000 with 16 state-of-the-science articles published together as an Environmental Health Perspectives supplement. Since that time, a substantial amount of new scientific research has been published that is relevant to assessing TCE health risks. Moreover, a number of difficult or controversial scientific issues remain unresolved and are the subject of a scientific consultation with the National Academy of Sciences coordinated by the White House Office of Science and Technology Policy and co-sponsored by a number of federal agencies, including the U.S. EPA. The articles included in this mini-monograph provide a scientific update on the most prominent of these issues: the pharmacokinetics of TCE and its metabolites, mode(s) of action and effects of TCE metabolites, the role of peroxisome proliferator-activated receptor in TCE toxicity, and TCE cancer epidemiology. Key words: epidemiology, mode of action, peroxisome proliferators, pharmacokinetics, trichloroethylene, risk assessment. Environ Health Perspect 114:1445-1449 (2006). doi:10.1289/ehp.8690 available via http://dx.doi.org/ [Online 9 May 2006]
Trichloroethylene (TCE; CAS Registry no. 79-01-6) is a chlorinated solvent that has been widely used as a metal degreaser, extractant, and chemical intermediate and is now a common environmental contaminant. TCE has been identified in at least 1,500 hazardous waste sites regulated under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA 1980) or the Resource Conservation and Recovery Act of 1976 (RCRA 1976). TCE can be released into the atmosphere from vapor degreasing operations, enter surface waters via direct discharges, and enter groundwater through leaching from disposal operations and Superfund sites. In addition, TCE can be released to indoor air from use of consumer products, vapor intrusion from groundwater through underground walls and floors, and volatilization from the water supply [Agency for Toxic Substances and Disease Registry (ATSDR) 1997; Hers et al. 2001; Wu and Schaum 2001].
Toxicologically, TCE is an inherently complex chemical in terms of metabolism, observed effects, and mode of action (MOA), and there is a wide spectrum of views on many scientific issues related to TCE health risks. Consequently, in updating its previous TCE health risk assessments [U.S. Environmental Protection Agency (U.S. EPA) 1985, 1987], the U.S. EPA solicited scientific perspectives from many different groups and individuals. Throughout this scientific outreach effort (e.g., meetings in Williamsburg, Virginia, in 1993 and 1995), the goal of the U.S. EPA was to encourage a diversity of views and encompass a broad range of expertise rather than seek consensus. These efforts culminated in 2000 when, under the sponsorship of the U.S. EPA, the U.S. Air Force, the U.S. Department of Energy, the National Institute of Environmental Health Sciences, and the Halogenated Solvents Industry Alliance, Inc., 16 state-of-the-science (SOS) papers were published as a monograph in a supplemental issue of Environmental Health Perspectives (Scott and Cogliano 2000). These papers presented reviews on a range of scientific subjects relevant to TCE health risk assessment, including pharmacokinetics, MOA, epidemiology, and dose-response analysis, and the U. …