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626613 
Journal Article 
Review 
A proposed methodology for selecting a trichloroethylene inhalation unit risk value for use in risk assessment 
Lewandowski, TA; Rhomberg, LR 
2005 
Regulatory Toxicology and Pharmacology
ISSN: 0273-2300
EISSN: 1096-0295 
41 
39-54 
U.S. EPA's 2001 draft assessment of trichloroethylene (TCE) toxicity reviews the existing human and animal data on TCE carcinogenicity and proposes a 20-fold range of cancer potency values for use in risk assessment. Each value in the range is derived from a different source of data, either animal bioassays or epidemiology studies, and thus the range does not represent a distribution which can be characterized by statistical parameters such as a mean or 95% confidence interval. The U.S. EPA suggests users choose a single slope factor from among those it describes as appropriate for the population of interest and mode of exposure, but little guidance is given for making this choice. We propose an approach for determining the most scientifically defensible carcinogenic inhalation unit risk estimate from the range of slope factors developed by U.S. EPA, one that relies on accepted principles for evaluating scientific studies. Based on these considerations, we identify the most appropriate interim unit risk for low-level inhalation exposure as 9 x 10(-7) per microg/m(3). This approach may have fairly broad utility if U.S. EPA elects to use a similar approach in future assessments of other chemicals. 
trichloroethylene; risk assessment; unit risk; inhalation 
Administration, Inhalation 
Animals 
Drug Evaluation, Preclinical 
Humans 
Mice 
Rats 
Reproducibility of Results 
Risk Assessment 
Solvents 
Trichloroethylene 
United States 
United States Environmental Protection Agency 
 

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