The Human Toxicity Potential and a strategy for evaluating model performance in Life Cycle Impact Assessment

The Human Toxicity Potential (HTP) is a quantitative toxic equivalency pote ntial (TEP) that has been introduced previously to express the potential ha rm of a unit of chemical released into the environment. HTP includes both i nherent toxicity and generic source-to-dose relationships for pollutant emi ssions. Three issues associated with the use of HTP in Life Cycle Impact As sessment (LCIA) are evaluated here. First is the use of regional multimedia models to define source-to-dose relationships for the HTP. Second is uncer tainty and variability in source-to-dose calculations. And third is model p erformance evaluation for TEP models. Using the HTP as a case study, we con sider important sources of uncertainty/variability in the development of so urce-to-dose models - including parameter variability/uncertainty, model un certainty, and decision rule uncertainty. Once sources of uncertainty are m ade explicit, a model performance evaluation is appropriate and useful and thus introduced. Model performance evaluation can illustrate the relative v alue of increasing model complexity, assembling more data, and/or providing a more explicit representation of uncertainty. This work reveals that an u nderstanding of the uncertainty in TEPs as well as a model performance eval uation are needed to a) refine and target the assessment process and b) imp rove decision making.