To clarify the interaction between science and values, I suggest to distinguish among factual, normative, and relational truth claims. Relational claims address the relation of factual knowledge and values and should follow the rules of logic. Arguments about impact assessment method development are relational and need to refer to normative judgments as well as scientific knowledge to be rational. A decision-analytic framework provides a consistent, systematic structure for impact assessment. These attributes relate to our fundamental objectives through causal relationships.
Decision analysis provides criteria for method development.
The comparative evaluation of environmental stressors serves to support environmental policy as well as private pollution prevention efforts. This thesis addresses the evaluation of toxic emissions in product life-cycle assessment, and it provides a framework and theoretical foundation for such comparative evaluations. The Human Toxicity Potential developed here, as well as the structure of the broader assessment, is applicable to other decision support tools in Industrial Ecology and environmental policy. It is based on the toxicity of a chemical as well as its potential dose. Applicable measures of toxicity are U.S. EPA s cancer potency and reference dose.