A number of scoring and ranking methodologies have been developed to help prioritize chemicals and emissions in a variety of application domains. The Waste Minimization Prioritization Tool (WMPT) was developed by the US EPA to assist in the ranking of chemicals in terms of their persistence, bioaccumulation and toxicity (PBT) properties. Similarly, the Environmental Defense Fund (EDF) uses Toxic Equivalency Potentials (TEPs) to rank chemicals, on a risk per unit mass release basis, in terms of potential toxicological impacts to human health. Both approaches consider fate, exposure and toxicity, albeit at significantly different levels of sophistication. Therefore the tools are comparable but can yield very different results. 

A comparison of the published scores from WMPT and EDF is first presented. Differences are associated with both the data used and the methodologies. A second comparison, based on a consistent data set, is then presented to help evaluate methodological differences. Through this detailed analysis it is demonstrated that the persistence, bioaccumulative and toxicological aspects of each approach can yield similar insights. However, the WMPT provides a more encompassing picture but with poor resolution whereas the TEP approach may provide a basis for greater distinction between scores but at the expense of comprehensiveness.