Comparison of two equivalency factor approaches with simplified risk assessment for LCIA of toxicity impact potential

Three approaches recommended for characterization of toxicity impact potent ial in a life cycle impact assessment (LCIA) are tested on a case study and compared. The two equivalency factor methods are the Persistence, Bioaccum ulation, and Toxicity (PBT) method and the Multimedia Fate Modeling (MFM) m ethod using a Mackay Level III model with state-specific environmental data . The simplified risk assessment (SRA) method involved dispersion modeling using site-specific environmental data. The life cycle inventory informatio n evaluated by all three methods was limited to manufacturing of the RDX-ba sed explosive in Kingsport, Tennessee. The effort to collect site-specific environmental data and conduct air dispersion modeling for the SRA method r equired about 24 times more effort than the PBT method and about 4 times mo re effort than the MFM method. Direct comparison of impact potential scores for the three approaches were limited to inhalation toxicity scores for ni ne air pollutants modeled by SRA. Correlations were made on the rank order of the impact potential scores for the nine air emissions evaluated for all three LCIA methods. Although the number of chemicals compared is very limi ted, the best correlation coefficient (0.96) was between the rank orders fo r the MFM and the SRA methods. The minimal effort and reduced accuracy of t he PBT approach make it best suited for screening large numbers of chemical s for further evaluation of the highest ranked chemicals. The intermediate effort and reasonable accuracy (includes transfers to other media) of the M FM approach make it well suited for LCIAs involving comparative assertions or governmental policy decisions. The maximum effort and assumption of high est accuracy make the SRA approach suitable only after limiting the locatio ns of interest to a few sites by screening with the other two approaches.