USEtox—the UNEP-SETAC toxicity model: recommended characterisation factors for human toxicity and freshwater ecotoxicity in life cycle impact assessment

Background, aim and scope In 2005, a comprehensive comparison of life cycle impact assessment toxicity characterisation models was initiated by the United Nations Environment Program (UNEP)–Society for Environmental Toxicology and Chemistry (SETAC) Life Cycle Initiative, directly involving the model developers of CalTOX, IMPACT 2002, USES-LCA, BETR, EDIP, WATSON and EcoSense. In this paper, we describe this model comparison process and its results—in particular the scientific consensus model developed by the model developers. The main objectives of this effort were (1) to identify specific sources of differences between the models’ results and structure, (2) to detect the indispensable model components and (3) to build a scientific consensus model from them, representing recommended practice. Int J Life Cycle Assess DOI 10.1007/s11367-008-0038-4 Electronic supplementary material The online version of this article (doi:10.1007/s11367-008-0038-4) contains supplementary material, which is available to authorized users. R. K. Rosenbaum (*) :M. Margni Department of Chemical Engineering, CIRAIG, École Polytechnique de Montréal, 2900 Édouard-Montpetit, Stn. Centre-ville, P.O. Box 6079, Montréal, QC, Canada H3C 3A7 e-mail: [email protected] T. M. Bachmann European Institute for Energy Research (EIFER), University of Karlsruhe, Emmy-Noether-Strasse 11, 76131 Karlsruhe, Germany L. S. Gold University of California Berkeley, and Children’s Hospital Oakland Research Institute (CHORI), Oakland, CA, USA M. A. J. Huijbregts :D. van de Meent Department of Environmental Science, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands O. Jolliet Center for Risk Science and Communication, University of Michigan, Ann Arbor, MI, USA R. Juraske :M. Schuhmacher Chemical Engineering School, Rovira i Virgili University, 43007 Tarragona, Spain R. Juraske :A. Koehler Institute of Environmental Engineering, Ecological Systems Design, ETH Zurich, Wolfgang-Pauli-Strasse 15, 8093 Zurich, Switzerland H. F. Larsen :M. Z. Hauschild DTU Management Engineering, Technical University of Denmark, Produktionstorvet, Building 424, 2800 Lyngby, Denmark Materials and methods A chemical test set of 45 organics covering a wide range of property combinations was selected for this purpose. All models used this set. In three workshops, the model comparison participants identified key fate, exposure and effect issues via comparison of the final characterisation factors and selected intermediate outputs for fate, human exposure and toxic effects for the test set applied to all models. Results Through this process, we were able to reduce intermodel variation from an initial range of up to 13 orders of magnitude down to no more than two orders of magnitude for any substance. This led to the development of USEtox, a scientific consensus model that contains only the most influential model elements. These were, for example, process formulations accounting for intermittent rain, defining a closed or open system environment or nesting an urban box in a continental box. Discussion The precision of the new characterisation factors (CFs) is within a factor of 100–1,000 for human health and 10–100 for freshwater ecotoxicity of all other models compared to 12 orders of magnitude variation between the CFs of each model, respectively. The achieved reduction of inter-model variability by up to 11 orders of magnitude is a significant improvement. Conclusions USEtox provides a parsimonious and transparent tool for human health and ecosystem CF estimates. Based on a referenced database, it has now been used to calculate CFs for several thousand substances and forms the basis of the recommendations from UNEP-SETAC’s Life Cycle Initiative regarding characterisation of toxic impacts in life cycle assessment. Recommendations and perspectives We provide both recommended and interim (not recommended and to be used with caution) characterisation factors for human health and freshwater ecotoxicity impacts. After a process of consensus building among stakeholders on a broad scale as well as several improvements regarding a wider and easier applicability of the model, USEtox will become available to practitioners for the calculation of further CFs.