USEtox—the UNEP-SETAC toxicity model: recommended characterisation factors for human toxicity and freshwater ecotoxicity in life cycle impact assessment
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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.
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.
Through this process, we were able to reduce inter-model 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.
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.
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.
KeywordsCharacterisation factors Characterisation modelling Comparative impact assessment Comparison Consensus model Freshwater ecotoxicity Harmonisation Human exposure Human toxicity LCIA Life cycle impact assessment Toxic impact
Most of the work for this project was carried out on a voluntary basis and financed by in-kind contributions from the authors’ home institutions which are therefore gratefully acknowledged. The work was performed under the auspices of the UNEP-SETAC Life Cycle Initiative which also provided logistic and financial support and facilitated stakeholder consultations. The financial support from ACC (American Chemical Council) and ICMM (International Council on Mining and Metals) is also gratefully acknowledged. A number of persons have contributed to the process and success of the model comparison and scientific consensus model development. The authors are grateful for the participation of Miriam Diamond, Louise Deschênes, Bill Adams, Andrea Russel, Jeroen Guinée, Pierre-Yves Robidoux, Stefanie Hellweg, Evangelia Demou, Stig Irving Olsen, Cécile Bulle, Sau Soon Chen, Manuel Olivera, Julian Marshall, Bert-Droste Franke, Peter Fantke, Oleg Travnikov, Dick de Zwart, Peter Chapman, Kees van Gestel and Thomas H. Slone.
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