USEtox: The UNEP-SETAC consensus model for life-cycle impacts on human health and ecosystems

Life cycle impact assessment (LCIA) characterizes emissions for the life-cycle assessment (LCA) of a product by translating these emissions into their potential impacts on human health, ecosystems, global climate and other resources. This process requires substance-specific characterization factors (CFs) that represent the relative potential of specific chemical emissions to impact human disease burden and ecosystem health. Within the Life Cycle Initiative, a joint initiative of the United Nations Environment Program (UNEP) and of the Society of Environmental Toxicology and Chemistry (SETAC), a consensus model called USEtox was established to develop internationally harmonized CFs. In 2005 the LCI initiated an international comparison of six models used to make CF calculations. In this paper we describe this model-comparison process and its results_in particular the consensus model. The comparison focused on model differences both in terms of results and model structure. In three workshops, the model comparison participants identified crucial fate, exposure and effect issues for which the models differed. This process identified important sensitivities, differences in assumptions, and model structures that could be harmonized among the different models. Through this process, we were able to reduce inter-model variation. This process also led to the development of a consensus model that contained only the most influential model elements. The consensus model provided a parsimonious and transparent tool for making human health and ecosystem CF estimates. The consensus model has now been used to calculate CFs for several thousand substances and is intended to form the basis of the recommendations from UNEP-SETAC‘s Life Cycle Initiative regarding characterization of toxic impacts in Life Cycle Assessment.