Towards consensus in comparative chemical characterization modeling for LCIA: Efforts within the UNEP/SETAC Life Cycle Initiative

The Task Force on Toxic Impacts under the UNEP/SETAC Life Cycle Initiative is developing recommendations on characterization models and characterization factors for human toxicity and ecotoxicity impacts in Life Cycle Impact Assessment (LCIA). Building on experience from earlier model development work within, for instance, the OECD, and guidance from a series of expert workshops held between 2002 and 2005, preliminary guidelines focusing on chemical fate, and human and ecotoxic effects were established. For further elaboration of the fate-, exposure- and effect-sides of the modeling, six models were compared, focusing on their structure and results in terms of characterization factors. Through three workshops, modelers identified crucial fate, exposure and effect issues for which the presently available models differ. Between the workshops, the models were harmonized, removing identified unnecessary differences. Based on the adapted set of models and their outcomes, and on the earlier guidelines for fate modeling, overall guidelines for toxicity modeling in LCIA were developed. In line with these overall guidelines, a simple consensus model was developed. This model is collectively owned by the Task Force and the model providers. While the compared models and their differences are important tools to further advance LCA science, the consensus model is intended to provide a generally agreed and scientifically sound method to calculate consistent characterization factors for use in LCA practice and to be the basis of the “recommended practice” for calculation of characterization factors for chemicals under authority of the UNEP/SETAC Life Cycle Initiative.