USEtox fate and ecotoxicity factors for comparative assessment of toxic emissions in Life Cycle Analysis: Sensitivity to key chemical properties

The USEtox model was developed in a scientific consensus process involving comparison of and harmonization between existing environmental multimedia fate models. For freshwater ecosystem toxicity, it covers the entire impact pathway, i.e., transforming a chemical emission into potential impacts based on quantitative modeling of fate, exposure, and ecotoxicity effects. Taken together, these are represented as chemical-specific characterization factors (CFs). Through analysis of freshwater CFs for approximately 2500 organic chemicals, with special focus on a subset of chemicals with characteristic properties, this work provides understanding of the basis for calculations of CFs in USEtox. In addition, it offers insight into the chemical properties and critical mechanisms covering the continuum from chemical emission to freshwater ecosystem toxicity. For an emission directly to water, the effect factor, which is obtained from laboratory measurements of substance toxicity to different phyla, strongly controls freshwater ecotoxicity, with a range of up to 10 orders of magnitude. Chemical-specific differences in multimedia transfer influence the CF for freshwater emissions by less than two orders of magnitude. However, for an emission to air or soil, differences in chemical properties may decrease the CF by up to 10 orders of magnitude, as a result of intermedia transfer and degradation. This result brings new clarity to the relative contributions of fate and freshwater ecotoxicity to the overall characterization factor.