Global spatial analysis of toxic emissions to freshwater: operationalization for LCA

PurposeThere is increasing interest in using fate and exposure models to spatially differentiate the impacts of chemical emissions. This work aims at exploring the operationalization in life cycle assessment (LCA) of spatially differentiated models for toxic emissions into freshwater. We analyse and compare the variability of fate and exposure factors at high resolution with aggregated factors at different levels of lower resolution.MethodsWe developed a spatially resolved fate and exposure characterization model and factors for toxic emissions into freshwater with global coverage at 0.5 degrees x0.5 degrees resolution, extending a global hydrological model to account for removal processes, namely chemical and biological degradation, sedimentation, and volatilization. We analysed the variation in fate and exposure factors for water ingestion, identifying the main factors of influence. We then developed archetypes for ecosystems and human fate and exposure. Using a case study of emissions of arsenic from red mud disposal as a waste from alumina production, we tested practical solutions to apply spatial characterization factors aggregated at different resolution in LCA, comparing archetype-based with region-based approaches.Results and discussionWorld maps show up to 5 orders of magnitude variation for chemical fate in fresh water across all 0.5 degrees x0.5 degrees grid cells and up to 15 orders of magnitude for human intake fractions. The freshwater residence time to the sea and the equivalent depthover all downstream cellswere the most influential landscape parameters. They were used to define four freshwater landscape archetypes. These archetypes capture variation in fate well, better than country or continent-aggregated values, but are not able to reflect variation in intake fraction. The case study on arsenic from alumina production shows that the determination of industry-specific weighted average represents a pragmatic way to account for sector-specific location of emissions. The population-weighted approach is primarily applicable for emissions that are related to population density, such as household emissions.ConclusionsThe developed global freshwater model demonstrates large spatial variations in fate and exposure. Archetypes for fate in fresh water provide substantial reductions in variability compared to country or continental averages, but are more difficult to apply to LCA than rural or urban archetypes for air emissions. The 0.5 degrees x0.5 degrees grid model and the fate archetypes may also be used in the context of ecological scenarios to identify hotspots. In practice, population-weighted and sector-specific average characterization factors may represent the most operational way to account for specific distribution patterns of toxic emissions in LCA.