MarILCA characterization factors for microplastic impacts in life cycle assessment: Physical effects on biota from emissions to aquatic environments

Although plastics emissions pose hazards to ecosystem quality, life cycle assessment (LCA) methodologies do not yet include quantification of the potential impacts of plastic leakage. To address this gap in LCA, the MarILCA working group was founded. This work contributes to MarILCA's output by providing characterization factors for assessing the impacts of aquatic (marine and freshwater) microplastic emissions through the impact category of physical effects on biota and ultimately the ecosystem quality damage category. First, the existing exposure and effect factor (EEF) for micro-and nanoplastic emissions in aquatic compartments (Lavoie et al., 2021) is updated using additional toxicity data, delivering a generic EEF of 1067.5 PAF m3/kgin compartment. Second, fate factors (FFs) are developed for eleven different polymers (EPS, PS, PA/Nylon, PP, HDPE, LDPE, PET, PVC, PLA, PHA, TRWP), three shapes (sphere/microbead, cylinder/microfiber, microplastic film fragments) and five sizes (1, 10, 100, 1000, 5000 & mu;m). To calculate the FFs, a detailed degradation model and a simplified sedimentation model are proposed. Polymer density and size play a major role in the fate, whereas the influence of the shape is less relevant. Ultimately, the EEF and FFs are combined to deliver midpoint and endpoint characterization factors (CFs). Uncertainty is calculated with Monte Carlo analysis. Default and archetype-based CFs are recommended to LCA practitioners in case the details of emission parameters are not fully known. CFs for 1 & mu;m microplastic size are proposed as interim CFs for nanoplastic emissions. Finally, endpoint CFs are tested in case studies within the UNEP report "Supermarket food packaging and its alternatives: Recommendations from life cycle assessments", assessing the relative magnitude of potential microplastic impacts compared to complete LCA results. The case studies confirm that the proposed methodology contributes to filling a gap in LCA and can assist environmental decision-making on single-use plastics and their alternatives.