Terrestrial ecotoxicity of plastics: Effect factors for life cycle impact assessment

Soils act as major sinks for plastic pollution, with potential implications for terrestrial ecosystem services. In life cycle assessment (LCA), such impacts are quantified using characterization factors that describe the fate, exposure, and effects of emitted substances. In this study, we develop terrestrial ecotoxicity exposure-and-effect factors (XEFs) for plastics in soil for application in LCA. We compiled 680 effect concentrations (ECs) from published ecotoxicity studies involving plants and invertebrates and converted them to EC10eq. values. Following the USEtox framework, species-specific average EC10eq. values were used to construct log-normal fitted species sensitivity distribution curves, from which XEFs were derived. The resulting XEF for plastics in soil equals 0.128 [0.07; 0.30] PAF•m3•kg-1. Specific XEFs for nanoplastics ≤1µm and plastics >1µm were estimated at 0.921 [0.11; 13.10] and 0.126 [0.07; 0.29] PAF•m3•kg-1, respectively. Specific XEFs for natural and agricultural soil were estimated at 0.159 [0.08; 0.40] and 0.236 [0.09; 0.77] PAF•m3•kg-1, respectively. Compared to existing estimates, the derived XEFs fall within the range of previous soil-based values but are substantially lower than aquatic and sediment XEFs, indicating that direct read-across between compartments is not justified. Overall, the proposed XEFs are fully compatible with the USEtox methodology and enable improved inclusion of plastic-related terrestrial ecotoxicity impacts in LCA.