Developing characterization factors for multi-component and high aspect-ratio nanomaterials: Advancing toxicity assessment in life cycle impact analysis

This study advances the development of fate factors (FFs) and characterization factors (CFs) within the USEtox framework to address gaps in life cycle impact assessment (LCIA) for Multi-Component NanoMaterials (MCNM) and High Aspect-Ratio Nanoparticles (HARN). We employ a novel non-equilibrium colloidal environmental fate model tailored for MCNM and HARN, deriving FF for nanomaterials (NMs) emissions to air, freshwater, sediment, and soil. Case studies of nano zinc oxide doped with manganese (nZnO-Mn) and silver nanowires (AgNWs) reveal that both materials exhibit their longest residence times in sediment (FFs exceeding 39,000 days), followed by soil (130.9 days for both), air (25.9 and 57.8 days, respectively), and the shortest in freshwater (22.6 and 3.4 days). Calculated CFs for nZnO-Mn and AgNWs are marginally higher than literature values for ZnO and Ag nanoparticles, but at least one order of magnitude lower than their bulk metal counterparts. This discrepancy is attributed to the higher dissolution rates of NMs in freshwater compared to bulk metals. Sensitivity analysis further identifies dissolution rate as the dominant parameter influencing freshwater CFs, overshadowing NM-specific properties such as density, diameter, and length. These findings underscore the necessity of precise dissolution rate quantification and improved toxicological data to ensure robust CF development, enabling better integration of NMs into life cycle assessments (LCAs). Future work should prioritize CF development for NM impacts on human health to guide sustainable nanotechnology applications.