Integrating dissolution kinetics into freshwater ecotoxicity characterization of inorganic metal compounds: Application to copper and zinc oxides

Current life cycle impact assessment (LCIA) practice for metals assumes full availability for partitioning in water, without accounting for the dissolution behavior of the emitted parent compound. This can overestimate freshwater ecotoxic impacts of poorly soluble metal forms. We propose a comparative ecotoxicity impact characterization framework that incorporates time-dependent release of metal ions into environmental fate and bioavailability modelling. The framework combines (1) the USEtox model for environmental fate modeling, (2) PHREEQC 3 for dissolution and liquid-phase speciation, and (3) the Free Ion Activity Model (FIAM) for updating effect factors based on global recommendations under the UNEP GLAM project. We demonstrate the application of the proposed framework for bivalent copper and zinc oxides (CuO, ZnO) across particle sizes from 10 nm to 100 μm emitted in seven EU freshwater archetypes of varying chemistry. For the USEtox default archetype (EU5), the characterization results ranged from 28 to 2.2∙10⁵ and 270 to 2.5∙10⁵ PAF·m³·day/kg for CuO and ZnO, respectively. The influence of the dissolution kinetics was significant for particles exceeding 1 μm for CuO and 10 μm for ZnO, with values one to four orders of magnitude lower than those currently used in LCIA for unspecified Zn(II) and Cu(II) forms. These findings highlight the need to consider dissolution kinetics in assessing toxic impact of metals in freshwater systems. We propose two pathways for practical implementation focusing on establishing consistent link with current and future life cycle inventories, where chemical forms are typically not specified.