Making fate and exposure models for freshwater ecotoxicity in life cycle assessment suitable for organic acids and bases

Freshwater fate and exposure factors were determined for organic acids and bases, making use of the knowledge on electrical interaction of ionizing chemicals and their sorption to particles. The fate factor represents the residence time in the environment whereas exposure factors equal the dissolved fraction of a chemical. Multimedia fate, exposure, and effect model USES-LCA was updated to take into account the influence of ionization, based upon the acid dissociation constant (pKa) of a chemical, and the environmental pH. Freshwater fate (FF) and exposure (XF) factors were determined for 415 acids and 496 bases emitted to freshwater, air, and soil. The relevance of taking account of the degree of ionization of chemicals was tested by determining the ratio (R) of the new vs. fate and exposure factors determined with USES-LCA suitable for neutral chemicals only. Our results show that the majority of freshwater fate and exposure factors of chemicals that are largely ionized in the environment are larger with the ionics model compared to the factors determined with the neutrals model version. RFF ranged from 2.4 × 10−1 to 1.6 × 101 for freshwater emissions, from 1.2 × 10−2 to 2.0 × 104 for soil emissions and from 5.8 × 10−2 to 6.0 × 103 for air emissions, and RXF from 5.3 × 10−1 to 2.2 × 101. Prediction of changed solid-water partitioning, implying a change in runoff and in removal via sedimentation, and prediction of negligible air-water partition coefficient, leading to negligible volatilization were the main contributors to the changes in freshwater fate factors.

► We provide freshwater fate and exposure factors for acids and bases. ► pKa and pH dependency of ionic chemicals are now included in the model. ► Predicted factors were compared to predictions of a neutrals model version. ► New fate factors were up to 2.0 × 104 larger compared to the neutral model. ► Differences in fate and exposure factors were larger for bases than for acids.