New method for calculating comparative toxicity potential of cationic metals in freshwater: application to copper, nickel, and zinc.

Current practice in chemical hazard ranking and toxic impact assessments is to estimate fate and toxicity assuming the chemical exists in dissolved and particulate phases and, for metals, that all dissolved species are equally bioavailable. This introduces significant error since metal effects are related to the truly dissolved phase and free metal ion within it, not the total dissolved phase. We introduce a Bioavailability Factor (BF) to the calculation of hazard or Comparative Toxicity Potentials (CTPs) (also known as Characterization Factors; CFs) for use in Life Cycle Impact Assessment (LCIA). The method uses for calculation (1) USEtox for environmental fate, (2) WHAM 6.0 for metal partitioning and speciation in aquatic systems, and (3) Biotic Ligand Model (BLM) for average toxicity. For 12 EU water-types, we calculated medians (range) of CTPs of 1.5 x 10(4) (1.5 x 10(2) to 1.2 x 10(5)), 5.6 x 10(4) (9.4 x 10(3) to 4.1 x 10(5)), and 2.1 x 10(4) (7 x 10(3) to 5.8 x 10(4)) day*m(3)/kg for Cu, Ni, and Zn, respectively, which are up to approximately 1000 times lower than previous values. The greatest contributor to variability in CTPs was the BF, followed by toxicity Effect Factor (EF). The importance of the choice of water-type is shown by changes in the relative ranking of CTPs, which are equally influenced by water chemistry and inherent metal-specific differences.