Using metal-ligand binding characteristics to predict metal toxicity: Quantitative ion character-activity relationships (QICARs)

Ecological risk assessment can be enhanced with predictive models for metal toxicity. Modelings of published data were done under the simplifying assu mption that intermetal trends in toxicity reflect relative metal-ligand com plex stabilities. This idea has been invoked successfully since 1904 but ha s yet to be applied widely in quantitative ecotoxicology. Intermetal vends in toxicity were successfully modeled with ion characteristics reflecting m etal binding to ligands for a wide range of effects. Most models were usefu l for predictive purposes based on an F-ratio criterion and cross-validatio n, but anomalous predictions did occur ii speciation was ignored. in genera l, models for metals with the same valence (i.e., divalent metals) were bet ter than those combining mono-, di-, and trivalent metals. The softness par ameter (sigma(p)) and the absolute value of the log oi the first hydrolysis constant (\log K-OH\) were especially useful in model construction. Also, Delta E-o contributed substantially to several of the two-variable models. In contrast, quantitative attempts to predict metal interactions in binary mixtures based on metal-ligand complex stabilities were not successful.