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Quantitative structure activity relationships (QSARs) were developed to predict toxicity of metal ions (from the aquatic environment and soil) by correlating the biological activity, A=log(1/EC₅₀), values with four ion descriptors, chosen to represent the binding tendencies of metals to ligands, electronic and electrical effects: the electronegativity coefficient (c), enthalpy of hydration (DH_hyd), the first hydrolysis constant (K_OH) and the log(Z²/rDE₀), where Z²/r reflects the energy of an ion when interacting electrostatically with a ligand and DE0 reflects the effects of atomic ionization potential. Most QSARs are developed for organic toxicants, with inorganic toxicants (metals) being under-represented. Successful predictive models for relative toxicity of metal ions (monovalent and divalent ones) using ion characteristics have been developed. Relative metal toxicity (Li⁺, Na⁺ , K⁺ , Ca²⁺ , Ba²⁺ , Cd2⁺ , Co²⁺ , Cu²⁺ , Sr²⁺ , Hg²⁺ , Mg²⁺ , Mn²⁺ , Ni²⁺ , Pb²⁺ and Zn²⁺ ) was predicted by least squares linear regression and several ion characteristics. Toxicity was most effectively predicted (R=0.84) with logK_OH (where K_OH is the first hydrolysis constant) and electronegativity, which reflects a metal ion tendency to bind to intermediate ligands such as biochemical functional groups with oxygen atom donors. These QSAR correlations could be useful in ecological risk assessment.

Keywords: QSAR, binding tendency, correlation, biological activity, hydrolysis