The standard electrode potential (Eθ) predicts the prooxidant activity and the acute toxicity of metal ions

The standard electrode potential (E(θ)) has been known for many decades to predict the toxicity of metal ions. We have compiled acute toxicity data from fifteen studies and find that the toxicity of thirty metal ions correlates with E(θ) at r(2)=0.868 when toxicity is expressed as log concentration of comparably effective doses. We have discovered an even stronger relationship between the prooxidant activity (PA) of metal ions and E(θ) (and electronegativity, χ). Data compiled from thirty-four studies demonstrate that the PA of twenty-five metal ions correlates with E(θ) at r(2)=0.983 (and χ at r(2)=0.968). PA was commonly measured as metal-induced peroxidation of cell membranes or accumulation of reactive oxygen species. None of the redox metals (capable of Fenton-like reactions) in our studies (i.e., Mn, Fe, Co, Ni, and Cu) was prooxidative or toxic beyond what was expected from E(θ) or χ. We propose that the formation of superoxide-metal ion complexes is greater at greater E(θ) or χ values and that these complexes, whether free or enzyme-bound, function in PA without redox cycling of the complexed ion.