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

The standard electrode potential (Eθ) 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 Eθ at r2 = 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 Eθ (and electronegativity, χ). Data compiled from thirty-four studies demonstrate that the PA of twenty-five metal ions correlates with Eθ at r2 = 0.983 (and χ at r2 = 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 Eθ or χ. We propose that the formation of superoxide–metal ion complexes is greater at greater Eθ or χ values and that these complexes, whether free or enzyme-bound, function in PA without redox cycling of the complexed ion.

Graphical abstractEθ has been known for many decades to predict the toxicity of metal ions. We have discovered an even stronger relationship between the prooxidant activity (PA) of metal ions and Eθ (and electronegativity, χ). PA is commonly measured as metal-induced peroxidation of cell membranes or accumulation of reactive oxygen species.Figure optionsDownload full-size imageDownload as PowerPoint slide