Carbonate-radical-anions, and not hydroxyl radicals, are the products of the Fenton reaction in neutral solutions containing bicarbonate.

The Fenton reaction, Fe(H2O)62+ + H2O2 → Oxidizing product, is of major importance in biology as the major cause of oxidative stress, and in advanced oxidation processes. It is commonly assumed that ·OH is the product of the Fenton reaction. The results presented herein point out that ·OH is indeed the oxidizing product in acidic solutions for [Fe(H2O)62+] > [H2O2]; FeIVaq is the active oxidizing product in neutral solutions; in slightly acidic solutions for [H2O2] > [Fe(H2O)62+] a mixture of ·OH and FeIVaq is formed. However CO3·- is the active oxidizing product in neutral solutions containing HCO3- even at low concentrations, i.e. under physiological conditions. The implications to our understanding of the origins of oxidative stress and of catalytic oxidations in advanced oxidation processes are discussed.