The role of cupric ions in the generation of superoxide in natural waters

Abstract

Photochemical generation of superoxide ions (O2{circled division slash}) in water bodies has been associated with both synthetic and naturally occurring organic compounds. Indirect superoxide measurements are usually made by determining the concentration of hydrogen peroxide (as a product of superoxide dismutation), or by measuring the amount of nitrite produced when superoxide oxidizes hydroxylamine. We have collected evidence that, under alkaline conditions, cupric ions generate superoxide in natural waters by a very sensitive catalytic reaction. This reaction is enhanced by hydroxyl and borate ions. Strong natural and synthetic ligands inhibit the reaction, suggesting that only free or hydrolyzed species are involved. Copper speciation studies were performed using this technique. These results bring a new parameter for evaluating copper toxicity to the aquatic biota, i.e. the toxicity via superoxide ions. © 1986.