CHEMISTRY OF THE SUPEROXIDE RADICAL (O-2(-)) IN SEAWATER - REACTIONS WITH INORGANIC COPPER-COMPLEXES

Copper-catalyzed dismutation has been proposed as an important sink of photoproduced superoxide radical (O-2(-)) in seawater. We have determ ined the effective rate constants of the reactions of superoxide with Cu(I) and Cu(II) in seawater, using pulse radiolysis and kinetic spect rophotometry. Due to the effects of ionic strength and complexation, t he observed rate constants, 1.98(+/-0.05) x 10(9) M-1 s(-1) and 0.663( +/-0.071) x 10(9) M-1 s(-1), for Cu(I) and Cu(II), respectively, are 1 order of magnitude lower than those reported for Cu+ and Cu2+ in low ionic strength media. Measurements of the rate of O-2(-) decay in the presence of catalytic concentrations of dissolved Cu agreed well with predictions based on the independently measured rate constants. Observ ed steady-state concentrations of Cu(I) in solutions exposed to a cons tant flux of O-2(-) were also consistent with the measured rate consta nts. From these results and available data regarding Cu speciation in coastal and open oceans, we calculate that O-2(-) reactions with Cu wi ll be a more important sink of O-2(-) than bimolecular dismutation, ev en if all organically complexed Cu species are unreactive.