Environ. Sci. Technol. 2008, 42, 2387–2393
Measurement and Implications of Nonphotochemically Generated Superoxide in the Equatorial Pacific Ocean A N D R E W L . R O S E , * ,†,‡ E R I C A . W E B B , §,4 T. DAVID WAITE,† AND J A M E S W . M O F F E T T ‡,4 Centre for Water and Waste Technology, School of Civil and Environmental Engineering, The University of New South Wales, Sydney, Australia, Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA and Department of Biology, Woods Hole Oceanographic Institution, Woods Hole, MA
Received September 30, 2007. Revised manuscript received December 22, 2007. Accepted January 5, 2008.
Superoxide, formed by the single electron reduction of oxygen, is important due to its ability to act as a mild reductant under typical environmental conditions. Using chemiluminescence detection with the reagent methyl Cypridina luciferin analog (MCLA), we have measured superoxide at picomolar concentrations in the water column of the Costa Rica Dome (CRD) seasonal upwelling region of the eastern equatorial Pacific Ocean. After 0.45 µm filtration, superoxide decayed in a pseudofirst order manner but more slowly than expected (rate constants varied from 0.70, and were all significant (P < 0.01 by F-test); Tables S1-S3), with pseudofirst order rate constants ranging from 7.3 × 10-4 s-1 to 9.7 × 10-3 s-1 (Figure 1) and corresponding superoxide half-lives from 71 s to 16 min. The contribution of reaction between O2- and its conjugate HO2 (disproportionation, a second-order process) to superoxide decay was at most 1%. This is consistent with the presence of organic compounds (7, 27) and/or strong metal-organic complexes that react with superoxide but are not affected by DTPA in the short time (
