AN INVESTIGATION OF HYDROGEN-PEROXIDE CHEMISTRY IN SURFACE WATERS OF VINEYARD SOUND WITH (H-2)-O-18(2) AND O-18(2)

O-18-labeled H2O2 and O2 have been used to determine absolute rates and pathways of peroxide formation and decay processes in surface waters of a coastal marine site. Reactions were followed by incubating seawater samples with O-18(2) or H2 O-18(2) and following the chemical transformation of the isotope label. Decomposition of H218O2 was dominated by biological processes and led to the formation of O-18(2) and H218O; the product distribution indicates that 65-80% of the decay was due to catalase with 20-35% due to peroxidase activity. Photochemical oxidation of H218O2 to O-18(2) was also observed. Particle-dependent, light-independent peroxide production was also observed in freshly collected samples, with rates ranging from 0.8 to 2.4 nM h-1. These rates are low relative to photochemical production rates in surface waters, but may be important under conditions of low light intensity. Experiments with a metabolic inhibitor suggest that at least some of this production was biologically mediated. However, there are no evidence for light-dependent biological production.