Environ. Sci. Technol. 1989, 23, 1425-1428
Neijassel, 0. M. et al., Eds.; Elsevier Science: Amsterdam, 1987; Vol. 3, pp 515-519. (5) Henson, J. M. et al. FEMS Microbiol. Ecol. 1988, 53, 193-201. ( 6 ) Fliermans, C. B. et al. Appl. Environ. Microbiol. 1988,54,
TTichloroetheneat the Department of Energy Kansas City Plant; ORNL/TM-llOM Oak Ridge National Laboratory:
1709-14. (7) Levenspiel, 0. Chemical Reaction Engineering, 2nd ed.; Wiley: New York, 1972; Chapter 9. (8) Garland, S. B. et al. The Use of Methanotropic Bacteria
Received for review January 17,1989. Revised manuscript received June 12,1989. Accepted July 24,1989. This work was supported by the Kansas City Plant, Office of Defense Programs, U.S. Department of Energy, under Contract DE-ACO5840R21400.
for the Treatment of Groundwater Contaminated with
Oak Ridge, TN, in press.
NOTES Hydrogen Peroxide Concentration in a Northern Lake: Photochemical Formation and Diel Variability William J. Cooper*,+and David R. S. Lead Drinking Water Research Center, Florida International University, Miami, Florida 33 199, and National Water Research Institute, P.O. Box 5050, Burlington, Ontario, Canada L7R 4A6
Diel changes in H202concentration in Jacks Lake, Ontario, suggested that photochemical processes were responsible for its formation. The concentrations of H202 reached 200-400 nM by late afternoon on a sunny day and declined to below 10 nM during the night. The depletion of H202observed in near-shore lake sampling sites was faster than the dark decay rate of H20z. The dark decay rate of H20z obeyed first-order kinetics and was much faster than those previously observed in marine environments. Rain was shown to have H202concentrations up to 34 pM and may contribute to the surface water H20z concentration. Introduction Sunlight-induced photochemical processes in natural waters have implications in redox cycling, pollutant transport, and possibly biological activity (1,2 ) . Of the possible reactive photochemical intermediates that can be formed, H202is one of the more stable species (3). While numerous studies have been published regarding the spatial and temporal variability of H202in oceanic (4-10) and estuarine ( 1 1 , 12) environments, relatively little is known about freshwater systems (13-20). The in situ photochemical formation of H202is thought to result from the disproportionation of superoxide, Of (17, 18, 21-26). As such, 02-may also be important in aqueous processes and H202may be used as a way of estimating the formation rates of 02-in water (23). Several reports of diel and seasonal changes in metal speciation in freshwater have appeared (27-30). It is possible that these changes result from reactions that are initiated photochemically and may involve Hz02,as observed in oceanic environments (7,10,31). Because of the influence of pH and chloride ion on iron and copper speciation it is difficult to extend marine systems studies to freshwater. However, it is possible that reactions of this 'Florida International University. 8 National Water Research Institute. 0013-936X/89/0923-1425$01.50/0
nature are at least in part responsible for the observation of reduced forms of metals in oxygenated water. Although H202is thermodynamically a good oxidant, it is usually kinetically limited, at natural water pH and in the absence of catalysts, when reacting with organic compounds (32,33). Superoxide, on the other hand, may react directly with some pollutants and may be important in determining their fate in natural waters (3). Two such examples are benzidine and benzo[a]pyrene, which have second-order rate constants with 02-in water of >2.5 X lo7 and
