Photochemical Formation of Hydroxyl Radicals from Chemical Species Dissolved in River Water

The hydroxyl radial, which is one of the most reactive free radicals in the environment, plays an important role in the photochemical degradation of natural organic matter and organic pollutants. The photochemical formation rates of hydroxyl radicals in 41 water samples collected from 6 rivers in Hiroshima Prefecture were determined and the sources of hydroxyl radicals were discussed. The hydroxyl radical photochemical formation rates in the Kurose and Seno rivers were much higher than those in the Ohta and Oze rivers. River water samples containing high nitrite concentrations were found to show high hydroxyl radical formation rates. In the samples which had the higher hydroxyl radical formation rates, nitrite was found to be the most important source of hydroxyl radicals. On the other hand, with decreasing photochemical formation rate of hydroxyl radicals, the percent contribution of unknown sources other than nitrate, nitrite and hydrogen peroxide increased.