Determination of photochemically-generated reactive oxygen species in natural water

Reactive oxygen species (ROS) can be produced by interactions between sunlight and light-absorbing substances in natural water environment. ROS may participate in the indirect photolysis of trace organic pollutants, therefore resulting in changes in their environmental fates and ecological risks in natural water systems. Bisphenol A (BPA), an endocrine-disrupting chemical, exits widely in natural waters. The photodegradation of BPA promoted by ROS (.OH, 1O2, HO2 /O2 .??), which were produced on the excitation of ubiquitous constituents (such as nitrate ion, humic substances and Fe(III)-oxalate complexes) in natural water under simulated solar radiation was investigated. Both molecular probe method and electron spin resonance (ESR) test were used for the characterization of the generated ROS. It was found that .OH was photochemically produced in the presence of nitrate ions, humic substances and Fe(III)-oxalate complexes and that 1O2 was produced with the presence of humic substances. The steady-state concentrations of .OH was 1.27 10??14 mol/L in a nitrate solution, and the second-order rate constant of BPA with .OH was 1.01 1010 L/(mol s).