| Halide salts are a common presence in many waters of relevance to environmental science and engineering, whether in oceans which constitute the vast majority of surface water on the planet, or in wastestreams of industrial processes such as oil drilling or chemical production. One of the major transformation pathways for chemicals in surface waters is indirect photolysis; however, in spite of their widespread presence, the role of halide ions on this process has not been well evaluated. In this work, the impacts of Cl-- and Br-- have been investigated for several environmentally relevant cases of indirect photolysis: hydroxyl radical (HO· ) treatment of organic contaminants in saline wastewaters, photo-processing of natural organic matter (NOM) in the ocean, and NOM-sensitized photo-degradation of organic contaminants in surface waters.;A novel method was developed for quantifying photo-excited organic compounds and used to investigate the effect of halide ions on excited states of NOM, showing that halides increase both formation and scavenging of triplet-excited NOM, a key photochemical intermediate. Further, concentrations of important secondary photo-oxidants, HO· and singlet oxygen ( 1O2), were significantly reduced in the presence of halide ions. Scavenging of HO· by halide ions lead to formation of halogen radicals which exhibited more selectivity than HO· in their ability to degrade organic contaminants and resulted in formation of halogenated by-products. Overall, the presence of naturally occurring concentrations of Cl-- and Br-- were found to increase photobleaching rates of NOM chromophores and reduce NOM-sensitized destruction of a model contaminant, 17beta-Estradiol, in saline matrices. |
