Photochemical formation of reactive intermediates from dissolved organic matter in aquatic systems

In recent years, urbanization has contributed to the seemingly ubiquitous presence of synthetic organic micropollutants and changed the level of carbon cycled through dissolved organic matter (DOM) in surface and ocean waters. In these waters, solar radiation acts as a driver to alter DOM composition and produce reactive intermediates, which include reactive oxygen species (hydroxyl radical and singlet oxygen) and triplet excited DOM. Reactive intermediates have the capacity to significantly degrade micropollutants, but their formation is based on the source and quality of DOM. Although micropollutants enter aquatic systems through both point and non-point systems, a primary entry route for surface waters is wastewater effluent. In addition to differences in DOM conformation, aquatic systems have complex background matrices, which make it difficult to model micropollutant degradation. Therefore, to properly evaluate their fate in aquatic systems, the formation of reactive intermediates must be established in the array of environmental conditions found in both ocean waters and surface waters.;The objectives of this thesis were to understand the influence of photochemical processes on the fate of components of the dispersant, Corexit, in ocean waters and to determine the impact of bromide and chloride on the photochemical formation of reactive intermediates (hydroxyl radical, singlet oxygen, and triplet excited dissolved organic matter). During the Gulf Oil Spill, 1.1 million gallons of the dispersant Corexit were applied to mitigate the impact of the oil. The photochemical degradation of two Corexit components were examined and found to have half- lives comparable to those of ocean water biodegradation. A majority of this degradation came through reactions with hydroxyl radical. In the ocean waters studied, the presence of hydroxyl radical varied based on the source of the organic matter, with terrestrial inputs from estuaries being the most efficient producers and open ocean waters contributing the least. As the impact of halides was not considered in the degradation of Corexit, a systematic evaluation of bromide and chloride on photochemical processes was subsequently undertaken. Halides were found to quench fluorescence and the apparent quantum yield of hydroxyl radical from organic matter isolates. However, the steady state concentration of triplet excited dissolved organic matter and the apparent quantum yields for singlet oxygen were enhanced under the same conditions. Despite the order of magnitude differences in concentration in the environment, the impact of bromide was similar to that of chloride. Beyond ocean waters and estuaries, these results can be applied to other aquatic systems with halides, such as wastewater-impacted streams. The results from these objectives contributed to the understanding of the photochemical behavior of DOM and the fate of synthetic organic micropollutants in natural systems.