No abstract

Dissolved organic matter (DOM) chemical composition varies depending upon the source of its precursor materials. Results show that the indirect photodegradation rate coefficients for the compounds sulfadimethoxine (SDM) and triclocarban (TCC) differ depending on the source of fulvic acids used as DOM surrogates. For sulfadimethoxine, little to no enhanced photolysis occurred for the terrestrially derived Suwannee River fulvic acid, but the rate coefficients for triclocarban increased 28 %. In contrast, a large photo-enhancement (48 % for SDM and 45 % for TCC) occurred in the presence of Pony Lake and Old Woman Creek fulvic acids, both of which are derived from predominantly autochthonous material. Conversely, the iron-promoted photodegradation of alachlor occurred more quickly in the presence of Suwannee River fulvic acid than another autochthonous fulvic acid isolated from Lake Fryxell, Antarctica. This pathway is dominated by reaction through hydroxyl radicals generated by the photolysis of the fulvic acids. Taken together, these data provide evidence that autochthonous fulvic acids are more reactive than allochthonous fulvic acids in promoting pathways involving triplet dissolved organic matter intermediates, whereas the latter are more reactive than the former in promoting degradation by some reactive oxygen species (ROS). Thus, more systematic studies are needed to determine the full extent of the linkage between fulvic acid composition and its ability to promote indirect photolytic processes and how the presence of other DOM fractions may affect these reactions.

Photolysis is an important attenuation pathway for the removal of wastewater effluent organic micropollutants from surface waters. In this work, direct and indirect processes leading to the degradation of the disinfectant, triclocarban were studied. Photo-irradiation experiments were conducted in water collected from Old Woman Creek (OWC) a tributary of Lake Erie near Huron, OH, USA and in solutions of fulvic acids isolated from the Suwannee River, Georgia, USA (SRFA), Old Woman Creek (OWCFA) and Pony Lake, Antarctica (PLFA). Photodegradation of triclocarban proceeded faster in the presence of all three fulvic acids relative to deionized water. PLFA, an autochthonous dissolved organic matter (DOM) was found to be more reactive than the other fulvic acids, while the mostly allochthonous SRFA exhibited the lowest reactivity toward triclocarban. The later observation can be in part explained by anti-oxidant moieties present in SRFA. Photosensitized triclocarban degradation in whole water DOM from OWC was entirely attributable to the fulvic acid fraction and suggests that this component is the most photo-reactive fraction of the DOM. Anoxic and methanol-quenched experiments revealed unexpected results whereby the former suggests oxidation through reaction with triplet DOM, while the later is indicative of reaction with photogenerated hydroxyl radicals. It is possible that methanol can quench excited DOM species, which would shut down the triplet oxidation pathway. Finally, we observed no enhancement of triclocarban-photosensitized degradation through the addition of iron.

No abstract