The role of fulvic acid composition in the photosensitized degradation of aquatic contaminants

. 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.