Photolysis of Metolachlor and Triclocarban Sensitized by Natural Water Constituents

Anthropogenic activity introduces a variety of synthetic organic compounds (SOCs) to surface waters. Among these are herbicides, pesticides, fertilizers, pharmaceuticals, and personal care products. Wetlands are known to be well suited to photolysis due to shallow depths and large surface area. In addition, they have been shown to contain species such as dissolved organic matter (DOM) and total nitrates (nitrate and nitrite) that can enhance the degradation of SOCs through indirect, or sensitized, photolysis. The major goal of this research is to determine to what extent these wetland constituents can increase the rate of degradation of an herbicide: metolachlor and an anti-bacterial compound: triclocarban. In particular, the significance of DOM origin on its reactivity was examined. For metolachlor, the influence of concentration on reactivity was also explored.In order to probe the significance of DOM origin, fulvic acid isolates were chosen to represent a spectrum of chemical composition. Pony Lake, Antarctica fulvic acid (PLFA) was chosen to represent microbially derived, aliphatic organic matter while Suwannee River fulvic acid (SRFA) from Fargo, Georgia, was chosen to represent terrestrially derived, aromatic organic matter. Fulvic acid isolated from Old Woman Creek near Huron, Ohio, (OWCFA) was chosen to represent the median between the microbial and terrestrial end-members. For 65 µM metolachlor, the source of DOM was not found to significantly influence reactivity. However, at 0.5 µM metolachlor, SRFA reacted significantly faster than either OWCFA or PLFA indicating terrestrially derived DOM is more reactive towards metolachlor. For 0.5 µM triclocarban, PLFA reacted significantly faster than OWCFA or SRFA. This indicates that DOM reactivity towards contaminants varies not only with DOM origin, but also with the contaminant being examined.To determine the degradation pathway for the two compounds examined, scavenging and sub-oxic experiments were performed. For metolachlor, isopropanol was used to quench hydroxyl radical (*OH) in the reaction solution. At 65 µM metolachlor, the reaction was quenched 20-30%, while at 0.5 µM metolachlor the reaction was quenched by 50-60%. Also for 65 µM metolachlor, the influence of the addition of nitrate on reactivity was examined and found to be much more significant than DOM at concentrations of nitrate above 0.2 mM. For triclocarban, methanol was used for quenching *OH. At 0.5 µM triclocarban, methanol quenched the reaction by 20-30% depending on the fulvic acid being used.For both chemicals, argon sparging of the working solutions was performed for 90 minutes to determine the importance of triplet DOM (3DOM). In the case of metolachlor, argon sparging did not significantly affect the rate of degradation indicating that neither 3DOM nor reactive oxygen species (ROS) such as singlet oxygen (1O2), peroxyl radical (ROO*), and superoxide (O2-) are primary transients leading to degradation. However, for triclocarban, argon sparging increased the rate of reaction from 26-56%…