Many contaminants, including PCBs, mercury, and trace organic compounds (e.g., pesticides and personal care products), reach the Great Lakes inadvertently every year.  Other compounds, such as the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) and the molluscicide 5-chlor-N-(2 chloro-4-nitrophenyl)-2-hydroxibenzamide (niclosamide), are added purposefully to tributaries of the Great Lakes to combat the invasive sea lamprey (Petromyzon marinus).  Despite their intentional addition, the fate and lifetime of these two compounds have not been fully characterized.  Our study assesses the role of direct and indirect photochemical degradation in the environmental fate of TFM and niclosamide. The study also proposes mechanisms for the degradation of these two compounds.  TFM degrades rapidly through direct photodegradation (t1/2= 0.98 hours at pH 7 under experimental conditions).  Conversely, niclosamide is more photostable (t1/2= 9.43 hours under the same conditions) and therefore persists longer in the aquatic environment.  To determine the contribution of indirect photochemical pathways, we quantified the photodegradation of TFM and niclosamide in the presence of river water samples collected from tributaries to Lake Michigan, as well as in solutions containing dissolved organic matter (DOM) isolates, (Suwanee River fulvic acid (SRFA) and Pony Lake fulvic acid (PLFA)).  These experiments demonstrated that TFM does not degrade through indirect photochemical pathways, and that the presence of DOM accelerates the photodegradation of niclosamide.  To more fully understand the indirect degradation pathway for niclosamide, we measured the contribution of reactive species (e.g., singlet oxygen, triplet DOM, hydroxyl radical and carbonate radical).  For example, reaction with singlet oxygen contributes 23.3% to the photodegradation of niclosamide in 10 mg C/L SRFA.  Determining the photochemical degradation mechanisms of TFM and niclosamide in the Great Lakes has implications for the compounds themselves, and also may benefit other structurally similar organic compounds (i.e., halogenated phenols) such as pesticides, estrogen disrupting compounds, and personal care products.

Evaluating the direct and indirect photodegradation pathways of two lampricides in tributaries of the Great Lakes

248th National Meeting (2014)

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