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Demonstration of the Photodegradation of Lampricides to Form Benign Products during in
Christina K. Remucal1, Megan McConville1, Terrance Hubert2, Adam Ward3 Jase Hixson3
1University of Wisconsin-Madison, 660 N. Park St., Madison, WI 53706
2USGS Upper Midwest Environmental Services Center, 2630 Fanta Reed Road, La Crosse, WI 54603
3Indiana University, 430 MSB-II, Bloomington, IN 47405
The photodegradation of 3-trifluoromethyl-4-nitrophenol (TFM) and 2’,5-dichloro-4’-nitrosalicylanilide (niclosamide) were studied under simulated sunlight in the laboratory and during three field applications. The laboratory results reveal that both compounds degrade to form a series of aromatic intermediates, simple organic acids, ring cleavage products, and inorganic ions. The laboratory kinetic results indicate that TFM photodegradation could potentially occur on the time scale of lampricide applications (e.g., t1/2 = 19.6 hours at pH 8 assuming continuous irradiation over a water depth of 55 cm), while niclosamide, the less selective lampricide, will undergo minimal direct photodegradation during its passage to the Great Lakes. The concentration of TFM was monitored during applications to Carpenter Creek and Sullivan Creek in 2015. No photodegradation products were detected during these treatments and results from a parallel time-of-passage study demonstrated that the loss of TFM in the system was attributable to physical processes (i.e., exchange with the hyporheic zone), rather than photodegradation. A larger field campaign was conducted during the application of both TFM and niclosamide to the Manistique River in 2016. While the lampricides had a residence time of 3.6 days during this treatment, no photodegradation products were detected. Adaptation of the laboratory photolysis rates to the conditions encountered in the field (i.e., less intense sunlight, a 2 m water depth, turbid water) reveal a predicted half-life of 110 hours of noon-time sunlight, supporting the observed results. Hydrodynamic modeling was employed to systematically assess under what conditions TFM will undergo photodegradation using data provided by U.S. Fish and Wildlife Service to constrain physical parameters (e.g., location, time of year, stream length and depth). Furthermore, for systems that are amenable to TFM photolysis, modeling was used to determine how the timing of lampricide addition (i.e., day vs. night) affects TFM transformation. Collectively, this research suggests that TFM photolysis will only be observed in long, shallow rivers. Because lampricide concentrations are boosted as the chemical block moves through large systems, it is likely that much of the TFM and niclosamide enters the Great Lakes without undergoing photolysis. Therefore, the fate of lampricides within the Great Lakes, which have a much deeper photic zone, warrants consideration.