Indirect photodegradation of the lampricides TFM and niclosamide.

3-Trifluromethyl-4-nitrophenol (TFM) and 2',5-dichloro-4'-nitrosalicylanilide (niclosamide) are lampricides used in tributaries of the Great Lakes to kill the invasive parasitic sea lamprey (Petromyzon marinus). Although the lampricides have been applied since the late 1950s, their photochemical behavior in natural environments is still not well understood. This study examines the indirect photodegradation of these two compounds and the resulting yields of organic and inorganic photoproducts in water samples collected from five tributaries of Lake Michigan. The tributaries were selected to span the length of Lake Michigan and its natural carbonate geologic gradient. In the presence of dissolved organic matter (DOM), the niclosamide photodegradation rate triples, while the rate of TFM photodegradation is unchanged. Additionally, the yield of lampricide organic products is influenced by DOM because many of the organic photoproducts themselves are prone to DOM-mediated indirect photodegradation. The indirect photodegradation of niclosamide is primarily mediated by reaction with singlet oxygen, which accounts for more than 50% of the increased photodegradation rate. Additionally, hydroxyl radicals and carbonate radicals (CO3-˙) influence niclosamide indirect photolysis, and their contribution is dependent on the specific river water chemistry. For example, CO3-˙ contribution to niclosamide photodegradation, while small, is greater in southern tributaries where there is higher carbonate alkalinity.

A field analysis of lampricide photodegradation in Great Lakes tributaries.

The lampricides 3-trifluoromethyl-4-nitrophenol (TFM) and 2',5-dichloro-4'-nitrosalicylanilide (niclosamide) are added to Great Lakes tributaries to target the sea lamprey, an invasive parasitic fish. This study examines the photochemical behavior of the lampricides in Carpenter Creek, Sullivan Creek, and the Manistique River. The observed loss of TFM in Carpenter and Sullivan Creeks (i.e., 34 and 19%) was similar to the loss of bromide in parallel time of passage studies (i.e., 30 and 29%), demonstrating that TFM photodegradation was minimal in both tributaries during the lampricide application. Furthermore, the absence of inorganic and organic photoproducts in the Manistique River demonstrates that TFM and niclosamide photodegradation was minimal in this large tributary, despite its long residence time (i.e., 3.3 days). Kinetic modeling was used to identify environmental variables primarily responsible for the limited photodegradation of TFM in the field compared to estimates from laboratory data. This analysis demonstrates that the lack of TFM photodegradation was attributable to the short residence times in Carpenter and Sullivan Creeks, while depth, time of year, time of day, and cloud cover influenced photochemical fate in the Manistique River. The modeling approach was extended to assess how many of the 140 United States tributaries treated with lampricides in 2015 and 2016 were amenable to TFM photolysis. While >50% removal of TFM due to photolysis could occur in 13 long and shallow tributaries, in most systems lampricides will reach the Great Lakes untransformed.