The lampricide, 3-triflouromethyl-4-nitrophenol (TFM) has been intentionally added to tributaries of the Great Lakes since the 1950’s to kill the invasive parasitic sea lamprey. In contrast to legacy contaminants and many chemicals of emerging concern, TFM is directly added to the Great Lakes ecosystem. Despite its widespread and intentional use, the fate of TFM in the environment is still poorly understood. We performed laboratory experiments to assess the susceptibility of TFM to photochemical degradation and conducted two field campaigns to quantify TFM photolysis during lampricide applications. The laboratory experiments indicate that TFM undergoes pH-dependent direct photolysis with a quantum yield of 1.22 × 10<sup>-4</sup> at pH 7, but is not susceptible to indirect photolysis. An extensive field campaign was conducted in two small tributaries to Lake Superior in 2015. By comparing TFM loss with results from a time of passage study using sodium bromide as a conservative tracer, we observed minimal loss of TFM due to photodegradation in these systems (hydraulic residence time = 1-3 hours). These results align with half-life estimates for TFM exposed to natural sunlight integrated over a depth of 55 cm (16.6 ± 0.2 hours at pH 9, 36.1 ± 1.0 hours at pH 7). To investigate the influence of photodegradation on large systems, samples were collected from seven sites along the Manistique River during a TFM application in 2016. Despite a longer residence time (&gt;3 days), there was minimal evidence of photoproduct formation. This study highlights the importance of incorporating a wide diversity of field conditions (i.e., cloud and canopy cover, depth, time of year) into degradation estimates. From these two field campaigns, we illustrate that TFM in both small and large systems may enter the Great Lakes with minimal photodegradation, which has important implications for Great Lakes ecosystems.

Photochemical fate of lampricides in tributaries of the Great Lakes

253rd National Meeting (2017)

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