Identification of Lampricide Formulations as a Potent Inducer of MFO Activity in Fish

White sucker caged in a Lake Superior tributary during a lampricide application showed marked induction of hepatic mixed function oxygenase (MFO) enzymes. Laboratory trials (0.5-5.8mg L−1, 24h exposure) with rainbow trout confirmed that field formulations of lampricides induce MFO activity. When the two primary components of the lampricide formulation were tested separately, MFO induction was associated with the 3-trifluoromethyl-4-nitrophenol (TFM) formulation, and not the 2’,5-dichloro-4’-nitrosalicylanilide (Bayer 73) component of the field application. Bioassays confirmed that reverse phase HPLC successfully separated the inducing component(s) of the TFM formulation. Induction was not associated with the HPLC fraction of the formulation containing TFM, which was corroborated by subsequent exposures of fish to purified TFM. These biochemical effects of lampricide exposure appear to be related to the presence of an unidentified contaminant in the field formulation. The significance of the MFO induction in terms of growth, reproduction, and survival is unknown, but exposure was associated with a transient decrease in circulating levels of steroid hormones.