Effects of water pH on the uptake and elimination of the piscicide, 3-trifluoromethyl-4-nitrophenol (TFM), by larval sea lamprey

Invasive sea lamprey (Petromyzon marinus) populations in the Great Lakes are controlled by applying the piscicide, 3-trifluoromethyl-4-nitrophenol (TFM), to infested streams with larval sea lamprey (ammocoetes). While treatment mortality is > 90%, surviving lamprey, called residuals, can undermine control efforts. A key determinant of TFM effectiveness is water pH, which can fluctuate daily and seasonally in surface waters. The objectives of this research were to evaluate the influence of pH on the uptake, elimination, and accumulation of TFM by larval sea lamprey using radio-labeled TFM (14C-TFM), when exposed to a nominal concentration of 4.6 mg TFM L− 1 or 7.6 mg TFM L− 1, 3 h or 1 h, respectively. TFM uptake rates were approximately 5.5-fold greater at low pH (6.86) compared to the high pH (8.78), most likely due to the unionized, lipophilic form of TFM existing in greater amounts at a lower pH. In contrast, elimination rates following the injection of 85 nmol TFM g− 1 body mass were 1.7-1.8 fold greater at pH 8.96 than at pH 6.43 during 2-4 h of depuration in TFM-free water. Greater initial excretion rates at pH 8.96 were presumably due to predicted increases in outward concentration gradients of un-ionized TFM. The present findings suggest that TFM is mainly taken-up in its un-ionized form, more lipophilic form, but there is also significant uptake of the ionized form of TFM via an unknown mechanism. Moreover, we provide an explanation to how small increases in pH can undermine lampricide treatment success increasing residual lamprey populations.