Toxicity of 19 adjuvants to juvenile Lepomis macrochirus (bluegill sunfish)

Nineteen adjuvants, many used as surfactants for aquatic herbicide applications, were applied in static bioassay to bluegill sunfish (Lepomis macrochirus) for 96 h to determine median lethal concentrations (LC50). Surfactants are added to the tank mix as a percentage (v/v) of the total volume, in contrast to herbicide application rates, which are usually expressed in kilograms per hectare. Two ethoxylated tallow amine products were the most toxic, having LC50 values of 1.6 and 2.9 ppm (all values v/v). Seven alcohol/glycol‐based surfactants had 96‐h LC50 values of 4.0 to 11.6 ppm (mean = 7.9 ppm). The polysiloxane‐ or silicone‐based surfactants had toxicities of 18.1 to 29.7 ppm (mean = 24.7). Two limonene‐based products had LC50 values of 10.2 and 30.2 ppm. A methylated seed oil with emulsifier had a LC50 of 53.1 ppm. Two acid/buffer utility adjuvants had LC50 values of 60.8 and 221 ppm. To compare the relative safety of the tested surfactants, we assumed maximum label rate applications to 1 m deep water with uniform mixing. This comparison of relative safety is based on mortality to 50% of the test organisms and does not imply application rates that would not result in any mortality. The two ethoxylated tallow amines, neither used or recommended for aquatic applications, had a relative safety factor of 12.6 or less. Relative safety factor varied from 6.2 to 20.4 for the seven alcohol/glycol surfactants, 38.4 to 63.2 for silicone‐based products, 5.5 to 16.1 for limonene products, 113 for methylated seed oil, and 132.2 to 315.7 for acid/buffer utility adjuvants. When used according to label recommendations under normal use conditions, these adjuvants should not be present in acutely toxic concentrations; however, the most toxic adjuvants in very shallow water (