Field evaluation of triclopyr ester toxicity to fish

Abstract

Two field experiments were conducted to assess the predictions of laboratory time-toxicity tests regarding lethal effects of triclopyr butoxyethyl ester (TBEE) on fish in standing and flowing water bodies. Large lake enclosures were treated with TBEE by backpack sprayer at concentrations of 0.25–7.6 mg/L, expressed as acid equivalents. Median dissipation times for TBEE in lake water ranged from 4–8 d.Effects of the treatments on survival and growth of caged rainbow trout were measured. All trout died by 3 d at initial concentrations of 0.69–7.6 mg/L. There was 43% mortality of rainbow trout in the enclosure treated at 0.45 mg/L, and no mortality in the 0.25 mg/L enclosure or the controls. The treatments at the two lower concentrations had significant adverse effects on the growth rates of surviving trout. TBEE was applied to sections of a forest headwater stream at nominal concentrations of 0.8 mg/L and 2.7 mg/L. These concentrations represent maximum-expected environmental concentrations in 50- and 15-cm deep bodies of water, respectively, when directly oversprayed at an application rate of 3.84 kg/ha. Concentrations of TBEE were rapidly dissipated (as much as 70% decline within 55 m) and exposure periods at concentrations above 0.1 mg/L varied from 25 min in the low-concentration area to 55 min in the high-concentration area. The applications of TBEE at both initial test concentrations did not result in any mortality of resident brook trout. There were no significant effects of the herbicide treatments on the growth of 1+ and 2+ brook trout, but there were indications that the growth of 0+ trout was reduced as a result of exposure to TBEE in the stream. These results were in general agreement with the predictions of laboratory time-toxicity tests.