FIELD-EVALUATION OF TRICLOPYR ESTER TOXICITY TO FISH

Two field experiments were conducted to assess the predictions of labo ratory time-toxicity tests regarding lethal effects of triclopyr butox yethyl ester (TBEE) on fish in standing and flowing water bodies. Larg e lake enclosures were treated with TBEE by backpack sprayer at concen trations of 0.25-7.6 mg/L, expressed as acid equivalents. Median dissi pation 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. Th ere was 43% mortality of rainbow trout in the enclosure treated at 0.4 5 mg/L, and no mortality in the 0.25 mg/L enclosure or the controls. T he treatments at the two lower concentrations had significant adverse effects on the growth rates of surviving trout. TBEE was applied to se ctions of a forest headwater stream at nominal concentrations of 0.8 m g/L and 2.7 mg/L. These concentrations represent maximum-expected envi ronmental concentrations in 50- and 15-cm deep bodies of water, respec tively, when directly oversprayed at an application rate of 3.84 kg/ha . Concentrations of TBEE were rapidly dissipated (as much as 70% decli ne 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 con centrations did not result in any mortality of resident brook trout. T here were no significant effects of the herbicide treatments on the gr owth of 1+ and 2+ brook trout, but there were indications that the gro wth of 0+ trout was reduced as a result of exposure to TBEE in the str eam. These results were in general agreement with the predictions of l aboratory time-toxicity tests.