Toxicity of the Herbicides Dinoseb and Picloram to Cutthroat (Salmo clarki) and Lake Trout (Salvelinus namaycush)

In static tests of the toxicity of two herbicides, dinoseb (2,4-dinitro-6-sec-butylphenol) and picloram (4-amino-3,5,6-trichloropicolinic acid), to cutthroat (Salmo clarki) and lake trout (Salvelinus namaycush), the 96-h LC50s ranged from 32 to 1400 μg/liter for dinoseb and from 2050 to 8600 μg/liter for picloram. Decreasing pH from 8.5 to 6.5 increased the toxicity of dinoseb by a factor of 43 and decreased that of picloram by a factor of 0.5. Generally, toxicity increased with increasing water temperature. Sensitivity of both species of fish increased with water hardness in tests of dinoseb but was not affected by water hardness in tests of picloram. The toxicity of both chemicals was not changed by aging in water for up to 4 wk or by exposing the fish longer than 96 h. Rate of yolk sac absorption and growth of lake trout fry was reduced in flow-through tests at concentrations as low as 0.5 μg/litev dinoseb or 35 μg/liter picloram. Chronic toxicity of both compounds on early life stages of lake trout is more significant than might be anticipated on the basis of only acute tests with fingerlings.