Acute Toxicity of Mixtures of Range Management Herbicides to Cutthroat Trout

Abstract

Six different paired mixtures of dicamba, picloram, 2,4-D butyl ester, 2,4-D isooctyl ester, and 2,4-D propylene glycol butyl ether ester were tested with cutthroat trout (Salmo clarki). Except for 2,4-D isooctyl ester, the LC50's resulting from mixtures of 2,4-D esters and picloram were lower than LC50's of those herbicides tested individually. Dicamba and 2,4-D isooctyl ester were the least toxic individually and mixtures of dicamba or 2,4-D isooctyl ester with the other herbicides tested did not result in increased toxicity. Our results reflect the importance of using combination exposures in determining the biological significance of the simultaneous occurrence of more than one herbicide in surface waters.