Emulsifiable oil preparations of benzene hexachloride were found to be 25 times more toxic to golden shiners than wettable powder formulations containing the same level of gamma isomer. Tests of the individual components of the oil preparation other than the pesticide indicated that none of these was toxic to fish at the levels normally applied. The addition of a hydrocarbon solvent to a formulation increased the toxicity many times. No difference was noted in the toxicity of the active ingredient used in the various formulations. Lethal dosages for copepods were not affected by formulation differences. Although aqueous solutions of the oil preparation killed much more quickly than the wettable powder, similar levels of activity produced equivalent results.
