Laboratory bioassays were conducted with some chlorinated hydrocarbon insecticides, organophosphate insecticides, other insecticides and acaricides, and with herbicides to determine their relative toxicities and immobilization values for two species of daphnids, Daphnia pulex and Simocephalus serrulatus. Both species are satisfactory bioassay organisms for the determination of a wide variety of pesticides, with D. pulex being the more sensitive.
The organophosphate insecticides were generally more toxic than the chlorinated hydrocarbons to both species. DDVP was the most toxic compound investigated. DDT was the most toxic chlorinated hydrocarbon tested, and lindane the least. There was a wide range in the toxicity of hydrocarbons to D. pulex, with 48-hour EC50 values ranging from 0.36 to 460 ppb. DDT was 2.9 times more toxic at 50 F than at 80 F. Malathion was 8.8 times more toxic at 50 F than at 70 F to S. serrulatus. Endrin was 12 times more toxic than dieldrin to D. pulex. DDT was 2.6 times more toxic at 60 F to first-instar organisms up to 18 hours old than to 7-day-old organisms.
