EFFECTS OF SUBLETHAL EXPOSURE ON LETHAL BODY BURDENS OF NARCOTIC ORGANIC-CHEMICALS IN DAPHNIA-MAGNA

This work examines the hypothesis that exposure of Daphnia magna to sublethal levels of narcotic contaminants may affect subsequent sensitivity of the animals. Prior exposure (24 h) of Daphnia to sublethal levels of acetone, acetophenone, benzene, benzoic acid, butanol, 1,2-dichlorobenzene, 2-methylnaphthalene 1,2,4-trichlorobenzene, 1,1,2,2-tetrachloroethane, and toluene had no effect on their sensitivity to effective levels of these chemicals in eight of 10 cases. Effective burdens (24-h acute exposure) were independent of the sublethal body burdens (24-h sublethal exposure)and of the sublethal water concentrations (P < 0.025) in eight of 10 cases. Butanol and benzoic acid were the exceptions. The null hypothesis was then accepted in 80% of the cases. These results imply that animals from polluted sites should be no more resistant to high body residues of pollutants than those from clean sites and that the toxicity of narcotic organic contaminants may be independent of the time course of uptake.