RELATIVE TOXICITY OF SELECTED INSECTICIDES TO BACTERIAL POPULATIONS IN WASTE DISPOSAL LAGOONS

The toxicity of several insecticides to bacterial populations in waste-disposal lagoons was compared at 5 concentrations. Dursban (O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate) and naled caused the highest levels of mortality to the bacterial population, having LD50''s of 0.028 and 0.02%, respectively. Abate (O,O-dimethyl phosphorothioate O,Odiester with 4,4[image]-thio-phenol) and fenthion with LD50''s of 0.9 and 0.66%, respectively, caused the lowest mortality. Bacterial mortality as low as that found in tests using 0.0001% (1 ppm) concentrations would probably not cause a functional disruption of the lagoon process. To control mosquito breeding, the daily addition of fecal material along with bacterial development in a lagoon could offset the bacterial mortality caused by insecticide application at 1 ppm or less.