The environmental impacts of four insecticides on non-target organisms in the Gezira Irrigation Scheme canals of Sudan.

The toxic effects of the insecticides endosulfan, decamethrin, dimethoate and dursban on the aquatic fauna of some of the Gezira irrigation canals were studied. The animal groups selected were fishes, arthropods and snails. Endosulfan was found to be highly toxic, particularly to Gambusia affinis, under field and laboratory conditions. All animals proved to be less sensitive to decamethrin in the field probably because this insecticide reacted with the organic matter and hence its toxicity was reduced. However in the laboratory it proved to be the most toxic chemical to all organisms probably because of the presence of the solvent in the emulsifiable concentrate formulation. The third insecticide, dimethoate had a very low toxicity to all organisms in the field or in the laboratory. Similarly dursban had a lower toxicity to fish than endosulfan under laboratory conditions, but higher toxicity to arthropods and snails. In the field the highest mortality among fish was obtained when dursban was mixed with endosulfan. For all insecticides, fish were the least tolerant of all animals tested, followed by arthropods and then molluscs.