Joint action of pollutant combinations (pesticides and metals) on survival(LC50 values) and acetylcholinesterase activity of Tigriopus brevicornis (Copepoda, Harpacticoida)

The joint toxicity of nine binary mixtures of a metal (arsenic, copper. or cadmium) and a pesticide (carbofuran, dichlorvos, or malathion) was determi ned in the marine microcrustacean Tigriopus brevicornis (Muller) (Copepada) by 96-h LC50 tests and measurement of acetylcholinesterase (AChE) inhibiti on. Acetylcholinesterase is used in the marine coastal environment as a bio marker to evaluate exposure to neurotoxic pollutants. including organophosp horous (OP) and carbamate (C) insecticides and most metals. A toxic unit (T U) approach was used to test the response addition model for mixtures of ch emicals with different action modes. Studies of mixtures showed synergistic lethal effects in all cases (the strongest acute effects being observed in copper-malathion. cadmium-malathion, dichlorvos-malathion, and cadmium-dic hlorvos combinations). At the sublethal level, the presence of the three me tals tested seemed to enhance the inhibitory effects of certain OP and C in secticides.