Acute toxicity of the insecticide methyl parathion and its hydrolytic product p-nitrophenol to the native Australian cladoceran Daphnia carinata

The toxicity of an organophosphorus (OP) insecticide, methyl parathion (MP), and its hydrolysis product, p-nitrophenol (PNP), to the native Australian cladoceran species, Daphnia carinata, was assessed. Both MP and PNP were stable in cladoceran water during the test period. D. carinata was sensitive to both MP and PNP; however, the parent compound was more toxic than its metabolite. This is the first study that demonstrated the acute toxicity of MP and PNP towards an Australian daphnid species. The present investigation emphasizes the need for including the native taxa as non-target test organisms while evaluating the toxicity of environmental pollutants.