Acute toxicity of organophosphate insecticide, dichlorvos in relation to selected water hardness for the freshwater zooplankters

Toxicity of organophosphate insecticide, i.e. dichlorvos has been investigated in relation to selected water hardness for the freshwater zooplankters such as Moina, Daphnia, cyclops and nauplii. Results revealed that dichlorvos was highly toxic to the tested zooplankters, as the LC(50) values are noticed in ppb. Trend of sensitivity for different zooplankters to dichlorvos was recorded as Moina < Daphnia < nauplii < cyclops. The LC(50) were found to change significantly with the change in water hardness. The zooplankters were more susceptible to dichlorvos at water hardness of 275 mgl(-1) as compared to water hardness of 540 mg(-1) as revealed from low LC(50) values. The range of safe dischargeable concentrations (1.063-1.137 ppb) were too low as compared to harmless or safe concentrations (43.895-89.194 ppb) for the zooplankters at both the hardness.