Biochemical, metabolic, and behavioural responses and recovery of Daphnia magna after exposure to an organophosphate.

The responses of various suborganismal and organismal endpoints of Daphnia magna to pulse exposure to sublethal levels of the organophosphate paraoxon-methyl were compared. The changes and recovery of biochemical, metabolic, and behavioural variables, as well as physiological responses, were observed. The cholinesterase (ChE), filtration, and swimming activities were all affected in a concentration-dependent manner, and these effects reached significance at concentrations of 1.0, 1.5, and 0.7 microg L(-1), respectively. The levels of these variables recovered significantly after detoxification for 24h in clean medium. ChE and swimming activities were affected significantly by lower concentrations of paraoxon-methyl than filtration activity, which had the same threshold as the physiological responses ((15)N abundance and body size). This study showed that among the parameters studied, swimming activity was the most sensitive, whereas changes in filtration activity had the most significant physiological consequences, and were therefore important in terms of effects propagation to the population level.