Altered Cholinesterase and Monooxygenase Levels inDaphnia magnaandChironomus ripariusExposed to Environmental Pollutants

Biochemical indices were investigated for their potential use as variables of sublethal toxicity inDaphnia(cholinesterase) andChironomus(cholinesterase and biotransformation enzymes). Parathion, dichlorvos, and aldicarb caused dose-related inhibition of cholinesterase (ChE) in 24-h bioassays with both species. Ratios ofDaphniaandChironomusChE IC50values to corresponding immotility EC50values derived from the same experiment covered the range 0.26 to 1.2. Estimates of the ChE inhibition caused by the immotility EC50were in the range 53–99% below control activity. ChE IC50values of dichlorvos, parathion, and aldicarb were 0.17, 0.61, and 95 μg/liter inDaphniaand 6.2, 2.9, and 27 μg/liter inChironomus, respectively. Cytochrome P450-dependent monooxygenase activities (ethoxyresorufin-O-deethylase, methoxyresorufin-O-deethylase, and ethoxycoumarin-O-deethylase) were detectable inChironomusbut not inDaphnia.Chironomusmonooxygenase activities were significantly inhibited to about 30% of control values after 4 days of exposure to 50 μg/liter 3,4-dichloroaniline but remained unchanged by 0.5 μg/liter parathion. An approximately 1.3-fold induction of monooxygenase activities was caused by the model inducer naphthalene (0.1mg/liter). These results suggest that cytochrome P450-dependent monooxygenase activities may be useful variables in toxicity tests with aquatic insects.