Altered cholinesterase and monooxygenase levels in Daphnia magna and Chironomus riparius exposed to environmental pollutants.

Biochemical indices were investigated for their potential use as variables of sublethal toxicity in Daphnia (cholinesterase) and Chironomus (cholinesterase and biotransformation enzymes). Parathion, dichlorvos, and aldicarb caused dose-related inhibition of cholinesterase (ChE) in 24-h bioassays with both species. Ratios of Daphnia and Chironomus ChE IC50 values to corresponding immotility EC50 values derived from the same experiment covered the range 0.26 to 1.2. Estimates of the ChE inhibition caused by the immotility EC50 were in the range 53-99% below control activity. ChE IC50 values of dichlorvos, parathion, and aldicarb were 0.17, 0.61, and 95 microg/liter in Daphnia and 6.2, 2.9, and 27 microg/liter in Chironomus, respectively. Cytochrome P450-dependent monooxygenase activities (ethoxyresorufin-O-deethylase, methoxyresorufin-O-deethylase, and ethoxycoumarin-O-deethylase) were detectable in Chironomus but not in Daphnia. Chironomus monooxygenase activities were significantly inhibited to about 30% of control values after 4 days of exposure to 50 microg/liter 3, 4-dichloroaniline but remained unchanged by 0.5 microg/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.