Effects of tributyltin at environmental levels on monooxygenase system of digestive gland in hard clam Meretrix meretrix

The effects on ethoxyresorufin O-deethylase (EROD), NADPH-cytochrome c reductase and NADH cytochrome b5 reductase activities of digestive gland in Meretrix meretrix exposed to tributyltin (TBT) at environmental levels (0.1, 1.0, 10.0 ng/dm³ as stannum concentration), in experimental condition, were evaluated.The EROD, NADH cytochrome b5 reductase activities were significantly inhibited after exposure to 10.0 ng/dm³ TBT for 8 and 20 d, the NADPH cytochrome c reductase activities were significantly inhibited after exposure to 0.1, 1.0 and 10.0 ng/dm³ TBT for 8 d and to 1.0 and 10.0 ng/dm³ for 20 d, as compared with the matched control, while NADH cytochrome b5 reductases and NADPH cytochrome c reductase activities were induced after exposure to 10.0 ng/dm³ TBT for 2 d.The EROD activity in the 10 ng/dm³ group, and the NADH cytochrome b5 reductases activities in 1.0 and 10.0 ng/dm³ groups, were significantly induced when transferred to clean recovery tanks for 7 d.The three enzymic activities in the clams exposed to TBT were recovered to the level corresponding to that of the control group after transfer to clean recovery tanks for 20 d.NADPH cytochrome c reductase activity in Meretrix meretrix seems to be more sensitive to exposure of TBT than that of the EROD and NADH cytochrome b5 reductases.The results suggest that induction and inhibition by TBT to the monooxygenase system enzymic activity in Meretrix meretrix would simultaneously exist.The enzymic activities were inhibited by exposure for a long time.The results suggest that inhibition of the monooxygenase system should be an indication of the exposure to environmentally relevant concentrations of TBT for a long time.