Abstract: Effects of pollution of the Grand Canal on activities of the superoxide dismatase(SOD),peroxidase(POD)and catalase(CAT)in the innards of Bellamya purificata in the Grand Canal,by means of indoor simulation,cage raising in sampled plots and direct sampling.Results show that activities of SOD,POD and CAT,components of the antioxidant defense system,in Bellamya purificata,are sensitive indicators of exposure to pollution.The monitoring findings tallied with the data of water chemical assessment.Within the range below the threshold,CAT activity decreased with the intensifying of pollution,while POD was activated,but amplitude of the rise varied from time to time.SOD fluctuated in activity,and is fit to serve as a short-term indicator.By comparing the three methods in determining effect of pollution on activities of SOD,POD and CAT in Bellamya purificata,the method of cage-raising is the optimal one,and the sampling method is not applicable.

Key words: Grand Canal, Bellamya purificata, protective enzyme, biomarker, pollution assessment