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[Toxicity evaluation on the effluent water from a sewage treatment plant in Zhengzhou City].

OBJECTIVE
To explore the acute toxicity and genotoxicity of inlet and outlet water of a sewage treatment plant in Zhengzhou to provide scientific basis for the safety of sewage reuse.


METHODS
Inlet water, secondary and tertiary processed outlet water were collected from the sewage treatment plant. Acute toxicity and genotoxicity of the inlet and outlet water were detected by luminescent bacteria toxicity test and Vicia faba root tip cell micronucleus test, respectively.


RESULTS
The luminosity inhibition rates of luminescent bacteria by inlet water, secondary and tertiary processed outlet water were (33.96 +/- 7.51)%, (14.32 +/- 7.36)% and (7.24 +/- 5.58)%, and the micronucleus rates were (12.67 +/- 2.08) per thousand, (6.33 +/- 1.53) per thousand and (2.67 +/- 0.58) per thousand, respectively. The pollution levels of these three samples were heavy, mild and scarce, respectively. The inhibition rates of luminescent bacteria by the secondary and tertiary processed water were significantly lower than that of inlet water (F = 12.159, P = 0.008). A similar result was observed for micronucleus rate (F = 56.850, P < 0.001).


CONCLUSION
The acute toxicity and genotoxicity of processed water were decreased greatly. However, some potential ecological risks of the processed water still existed for environment.