Objective To detect the concentrations of Giardia and Cryptosporidium in treated effluent feeding a tributary river in a suburb park in Tianjin and their potential health risks.
Methods Water samples (n=9) were collected every two weeks from a wastewater treatment plant upstream of a tributary river in March to July 2014. Giardia and Cryptosporidium concentrations were measured following a method involving flocculation, flotation with density gradient, immunofluorescence stain, and counting under microscope. Quantitative microbial risk assessments on Giardia and Cryptosporidium exposure via greenland irrigation and playing with water were performed based on their concentrations in effluent.
Results Both Giardia and Cryptosporidium were detected in the water samples. The concentration of Giardia in the effluent was between 11 to 53 cysts/L, while that of Cryptosporidium was between 0 to 20 oocysts/L. The annual infection rates caused by Giardia and Cryptosporidium in effluent treated by chlorination were estimated to be 5.69×10-3 and 2.46×10-3, respectively. Both of them were higher than the reference risk level (1.0×10-4) suggested by the United States Environmental Protection Agency. In contrast, the annual infection rates caused by Giardia or Cryptosporidium in effluent treated by UV or ozone were both 2.75×10-5.
Conclusion Giardia and Cryptosporidium are detected in the treated effluent of the waste water treatment plant in Tianjin and their concentrations are similar to prior domestic and international studies. The effluents treated by chlorination still pose potential health risks to people through greenland irrigation or water playing. UV or ozone treatment could reduce the risk of human exposure to Giardia and Cryptosporidium.
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