Embryotoxic and genotoxic potential of sewage system biofilm and river sediment in the catchment area of a sewage treatment plant in Switzerland.

In the present study an embryo toxicity test with zebrafish and the comet assay with primary cells isolated from the embryos were combined to assess the toxicity of native biofilms from the sewage system of the sewage treatment plant (STP) Mittleres Wynental and native sediments from the river Wyna (Switzerland). The aim of the study was to evaluate the applicability of the test system to investigate biofilms and to rank the results of the biofilm and sediment sampling sites with regard to embryotoxic and genotoxic effects. We demonstrated that the zebrafish embryo toxicity test in combination with the comet assay with embryo primary cells is a tool that can basically be applied for investigating the bioavailable toxic potential of native biofilms. By ranking the results for embryo toxicity and genotoxicity, we found clear differences in the toxic potential of the biofilm from different sewage system sections. Significant genotoxicity was determined in all biofilm samples and the sediments revealed a lower genotoxic potential upstream of the STP discharge compared to samples downstream and directly at the discharge. Temporal variability from samplings in autumn and spring were found for two of the five biofilm and for one of the three sediment samples. Based on the results of our study we suggest that ecotoxicological bioassays (such as the embryo toxicity test and comet assay with zebrafish) using biofilm can be a useful tool to assess (waste) water quality.