Genotoxicity in German Surface Waters - Results of a Collaborative Study

As surface waters are widely used for the preparation of drinking water, appropriate test systems are required for the monitoring of possible genotoxic contaminations. In the course of a BMBF-funded collaborative project several methods (Ames test, umu test, alkaline elution, DNA unwinding assay, Comet assay and unscheduled DNA-synthesis test) have been examined for their ability to measure genotoxicity particularly in natural surface waters. The project was subdivided into two parts: In the first part appropriate test versions were developed (sensitized Ames test, luminometric umu test, alkaline elution using clams, Comet assay with fish cells or aquatic plants), adapted to the test subject and validated regarding their sensitivity towards standard genotoxins. All test results were statistically evaluated. In the course of the second part both natural and concentrated samples of the rivers Rhine, Elbe, Mulde, Wupper and one drinking water resource (Wahnbachbarrage) were tested. In parallel all samples were chemically analyzed. Among the unconcentrated samples several statistically positive test results were obtained both for the rivers Elbe and Rhine especially with the Ames test and the Comet assay. Only one river (Wupper) showed significant genotoxicity in the umu test. In this case chemical analysis revealed concentrations of about 41 and 47 µg/l of fluoroquinolonic acid, a bacterial gyrase inhibitor which may be responsible for this effect. No genotoxicity could be found in the drinking water resource even after concentration. The water extracts clearly showed different background genotoxicity in the umu test corresponding to increased pollution along the Rhine (Karlsruhe < K ln < D sseldorf). The eucaryotic in vitro tests revealed comparable results with nonconcentrated water samples. As a conclusion of the study we propose a graduated testing battery consisting of a bacterial (umu or Ames test) and an eucaryotic test like the Comet assay or the alkaline elution assay followed by an additional eucaryotic test (UDS test or micronucleus test) in a decisive function. There is a need for further evaluation by effect-orientated chemical analysis which should be done in the case of positive genotoxicity results in at least two tests or persistent positive results in only one.