Genotoxic effects in the Eastern mudminnow (Umbra pygmaea) after prolonged exposure to River Rhine water, as assessed by use of the in vivo SCE and Comet assays.

The production of drinking water from river water requires a certain minimal river water quality. The Association of River Rhine Water Works (RIWA), therefore, operates a monitoring network. In vitro mutagenicity studies have shown that the genotoxicity of the River Rhine water steadily decreased from 1981 until 2001. Compared to a study in 1978, a decrease in genotoxicity was also observed in an in vivo genotoxicity study in 2005, in which Eastern mudminnows (Umbra pygmaea) were exposed to River Rhine water, and gill cells were used for the Sister Chromatid Exchange (SCE) test and the Comet assay. In this 2005 study, the in vivo genotoxicity increased upon extending exposure of the fish from 3 to 11 days. Therefore, the objectives of this study were to investigate (i) whether new data corroborate that in vivo genotoxicity of River Rhine water is at present lower than in 1978, (ii) whether the Comet assay is a suitable alternative to the SCE assay, and (iii) whether further prolonged exposure results in a further increase in in vivo genotoxicity. The new data corroborate that in vivo genotoxicity of River Rhine water is at present lower than in 1978. The Comet assay is a useful addition but does not provide a substitute for the SCE endpoint in these in vivo genotoxicity studies. Prolonging the exposure time of Eastern mudminnows to River Rhine water from 11 to 42 days did not give a significant increase in SCEs and DNA damage (Comet assay) in gill cells.

Genotoxic effects in the Eastern mudminnow (Umbra pygmaea L.) after exposure to Rhine water, as assessed by use of the SCE and Comet assays: a comparison between 1978 and 2005.

Surface water used for drinking-water preparation requires continuous monitoring for the presence of toxic compounds. For monitoring of genotoxic compounds fish models have been developed, such as the Eastern mudminnow (Umbra pygmaea L.) because of its clearly visible 22 meta-centric chromosomes. It was demonstrated in the late seventies that Rhine water was able to induce chromosome aberrations and sister chromatid exchange in this fish species. Although in vitro mutagenicity studies of the RIWA (Rhine Water Works, The Netherlands) have shown that the genotoxicity of the river Rhine steadily decreased during the last decades, there is still concern about the presence of some residual mutagenicity. In addition, in most studies the water samples have been tested only in in vitro test systems such as the Salmonella-microsome test. For this reason, and in order to be able to make a comparison with the water quality 27 years ago, a study was performed with the same experimental design as before in order to measure the effect of Rhine water on the induction of SCE in the Eastern mudminnow. As a new test system the single cell gel electrophoresis assay (Comet assay) was performed. Fish were exposed to Rhine water or to groundwater for 3 and 11 days in flow-through aquaria. Fish exposed for 11 days to Rhine water had a significantly higher number of SCE and an increased comet tail-length compared with control fish exposed to groundwater. After exposure for three days to Rhine water there was no difference in SCE and a slightly increased comet tail-length compared with the control. It was concluded that genotoxins are still present in the river Rhine, but that the genotoxic potential has markedly decreased compared with 27 years ago. Furthermore, the Comet assay appears to be a sensitive assay to measure the genotoxic potential of surface waters in fish.