De toxiciteit van Maas- en Rijnwater in 1992

Abstract

This report presents the results of 1992 measurements on the organic toxicity contained in the water of the rivers Rhine and Meuse. In cooperation with RIWA, the water of the river Meuse was sampled every two months at seven locations from France (Remilly) to the Netherlands (Keizersveer). RIZA performed a monthly sampling scheme at the Lobith location on the river Rhine and at the Eijsden location on the river Meuse. Additionally two major lakes (IJsselmeer and Markermeer) in the Netherlands were sampled every two months. The toxicity of the sampled water was measured with the Microtox method after concentrating the organic constituents of the water. The Microtox method measures the toxic effect as a reduction of the light output of a population luminescent bacteria. The toxicity is expressed as the so-called pT-value (10log(EC20/100)) indicating the ecotoxicological risk for the ecosystem. According to the calculated pT-values, none of the studied surface waters ever reached environmentally safe conditions with respect to toxicants. This judgement may, however, be biased due to an unbalanced scaling of the pT-value. The report contains vieuws on how to circumvent this bias in future research. Every series of measurements along the river Meuse shows the same tendency of a low toxicity in France, followed by a steady increase of toxicity up to Liege/Eijsden, followed by a light improvement of conditions in the stretch between Eijsden and Keizersveer.<br>