Abstract

This report presents the results of a bimonthly evaluation of the organic toxicity contained in water of the rivers Rhine (3 stations) and Meuse (8 stations) in 1993. The toxicity of untreated water samples as well as selectively concentrated organic constituents was measured with the luminescent bacteria test, Microtox. The toxicity is expressed as the so-called pT-value (10log (EC20,t=.../100)), relating toxicity to environmental acceptability criteria. According to preformulated acceptability criteria, hardly any of the observed pT-values reflects favourable conditions. Throughout the year, the concentrated organic toxicity contained in the water of the River Meuse shows the same tendency of low toxicity at the most upstream station in France, to high toxicity around the city of Liege in Belgium, generally followed by a slight and gradual decrease of toxicity in the downstream Dutch stretch of the river. In the untreated water samples, only one (June, Eijseden, NL) demonstrated a quantifiable toxicity producing 20% reduction of the bacterial luminescence when the sample was diluted to about 20%. The toxicity as observed in water of the River Meuse is of the same order of magnitude as the toxicity observed in Rhine water.