Organic concentrates of River Meuse water were tested for toxicity with a five minutes test (Microtox*) on luminescent bacteria (Photobacterium phosphoreum). Over the year 1992, the surface water was sampled six times at seven stations in the stretch between Remilly (France) and Keizersveer (The Netherlands).

Unfiltrated water samples were concentrated by neutral adsorption on XAD resin followed by elution with acetone. The measured toxicity is expressed as the concentration factor causing 20% reduction in bacterial luminescence after five minutes of exposure (EC20,5). The observed toxicity is transformed into a so called pT-value, pT=10log(EC20,5/100), relating toxicity to acceptability criteria.

Along the river, the toxicity attributable to organic pollution did not reach environmentally acceptable levels. The toxicity in the French and Belgian parts of the river increased gradually to a maximum toxicity generally observed near the industrial centre Liège. In the Dutch stretch, the organic toxicity generally decreased as a consequence of lower pollutant input, pollutant degradation, or pollutant adsorption to newly formed particulates.