The aim of the Rhine Action Program is to create conditions for the return of (higher) indigenous species. To obtain an impression of current levels of contamination, several separate studies were carried out. The methods applied are discussed briefly and several representative results are given. The focus will be on the integration of the conclusions with respect to the goals of the Program.

First, concentrations of traditional microcontaminants in sediment, water and organisms, collected in monitoring programs, are presented. Concentrations of some compounds, such as cadmium, have decreased substantially while concentrations of other compounds, like PCB153, remain on the same level as they were in the late seventies. The current levels will be compared to Dutch quality standards that are thought to protect most of the aquatic community.

Secondly, responses in biological assays with Rhine water are presented. In the seventies, laboratory species died immediately after exposure to Rhine water. Nowadays, water has to be concentrated to induce acute mortality. Remarkably, only a few percent of the mortality observed after XAD-concentration can be explained by the organic microcontaminants identified by GC/MS. To cover calamities that are missed by these static assays and by daily chemical analysis, biological early warning systems are positioned along the river. In the past, monitors with the fish species ide (Leuciscusidus) have registered several calamities that were not detected by chemical early warning. Currently monitors with waterfleas (Daphniamagna) are being tested, in order to broaden the spectrum of concentrations and compounds covered.

Thirdly, measured data are combined with literature information to obtain an impression of hazards for combinations of chemical compounds and biological taxa. Differences in exposure can be derived from knowledge on habitat and food composition, while information on sensitivity for a chemical can be estimated from data on related taxa. The assessment indicates that most taxa, included target taxa such as Salmonidae, are threatened by current concentrations of different groups of microcontaminants.

Finally, some illustrative (semi-)field observations from the Rhine-delta area will be mentioned as a qualitative validation of the extrapolation from experimental and theoretical analysis.

Author notes

In cooperation with: BKH Consulting Engineers, Delft; Netherlands Institute for Fishery Research, R.I.V.O., Ijmuiden; Netherlands Waterworks Testing and Research Institute, K.I.W.A., Nieuwegein