MONITORING RESPONSE OF XAD-CONCENTRATED WATER IN THE RHINE DELTA - A MAJOR PART OF THE TOXIC COMPOUNDS REMAINS UNIDENTIFIED

In this study a part of the organic compounds present in Rhine water was isolated by XAD-resins and fractionated. Isolates as well as fractions were tested for mutagenicity and toxicity. The highest mutagenic effects in the Ames test were observed with Salmonella typhimurium strain TA98 in the pH 7 isolate. Comparison of past data showed that mutagenicity remained the same in the period 1980-1990. The water samples had to be concentrated at least 25 times by XAD to induce short-term mortality in waterfleas (Daphnia magna), which indicates a substantial improvement in comparison with pollution during the seventies. Chronic toxicity was observed in Daphnia magna after lower levels of XAD-concentration. Extrapolation of these results to field cladocerans is discussed. Most mutagenicity was recovered in the moderately hydrophilic diethylether, ethylacetate and ethanol fractions, but toxicity was almost exclusively located in the lipophilic cyclohexane fraction. However, assuming concentration addition to be dominant in mixtures, the major part (more than 89%) of the toxicity in the cyclohexane fraction could not be attributed to the GC-MS-identified compounds, for which EC(50) values were obtained from databases. Several probable causes for this discrepancy are discussed. However, the major contribution lacking is expected to be from identified compounds for which no information was found in the databases or from compounds that could not be identified by GC-MS. It is concluded that the emission reduction along the Rhine should continue, with a more important role for toxicological assays. Our study did not cover metals, very hydrophilic or very lipophilic compounds.