MONITORING CONCENTRATIONS OF MICROCONTAMINANTS IN AQUATIC ORGANISMS IN THE RHINE DELTA - A COMPARISON WITH REFERENCE VALUES

In this study, we measured residues of accumulating microcontaminants in seven aquatic species at seven locations in the Dutch Rhine delta and collected additional data from other papers. Comparison with preliminary quality standards suggests that a certain impact of micropollutants on biota of the aquatic community cannot be excluded. Concentrations of some traditional micropollutants, like chlorobiphenyls, mercury, and DDT tend to increase slightly in a downstream direction with exception of the last section. Residues of heavy metals are higher in invertebrates than in fish. On average, accumulation of organic compounds in invertebrate fat is half the level in fish fat. Residues that are somewhat higher than reflected by these ratios have been observed for chlorobiphenyls in fish and for mercury in pike-perch, Stizostedion lucioperca. Residues in livers of cormorants, Phalacrocorax carbo, from Ketelmeer are one order of magnitude higher. Comparison with previous studies shows that residues of many traditional compounds have decreased substantially during the last decade. But recently the decline is suspected to level off. Residues of some other compounds have not declined. This trend is most striking for PCB153 and PCB180 in eel, Anguilla anguilla.