Fish reflects the pollutant content of sediments and of the entire aquatic ecosystem, in particular the accumulation of pollutants in the food chain.
Data existing in the Rhine bordering countries for the period 2000 to 2010 on the contamination of fish in the Rhine and its tributaries with various pollutants were presented in Report no. 195.
While eel in the Rhine and in many tributaries – apart from Lake Constance and one old branch of the Rhine – were often heavily contaminated with dioxins, furans and dioxin-like PCB. Considerably lower values were mostly determined in carp species. Measurements in fish of all species analyzed revealed considerable variations in contents. Due to their high fat content, these pollutants accumulate most in eels. Otherwise, the contamination is not species-specific but depends on the pollution situation at the sampling site of the water body concerned and on the age and fat content of the individual fish.
The limits for indicator PCBs are sporadically exceeded in the Rhine itself and in the Moselle and Main, namely in older, fat-rich eel and bream, but not in other fish species. In the Rhine delta (sedimentation area of the R. Waal and the Ketelmeer), the contamination of eels with the indicator PCB has distinctly fallen. A similar trend is perceptible in the Moselle and, to a lesser extent, in the Saar.
Apparently, the contamination with hexachlorobenzene (HCB) is in particular decreasing in the Delta Rhine.
An analysis of perfluorinated tensides (PFT) revealed distinctly elevated contents of perfluorooctanesulfonic acid (PFOS) in Rhine fish (Delta Rhine, Lower Rhine, Upper Rhine, High Rhine). A Dutch trend analysis shows rising contents from the 1970ies until the middle of the 1990ies and subsequently a decline. For other PFTs, the values in the whole Rhine area were generally below the detection limit.
The decline of mercury concentrations in Rhine observed in the 1980s and 1990s did not continue after 2000.
The HCB contents in fish and sediments originate from a chemical plant near Rheinfelden where this substance occurred as by-product. This plant has in the meantime been shut down. PCBs in sediments are equally due to historic pollution. Formerly, these substances were mainly used as hydraulic fluid in transformers.