The Netherlands Institute for Fisheries Research (Rijksinstituut voor Visserijonderzoek, RIVO) performs these measurements on behalf of the Ministry of Agriculture, Nature Management and Fisheries. Eels are caught at 22 fishing locations in the Netherlands. The locations include large rivers such as the Maas (at Eijsden) and the Waal (at Tiel), lakes such as the IJsselmeer and the Ketelmeer and a number of canals.
Diverse eels are caught in each location. These are then combined in one composite sample per location. The chosen fishing waters give a picture of the pollution that a recreational fisherman is subjected to when eating locally caught fish. The extent of pollution in the diverse fishing waters relates among other things to the presence, either previously or now, of industries or agricultural activity. Eels from the IJsselmeer are most representative of the eels sold from the commercial fisheries.
More than two hundred different PCBs have been identified. Nine are measured in the monitoring programme. These nine serve as an indicator of the presence of the other PCBs. The highest PCB levels are found in eels originating from the big rivers. Violations of the limits set in the Commodity Act were recorded in 1997 in the West Haringvliet, the Maas (Keizersveer), the New Merwede and the Roer (at Vlodrop). PCB-138 and PCB-153 are fairly representative of the pollution of fish with PCBs.
A number of organochlorine compounds are also covered in the monitoring. It would not be relevant here to incorporate a graph of trends for every compound at every location. Those interested in this information can obtain it from the KAP databank. However some findings are discussed here. A-Hexachlorocyclohexane (a -HCH) and ß-hexachlorocyclohexane (ß-HCH) are persistent pollutants formed in the production of the pesticide lindane.
ß-HCH can have a similar effect in the body to the female hormone. As a consequence of local lindane production in the past, eels caught today in the Twentekanaal near Hengelo contain high levels of a -HCH and ß-HCH. At the other locations no violations for these chemicals were found. The levels of a -HCH and ß-HCH in the Twentekanaal do whoever show a declining trend.
The levels of lindane (g -hexachlorocyclohexane) and total DDT in eels originating from the diverse locations were well below the legal limits. The levels of DDT in 1997 are generally comparable to those in 1996. DDT may no longer be used as such in the EU. However a number of other pesticides that are permitted still contain DDT (in low concentrations), which partly explains why the levels are not declining.
Hexachlorobenzene (HCB) and octachlorostyrene (OCS) are substances that are released in the chemical industry during the preparation of trichloro-ethene and tetrachloro-ethene. The use of HCB as a fungicide is forbidden. These substances are suspected of being carcinogenic. In 1997 no further infringements of the limits were found.
The highest mercury levels were measured in eels from the eastern part of the Haringvliet and the Lek (at Culemborg). Mercury levels are generally declining, and no violations of the limit were found.