Hazardous substances in lakes

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There is limited information on heavy metals (and other hazardous substances) in European lakes. The most comprehensive information is from the Nordic countries.

The Nordic lake survey of 1995 measured heavy metal concentrations in the water of 3 000 lakes. The survey revealed that the concentrations of lead are low (< 0.3 µg/l) in the northern parts of the countries and in areas of high altitude, corresponding to areas with low population density and low consumption of gasoline. In the southern parts of the countries, there are often elevated concentrations of up to 1-10 µg/l. High concentrations are particularly evident in south-western Norway due to high deposition from long-range air pollution. Cadmium and zinc follow a similar general geographical distribution whereas the occurrence of other heavy metals are, to a greater extent, determined by bedrock geology in combination with indirect effects from acidification (for example, acid dissolution of bedrock).

The concentrations of some hazardous organic substances have been monitored in a number of Swedish lakes since the 1960s. The concentration of PCBs and DDT in pike tissue has fallen since the late 1960s. In addition to this, concentrations of a-HCH and HCB have also fallen. Contrary to this, the concentrations of brominated flame retardants have been stable in lake Bolmen after an increase during the 1970s. While PCB and DDT are found in the highest concentrations in southern Sweden where they have been used most intensely, the more volatile HCH and HCB are found in similar concentrations throughout the country due to long-range air transport. The fish of Norwegian lakes showed that the levels are generally low, with a few exceptions. In fish from the large lakes Mjøsa and Randsfjorden, there were elevated levels of PCBs and DDTs, particularly in predatory fish such as trout and burbot. The livers of burbot in Mjøsa also had very high concentrations of brominated flame retardants and the trout in lake Mårvatn contained high concentrations of dioxins.