All kinds of soil and rocks contain metals in varying rates. Mostly they are solidly bound and only a small quantity is washed out naturally into the surface water. Above all human activities like mining and further processing can mobilize the metals and they reach the surface water on different pathways.

Some heavy metals like zinc and copper are important trace elements and show toxic effects only in high concentrations. Others like lead, mercury and cadmium have no biological function at all and only act as harmful substances.

In contrast to many other environmental chemicals, heavy metals cannot be degrades and they bio-accumulate through the food chain. One of the well known sources of heavy metal contamination of Aller and Weser is the Harz with his long-time mining activity.

With the heavy metal load of the Aller the water quality of the Weser is polluted most of all by lead, cadmium and zinc.

Heavy metals prefer to accumulate at the suspended matter of the river waters. Therefore the fixed rate can be several times higher than the dissolved rate.

The contamination of suspended matter can cause negative affects to the aquatic biocenoses and restricted use of dredged material. Therefore the examination of samples of suspended matter has environmental relevance despite its higher efforts.

The suspended matter (<20µm fraction) in Werra (Gerstungen), Fulda (Hann. Münden) as well as Upper and Lower Weser (Hemeln and Porta) show a moderate, in some cases only small pollution with lead. The increased pollution of the Aller, caused by the early mining tradition in the Harz, is not only shown at the station Verden, but in the Weser at Hemelingen. This also applies to zinc, but with generally higher pollution.

Data metals
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