Editing Aller (Germany) (section)

=== Heavy metal pollution ===
The pollution of the Aller by [[heavy metal (chemistry)|heavy metal]]s has resulted from centuries of [[Mining in the Upper Harz|mining in the Harz mountains]]. Harz rivers, such as the Aller tributary of the [[Oker]], picked up heavy metals from the mines and their spoil heaps. These were mainly cadmium, zinc and lead compounds that were concentrated into the [[suspended solids]] in the river. In this way, these chemicals were transported by the Oker into the Aller and Weser where they were deposited in the slacker-moving sections as [[sediment]]s.

In 1999, investigations were carried out into the heavy metal content of the suspended material in the Aller near Verden. They showed that the Aller was polluting the Weser disproportionally with [[lead]], [[cadmium]], [[zinc]] and [[mercury (element)|mercury]].<ref>Dieter Steffen: ''Schwermetallfrachten der Aller und deren Auswirkung auf die Weser-Bilanzierung auf der Basis von Schwebstoffuntersuchungen des Jahres 1999''</ref>