Water pollution with residues of pharmaceuticals has become a rather common phenomenon. In all German rivers, for example, the concentration of gadolinium, a high-tech metal that belongs to the group of rare earth elements, occurs in anomalously high concentrations. Gadolinium is used as a contrast agent in magnetic resonance imaging (MRI). It is not metabolized by the human body and quickly excreted through the kidneys into the sewage system.

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http://jacobs-university.de/2014/09/gadolinium-contrast-agents-and-residues-pharmaceuticals-are-widespread-german-drinking-water