Metals and selenium are found in the environment in various different compounds. Their geogenic concentrations (background concentrations ) vary. Some metals and selenium are essential for organisms at low concentrations.

The assessment of metals is based on dissolved concentrations (lead, cadmium, nickel, mercury, selenium, silver, thallium), concentrations of suspended solids/sediment (arsenic, chromium, copper, zinc) and in biota (mercury). The assessment of metals is based on environmental quality standards (chemical status) which are valid throughout the EU for lead (dissolved: 1.2 µg/l), cadmium (dissolved: 0.08 µg/l (class 1 of water hardness)), nickel (dissolved: 4 µg/l) and mercury (fish: 20 µg/kg wet weight) and on the national EQS to determine ecological status for arsenic (suspended solids: 40 mg/kg), chromium (suspended solids: 640 mg/kg), copper (suspended solids: 160 mg/kg), zinc (suspended solids: 800 mg/kg), selenium (dissolved: 3 µg/l), (silver(dissolved: 0.02 µg/l) and thallium(dissolved: 0.2 µg/l).

Whereas data for the assessment of suspended solids/sediment and dissolved concentrations is available from a large number of LAWA monitoring sites, measurements on biota (fish) for mercury and other pollutants have only been established in recent years at selected monitoring sites.

Mercury loads have decreased considerably in recent decades, as reflected for example in the suspended solids concentrations measured at the Schnackenburg/Elbe measuring station and Kleve-Bimmen/Rhine (see images) and by the Environmental Specimen Bank.  Especially in the Elbe is this recognizable. There is a rapid decrease in concentrations from 1991. The reason were the cessation of industrial discharges after e.g. Operational closings. But historical mercury deposits are located in the Elbe and Saale still. There fore the concentration of mercury decreases only slowly after that.
The measurements by the Laender on fish indicate that the environmental quality standard for mercury of 20 µg/kg, which was derived for the conservation of wild fauna that feed on fish, such as otters and fish eagles, is still exceeded almost everywhere. It is estimated that, alongside long-distance transportation, historical mercury deposits in water body sediments, for example in still water regions, are the principal cause (see Elbe).

In 2014-2016, the environmental quality standard for suspended solids/sediment was exceeded a number of times in the case of zinc, copper and arsenic. The environmental quality standards for dissolved concentrations was likewise exceeded at a number of monitoring sites in the case of nickel, silver, cadmium and lead (Figures). In the case of nickel, assessment was based on the dissolved concentration. If nickel concentrations are related to the bioavailable concentrations, the number of monitoring sites that exceed the annual average environmental quality standard (AA-EQS) is likely to be lower.. Whereas problems with arsenic and cadmium occur at monitoring sites with tunnels from mining legacies in the catchment area (such as Mulde), cases where the environmental quality standard for copper was ascertained were primarily downstream of conurbations (such as the mouth of the River Spree in Berlin). In the case of zinc, there are large cities or historical mining in the catchment area of the polluted monitoring sites. No pollution hot-spots have been identified for nickel and silver.

Concentration of mercury

  1. EQS metals 2016 - 2018
  2. concentration of mercury, monitoring site Schnackenburg (Elbe)
  3. Annual average concentration of mercury, monitoring site Kleve/Bimmen (Rhine)