GcBÜK400 — Cadmium in the upper floor

Cadmium deserves special attention among heavy metals, as its toxicity to animals and humans is significantly greater than that of other heavy metals. As an accumulation poison, it is enriched in the body and can remain there for decades. Due to its chemical kinship to zinc, it occurs almost exclusively with it, especially in all zinc-bearing minerals (including zinc aperture, galmei) and rocks. The average Cd concentration of the rocks of the upper continental earth crust (Clark value) is 0.1 mg/kg, in soils content is usually 0.50 mg/kg. In contrast to As and other heavy metals (e.g. Cr, Ni), no geochemical specialisation in Cd is detectable in the near-surface Saxon main rock types. The petrogeochemical component is 0.1 mg/kg in the Clark value range. In the ore deposits, Cd is mainly bound to the zinc ores of the polymetallic hydrothermal aisles and partly to the skarn deposits and straty-stratiform formations (chalkogenic component). Since the beginning of industrialisation, cadmium has entered the environment anthropogenically through emissions from the non-ferrous metalworks, the combustion of coal and petroleum, and more recently via electroplating, waste incineration, fertilisers, sewage sludges and composts. Whereas low levels dominate in the upper soils of North and Middle Axis (Cd-poor periglaciary sandy to loamy substrates; Löss), a relative enrichment occurs in the weathering soils over solid rocks. A dependency on the clay content can therefore be observed that the sandy substrates have slightly lower Cd levels compared to clayy substrates. Higher Cd levels are found in arable and grassland sites compared to the forest sites in the upper soil, as a result of the very low pH values under forestry, Cd mobilisation and relocation to larger soil depths take place. Particularly high Cd loads are located in the Freiberg region, which are caused by the geogenic Cd enrichment in the formation of non-ferrous metal veins, but above all anthropogenic by the prevention of zinc ores. The highest levels can be found in the upper soils in the immediate vicinity of the metallurgical sites and at lower concentrations east of it (in the main wind direction). Other deposits with zinc debris in the Western Ore Mountains and the Ore Mountains border zone have only slightly increased grades. The meadows of the Freiberger and the United Mulde occupy a special position in the load with cadmium. Due to the removal of soils with geogenic enrichments in the catchment area and the enormous additional anthropogenic loads caused by the ore processing and the metallurgy industry, high Cd enrichments occur when the river sediments and swine parts are deposited in the flooding areas. In the floodplains of the Elbe and Zwickauer Mulde, on the other hand, significantly lower levels occur. The geogenic and anthropogenic processes in the Freiberg area and in the floodplains of the Freiberger and United Mulde lead to extensive exceedances of the test and measures values of the Federal Soil Protection and Contaminant Ordinance (BBodSchV) for cadmium.