GcBÜK400 - Zinc in the topsoil

Zinc is an essential trace element for plants, animals and humans, but at extremely high levels it can have a toxic effect on plants and microorganisms. The concentration of Zn in the upper continental crust (clarke value) is 52 mg/kg, but it can vary greatly depending on the rock type. The mean Zn-contents (median) of the Saxon main rock types are between 11 and 140 mg/kg, the regional clark of the Ore Mountains is about 79 mg/kg. Sphalerite (zinc orifice) leading polymetallic deposits can locally lead to additional geogenous Zn enrichments in the soils. Anthropogenic Zn entries are mainly made by ferrous and non-ferrous metallurgy or by the Zn processing industries (paints, alloys, electroplating) and by large combustion plants. In the area of agglomerations, Zn enrichments can be observed relatively frequently. Anthropogenic Zn entries are possible in agriculture through the use of organic and mineral fertilizers. For unpolluted soils, Zn levels of 10 to 80 mg/kg are considered normal. The regional distribution of the Zn-contents in the Saxon soils is mainly determined by the geogenetic imprinting of the substrates; low to medium grades are to be expected above the periglacian sands and clays in the north and loess soils in central Saxony (10 to 50 mg/kg) as well as the weathering soils above the solid rocks of the Ore Mountains/Vogtland (50 to 150 mg/kg). Within the basement units, significant positive Zn anomalies occur over the polymetallic deposits of the Ore Mountains, depending on the intensity of the mineralization (Freiberg, Annaberg-Buchholz - Marienberg, Aue - Schwarzenberg). Soils over substrates with extremely low Zn content (granite from Eibenstock, orthogneise of the Erzgebirgs central zone, Osterzgebirgischer eruptive complex, Cretaceous sandstones) appear as negative Zn anomalies in the map image. Increased Zn accumulations can be observed in the floodplain soils of the trench system. Due to the higher geogenic base contents in the water catchment area, the occurrence of Zn-bearing polymetallic mineralization and in particular the mining and metallurgical activity in the Freiberg area, high Zn concentrations occur especially in the floodplain soils of the Freiberger and Vereinigte Mulde (median contents 370 and 240 mg/kg). The Federal Soil Protection and Contaminated Sites Ordinance (BBodSchV) did not stipulate any test and action values for total contents for the soil-human and soil-plant impact pathways, as Zn is only of minor importance in the risk assessment.