GcBÜK400 - Lead in the topsoil

Lead is a toxic heavy metal and is ubiquitous in the environment due to its multiple industrial uses. The input sources are not limited to the area of ore deposits (mainly lead sulfide and its oxidation minerals). Lead is also introduced into the soil through the smelting of lead, copper and zinc ores, the long-range exhaust gas pollution of motor vehicles (up to 60% of atmospheric pollution until the introduction of lead-free petrol), lead scrap recycling plants, the use of sewage sludge and compost containing heavy metals, and coal incineration plants. For unpolluted soils, a Pb content of 2 to 60 mg/kg is given depending on the initial rock. The average Pb concentration of the upper continental crust (clarke value) is 17 mg/kg, the area-related mean Pb content for the Saxon main rock types is 20 mg/kg. The rocks of Saxony have no or little geochemical specialisation with regard to lead. In the northern and northeastern part of Saxony, relatively low Pb levels occur in the upper soils above the loose sediments of the Cenozoic period (periglacian sands, gravel, loess) and the granodiorites of Lusatia. In the case of loose sediments, the Pb content increases slightly with increasing clay content. The weathered soils above the solid rocks of the Ore Mountains, Vogtland and partly the Elbe zone usually have significantly higher lead contents, which are caused by a relative enrichment in the soil starting rocks. The highest lead-contaminated area in Saxony is the Freiberg area. Due to the economically important polymetallic mineralizations (Pb-Zn-Ag), which are also relatively widespread in terms of area, there was a particularly strong Pb enrichment in the secondary rocks and consequently also in the formation of the soils over the gneiss. In addition, enormous anthropogenic pressures have arisen from the centuries-long smelting of primary ores and, more recently, from the recycling of lead-acid batteries. Particularly high Pb contents occur in the immediate vicinity of the smelter sites, including the main wind directions, in the central part of the quartz-sulphide mineralization and in the floodplains. Further areas with large-scale elevated Pb contents are mainly located in the Osterzgebirge, in an area that extends from Freiberg in a south-easterly direction to the national border in the Altenberg area and in the ore regions of the Central and Westerzgebirge, such as Seiffen, Marienberg - Pobershau, Annaberg, Schneeberg, Schwarzenberg and Pöhla. However, the proportion of Pb minerals in the ores of these regions is significantly lower. Due to the frequent socialization of Pb and As in the mineralizations, the distribution area of the elevated Pb contents in the Osterzgebirge and subordinate in the Westerzgebirge as well as in the floodplains of the Freiberger and Vereinigte Mulde is similar to that of the arsenic. The floodplain soils of the Freiberger Mulde lead extremely high lead contents from the Freiberger reservoir area, which continue into the floodplain soils of the United Mulde in northwestern Germany. The floodplains of the Elbe and the Zwickauer Mulde also have areas with higher lead contents due to geogenous or anthropogenic sources (storage sites, industry) in the catchment area. The lead content of the soils in the Freiberg area and in the floodplain soils of the Freiberger and Vereinigte Mulde exceeds the test and action values of the Federal Soil Protection and Contaminated Sites Ordinance (BBodSchV) in some cases.