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.镉在重金属中备受关注，因其对动物与人类的毒性显著高于其他重金属。作为蓄积性毒物，镉可在生物体内富集并滞留数十年。由于其与锌具有化学亲和性，镉几乎始终伴生锌存在，尤其广泛赋存于各类含锌矿物（包括闪锌矿（zinc aperture）与方铅矿（galmei））及岩石中。大陆上地壳的平均镉浓度（克拉克值（Clark value））为0.1 mg/kg，土壤中镉含量通常为0.50 mg/kg。与砷（As）及其他重金属（如铬Cr、镍Ni）不同，萨克森州近地表主要岩石类型中未检测到镉的地球化学分异现象，其岩石地球化学背景值处于克拉克值范围（0.1 mg/kg）内。在矿床中，镉主要赋存于多金属热液脉的锌矿石中，部分赋存于夕卡岩矿床及层状-层控地层（白垩纪成因组分）。自工业化起步以来，人类活动便通过有色金属冶炼厂排放、煤炭与石油燃烧，以及近年来的电镀、垃圾焚烧、化肥施用、污泥与堆肥利用等途径将镉释放至环境中。北轴与中轴地区的上部土壤以低镉含量为主，对应贫镉的冰缘期砂质至壤质基质与黄土；而基岩风化形成的土壤中则出现镉的相对富集。由此可观察到镉含量与黏土含量的相关性：砂质基质中的镉含量略低于黏土质基质。相较于森林土壤，上部土壤中的耕地与草地样点镉含量更高，这是由于森林环境下极低的pH值会促使镉活化并迁移至土壤更深层。弗莱贝格地区镉负荷尤其高，这一方面源于有色金属脉形成过程中地质成因的镉富集，更主要的则是锌矿石开采加工带来的人为活动影响。冶金场地紧邻区域的上部土壤镉含量最高，而在其东侧（主风向一侧）浓度较低。西厄尔士山脉及厄尔士山脉边境带的其他含锌碎屑矿床，镉含量仅略有升高。弗莱贝格与联合穆德河沿岸的草甸在镉负荷方面具有特殊性。由于流域内富含地质成因镉的土壤被移除，加之矿石加工与冶金行业带来的大量额外人为负荷，当河流沉积物与猪粪在漫滩沉积时，便会出现显著的镉富集。而在易北河与茨维考穆德河的漫滩中，镉含量则显著更低。弗莱贝格地区以及弗莱贝格联合穆德河漫滩的地质与人为过程，导致镉含量大幅超过《联邦土壤保护与污染条例（BBodSchV）》规定的镉检测与管控限值。