GcBÜK400 – Mercury in the topsoil

The Hg concentration in the upper continental crust is 0.06 mg/kg. For uncontaminated soils, Hg levels of 0.02 to 0.5 mg/kg are considered normal. The regional distribution of elevated Hg levels in the Saxon soils can only be attributed to geogenous and anthropogenic causes and influences subject to reservation, as the knowledge of Hg distribution in rocks and soils is relatively low compared to other heavy metals. The Hg content in the mineral topsoil is significantly increased compared to that of the subsoil, indicating increased ubiquitous atmospheric input. The initial rocks of soil formation in Saxony do not differ significantly in terms of their lithogenic Hg content. The northern and western parts of the country covered by younger loose rocks have slightly lower Hg levels than the metamorphic rocks of the Ore Mountains/Vogtland. Weak geogenous Hg enrichments are only known from the Silurian alum and pebble slates as well as the tertiary basalts, which, however, are only partially effective on the scale of these studies due to their low area distribution. Furthermore, the soils above the clay and sludge slates of the Ordovician of the West Erzgebirge and Vogtland have slightly increased natural Hg levels compared to the subsequent mica slates and gneisen. HG-bearing mineralisations (Zinnober/HgS), which are not of greater importance in Saxony, can lead to additional geogenous Hg enrichments locally. Anthropogenic Hg entries into the soil are mainly caused by emissions from large combustion (coal, gas) and waste incineration plants, by ore smelting, paints and pharmaceuticals. In aquatic systems, Hg is mainly registered by industrial wastewater from chlorine-alkali electrolyses and the wood and metal processing industry. In the past, Hg-containing fungicides were recorded on agricultural soils as seed pickling agents for cereals. Hg also got into the soil with the application of sewage sludge and composted municipal waste. With an overall relatively low basic level, elevated Hg levels occur in Saxony, especially in the Freiberg area. This anomaly was caused by the centuries of operation of the amalgamation plants and smelters. Increased Hg accumulations can also be observed in the floodplains of the Elbe, Freiberger and Vereinigte Mulde, which are caused by Hg-containing industrial and municipal wastewater. The former Amalgamierwerk Halsbrücke and the hut site in Muldenhütten near Freiberg are located in the immediate vicinity of the Freiberger Mulde and due to the centuries-long emission pollution certainly still have a share of the Hg load of the floodplains of the Freiberger and Vereinigte Mulde to Eilenburg. Mercury is a powerful poison for animals and humans. The measured Hg levels are hardly relevant for the action path soil – humans, as the test value according to BBodSchV is 10 mg/kg for direct intake and is rarely achieved. The test value for the soil – plant path (farming and horticulture) is 5 mg/kg. For grassland use, the measure value shall be 2 mg/kg.