Background values for Mercury (Hg) in German soils 1:1,000,000

New, nationwide background values for 16 heavy metals and trace elements were published by the LABO in 2017. They are based on profile descriptions and measurements of aqua regia extracts, which were combined and homogenized by the BGR. Measurements with high quantification limits were excluded from further evaluation according to certain criteria in order to avoid their influence on the derivation of background values. To prevent the background values from being disproportionately influenced by regions with high sample densities, spatial thinning was partially performed. The values of several horizons of a site were combined to one value by depth-weighted averages. For evaluation, the available measured values were assigned to different groups of soil parent materials. In addition, a distinction was made whether the samples were taken in the topsoil, in the subsoil or in the underground. In the case of topsoil, the different land use (arable land, grassland, forest) was also taken into account for the evaluation. Unconsolidated rocks were evaluated separately for northern and southern Germany due to their different composition. By dividing the data into sub-collectives, reliable case numbers were not achieved in all cases. Consequently, only background values with case numbers ?20 are presented. The exact derivation procedure can be found in the report of the LABO-Bund/Länder-Arbeitsgemeinschaft Bodenschutz (2017): 'Hintergrundwerte für anorganische und organische Stoffe in Böden', 4th revised and supplemented edition.2017年，土壤保护联邦-州联合工作组（LABO）发布了全新的16种重金属与微量元素全国范围背景值数据集。该数据集基于土壤剖面描述与王水浸提液测量数据构建，相关数据由联邦地质科学与原材料研究所（BGR）完成合并与均质化处理。为避免对背景值推导造成干扰，依据特定标准剔除了定量限较高的测量数据，未纳入后续评估环节。为防止背景值受高采样密度区域的过度影响，研究团队对部分数据开展了空间稀疏化处理。某一测点的多个土壤发生层数值通过深度加权平均法合并为单一数值。评估阶段，有效测量数据被按不同土壤母质类型进行分组。此外，还依据采样深度将样本划分为表土层、心土层及地下层样本；针对表土层样本，评估过程还需兼顾耕地、草地、林地等不同土地利用类型的差异。鉴于德国南北部未固结岩石的组分存在显著差异，对其分别开展了独立评估。尽管通过划分数据子集合开展分析，但并非所有分组都能获得可靠的样本量。因此，本次仅公布样本量≥20的背景值结果。详细的推导流程可参阅土壤保护联邦-州联合工作组（LABO）2017年发布的报告《土壤中无机与有机物质背景值》（第四版修订增补版）。