Background values for Chrom (Cr) 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.德国土壤保护联邦与州联合工作组（LABO）于2017年发布了涵盖16种重金属及微量元素的全新全国性土壤背景值数据集。该数据集基于土壤剖面描述与王水浸提物检测结果构建，相关数据由德国联邦地质资源局（BGR）完成合并与均质化处理。为避免高定量限检测结果对背景值推导产生干扰，研究团队依据特定标准将此类数据排除于后续评估流程之外。为防止背景值受高采样密度区域的不成比例影响，研究团队对部分数据开展了空间稀疏化处理。研究采用深度加权平均法，将同一采样点多个土壤发生层的检测值整合为单一数值。评估阶段，有效检测数据被划分为不同的土壤母质类别。此外，研究还根据采样深度将样本区分为表土层、亚表层土壤与地下岩层三类。针对表土层样本，评估阶段还需兼顾不同土地利用类型的影响，涵盖耕地、草地与林地。鉴于德国南北部未固结岩石的组分存在显著差异，研究对该类样本分别开展南北分区评估。尽管将数据划分为多个子数据集，但并非所有分组均可获得可靠样本量。因此，本次发布仅包含样本量不低于20的背景值结果。详细的背景值推导流程可参阅土壤保护联邦与州联合工作组（LABO-Bund/Länder-Arbeitsgemeinschaft Bodenschutz）2017年发布的《土壤中无机与有机物质背景值》（第四修订增补版）报告。