Background values – HGW: Chromium, Medium total content (surface)

Soils were created in thousands of years by the interaction of diverse natural processes. For centuries, however, they have increasingly been characterised by human activities such as land use and material inputs. For most inorganic substances, the initial substrate of soil formation largely determines the natural (cooked) base content of a soil. In addition, there is an anthropogenic component, whereby the ratio of geogeneous and anthropogenic proportions varies greatly. Background values characterise the typical background contents of a substance or group of substances in the soil. In accordance with the procedure of the Federal-Länder Working Group on Soil Protection (LABO), the statistical parameters are 50. Percentile (median) and the 90th. Percentile used. The median represents the average background content, the 90. Percentile represents the upper limit of the typical background content. For the purpose of determining the background content, the anthropogenic proportion must not come from an identifiable single source or a single cause of exposure. Rather, they must be diffuse, i.e. they must be the result of general large-scale (ubiquitous) and over longer periods of material distributions. Prior to the calculation of background values, specifically contaminated soils must therefore be removed from the data. The substrate is the most important differentiation criterion for natural content of inorganic substances. The next deeper plane of divisions are horizon groups such as upper and subsoil as well as subsoil. If there is still a sufficient number of cases, the group of upper-soil horizons is further subdivided into usage classes. For many years, the Rhineland-Palatinate State Office for Geology and Mining has been involved in physical and chemical investigations of soils as well as through cooperation with other state authorities. The information bases were significantly improved with data collected during the Rhineland-Palatinate soil pollution cadastre project. Since this project, the Rhineland-Palatinate soil status report has been progressively continuing extensive soil investigations. This long-term project of the Ministry of the Environment, Forestry and Consumer Protection is carried out on behalf of the State Office for the Environment, Water Management and Trade Inspectorate. Meanwhile, about 18 % of the country’s area with at least one site per km² is covered. The data base on the spatial distribution of the substrate groups comes from the specialised information system Boden (FISBO) of the LGB. This system manages data derived from heterogeneous soil maps (scale level 1:25.000 to 1:200.000). Although this leads to noticeably different resolutions and demarcation problems, for nationwide surveys in small-scale applications above the scale of 1: However, 50.000 these data are suitable despite their inhomogeneity. Further information on this topic can be found in the loose sheet collection background values of the soils of Rhineland-Palatinate.:The median (synonym: 50. Percentile, central value) used. It is the value above or below which 50 % of all cases in a data group are located. The calculation is carried out on outlier-adjusted data collectives. The total content is determined from the royal water extract (according to DIN ISO 11466 (1997)). The concentration is given in mg/kg. The salary classes take into account, inter alia, the pension values of the BBodSchV (1999). These are 30 mg/kg for the soil type sand, for clay, sludge and heavy sluggish sand at 60 mg/kg and for clay at 100 mg/kg. According to LABO (2003), a sample count of >=20 is required for the calculation of background values. However, groups with a sample count >= 10 are also shown in the map. This information is then only informal and not representative.土壤历经数千年，由多种自然过程相互作用孕育而成。然而数个世纪以来，人类活动（如土地利用、物质投入）日益成为塑造土壤特性的主导因素。对于多数无机物质而言，土壤形成的初始母质在很大程度上决定了土壤的天然基础含量。除此之外，土壤还包含人为成因组分，地球成因与人为成因组分的占比差异悬殊。背景值指的是土壤中某单一物质或某类物质的典型本底含量。按照联邦与各州土壤保护工作组（Federal-Länder Working Group on Soil Protection, LABO）的规范，本次计算采用50百分位数（中位数）与90百分位数作为统计参数：中位数代表平均本底含量，90百分位数则代表典型本底含量的上限。在计算本底含量时，人为成因组分不得源自可明确识别的单一污染源或单一暴露诱因，而应是弥散性的，即由大范围（普遍分布）且长期的物质弥散过程所形成。因此，在计算本底值前，需从数据集中剔除受特定污染的土壤样本。母质是决定无机物质天然含量的首要区分依据。次级分类层级为土壤发生层组，涵盖表土层、心土层与底土层（原文此处存在重复表述，已按土壤分层逻辑调整）。若样本量充足，表土层发生层组还可进一步按土地利用类别划分。多年来，莱茵兰-普法尔茨州地质与矿业局（Rhineland-Palatinate State Office for Geology and Mining, LGB）始终协同其他州级主管部门，开展土壤理化性质调查工作。莱茵兰-普法尔茨州土壤污染地籍项目所采集的数据，大幅完善了本数据集的信息基础。自该项目启动以来，莱茵兰-普法尔茨州土壤状况报告项目持续推进大规模土壤调查工作。该项目由环境、林业与消费者保护部牵头，委托环境、水利管理与贸易监察局执行。目前该项目已覆盖该州约18%的区域，采样密度不低于1个样点/平方公里。母质组空间分布数据源自莱茵兰-普法尔茨州地质与矿业局（LGB）的专业土壤信息系统Boden (FISBO)，该系统整合了多套异构土壤图数据，比例尺覆盖1:25000至1:200000。尽管这会导致分辨率差异显著且存在边界划分问题，但对于比例尺不小于1:50000的小范围调查而言，该异构数据集仍具备可用性。关于本主题的更多细节，可查阅《莱茵兰-普法尔茨州土壤本底值活页汇编》：本次采用的中位数（别称：50百分位数、中心值），指数据组中50%的样本数值位于其上下两侧的数值。本底值计算基于剔除异常值后的数据集。总含量通过王水提取法测定（依据DIN ISO 11466:1997标准），浓度单位为mg/kg。土壤分级标准参考了《德国土壤保护条例（BBodSchV, 1999）》中的限值：砂土类型的限值为30 mg/kg，粉土、淤泥与重黏滞砂土为60 mg/kg，黏土为100 mg/kg。根据LABO 2003年规范，本底值计算的最小样本量需≥20；但样本量≥10的组别也可在地图中展示，不过此类信息仅作参考，不具备代表性。