Background values – HGW: Lead, 90.Percentile (information in mg/kg)

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 Loteblatt collection background values of the soils of Rhineland-Palatinate.:As 90.P background value is 90. Percentile of a data collective. It is the value in which 90 % of the cases observed so far have lower levels. The calculation is carried out after cleaning the data group of outliers. The 90th. Percentile often serves as the upper limit of the background range to delineate unusually high grades. 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 at 40 mg/kg for the soil type sand, for clay, silt and heavy sluggish sand at 70 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.土壤是历经数千年由多种自然过程相互作用形成的。然而数个世纪以来，人类活动（如土地利用与物质投入）正日益塑造着土壤的特征。对于绝大多数无机物质而言，土壤形成的初始母质在很大程度上决定了土壤的自然本底基准含量。此外，土壤还存在人为成因组分，其中地质成因与人为成因的占比差异悬殊。 背景值（background values）表征了土壤中某一物质或某类物质的典型本底含量。按照联邦-州土壤保护工作组（Federal-Länder Working Group on Soil Protection, LABO）的规程，统计参数采用50百分位数（中位数，median）与90百分位数（percentile）。其中，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。 为确定本底含量，人为成因组分不得来自可识别的单一污染源或单一暴露诱因，而必须是弥散性的，即源于大范围（普遍存在）且长期持续的物质扩散过程。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。 母质是区分无机物质自然含量的最核心分类依据。进一步的划分层级为发生层组，如耕作层、亚表土层与底土层。若样本量足够充足，耕作层发生层组还可进一步按土地利用类别细分。 多年来，莱茵兰-普法尔茨州地质与采矿局（Rhineland-Palatinate State Office for Geology and Mining）一直致力于土壤理化调查，并与其他州级主管部门开展合作。莱茵兰-普法尔茨州土壤污染地籍项目所采集的数据，显著完善了本研究的信息基础。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。这项由环境、林业与消费者保护部牵头的长期项目，由州环境、水利管理与贸易监察局负责执行。目前，该项目已覆盖该州约18%的区域，每平方公里至少布设1个采样点。 母质组空间分布的数据集源自莱茵兰-普法尔茨州地质与采矿局（LGB）的专业土壤信息系统（Fachinformationssystem Boden, FISBO）。该系统管理着多套不同比例尺的土壤图数据（比例尺范围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难题，但对于比例尺大于1:50000的小范围全国性调查而言，即便数据存在不均一性，该数据集仍具备适用性。 关于本主题的更多细节可参阅《莱茵兰-普法尔茨州土壤背景值专题辑录》： 1. 90百分位背景值指某一数据集的90百分位数，即已有观测样本中90%的数值均低于该值。其计算需先对数据组进行异常值清洗。90百分位数常被用作本底范围的上限，以区分异常偏高的含量水平。 2. 总含量通过王水浸提法（royal water extract）测定，依据标准为DIN ISO 11466 (1997)，浓度单位为mg/kg。 3. 浓度分级标准还参考了《德国联邦土壤保护条例》（BBodSchV, 1999）中的阈值：砂土类别为40 mg/kg，黏土、粉土与黏重砂土为70 mg/kg，黏土类别为100 mg/kg。 4. 根据LABO（2003）的要求，计算本底值时样本量需≥20。但地图中也会展示样本量≥10的分组，不过此类信息仅作参考，不具备代表性。