Geochemical mapping of risk element concentrations in soils is performed in countries around the world. It results in large datasets of high analytical quality, which can be used to identify soils that violate individual legislative limits for safe food production. However, there is a lack of advanced data mining tools that would be suitable for sensitive exploratory data analysis of big data while respecting the natural variability of soil composition. To distinguish anthropogenic contamination from natural variation, the analysis of the entire data distributions for smaller sub-areas is key. In this article, we propose a new data mining method for geochemical mapping data based on functional data analysis of probability density functions in the framework of Bayes spaces after post-stratification of a big dataset to smaller districts. Proposed tools allow us to analyse the entire distribution, going beyond a superficial detection of extreme concentration anomalies. We illustrate the proposed methodology on a dataset gathered according to the Czech national legislation (1990--2009). Taking into account specific properties of probability density functions and recent results for orthogonal decomposition of multivariate densities enabled us to reveal real contamination patterns that were so far only suspected in Czech agricultural soils. We process the above Czech soil composition dataset by first compartmentalising it into spatial units, in particular the districts, and by subsequently clustering these districts according to diagnostic features of their uni- and multivariate distributions at high concentration ends. Comparison between compartments is key to the reliable distinction of diffuse contamination. In this work, we used soil contamination by Cu-bearing pesticides as an example for empirical testing of the proposed data mining approach.

翻译：世界各国均开展土壤中风险元素浓度的地球化学填图工作，从而获得高质量分析的大规模数据集，可用于识别违反食品安全生产单项立法限值的土壤。然而，目前缺乏适用于大数据敏感探索性数据分析，同时兼顾土壤成分自然变异性的先进数据挖掘工具。为区分人为污染与自然变异，对较小区域的全数据分布进行分析至关重要。本文提出一种基于贝叶斯空间框架下概率密度函数函数数据分析的新型地球化学填图数据挖掘方法，该方法在将大数据集进行后分层后应用于较小区域。所提工具可分析整个分布，超越对极端浓度异常的浅层检测。我们根据捷克国家立法（1990-2009年）收集的数据集对所提方法进行验证。通过考虑概率密度函数的特定性质及多元密度函数正交分解的最新成果，我们得以揭示捷克农业土壤中此前仅被怀疑的真实污染模式。我们首先将上述捷克土壤成分数据集按空间单元（特别是行政区）进行分区，随后根据各行政区在高浓度端单变量与多变量分布诊断特征进行聚类。区域间比较是可靠区分扩散污染的关键。本研究以含铜农药造成的土壤污染为例，对所提数据挖掘方法进行实证检验。