Assessing natural background concentrations of chemical elements in urban soils: A case study in Benevento (Italy)

The main objective of this study is to propose a method to determine, as accurately as possible, the natural background content of a chemical element in urban soils, identify potential sources, and quantify emissions from human activities. To achieve this, 156 topsoil samples were taken from the surface horizon of the soil (first 20 cm) and analysed for 25 elements using a combination of inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS), after aqua regia digestion. The concentration data obtained were rigorously analysed using multivariate statistical analysis methods, including compositional data analysis (CoDA), clustering and dimension reduction techniques. This analysis separated the data into distinct populations, each characteristic of a natural or anthropogenic phenomenon. The ProUCL 5.2.0 software package was then used to calculate the natural background levels of each element for each data population. The background of some elements, including Co and Tl, exceeds the threshold values imposed in Italy by environmental law in some areas. These findings, together with the use of specific indices, allowed us to precisely define the degree of potentially toxic elements enrichment and the potential ecological risk of the studied area, thus providing valuable information for decisions on urban planning and environmental policy and potentially influencing future strategies for managing urban soil health.