Abstract
Data on the regional geochemical background and threshold values of heavy metals are required to establish anomalies and assess soil pollution. As a rule, the background values are the average contents of elements in natural undisturbed soils, or the threshold values for the study area, obtained by statistical methods. The aim of the study is to obtain geochemical threshold values of heavy metals in the soils of the Lower Don and the Taganrog Bay coast using different statistical approaches. A total of 86 topsoil samples were collected from the study area. The concentrations of Cr, Mn, Ni, Сu, Zn, As, Cd, and Pb were analyzed by X-ray fluorescence. The median element concentrations in the soils of the study area were consistent with world soil average and metal concentrations in background soils of protected area. Using a ‘geochemical’ approach is not suitable for this dataset because it does not take into account the natural variability of concentrations in different soil types. The Tukey inner fence method delivers estimates that do not detect outliers for Ni, As, Cd, and Pb. The ‘median + 2 median absolute deviations’ method was the most appropriate, as it consistently provided the most conservative background values.
Highlights
The floodplain of the Lower Don and the Taganrog Bay coast are territories with a high population density, intensive agriculture, developed industry and transport infrastructure
This study aims to 1) determine the levels of of Cr, Mn, Ni, Сu, Zn, As, Cd, and Pb in soils of the Lower Don and the Taganrog Bay coast, 2) evaluate regional geochemical threshold values for heavy metals (HM), and 3) compare the statistically derived threshold values with the concentrations of HMs in soils of protected area
The median content of HMs in the soils of the study area was consistent with that identified in the Fluvisols of the Chumbur-Kosa protected area [10], with the exception of cadmium (3.7 times excess)
Summary
The floodplain of the Lower Don and the Taganrog Bay coast are territories with a high population density, intensive agriculture, developed industry and transport infrastructure. Since HMs enter soils from both natural and anthropogenic sources, it is necessary to establish a ‘normal’ range of the contents of individual elements, reflecting the heterogeneity of the environment [4]. There are two main groups of methods for determining the background values of metals in soils, namely ‘geochemical’ and ‘statistical’ ones [6]. The most widely used method for geochemical threshold determination is the calculation of the ‘mean + 2 standard deviations’ (‘mean + 2SD’), that requires a normal distribution and independence of the sampling points [7]. The ‘geochemical’ approach to determining the background values assumes that the compared soils are similar to the background ones in terms of their physicochemical properties and are formed in similar landscape conditions
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