Combination of Portable X-Ray Fluorescence With Soil Magnetometry as an Effective Tool for Distinguish Different Pollution Sources

Abstract

To improve the efficiency of soil management and the identification of polluted areas to apply joint measurement technique including soil magnetometry (following the ISO 21226:2019 standard) and portable X-ray fluorescence spectrometry (pXRF). The measurements were conducted in two forest areas of the Silesian region (South Poland) with similar geological background, soil types and geomorphology, affected by different pollution sources. The results obtained using three pXRF measurements procedures (field measurement, laboratory measurement of fresh and dry samples) were verified in a chemical laboratory (ICP-OES technique with aqua regia). Based on the results, the most reliable values were obtained when using air-dried, sieved and homogenised soil samples. Field measurements were characterised by low measurement repeatability because of the heterogeneity of the measured soil surface (high porosity, variable granulation, high content of organic matter) and the high litter moisture. When determining the concentration levels of Co, Mn, Pb, V and Zn in dry samples, the values measured by pXRF were comparable to those obtained via ICP-OES. In the case of As, the average values were 50% higher than those determined via ICP-OES, whereas the Cr and Ni concentrations were underestimated. The Spearman's rank correlation between magnetic susceptibility and the concentrations of Pb, Zn, As (rs = 0.84, 0.88, 0.85, respectively) as well as the pollution load index (PLI), were sufficiently high to apply the soil magnetometry method on both tested sites. However, in the site affected by magnetic particles from one dominant pollution source, the correlation values were significantly higher than those in the site with overlapping emission sources (urban and industrial sources).