Portable X-ray fluorescence (pXRF) application to the determination of major and trace elements in large soil datasets for geochemical background assessment

Regional soil geochemical surveys are essential for land-use planning and human health. However, projects involving large sample sets characterised using traditional laboratory techniques are costly, time-consuming and require a large number of reagents. Therefore, the use of portable X-ray fluorescence (pXRF) with an optimised measurement time and methodology, along with minimal sample preparation, allows for fast and effective measurements. In this study, using Soil-Fundamental Parameters (S-FP) method, a measurement time of 45 s and low sample preparation yielded acceptable results for K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, As, Rb, Sr, Zr, and Pb, which were monitored with benchtop XRF equipment. The application of this methodology in Cuenca province, Spain, and the comparison with different European and national programmes provides consistency in the results, despite using different analytical techniques. It was observed that a systematic and regular sampling strategy avoids geochemical gaps, increasing the representativeness of the soil parent material in the samples. Distinct geochemical patterns have been identified, with a major group comprising Ti, Mn and Fe, and trace elements such as Cr, Ni, Cu, Zn, As, Rb, Sr, Zr and Pb, while K, Ca and Sr display individual distribution trends. Therefore, this study provides a rapid and economical way to characterise soil geochemistry in large areas and to establish background and reference levels over extensive regions. • Analysis optimization: Soil method with pXRF at 45 s analyses with low preparation • Acceptable recoveries for K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, As, Rb, Sr, Zr and Pb • Systematic regular sampling provides enough representativity of parent lithology. • Rapid and cost-effective technique for producing large soil datasets