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Total trace element contents in natural soils by two methods

Anthropogenic metal accumulation such as for instance in agricultural and urban soils has generated a great amount of information in the past. Nowadays, there is an increasing demand to measure background levels of trace elements in soils because of the need to supply interpretations of both contaminated and non-contaminated profiles in an environmental context. The main goal of this study was to provide background levels for Cu, Mn, Ni, Pb, Zn and Cr for natural soils in Galicia (Spain). 38 horizons from 10 natural soil profiles developed over a wide variety of soil parent materials, including serpentine soils, which have naturally elevated Cr and Ni levels, were sampled. Total metal concentrations measured by two different methods were compared. So, trace elements were determined semi-quantitatively by X-ray fluorescence spectrometry (X-RF) and quantitative determination of samples was achieved by inductively coupled plasma-mass spectrometry (ICP-MS) after acid digestion (HNO3+ HCl+ HF+aqua regia). The results showed that metal concentrations of native soils varied widely, and differences between methods may be attributed to interferences and biases of the X-RF technique and also to losses in the solution prepared for ICP-MS. Except for Pb and Cu, all the correlation coefficients of the trace elements studied were higher than 0.85. In spite of its semi-quantitative nature, X-RF can offer substantial benefits in the investigation of trace elements in natural soils, also by metal enrichment, allowing assessments for diverse applications. However, trace metal data are method-dependent and care should be taken when performing specific environmental studies.