Comparison of portable X-ray fluorescence spectrometry and laboratory-based methods to assess the soil elemental composition: Applications for wetland soils

The portable X-ray fluorescence spectrometry (pXRF) can be considered one of the most novelty for soil characterization. In tropical regions (e.g., Brazil), some studies have showed a consistent correlation between pXRF and laboratory-based methods. However, there is no any work dedicated exclusively for hydromorphic soils (gley or organic-rich soils). This study aims to assess the total elemental composition reported by portable X-ray fluorescence (pXRF) spectrometry and to compare it to laboratory-based wet digestion method and wavelength dispersive X-ray (WDXRF) spectrometry. A collection of 144 hydromorphic soil samples from six wetlands located in the Cerrado biome (Savannah), Brazil, was used for this investigation. Soil samples were disaggregated and passed through a 150-μm nylon mesh and subjected to wet digestion (US EPA 3051a) followed by elemental determination via atomic absorption spectrometry (AAS). Subsamples of each ground soil were also directly analyzed via both pXRF and WDXRF. Linear regressions were performed to establish the relationship between methods. Several elements (Pb, Cu, Zn, Cr, Fe, Ti, Sr, and Y) determined via pXRF were successfully correlated to other methods (USEPA 3051a and WDXRF). Specially for Pb, a very strong correlation (R > 0.90) was observed between pXRF, WDXRF and US EPA 3051a methods. The pXRF revealed also to be a useful tool for characterization of hydromorphic soils and future studies can be conducted directly in the field to assess the elemental composition of Cerrado wetland soils.