Screening Trace Elements in Areas of Intensive Agriculture in Brazil with a Field-Portable XRF Analyzer.

Portable XRF analyzers have been routinely used for environmental purposes, mainly in areas with high contents of trace elements (TE). However, their use in the analysis of TEs in soils of agricultural areas is still limited, especially in Brazil. Portable XRF might not replace atomic absorption spectroscopy when sub-parts per million levels are required. Yet it offers some advantages that are very important for field applications such as minimal sample preparation and fast identification of many TEs of interest. Also, portable XRF is a promising technique because it generates a minor amount of residues and has low cost for reagents.  In order to check if such technique can provide accurate quantitative results for TEs, we tested surface soils samples (n = 68) collected under native vegetation and cultivated areas of the state of Mato Grosso (MT), which is the largest producer of soybeans, corn, and cotton in Brazil and also the greatest consumer of agricultural inputs that may represent a diffuse source of TEs to agricultural ecosystems. Results obtained by the portable XRF analyzer were compared with data using the USEPA 3051A procedure for TE extraction followed by quantification via atomic absorption spectroscopy, using soils standard reference materials for QA/QC protocols. Although we have obtained good recoveries (SRMs) for the analyzed TEs (As, Cu, Mn, Pb, and Zn) using both techniques, there was no correlation for data obtained between the two selected analytical methods. This can be explained by the low TE contents in the studied samples, which are uncontaminated soils and also by the fact that the portable XRF apparatus have much higher detection limits. Sponsored by CAPES, CNPq, and FAPEMIG.