Avaliação de teores de prata em solo contaminado com uso da técnica de fluorescência de raios X (pXRF): estudo de caso em Resende - RJ

Abstract

Portable x-ray fluorescence (pXRF) technology have been used to rapid and cost-effective determination of trace elements in different matrices, including soil samples. This research evaluates the use of a portable X-ray fluorescence spectrometer (pXRF) for the measurement of silver contamination on soil samples colected at UERJ’s Regional Resende Campus (CRR), where radiographic film production companies previously existed. Therefore, samples of topsoil (0,05 m) were prepared by different expeditious methodologies, whose processing included: drying, disaggregation, sieving and grinding. Samples with different preparations were pressed manually in small plastic containers and analyzed by pXRF. To validate the results, some samples were chosen for analysis by the method of inductively coupled plasma atomic emission spectrometry (ICP-AES), a reference technique for the determination of trace elements. Statistical analyzes were carried out and isoconcentration maps generated from interpolation techniques (ordinary krigagen and thin plate splines) were compared using different sampling point meshes. The results indicated high concentrations of silver near the building that used to produce silver nitrate. The multi-element analysis of pXRF also indicated anomalies for: mercury, lead, selenium and zinc. Outside of silver, the other elements observed are not related to previous use.. The pXRF provides qualitative and semi-quantitative evaluation of silver in the soil, with a good correlation to ICP-AES up to the concentration of 1510 mg kg-1, regardless of the type of processing of the samples. At higher concentrations, no correlation was observed between this two analytical methods, possibly due to the partial extraction method - USEPA 3050 B - used for the ICP analyzes, which underestimated the results. In the evaluation of isoconcrete maps, the reduction in the sampling grid did not change hot spot’s location, however significant variations in concentrations were observed.