Rare earth elements in brazilian biome-differeniated soils

Abstract

The aim of this research was to generate data on the occurrence and behaviour of major, trace, and rare earth elements in benchmark soils of Brazilian biomes, in order to understand their distribution and quantify their natural or anthropogenic concentrations in biomes. In addition, the natural contents of the major and trace elements were determined together with the establishment of quality reference values for rare earth elements for each biome, since the biome expresses the particularities of the environments. For this purpose, samples of benchmark soils from a Brazilian soils databank were selected in order to represent the geological, geomorphological, pedological, climatic, and edaphic diversity of the studied regions. Determination of the semi total contents of rare earth elements in soil samples was performed through a microwaved-assisted nitric-acid digestion procedure, followed by quantification with inductively coupled plasma mass spectrometry. On the other hand, the quantification of the total contents of the major and trace elements was performed using the technique of total reflection X-ray fluorescence spectrometry. The analytical procedures followed a rigorous quality assurance/quality control protocol, including the use of certified reference materials in order to validate the methodologies. The results showed high variability in the concentrations of major, trace, and rare earth elements in soils, which were mainly influenced by parent material referring to terrestrial crust and pedogenetic processes, having the climate a prominent role. These factors promoted a differential removal of the major, trace, and rare earth elements in some biomes (Amazon Forest, Cerrado, Atlantic Forest, and Pantanal) and smaller removal in others (Caatinga). Particularly, the application of phosphogypsum and phosphate fertilizers carrying rare earth elements in agricultural areas has involuntary increased the content of these elements in soils. Finally, the natural contents of the major and trace elements and the proposed quality reference values for rare earth elements can give support to environmental survey while also providing important science-based information for future public policies and environmental regulations.