Rare Earth Elements Distribution and Quantification in Brazilian Soils.

Rare earth elements (REEs) are crucial to many modern industries and have been increasingly used in our society. Furthermore, in recent years, their use has been extended to agriculture. This worldwide use may increase their levels in various environmental compartments, soils included. Information concerning background levels of REEs in Brazilian soils is incipient, which speaks for the need of qualitative as well as quantitative data for assessing reference levels of REEs in natural and anthropogenic soil environments. This study is part of a project that intends to: i) quantify total amounts of REEs in soils covering a wide range of Brazilian soil classes; ii) establish reference values for supporting future legislation concerning background as well as soil screening levels for REEs in Brazil; and, iii) build a database correlating REE levels with representative soil attributes from a widerange of soil classes to develop models that could predict REE levels in Brazilian soils. Selected samples (A and B horizons, n = 313) from different parent materials and pedoenvironments were chosen from a georeferenced soil database of the Brazilian Agricultural Research Corporation (Soil Science Division) and the total contents of selected REEs were determined by total reflection X-ray fluorescence spectrometry (TXRF) using synchrotron radiation. A certified reference material (Calcareous Soil ERM® CC690) was used for QA/QC and selected estimated method detection limits (DL, mg kg^-1) were: Sc = 0.114 ± 0.01, Ce = 0.868 ± 0.02, and Nd = 0.561 ± 0.01. In addition, certified/determined values (mg kg^-1) for the CRM were: La (24.4 ± 1.7/4 ± 1), Ce (49.1 ± 2.5/48.8 ± 0.7), Nd (19.1 ± 2.2/17 ± 1), Sm (3.5 ± 0.4/4.1 ± 0.4) and Sc (7.9 ± 0.9/5 ± 6). Total REE contents in Brazilian soils (mg kg^-1) varied quite a lot, ranging in topsoil from 0.08 to 150 for Sc, 0.23 to 560 for La, 2 to 1153 for Ce, 0.07 to 94 for Pr, 0.69 to 442 for Nd, 1 to 1964 for Pm, 0.24 to 185 for Sm, and 0.61 to 1177 for Eu.  Values for subsoil samples ranged from 0.08 to 119 for Sc, 0.3 to 1003 for La, 2 to 2019 for Ce, 0.07 to 174 for Pr, 4.8 to 770 for Nd, 1 to 1287 for Pm, 0.12 to 219 for Sm, and 0.61 to 656 for Eu. The parent material plays a major role in the total REEs contents found for topsoil and subsoil samples.