Distribution of rare earth elements in soils of contrasting geological and pedological settings to support human health assessment and environmental policies

Abstract

Establishing quality reference values (QRVs) for rare earth elements (REEs) in soils is essential for the screening of these emergent contaminants. Currently, Brazil has the second-largest reserve of REEs, but data regarding background concentrations and distributions in soils remain scarce. The aim of this study was to establish the QRVs and assess the spatial distribution of REEs in soils, including REE fractionations and anomalies in (Piauí) state (251,529.186 km 2 ), northeastern Brazil. This study reports the most detailed data on REE geochemistry in Brazilian soils. A total of 243 composite soil samples was collected at 0-20 cm depth. The mean background concentrations in soils followed the abundance of the earth's upper crust:REEs (mg kg -1 ) showed the following order based on the individual mesoregions of Piauí state: Southeast (262.75) ). The highest QRVs were observed in the Southeast mesoregion. The establishment of QRVs based on the mesoregion scale improves data representativeness and the monitoring of natural REE values by identifying hot spots. Geostatistical modeling indicated significant local variability, especially in the Southeast mesoregion. The levels of these elements in this spatial zone are naturally higher than the other values across Piauí state and the mesoregion itself and indicate a high potential to exceed the QRVs. Our approach provides much needed data to help strengthen policies for both human health and environmental protection.

Evaluation of Rare Earth Element Mine Sites for Environmental Impact

“…Many soil studies have been conducted to determine if soil rare earth element concentrations may have sufficient soil variability to influence environmental responses. In Brazil, Landim et al [14] established soil rare earth element quality references and assessed their spatial distributions. The mean background concentrations in soils followed the abundance of the earth's upper crust: Ce > La > Nd > Pr > Sm > Dy > Gd > Er > Yb > Eu > Tb > Lu.…”

“…The mean background concentrations in soils followed the abundance of the earth's upper crust: Ce > La > Nd > Pr > Sm > Dy > Gd > Er > Yb > Eu > Tb > Lu. In the Piaui state in Brazil, the ∑REEs across the mesoregions were (i) southeast (263 mg kg −1 ), (ii) north and central-north (90 mg kg −1 ), and (iii) southwest (40 mg kg −1 ) [14].…”