Impact of sugarcane cultivation on the geochemistry of rare earth elements in Cretaceous rhyolite-derived soils, Northeastern Brazil

Abstract

Rare earth elements (REEs) have recently been identified as emerging pollutants, with phosphate fertilizers representing a significant source of their introduction into agricultural soils. Brazil is the world’s foremost producer of sugarcane, the most prevalent agricultural crop in the Cabo Basin. Nevertheless, despite the region’s significance, no studies have yet addressed REE concentrations in the agricultural soils of this region. This research explored the geochemistry of rare earth elements (REEs) in rhyolite-derived soils that have been under intensive sugarcane cultivation since 1930 has resulted in soil contamination. Furthermore, the study examined the influence of soil properties on REE geochemistry. The higher concentration of REEs on the surface of soils under sugarcane cultivation, in comparison to the absence of REE enrichment in preserved areas, indicates that agricultural activities contribute to the accumulation of REEs in the Cabo Basin. Significant increases in the enrichment factors for Sm, La, Pr, Nd, Gd, Tb, Ho, Lu, and Y were observed in soils utilized for sugarcane cultivation. Cluster analysis effectively identified the enrichment of REEs in agricultural soils. The geochemical behavior of light rare earth elements (LREEs) was not influenced by soil properties. However, heavy rare earth elements (HREEs) demonstrated a robust positive correlation with pH, CEC, and OC. The chemical and mineralogical composition of the parent material exerts a pronounced influence on REE concentrations in the soils. These findings play a critical role in predicting and mitigating the prospective effects of REE accumulation due to agricultural activities and underscore the urgent necessity for specific legislation in Brazil to regulate REE levels in soils.