Effects of Artisanal Monazite and Cassiterite Mining in the Amazon on Uranium and Thorium Concentrations

Abstract Artisanal monazite and cassiterite mining can alter soil properties and promote the accumulation of naturally occurring radionuclides, such as uranium (U) and thorium (Th), in the generated mining residues. This study aimed to quantify U and Th concentrations and assess the potential for contamination and ecological risk in tailings and overburden from artisanal mining areas in the municipality of São Félix do Xingu, Pará, Brazil. Samples were collected from seven areas, including active mining sites, inactive areas, and natural forest soil as a reference. Chemical and particle-size properties, as well as U and Th concentrations, were determined. Contamination was assessed using the contamination factor (CF), enrichment factor (EF), geoaccumulation index (Igeo), and pollution load index (PLI), complemented by Spearman correlation analysis and principal component analysis. U and Th concentrations were higher in the mining materials than in the reference area, particularly in the tailings from the area inactive for 10 years, which showed the highest concentrations. The CF values indicated moderate contamination, whereas the EF indicated minimal enrichment. The Igeo classified the materials as unpolluted to slightly polluted, while the PLI indicated pollution in the mining areas. The results demonstrate the persistence of radionuclides in mining residues even after mining activities have ceased, reinforcing the need for environmental monitoring and remediation strategies.