Environmental Geochemical Analysis in the Yanomami Indigenous Land, Mucajaí River Basin, State of Roraima, Brazil.

The Yanomami Indigenous Land in the Amazon has a long history of illegal artisanal gold mining, leading to concerns about mercury (Hg) contamination. This study has conducted a geochemical analysis to assess Hg contamination from these mining activities. Geological materials, including river water and stream sediments, were collected from 14 predetermined points based on the Geological Survey of Brazil's methodology. The results revealed that water samples did not show Hg contamination above the limits set by the National Council of the Environment (Conama) Resolution 357. However, two stream sediment samples, particularly PJS009 and PJS010 collected from the Mucajaí River, exceeded the Conama Resolution 454's limit of 0.17 mg/kg. A Hg content of 0.344 mg/kg was found in the sediment sample PJS009, the one collected further upstream in the Mucajaí River, and 1.386 mg/kg was found in sample PJS010, also in the Mucajaí River in the region shortly before the Fumaça Waterfall, indicating that the sediments of the Mucajaí River may be contaminated with Hg from the Fumaça Waterfall upstream.

Relationships between natural radionuclides activity concentration in soils of the State of Alagoas, Brazil and WRB/FAO soil classification, types of parental rocks and rainfall variability.

Climate, soil type and geology that can influence the activity concentrations of natural radionuclides in soils. For this, 41 samples were collected in the first 25 cm of soil from the state of Alagoas, Northeast Brazil. This sample collection represents the mains soils classifications, parental rocks, and rainfall variability in this locality. The samples of soils were processed and analyzed by means of gamma-ray spectrometry for the 40K, 226Ra and 228Ra. The non-parametric Mann-Whitney U test was applied to perform the statistical inference on the differences in activity concentration for each soil class studied. There was a significant difference in the 40K activity distributions between the combination for most soil types. The results for 226Ra show no significant difference. However, Planosols differ significantly from Yellow Acrisols and Regosols for 228Ra. The strong relationship of the 40K concentration with the rock classes was shown. On the other hand, an association of the activity concentration of 226Ra and 228Ra with the rock type was not evidenced. There was a negative correlation between the 40K activity concentration and the rainfall index. 226/228Ra concentrations showed no correlation with the rainfall index.

137Cs activity concentration in soil of Alagoas State, Brazil.

Cesium 137 is present in worldwide. To evaluate its deposition in the Brazilian state of Alagoas a total of 41 samples were collected by the Geological Survey of Brazil, then processed and analyzed by gamma-ray spectrometry with hyperpure germanium detectors. The activity concentration varied from (0.3 ± 0.1) Bq/kg to (1.1 ± 0.4) Bq/kg. The present study shows that the Borborema Plateau acts as a natural barrier to rainfall, favoring the deposition of 137Cs on the local soil.

Spatial distributions of natural radionuclides in soils of the state of Pernambuco, Brazil: Influence of bedrocks, soils types and climates.

To investigate whether and in which extension the levels of natural radionuclides in soils vary with parent rock, soil type, and climatic condition factors, a large-scale survey was carried out to cover the semiarid and tropical wet climate regions of the territory of Pernambuco state (Brazil). The radionuclide concentrations were analyzed by gamma spectrometry. The median values of the activity concentrations of 226Ra (20), 228Ra (38) and 40K (458) (Bq kg-1) in the soils agreed with the values reported worldwide. The concentrations of 40K in the soils from the semiarid region were higher than those in the soils from the tropical region, whereas the radium isotope levels were higher in soils from the tropical region. The less-developed soils from the semiarid region, such as Leptosols and Neosols, had the highest 40K levels, unlike the more developed soils (Acrisols and Ferrosols) from the tropical wet area, which showed the lowest contents of 40K and the highest content of radium isotopes. The low 40K contents in well-developed soils may be attributed to the leaching of 40K by the high rainfall rates of the tropical area. In contrast, the rainfall scarcity and high potential evaporation rates of the semiarid environment may be responsible for 40K accumulation in soils. The highest Ra isotope concentrations in the well-drained soils from the tropical climate may be ascribed to the presence of heavy minerals and adsorption on Fe oxyhydroxides, which are very common in those soils. The more developed the soil the lower the K concentration, regardless of the climate. For Ra, the differences are more significant for well-drained soils, and in this case, the tropical climate, with its high rainfall rate, makes the difference. As a conclusion, climate and soil formation time showed high and contrasting influence on the 40K and radium isotope contents in soils. Less developed soils from semiarid had the highest content of 40K, whereas the more developed soils from tropical areas had the highest content of radium.