Geochemical Distribution and Environmental Risks of Radionuclides in Soils and Sediments Runoff of a Uranium Mining Area in South China.

Uranium mining activities have contributed to the distribution and uptake of radionuclides, which have increased the active concentrations of natural radionuclides in environmental media, causing elevated human health risks. The present study aims to assess the spatial distribution characteristics of natural radionuclides in the surface soils and river sediments of the typical granite uranium mining area in South China, as well as investigate the geochemical features of natural radionuclides in the soil and sediments to understand their migration processes. The activity concentrations for 238U, 226Ra, 232Th, and 40K ranged from 17-3925 Bq/kg, 50-1180 Bq/kg, 29-459 Bq/kg, and 240-1890 Bq/kg, respectively. The open-pit mining areas and tailings pond locations exhibited the highest concentrations of activity for all these radionuclides. This distribution points to an elevated potential health risk due to radiological exposure in these specific areas. Additionally, the values of radium equivalent activity (Raeq) and annual gonadal dose equivalent (AGDE) in those areas were higher than the limits recommended by ICRP (2021). 238U and 226Ra have a significant correlation (0.724), and the cluster analysis was showing a statistically meaningful cluster below 5 indicated that they have similar behavior during parent rock weathering and watershed erosion, and the distribution of 232Th and 40K were influenced by the addition of rock types. The activity ratios of 226Ra/238U, 226Ra/232Th, 238U/40K, and 226Ra/40K variation indicated that 40K more mobile than 226Ra and 238U, U(VI) was reduced to U(IV) by organic matter in the downstream area and re-entered into the sediment during the sediment surface runoff in the small watershed of the uranium ore open-pit mining area. Therefore, it is necessary to further seal up and repair the tailings landfill area.

Geochemical distributions of natural radionuclides in surface soils and sediments impacted by lead-zinc mining activity.

This study investigated the distribution features of uranium-238 (238U), radium-226 (226Ra), thorium-232 (232Th), and potassium-40 (40K) and evaluated the associated environmental radiological hazards of the topsoil and river sediments in the Jinding lead-zinc (Pb-Zn) mine catchment from Southwest China. The activity concentrations of 238U, 226Ra, 232Th, and 40K ranged from 24.0 ± 2.29-60.3 ± 5.26 Bq.kg-1, from 32.5 ± 3.95-69.8 ± 3.39 Bq.kg-1, from 15.3 ± 2.24-58.3 ± 4.92 Bq.kg-1, and from 203 ± 10.2-1140 ± 27.4 Bq.kg-1, respectively. The highest activity concentrations for all these radionuclides were primarily found in the mining areas and decreased with increasing distance from the mining sites. The radiological hazard indices, including radium equivalent activity, absorbed gamma dose rate in the air, outdoor annual effective dose equivalent, annual gonadal dose equivalent, and excess lifetime cancer, revealed that the highest values were observed in the mining area and downstream, specifically in the vicinity of the ore body. These elevated values exceeded the global mean value but remained below the threshold value, suggesting that routine protection measures for Pb-Zn miners during production activities are sufficient. The correlation analysis and cluster analysis revealed strong associations between radionuclides such as 238U, 226Ra, and 232Th, indicating a common source of these radionuclides. The activity ratios of 226Ra/238U, 226Ra/232Th, and 238U/40K varied with distance, suggesting the influence of geological processes and lithological composition on their transport and accumulation. In the mining catchment areas, the variations in these activity ratios increased indicated the impact of limestone material dilution on the levels of 232Th, 40K, and 238U in the upstream region. Moreover, the presence of sulfide minerals in the mining soils contributed to the enrichment of 226Ra and the removal of 238U caused those activity ratios decreased in the mining areas. Therefore, in the Jinding PbZn deposit, the patterns of mining activities and surface runoff processes in the catchment area favored the accumulation of 232Th and 226Ra over 40K and 238U. This study provides the first case study on the geochemical distributions of natural radionuclides in a typical Mississippi Valley-type PbZn mining area and offers fundamental information on radionuclide migration and baseline radiometric data for PbZn deposits worldwide.

Trace elements accumulation over a century in sediment cores from a tectonic lake on the Qinghai-Tibet plateau: Source identification and risk assessment.

A record of trace elements in lake sediment can help in assessing the impact of anthropogenic activities on aquatic environments. In the present work, the trace elements profiles (Cu, Cr, Pb, Zn, As, and Cd) were determined in four sediment cores (QH01, QH02, QH07, and Z04) collected in 2012 and 2014 from Lake Qinghai to reconstruct the history of anthropogenic activity in the watershed and to evaluate the pollution status and eco-environmental risks of a typical Third Pole lake environment over the past century. The concentrations of Cu, Cr, Pb, Zn, As, and Cd in these studies ranged between 19.4 and 34.2 µg g-1, 35.6-53.6 µg g-1, 3.10-26.8 µg g-1, 56.4-93.5 µg g-1, 6.20-15.3 µg g-1, and 0.086-0.572 µg g-1, respectively. Statistical analyses indicated that the Pb, Zn, and Cd contents combination of coal, gasoline burning, and agricultural activities in the Lake Qinghai catchment and larger-scale atmospheric inputs during the past 60 years. The enrichment factors for Pb, Zn, and Cd in the sediments of Lake Qinghai are considered to be related to the region of the Qinghai-Tibet Plateau and national socioeconomic development. Enrich factor of Cd values was higher than 3.5 and maximum values of the geo-accumulation index of Pb and Cd were observed in the top layer of the sediment (0-2 cm), indicating moderate contamination. The RI values suggest that the risks to the ecological environment of Lake Qinghai are increasing since the 1950s. The results of this study illustrate that Lake Qinghai is still experiencing high trace elements pollution pressure due to the rapid environmental changes caused by anthropogenic activities on the remote and isolated Qinghai-Tibet Plateau.

Potential Sources, Pollution, and Ecological Risk Assessment of Potentially Toxic Elements in Surface Soils on the North-Eastern Margin of the Tibetan Plateau.

Due to increased levels of human activity, various pollutants are frequently detected on the Tibetan Plateau, where the environment is extremely fragile and sensitive. Therefore, this study investigated the sources, pollution, and ecological risks of soil potentially toxic elements (PTEs) in different landscape areas within the Qaidam Basin in the northeastern part of the Qinghai−Tibet Plateau. The contents of seven PTEs (Cd, Cu, Pb, Zn, As, Cr, and Ni) in 32 topsoil samples (0−2 cm) were analyzed in different regions of the Qaidam Basin. The concentrations of As, Cd, Cr, Cu, Ni, Pb, and Zn were 10.4−29.9 mg/kg, 0.08−4.45 mg/kg, 19−66 mg/kg, 8.2−40 mg/kg, 11.7−30.8 mg/kg, 11.1−31.2 mg/kg, and 32−213 mg/kg, respectively. The correlation between Pb and Cd in unpopulated areas was 0.896 (p < 0.01). The correlations among Pb, Cd, and Zn in agricultural areas, among As, Cd, Cr, and Zn in saline lake areas, and among As, Cd, Cr, Cu, Ni, Pb, and Zn in residential areas were all greater than 0.65 (p < 0.05). The principal component analysis results showed that Pb and Cd in unpopulated areas, Pb, Cd, and Zn in agricultural areas, As, Cd, Cr, Zn, and Pb in saline lake areas, and As, Cd, Cr, Cu, Ni, Pb, and Zn in residential areas were affected by human activities (significant factor >0.70). Based on the geological accumulation index and single-factor pollution index results, the maximum Cd values were found to be 4.93 and 45.88, respectively; Cd was thus the most serious PTE pollutant. The comprehensive pollution index of Nemero showed that moderately and severely polluted areas accounted for 18.89% and 18.46% of the total area, respectively. The results of the potential risk index showed that very strong and strong ecological risk points together accounted for 18.8% of the total points. The spatial variations in PTE pollution and the potential ecological risk index had similar patterns; both increased from the unpopulated areas in the northeastern Qaidam Basin to Golmud city in the south-western Qaidam Basin. These results indicate that human activities negatively impacted the soil ecological environment in the Qaidam Basin during the rapid development of the economy and urbanization and that these negative impacts tended to spread to unpopulated areas. Therefore, it is necessary to emphasize the significant impacts of human activities on environmental quality and formulate preventive measures to reduce PTE pollution in the Qinghai−Tibet Plateau.

Effects of salinity and particle size on radium desorption from river sediments in the Qinghai-Tibet Plateau.

Natural radium isotopes have been widely used to study groundwater discharge in different systems. Therefore, it is of great significance to understand the desorption behavior of radium isotopes on sediments to trace water-land exchange processes. However, there is very limited studies observing the desorption Ra isotopes to lake water of the brine lake. 224Ra desorption experiments with different salinities and particle sizes were carried out by collecting samples of brackish water from Qinghai Lake, brine from Dabuxun Lake and river sediments entering the lakes. The results show that the desorption activity of 224Ra from the river sediments to lake water of Qinghai Lake is 0.2 dpm/g when the salinity is 10.07‰. The maximum desorption activity of 224Ra from river sediments to lake water of Dabuxun Lake is 0.195 dpm/g at a salinity of 40.81‰. A salinity of 41.81‰ and particle size of 16.28 µm are the threshold points affecting the desorption behavior of Ra. When the salinity is less than 40.81‰, the desorption activity of Ra increases linearly with increasing salinity. When the salinity is greater than 40.81‰, the desorption activity of Ra decreases nonlinearly with increasing salinity and tends toward a stable low value. When the particle size is larger than 16.28 µm, the small particle size promotes desorption. The smaller the particle size is, the greater the desorption activity is. When the particle size is less than 16.28 µm, the small particle size inhibits desorption. The smaller the particle size is, the smaller the desorption activity. The co-precipitation of Ra2+ with supersaturated Ca2+, SO42- and other ions may be the main reason for the threshold point of salinity and particle size in Ra desorption process in salt lake system.