Soil tungsten contamination and health risk assessment of an abandoned tungsten mine site.

The mining and beneficiation of tungsten ores, including waste treatment and tailings disposal, may cause soil contamination in the mining area and environments. Few studies have addressed soil contamination in tungsten mine sites. The current research quantitated the leachates in the surface and subsurface soil samples from mining and beneficiation areas, peripheral area, sand-making area, dumping area, and tailings pond of an abandoned tungsten mine site in Ganzhou City, Jiangxi Province of China. We further evaluated the degree of soil tungsten pollution and the risk to human health. The results showed that soil tungsten contamination mainly occurred in the sand-making area where tailings were used to make sand. The highest tungsten content in the surface and subsurface soils of the sand-making area was 1250 and 3020 mg/kg, respectively, exceeding the EPA's Regional Screening Level of tungsten (930 mg/kg) for industrial land use. The leaching concentrations of soil tungsten had similar distribution patterns to that of total soil tungsten, with the highest leaching concentration (0.860 mg/L) found in the sand-making area. The geo-accumulation index evaluation indicated heavy tungsten contamination at the sand-making area and tailings pond. The hazard quotient (HQ = 1.34) of tungsten contamination in the surface soils of the sand-making area exceeded the acceptable level (HQ = 1), implying a significant risk to human health. The present study provided valuable information for pollution control and risk management of soil contamination in tungsten mine sites. CAPSULE: We studied the degree of soil tungsten pollution and health risk assessment in an abandoned tungsten mining area to provide helpful information for soil pollution control and risk management in China's tungsten mining areas.

Role of Manganese Oxyhydroxides in the Transport of Rare Earth Elements Along a Groundwater Flow Path.

Rare earth elements (REE) are known to be emerging contaminants in hydrosphere, but roles of hydrous manganese oxyhydroxides (HMO) in REE transport in groundwater remains unknown. In this study, groundwater was sampled along a flow path in the North China Plain to determine the behavior of REE surface complexation to HMO by a modeling and field study approach. Results show that the proportion of neodymium (Nd) complexed by HMO ranges from 0.2% to 95.8%, and from 0.3% to 99.6% in shallow groundwater and deep groundwater, respectively. The amount of complexed REE increases along the flow path. REE bound to HMO exhibit decreasing trends with increasing atomic number. The process was determined to be independent of pH, HMO content, and metal loading. This finding further demonstrates HMO-REE complexation plays a key role in transport of REE in groundwater through preferential scavenging of light REE (LREE) over heavy REE (HREE). Nevertheless, carbonate ligands appear to be robust competitors in reducing the amount of REE sorbed to HMO when solution pH rises above 8.0. Assuming that 50% of Mn concentration occurs as HMO, the amount of complexed REE was predicted to show a more marked decrease in LREE compared to that of HREE.

Sources of groundwater salinity and potential impact on arsenic mobility in the western Hetao Basin, Inner Mongolia.

The quality of groundwater used for human consumption and irrigation in the Hetao Basin of Inner Mongolia, China is affected by elevated salinity as well as high arsenic (As) concentrations. However, the origin of high salinity and its potential impact on As mobility in the Basin remain unclear. This study explores both issues using stable isotopic compositions and Cl/Br ratios of groundwater as well as the major ions of both groundwater and leachable salts in aquifer sediments. Limited variations in δ18O and δ2H (-11.13 to -8.10, -82.23 to -65.67) with the wide range of Total Dissolved Solid (TDS, 351-6734mg/L) suggest less contribution of direct evaporation to major salinity in groundwater. Deuterium excess shows that non-direct evaporation (capillary evaporation, transpiration) and mineral/evaporite dissolution contribute to >60% salinity in groundwater with TDS>1000mg/L. Non-direct evaporation, like capillary evaporation and transpiration, is proposed as important processes contributing to groundwater salinity based on Cl/Br ratio and halite dissolution line. The chemical weathering of Ca, Mg minerals and evaporites (Na2SO4 and CaSO4) input salts into groundwater as well. This is evidenced by the fact that lacustrine environment and the arid climate prevails in Pleistocene period. Dissolution of sulfate salts not only promotes groundwater salinity but affects As mobilization. Due to the dissolution of sulfate salts and non-direct evaporation, groundwater SO42- prevails and its reduction may enhance As enrichment. The higher As concentrations (300-553µg/L) are found at the stronger SO42- reduction stage, indicating that reduction of Fe oxide minerals possibly results from HS- produced by SO42- reduction. This would have a profound impact on As mobilization since sulfate is abundant in groundwater and sediments. The evolution of groundwater As and salinity in the future should be further studied in order to ensure sustainable utilization of water resource in this water scarce area.