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7 Co-occurrence of High Levels of Uranium, Arsenic and Molybdenum in Groundwater of Dornogobi, Mongolia
Analysis of 202 water samples from randomly selected wells in Dornogobi Aimag (Province) of Mongolia showed elevated concentrations of uranium (range <0.24 to 429 μg/L; mean = 36.2 μg/L), arsenic (range 0.075-122 μg/L; mean = 6.0 μg/L) and molybdenum (range 0.59-296 μg/L; average = 21.9 μg/L). In total, 36% of samples tested had uranium concentrations above the WHO guideline (30 μg/L) and 20% had arsenic at levels that exceeded the WHO’s drinking water guideline of 10 μg/L. Average uranium and arsenic concentrations in 8 and 5 of the 14 soums (counties) respectively exceeded the WHO guidelines. Higher concentrations of U and As were found in shallow (< 10 m) aquifers compared to the deep (> 50 m) aquifers. The Co, Ni, Cu, and Pb were strongly correlated with iron (r ≥0.59; p-value ≤ 0.05 for pair-wise associations with iron), while U only co-varied with Mo and Mn. Arsenic was strongly associated only with the pH of the groundwater. These inter-element relationships reflect interesting contrasts in the mechanisms of leaching arsenic and uranium into the groundwater. The concentrations of U and As in Dornogobi groundwater exceed the levels associated with adverse health effects in human populations. Discovery of elevated levels of molybdenum in the groundwater is of concern since this element acts as an antagonist against copper absorption and hence can potentiate copper deficiency in local food chain and human population. Although individual guidelines have been established for uranium and arsenic in drinking water, little is currently known about the health effects of exposing communities to unsafe levels of the two elements together in places like Dornogobi. Multiple metal contamination of groundwater is an issue of global concern but our understanding of the accompanying health risks is very limited and current remediation strategies would seem to be inadequate or inappropriate.
• We analyzed water samples from 202 randomly selected wells in the Dordogobi Aimag (Province) of Mongolia for total uranium, arsenic and molybdenum along with manganese, zinc, cadmium, copper manganese, iron, cobalt, nickel and lead.
• We found that levels of uranium and arsenic in 36% and 20% of the samples exceeded the current WHO’s guidelines for drinking water
• Dornogobi is rich in minerals and the high levels of uranium, arsenic and molybdenum were derived naturally from local rocks and soils
• The health effects of exposing communities to unsafe levels of uranium and arsenic together in places like Dornogobi is of concern
• Multiple metal contamination of groundwater is an issue of global concern but our understanding of the accompanying health risks is very limited and current remediation strategies would seem to be inadequate or inappropriate.