Nolan and Weber opine that uranium (U) contamination of groundwater has been primarily associated with anthropogenic activities such as mining, milling, nuclear testing, and disposal of spent nuclear fuel. However, groundwater U concentrations across the United States exceed the U.S. EPA MCL of 30 mg/L in many regions, including those without anthropogenic U activity, indicating a source of natural U contamination. This is significant because consumption of U-contaminated drinking water has been linked to nephrotoxicity and osteotoxicity and, thus, poses a health risk. Groundwater geochemical data collected from two major U.S. aquifers, High Plains (HP) and Central Valley (CV), reveal that naturally occurring groundwater uranium (U) exceeding the U.S. EPA maximum contaminant level (MCL = 30 mg/L) across 22,375 km2 where 1.9 million people live. Analysis of geochemical parameters revealed a moderately strong correlation between U and nitrate, a common groundwater contaminant, as well as alkalinity and calcium [Spearman rho = 0.30, p < 0.001]. Nitrate is recognized to alter U solubility by oxidative dissolution of reduced U(IV) minerals. Approximately 78% of areas where U concentrations were interpolated above the MCL were correlated to the presence of nitrate (Pearson r = 0.5, p < 0.05). Shallow groundwater was determined to be the most susceptible to co-contamination (HP, rho = 0.46, CV, rho = 0.52). Together, these results indicate that nitrate, a primary contaminant, should be considered as a factor leading to secondary groundwater U contamination in addition to the recognized role of alkalinity and calcium. Conclusions require further consideration ....
Original URL: https://pubs.acs.org/doi/abs/10.1021/acs.estlett.5b00174
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