Co-occurrence of geogenic uranium and fluoride in a semiarid belt of the Punjab plains, India

Abstract

The inordinate presence of uranium (U) and fluoride (F−) in shallow aquifers of arid/semi-arid regions in northern India has raised a serious health concern; the Muktsar district of Punjab is one such example. In the present study, a total of 38 groundwater samples (17 from <100 ft (very shallow; VSL), 21 from >100 to 180 ft (shallow; SL)) were collected from this district to understand the current health risk associated with U and F− and the major factors/processes influencing these contaminants. Groundwater in the study area is mostly alkaline and oxic in nature. The concentration of U ranged from 18.5 μg/L to 456 μg/L exceeding the WHO permissible limit (>30 μg/L) in 93 and 100% samples from VSL and SL respectively, while F− concentration (ranged from 0.3 to 14.4 mg/L) above the limit (>1.5 mg/L) were found in 75 and 57% samples from VSL and SL respectively. As per the depth-wise distribution of U and F−, there is no significant difference between VSL and SL samples, with a few exceptions. Spearman rank correlation (ρ) shows a significant positive correlation (p-value < 0.05) between U and F− (ρ = 0.5), and U with total dissolved solid (TDS) (ρ = 0.5), salinity (ρ = 0.6), and bicarbonate (HCO3−) (ρ = 0.7) and a positive association of F− with TDS (ρ = 0.3), salinity (ρ = 0.3), and HCO3− (ρ = 0.3), indicating these parameters are responsible for the co-occurrence of U and F−. Moreover, this geochemical signature is attributed to their geogenic origin. Uranium speciation data show that UO2(CO3)22− and UO2(CO3)34− are dominant species, while F− predominantly occurs as F− species. The regions with high concentration of U and F− in groundwater primarily have mixed type species (Na–HCO3 and NaCl type). Geochemical modelling revealed that the precipitation of calcite, dolomite, and aragonite is favourable for mobility of F− in groundwater. The hazard quotient (HQ) of F− for adults and children exceeds 1 in 57.8% and 65.7% of samples, respectively, while in case of U, 94.7% and 100% samples exceed 1, respectively, indicating the latter is having greater health impact on local people. The current data indicated an urgent demand to develop low-cost and effective remedial techniques to manage groundwater contamination in this region.