Meta-analysis of uranium contamination in groundwater of the alluvial plains of Punjab, northwest India: Status, health risk, and hydrogeochemical processes

Despite numerous studies, there are many knowledge gaps in our understanding of uranium (U) contamination in the alluvial aquifers of Punjab, India. In this study, a large hydrogeochemical dataset was compiled to better understand the major factors controlling the mobility and enrichment of uranium (U) in this groundwater system. The results showed that shallow groundwaters (<60 m) are more contaminated with U than from deeper depths (>60 m). This effect was predominant in the Southwest districts of the Malwa, facing significant risk due to chemical toxicity of U. Groundwaters are mostly oxidizing and alkaline (median pH: 7.25 to 7.33) in nature. Spearman correlation analysis showed that U concentrations are more closely related to total dissolved solids (TDS), salinity, Na, K, HCO3-, NO3-Cl-, and F- in shallow water than deep water, but TDS and salinity remained highly correlated (U-TDS: rho = 0.5 to 0.6; U-salinity: rho = 0.5). This correlation suggests that the salt effect due to high competition between ions is the principal cause of U mobilization. This effect is evident when the U level increased with increasing mixed water species (Na-Cl, Mg-Cl, and Na-HCO3). Speciation data showed that the mast dominant U species are Ca2UO2(CO3)(2-) and CaUO2(CO3)(3)(-), which arc responsible for the U mobility. Based on the field parameters, TDS along with pH and oxidation-reduction potential (ORP) were better fitted to U concentration above the WHO guideline value (30 mu g.L-1), thus this combination could be used as a quick indicator of U contamination. The strong positive conflation of U with F- (p = 0.5) in shallow waters indicates that their primary source is geogenic, while anthropogenic factors such as canal irrigation, groundwater table decline, and use of agrochemicals (mainly nitrate fertilizers) as well as climate-related factors i.e., high evaporation under arid/semi-arid climatic conditions, which result in higher redox and TDS/salinity levels, may greatly affect enrichment of U. The geochemical rationale of this study will provide Science-based-policy implications for U health risk assessment in this region and further extrapolate these findings to other arid/semi-arid areas worldwide.

Automated summary

Despite numerous studies, there are still many knowledge gaps in understanding uranium (U) contamination in alluvial aquifers in Punjab, India. This study compiled a large hydrogeochemical dataset to identify major factors controlling U mobility and enrichment in groundwater. The results showed that shallow groundwaters are more contaminated with U than deeper depths, with salinity and total dissolved solids playing a significant role in U mobilization.