Sources, controls, and probabilistic health risk assessment of fluoride contamination in groundwater from a semi-arid region in Gujarat, Western India: An isotope-hydrogeochemical perspective

Fluoride contamination in groundwaters of a rural region in semi-arid Western India has been studied using combination of geochemical-and-isotopic techniques, in conjunction with Health Quotient assessment approach. The objective of this study is to determine the sources and controls on fluoride content and to evaluate probabilistic non-carcinogenic risk associated with its long-term consumption. F- ranges from 0.3 to 12 mg L-1, shows high spatial variability, and similar to 35% of the samples have F- > 1.5 mg L-1 (WHO maximum limit for drinking). Two sources are identified: high F- results from water-rock interaction of F-bearing minerals in granites and gneisses, while phosphate fertilizers can contribute up to similar to 0.46 mg L-1 of groundwater F- that can be significant for low F- samples. High F- samples are characterized by high pH, Na and alkalinity, and low Ca. Calcite precipitation drives the solubility of F-bearing minerals. Kinetic fractionation of water isotopes (O-18 and H-2) demonstrates that evaporation plays role in enriching groundwater F-. Non-carcinogenic risk, estimated by Hazard Quotient (HQ(oral)(F)), ranges from 0.13-5.72 to 0.26-11.86 for adult and children, respectively. Conservative estimate shows that similar to 0.467 million of adults and similar to 0.073 million of children in four sub-districts are under the risk of fluorosis-while the residents of other five sub-districts remain safe from it. Finally, we suggest stakeholders to install F- treatment plants to ensure the health safety of local residents in the high-risk zones, create awareness in farmers for optimum use of fertilizers, and promote rainwater harvesting, for better management of groundwater resources and quality in the region.

Automated summary

This study investigated fluoride contamination in groundwaters of a rural region in semi-arid Western India using geochemical and isotopic techniques, along with Health Quotient assessment. It found that high fluoride levels were mainly from water-rock interaction and phosphate fertilizers. Samples with high fluoride content were characterized by high pH, Na, and alkalinity, and low Ca, with calcite precipitation affecting the solubility of fluoride-bearing minerals. Estimated non-carcinogenic risks revealed that hundreds of thousands of adults and children may be at risk of fluorosis.