Highlights

  • Field kits correctly classified 91% of wells relative to 1.5 mg/L WHO guideline for F-.
  • Overall 9% of 28,648 wells contained >1.5 mg/L F; 7% in floodplains and 12% in doabs.
  • Precipitation and/or dissolution of fluorite influenced by Ca2+ regulates groundwater F.
  • Ion exchange of Ca2+ with Na+ in clay minerals may lead to higher groundwater F.
  • Reducing F? exposure requires massive testing, which is possible only with field kits.

Abstract

Chronic exposure from drinking well-water with naturally high concentrations of fluoride (F) has serious health consequences in several regions across the world including South Asia, where the rural population is particularly dependent on untreated groundwater pumped from private wells. An extensive campaign to test 28,648 wells was conducted across the Punjab plains of Pakistan and India by relying primarily on field kits to document the scale of the problem and shed light on the underlying mechanisms. Groundwater samples were collected from a subset of 712 wells for laboratory analysis of F and other constituents. A handful of sites showing contrasting levels of F in groundwater were also drilled to determine if the composition of aquifer sediment differed between these sites. The laboratory data show that the field kits correctly classified 91% of the samples relative to the World Health Organization guideline for drinking water of 1.5 mg/L F. The kit data indicate that 9% of wells across a region extending from the Indus to the Sutlej rivers were elevated in F relative to this guideline. Field data indicate an association between the proportion of well-water samples with F > 1.5 mg/L and electric conductivity (EC) > 1.5 mS/cm across six floodplains and six intervening doabs. Low Ca2+ concentrations and elevated bicarbonate (HCO3 > 500 mg/L) and sodium (Na+ > 200 mg/L) in high F groundwater suggest regulation by fluorite. This could be through either the lack of precipitation or the dissolution of fluorite regulated by the loss of Ca2+ from groundwater due to precipitation of calcite and/or ion exchange with clay minerals. Widespread salinization of Punjab aquifers attributed to irrigation may have contributed to higher F levels in groundwater of the region. Historical conductivity data suggest salinization has yet to be reversed in spite of changes in water resources management.

Graphical abstract

https://ars.els-cdn.com/content/image/1-s2.0-S0048969721064317-ga1_lrg.jpg


*Original abstract online at https://www.sciencedirect.com/science/article/abs/pii/S0048969721064317

**Full paper available at Research Gate at https://www.researchgate.net/publication/355779214_Groundwater_fluoride_across_the_Punjab_plains_of_Pakistan_and_India_Distribution_and_underlying_mechanisms


Funding source

Funding for this project was provided by the National Institute of Environmental Health Sciences (NIEHS) P30 ES006096, R00 ES024116,R01 ES019890, R01 ES11170, and R01 ES027224 and the National Center for Advancing Translational Sciences (NCATS) UL1 TR001425. The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.