H089-0007
Fluoride distribution in the Transboundary Indus River Basin, Pakistan and India

Thursday, 10 December 2020
Poster
Junaid Ali Khattak1, Abida Farooqi1, Ishtiaque Hussain1, Anand Kumar2, Chander K Singh3, Brian Mailloux4, Tyler Ellis5, Benjamin C Bostick6 and Alexander van Geen5, (1)Quaid-i-Azam University, Department of Environmental Sciences, Islamabad, Pakistan, (2)TERI School of Advanced Studies, Department of Energy and Environment, New Delhi, India, (3)TERI School of Advanced Studies, Department of Energy and Environment,, New Delhi, India, (4)Barnard College, Environmental Science, New York, NY, United States, (5)Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, United States, (6)Lamont-Doherty Earth Observatory of Columbia University, Center for Climate and Life, Palisades, NY, United States
Abstract:
The long-term consumption of well-water with naturally high levels of fluoride (F-) has serious health consequences. To document the distribution and understand the underlying mechanisms of high levels of F-, a blanket testing campaign relying primarily on field kits was carried out over several years in the Indus Basin. A subset of 402 quality control samples analyzed in the laboratory by ion chromatography showed field kits correctly classified 94% of the samples with respect to F- 1.5 mg/L, the World Health Organization guideline for drinking water.

The kit data show that 9% of the tested wells (n=28,648) contained F- >1.5 mg/L. In river floodplains and intervening doab regions, these proportions were 7% (n=16,843) and 12% (n=11,805), respectively. At the level of geomorphological units consisting of 6 individual floodplain and 6 intervening doabs, we document a systematic association between the proportion of wells with F-> 1.5 mg/L and wells with > 1.5 mS/cm in electrical conductivity (EC). For reasons still unclear, this relationship breaks down when considering proportions of high F- and EC wells at level of individual villages. Because of a highly heterogeneous distribution, a sizeable proportion of wells in most villages are low in F- and could potentially be shared to lower exposure.

Our laboratory data for calcium (Ca2+) suggest that saturation with respect to fluorite exerts a strong control on maximum F- levels. High F- wells in floodplains as well as doabs share certain common characteristics such as high levels of sodium (Na+ > 200 mg/L) as well as low levels of Ca+2 values < 50 mg/L. This suggests that ion exchange between groundwater and clay minerals along groundwater flow paths plays an important role in regulating groundwater F- levels. For that reason, widespread salinization in the Punjab plains attributed to the Indus river irrigation system may have enhanced naturally elevated groundwater F- concentrations in the region

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