Fluoride contamination in groundwater resources of Alleppey,southern India

Alleppey is one of the thickly populated coastal towns of the Kerala state in southern India.Groundwater is the main source of drinking water for the 240,991 people living in this region.The groundwater is being extracted from a multi-layer aquifer system of unconsolidated to semi-consolidated sedimentary formations,which range in age from Recent to Tertiary.The public water distribution system uses dug and tube wells.Though there were reports on fluoride contamination,this study reports for the first time excess fluoride and excess salinity in the drinking water of the region.The quality parameters,like Electrical Conductivity（EC） ranges from 266 to 3900 μs/cm,the fluoride content ranges from 0.68 to2.88 mg/L,and the chloride ranges between the 5.7 to 1253 mg/L.The main water types are Na-HC03,NaCO3 and Na-Cl.The aqueous concentrations of F- and CO32- show positive correlation whereas F- and Ca2＋ show negative correlation.The source of fluoride in the groundwater could be from dissolution of fluorapatite,which is a common mineral in the Tertiary sediments of the area.Long residence time,sediment-groundwater interaction and facies changes（Ca-HCO3 to Na-HCO3） during groundwater flow regime are the major factors responsible for the high fluoride content in the groundwater of the area.High strontium content and high EC in some of the wells indicate saline water intrusion that could be due to the excess pumping from the deeper aquifers of the area.The water quality index computation has revealed that 62%of groundwater belongs to poor quality and is not suitable for domestic purposes as per BIS and WHO standards.Since the groundwater is the only source of drinking water in the area,proper treatment strategies and regulating the groundwater extraction are required as the quality deterioration poses serious threat to human health.

Groundwater fluoride contamination:A reappraisal

Dissolution of fluorite （CaF2） and/or fluorapatite （FAP） [Cas（PO4）3F], pulled by calcite precipitation, is thought to be the dominant mechanism responsible for groundwater fluoride （F） contamination. Here, one dimensional reactive-transport models are developed to test this mechanism using the published dissolution and precipitation rate kinetics for the mineral pair FAP and calcite. Simulation results correctly show positive correlation between the aqueous concentrations of F and CO2 and negative correlation between F- and Ca^2＋. Results also show that precipitation of calcite, contrary to the present understanding, slows down the FAP dissolution by 10G orders of magnitude compared to the FAP dissolution by hydrolysis. For appreciable amount of fluoride contamination rock-water interaction time must be long and of order 106 years.

Environmental fate and health exposures of the geogenic and anthropogenic contaminants in potable groundwater of Lower Ganga Basin,India

The study evaluated the sources and controlling factors of the groundwater contaminants in an agroeconomic region of Lower Ganga Basin using principal component analysis(PCA),multivariable linear regressions(MLR),correlation analysis,and hierarchical cluster analysis,and evaluated the public health risks using the Latin Hypercube Sampling,goodness-of-fit statistics,Monte Carlo simulation and Sobol sensitivity analysis based on the 1000 samples collected in two sampling cycles(N=1000).The study reveals that the dissolution of fluoride-bearing minerals and semi-arid climate regulate the fluoride concentrations(0.10–18.25 mg/L)in groundwater.Extensive application of inorganic nitrogenous fertilizers and livestock manure mainly contributed to elevated nitrate levels(up to 435.0 mg/L)in groundwater.The health risks analysis indicates that fluoride exposure is more prevalent in the residents of each age group than the nitrate and both contaminants exhibited higher non-carcinogenic health risks on the infant and child(minor)age groups compared to adolescents and adults.Based on the cokriging interpolation mapping,the minor residents of 17.88%–23.15%of the total area(4545.0 km^(2))are vulnerable to methemoglobinemia whereas the residents of all age-groups in 38.47%–44.45%of the total area are susceptible to mild to severe dental/skeletal fluorosis owing to consumption of untreated nitrate and fluoride enriched groundwater.The Sobol sensitivity indices revealed contaminant levels,groundwater intake rate and their collective effects are the most influential factors to pose potential health risks on the residents.Artificial recharge and rainwater harvesting practices should be adopted to improve the groundwater quality and the residents are advised to drink purified groundwater.