A recent study by the National Remote Sensing Centre (NRSC) has highlighted significant fluoride contamination in groundwater across India. 

About Fluoride

• Fluoride is an inorganic, single-atom anion of the element fluorine with chemical formula F−.
• Fluoride salts are usually white or colorless, have a bitter taste, and are odorless.
• It is found naturally in groundwater, and comes from the Earth’s crust (0.06-0.09%). 
• It enters the water through the leaching and dissolution of fluoride-bearing minerals in underground aquifers.
• According to WHO, the safe limit for fluoride in drinking water is 1.50 mg/litre, and levels above this are considered unsafe.

Key Findings of the Study on Fluoride Contamination in Groundwater

• Fluoride Contamination in Groundwater
  • Western India: Groundwater in western Indian regions, characterized by arid and dry climates, generally has higher fluoride concentrations.
    • Highest pre-monsoon and post-monsoon fluoride concentrations: Rajasthan recorded the highest levels of fluoride in groundwater during both pre-monsoon and post-monsoon periods.
      • Its Pre-monsoon concentration was 1.41 mg/litre and post-monsoon was 1.44 mg/litre, close to the maximum permissible limit.
    • Jaisalmer district worst affected: The Jaisalmer district in Rajasthan exhibited the worst fluoride contamination.
  • Southern India:  
    • Several other states, including Karnataka, Tamil Nadu, and Jharkhand also showed post-monsoon fluoride levels higher than the permissible limit.
  • Eastern India: Jharkhand, Bihar, and Chhattisgarh have elevated fluoride levels.

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• Seasonal Variation in Contamination
  • The highest levels of fluoride contamination in groundwater were observed during the dry, pre-monsoon months (March-May).
    • During this period, fluoride levels were 8.65% above the permissible limit.
  • Post-monsoon months also showed significant contamination, with levels 7.1% above normal.
• Risk of Fluorosis
  • Skeletal fluorosis: Even a 2% fluoride concentration in groundwater poses a significant risk of skeletal fluorosis.
    • Skeletal fluorosis is a bone disease caused by too much fluoride in the body, which makes the bones weak.
  • Dental decay: This risk increases if fluoride levels reach 40% in groundwater.
• Factors Affecting Fluoride Contamination
  • Geology: The type of rocks and soil in an area can influence fluoride levels.
  • Climate:.Arid and dry regions, especially in western India, are more prone to high fluoride levels compared to humid areas.
  • Season: Fluoride levels tend to be higher during dry, pre-monsoon months.

Fluoride Remediation Using Biochars

• Fluoride remediation is defined as the process in which excess fluoride is removed from the water. 
• Biochars:  it is a charcoal like material which is made by heating biomass in a low oxygen environment. 
  • The process of heating organic substances at high temperatures is called”pyrolysi”. 
  • Working of Biochars
    • Absorption: porous structure of biochars help in absorbing fluoride ions from water. 
    • Ion Exchange: In biochars, fluoride ions are exchanged with other ions.
    • Precipitation: In some cases, fluoride ions react with compounds to form insoluble fluoride compounds that precipitate out of the water.

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