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