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Deflouridation of water from park textbook of spm

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Defluoridation of Water - Park's Textbook of Preventive and Social Medicine

Background: Fluoride in Drinking Water

Fluorine is naturally present in water supplies - it is, in fact, the main dietary source of fluoride. The relationship with health is dose-dependent:
  • Deficiency (below optimum): associated with dental caries
  • Optimum level: 0.5-0.8 ppm in India (tropical climates); 1 ppm in temperate climates (where water consumption is lower)
  • Excess (above optimum): causes dental fluorosis and skeletal fluorosis

Endemic Fluorosis (the problem requiring defluoridation)

In areas where drinking water contains 3-5 mg/L of fluorine, endemic fluorosis occurs. High-burden districts in India include parts of Andhra Pradesh (Nellore, Nalgonda, Prakasam), Punjab, Haryana, Karnataka, Kerala, and Tamil Nadu.
Manifestations of fluorosis:
  1. Dental fluorosis - Occurs when excess fluoride is ingested during the first 7 years of life (tooth calcification period). Characterized by "mottling" of dental enamel, reported at levels above 1.5 mg/L. Teeth develop chalk-white patches that turn yellow, then brown or black. In severe cases, enamel is lost, giving a corroded appearance. Mottling is most visible on upper incisor teeth.
  2. Skeletal fluorosis - Associated with lifetime intake of 3.0-6.0 mg/L or more. Heavy fluoride deposition in the skeleton occurs. At concentrations exceeding 10 mg/L, crippling fluorosis can result, causing permanent disability.
  3. Genu valgum - A form of fluorosis with genu valgum (knock-knee) and osteoporosis of the lower limbs, reported in Andhra Pradesh and Tamil Nadu. Observed in people whose staple food was sorghum (jowar), which promotes higher retention of ingested fluoride compared to rice-based diets.

Defluoridation - Definition

Defluoridation is the process of reducing excess fluoride levels in water down to the optimum level in geographic areas where water naturally contains high fluoride concentrations.

Interventions (as per Park's)

(a) Changing the water source The first-line solution is to find a new water source with lower fluoride content (0.5-0.8 mg/L). Running surface water generally contains lower fluoride quantities than groundwater sources such as wells.
(b) Chemical treatment - The Nalgonda Technique (most important) If changing the source is not possible, water can be chemically defluoridated in a water treatment plant (though it is moderately expensive). The National Environmental Engineering Research Institute (NEERI), Nagpur developed this technique.
Steps of the Nalgonda Technique:
  1. Addition of lime
  2. Addition of alum (in sequence)
  3. Flocculation
  4. Sedimentation
  5. Filtration
The technique is named after Nalgonda district in Andhra Pradesh, one of the most severely affected areas for endemic fluorosis in India.
(c) Other measures
  • Fluoride supplements should not be prescribed for children who already drink fluoridated water
  • Use of fluoride toothpaste in areas of endemic fluorosis is not recommended for children up to 6 years of age

Defluoridation Using Phosphate

In some geographic areas with high natural fluoride, water can also be defluoridated using phosphate to reduce fluorides to optimum levels (this is the brief definition entry under water treatment in the textbook).
Source: Park's Textbook of Preventive and Social Medicine, Chapter on Water Supply & Sanitation / Endemic Diseases (pp. 740, 828-829)
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