This article published in Current Science presents information on the state of flouride contamination of water in Karnataka. Fluoride is known to contaminate groundwater reserves globally. Sporadic incidence of high fluoride content in groundwater has been reported from India, China, Sri Lanka, West Indies, Spain, Holland, Italy, Mexico, and North and South American countries.

In India, its occurrence in top aquifer system is endemic in many places of Andhra Pradesh, Tamil Nadu, Karnataka, Gujarat, Rajasthan, Punjab, Haryana, Bihar and Kerala. A high concentration of 5.2 mg/l has been reported in Medak district, Andhra Pradesh1, 15 mg/l in Nawabganj Block, Uttar Pradesh2 and 18 mg/l in Jaipur, Rajasthan3 as against its critical limit of 1.5 mg/l in drinking water4. The
levels above this pose serious health hazards to humans and irreversible damage
to plants.

High profile of fluoride in shallow zone groundwater is due to the geochemical disposition in the vicinity of the groundwater extraction structures. The toxicity of fluoride is also influenced by high ambient temperature, alkalinity, calcium and magnesium contents in the drinking water. Fluorospar occurs in structurally weak planes like shear fracture zones, joints and at the contact of host rock and vein quartz. Rock minerals weather and form calcium and magnesium carbonates, which serve as good sinks for fluoride ions9.

However it is the leachable state of fluoride ions that determines the water fluoride levels. The leachability is governed by (i) pH of the draining solutions and (ii) dissolved carbon dioxide in the soil. The present study pertains to the fluoride in phreatic groundwater (the top aquifer system) and it is in this regimen that hand pumps, dug and borewells have been constructed.

The present study includes 15 villages from each of the above mentioned six districts with noticeable levels of fluoride. The concentrations of fluoride vary from 1 to 7.4 mg/l. Occurrence of fluoride is very sporadic and marked differences in concentrations occur even at very short distances, sometimes even less than 2 to 3 km. Natural contamination of groundwater by fluoride causes irrepairable damage to plant and human health. High oral intake of fluoride results in physiological
disorders, skeletal and dental fluorosis, thyroxine changes and kidney damage
in humans13.

High fluoride levels inhibit germination, cause ultrastructrual malformations, reduce photosynthetic capacities, alter membrane permeability, reduce productivity and biomass and inflict other physiological and biochemical disorders in plants. Several physical and chemical defluoridation methods have been designed to treat high fluoride waters. However ion exchange and chemical treatments are cost intensive, while physical methods suffer limitations like frequent change of defluoridant beds and inability to reduce fluoride to non-toxic levels.

Biological defluoridation can serve as a best alternative to the conventional methods of defluoridation. Such methods would be cost effective and material employed would be biodegradable. Efforts are on in this direction and the preliminary laboratory trials conducted in the Plant Physiology Laboratory, Department of Botany, Bangalore University, have yielded
promising results.

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