GUWAHATI, Nov 16 � Poisonous chemical fluoride has been found beyond the permissible limits of 1parts per million (ppm) in the groundwater of many Guwahati areas causing worries to experts. In most parts of the city groundwater is the only source of water for the residents.
Increase in fluoride concentration and its presence in groundwater in hitherto unknown areas like Dispur, Rukminigaon, Sijubari etc areas, has been described to be the most disturbing by the experts.
It needs mention here that very high fluoride content in the groundwater of Bonda-Matgharia area, along with crippling fluorosis patients, was first detected by the then Additional Chief Engineer of the Public Health Engineering Department (PHED) A B Paul in early 2000. Then, fluoride was detected in the groundwater of the eastern and southern plains of Guwahati by a group of researchers from Tezpur University (TU) and the Defence Research Laboratory (DRL), Tezpur.
A few of the samples tested by this group of scientists showed high nitrate and sulphate contents, which is another cause of concern.
The scientists include Babulal Das, Jitu Talukdar, Surashree Sarma, Biren Gohain, Robin K Dutta of TU and Himangshu B Das and Subhash C Das of the DRL.
The sources of fluoride and nitrate were suspected by these scientists to be minerals from the Precambrian granite, which forms the basement of the city and also outcrops at several places in the city.
It may be mentioned that presence of granite with fluoride containing minerals like Apatite, Biotite, Muscovite etc in Karbi Anglong, the worst fluoride-affected district, had been confirmed earlier through geotechnical assessment of fluoride research study by A B Paul and a group of six scientists of the North East Institute of Science and Technology (NEIST), Jorhat.
The city, with its geographical location, where the groundwater is likely to be recharged and diluted by the Brahmaputra, is not apparently expected to have fluoride in its groundwater. The presence of fluoride in groundwater can be attributed to geological reasons, said the TU and DRL scientists in their paper published in Current Science, Vol 85, No 5.
City�s eastern part of the southeastern plains that includes Birkuchi, Narengi, Satgaon, Chandmari, Six-Mile, Baghorbari, Beltola Chariali, Hatigaon, Saukuchi etc areas, has high fluoride concentration. It is interesting to note that the fluoride concentration of the groundwater in this area gradually decreases from the east towards the west.
The groundwater samples of the western part of Guwahati were found to be mostly deficient in fluoride content, said these scientists. The fluoride in the groundwater of the western part of the city is probably diluted by the Brahmaputra, where the fluoride concentration has been found to be 0.18 ppm.
The crippling flourosis caused by high fluoride contents in water is not curable. This is why the experts call for immediate health screening, supply of sufficient safe water and introduction of medical mitigation in the fluoride endemic areas of the city.