Article From News From Bangladesh archives
Dugwells in the arsenic-affected villages of West Bengal (India) and Bangladesh are almost safe with respect to arsenic, the findings of a recent study conducted under the supervision of Dipankar Chakrabarti, Head of the department of Environmental Sciences, Jadavpur University, Calcutta shows.
The study conducted between 1989-2000 showed that arsenic concentration was below three microgram per litre in 160 out of 443 dugwells covered. A total of 220 of those dugwells had arsenic in the range of three to ten micrograms per litre, in 60 of those the range was between 10 and 50 micrograms per litre and in 60 others 50 micrograms and above per litre.
During 5-8th December 2000 and 25-29th December 2000, the group comprising 17 members with a medical team studied the arsenic-affected villages of Jalangi Block, District Murshidabad, very close to Rajshahi and Kushtia districts of Bangladesh.
The group found 5 dugwells from which people are still using water for drinking and cooking. And when many people in the village were showing arsenical skin lesions, none of those using dugwell water had arsenical skin lesions.
Whereas a dugwell at village Sakherdar-Gadagari in Murshidabad district showed arsenic concentration of little over three micrograms per litre, arsenic concentration in hand tubewells within a radius of about 200 metres from the dugwell ranges from 188 micrograms per litre to as high as 1390 micrograms per litre.
Findings in other dugwells and hand tubewells surrounding those were similar. Some of the hand tubewells were as close as 10 metres to the dugwells with which the quality of water was compared for the purpose of the study.
Dr. Chakrabarti has written that in those houses where people have a dugwell along with tubewell, they normally use tubewell's water for drinking but dugwell's water for washing clothes and cooking foods.
Villagers said, when they washed clothes with tubewell water, the clothes became brown due to iron but it did not happen with dugwell water. According to them cereals get easily boiled in dugwell water because such water is soft unlike tubewell water.
Women prefer dugwell water to wash their hair, as it becomes less sticky than when washed with tubewell water.
Dr. Chakrabartis team analysed water of several ponds which were filled with arsenic-contaminated tubewell water during March-May to keep fish alive. The analyses show that arsenic-contaminated tubewell water also contained huge amounts of iron. But the same water from the pond analysed after a few days show less iron and arsenic below 10 micrograms per litre.
In an arsenic-contaminated village of Nadia, West Bengal the group have found, in 1994, all were drinking from the same tubewell and in every family there were at least 1 or 2 persons having arsenical skin lesions. But in one family no one had arsenical skin lesions and no complaint of arsenic toxicity (cough, burning sensation, weakness etc.).
It later found out that because there was too much iron in the water, that family did not drink the water directly from the tubewell. Instead, they filled up two buckets every evening from same contaminated tubewell and allowed the water to settle for 3-4 hours.
Normally, before going to bed, they transferred the water in a mud-jar fitted with a simple filter (which the family had received from their relative who runs a filter business) and next day all drank that filtered water. The head of the family told investigators that after filtration the water remained crystal clear even if it was kept for a few days. Through this process the arsenic concentration came down from 400 micrograms per litre to about 90 micrograms per litre, the study showed.
The group made a large number of experiments in laboratory and found that if hand tubewells contained huge iron then just by letting the water settle for a few hours and then filtering it led to a 60-80 per cent removal of arsenic. Higher the iron in tubewell better is the efficiency arsenic removal through this process.
Narrating 13 years of his experience regarding Dugwell from arsenic-affected villages of West Bengal and 6 years in Bangladesh, Dr. Chakrabarti said he has learnt more as a field worker in villages than sitting in the 4 walls of the laboratory.
Explaining the reason for relatively lesser concentration of arsenic in dugwell water he said that iron is present in dissolved state underground. When it comes out and gets contact of air it is oxidised. Through this process of oxidisation 100 per cent removal of arsenic is theoretically possible, he said.
Owing to these factors arsenic is dugwell water coprecipitates with iron and goes to sediment.
Thus both iron and arsenic are less in dugwell water. Analyses of the sediment of some dugwells did not show arsenic as much as was expected. The team does not know the exact reason but suggests that microbial system may be involved to release arsenic in methylated form from the sediment. Some other factors may also be responsible for dugwell water being less contaminated in arsenic affected areas of West Bengal-India and Bangladesh.
Among the other possible factors the group listed (a) catalysis(transitional metals present in water), (b) microbial activity, (c) when we collect water by a rope and bucket, water is splashed and aerated and (d) tropical climate.
However, this does not mean all dugwells will be free of arsenic contamination. About 1000 kilometres from W. Bengal, in Rajnandangaon, Madhya Prodesh, in a gold mining area, Dr. Chakrabarti found high arsenic in a Dugwell in which the iron concentration was very low. ( The Independent )
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