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New Zealand Engineering 1999 July Infrastructure
Water for Survival Arsenic Contamination of Water Supplies in Bangladesh and India Arsenic contamination of water supplies has recently become an issue of major international significance. In the River Ganges delta, millions of people in Bangladesh and West Bengal are affected by drinking underground water. But there are also problems of excessive arsenic levels in southwestern Taiwan, Cordoba, Argentina and Tacna, Peru. John La Roche describes the problems and the methods used to tackle them. Although arsenic contamination is often associated with industrial pollution, particularly from mining operations, the groundwater contamination in Bangladesh and West Bengal is naturally occurring. There is much debate about the mechanism of just what has caused the contamination. It is thought that decomposition of the sedimentary material containing arsenic caused by over-extraction for agriculture has caused the arsenic to dissolve, allowing it to migrate with the groundwater. It is thought that arsenic-containing rocks possibly originating in the Meghalaya hills to the north of the Ganges delta, weathered thousands of years ago releasing ionic arsenic into river water. This arsenic was carried downstream mixing with iron hydroxide coated sand grains in the water. Arsenic was adsorbed on to these sand grains and the sand was deposited and buried forming the aquifers from which water is drawn today. Organic material buried at the same time, created a reducing environment causing the iron hydroxide to dissolve releasing arsenic and making it mobile. Concentrations of over 3 mg/l have been found – more than 300 times the World Health Organisation standard of 0.01 mg/l. Concentration varies widely, even between wells of the same depth within 100 metres of each other. An explanation for this may be variable strata thickness. The medical effects are first noticed as skin lesions, (keratosis), and are often noted in people with an apparently low exposure to arsenic in drinking water. Alan Smith, Professor of Epidemiology at the University of California, Berkeley with a team of researchers has been conducting investigations into the medical effects of arsenic in USA, Argentina, Chile and West Bengal, India. In the Ganges delta the areas affected are estimated to cover 65,000 km�, home to 51 million people in Bangladesh and 34 million people in West Bengal. It is not known how many of these people drink the arsenic affected water, even though one report from West Bengal suggests that at least 800,000 people have been doing so. A recent report from Bangladesh quotes 4,600 people with arsenicosis, a condition that can lead to various cancers. The first signs of arsenic poisoning are lesions on the hands and feet and discolouration of the skin. In later stages arsenic causes skin cancer and other internal cancers such as bladder and lung. In the early stages, which may last 10 years, switching to arsenic free water will cause a reversal of all symptoms. Not all people are affected in the same way. In the same family some may not be affected at all, while others will suffer severely from arsenic poisoning. A recently published study by Professor Smith and others, examined 7,818 individuals including 4,093 females drinking arsenic contaminated water between 0.05 mg/l and 0.8 mg/l. Keratosis was found in 1.2 percent of females and 3 percent of males. Hyperpigmentation was found in 3.1 percent of females and 6.4 percent of males. The higher incidence for males was not explained by the fact that males drink more water. Tube wells in most parts of the world are a very safe and environmentally acceptable water supply for millions of people, particularly in third world countries. Bacteriologically contaminated surface water claims millions of lives annually. In Bangladesh there are many hundreds of deaths daily from diarrhoeal disease, compared to very few deaths from arsenic. For populations with arsenic affected water, to suddenly change back to using surface water might put them at even greater risk. Contaminated tube wells are marked and people are advised not to stop using the contaminated well immediately but encouraged to find a safer source at least for drinking and cooking. Many people are looking for acceptable methods which villagers can use, to either treat arsenic contaminated water or to find alternative sources. Dr Richard Anstiss of Auckland Institute of Technology, with funding for implementation from the NZ Ministry of Foreign Affairs and Trade has developed a method using ferric-oxyhydroxide, a readily available local material that can be added to small household sand filters to precipitate out the arsenic. While excellent results have been obtained to date and the method looks very promising, final tests and organisation of larger scale implementation are required. The involvement of village communities in Bangladesh is a key component to ensure that they can use the method effectively and easily. Another solution proposed for some areas of West Bengal, in particular, is to drill through the arsenic contaminated layer to uncontaminated aquifers at 300 to 400 m depth. There is some concern about the possibility of the deep bores becoming cross-contaminated from higher levels. Sealing and double casing have been proposed as possible methods to overcome this problem, although I wonder if adjacent bores without such measures might cause long-term problems. An Australian report suggested that merely exposing water to sunlight and air would help the dissolved oxygen to oxidise the arsenic to a less dangerous form that could then be precipitated. Their idea was to use troughs dug in the earth and lined with plastic sheets to hold the water. Other proposals include surface ponds that would be exclusively reserved for drinking water. Although there are many ponds in the region used for growing fish, watering agricultural crops, stock watering, bathing and washing places for villagers, most are heavily polluted. Rainwater catchment and storage is another option, which is being considered. The problem really came to public attention in 1996 when the Dhaka Community Hospital in Bangladesh identified the first cases of arsenic poisoning. A full-scale research project was then undertaken by the Hospital, Bangladesh Council for Scientific and Industrial Research and the School of Environmental Studies at Jadavpur University in West Bengal. Other agencies are involved including the World Bank, United Nations Development Programme, United Nations Children’s Fund, the British Geological Survey and the Department of Geo-engineering at Miyazaki University in Japan. Major conferences have been held to discuss the issue, the most recent in December 1998. Water for Survival has been approached by a number of non-governmental community organisations in West Bengal seeking assistance. For a number of reasons including the uncertainty of the most appropriate solution to the problem, Water for Survival is waiting for more information about the issue before proceeding, or possibly handing it over to other larger agencies. Water for Survival has funded a number of tube wells in West Bengal and is at present funding tube wells in Dhaka slums. However, we are assured these tube wells are outside the arsenic contaminated area. We have also funded horizontal roughing/slow sand filters in India. These filters have been successfully used to treat very turbid pond water in West Bengal. John La Roche, Water for Survival "Arsenic levels in Drinking Water and the prevalence of skin lesions in West Bengal, India," AH Smith, D N G Mazumder, R Haque, N Gosh, B K De, A Santra, D Chakraborty, International Journal of Epidemiology 1998; 27 871-877. "Programme in Arsenic Health Effects Research", University of California, Berkeley. Source Bulletin April 1999, International Water & Sanitation Centre, The Netherlands. Arsenic Pollution in Groundwater of Bangladesh Prof. Mahumder Raham, Dhaka Community Hospital. WaterAid Report by Clarissa Brocklehurst, Country Representative Bangladesh. World Water Day 1998 News Stories, International Water & Sanitation Centre. Private Correspondence with Mrs Meera Smith & Dr Richard Anstiss. |
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