Hazards of arsenic contaminated ground water
Bangladesh is a tropical riverine country of about 120 million people, out of which 51.5% are male and 48.5% are female. The population density of this country is the highest in the world which is 755 person per square kilometre. The country's economy is largely agrarian but 53% of the population are landless. Situated in the largest deltaic region of the world, Bangladesh is richly endowed with natural resources.
Extremely high population density in Bangladesh is a factor contributing to the intense use of land, forest, and fisheries and to the water resources. This leads the country to severe environmental pressure, like intense cultivation that threatens soil fertility and swamps the country with agrochemical; excessive extraction of water for irrigation that depress the water table; flood control measures that block fish migration paths and commercial fish farming that floods agricultural land with salt water. Added to this pollution, faecal pollution is by far the most serious water contamination problems, while water and air pollution is causing increasing concern in the rapidly growing urban areas. A recent incident of pollution of ground water by Arsenic creates an alarming situation for the country's public health.
Of the three main sources of water, namely, surface water, ground water and rain water, the later two sources generally meet the most important criteria of drinking water in their natural condition. These waters are usually consumed directly without treatment. Harness of ground water is cheaper and safer in comparison with rainwater. On the other hand, surface water is plenty during monsoon but scarce in dry season and it is highly polluted. Thus, it can not be consumed without prior treatment. Treatment of surface water is relatively complicated and expensive.
In view of the fact that ground water is safe for drinking and its harness is cheaper and sustainable, public as well as private water supplies are heavily dependent on these sources. Unfortunately, when most of the people have developed the habit of drinking tubewell water (ground water) being aware of its importance to avoid attack of diarrhoea diseases and when almost 97 percent of population have got the access to safe water through more than 4 millions of tubewells, arsenic has been found in unacceptable concentrations in tubewell waters in many parts of Bangladesh.
Hundreds of tubewells in rural Bangladesh have been identified with high arsenic concentration and many more are feared to have been contaminated with the same. So far 50,000 tubewells were tested and 63 percent of them were found to be contaminated by unacceptable concentration of arsenic. Bangladesh has recognised the acceptable limit of arsenic concentration in water at 0.05 milligram/litre. Many people are suffering from arsenocosis and many more are at risk. Government is conducting surveys to identify arsenicosis patients. Till date, 4000 cases of Arsenicosis patients have been identified. The cause of arsenic contamination in ground water is not yet known. Extensive research has yet to be conducted in this regard to accentuate the knowledge base. However, natural geological changes are presumed to be the primary mason for arsenic contamination. The basis for such belief lies with the studies conducted in West Bengal, India, having similar alluvial deposits. Arsenic contamination in groundwater is due to the various natural geological processes those exist in the geological environment.
The source of arsenic in sediments is mainly the parent rock materials from which it is derived. Arsenic associated with sediment particles can be a major source of arsenic contamination when particles are detached and carried as sediments during erosion. Sediments on contain substantial amounts of total arsenic. During the formation of sedimentary rocks, arsenic is carried down by precipitation of iron hydroxides and sulphides. In a moist climate, arsenic sulphides are easily oxidised, become water soluble, are washed out of the sediment particles by meteoric precipitation, and are transported with run off.
Arsenic undergoes reactions of oxidation reduction, precipitation, absorption description, and organic and biochemical methylation. All of these reactions control mobilisation and accumulation of arsenic in the environment. A biotic reactions between arsenic species and the substrates on the species and the substrates on the sediment surface, as well as physical disturbance of sediments, all ply very important roles in controlling the mobilisation of arsenic.
In nature, arsenic bearing minerals undergo oxidation and release arsenic to water. The problems of arsenic in Bangladesh in it's Ganges delta region, however, because of the complexity and the size of the problems, the geological studies are yet to land in a conclusive finding.
Various following conceptual hypothesis have been put forward by many research workers based on various direct findings as well as indirect supporting evidences on arsenic contamination in the Ganges delta.
a) oxidation of pyrite and arsenopyrite due to excessive withdrawal and lowering of ground water is responsible for arsenic contamination in ground water,
b) reduction of oxyhydroxides is the source for arsenic contamination in ground water,
c) unconfined aquifers subjected to oxidation and reduction, and underlain by peaty clay and/or clay layer is responsible for arsenic contamination. Mine wastes, specially carbonaceous shale, dumped to the surface from coal mining in the Rajmahal basins are transported and deposited along with the river and flood born sediments may be responsible for the formation of peaty clay layer in the deltaic domain. The continued abstraction of water from unconfined aquifer releases pentavalent arsenic and is transformed into trivalent arsenic on reduction to become soluble and mobile in water. However, all. The three hypothesis may be operative in the Ganges delta region and responsible for arsenic contamination.
Although arsenic contamination in ground water has been reported from various regions of the World viz. Taiwan, Argentina, Alaska, Chile, Mexico, China, Mongolia, Ghana and Hungary, the single largest contamination so far has occurred in the lower Ganges delta region bounded by the rivers Bhagirathi, Ganges/ Padma lower Meghnia. The people of this vast region are continuously getting exposed to the arsenic toxicity causing serious health hazards which is very alarmingly engulfing this vast delta region. At his moment the contamination of he underground water has become a great challenge for provision of safe drinking water to the majority of the population. The health hazards due to this contamination has raise the serious concern for public health. Arsenicosis, a disease born by drinking arsenic contaminated water which may lead to a very painful death. Arsenite and arsenate are known as carcinogen and have got affinity to deposit in hair, nail, bone etc. Arsenic is found in high concentration in liver, spleen kidney and lungs as well.
Toxic effects of arsenic involve these organs. Toxicity of arsenic depends on its accumulation in the body. The time taken to develop symptoms in the human depends on the exposure, body defence mechanism, nutritional status etc. It is thought that it may take 2 20 years to develop symptoms.
The arsenic poisoning from the contamination of ground water is very chronic in nature. Most of the time the victims do not complain of the above symptoms until they are detected through screening. The above symptoms am are very difficult to identify from other clinical conditions. The present experience to identify the arsenic cases are by external manifestations specially with the presentation on the skin called melanosis (blackening of skin) and keratosis (hardening of palms and soles) with the history of consuming arsenic contaminated source water.
Gangrene of peripheral organs and ulceration due to toxic effect on the small blood vessels may also be found. Cancer of skin along with cancer of some internal organs liver, kidney, bladder is not uncommon. The stage of keratosis is known as potentially malignant. It is also observed that even if a person having no manifestations after consuming contaminated water the chance of having cancer cannot be ruled out.
It is very difficult to differentiate the arsenical manifestation in stages. A person without external manifestation may face serious consequences of arsenicosis leading to cancer or acute renal failure. This is very simple to classify the arsenicosis as subclinicall and clinical from. Clinically the mks sign in the skin may be the melanosis then the keratosis and others. The systemic involvement is variable and may appear before and after the melanosis or keratosis. Subclinical cases deserve early identification and follow up.
Experiences from the observation suggest that at least some stages of arsenicosis (Melanosis) are reversible if the contaminated water consumption is stopped. The use of arsenic free water may probably stop the detoriation of the symptoms but information of complete recovery is not yet known. The supportive treatment for nutrition improvement may play some role to diminish symptoms and may help to reverse some cases of melanosis stage.
The main challenge is how to provide the millions of people at --- with arsenic free, bacteriologically as well as chemically safe, and a-- ally acceptable alternative source of drinking water. The factors remain this challenge are:
* Identification of arsenic free tubewells; in the known affected area
* Identification of arsenicosis patients
* Treatment of the patients with arsenicosis
* Treatment of arsenic contaminated water where no other safe source exists
* Identification of arsenic free aquifers
* Extent of Me potential alternative Owen namely surface water and rain water
* Habit, culture and custom of the people
* Economic condition of the people, and their willingness and ability to pay for Me service
* Community motivation to face the challenge collectively
* Research and Development
* Institutional support
It has been observed that tubewells public and private, exist in several numbers in nay cluster or community. It has also been found that generally not all tubewells in an area are affected by arsenic. Therefore, the immediate challenge is to find out the unaffected ones in the affected areas and commence routine monitoring in order to stop using the currently affected tubewells as soon as arsenic is detected.
Government of Bangladesh has formed a national steering committee for arsenic contamination mitigation activities headed by Hon'ble Minister for Health & Family Welfare under which one scientific committee and a technical committee are doing their respective jobs under specific terms of references. Both the committees send their activities reports to the national steering committee which regularly seats after three months intervals. This committee consists of all agencies working in the field of arsenic related problems. Government has so far taken three major strategiesTo identify the number of arsenic contaminated tubewells labelled them with red colour for danger ones and green with safe ones. Conduct surveys.
To provide deep tubewells as an emergency measure in those location where most of the tubewells are found to be contaminated by arsenic as aquifers at the level below 800 feet are found arsenic free)
To provide treated safe surface water through pipes to the people. Simultaneously efforts are taken to aware the people regarding the danger of arsenic contamination of groundwater and what needful they should do in such situation.
The environmental initiatives undertaken by Bangladesh demonstrates the commendable efforts made to deal with priority problems related to * physical environment. An action plan on Health and Environment has been formulated to identify the arm of concern and pertinent issues, determine Me mum ad define possible solutions. He arsenic contamination of groundwater problem is a newer one and it is impossible for a developing country like Bangladesh to mitigate through it's own resource. Bangladesh government has already mobilise it's own resources for this programme. Three projects under Ministry of Health & Family Welfare has just completed their first phase in which activities like contaminated tubewell identification, colour marking, patients finding, and patient treatment wed done. These activities will be continued in the next phases. UNDP is providing continuous support to one of these project. Besides these, a GOB World Bank supported Arsenic Mitigation Water, Supply Project has started its function under Department of Public, Health Engineering. Some donor partners have extended their desire to support government is initiatives. A few donor supported projects are in pro But these are too little to combat this public health problem. It is n question of which country's peoples are suffering, it is the suffering of mankind. Everybody should come forward to save these sufferers.
Courtesy: Arsenic Contamination Mitigation Projects, Ministry of Health & Family Welfare Government of the People's Republic of Bangladesh.
Source: The Independent Friday 5 January 2001