The biggest mass-poisoning case the world has known is now underway in Bangladesh. Arsenic-poisoning is not only a tragedy for the people but also a test of the country's concern and integrity, for arsenic-contamination of ground water is seen by many as an opportunity to get rich. Now looked upon by man as a God-sent gift or bonanza, or at best a chance to prove a theory or sell a ready-made "remedy," it is apparent that there are a pitiful few who see it for what it really is, a disaster of such a potential it will not be easy to overcome, at least not without the loss of a substantial number of lives.
Shallow tube-wells extract water from the upper and intermediate aquifers. The intermediate aquifer is just below the 1st impervious layer. As a result arsenic is leaching from the 1st impervious layer and remains soluble in the water of the intermediate aquifer. The oxidation theory also justifies the occurrence of acid sulfate soils in Jessore, Faridpur, Khulna. The Ganges sediments are calcareous in nature, this calcium (Ca) neutralised the acid formation. Otherwise we might have had lots of acid sulfate soils like in Thailand and Vietnam.
The recent euphoria over the award of this year's Nobel Prize for Peace referred to the end to the thirty year old secular conflict that had cost 3,500 lives - the mass-poisoning case in Bangladesh has already cost over 2,500 lives in a matter of months so it will not take long to exceed their loss, if things are allowed to continue unchecked. Some blame the World Bank for the delay in coming to grips with the problem but as the first indication it received was in 1993, some years after the first indication of trouble, the delay, if there was any, was mainly in the cautious way the Bank operates. As a result it took until after 1995 to confirm that there was indeed contamination but by that time, the high levels of arsenic in the millions of shallow and deep wells that had been sunk in various parts of the country were dispensing their own particular brand of poison.
Now it was a public health matter and a real concern for a country where health services were already under intense pressure for as contamination spread the pressure increased for by that time a large number of people had been affected by drinking water from the wells in more than half the 64 districts of Bangladesh, mainly in the south western, middle and north-eastern parts of the country. Arsenic-contamination and its effect on the health and well-being of the people of Bangladesh had now reached crisis proportion because for most of the victims, there was no alternative to tube well water unless it was to go back to drinking polluted surface water.
Faced with such a quandary, the World Bank took on the job of acting as the co-ordinating body for the donor community and the Government of Bangladesh. The only question is, does the World Bank understand its responsibility to the people of this beleaguered land? Hopefully they did for their first response was to provide US$ 50 million for "investigations." What investigations were actually carried out is hard to assess and it can only be hoped the money was well spent. The Bank followed this with a credit of US$ 32.4 million for the "arsenic mitigation programmes" needed to stave off further illness and deaths caused by drinking arsenic-contaminated groundwater.
Specifically, the project will provide alternative water supplies and medical relief in the affected areas; establish the extent, nature and causes of arsenic poisoning; and put in motion concrete action for long-term solutions - including water treatment, public awareness and increasing people's and government capacity to address similar crises. Through on-going research, the Bank has been looking into the linkage between the pumping of groundwater and arsenic-contamination and the impact of arsenic-contaminated water on crops which has given rise to a report known as the British Geological Survey (BGS) report.
The main point of this survey by the BGS is that the arsenic-contamination of groundwater that has put millions of lives at risk is "natural and not man-made" which may be true but does not tell us how to deal with the many cases of arsenic-poisoning or help us to provide alternative sources of pure drinking water. There is also some confusion, for the earlier belief that arsenic, already deposited in the soil, combined with the ground water when the atmospheric oxygen invaded the aquifer in response to a lowering of water level by extraction, is still very strong.
According to the report, the BGS team tested more than 9000 samples of groundwater collected from the shallow and deep tubewells drilled at various depths across the country. It is now essential for these results to be made public so that individual researchers around the world can follow up on this information. As some of the laboratory tests were conducted in Bangladesh and some in the UK, releasing this information to the public is not difficult and individual analysis may come up with something new. However, as random sampling without considering the regional ground water flow could lead to erroneous results, it is assumed that the BGS took this into account.
Although the arsenic-contamination of groundwater has been declared a national disaster by the government, its seriousness is yet to be fully comprehended by people, but as soil samples collected from fresh shallow and deep aquifers confirms the presence of arsenic at various concentrations, there is an immediate need to raise awareness through the proper dissemination of information. Laboratory analysis of the soil and water samples have indicated that arsenic-contamination is "prominent" in the shallow aquifers from which most people draw their supply of water.
As arsenic has been found in high concentration mostly at a depth of between 30 and 100 feet, it is incumbent on us now to find alternative sources of water as most of the very high levels, that is more than 0.25 mg/L arsenic, occur within a narrow range of 20 to 40 meters beneath the earth. Below 100 meter depth few water samples show concentration of arsenic at levels of over 0.1 mg/L however, although arsenic-contamination of deep tubewells sunk below 250 meters has not been reported this possibility, according to the BGS, cannot be ruled out and they say "there is every likelihood the deep aquifer is not free from arsenic either."
"As the arsenic-rich groundwater is mostly restricted to the alluvial aquifers of the Ganges delta, the source of arsenic-rich oxyhydroxides must therefore lie in the Ganges source upstream of Bangladesh," says the report. If this is true, Bangladesh could now be in for further trouble as the recent floods have deposited what may be "arsenic-rich silt" across the country. This could mean that in the coming dry season, the arsenic-contamination that now threatens more than half the country will spread to even those places where formally there was none. What a frightening prospect this is - but unfortunately there are very few who appear to have given this much thought for although arsenic can be detected in traces everywhere - its abundance in the earth's crust is 1.8 ppm i.e., making it roughly as abundant as molybdenum or tin, arsenic concentration is considerably higher in soils and shales than in the earth crust.
Levels of arsenic in the soil of various countries have been said to range from 0.1 to 40 ppm (mean 6 ppm). It is a major constituent of at least 245-320 different minerals. Arsenic in soil is highly mobile, resulting in possible groundwater contamination. Any retention of arsenic by soils would occur by adsorption, especially if the soil contains iron or aluminum oxides. This is especially true in very acid pyritic soils, acid sulphate soils, or high in iron oxide as in some areas of Bangladesh, where arsenic is many times more than expected.
The West Bengal Government's investigation revealed that a 450 km long layer of arsenic rich silt clay is lying between the depths of 70 and 200 feet below the surface of the upper deltaic plain of river Bhagirathi. All these zones are located between the Ganges-Bhagirathi river and the western border of Bangladesh. The sediments on both sides of the border have the same depositional history and geological environment. This area is a part of the Ganga-Brahmaputra delta. The delta proper as well as the flanking areas forming the so-called Bengal basin is divided into six macro-process regions: laterite upland, Barind, upper delta plain of meander belt, valley margin fan, marginal plain, lower delta plain and delta front. The aquifer of the contaminated zone in West Bengal and Bangladesh are hydraulically connected.
Arsenic in sediment or water likes to move in adsorbed phase with iron, which is available in plenty in the Himalayas. Combining with iron oxides, about 100-300 mg arsenics/kg can be found in sediments under oxic conditions. When these sediments were deposited in the tidal environment (Bengal basin was under tidal condition), it came under anoxic condition. Sulphur reducing bacteria combined the oxygen from sulphates (available in tidal basin) through oxidation of organic carbon. As a result, organic carbon was lost as carbon dioxide (CO2) or remained as bi-carbonate, and the sulphate was reduced to hydrogen sulphide. Iron minerals and hydrogen sulphide rapidly tie together to form iron sulphide containing arsenic because arsenic has been adsorbed on the surface of the iron minerals. That gives either arsenic substituted iron sulphide or arsenopyrite. These formations are stable unless they are disturbed or exposed to oxygen.
Bangladesh and adjacent West Bengal has three aquifers: 1st one 2-15 meters, 2nd 40-80 meters and 3rd one below 100 meters. These aquifers are also hydraulically connected to the major streams in Bangladesh, especially the Ganges in the Northwestern region of Bangladesh. Ground water recharge is low due to less rainfall and upstream diversion of Ganges water by India. During the dry season, the water table falls to below more than 25-30 feet. After the eighties the ground water fell drastically during the dry season and a "drying zone" gradually developed. This caused a rapid diffusion of oxygen within the pore spaces of the soil/sediments as well as an increase in dissolved oxygen in the upper part of the ground water. As this "oxic water" or oxygen came into contact with the 1st impervious layer within 30-50 meters, the arsenic-laden pyrite became partially oxidised and formed acid which became soluble and released the arsenic (As), iron, (Fe) and sulphate plus hydrogen (acid). The oxygen is rapidly consumed in forming sulphate, the Fe+2 acts as a catalyst to further decomposition the as pyrites. This two-fold reaction released the arsenic in the water.
The reduced flow of the Ganges not only caused reduction in ground water, it also extended the dry season from March to May to December to May. During the 1980's the flow of the Ganges was at a record low. During these periods Bangladesh sometimes got only 6790 cusecs of water. (India Today - January 15, 1997 or April 30, 1997 by Rupen Banerjee or Kamaluddin and Bailey). When there is a reduced flow in the river, the riverbeds dry-up, the groundwater goes down, so people use more groundwater through pumping from deep down. During 1975, people used to use tubewells at a very shallow depth, over time they had go down deeper and deeper to find water. Because a sufficient quantity of water was not available at a shallow depth, WASA had to change its well site quite often in Dhaka. When there is groundwater deep down, oxygen can easily go down because of partial pressure increase of gases.
Although there are two layers south of West Bengal and in Bangladesh, these 2 layers combined together to form a thick layer in the northwestern part, especially in the Malda district of West Bengal. As the aquifers are hydraulically connected, people should get some arsenic. It depends on the thickness of the layer and aquifers. Arsenic in certain solid phases within sediments, particularly iron oxides, organic matter, and sulphides may be the primary source of arsenic in groundwater. It is known that pyrite is the carrier of arsenic. Excessive groundwater withdrawal may be one of the reasons for creating a zone of aeration in the clay layers containing pyrite which in turn decomposes to form iron sulphate and releases arsenic in the percolating subsurface water. Mobilisation of arsenic in sedimentary aquifers may be in part, a result of changes in the geohydrochemical environment due to agricultural irrigation. In the deeper subsurface, elevated arsenic concentration is associated with compaction caused by groundwater withdrawal. Experts say that "an understanding of geochemical principles is essential for an explanation of the mobilisation of arsenic by natural processes. Along with supergenic mobilisation of elements arsenic is transferred from one phase to another or within a heterogeneous phase such as soil by microbial mediated processes. Aerobic bacteria and fungi often transform arsenic into coordination complexes that are more mobile in soil water than the uncomplexed cation. Environmental characteristics also strongly influence arsenic (As) movement in soils. Movement is a strong function of speciation and soil type. For a non-adsorbing soil (sand), the mobilisation of As (III) and As (V) in groundwater are dependent on the dispersion coefficient and permeability for solute transport. Soil pH also influences arsenic mobility. At a pH of 5.8, As (v) is slightly more mobile than As (III). As pH changes from acidic to neutral to basic, As (III) tends to become the more mobile species, though the mobility of both increases with increasing pH. Arsenic is transported at a slower rate in a strongly adsorbing soil as compared to the sandy soils." That it is now very important to review all the data and information that has been collected is clear. This data should be made available to a central data bank where it can be sifted and analysed. Hopefully a solution to the problem can then be found for people are not only getting arsenic from groundwater, but also from food such as rice, fish and vegetables. The urgency of coming to grips with the problem cannot therefore be over-emphasised for the "mining" of water, (which closely mirrors what happens in a metal mine), has certainly exposed the arsenic-containing rocks to oxygen, thus releasing the arsenic into the ground water. But as sifting fact from fiction or even from conjecture is not easy, whatever maybe the truth about the cause/causes of the current arsenic-contamination of Bangladesh, one thing cannot be disputed, it's effect on human health, human lives and human relationships - and something has to be done about that before it is too late. The author gratefully acknowledges the special contribution of Mr. Khondker Rafiqul Islam of Maryland University, USA. Other acknowledgements: 1) The report of the British Geological Survey 2) Dr. Delvin S. Fanning - Maryland University, USA. 3) Dr. Tom Lawand - The Brace Research Institute - McGills University, Quebec, Canada. **************************************************************************** ***
Published in The Bangladesh Observer & NFB
The World Bank has recently conducted a series of high level meetings consisting of water experts from all over the world plus local government agencies, donors and other interested parties. However, as these meetings were inconclusive, the WB is contemplating a myriad of approaches aimed at ridding the people of Bangladesh of arsenic in tube-well water. In view of their claim that a lack of reliable data has made decision-making virtually impossible one is constrained to ask how they propose to do it because, according to reports, they are not able to formulate a complete picture of the range and extent of arsenic contamination in the country. Under these conditions it is a fair assessment that both short term and long term plans to mitigate the problem has already run into substantial difficulties. This fear has been fuelled by the doubtful nature of the local survey undertaken to determine the nature and the extent of arsenic contamination in the region under a project entitled The Emergency Arsenic Project which has been funded by the United Nations Development Programme (UNDP) reportedly without any responsibility for conducting the project. However, an official of the World Health Organisation (WHO) has conceded that the tests being carried out might give misleading results and might affect future programmes that would be based on it.
Local experts however, say that the data so far collected is generally reliable but, as doubt has been cast on this reliability, the WB would like to resolve this problem through the establishment of a data base to be fed with new data gathered during new surveys of suspect areas. However, as new surveys will take time, this will delay any project taken up for mitigating the problem. As many of the local experts believe we are now running out of time, any further delay in tackling the problem may result in widespread cases of arsenic-poisoning and ultimately additional deaths.
However, the WB is also reported to be going ahead with its four year long plan of action which will cover all the known arsenic-affected areas but even so they are reportedly handicapped by the absence of detailed maps as maps have not been made available to them. This is a serious charge because the absence of reliable maps makes it impossible to plot in detail the affected thanas, villages, tube-wells, etc. Some maps have been produced by different agencies, both local and foreign, which although highlighting the districts where contamination has been confirmed, lack in detail. Yet another group have prepared a few digital maps on the basis of satellite images, but these are also not clear and the few places that have been marked as the location of the affected tube-wells are too few to give a composite picture of contamination.
On the practical side at least one member of the WB team says he is working on a plan to reduce arsenic at source within eighteen months and will bring relief to about 70 per cent of those known to be drinking arsenic-contaminated water. But we would like to point out that, no matter how good the plan or effective the outcome, this still leaves 30 per cent of those at risk outside its purview. Translated into numbers this might means that 20 million people will not be brought under any public health programme.
It may seem to many that the WB team is down-playing the threat by saying arsenic has been present in this region ever since the delta was forming and although this may be true, and arsenic may have come down river from the Himalayas, the presence of arsenic in ground water is only a fairly recent discovery, and became a threat to human life and health only after too much sub-soil water was withdrawn for irrigation purposes. In other words, during the lifting of water by the use of pumps, air has managed to get in and dissolved the arsenopyrites through a process called oxidization. Once the arsenic got mixed in with the water, possibly during the late eighties or early nineties, the situation has become explosive but as stopping the use of ground water for irrigation is too difficult an option for Bangladesh because most of the gains in agricultural output were based on irrigation, it is unlikely that this process will be discarded. Nor is either the government or the WB, willing to discard the three million tube-wells that now supply drinking water to ninety per cent of the population because this will pose other health problems.
But the problem goes deeper than this because some cases of arsenic-poisoning are emerging. Treatment is however, minimal and mainly restricted to giving victims a handful of multivitamin tablets to help their bodies cope with the arsenic ingested when doctors and health workers know the best treatment is to stop people from continuing to drink the arsenic-contaminated water. An added confusion arises because the signs and symptoms of arsenic poisoning are not at all uniform either. For example, only one or two members of a household may be affected and at present there appears to be no explanation for why the disease is being so discriminatory. Possibly it is the state of nutrition or otherwise of the individual, for malnutrition is believed to be an important factor in the ability of a person to deal with the arsenic ingested.
The WB emphasizes that it is not the dearth of technology that is the problem for solutions are many as there are now several technologies available for reducing the level of arsenic in tube wells, or for disinfecting surface water to make it drinkable. This apart, it does seem that the World Bank is either confused or undecided on how to proceed or which action will be most appropriate under known conditions. It is also not very clear whether or not the final choice will be confined to the use of only one option/technology, or a combination of options and technologies. One team member said the technology is there but there is a dearth of management skills, especially at village level, which will make any technology difficult to maintain.
As the management of any programme for arsenic mitigation will ultimately fall to the local government officials to manage, training them to meet this disaster must begin now. Although the WB and possibly the government are emphatic that a return to surface water sources is not the answer because of the high load of faecal coliform bacteria, now that there are more cost-effective technologies on the market, this option should not be rejected out of hand for boiling surface water is not a viable option for people because of the cost and shortage of domestic fuel. Consuming pond water without treatment will of course, almost certainly result in a large number of deaths from diarrhoea/cholera etc., but it should not be completely ruled out as it may that ultimately this will be the only alternative. However the WB is bending toward chemical removal of arsenic or through filtration method.
As much seems to depend on the accuracy of the tests undertaken or to be undertaken, it could be far wiser if all samples are double checked by those organisations like the Bangladesh Atomic Energy Commission which has the equipment for carrying out such tests using atomic absorption spectrophotometries. There are also some machines at the Science Laboratories and the Chemistry Department of Dhaka University which can be put to use for the national good. Apart from this, there are ten units of the latest equipment for testing water samples under the reliable electro analytical method. As all these facilities are capable of giving accurate readings, why they are not being utilised is an unanswered question.
As at the present time, the people seem to be left with only one of two choices, to drink arsenic-free untreated surface water with its risk of diarrhoea and perhaps a quick death or drink arsenic-contaminated water which may keep people alive up to ten years or so, before succumbing to a painful death from arsenic poisoning. But as ignorance is said to be bliss and as most villagers are ignorant of the potential disaster about to come crashing down on their heads, the temptation to leave them in ignorance may prove too strong especially as arousing an awareness of the problem could cause a panic but this would be skirting the issue. However, to inform people of what may be their fate without providing an alternative source of water - and showing them how to purify it - would be immoral therefore only correct information must be disseminated and then only when the alternatives are already in place which, as things now stand appears to be a long way off. But time is something we do not have for Time - with a capital Tee - is fast running out.