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Arsenic Revisited

by Sylvia Mortoza

Due to the more pressing problem of the flood and its aftermath, the presence of arsenic in the ground water has all but been forgotten. But this in itself spells danger for once forgotten, long-term problems of this nature are likely to be shelved until they regain their former virulence. Yet to a thinking person, it is hard to imagine how a problem as severe and serious as wholesale poisoning can be elbowed aside for any reason.

What is especially astonishing and at the same time distressing is that this is the worst case of mass-poisoning the world has ever known, as such, the inability of most people to comprehend its portent is quite remarkable especially as this topic has caught the media's attention for some time now. The fact that inorganic arsenic has been a recognised poison since ancient times does not help us, for the presence of arsenic in ground water can only be viewed by this over-populated country as alarming. Yet, judging from the lack of correspondence in the press on this subject, few people, if any, seem unduly alarmed about something that could increasingly become a threat to life and limb, for them and their families. Yet the slow ingestion of arsenic over a long period of time can cause several forms of cancer like skin, liver, lung, kidney and bladder, as well as other diseases. Already the manifestation of arsenic-related illnesses is becoming alarming high in some parts of the country. Apart from the human cost, it is very likely to become an unwarranted large burden on the already hard-pressed health services. WHO estimates the time factor for the appearance of cancer is between ten to twenty years of exposure and, although this may mean it is too early to detect any increase in mortality from cancer, this factor cannot be ignored.

As long term exposure to arsenic can lead to hyper-keratosis, conjunctivitis, hyper-pigmentation, gangrene in the limbs as well as the cancers previously described, allowing people to have access only to contaminated water is inconceivable, and as arsenic is also in the food chain, the urgency must be given the recognition it deserves. Recent research from China (September, 1998), showed that rice grown on As-polluted soil contained 0.7 mg As/kg. Some plants such as mustard, cabbage, cauliflower etc. accumulate metals and metalloid (like arsenic). The major portion of absorbed arsenic is excreted through the urine (about 50 per cent); a small portion through faeces; skin; hair; and nails, and as it can be stored by the body in metabolically dead tissues and then slowly eliminated, some people may be tempted to play down the problem. That people handle arsenic differently, is known, for even here, although people are drinking from the same water source, one may be ill while others are not. But this does not detract from the fact that we are all in danger if we continue to drink arsenic-contaminated water.

A continuous consumption of arsenic-contaminated water can in time, result in three distinct types of chronic arsenic poisoning. The first begins with an irritation of the gastro-intestinal and upper respiratory tracts. The second is in an overgrowth of the Kasatin skin-structure with the development of numerous warts, ridges on the finger-nails, and coarseness of the hair and the third results in inflammation of the peripheral nerves. If this condition is allowed to persist, palsies may set in and the patient becomes listless.

As the only positive treatment for arsenic-poisoning is to find the source of the poisoning - and stopping it - the only way to avoiding further lethal doses is to stop drinking arsenic-contaminated food and water. Neither is arsenic-contaminated water suitable for washing clothes or bathing or for any other domestic purpose for arsenic can be absorbed through the pores too. Besides the waste water will be returned to the ground and re-absorbed into the soil. But despite this knowledge, efforts made to reduce dependence on arsenic-contaminated tube well water is not very much in evidence and this aspect of mitigation needs to be speeded up.

When people are faced with a problem of this size the easy way out is to deny there is a problem at all but ignoring it will not make it go away. Once we all take our collective heads out of the sand, only then will it be possible to find a solution. One way is to motivate the affluent section of society and persuade them to come forward to invest in small water purification plants, plants that are well within their capacity to provide. Although small water purification plants that serve around 1000 people may seem insignificant in a country with a population of 114 million, no effort no matter how small, can be termed insignificant even if at the moment it seems just a drop in the ocean.

If this can be the beginning of a programme where "self help is the best help," these little drops of water can soon become an ocean for with numbers affected by arsenic-poisoning increasing, there is clearly no time to waste even though there are supposedly various treatments available for removing the arsenic from the drinking water. The problem with these is it is effected through a physical-chemical method which may not prove so easy or foolproof when dealing with a largely illiterate population. Besides none of them appear to be completely free from risk, so for general use, these may not be advisable because all leave behind a quantity of arsenic-sludge that is as dangerous as nuclear waste or radon. However, while scientists and water experts intensify their search for a solution, how we cope with a disaster of this kind will be up to us.

Although cheaper solutions which can render polluted water safe are available, if only the government agencies and the NGOs would take the trouble to go among the people and teach them the simple technology, this is not very likely for one reason and one only - there is no money to be made from imparting this "solar photo-oxidative disinfection" technology. All that is required is to show people how to fill transparent glass or plastic containers with water and place it in the sun for two to three hours before it is rendered safe to drink. This technology is based on research that has demonstrated that provided the water contains a sufficient amount of oxygen, sunlight will destroy much of the faecal bacteria present in contaminated water but, until some of the NGOs can be motivated to take this technology to the people, as things now stand, providing people with the minimum amount of water they need a day (estimated to be 15 litres), getting pure water to just those who have already succumbed to arsenic-related diseases, is a Herculean task beyond the capacity of the government.

In the face of this "No-win" situation, without the active support of concerned people, conquering arsenic poisoning is a task likely to overwhelm us. However for the moment it could be that we have received a reprieve of sorts for the extreme flooding may have "diluted" the arsenic in the ground water and driven out the air due to the replenishment of the water table. But do not think for a moment the problem has resolved itself, for once we start using the tube wells again - "mining" for water if you like - this is a problem likely to return - and with a vengeance - and it could even be we shall find arsenic in those places where there was previously none.

As we know the use of tube wells is unlikely to diminish, at least not in the forseeable future, in no time at all air will again get inside the aquifers to do its devilish work so, in other words, although the floods may be seem to be God-sent - in so far as arsenic is concerned - this will depend on how well we can prevent water from being extracted from below the earth's crust. Of course this is based on the assumption that the source is geological.

As a theory, the geological source is gaining in credibility for most of the water samples have shown a mixture of arsenic and arsenate. Soil erosion and agricultural run-offs are also believed to have contributed to arsenic concentration in sediments. High arsenic levels have been reported to be associated with sediments and the potential exists for it to be released in overlying waters in hazardous amounts. While it is acknowledged there may be more than one source of arsenic-contamination in Bangladesh, the size and extent of the problem seems to be pointing more to a geological origin as the most important. Most of Bangladesh, except for the hills in the eastern parts of the country, is composed of a vast thickness of alluvial and deltaic sediments which can be divided into two main parts - the recent floodplain and the terrace areas. The floodplain and the sediments beneath them are only a few thousand years old and can be classified according to which of the river systems (Ganges, Brahmaputra, Tista and Meghna etc.) deposited them. The terrace areas, known as the Madhupur and Barind Tracts, and the sediments underlying them are much older than the adjacent floodplain (and may be as much as a million years old). Most of the arsenic is occurring in the younger sediments derived from the Ganges Basin. Although arsenic is occurring in the alluvial sediments, the ultimate origin of the arsenic is probably in the outcrops of hard rocks higher up the Ganges catchment that were eroded in the recent geological past and re-deposited in West Bengal and Bangladesh by the ancient courses of the Ganges. At present, these source rocks have not been identified.

It is also important to understand that arsenic does not occur at all depths in the alluvial sediments. Although there is not enough evidence to draw firm conclusions, it appears that high concentrations are restricted to the upper 150 metres of the alluvial sediments and offers prospects of obtaining arsenic free waters from deeper layers. However, this remains to be confirmed.

The World Health Organization (WHO) has given advice on innovative alternative sources of drinking water such as pond sand filters, infiltration galleries, or Ranney (collector) wells and in some places rain water harvesting is being encouraged. As in some cases safe water sources are not available, and as arsenic removal processes, even as a short-term solution appears to be increasingly risky, due to the residual sludge, more permanent arrangements must be put in place. Although the sludge can be placed on a dung heap where the arsenic is converted by bacteria into a less toxic organic form, the sludge still has to be transported from its source to the dung-heap, which could expose women to poisoning.

UNICEF has also played its part in battling the problem by purchasing test equipment for zonal laboratories in the form of 500 field testing kits. The staff of the DPHE surveyed several wells with these field kits and later verified any positive results through analysis in the laboratory but as even these kits are subject to conjectures by environmental engineers who say that, coagulant kits and other quick removal options that are being distributed to people could, when such containers are cleaned, expose people to the precipitated arsenic based compounds. They recommend that proper warnings be provided with these kits about the wastes generated and their proper disposal. This in itself may pose a problem as thrown on open dumps or unmanaged disposal sites, the arsenic may find its way back into the soils and eventually into the water.

The Royal Dutch Government is also funding projects for providing safe drinking water or for treating contaminated water. These projects include drilling deep tube wells in the arsenic affected districts and the construction of an arsenic removal treatment plant in Meherpur town. The sludge produced from the plant will be stored in a concrete tank which has a capacity lasting fifty years. Other organisations like UNDP took up a "TOKTEN Programme" which concentrated on the development of sensitive and selective Analytical Methods for Chemical Analysis of trace elements (at very low concentrations, e.g. 10-9g or less) such as Pb, Hg, Cd, As, Cr, Cu, Zn, etc in food, water, soil, air, human hair, blood, urine, etc, in the laboratories of the Atomic Energy Centre, Dhaka (AECD). The basic objective was to provide national services in time of need.

Suspected arsenic-poisoning cases were referred to Calcutta for diagnosis and treatment. Most of the field analyses were done in the SOES, Jadavpur University, Calcutta, in collaboration with the Dhaka Community Hospital. In 1993, under the Small-Scale Irrigation Project, the AECD was approached for analysis of groundwater samples for different parameters, including arsenic. In the face of increasing reports of arsenic-contamination and arsenic-related diseases, the concerned ministries and departments of GOB responded by constituting three different committees. What was the constitution of these committees is not known, nor was the Plan of Action (if any) revealed to the public. There was also an assumption by donor agencies that Bangladesh does not have the expertise to handle the problem. This pre-conceived notion was reinforced by the fact that the concerned GOB Departments for scientific and technical matters, suffered from this weakness, whereas other bodies did not. This has resulted in a fragmented view of the arsenic problem as each discipline tried to solve it separately and in accordance with their own light so, instead of taking a coordinated view of the problem, individual efforts replaced the inter-disciplinary approach that was truly needed for a problem of this type. Under present circumstances, opinions are pouring into various government departments in an effort to help the government out of the problem.

One of the Terms of Reference of the National Committee for Research and Development on the arsenic problem, was to organise the analytical work and to ascertain which method should be chosen to investigate the nature of the problem. But the Government is being "helped" with outdated technologies (Kit method) and visible spectrophotometric method. It is now understood that the World Bank is setting up a modern laboratory, possibly at Khulna or Satkhira, for proper analysis.

The aquifers in Bangladesh are hydraulically interconnected. As a result of the Ganges water diversion by India, plus large-scale withdrawal of groundwater from deeper aquifers, the water table dropped with a gradual development of the drying zone. This caused 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 ground water. As these oxic water or oxygen comes in contact with the 1st impervious layer within 30-50 meters, the Arsenic-laden pyrite is partially oxidized to form acid and becomes soluble, it is then released as arsenic, iron and sulphate, plus hydrogen (acid). The oxygen rapidly consumes the arsenic and forms sulphate, the iron acts as catalyst to further the decomposition of arsenopyrites. These two-fold reactions released arsenic into the water.

The depositions are in 2 impervious layers under the modern delta formation of the Gangetic plain. One within 15 to 30 meters depth and the other one below 100 meters depths. These layers contain arsenopyrite, pyrite, iron sulfate, iron oxides as revealed by x-ray, diffraction, electronic probe, micro analysis and laser micro probe mass analysis. The Himalayas have pyrites and sedimentary formations as it is marine in origin. Marine conditions are the ultimate resting place for metals or elements or compounds. For example, the Indians recovered 150 kg of arsenic/year from the water of one solitary tube well. This means the arsenic found in the groundwater is certainly a geological source because no organic arsenic compounds were found at high concentration.

Bangladesh and the adjacent West Bengal have three aquifers: 1st one 2-15 meters; 2nd 40-80 meters; and the 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 25-30 feet below the surface. Added to this, extraction of ground water for irrigation from 100 feet deep wells resulted in a drying zone within 200-300 feet below, maybe even more (Water Resources Policy in Asia) edited by Md. Ali (1985). That this newly introduced oxygen oxidised the arsenic in the arsenopyrites and released it into the water is now the accepted theory for when arsenic comes into contact with water and air, it forms hydrated arsenate which is highly soluble and very soft. The light pressure from the tubewell water helps to break down the hydrated arsenic into fine particles and the arsenic gets dissolved. If water is pumped incessantly over a long period of time, the quantity of arsenic will gradually increase.

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 justified the occurrence of acid sulphate soils in Jessore, Faridpur, Khulna. As the Ganges sediments are calcareous in nature, the calcium neutralises the acid formation otherwise we might have had more acid sulphate soils. The Ganges water is itself neutral to slightly alkaline and contains a high level of dissolved oxygen (which is why it does not putrefy when kept in bottles).

But as the people are getting arsenic also from food such as rice, fish and vegetables, the problem grows ever larger. Mr. Mustak Ahmed, a former student of Soil Science at Dhaka University reported that if you irrigate land with 50 cm of water containing 35 u Arsenic/Litre, the soil will end up with an accumulation of 0.1 ppm arsenic in the soil. The Farakka barrage caused wet desertfication in Bangladesh. A study was conducted by Dr. Jabber et al. (1985 or 1986) to delineate desert-like area in Rajshahi. India has built embankments along the banks of the Ganges to canalise the flow of water with the result that, during the monsoon, India can release as much water downstream as it likes so as to ameliorate its own flood problem. India is now planning to build a dam on the Ganges at Tehri (8000-10000 ft above mean sea level), Garwal of Utter Pradesh. This project will divert more water for irrigating Basmati rice.

Although health issues relating to second-hand smoke were once greeted with skepticism, these are now standard working environments. Like the smoke-free working environment, employers today are now considering safe, fresh drinking water to be a priority area saying a corporate move to safer drinking water could provide significant improvements in absenteeism and reduce medical costs. In view of the arsenic problem, a governmental move toward safe drinking water would now be appropriate.

The West Bengal Government's investigation revealed there is a 450 km long layer of arsenic rich silt clay 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. The 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. Although the arsenic poisoning of ground water in the lower Gangetic delta is posing a serious threat but in spite of arsenic-contamination of the ground water, this has not received the media attention they deserve, especially abroad. However, unless people are willing to throw their weight behind the solving of this issue by providing alternative sources of drinking water, this problem, unlike the arsenic, will become insoluble.


  1. Dr. S.S.M.A. Khorasani - Dhaka University.
  2. Dr. Tom Lawand - Brace Research Institute, Canada.
  3. Ms. Samira Abbasi - Environmental Engineer.
  4. Dr. A. H. Khan - Dhaka University.
  5. Mr. Khondker Rafiqul Islam - Maryland University, USA.
  6. Dr. Fanning - Maryland University, USA.


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