Arsenicosis
Arsenicosis an illness with its early manifestations being the appearance of dark or white patches on the skin and hardening of the skin as a result of accumulation of excessive arsenic in blood. The usual source of such arsenic toxicity is drinking water contaminated with arsenic. Underground water pumped by tube wells is often the major source of such arsenic-contaminated water. How the underground water is contaminated with arsenic is not clear. But it is believed that in the affected area excessive lifting of underground water for irrigation purposes has been gradually lowering the ground water level causing movement of oxygen in the empty space created by water withdrawal. Oxygen can trigger oxidative changes in arsenic-containing rocks which is present underneath, the consequence of which is the release of inorganic arsenic into the water.
Ingested arsenic is quickly transported into the liver. Inorganic arsenic is a potent metabolic poison which affects some of the oxidative reactions associated with the breakdown of sugar for energy generation. Enzymes containing sulphydryl (SH) groups are particularly sensitive to arsenic.
A sodium salt of arsenic, sodium arsenite or trivalent arsenic, is most toxic in humans. The other sodium salt, sodium arsenate, is the pentavalent form of arsenic which is generally less toxic. Inside the human body, inorganic arsenic such as sodium arsenite or sodium arsenate can undergo methylation by the addition of methyl groups. The methylated arsenic can form molecular complexes with different organic molecules. The methylated organic form of arsenic is less toxic than inorganic arsenic.
The degree of methylation of arsenic apparently correlates with the toxicity of arsenic - arsenic with one methyl group is more toxic than arsenic with three methyl groups. Thus, enhanced methylation of arsenic in the body may reduce the magnitude of arsenic toxicity, but there is no way known to achieve this inside the human body.
The arsenic problem was first detected in the northern parts of Bangladesh in the late 1980s following similar problems in the neighbouring Indian state of West Bengal a few years earlier. It is estimated that about 52 of the 64 districts of Bangladesh now confront an arsenic problem with 50 million people at risk and an estimated 4 million cases of arsenic- related illness in the country at present.
Arsenicosis is a general term given to adverse clinical conditions resulting from arsenic toxicity. Clinical manifestations of arsenicosis include melanosis (dark patches on the skin), leukomelanosis (white skin patches) and keratosis (hardening of skin). In one recent study carried out by icddr,b involving 6,000 individuals with symptoms of arsenicosis, it was found that melanosis is most common, occurring in approximately 94% cases, followed by keratosis in 68%, leukomelanosis in 39% and hyperkeratosis (severe degree of skin hardening) in 37% cases. This indicates that a person may exhibit more than one type of arsenicosis symptoms.
At present the World Bank, UNICEF, Department of Public Health Engineering (DPHE), Bangladesh Water Development Board, British Geological Survey, and other bodies are engaged in assessing the extent and level of arsenic contamination. Arsenicosis develops slowly over a period of 5 to 15 or more years but always takes the form of a progressive and fatal disease. It may also cause cancer of vital organs like the liver and kidney with severe and often fatal consequences. The acceptable level of arsenic in drinking water in Bangladesh is 0.05 mg/l (WHO). It is however observed that water from deep tubewells below 150 to 200 meters appears to be essentially free from arsenic contamination. On the other hand, the top of a shallow aquifer, at a depth of less the 10 meters is much contaminated by arsenic and shallow hand-dug wells are usually uncontaminated though they may be highly contaminated with microbes (responsible for various diarrhoeal diseases).
Arsenic toxicity can be ameliorated by avoiding arsenic contaminated water in drinking and cooking. Surface water such as water from ponds, lakes and rivers is free from arsenic but such water carries high risk of contamination of waterborne pathogenic bacteria and viruses that cause diarrhoea, typhoid fever and certain types of viral hepatitis. Boiling of water can eliminate most of these pathogenic agents and is the usual recommended method to ensure safety of surface water. However, in the villages the practice of boiling drinking water is not easy to implement because of the cost factor involved as cooking fuel in the villages is still wood and dried straw, the supply of which is scarce. Then also there are cultural preferences for drinking fresh pond water for its supposedly better taste.
Removal of arsenic from contaminated water can be achieved through filtration by passing the water through columns containing materials that have an affinity for arsenic so that arsenic is absorbed by the column as the water passes through the column. But these methods are costly, and reliable and practical methods are still not available for mass use. There are also problems with their implementation at the village level without perhaps extensive training programmes on their use. Thus filtration methods are not considered to be feasible and effective in the socio-economic context of Bangladesh. Using properly maintained ponds exclusively for use as sources of drinking water is believed to be among the more practical approaches to prevent arsenicosis. Harvesting rainwater at the community level or domestic level is also an option for Bangladesh because of the large amount of rainwater available during the monsoon. [M Serajul Islam]
