Arsenic and contamination of drinking-water in Bangladesh: a public-health perspective.

Abstract

The article by Mitra and colleagues in this issue of the Journal presents an interesting scenario on arsenic contamination from Bangladesh (1). The paper further confirms the health effects of arsenic and contributes to the literature, especially regarding the inverse relationship between body mass index and the duration of disease. Many tubewells in Bangladesh have been contaminated with arsenic that exceeds both the World Health Organization (WHO) guideline of 10 µg/L and the Bangladesh permissible limit of 50 µg/L. This arsenic calamity of well-water in Bangladesh can be described as the largest known mass poisoning in history, with more than 29 million people exposed through their drinkingwater (2-5). Numerous other occurrences of arsenic have been reported worldwide. Some countries, such as Taiwan, Chile, and Argentina, have been recognized for several decades, while others, e.g. Nepal and Vietnam, have been recognized more recently (Table 1).Bangladesh perspectiveIn 1983, Krishna Chandra Saha identified the initial cases of arsenic-induced skin lesions at the Department of Dermatology, School of Tropical Medicine in Kolkata, India (6). By 1987, he had already identified several cases who came from neighbouring Bangladesh. In 1993, the Department of Public Health Engineering of Bangladesh confirmed arsenic contamination in Nawabganj district (Barughuria union, Sadar upazila). In 1995, Dipankar Chakraborti, School of Environmental Studies, Jadavpur University, Kolkata, convened an international conference on arsenic and raised the awareness about the arsenic problem of West Bengal and the urgent need for more detailed studies in Bangladesh. Since then, several studies have been conducted on arsenic contamination of drinking-water in Bangladesh. To raise awareness of the seriousness of the arsenic problem in Bangladesh, the Dhaka Community Hospital and the School of Environmental Studies, Jadavpur University, Kolkata, convened another international conference on arsenic encompassing a great number of aspects (7). The evidence about the health problems connected with arsenic exposure that has accumulated since 1993 only confirmed that this is a public-health threat of great magnitude (2-5).GeologyThe arsenic contamination of groundwater derives from geological strata underlying Bangladesh. Arsenic occurs in two oxidation states in water. In a number of areas worldwide, oxidation and dissolution of arsenian pyrite [Fe(AsS)2] and arsenopyrite [FeAsS] are additional processes that lead to high concentrations of dissolved arsenic (8). The oxidation can be promoted naturally through infiltrating oxygenated groundwaters (9) or through lowering of the groundwater table (by pumping) into stratigraphic zone containing arsenic-rich sulphides (10). Arsenic was naturally transported in the river systems of Bangladesh and adsorbed into fine-grained iron or manganese oxyhydroxides. These were deposited in floodplains and buried in the sedimentary column. Due to the strongly reducing conditions, which developed in the sediments in certain parts of Bangladesh, the arsenic was released into groundwater.Health effectsThe characteristic health effects that result from ingestion of arsenic-contaminated drinking-water are slowly manifested, and the diagnosis is usually straightforward. Skin lesions, i.e. diffuse melanosis followed by spotted melanosis, hyperpigmentation, and keratosis, are common and are the first recognized health effects. The new findings by Mitra and colleagues revealed that 82% of patients had moderate to severe skin lesions, and 72% were young adults (1). Skin alteration is a consistent feature of chronic exposure to arsenic, but there is a considerable variation in clinical presentation. The latency (i.e. the time from first exposure to manifestation of disease) for arsenic-caused skin lesions, particularly keratosis, is typically in the order of 10 years (11). The rapidity of the appearance of skin lesions seems to be dose-dependent (11). …