Introduction

Bangladesh is grappling with the largest mass poisoning of a population in history because ground-water used for drinking has been contaminated with naturally occurring inorganic arsenic. It is estimated that of the 125 million inhabitants of Bangladesh between 35 million and 77 million are at risk of drinking contaminated water (1, 2). The scale of this environmental disaster is greater than any seen before; it is beyond the accidents at Bhopal, India, in 1984, and Chernobyl, Ukraine, in 1986. This paper suggests guidelines for responding when a population is exposed to arsenic, and it is based on information from several visits to Bangladesh made by Allan H. Smith as a consultant for the World Health Organization between 1997 and 1998 (3–5).

In 1983, the first cases of arsenic-induced skin lesions were identified by K.C. Saha then at the Department of Dermatology, School of Tropical Medicine in Calcutta, India (6). The first patients seen were from West Bengal, but by 1987 several had already been identified who came from neighbouring Bangladesh. The characteristic skin lesions included pigmentation changes, mainly on the upper chest, arms and legs, and keratoses of the palms of the hands and soles of the feet (Fig. 1). After ruling out other causes, water sources used by the patients were analysed, and the diagnosis of arsenic-caused disease was confirmed. The primary drinking-water sources for the patients were tube-wells, which drew water from underground aquifers (Fig. 2)(6).

Tube-wells have been used in Bangladesh since the 1940s (7). However, the problem of arsenic-contaminated water has only recently come to light due to the increasing number of tube-wells used over the past 20 years and the subsequent increase in the number of individuals drinking from them. Historically, surface water sources in Bangladesh have been contaminated with microorganisms, causing a significant burden of disease and mortality. Infants and children suffered from acute gastrointestinal disease resulting from bacterial contamination of stagnant pond water. Consequently, during the 1970s the United Nations Children's Fund (UNICEF) worked with the Department of Public Health Engineering to install tube-wells to provide what was presumably a safe source of drinking-water for the population. These wells consist of tubes that are 5 cm in diameter that are inserted into the ground at depths of usually less than 200 m. The tubes are then capped with a cast iron or steel hand pump. At the time the wells were installed, arsenic was not recognized as a problem in water supplies, and therefore standard water testing procedures did not include tests for arsenic (7).

Fig. 1 Skin lesions due to arsenic poisoning (WHO 00229)

Table 1. Percentage of groundwaters surveyed in 1998 by the British Geological Survey with arsenic levels over 50 µg/l

During the 1980s, UNICEF's support for installing tube-wells decreased because the private sector was able to supply and install millions more of them (7). By 1997, UNICEF indicated in its country report for Bangladesh that it had surpassed its goal of providing 80% of the population by 2000 with access to "safe" drinking-water in the form of tube-wells, ring-wells and taps (8). Presently, three out of four tube-wells in Bangladesh are privately owned (7).