The slow poisoning of Bangladesh: metals in drinking water. (Science Selections).

The quest for safe drinking water in the People's Republic of Bangladesh currently seems to be a lose-lose endeavor. The people of Bangladesh used to get almost all their drinking water from surface sources, which were often contaminated with bacteria causing such life-threatening health effects as diarrheal disease, cholera, and typhoid. To reduce the incidence of these diseases, millions of tubewells have been installed in Bangladesh since 1971, and this transition to groundwater has significantly reduced deaths from waterborne pathogens. However, new evidence from an international volunteer team of researchers led by Bibudhendra Sarkar of Toronto's Hospital for Sick Children suggests that illness from poisoning with arsenic and other toxic elements in groundwater now affects large areas of Bangladesh [EHP 110:1147-1153]. In addition to studying the extent of arsenic poisoning in Bangladesh, this exposure assessment studies for the first time metals that may affect arsenic toxicity.

Currently, 97% of Bangladesh's 127 million people drink tubewell water. Vast areas of the country contain groundwater contaminated with naturally occurring arsenic in concentrations above the World Health Organization (WHO) drinking water guideline of 0.01 mg/L. According to a survey by the U.S. Agency for International Development, 45% of Bangladesh's groundwater shows arsenic concentrations in excess of the country's own drinking water standard of 0.5 mg/L.

Symptoms of toxic metal poisoning include serious skin diseases such as melanosis, leukomelanosis, keratosis, nonpitting edema, gangrene, and skin cancer. The first case of poisoning attributed to arsenic-contaminated groundwater was diagnosed in 1993. From 1993 to 1999, a total of 2,953 cases of chronic arsenic poisoning were diagnosed in Bangladesh, but the actual number of cases may be in the tens or even hundreds of thousands.

Sarkar and colleagues collected groundwater samples from 112 tubewells throughout Bangladesh from 20 December 1998 to 18 January 1999. One sample was taken from each well and analyzed for arsenic plus 29 other elements or ions. The team found that arsenic is not the only geochemical contaminant occurring at levels exceeding WHO guidelines. About 50% of the samples had manganese concentrations above the WHO guideline, and 3% had lead above the WHO guideline. In some small areas, concentrations of barium, boron, chromium, lead, molybdenum, nickel, and uranium were found to exceed WHO guidelines. Because of the high percentage of Bangladeshis that drink water from tubewells, these data suggest that tens of millions of people are ingesting unsafe levels of toxic elements.

In assessing the symptoms of poisoning, Sarkar and colleagues came to suspect that other elements play a role in arsenic poisoning. One example is antimony, which intensifies arsenic poisoning and was detected in 98% of the water samples. Moreover, none of the samples contained detectable levels of selenium or zinc, both of which inhibit chronic arsenic poisoning. Bangladeshis may therefore show deficiencies in these elements that would magnify arsenic toxicity.

However, arsenic in tubewell water poses the most significant health risk, say the researchers. This risk could be mitigated through systematic groundwater monitoring, drilling deeper tubewells, and appropriate treatment options. Abatement efforts should not be limited lo arsenic, though; health risks from other toxicants such as chromium, lead, manganese, and nickel in Bangladesh's drinking water also must be addressed. Strategies to supply the country with safe drinking water need to be studied, developed, and quickly implemented.