American Scientist

Millions of years ago, the Indian subcontinent, drifting northward, struck Asia, wedging up the Tibetan Plateau and lifting the towering Himalayas. Two rivers, not far apart, begin north of the Himalayas; together they enfold and drain both slopes of that great range. The Ganges flows counterclockwise, crossing populous Northern India, and the Brahmaputra (using several passports) flows clockwise until it bends to join the Ganges in the lowland Bengal Basin. There, the rivers give way to a skein of smaller rivers and enter the salt sea.

The Ganges-Brahmaputra Delta forms about half the area of the nation of Bangladesh; a third of the delta, West Bengal, lies within India. This tropical delta is subject to the same influences that made the deltas of the Mississippi or Nile. Recent borehole dating has revealed the youth of this complex chunk of active wetland. Most Bengal delta layers were laid down during ten post-glacial millennia; change continues as the rivers rapidly transport an immense load of sediment to the sea: about 2.5 gigatons per year, the weight of the Rock of Gibraltar passing by each year or two. Despite the continual addition of sediment, the surface of the delta remains close to sea level as its base slowly subsides.

The sediments contain a fine-grained mixture of sands, silt and clay washed out of the mountains. The layers include the minor elements found in rock: commonplace iron and sulfur, but many trace elements as well, arsenic among them. Geochemists estimate that average crustal rocks around the world contain about 2 parts per million of arsenic by weight. The rivers take a sample of arsenic from Himalayan rocks to the delta as they grind through thousands of miles of rocky slopes. Seasonally, the broad rivers swell, flooding the plains during four months of monsoon rainfall, which pour some of the highest recorded annual rainfall on parts of this delta.

In the past, during the long dry season, shallow, dug wells and small family pools supplied scarce water to the flatland villagers. Cholera and its kindred afflictions visited seasonally. Since the 1960s the international lab in Bangladesh's capital, Dhaka, an upland city of around six million, has been a leader in the global battle to defeat deadly microbes, using inexpensive oral rehydration. Beginning in the early 1970s, the dug wells and pools were widely replaced by about four million tube wells, most hand pumped, which now largely supply the people's drinking water.

A third of this fast-growing nation of 130 million lives across the floodplains and the lake-studded delta. The people, predominantly village farmers, form a dense rural population; the average annual income is now about a dollar a day. The people win their food from the watery world; their great staple is rice. Life is not easy on these wide alluvial flats; fierce storm surges, tidal incursions and river floods, drought when the monsoons fail and occasional cyclones have brought about almost one-tenth of all the deaths since Bangladesh won its independence in 1973. More than 95 percent of these articulate people share a faith in Islam. Their language, Bengali, has a rich literature, and since 1991, Bangladesh has been a parliamentary democracy.

The wells that now supply the people's drinking water are sealed from bacterial contamination; their tight concrete tubes reach down 60 feet or more, past surface contamination. The big investment in concrete wells, originally made by UNICEF and the World Bank, has beaten back diarrheal diseases, making a real contribution to the vigor and quality of life of the people here.

A Chronic Dose of Arsenic

But a new calamity as astonishing as it is threatening confronts the country people of the Bengal Basin. Natural arsenic has been found widely dissolved in a large sample of the millions of tube wells in the delta, in both West Bengal and Bangladesh. The drinking water, though sealed from infection, can hold a chronic dose of invisible, tasteless, odor-free dissolved arsenic. Arsenic has a many-sided chemistry. Arsenic bound in rock is harmless, merely a dark stain on common mineral grains. But several chemical processes can affect the oxidation state of arsenic and allow it to dissolve freely in water. For example, oxidation forms the white arsenic of the Borgias, which dispatched bishops and cardinals during the Renaissance. The geochemical processes in the delta are complex, probably affected by bacteria, and the oxidation states of arsenic atoms in place may even alternate over time. These complexities could account for the spotty presence of dissolved arsenic despite the ubiquity of those atoms.

That trace presence is a public poison. The World Health Organization (WHO) set the limit for arsenic in drinking water at 10 parts per billion; the mountain rocks themselves supply thousands of parts per billion. Experience has shown 50 parts per billion in drinking water to be marginally unsafe; the WHO limit was set there (the U.S. standard too) for many years. Consider that 100 parts per billion implies that those who drink such water imbibe only enough arsenic to fill the volume of a grain of rice in five years. The daily doses can go without notice until chemical analysis or clear symptoms proclaim the poison's presence. A couple of "grains of rice" of soluble arsenic taken into the body can induce a serious skin disorder. Double that amount increases the chance of skin cancer greatly. Still more—a lifetime of daily intake—and fatal cancers of several vital internal organs may follow.

The threat can be roughly extrapolated from long experience with other localities, for example in Chile, Argentina, Taiwan and western China, where people became aware of non-contagious disorders, and analysts then found arsenic. The danger to Bangladesh first became clear in 1983 by illness then visible within India's West Bengal, although the danger was traced explicitly to the tube wells only 10 years later, after repeated warning by a Bangladeshi chemist in Calcutta, Dipankar Chakraborti.

Studies suggest that nearly three out of ten wells are contaminated and that 30 or 40 million people are now at risk of arsenic poisoning at some damaging level. The dangers vary considerably across the country's districts and even among neighboring wells, but present analyses lead to a grim conclusion: If nothing changes, close to two million people now living in Bangladesh will contract the skin disorders of arsenic poisoning; a fraction will suffer more gravely still.

This calamity is no cool statistic, but a massive human burden. A single recent tale: Pinjira, age 25, mother of three, was told that her strange skin discoloration, raindrop-shaped dark spots on her skin, was widely shared by her neighbors. Her husband Masud was hard in judgment, saying, "She was pretty once, but now she is too thin and smells bad and is uglier by the day." He took a second legal wife, while Pinjira is bedridden and feverish. Elsewhere, as an official walks by, people come out of their one-room homes to show another stage of this damage: reddened lesions on palms and on the soles of the feet, often turning ulcerous enough to prevent working or walking. Imagine multiplying the cases a million-fold for a decade or two more.

What can be done to ward off a growing calamity? International attention is intense, and a long list of organizations is offering help. The proposed solutions are varied. Testing and labeling the well spouts—green when the water is free of arsenic, red when it is unsafe—allow people to select drinking water from safe wells. In some cases, mere dilution may help, where people can use several sources of water and avoid hotspots. Drilling deeper wells may be another solution; although surface waters can be contaminated with microbes, and many of the present tube wells are contaminated with arsenic, deeper tube wells, going down 300 to 600 feet, at present appear to contain much less arsenic.

Maybe the people can return to using water in surface ponds and pools, this time filtering the pollution from it first. Filtering through sari cloth may be enough. Rita Colwell, an aquatic microbiologist and current director of the U.S. National Science Foundation, has shown that in Bangladesh cholera organisms are largely held in the gut of plankton, so simple filtering may permit safe use of surface water. A field trial of this scheme is planned soon. Families may be able to use other filtration methods to remove the arsenic from tube-well water; one way in use already is to drip water through a series of pots, usually three, containing soils, iron chips or other substances. Researchers are currently evaluating various filtration schemes in field studies. Yet another method already used in some places in the country is to collect some of the abundant monsoon waters; rain falling on a rooftop covered with tin or a sheet of plastic can be stored safely in large cement tanks indefinitely without becoming contaminated with bacteria.

Ultimately, a combination of approaches may mitigate a larger catastrophe. The world of science owes these people reliable alleviation of their hazard, and lasting empathy.

© Philip Morrison

Acknowledgments

We are grateful to the Harvard and MIT researchers (W. H. Yu, C. M. Harvey and C. F. Harvey) who generously lent us their subtle estimates of the possible toll of future arsenic poisoning.