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HOME > PAST ISSUE > May-June 2002 > Article Detail

MARGINALIA

No One Checked: Natural Arsenic in Wells

Philip, Phylis Morrison

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.

Figure 1. A boy pumps water from a tube well . . .Click to Enlarge Image

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.








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