BANGKOK (AP) — Ponds dug for fish rearing and storing water for agriculture in Bangladesh are a primary source of arsenic-contaminated drinking water which has caused widespread poisoning in the densely populated South Asian nation, according to a study released Monday.
The findings of the study, published in the journal Nature Geoscience, could help the Bangladeshi government as it draws up strategies to provide safe drinking water and also benefit countries like Cambodia and Vietnam wrestling with similar problems.
Odorless and tasteless, arsenic enters water supplies from natural deposits in the ground or from agricultural and industrial waste. Consuming even small amounts over a long period can cause cancer, skin problems, abnormal heart rhythms and death.
Some 25 million people in Bangladesh are exposed to arsenic contamination in their drinking water, and researchers have said hundreds of thousands of people are likely to die from cancers of the lung, bladder and skin caused by arsenic.
Charles Harvey, an associate professor of civil and environmental engineering at the Massachusetts Institute of Technology and one six authors on the study, said he had expected that rice fields would be the source of the contaminated water that is pumped from aquifers.
An aquifer is an underground layer of water-bearing rock or sand into which wells are dug.
But after tracing the origins of the contaminated water, Harvey said he and his colleagues found that water from rice fields had low concentrations of arsenic while the levels spike for water that percolates through artificial ponds.
The reason, Harvey said, is the ponds become a dumping ground for all sorts of debris.
"They are nasty. There is a lot of grunge at the bottom of the pond and it's there all year," he said.
"It's full of organic carbon, human waste, dead plants," he said. "When the water passes through this organic carbon, it takes some with it and that fuels the microbes down in the aquifer. The microbes dissolve minerals that releases arsenic into the water."
Farid Uddin Akhtar Khan, an official at the government's Department of Public Health Engineering and who oversees the water supply in rural areas, said authorities would take a look at the study to determine if any policy changes were necessary.
"We need to know if this is isolated phenomenon or it's happening across the country," Khan said. "In Bangladesh, there are areas where arsenic contamination is high and it is found in the upper layer of water too. So, if the ponds are located in such areas, there will obviously be high contamination of arsenic in the water."
Millions of dollars have been spent on providing safe drinking water since arsenic was first discovered in groundwater in Bangladesh and reports of widespread poisoning emerged two decades ago. Yet most people in the country of 150 million still depend on wells for their drinking water, and about 80 percent of wells in more than 8,000 Bangladeshi villages are highly contaminated, according to UNICEF.
The study recommends that villagers avoid digging artificial ponds above wells and calls for relocating wells to deeper aquifers dating to the Pleistocene period from at least 3.75 million years ago until about 11,000 years ago where arsenic concentrations are low. It also suggested that shallow wells below rice fields could be a good source of safe drinking water.
"It's necessary to have this fundamental understanding to make long term strategies" for providing safe drinking water, Harvey said. "In the short term, the understanding will help to decide where to put wells that are safe."
Lex van Geen, a geochemist at Columbia University's Lamont-Doherty Earth Observatory who has studied arsenic contamination in Bangladesh and did not participate in the study, praised it as a "major contribution."
He said the findings were more convincing than an earlier study which found irrigation pumps played a key role in arsenic contamination.
"All in all, a major achievement likely to be discussed extensively and followed up with complementary experiments," Van Geen said. "I just worry that, given the remaining uncertainties, the policy implications may be a little overstated."
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