Bangladesh aquifers have high arsenic levels
There is potentially bad news involving arsenic and Bangladesh, where contaminated groundwater has affected millions of people.
Wells that have been dug into relatively shallow aquifers produce drinking water with levels of arsenic far above those considered safe.
But not all of the water in the aquifers ends up in wells. During the dry season, some of it discharges into major rivers, and now a study in The Proceedings of the National Academy of Sciences shows that river sediments have become heavily contaminated with arsenic, with the potential to contaminate groundwater even further.
Yan Zheng of the Lamont-Doherty Earth Observatory and Queens College and colleagues sampled sediments along the Meghna River, which, with the Ganges and Brahmaputra, forms a vast delta both in India and Bangladesh.
The proof
Samples taken to a depth of about 2 inches showed relatively low arsenic concentrations, but those from depths of 3 feet to 10 feet had concentrations that were two orders of magnitude higher.
The researchers suggest that as the arsenic-rich water enters the river, the chemistry causes it to precipitate and adhere to iron-bearing minerals in the sediments.
In effect, they say, the sediments form an “iron curtain” to keep the arsenic out of surface water in the river.
But recycling of these arsenic-laden sediments to the Ganges-Brahmaputra-Meghna delta aquifer may lead to further groundwater contamination. — © 2009 The New York Times News Service
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