Millions of people in South and Southeast Asia may be at risk of arsenic poisoning as massive pumping of groundwater pushes tainted water closer to uncontaminated aquifers, scientists warned in a new study published in the journal Nature.
The study, published by experts from Switzerland, the US and Vietnam, examined changing groundwater flow over one decade in Vietnam’s capital, Hanoi.
Hanoi is expanding rapidly, as is water demand. Pumping for municipal water supplies doubled between 2000 and 2010, to around 240 million gallons daily. In the city, water is filtered and treated, but in areas just a few kilometres outside, near the Red River, many households use private untreated wells.
In the past, higher water levels in the aquifer (underground layer of water-bearing rock, sand or silt) meant water from these wells was generally safe. But as more groundwater has been pumped, water from arsenic-rich sediments is increasingly intruding into the previously uncontaminated aquifer.
Arsenic, one of the most common inorganic contaminants found in drinking water worldwide, can be highly toxic to humans. Even in low concentrations arsenic can damage health if ingested over long periods. It is associated with cancer of the skin, lungs, bladder and kidneys.
At some sites in Vietnam investigated for the study, arsenic concentrations were up to 50 times higher than the internationally recommended limit of 10 micrograms of arsenic per litre.
The study focused on a village on the outskirts of Hanoi, Van Phuc, where residents have private wells. Although the sample was small, it is believed similar processes may be underway elsewhere in large Asian cities that are pumping more groundwater, said co-author Michael Berg, a geochemist at the Swiss Federal Institute of Aquatic Science and Technology.
“The processes in nature should be the same anywhere,” he told IRIN, adding that changes in water quality were easier to study in this village because groundwater flow was in one direction - to Hanoi.
"We know exactly where the groundwater is flowing to and we precisely identified where this contaminated water is now intruding into previously safe water," he explained.
Over the last four to six decades, water from the contaminated aquifer has migrated more than 2km toward the city centre, according to the study. However, substantial arsenic contamination moved at a slower pace, only about 120m.
“In some ways it’s not a hugely alarming picture. The water is moving but the arsenic isn’t moving nearly as fast as the water,” said co-author Benjamin Bostick, from Columbia University's Lamont-Doherty Earth Observatory.
This could buy time, perhaps decades, for water managers to try and solve the problem, lead author, Alexander Van Geen, a geochemist at the same observatory, told IRIN from New York.
“But I think there are enough people in trouble now, and this needs to be addressed. We can’t sit back and wait for things to happen. There’s action needed now,” he said.
To tackle contamination, authorities in Van Phuc set up a water cooperative and built a water-treatment facility next to the local health station that serves around 1,000 households.
Berg said this is a good long-term solution and called for local governments to centralize drinking water systems with large treatment facilities capable of serving up to 10,000 people. Residents on Hanoi’s outskirts currently rely on private wells drilled into a patchwork of clean or polluted sands with no central filtering system.
“The challenge there is setting up a distribution network. You have to pipe this water, and the piping is difficult. It’s costly, of course,” said Berg.
Setting up a piped water system is even more difficult in a country like Bangladesh, where there is generally a low level of formal education and weak governance in villages, Van Geen added.
In Bangladesh, the acceptable level of arsenic in drinking water has been set by the national government at five times higher than the international limit. Of the estimated 8.6 million tube wells nationwide, some 4.7 million have been tested, according to UN Children’s Fund (UNICEF); of these 1.4 million were contaminated.
UNICEF estimates some 20 million people in Bangladesh are drinking water from wells with higher-than-government approved levels of arsenic.
The first step across the region should be to test every well, Van Geen said. “This is not happening enough anywhere in South and Southeast Asia, and we’re trying to come up with a semi-commercial approach to the problem.”
Van Geen and researchers in India recently tested the willingness of rural households in the Indian state of Bihar to pay for arsenic testing. Of some 1,800 households offered a test, almost 1,200 agreed to pay a fee to test their tube wells. The researchers found that two out of three households were willing to pay the 20 rupees (US$0.31) necessary to cover the tester’s time and travel, but not the total actual cost of testing (up to $2.37), a gap that would need to be subsidized in a testing campaign.
These and other solutions should be explored now, said Van Geen.
“What we did in Vietnam was important to make people understand that if you have a safe well, it’s not going to become unsafe overnight, so the 10-year policy [timeframe of study] should be for countries to take advantage of that rather than throwing their hands in the air saying ‘I don’t see a solution to that’ or coming up with solutions that are not practical.”