Overexploitation of groundwater poisoning water supply in the Mekong Delta
Laura Erban, lead author of the study on arsenic in groundwater in Vietnam, samples a well in the Mekong Delta. Groundwater, the major supply of tap water in the region, has been increasingly contaminated with arsenic, a carcinogenic substance. Photo by Laura Erban
Nguyen Van Minh's parents are among at least 50 people in a commune in Tien Giang Province who have died of cancer over the past five years, and concerns over arsenic-laden groundwater are escalating in the Mekong Delta.
"My father died of stomach cancer and my mother died of blood cancer. Neither smoked nor drank," said the farmer who lives in Thoi Son Commune, which is located in the province's My Tho Town.
Do Tien Hoa, a medical worker in the commune's Thoi Hoa Hamlet and many local residents believe that arsenic, a carcinogenic substance, in their tap water is responsible for the high incidence of cancer in their locality.
It appears that the residents' suspicions are well founded.
Unlike previous studies that linked arsenic contamination to groundwater near the surface, a recent study by a group of California-based scientists found increasing contamination of carcinogens in numerous deep wells in the Mekong Delta.
New poison depths
Chronic arsenic poisoning is said to be a factor in cardiovascular diseases, skin lesions and numerous forms of cancer. These diseases may take years to manifest. While the symptoms of arsenic poisoning are treatable in the short-term, there is no way to reverse its long-term affects.
Faced with arsenic contamination, many people have dug deeper wells for cleaner water, but scientists have recently found increased arsenic contamination in the new depths as well.
Drilling deeper wells has become common in the search for clean water but new research from Stanford University's School of Earth Sciences has found that even deep wells might not remain arsenic-free.
Researchers suggest that the contamination occurs as arsenic is squeezed from ancient clay sediments surrounding the wells.
The scientists reviewed 42,000 well measurements taken throughout the multi-aquifer system of Vietnam's Mekong Delta and in an area spanning more than 1,000 square kilometers (386 square miles), arsenic was found in nearly 900 deep wells.
"Historically, deep wells often tested arsenic-free," said Laura Erban, a doctoral student in environmental Earth system science at Stanford and the lead author of the study.
In some cases, the wells were contaminated when deep-pumping projects inadvertently transported shallow arsenic, or other substances that help mobilize arsenic, to greater depths. But in the Mekong Delta, it appears that there is an entirely different, and previously unsuspected, process contaminating deep wells, the report said.
It said when water is heavily pumped from an aquifer, surrounding clay layers compact, and water is expelled as the land sinks.
"If this expelled water contains substances such as arsenic, the groundwater can become contaminated. Land subsidence the gradual sinking of land due to excessive pumping is common in delta environments and can be measured," the report said.
The impacts of arsenic contamination from deep groundwater extraction may be reduced by quantifying the extent of deep groundwater arsenic, limiting heavy pumping and treating extracted groundwater to meet health standards, it said.
According to Steven Gorelick of the Stanford University, co-author and project investigator on the study, the implication of these findings for the Mekong Delta region, and potentially other arsenic-prone aquifer systems like it is that deep, untreated groundwater is not a safe long-term water source.
"Deep wells that test clean upon installation, as do those bordering the focus area, may not remain arsenic-free over time as pumping promotes compaction and release of arsenic or arsenic-mobilizing solutes from deep clays."
To reduce the impacts of arsenic contamination from deep groundwater extraction, water managers should consider a suite of measures, he said.
"These include first understanding the nature and extent of deep groundwater arsenic, limiting intensive extraction, treating or blending extracted groundwater to meet health standards, and possibly screening pumping wells over intervals of deep aquifers that are distant from confining clays, among other water management strategies aimed at health-risk reduction."
People in Tien Giang's Thoi Son Commune were using tap water supplied by two stations pumping from two deep wells without any treatment for drinking and cooking, the Voice of Vietnam news website quoted Hoa, the medical worker, as saying.
Tran Thanh Thao, deputy director of the Tien Giang Health Department, said relevant agencies had collected tap water samples in the commune and found a high concentration of arsenic.
However, it is unclear if arsenic contamination is responsible for cancer in the commune, local authorities said. Scientists from the Pasteur Institute in Ho Chi Minh City have collected hair and urine samples of 100 local residents for testing but the results are not available, they said.
Increasing pollution as well as salination of surface water have over the years forced many residents to switch to groundwater, leading to overexploitation of the resource and, experts say, rising arsenic threat.
To Van Truong, former director of the Southern Institute for Water Resources Planning, said increasing demand due to growing population and seawater encroachment has led to a reliance on groundwater.
"This increases the risks of arsenic consumption for local residents in the Mekong Delta," he said.
According to the Center for Water Resources Planning and Investigation, groundwater has been declining both in quality and quantity nationwide.
Results from many monitoring stations show increasing contamination of manganese, arsenic and ammonia, according to a report the agency released in July.
In May, authorities in Tien Giang's Cai Lay District announced that a source of tap water for more than 200 households in Phu Cuong Commune has a high concentration of arsenic.
Many residents, fearful that they have been consuming the carcinogenic substance, are using bottled water as an alternative, while waiting for the commune authorities to drill a new well.
Concerns over arsenic-laden tap water have spread widely in the Mekong Delta.
There are more than 400 well water stations in Dong Thap Province, but not many people have been using their water recently, fearing that it is not safe.
According to the provincial Preventive Health Center, a test of 295 stations in late 2011 found 191 of them supplying unsafe water, including 110 with high concentrations of arsenic.
There are dozens of thousands of household wells in the Mekong Delta, from 100-300 meters deep, the Ministry of Natural Resources and Environment said.
Duong Van Ni, a lecturer at the Can Tho University, said many people in the Mekong Delta provinces of Ca Mau and Bac Lieu have been using groundwater to mix with sea water to breed shrimp.
"It's so wasteful. Many people think groundwater is endless and that they can just drill new wells if the old ones get polluted or go dry," he said.
"Arsenic can leak into groundwater in abandoned wells."
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