Groundwater Arsenic Contamination: Can It Happen In The Mekong Delta ?
A Vietnamese Perspective
Mai Thanh Truyet, Ph. D. & Pham Phan Long, P.E.
In the late 18th Century, Emperor Quang Trung, the most revered hero of Vietnam history, led the expeditious defensive attack to free Thang Long, the capital of Vietnam, from the Chinese occupying force and prevented Vietnam from falling under the Chinese domination the 6th time. The victorious but visionary Emperor immediately and humbly sought the Chinese Emperor Qing-Long's blessing for his throne, proposed his marriage to a Chinese Princess, and entered a peace treaty to end the conflict and suffering for both countries. Unfortunately, only four years later, the Emperor died from food poisoning and the poison was thought to be arsenic contamination. This unesolved conspiracy was over 200 hundred years ago; today, millions of Vietnamese would be extremely concerned on the question if the same poison that possibly took the life of their Emperor may now be present in the thousands of their ground water supply sources.
Arsenic standard: According to US EPA, arsenic is a persistent, bioaccumulative and toxic (PBT) substance. Arsenic is stable in air, soil and water. Arsenic is also classified as a carcinogen by NIOSH and is among the top 20 most toxic substance identified by US Agency for Toxic Substances and Diseases Registry (ATSDR). The World Health Organization's (WHO) standard
for arsenic in drinking water is 0.010 mg/L, the French current standard is 0.015mg/L, Vietnam and US EPA standard is 0.050 mg/L. The US is in the process of lowering that to 0.010 mg/L.
Arsenic has been discovered in ground water in several countries in all five continents, but the worst and most recent calamity of all was in West Bengal, India and Bangladesh. There, arsenicosis caused by drinking water from tube wells was discovered first by Dr. K. C. Saha in 1982, but was not made known to the world until 1993. That was after 200,000 people had already been diagnosed with arsenicosis . Now, this number has reached 300,000, and 70 million people in India and 65 million in Bangladesh are considered being exposed to this cancer threat . Ironically, three of the five millions wells in these regions were funded by UNICEF to help the poor population avoid water related diseases like cholera, diarrhea and typhoid. The population however encountered with another water related diseas -arsenicosis- equally if not more deadly than others because of arsenic colorless and tasteless properties.
The question from Vietnam is can this horrifying experience be repeated in the Mekong Delta where 17 million poor people live? In the last 16 years, UNICEF has actively promoted the use of ground water in Vietnam. UNICEF has put into use about 200,000 water supply points and claims the success in providing clean water to 23 million people. But how clean is this really? UNICEF has not provided curious public [including Mekong Forum] any specific information although UNICEF takes about 400 samples from these wells for analysis annually. A friendly search at the UNICEF library in Hanoi did not produce any water quality data.
Several processes have been proposed to explain the release of sedimentary arsenic into ground water:
1. Oxydation of iron pyrite by air: Charkraborti and his colleagues studied and confirmed the presence of arsenic in iron pyrite sediments. They suggested that the high volume extraction of
ground water in the region has exposed the deltaic sediments to air, which through oxidation reaction causes the decomposition of iron pyrites to ferrous sulfate (FeSO4), ferric sulfate (Fe2(SO4)3) and sulfuric acid. The process frees up arsenic which is then oxidized into arsenite and arsenate both of which are soluble in ground water . In the last two decades, the Green Revolution at Bengal, had lowered the ground water level and thus the release of arsenic .
2. Reduction reaction of arseniferrous iron-oxyhydroxides: The oxydation theory however fails to explain the increase in arsenic level in deeper wells and anoxic condition. Ross Nickson of the University College London suggested that in deep wells, arsenic is released when arseniferous iron-oxyhydroxides are reduced in anoxic water. Nickson observed that arsenic-rich ground water is mostly restricted to the alluvial aquifers of the Ganges Delta and concluded that the source of arsenic must lie in the Ganges source region upstream of Bangladesh .
3. Microorganism: Le Blanc's analyses of surface water samples taken from around Montpellier (France), a region with large heavy metal deposits. Le Blanc's data indicated that the pH's fall in the range from 2.5 to 3.5, and arsenic contents fall in the range of 100 to 300 mg/L. The presence of a group of microorganism, the stromatolytique was found which Le Blanc considered the main cause of the high level of arsenic content in water. Le Blanc explained that the microorganism acts as catalyst and provides oxygen for the oxydation of metal sulfides producing sulfuric acid and metals. The acid then attacks on the metals to produce metal sulfate and release soluble arsenic in water .
As contaminated well in Bangladesh
The above hypotheses are attempts to explain the events after their
occurance. In the case of West Bengal and Bangladesh, the hypotheses are developed based on arsenic content of water and soil samples at various depth. More knowledge would be made available when full chemical properties such as pH, Eh, DO, TDS, temperature are also studied from samples taken over longer period and over the entire basin , especially when geochemical scientists have established that these parameters are extremely important to assess the mobility of water contaminants.
The concern on arsenic contamination in Mekong Delta ground water can be easily dismissed by tests, but to date, no responsible agency has come forth with their test data. In light of Bangladesh, it seems strange that the question has not been asked, and odd to say the least, that no organization has taken on the issue seriously in proportion to the risk and population in the Mekong Delta. Dr. K.C. Saha almost lost his job for his discovery of arsenic problem in drinking water at Calcutta. This may discourages others to come forth with same findings, especially from the developing countries.
The presence of arsenic is highly probable to inevitable in the Mekong Delta for the following reasons:
1. The higher than normal arsenic content in Mekong Delta acid sulphate soil: Average arsenic in uncontaminated soil is about 1.8-5.0 mg/kg . Charkraborti reported soil test data in West Bengal in the range of 133-290 mg/kg . The British Geological Survey and Mott MacDonald (UK) reported to the Government of Bangladesh that the arsenic content of alluvial sediments in Bangladesh is usually in the range of 2-10 mg/kg . Jon Petter Gustafsson of the Ground Water Research Group (GRAG), Sweden and Nguyen Thanh Tin of Vietnam Water Quality Monitoring Network (WQMN) who conducted solid phase analysis of Mekong delta acid sulfate soil (ASS) reported that arsenic content in Mekong Delta ASS is 10-30 mg/kg  or 2 to 6 times higher than normal soil arsenic level.
2. The inseparable co-existence of arseno-pyrite (FeAsS) and pyrite (FeS2) is fact of nature in chemistry due to their prismatic orthohomic crystal structure. Based on findings from Bangladesh, Sylvia Motoza stated that the retention of arsenic is especially true in acid pyritic soil and acid sulfate soil . If this is true then Mekong Delta is unfortunate for it is the world single largest deposit of ASS, Le Quang Tri estimated that 1.6 million out of 3.9 million hectares of Mekong Delta are either acid sulfate soil or potential acid sulfate soil .
3. pH Level: Mobility of contaminants is highly sentitive to acidity pH and redox potential Eh. Arsenic dissolves easily in low pH solutions. The soil pH in Bangladesh is around neutral while the soil in the Mekong Delta is acidic, ASS in Mekong Delta is however clearly acidic with pH being in the low range of 2-4. The inherently abundance of ASS and therefore arseno-pyrite in the Mekong Delta, along with the low pH are favorable conditions for the release of arsenic over a very large area.
4. Both the Ganges and the Mekong originate from the Himalayas of the Tibetan Plateau thus their deltaic sediments are likely to be of similar characteristics. Although the Mekong Delta is about 10,000 year old, much younger than the Ganges-Brahmaputra Delta which is hundreds of million years old. The problem of Bangladesh was reportedly associated within their younger deltaic aquifers. The BGS and Mott MacDonald report stated that the burial of sediments, rich in organic matter, would lead to strongly reduced conditions would result in greater arsenic concentration . This exactly is the case in the Mekong Delta.
5. The Mekong River runs through the Yunnan province of China where it picks ups runoff and sediments from the weathering of hard rocks from Yunnan highland. Yunnan province contributes less than 20% of the river total discharge but as high as 50% of the river total sediments loading. Yunnan is known for its large deposit of copper, gold, lead, maganese, zinc, silver and lignite. Yunnan is the home of 26 Chinese metal industries producing 65,000 tons of lead-zinc, 60,000 ton of sulfuric acid. Yunnan also treats zinc oxide ore and zinc sulfide ore . The transport of these materials to the Mekong Delta is almost a natural certainty offering no comfort to concerning scientists.
6. The lowering of groundwater in the Mekong Delta seem to duplicate what had happened to the Ganges-Brahmaputra-Meghna Delta. In the quest for more and better water quality, increasingly deeper wells are being drilled by the growing population to satisfy the expanding economy and meet ever higher agricultural goals. The production from the Mekong Delta has made Vietnam the second biggest rice exporter surpassing even the USA. Unfortunately, the impact of arsenic in agricultural product is unknown and one can only wish that being inorganic in nature, arsenic in agricultural products if any would eventually be proven harmless or rules out.
7. Due to the above observations and reasoning, the Mekong Delta groundwater may not escape from an arsenic contamination problem. Fortunately, the Mekong Delta inhabitants have the habit of harvesting rain water and store in large vessels (50-100 gallon each) in several units per family for their domestic consumption. For those must use surface water, they traditionally treat the water with alum, borax, or lime. They also have the practice of placing "bi dao" (pumpkin) in the vessel to enhance the taste and agglomerate settling solids at the bottom of the vessels.
Although not intended, coincidentally those who practice the above traditions may have helped themselves alleviate or even escaped from the arsenic problem. Meanwhile, the arsenic problem in the Mekong Delta has not escalated itself into a known major public health disaster such as in Bangladesh. No outbreak of arsenic related disease has been reported to the international health community, although that does not mean there is none, or they were not mistakenly dismissed as something else. The Mekong Delta may have a little more time than Bangladesh but cdeertainly no time to waste either. The pressure of the population growth and local economic development has led to the rapid extraction of ground water going down an identical path to Banghladesh and West Bengal.
More importantly, the proposed diversion of 8.8 BCM (billion of cubic meters) of water from the Mekong River in Thailand and the planned development of 37 MW of hydropower reservoirs in China and Laos  would exacerbate the arsenic problem into a catastrophe.
At this time, instrumentation in laboratories in Vietnam cannot analyze arsenic at ppm level, not to mention ppb level at which arsenic should be measured for health risk assessment. Furthermore, the lack of standard solutions, training, and research funding actually bind the hands of even the most alert and conscientious scientists. Under then pending threat, Mekong Delta people are left in truly helpless condition.
Sign of problems have already emerged: Salt-water intrusion has invaded up to 70-km inland. Last year, water level in the region fell to a 70-year record. The slow and insidious attack of arsenic may give Mekong Delta the time to prepare for it. But time can be lost very quickly due to the reckless act of man. That ignorance would be paid for by the health security of the million poorest of the poor. Lesson from Bangladesh must be learned, the arsenic problem in Mekong Delta must be investigated by the UNICEF, the developers, the authority of Vietnam. This paper should be taken as a warning and request for action of all responsible parties and international aids agencies.
Arsenic poisoning in Bangldesh.
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9. Nguyen Thanh Tin,
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15. Jim Castro, Environmental Goechemistry Geology 431 Lecture 2 Notes,
· ATSDR: US Agency for Toxic Substances and Diseases Registry
· BCSIR: Bangladesh Council for Science and Industrial Research
· NIOSH: US National Institute of Occupational Safety and Health
· ppb: part per billion
· ppm: part per million
· UNICEF: United Nations International Children's Emergency Fund
· US EPA: United States Environmental Protection Agency
· WHO: World Health Organization
UNICEF Hanoi UNICEF Email: [email protected] c/o UNICEF EAPRO 72, Ly Thuong Kiet St. Telephone: (84.4)8261170-75 P.O. Box 2-154 Hanoi, Vietnam Facsimile: (84.4)8262641 Bangkok 10200, Thailand