Groundwater
Arsenic Contamination: Can It Happen In The Mekong Delta ?
A
Vietnamese Perspective
Mai
Thanh Truyet, Ph. D. & Pham
Phan Long, P.E.
Contents
·
How Did Arsenic Enter
Groundwater ?
·
The Basis For Concern At The
Mekong Delta
·
A Catastrophe Awaiting Eruption
Introduction
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 ore
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 [1]. 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 [2]. 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. How did arsenic enter
ground water ? 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 [3]. In the last two
decades, the Green Revolution at Bengal, had lowered the ground water level and
thus the release of arsenic [4]. 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
[5]. 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 [6]. The above hypotheses are attempts to
explain the events after their The basis for the
concern at the Mekong Delta 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 [7]. Charkraborti
reported soil test data in West Bengal in the range of 133-290 mg/kg [3]. 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 [8]. 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 [9] 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 [10]. 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 [11]. 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 [8]. 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 [12]. 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. A Catastrophe
Awaiting Eruption 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
[13] 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. 1.
Lepkowski, W., Arsenic
Crisis in Bangladesh, Chemical & Engineering News (C&EN), November 16,
1998, Washington, USA.
2.
Tabibul Islam, Health
Bangladesh: Cleaning Water Turns Poisonous, World News, Inter Press Service,
Feb 26, 1998.
3.
Charkraborti
et.al., Arsenic in ground water in six districts of West Bengal, India,
Environmental Geochemistry and Health, 18, 5-15, 1996. 4.
Tsushima, Sachi,
Arsenic Contamination in Ground Water in Banggladesh, Asia Arsenic Network 5.
Nature: Arsenic Poisoning
of Bangladesh Groundwater, Volume 395, 338, September 24, 1998. 6.
Le Blanc et al.:
Mineral Deposits: From their environmental impacts, Bulkema, Rotterdam, 1995. 7.
La Force M.J., Trace
Element Cycling in Nature 9.
Nguyen Thanh Tin, 10. Mortoza, S., Arsenic
Contamination: A Too Formidable a Foo, Arsenic Contamination Center, 1998, 11. Le Quang Tri, Development Management Packages for
Acid Sulphate Soils Based on Farmer and Expert Kowledge, Thesis at the
Unversity of Wageningen, 1996. 12. China
Yunnan Metallurgival General Company, 13. Pham L.P., The Dangers of Hydropower Devleopment on
the Mekong Delta and TonLe Sap Lake, Mekong River Conference, Garden Grove,
1999. 14. Khalequzzaman
Md., Comments on Arsenic Study in Bangladesh, 15. Jim Castro,
Environmental Goechemistry Geology 431 Lecture 2 Notes, Abbreviations: ·
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: hanoi@unicef.ac.vn 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 June 1999 
Arsenopyrite
As contaminated well in Bangladesh
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 [14], especially
when geochemical scientists have established that these parameters are
extremely important to assess the mobility of water contaminants. 
Arsenic poisoning in Bangldesh.