Arsenic Contamination of Ground and Drinking
Water in Vietnam: A Human Health Threat
Michael Berg,
*,†
Hong Con Tran,
‡
Thi Chuyen Nguyen,
‡
Hung Viet Pham,
‡
Roland Schertenleib,
†
and Walter Giger
†
May 7, 2001
Revised Manuscript ES010027Y
†
Swiss Federal Institute for Environmental Science and Technology (EAWAG),
CH-8600 Dübendorf, Switzerland
‡
Centre of Environmental Chemistry, Hanoi University of Science, Hanoi, Vietnam
*Corresponding author. Phone: +41-1-823 50 78; Fax: +41-1-823 50 28
E-mail: michael.berg@eawag.ch
This document is the Accepted Manuscript version of a Published Work that appeared in final form in
Environmental Science and Technology, copyright © American Chemical Society after peer review and technical
editing by the publisher. To access the final edited and published work see http://doi.org/10.1021/es010027y
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Abstract
This is the first publication on arsenic contamination of the Red River alluvial tract in the city
of Hanoi and in the surrounding rural districts. Due to naturally occurring organic matter in
the sediments, the groundwaters are anoxic and rich in iron. With an average arsenic
concentration of 159 µg/L the contamination levels varied from 1–3,050 µg/L in rural
groundwater samples from private small-scale tubewells. In a highly affected rural area, the
groundwater used directly as drinking water had an average concentration of 430 µg/L
arsenic. Analysis of raw groundwater pumped from the lower aquifer for the Hanoi water
supply yielded arsenic levels of 240–320 µg/L in three of eight treatment plants and 37–82
µg/L in another five plants. Aeration and sand filtration that are applied in the treatment
plants for iron removal lowered the arsenic concentrations to lower levels of 25–91 µg/L but
50% remained above the Vietnamese Standard of 50 µg/L. Extracts of sediment samples
from five bore cores showed a correlation of arsenic and iron contents (r
2
0.700, n=64). The
arsenic in the sediments may be associated with iron oxyhydroxides and released to the
groundwater by reductive dissolution of iron. Oxidation of sulfide phases could also release
arsenic to the groundwater but sulfur concentrations in sediments were below 1 mg/g. The
high arsenic concentrations found in the tubewells (48% above 50 µg/L, 20% above 150
µg/L) indicate that several million people consuming untreated groundwater might be at a
considerable risk of chronic arsenic poisoning.
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Introduction
Natural contamination of groundwater by arsenic has become a crucial water quality problem
in many parts of the world, particularly in the Bengal delta (Bangladesh and West Bengal,
India) (1-8). Smith et al. (9) have stated that "the contamination of groundwater by arsenic in
Bangladesh is the largest poisoning of a population in history, with millions of people
exposed". In the U.S., the Environmental Protection Agency has proposed lowering the
maximum contaminant level for arsenic in drinking water from 50 µg/L to 10 µg/L but the
feasibility of the proposed standard is currently being evaluated (10). The European
maximum admissible concentration and the World Health Organization guideline for arsenic
in drinking water are both set at 10 µg/L. On the other hand, developing countries are
struggling to find and implement measures to reach standards of 50 µg/L in arsenic affected
areas.
The Vietnamese capital Hanoi is situated at the upper end of the 11,000 km
2
Red River delta
of northern Vietnam, which is inhabited by 11 million people and is one of the most
populous areas in the world. Together with the Mekong delta, the Red River delta (Bac Bo
plain) has become one of the most productive agricultural regions of South East Asia. The
rural population is growing rapidly and has, in the last 5–7 years, moved away from using
surface water or water from shallow dug wells as sources for drinking water in favor of
groundwater pumped from individual private (family based) tubewells. Groundwater
exploitation in the city of Hanoi began 90 years ago. Today, eight major well fields supply
water to city treatment facilities which process 500,000 m
3
of water per day (11).
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The Red River basin stretches from N 20°00' to N 25°30' and E 100°00' to E 107°10' and is
bounded by the Truong Giang and Chau Giang River basins in the north, the Mekong River
in the west, the Ma River basin in the south and the Gulf of Tonkin in the east. The Red
River basin has a gross catchment area of 169,000 km
2
(12), and a total length of 1,150 km. It
is dominated by tropical monsoon climate and is subject to rainy (May–September) and dry
seasons (October–April). The average temperature in Hanoi is 23.4°C and the average
rainfall is 1,800 mm/year (13). During the rainy season, the Red River in Hanoi may reach a
water discharge of 9,500 m
3
per second (14). The long-term average flow is 3,740 m
3
/s (13)
but the river volume is highly variable throughout the year. The River carries huge quantities
of silt, rich in iron oxide, because of the large proportion of easily crumbled soil in its basin
(14). The suspended solid load may reach over 6 kg/m
3
in the lower Red River during food
seasons when over 90% of the annual load is transported (13).
The Bac Bo plain is a flat area with a ground level of 5–8 m above mean sea level. It has a
complicated geological history with up and down movements, transgressions, erosion and
stream activities that formed the alluvial sediments (13, 15). The result of these geological
processes is a relatively thick Quaternary formation (50–90 m in Hanoi) with loose and
altering sediment beds (13), often containing organic material(15). In general, the Quaternary
formation can be divided into two sequences, (i) the upper, composed of fine sediment clay,
sandy clay and fine sand, and (ii) the lower part, containing gravel with cobbles and coarse
sand (13, 15). The Quaternary sediments are underlain by Tertiary deposits of Neogene age
that are composed of conglomerate sandstone, clay and siltstone (13). In total the deposits
exceed 400 m. More detailed information can be found in references (13, 16).
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Naturally anoxic conditions in the aquifers are due to peat deposits (15)), and, consequently,
the groundwaters contain large amounts of iron and manganese that are removed in the Hanoi
drinking water plants by aeration and sand filtration (13). The urban water treatment plants
exclusively exploit the lower aquifers at 30–70 m depth, whereas private tubewells
predominantly pump groundwater from the upper aquifer at 12–45 m depth (11).
Based on geological analogies to the Bengal delta (i.e., relatively young alluvial sediments
and anoxic groundwater) and similar composition of the groundwater as in Bangladesh (17)
we anticipated elevated arsenic concentrations in the aquifers of the Red River basin. Thus,
the objective of our study was to survey arsenic levels in the aquifers of the region around
Hanoi. Our initial overview provides preliminary conclusions regarding the sources and
mechanisms for arsenic release to the groundwater that have resulted in the high arsenic
concentrations we have recently discovered in the ground and drinking waters of the Hanoi
area.