Arsenic Special Issue, BCAS Newsletter
Jan-Mar 97 Vol. 8 No. 1, (c) Bangladesh
Centre for Advanced Studies
Reprinted with permission BCAS.
Table of contents
Arsenic in Groundwater
Introduction
In the last two years it has become widely recognised that there is
a problem of arsenic in tubewell water in parts of Bangladesh and adjoining
areas of West Bengal in India. The problem was identified in India where
Professor Dipankar Chakraborty has played a key role in drawing attention
to the issue. Concern abroad developed rapidly following the holding of
an international conference in Calcutta in February 1995. Various agencies
in the health and water sectors such as NIPSOM, DPHE, BWDB and others began
sampling well water and looking for medical symptoms as evidence of arsenic
contamination. Quickly it became clear that there was a significant problem
in Bangladesh. The number of water samples analysed increased during 1996
and early 1997, and it has become possible to draw maps of the distribution
of arsenic in groundwater. An example is shown in Figure 1 [not
included]. However, it must be emphasised that there is considerable
uncertainty in extrapolating the results of individual water analyses or
medical diagnoses to make estimates of the total number of people affected.
The distribution of arsenic is complicated by two scales of variability.
On the one hand, there is a local variation from one well to another, while
at another scale there is a systematic variation related to the geology
as discussed below. Arsenic contamination
In different countries, arsenic contamination of water supplies is known
to have been caused by dissolving naturally occurring geological deposits,
from industrial discharges and from application of pesticides. While it
acknowledged that there may be more than one source of arsenic contamination
in Bangladesh, the size and extent of the problem points clearly to the
geological origin being by far the most important.
Previously the possibility of arsenic or other toxic elements in groundwater
posing a problem had not been seriously considered because of the alluvial
sediments and the abundant rainfall (compounded by the limited availability
of laboratory facilities). And indeed even after its discovery, the occurrence
of arsenic in the alluvial sediments remains a surprise to most scientists.
The reasons for this surprise may be appreciated by considering where else
in the world arsenic poisoning has occurred. Most cases arsenic poisoning
are associated with present or ancient volcanic activity and usually with
metalliferous mining such as in Argentina, Chile, Ghana and Thailand. The
most common arsenic mineral is arsenopyrite (iron arsenic sulphide) which
often occurs as impurity in ore deposits, but it is rarely an important
mineral in alluvium.
Relation of Arsenic to Geology
Figure 1 [not included] shows a geological map of Bangladesh.
Apart from the hills in the eastern parts of the country, most of Bangladesh
is formed of a vast thickness of alluvial and deltaic sediments, which
can be divided into two main parts - the recent floodplains and the terrace
areas. The floodplains and the sediments beneath them are only a few thousand
years old and can be classified according to which of the river systems
(Ganges, Brahmaputra, Tista and Meghna etc.) deposited them. The terrace
areas are better known as the Madhupur and Barind Tracts, and the sediments
that underlie them are much older than the adjacent floodplains (and may
be as much a million years old). As shown on the map, most of the arsenic
occurs in the younger sediments derived from the Ganges Basin.
Although arsenic occurs in alluvial sediments the ultimate origin of
the arsenic must be in the outcrops of hard rocks higher up the Ganges
catchment that were eroded in the recent geological past and then re-deposited
in West Bengal and Bangladesh by ancient courses of the Ganges. At present,
these source rocks have not been identified.
It is also important to understand that arsenic does not occur at all
depths in the alluvial sediments. Although there is not enough evidence
to draw firm conclusions, it appears that high concentrations are restricted
to the upper 150 metres of the alluvial sediments and offers prospects
of obtaining arsenic free waters from deeper layers. However, this remains
to be confirmed.
Solutions to Water Supply Problems
Safe water supplies are an unavoidable requirement. Simply abandoning
arsenic contaminated tubewells and reverting to untreated streams or ponds
will reduce arsenic related illness at the cost of death and illness from
diarrhoeal diseases. There are three options for safe water supplies (i)
treatment of well water before consumption, (ii) sinking wells in arsenic
free aquifers, and development of surface water sources with treatment.
All of these approaches probably have a role to play, but all have some
disadvantages which will form a research agenda for the next few years.
In the short term, option (ii) is the best but may not possible in all
areas and in the long term may result in migration of arsenic between aquifers.
The two treatment options are both likely to be costly and have practical
problems in operation and maintenance. Groundwater treatment has in already
been implemented at Meherpur Town using a modified iron removal plant,
but all removal systems carry with them the problem of disposing of arsenic
enriched sludge.
Understanding Arsenic Chemistry and Toxicity
To understand the extent of the problem of arsenic in Bangladesh it
is important to have a basic understanding of the chemistry of arsenic.
Arsenic exists in many different chemical forms in nature, but in groundwater
is found almost exclusively as arsenite (arsenic III), or arsenate (arsenic
V). Arsenite can be converted to arsenate under oxidizing conditions (e.g.
well-aerated surface water). Likewise, arsenate can become arsenite under
reducing conditions (e.g. anaerobic groundwater). However, the conversion
in either direction is quite slow, so the reduced species can be found
in oxidized environments and vice versa. Most studies measure total arsenic
without distinction, but one study in West Bengal found equal amounts of
arsenite and arsenate. Microbes, plants, and animals can all convert these
inorganic arsenic species into organic compounds (involving carbon and
hydrogen atoms) such as monomethylarsonic acid (MMAA) and dimethylarsinic
acid (DMAA). These compounds are much less commonly found in natural waters.
The toxicity of arsenic is greatly dependent on its speciation: arsenite
is as much as sixty times more toxic than arsenate, due to its reactions
with enzymes in human metabolism. Arsenate is also significantly less mobile
in groundwater than arsenite. Organic arsenic is much less toxic than either
arsenite or arsenate.
In 1993, the World Health Organization (WHO) decreased its recommended
maximum value for arsenic in drinking water from 0.05 to 0.01 mg/l, in
light of recent epidemiological evidence linking arsenic and cancers. The
USEPA and EC are considering revising their limits, currently at 0.05 mg/l.
All of the standards are based on total arsenic content, regardless of
speciation.
Medical Aspects of Arsenic
Arsenic poisoning can happen in two ways: acute poisoning results from
ingesting a large amount of arsenic in a short time, while ingestion of
small amounts of arsenic over long time periods leads to chronic poisoning.
Arsenic tends not to accumulate in the body, but is excreted through
the kidneys. If ingested faster than it can be excreted, arsenic does accumulate
in hair and fingernails.
In Bangladesh each of the four recognized stages of arsenicosis, or
chronic arsenic poisoning, have been identified.
- Preclinical: the patient shows no symptoms, but arsenic can be detected
in urine or body tissue samples.
- Clinical: at this stage various effects can be seen on the skin. General
darkening of the skin (melanosis) is the most common symptom, often observed
on the palms. Dark spots on the chest, back, limbs, or gums have also been
reported. Oedema (swelling of hands and feet) is often seen. A more serious
symptom is keratosis, or hardening of skin into nodules, often on palms
and soles. WHO estimates that this stage requires five to ten years of
exposure to arsenic.
- Complications: clinical symptoms become more pronounced, and internal
organs are affected. Enlargement of liver, kidneys, and spleen have been
reported. Some research indicates that conjunctivitis (pinkeye), bronchitis
and diabetes may be linked to arsenic exposure at this stage.
- Malignancy: tumors or cancers (carcinoma) affect skin or other organs.
In this stage the affected person may develop gangrene or skin, lung, or
bladder cancer.
While abundant evidence links arsenic with cancer formation, it is difficult
to say what dose results in what effect. The USEPA estimates that the risk
of developing skin cancer from a lifetime of drinking contaminated water
is 5 in 100,000 per microgram/L arsenic. The required exposure times are
not well understood, and doubtless depend on concentration, but WHO estimates
that carcinoma can develop after ten to twenty years of exposure. If exposure
in Bangladesh began fifteen years ago it may be too early to detect an
increase in mortality from cancer.
In addition to the above clinical signs, arsenic poisoning can cause
weakness, loss of appetite, nausea, and diarrhoea. In the first two stages
or arsenicosis, if the patient switches to an arsenic-free source of water,
complete recovery is likely. The third stage may be reversible; the fourth
is not.
There is some evidence that providing patients with vitamins (especially
vitamin A) and an enriched diet aids in recovery. For this reason, patients
are advised to eat plenty of vegetables, especially leafy greens. However,
the top priority in treatment is to provide the patient with drinking water
free of arsenic.
Who is Doing What in Bangladesh
Arsenic was first detected in Bangladesh in 1993 by the Department of
Public Health Engineering (DPHE). Since then DPHE has been periodically
carrying out sampling of existing tubewells which are suspected of being
high in arsenic concentration. Four zonal laboratories have been set up,
in Khulna, Rajshahi, Mymensingh, and Comilla. To date 1487 wells have been
tested by the DPHE, of which 48% exceeded the WHO limit of 0.01 mg/l, and
32% exceeded the former WHO limit of 0.05 mg/L. Arsenic has been found
in 27 of the 37 districts tested. DPHE has sealed many wells due to high
arsenic content.
Recently DPHE has undertaken a project in which test wells were installed
at depths of 250-850 feet in the arsenic-affected western region of Bangladesh.
Arsenic was found in some of the deep wells, but at lower concentrations
than in adjacent shallow wells. However, in some cases arsenic levels still
exceeded WHO limits, and in some wells the groundwater is too saline for
use.
Since 1996, a large amount of research has been done by medical teams
in response to cases of skin disease. The Dhaka Community Hospital Trust
(DCH) and the National Institute for Preventative and Social Medicine (NIPSOM)
have both been very active in visiting affected areas, diagnosing cases
of arsenicosis, and verifying diagnoses with laboratory tests of tissue
and groundwater samples.
DCH has examined almost 2000 skin disease patients, identifying 825
adult and 71 adolescent cases of arsenic poisoning. They have also analyzed
3035 tubewell water samples and 1828 biological samples. Of the 2147 water
samples analyzed with atomic absorption (the most reliable technique),
45% and 26% exceeded the current and former WHO limits, respectively. The
highest concentration found was 1.625 mg/L.
DCH is actively involved in arsenic information campaigns. They have
set up arsenic information centers in Dhaka and Pabna, and conducted 'Arsenic
Camps' in twenty districts. Their doctors have trained Government and NGO
health workers in identification and treatment or arsenic poisoning. DCH
has held two national seminars, and is hosting an international arsenic
workshop to be held in Dhaka next February.
NIPSOM has also been compiling a list of people who are suffering from
various afflictions due to arsenic poisoning. The NIPSOM survey has identified
93 affected villages in 23 districts, and 1360 cases of skin lesions caused
by chronic arsenic poisoning. NIPSOM has tested 1592 tubewell samples for
arsenic with field kits. 31% showed concentrations greater than 0.01 mg/L,
and 18% greater than 0.05 mg/L. NIPSOM is also involved in public education,
including training people to use field kits.
At Jadavpur University (Calcutta) Dr. Dipankar Chakroborti has been
studying arsenic contamination in West Bengal for over ten years. He has
made several trips to Bangladesh, and participated in studies with DCH
and NIPSOM, and Rajshahi University. His research indicates that in West
Bengal, 25-30% of wells in affected areas exceed the WHO limit for arsenic.
In Bangladesh, the situation is more serious, with 55-60% of wells affected.
In West Bengal, only 40 of 37,000 tubewell samples had extremely high arsenic
content (>1.0 mg/L). In Bangladesh, 50 of 3,427 analyzed samples exceed
this concentration (60% had more than 0.01 mg/L, and 40% exceeded 0.05
mg/L). Of the 98 water samples analyzed from Dhaka, low but significant
(from 0.01 - 0.049 mg/L) arsenic concentrations were found in 11 samples.
It should be noted that these surveys were conducted in arsenic-affected
areas, and thus do not reflect average rates of arsenic incidence.
Other Research
As part of the DPHE/Dutch Government 18 District Town Project, groundwater
samples were taken from 126 wells in 18 towns in different districts of
Bangladesh. Of the 149 samples taken, 66 showed arsenic above the WHO limit.
All but two of these samples were in the southwestern part of Bangladesh
(Manikganj, Magura, Narail, Shatkira, and Meherpur).
A Japanese-sponsored team visited a village in Jessore known to be affected
and analyzed groundwater samples from all of the wells for arsenic and
other compounds. They found extremely high arsenic concentrations, with
92% of the 282 tubewells containing more than 0.05 mg/L arsenic.
The Bangladesh Water Development Board (BWDB) has analyzed several dozen
groundwater samples and is starting a collaboration with Dhaka University
to do mineralogical studies on sediments in affected areas.
The Geological Survey of Bangladesh (GSB) has measured arsenic concentrations
in several rock and mineral samples in Bangladesh.
The International Center for Diarrhoeal Disease Research, Bangladesh
(ICDDR,B) has equipment for measuring arsenic concentrations. Dr. Bilqis
Amin Hoque has tested several arsenic removal technologies at the Centre.
The Bangladesh Council of Scientific and Industrial Research is also
providing commercial arsenic testing services.
The NGO Forum for Drinking Water Supply and Sanitation has tested 153
tubewells, with 50 positive results. BRAC has also tested tubewells in
Faridpur, finding very high arsenic concentrations (up to 0.3 mg/L).
Other academic researchers from Dhaka University, Jahangirnagar University,
BUET, and Rajshahi University are involved in various arsenic-related studies.
Addressing the Issue
The Government of Bangladesh has established a high level committee
to address arsenic contamination. At the request of the Government, the
World Bank/UNDP Joint Program on Water and Sanitation has taken a position
of leadership and coordination regarding arsenic projects in Bangladesh.
According to the Government/World Bank action plan, the DPHE will be the
key agency for water and water supply issues, while NIPSOM will have responsibility
for medical surveys and treatment of patients. Both agencies will get support
from other Government bodies such as the Bangladesh Water Development Board,
Geological Survey of Bangladesh, Local Government Engineering Department,
etc... Finally, the Atomic Energy Commission will serve as the official
reference laboratory in Dhaka.
The Joint Program is also funding several emergency interventions as
part of a 'crash' program modeled after the Japanese study to target areas
already known to have severe arsenic contamination. Teams of workers from
DPHE, NIPSOM, DCH, and local NGOs will visit affected villages, and conduct
medical and tubewell surveys. At the same time, they will provide the population
with information about the hazards of arsenic in drinking water and possible
alternatives. Based on the concerns of the villagers, teams will recommend
short-term solutions such as using wells that are shown to have low levels
of arsenic (that may be inconveniently far away), rainwater catchment,
or arsenic removal. These teams will also educate people about the importance
of protein and vitamin rich diets in combating arsenicosis.
In April, the World Bank sponsored a team of geologists from the British
Geological Survey (BGS) to visit Bangladesh. This team recommended that
a 6-month technical study be done immediately to assess the situation and
identify the arsenic source. The British Department for International Development
(DFID) will fund the technical study, possibly to start as soon as July.
BGS, possibly with the help of a local consulting firm, will conduct geochemical
and hydrogeological studies, consolidating existing data and taking new
samples when necessary. These data will be used to produce maps of aquifers
and arsenic distribution in Bangladesh. This technical study will serve
as the foundation for a long-term intervention strategy for the World Bank,
if such an intervention is necessary.
The World Health Organization is cooperating with the crash program,
providing technical support in the form of new analytic equipment and chemical
supplies to strengthen the analytical capabilities of the DPHE zonal laboratories.
WHO also has provided advice regarding innovative alternative sources of
drinking water such as pond sand filters, infiltration galleries, or Ranney
(collector) wells. In some cases safe water sources are unavailable, and
WHO recommends arsenic removal as a short-term solution.
WHO is promoting a low-cost, simple arsenic removal treatment that has
been used on a large-scale in the United States. A small teabag-like packet
containing oxidizing and coagulating chemicals is placed in a large container
of water overnight. The chemicals cause solids to form and settle to the
bottom of the container, taking arsenic with them. The pure water can then
be removed, and the solids discarded. If the sludge is placed on a dung
heap, the arsenic can be converted by bacteria to a less toxic organic
form. The chemicals needed are locally available, and the packets could
be produced domestically.
UNICEF, like WHO, is working to strengthen the capacity of the DPHE
to measure arsenic concentrations. UNICEF has purchased testing equipment
for the zonal laboratories and 500 field testing kits. DPHE staff will
survey wells with the field kits, and verify positive results with laboratory
analysis.
The Royal Dutch Government is funding projects to provide safe drinking
water or treat contaminated water. Projects include drilling deep tube
wells in arsenic affected districts and the construction of an arsenic
removal treatment plant in Meherpur town. The sludge produced from the
plant will be stored in a concrete tank with a capacity lasting fifty years.
Suffering from Arsenic Poisoning: the Story
of Narayan Sil
Narayan Sil from Faridpur district, has been suffering from arsenic-related
problems for fifteen years. His body is swollen, ulcers cover his legs,
and his toes are affected by gangrene. As a result of his very visible
symptoms, he is shunned in his community, and not allowed to sit at the
village tea-stall. He is permitted to buy tea, but has to bring his own
cup and cannot stay to drink. His two young daughters are also affected
with dermatosis. Some of the village people believe that the family has
leprosy. Ironically, his wife is unscathed, although she drinks the same
water and is malnourished. This illustrates that some people are more vulnerable
to arsenic poisoning than others.
Truths About Arsenic
- Arsenic poisoning is not contagious or hereditary. You cannot get it
from even sleeping with someone.
- Arsenic poisoning is often reversible.
- Bangladesh is not alone in this problem. Many other countries have
similar problems, such as India, Taiwan, Chile, Argentina, Mexico, the
United States, China, Japan, Mongolia.
- The arsenic in groundwater does not come from telephone poles.
- The widespread arsenic contamination is not due to pesticide use. While
pesticide use is a possible source, it would not explain the regionalization,
or the finding of arsenic in deep tubewells.
- This is not Allah's curse.
|