Fact Sheet No 210
Revised May 2001
ARSENIC IN DRINKING WATER
may be found in water which has flowed through arsenic-rich rocks.
Severe health effects have been observed in populations drinking
arsenic-rich water over long periods in countries world-wide.
- Arsenic is widely distributed throughout the earth's crust.
- Arsenic is introduced into water through the dissolution of
minerals and ores, and concentrations in groundwater in some areas
are elevated as a result of erosion from local rocks.
- Industrial effluents also contribute arsenic to water in some
- Arsenic is also used commercially e.g. in alloying agents and wood
- Combustion of fossil fuels is a source of arsenic in the
environment through disperse atmospheric deposition.
- Inorganic arsenic can occur in the environment in several forms
but in natural waters, and thus in drinking-water, it is mostly
found as trivalent arsenite (As(III)) or pentavalent arsenate (As
(V)). Organic arsenic species, abundant in seafood, are very much
less harmful to health, and are readily eliminated by the body.
- Drinking-water poses the greatest threat to public health from
arsenic. Exposure at work and mining and industrial emissions may
also be significant locally.
- Chronic arsenic poisoning, as occurs after long-term exposure
through drinking- water is very different to acute poisoning.
Immediate symptoms on an acute poisoning typically include vomiting,
oesophageal and abdominal pain, and bloody "rice water"
diarrhoea. Chelation therapy may be effective in acute poisoning but
should not be used against long-term poisoning.
- The symptoms and signs that arsenic causes, appear to differ
between individuals, population groups and geographic areas. Thus,
there is no universal definition of the disease caused by arsenic.
This complicates the assessment of the burden on health of arsenic.
Similarly, there is no method to identify those cases of internal
cancer that were caused by arsenic from cancers induced by other
- Long-term exposure to arsenic via drinking-water causes cancer of
the skin, lungs, urinary bladder, and kidney, as well as other skin
changes such as pigmentation changes and thickening (hyperkeratosis).
- Increased risks of lung and bladder cancer and of
arsenic-associated skin lesions have been observed at drinking-water
arsenic concentrations of less than 0.05 mg/L.
- Absorption of arsenic through the skin is minimal and thus
hand-washing, bathing, laundry, etc. with water containing arsenic
do not pose human health risk.
- Following long-term exposure, the first changes are usually
observed in the skin: pigmentation changes, and then hyperkeratosis.
Cancer is a late phenomenon, and usually takes more than 10 years to
- The relationship between arsenic exposure and other health effects
is not clear-cut. For example, some studies have reported
hypertensive and cardiovascular disease, diabetes and reproductive
- Exposure to arsenic via drinking-water has been shown to cause a
severe disease of blood vessels leading to gangrene in China
(Province of Taiwan), known as ‘black foot disease’. This
disease has not been observed in other parts of the world, and it is
possible that malnutrition contributes to its development. However,
studies in several countries have demonstrated that arsenic causes
other, less severe forms of peripheral vascular disease.
- According to some estimates, arsenic in drinking-water will cause
200,000 – 270,000 deaths from cancer in Bangladesh alone (NRC,
1998; Smith, et al, 2000).
- Accurate measurement of arsenic in drinking-water at levels relevant
to health requires laboratory analysis, using sophisticated and
expensive techniques and facilities as well as trained staff not
easily available or affordable in many parts of the world.
- Analytical quality control and external validation remain
- Field test kits can detect high levels of arsenic but are typically
unreliable at lower concentrations of concern for human health.
Reliability of field methods is yet to be fully evaluated.
PREVENTION AND CONTROL
The most important remedial action is prevention of
further exposure by providing safe drinking- water. The cost and
difficulty of reducing arsenic in drinking-water increases as the
targeted concentration lowers. It varies with the arsenic
concentration in the source water, the chemical matrix of the water
including interfering solutes, availability of alternative sources of
low arsenic water, mitigation technologies, amount of water to be
Control of arsenic is more complex where
drinking-water is obtained from many individual sources (such as
hand-pumps and wells) as is common in rural areas. Low arsenic water
is only needed for drinking and cooking. Arsenic-rich water can be
used safely for laundry and bathing. Discrimination between
high-arsenic and low-arsenic sources by painting the hand-pumps (e.g.
red and green) can be an effective and low cost means to rapidly
reduce exposure to arsenic when accompanied by effective health
Alternative low-arsenic sources such as rain water
and treated surface water may be available and appropriate in some
circumstances. Where low arsenic water is not available, it is
necessary to remove arsenic from drinking-water:
- The technology for arsenic removal for piped water supply is
moderately costly and requires technical expertise. It is
inapplicable in some urban areas of developing countries and in most
rural areas world-wide.
- New types of treatment technologies, including co-precipitation,
ion exchange and activated alumina filtration are being
- There are no proven technologies for the removal of arsenic at
water collection points such as wells, hand-pumps and springs.
- Simple technologies for household removal of arsenic from water
are few and have to be adapted to, and proven sustainable in each
- Some studies have reported preliminary successes in using packets
of chemicals for household treatment. Some mixtures combine arsenic
removal with disinfection. One example, developed by the WHO/PAHO
Pan American Center of Sanitary Engineering and Environmental
Sciences in Lima, Peru (CEPIS), has proven successful in Latin
WHO’S ACTIVITIES ON ARSENIC
WHO’s norms for drinking-water quality go back to
1958. The International Standards for Drinking-Water established 0.20
mg/L as an allowable concentration for arsenic in that year. In 1963 the
standard was re-evaluated and reduced to 0.05 mg/L. In 1984, this was
maintained as WHO’s "Guideline Value"; and many countries
have kept this as the national standard or as an interim target.
According to the last edition of the WHO Guidelines for Drinking-Water
- Inorganic arsenic is a documented human carcinogen.
- 0.01 mg/L was established as a provisional guideline value for
- Based on health criteria, the guideline value for arsenic in
drinking-water would be less than 0.01mg/L.
- Because the guideline value is restricted by measurement
limitations, and 0.01 mg/L is the realistic limit to measurement,
this is termed a provisional guideline value.
The WHO Guidelines for Drinking-water Quality
is intended for use as a basis for the development of national standards
in the context of local or national environmental, social, economic, and
The summary of an updated International Programme on
Chemical Safety Environmental Health Criteria Document on Arsenic
published by WHO is available at http://www.who.int/pcs/ehc/summaries/ehc_224.htm#English.
It addresses all aspects of risks to human health and the environment.
The full text will be published in late 2001.
A UN report on arsenic in drinking-water has been
prepared in cooperation with other UN agencies under the auspices of an
inter-agency coordinating body (the Administrative Committee on
Coordination’s Sub-committee on Water Resources. It provides a
synthesis of available information on chemical, toxicological, medical,
epidemiological, nutritional and public health issues; develops a basic
strategy to cope with the problem and advises on removal technologies
and on water quality management. The draft of the report is available at
Information on arsenic in drinking-water on a
country-by-country basis is being collected and will be added to the UN
report and made available on the web site.
As part of WHO’s activities on the global burden of
disease, an estimate of the disease burden associated with arsenic in
drinking-water is in preparation. A report entitled "Towards an
assessment of the socioeconomic impact of arsenic poisoning in
Bangladesh" was released in 2000.
A United Nations Foundation grant for 2.5 million
approved in July 2000, will enable UNICEF and WHO to support a project
to provide clean drinking-water alternatives to 1.1 million people in
three of the worst affected sub-districts in Bangladesh. The project
utilizes an integrated approach involving communication, capacity
building for arsenic mitigation of all stakeholders at subdistrict level
and below, tube-well testing, patient management, and provision of
alternative water supply options.
- Large-scale support to the management of the problem in developing
countries with substantial, severely affected populations.
- Simple, reliable, low-cost equipment for field measurement.
- Increased availability and dissemination of relevant information.
- Robust affordable technologies for arsenic removal at wells and in
The delayed health effects of exposure to arsenic,
the lack of common definitions and of local awareness as well as poor
reporting in affected areas are major problems in determining the extent
of the arsenic-in-drinking-water problem.
Reliable data on exposure and health effects are
rarely available, but it is clear that there are many countries in the
world where arsenic in drinking-water has been detected at concentration
greater than the Guideline Value, 0.01 mg/L or the prevailing national
standard. These include Argentina, Australia, Bangladesh, Chile, China,
Hungary, India, Mexico, Peru, Thailand, and the United States of
America. Countries where adverse health effects have been documented
include Bangladesh, China, India (West Bengal), and the United States of
America. Examples are:
- Seven of 16 districts of West Bengal have been reported to have
ground water arsenic concentrations above 0.05 mg/L; the total
population in these seven districts is over 34 million (Mandal, et
al, 1996) and it has been estimated that the population actually
using arsenic-rich water is more than 1 million (above 0.05 mg/L)
and is 1.3 million (above 0.01 mg/L) (Chowdhury, et al, 1997).
- According to a British Geological Survey study in 1998 on shallow
tube-wells in 61 of the 64 districts in Bangladesh, 46% of the
samples were above 0.010 mg/L and 27% were above 0.050 mg/L. When
combined with the estimated 1999 population, it was estimated that
the number of people exposed to arsenic concentrations above 0.05
mg/l is 28-35 million and the number of those exposed to more than
0.01 mg/l is 46-57 million (BGS, 2000).
- Environment Protection Agency of The United States of America has
estimated that some 13 million of the population of USA, mostly in
the western states, are exposed to arsenic in drinking- water at
0.01 mg/L, although concentrations appear to be typically much lower
than those encountered in areas such as Bangladesh and West Bengal.
ARSENIC IN BANGLADESH
In Bangladesh, West Bengal (India) and some other
areas, most drinking-water used to be collected from open dug wells and
ponds with little or no arsenic, but with contaminated water
transmitting diseases such as diarrhoea, dysentery, typhoid, cholera and
hepatitis. Programmes to provide "safe" drinking-water over
the past 30 years have helped to control these diseases, but in some
areas they have had the unexpected side-effect of exposing the
population to another health problem - arsenic.
Arsenic in drinking-water in Bangladesh is attracting
much attention for a number of reasons. It is a new, unfamiliar problem
to the population, including concerned professionals. There are millions
of people who may be affected by drinking arsenic-rich water. Last, but
not least, fear for future adverse health effects as a result of water
- In recent years, extensive well drilling programme has contributed
to a significant decrease in the incidence of diarrhoeal diseases.
- It has been suggested that there are between 8-12 million shallow
tube-wells in Bangladesh. Up to 90% of the Bangladesh population of
130 million prefer to drink well water. Piped water supplies are
available only to a little more than 10% of the total population
living in the large agglomerations and some district towns.
- Until the discovery of arsenic in groundwater in 1993, well water
was regarded as safe for drinking.
- It is now generally agreed that the arsenic contamination of
groundwater in Bangladesh is of geological origin. The arsenic derives
from the geological strata underlying Bangladesh.
- The most commonly manifested disease so far is skin lesions. Over
the next decade, skin and internal cancers are likely to become the
principal human health concern arising from arsenic.
- According to one estimate, at least 100,000 cases of skin lesions
caused by arsenic have occurred and there may be many more (Smith, et
- The number of people drinking arsenic-rich water in Bangladesh has
increased dramatically since the 1970s due to well-drilling and
- The impact of arsenic extends from immediate health effect to
extensive social and economic hardship that effects especially the
poor. Costs of health care, inability of affected persons to engage in
productive activities and potential social exclusion are important
- The national standard for drinking-water in Bangladesh is 0.05 mg/L,
same as in India.
- District and sub-district health officials and workers lack
sufficient knowledge as to the identification and prevention of
- The poor availability of reliable information hinders action at all
levels and may lead to panic, exacerbated if misleading reports are
made. Effective information channels have yet to be established to
those affected and concerned.
- Within Bangladesh, a number of governmental technical and advisory
committees have been formed and a co-ordinating mechanism established
among the interested external support agencies. These committees
include the Governmental Arsenic Co-ordinating Committee headed by the
Minister of Health & Family Welfare (MHFW) and several technical
committees. One of the positive outcomes of this collaboration
(including work with local institutes) has been the testing of new
types of treatment technologies.
- So far, many initiatives have focused on water quality testing and
control with a view to supplying arsenic-free drinking-water, thereby
reducing the risk of further arsenic-related disease. The amount of
testing required and the need to provide effective feedback to those
using well water, suggest use of field testing kits.
- Only a few proven sustainable options are available to provide safe
drinking-water in Bangladesh. These include: obtaining low-arsenic
groundwater through accessing safe shallow groundwater or deeper
aquifers (greater than 200 m); rain water harvesting;
pond-sand-filtration; household chemical treatment; and piped water
supply from safe or treated sources.
For further information, journalists can contact :
WHO Press Spokesperson and Coordinator, Spokesperson's Office,
WHO HQ, Geneva, Switzerland / Tel +41 22 791
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