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Arsenic in Drinking Water
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 World
Health Organization
Fact sheet N°210
Revised May 2001
Arsenic in
drinking water
Arsenic 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.
Source
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Arsenic is widely distributed throughout the earth's crust.
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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.
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Industrial effluents also contribute arsenic to water in some areas.
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Arsenic is also used commercially e.g. in alloying agents and wood
preservatives.
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Combustion of fossil fuels is a source of arsenic in the environment
through disperse atmospheric deposition.
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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.
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Drinking-water poses the greatest threat to public health from
arsenic. Exposure at work and mining and industrial emissions may also
be significant locally.
Effects
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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.
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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 factors.
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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).
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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.
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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 develop.
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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 effects.
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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).
Measurement
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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
problematic.
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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 treated, etc.
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 education.
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:
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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.
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New types of treatment technologies, including co-precipitation, ion
exchange and activated alumina filtration are being field-tested.
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There are no proven technologies for the removal of arsenic at water
collection points such as wells, hand-pumps and springs.
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Simple technologies for household removal of arsenic from water are
few and have to be adapted to, and proven sustainable in each different
setting.
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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 America.
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 Quality (1993):
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Inorganic arsenic is a documented human carcinogen.
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0.01 mg/L was established as a provisional guideline value for
arsenic.
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Based on health criteria, the guideline value for arsenic in
drinking-water would be less than 0.01mg/L.
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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 cultural conditions.
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/pubs/pub_ehc_num.html. 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
http://www.who.int/water_sanitation_health/dwq/arsenic3/en/
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.
Urgent
requirements
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Large-scale support to the management of the problem in developing
countries with substantial, severely affected populations.
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Simple, reliable, low-cost equipment for field measurement.
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Increased availability and dissemination of relevant information.
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Robust affordable technologies for arsenic removal at wells and in
households.
Global situation
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:
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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).
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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).
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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. (USEPA, 2001)
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 already consumed.
Background
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In recent years, extensive well drilling programme has contributed
to a significant decrease in the incidence of diarrhoeal diseases.
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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.
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Until the discovery of arsenic in groundwater in 1993, well water
was regarded as safe for drinking.
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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.
Situation
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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.
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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
al, 2000).
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The number of people drinking arsenic-rich water in Bangladesh has
increased dramatically since the 1970s due to well-drilling and
population growth.
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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
factors.
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The national standard for drinking-water in Bangladesh is 0.05 mg/L,
same as in India.
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District and sub-district health officials and workers lack
sufficient knowledge as to the identification and prevention of arsenic
poisoning.
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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.
Remedial actions
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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.
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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.
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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.
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Reference:
"Arsenic in Drinking Water," World
Health Organization.
July 2, 2004. <http://www.who.int/mediacentre/factsheets/fs210/en/print.html>.
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