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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
- 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 areas.
- Arsenic
is also used commercially e.g. in alloying agents and wood preservatives.
- 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.
EFFECTS
- 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 factors.
- 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 develop.
- 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.
- 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 - 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.
- 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:
- 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 field-tested.
- 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 different setting.
- 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):
- Inorganic
arsenic is a documented human carcinogen.
- 0.01
mg/L was established as a provisional guideline value for arsenic.
- 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 cultural conditions. 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. 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 - 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 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:
- 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.
(USEPA, 2001)
| Information
extracted from:
Guidelines
for drinking-water quality, 2nd
ed.
Geneva,
World Health Organization, 1996. | |
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