CHAPTER 2. BACKGROUND TO THE ARSENIC PROBLEM
Bangladesh faces multi-faceted problems in relation to
groundwater. At present there is a new threat - arsenic contamination in
groundwater. Arsenic is a shiny, grey, brittle element possessing both metallic
and non-metallic properties (Train, 1979). Arsenic compounds are ubiquitous in
nature, insoluble in water, and occur mostly as arsenides and arsenopyrites.
Arsenic exists in the trivalent and pentavalent states in nature and its
compounds may be either organic or inorganic. Trivalent inorganic arsenicals are
more toxic than the pentavalent forms both to mammals and aquatic species.
Though most forms of arsenic are toxic to humans, arsenicals have been used in
the medical treatment of spirochaetal infections, blood dyscrasias, and
dermatitis (Merck Index, 1968).
The degree of toxicity of arsenic depends on its chemical
form and speciation. Humans are exposed to arsenic mainly through ingestion and
inhalation. The World Health Organization (WHO) has recently revised its
original guideline value for arsenic in drinking water of 0.05mg/l (WHO, 1984)
to a provisional guideline value of 0.01 mg/L (WHO, 1993). The Bangladeshi
government level is 0.05 mg/l (DoE, 1991). Water with high levels of arsenic
leads to health problems such as melanosis, leuko-melanosis, hyperkeratosis,
black foot disease, cardiovascular disease, hepatomegaly, neuropathy and cancer
(Khan and Ahmad 1997). Arsenic tends not to accumulate in the body but is
excreted naturally. If ingested faster than it can be excreted, arsenic
accumulates in the hair and fingernails (Khan, 1997). The toxicity of arsenic
depends on the chemical and physical forms of the compound, the route by which
it enters the body, the dose and the duration of exposure, dietary compositions
of interacting elements and the age and sex of the exposed individuals.
As regards manifestation in a person’s body, the symptoms
of arsenic toxicity may take several months to several years. This period
differs from person to person, depending on the quantity and volume of arsenic
ingested, nutritional status of the person, immunity level of the individual and
the total time period of arsenic ingestion (DCH, 1997). Malnutrition and poor
socio-economic conditions aggravate the hazards of arsenic toxicity. Although
arsenicosis is not an infectious, contagious or hereditary disease, arsenic
toxicity creates many social problems for the victims and their families (Khan
and Ahmad, 1997).
There is a need to know more about the impact of arsenic
poisoning on human health. For instance, there is no clear understanding of why
some members of a family or community are affected, while others in the same
family or community who are subject to the same contamination are not. Early
symptoms of arsenic poisoning can range from the development of dark spots on
the skin to a hardening of the skin into nodules - often on the palms and soles.
The World Health Organization (WHO) estimates that these symptoms can take 5 to
10 years of constant exposure to arsenic to develop (DCH, 1997). Over time,
these symptoms can become more pronounced and in some cases, internal organs
including the liver, kidneys, and lungs can be affected. In the most severe of
cases, cancer can develop in the skin and internal organs, and limbs can be
affected by gangrene. While evidence exists that links arsenic to cancer, it is
difficult to say how much exposure and for what period of time, will result in
this disease.
The source of arsenic in drinking water is geological.
Arsenic occurs naturally in the sediments of Bangladesh bound to amorphous iron
oxyhydroxide. Due to the strongly reducing nature of groundwater in Bangladesh,
this compound tends to break down and release arsenic into the groundwater (Nickson
et al., 1998). Although arsenic occurs in alluvial sediments, its ultimate
origin must be 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 the 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 of
arsenic are restricted mainly to the shallow aquifer (less than 50 meters deep)
(DPHE/BGS/DFID, 2000).
However, there are lots of controversies over the origin of
arsenic in the groundwater. Indiscriminate use of agro-chemicals in the
agricultural field for higher rice production and excessive use of groundwater
for irrigation purposes i.e. oxidation process, are also some of the
alternative hypotheses for the release of arsenic in groundwater. Therefore, it
is very important to find out the exact cause in order to be able to implement
different options.
Many organizations have implemented different arsenic
programmes, most of which have focused on testing tube well water for arsenic.
The World Bank is taking the lead in co-coordinating an integrated response to the
arsenic crisis and through the Government of Bangladesh is supporting the
Bangladesh Arsenic-Mitigation Water Supply Project (BAMWSP). A key component of
the BAMWSP will be the use of community-based, demand driven projects, in which
community members play an active role in choosing and implementing solutions to
the site-specific problems of arsenic contamination.
2.1 The arsenic problem elsewhere in the world
Arsenic contamination is not unique to Bangladesh. Highly
elevated levels of arsenic of natural origin have been reported in groundwater
in many parts of the world. Arsenic poisoning due to excessive exposure to
natural and anthropogenic arsenic in drinking water has been reported in
Argentina, China, Taiwan, Thailand, India, Mexico, USA, Ghana, Hungary, United
Kingdom, Chile, New Zealand, and Russia (CSIRO, 1999). The following are brief
descriptions of the arsenic problem in each of these countries:
Argentina
In Argentina, groundwater arsenic concentration in some
places ranges from 100 to 2000 microgram/l. Reports from epidemiological studies
in Argentina indicated that 0.3mg/l arsenic in drinking water resulted in
increased incidences of hyperkeratosis and skin cancer with an increased
consumption of water (Trelles, et al., 1970).
China
According to a survey carried out in some parts of China, the
main sources of arsenic poisoning in drinking water are deep wells in basin
areas rather than shallow hand tube wells. The arsenic concentrations range as
high as 0.6 to 1.2 mg/l. The epidemiological data demonstrated the evident
association of arsenic poisoning with the arsenic concentration in drinking
water (Nie et al., 1997).
Thailand
The sources of arsenic contamination of groundwater in
Thailand are high-grade arsenopyrite waste piles and alluvial mineral deposits.
In some parts of Thailand shallow tube wells were found to be contaminated with
arsenic at concentrations of more than 5mg/l but the deeper aquifer was less
contaminated (Fordyce et al., 1995).
Taiwan
In Taiwan the groundwater arsenic problem was reported as
early as 1968 and a large number of people suffered from arsenical dermatosis.
They gave arsenicosis the name ‘black-foot disease’. Arsenic concentrations
in the tube wells ranged from 10 to 1820 microgram/liter, and 19% of the wells
had arsenic levels of over 50 microgram/liter (Hsu et al., 1997).
West Bengal
Six districts of West Bengal including 466 village and many
municipal areas were found to be contaminated with arsenic. About one million
people were drinking arsenic-contaminated water and about 200,000 people already
showed the symptom of arsenical skin lesions (Das et al., 1996).
USA
The sources of arsenic in well water in Nevada, Arizona and
California are geological, though the nature of the arsenic-enriched deposits is
as yet unknown. In Nevada, elevated concentrations of arsenic occur in several
groundwater basins, and five community water systems exceed the current 0.05mg/l
standard for the USA (Fontaine, 1994).
Mexico
In some parts of northern Mexico, chronic arsenic poisoning
is endemic, leading to changes in skin pigmentation, keratosis, skin cancer,
black-foot disease and gastro-intestinal problems. An average concentration of
0.4 mg/l of arsenic was recorded in some parts of northern Mexico (Del Razo et
al., 1994). The source of arsenic was assumed to be geological.
Hungary
In the south-eastern part of Hungary, drinking water wells
were contaminated with arsenic in concentrations high enough to pose long term
health hazard to about 0.4 million people. Arsenic pollution in Hungary was
believed to spread due to the use of pesticides containing arsenic (Halvay,
1988).
United Kingdom
Arsenic levels higher than the current Environmental
Protection Agency standard have been discovered in private wells in New England,
New Hampshire, Cornwall. A study of arsenic in surface waters in Cornwall has
shown soluble arsenic in specific catchments to range from 10 to 50 microgram/l
(Aston et al., 1975). However, extraction of surface water for processing
and distribution avoids water contaminated by past mining activities, and water
processing using aluminium hydroxide removes the majority of the soluble
arsenic. As a result arsenic in drinking water in Cornwall rarely exceeds 10
microgram/l (MAFF, 1982).
Chile
Chronic arsenic poisoning has been reported in a population
exposed to elevated concentrations of arsenic in surface waters (rivers, creeks,
lakes, etc.) used for drinking water and irrigation purposes. The sources of the
arsenic have been reported as being volcanic sediments, minerals and soils (Carceres
et al., 1992). Dermatological manifestations of arsenicism were noted in
children in Antofagasta, Chile who used a water supply containing an arsenic
concentration of 0.8 mg/l (Borgonno and Grieber, 1972).