Groundwater Arsenic Contamination in Bangladesh

Nadiah Mohd Nordin

Erica Islas

Arsenic Contamination in Bangladesh

By the late 1980s surface water was the main source of drinking water.

Unfortunately, it was severely polluted So the government, UNICEF and a few other groups

decided that they should use groundwater as an alternative.

Ironically, the installations of tube wells triggered the naturally occurring arsenic that already existed in the earth to dissolve into the drinking water.

The arsenic that was present in the water was colorless, tasteless and odorless, therefore people did not realize that their drinking water was contaminated by arsenic until there was a widespread of people suffering from various diseases, such as warts, skin lesions, and cancers.

Causes of Arsenic Contamination in Bangladesh

Pyrite Oxidation Hypothesis Arsenic is assumed to be

present in certain sulphide minerals (pyrites) that are deposited within the aquifer sediments. Due to the lowering of water table below deposits, arseno-pyrite oxidized in the vadose zone releases arsenic as arsenic adsorbed on iron hydroxide. During the subsequence recharge period, iron hydroxide releases arsenic into groundwater. According to this hypothesis, the origin of arsenic rich groundwater is man-made, which is a recent phenomenon.

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Oxy-hydroxide Reduction Hypothesis Arsenic is assumed to be present in alluvial sediments

with high concentrations in sand grains as a coating of iron hydroxide. The sediments were deposited in valleys eroded in the delta when the stream base level was lowered due to the drop in sea level during the last glacial advance. The organic matter deposited with the sediments reduces the arsenic bearing iron hydroxide and releases arsenic into groundwater. According to this hypothesis, the origin of arsenic rich groundwater is due to a natural process, and it seems that the arsenic in groundwater has been present for thousands of years without being flushed from the delta.

Arsenic in Nature

Rock contains 1.5-2.0 milligram of arsenic per kilogram. But, in contaminated soil, concentration of arsenic may be up to 500 mg/kg.

Arsenic content of natural water may be up to 1-2 g/L. Most fruits, vegetables, meats and fishes contain arsenic; but

arsenic levels in sea water and sea fishes are higher. Sea fish may contain 5 mg of arsenic per kg weight.

An intake of 150 microgram of arsenic per day should not cause any harmful effect to human being, but very sensitive person often becomes sick with as low as 20 microgram of arsenic a day

Chemistry of Arsenic

H2AsO4- + 3H+ + 2e- H3AsO3 + H2O

In the environment, arsenic can occur in several oxidation states (-3, 0, +3, +5)

In natural waters, arsenic is mostly found in inorganic form as oxyanions of trivalent arsenite [As(lll)] or pentavalent arsenate [As(V)].

As(lll) is more toxic (40-60 times) than As(V) As(lll) exists in most natural water as As(OH)3 (pKa =

9.2) and is more mobile than As(V) because it is less strongly absorbed on most mineral surfaces than the negatively charged As(V) oxyanions (H3AsO4; pKa = 2.22, 6.98, 11.53).

However, it is widely believed that arsenate is the major water-soluble species in groundwater because arsenite is usually prevalent in anaerobic conditions.

What makes Arsenic Unique as a Contaminant?

Most toxic trace metals occur in solution as cations (e.g. Pb2+, Ni2+, Cd2+) which become insoluble as the pH increases.

However, arsenate, like most oxyanions, tend to become less strongly sorbed as the pH increases.

As a result, arsenic anions can persist in solution at relatively high concentrations (tens of g l-1) even at near-neutral pH values.

Arsenic is problematic in the environment due to its relative mobility over a wide range of natural processes, such as:

Weathering reactions Biological activity Volcanic emissions Range of anthropogenic activities

Arsenic is also distinct by becoming relatively mobile under reduced conditions. Its oxyanions can be found at concentrations in the mg l-1 range when all other oxyanion-forming elements are present in the g l-1 range. Example:

Selenium is mobile as selenate (SeO42-) oxyanion under oxidising conditions, but

immobilized under reducing conditions. Chromium behaves like other trace cations (i.e. is relatively immobile at near-

neutral pH values) under reducing environments.

Arsenicosis: Toxic Effects of Arsenic in Humans

Arsenic is a poison and its lethal dose for human is 125 milligram.

It is 4 times as poisonous as mercury. Toxicity depends on the amount of arsenic intake, which

is classified into acute, sub-acute and chronic toxicity respectively. Drinking water contamination causes the last variety of toxicity.

Most of the ingested arsenic is excreted from the body through urine, stool, skin, hair, nail and breath. In excessive intake, some amount of arsenic is deposited in tissues and inhibits cellular enzyme activities.

Almost all organs are affected; but clinical symptoms appear insidiously after 6 months to 2 years or more depending upon the amount of arsenic intake.

Arsenic Toxicity in Different Organ Systems

Organ System Problems

Skin Symmetric hyperkeratosis of palms and soles, melanosis or depigmentation, bowen's disease, basal cell carcinoma and squamous cell carcinoma.

Liver Enlargement, Jaundice, cirrhosis, non-cirrhotic portal hypertension

Nervous System Peripheral neuropathy, hearing loss

Cardiovascular System Acrocyanosis and Raynaud's Phenomenon

Hemopoietic System Megalobastosis

Respiratory System Lung Cancer

Endocrine System Diabetes mellitus and goiter

Effects on human health

Cancer Melanosis

Hyperkeratosis

PRE-CLINICAL STAGE

INITIAL STAGE

SECOND STAGE

LAST STAGE

No clinical manifestation

Melanosis, keratosis, conjunctivitis, bronchitis, gastroenteritis

Depigmentation (leucomelanosis), hyperkeratosis, non-pitting edema of legs, peripheral nephropathy, hepatopathy

Nephropathy, hepatopathy, gangrene, cancer of skin, bladder and lung

Clinical Feature of Arsenicosis observed in Bangladesh

• In Bangladesh, majority of patients are in initial and second stages

Treatment for Arsenicosis

Unfortunately there is no specific treatment for chronic arsenicosis. Stopping further intake of arsenic contaminated water and drinking arsenic-free water improves the cases.

A recent report of DCH (2000) states that chronic arsenicosis cannot be cured, but the symptoms are reversible up to certain point if a patient discontinues ingesting contaminated water.

Chelation therapy helps relief of symptoms and improves clinical manifestations. D-penicillamine (250 mg 3-4 times a day for 3 months) Dimercapto succinic acid (10 mg/kg body weight daily for 7 days followed by 10 mg/kg

body weight thrice daily for 14 days) Dimercapto procane sulphonate (100 mg 3-4 times a day every alternate weeks up to 3

such courses). Vitamins:

Vitamin A- 50,000 i.u. daily, Vitamin E- 200 mg daily and Vitamin C- 500 mg daily for adults.

Symptomatic treatments, viz. antihistamines, local ointments, etc. Nutritious diets.

If a patient crosses this threshold, he/she still needs medical assistance to save his/her life. For instance, amputation may save the life of a patient suffering from gangrene. Palliative drugs may also be administered along with micronutrient supplement.

In Bangladesh, following de-arsination methods are used:

Arsenic Removal Chemical Method Developed by the Department of Occupational and Environmental

Health of NIPSOM, which is based on the principle of iron coagulation with a pre-oxidation step. Removal of arsenic by this method is almost 99%.

Alum Method This cheap method allows 70% removal of arsenic. 300-500 grams of

alum wrapped in a clean cloth is sinked in a bucket full of arsenic contaminated water for 12 hours. Upper 2/3rd of the water is separated using decantation or two layered clean cloth. Lower third of water contains arsenic and not suitable for drinking.

Ferric oxide-manganese dioxide clay based filter columns This earthen column packed with the above substances is attached to

the tube well outlet. The method is claimed to remove significant amount of arsenic at the water flow rate of 90-110 mL/minute and the system can filter up to 5000 L of water before disposal.

Control Measures Taken by Government of Bangladesh

Short Term Programs Conduct survey to detect problem prone population group who is

drinking arsenic contaminated water. Detect arsenicoses patients Provide treatment to arsenicoses patients and ensure follow-ups. Create alternate source of drinking water in problem prone areas.

Distribute de-arsination filters and digging deep tube wells. Encourage people use alum to de-arsinate contaminated water.

Create laboratory facilities for quantitative analysis of arsenic and determine its toxicity levels in humans.

Conduct training courses for officers and staff in the health services. Conduct national survey to identify new problem prone areas. Conduct appropriate health education campaigns. Create outpatient services for detection and treatment of arsenicoses

patients throughout the country. Build communications programs with national and international

organizations for collaboration in the control measures.

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Long Term Programs Find out causes of arsenic contamination of soil water, identify sources

and take control measures. Create a Surveillance Team starting from grass-root level up to the

central level to identify, treat, follow up and conduct water-testing activities.

Establish 10-bed arsenic hospitals in the affected districts with a view to provide treatment to the complicated patients and also conduct research.

Launch a national training course for the health personnel and staff. Find out long term alternate source of safe drinking water. Launch effective water management scheme for encouraging people

ensure rational use of ground water. Include media people in the prevention of arsenic contamination

program. Develop necessary information, education and communication (IEC)

materials to enhance awareness of the people.