Monitoring arsenic in water



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Technical Bulletin No.8

MONITORING ARSENIC IN WATER

Background
The exploitation of ground water to replace the use of surface water in the beginning of the 1970s was instrumental in reducing the incidence of water born diseases, and made an important contribution to the improvement of public health in many developing countries. Since then, the number of tube wells has been increasing. In Bangladesh alone, there are over six million wells. A more accurate figure is unavailable because the private sector has driven most of the shallow tube wells and records are incomplete.
However, the improvement in water quality has been negatively affected by the presence of arsenic in ground water. The first study that reported the existence of arsenic in ground water was published in
India in 1976. Further studies were carried out in India and neighbouring countries and raised concern among various governments, organizations and researchers.
Severe poisoning can arise from the ingestion of as little as 100mg of arsenic trioxide. Chronic effects may result from the accumulation of arsenic compounds in the body at low intake levels. Arsenite (AsIII) is many times more toxic than arsenate (AsV). The maximum level of arsenic in irrigation water recommended by the Food and Agriculture Organization (FAO) is 0.1 mg/L. The World Health
Organization (WHO) recommends that the maximum level of arsenic in drinking water should not exceed
0.01 mg/L (10 ppb). Some countries still accept the level of 0.05 mg/L (50 ppb) in their national standards. However, some studies suggest that there is a high possibility of arsenic being taken in by plants from soil or irrigation water, which eventually transfers to humans. Further studies are needed, especially surrounding the effects of arsenic on main crops and vegetables.
Occurrence
Arsenic occurs naturally in sulphide minerals such as pyrite. It is found in many countries but especially those located south of the Himalayas, such as Bangladesh, India (West Bengal), and China.
The main challenge in tackling arsenic in ground water is that it does not follow a specific pattern. For example, it can occur in one tube well and not in another one located less than 100 metres away.
Furthermore, a tube well that was previously tested to show an acceptable amount of arsenic might test non-acceptable at a later date.
It is therefore vital to test and monitor on a continual basis, with blanket coverage of all tube wells in those countries affected. It is equally important to ensure that people are made aware of the arsenic content in tube well water and promote arsenic mitigation activities.
Monitoring
Monitoring arsenic in ground water should be planned nationally, starting with random testing of tube wells throughout the country to determine the extent of the problem. Subsequently, blanket testing of all wells in selected districts should follow, to identify each and every contaminated well. Blanket testing programmes could also include other activities that are essential for additional monitoring and management operations, such as the location of each well using a Geographic Information System
(GIS), the diagnosis of arsenicosis patients in the district surveyed, and the introduction of various water treatment measures in that district.
Water testing for arsenic can either be done in a laboratory, where the water samples are delivered, or can be done using field testing kits. Each methodology has its own advantages and disadvantages that vary according to the resources available within each country.


Laboratory testing
Training of testing personnel
Standard field testing kits



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