Abstract

Md. Rafique Ullah and Shakila Rahman

Widespread arsenic contamination of groundwater has become a major concern in Bangladesh where the water supply, particularly the rural water supply in irrigation, is heavily dependent on groundwater extracted from shallow aquifers. Oxidation of sulfide minerals and release from Arsenic rich iron oxyhydroxides are the most commonly identified processes that may lead to widespread arsenic contamination of groundwater. Use of phosphate fertilizer can potentially enhance release of arsenic as a result of replacement of Arsenic by phosphate ions on the adsorption sites of iron oxyhydroxides. Arsenic may also be released from oxidation of sulfide minerals such as arsenopyrite (FeAsS) and Arsenic rich pyrite (FeS2) and this oxidation may be greatly enhanced by heavy withdrawal of groundwater and consequent lowering of groundwater label which may expose sulfide minerals to atmospheric oxygen. In the present work highly arsenic contaminated areas were identified, determined the rate of arsenic absorption by Duckweeds, determined the arsenic content in the treated groundwater, determined the effect of some astastical factors on the rate of arsenic absorption by Duckweeds. Present study shows that the aquifer layer is As containing layer. Ground water of this layer is highly contaminated having the As concentrations upto 5.0 mg/I in some area. The depth of this layer varies from locality to locality and in many localities the depth of this layer remains between 80-140 feet. People are using ground water from this depth for irrigation, domestic and also drinking purpose. The surface water in the country have As concentrations well below the toxic levels. Use of highly contaminated ground water in irrigation is very dangerous. No crops particularly rice, vegetables should grow on soils irrigated with contaminated ground water. Present As toxicity in our country is eugenic. The probable underlying process involved in the release of As from its compound to the water indicates that among many other factors, presence of iron and phosphate are influencing ingredients. So sources of these iron and phosphate should be identified. Fertilizers containing these ingredients should be used more carefully. Otherwise these ingredients would release large quantities As to the surrounding soil and ground water as well as surface water also as soon as they degrade.

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