Natural arsenic in groundwater of Indus delta in the province of Sindh, Pakistan

摘要

The worst arsenic-affected parts of Pakistan lie in the lower Indus basin of Sindh province. Twenty four out of 41 groundwater samples collected from both shallow and deep wells of Tando Allayar and Tando Mohammad Khan districts are contaminated with arsenic ranging from 10 to 500 μg/L. This area is one of the most fertile parts of Indus deltaic flood plains, mostly cultivated by rice, sugarcane and vegetables depending on extensive groundwater irrigation. About half of these wells are also sewage impacted. Local unlined sanitation is also responsible for contamination of water resources and increased As toxicity in the area. The pH of As-enriched.but sewage free groundwater samples ranges from 6.8 to 8.1 with high bicarbonate content (110 to 520 mg/L) indicating the weathering of carbonate and degradation of organic matter under local reducing conditions.