Arsenic contamination status in the Holocene alluvial aquifers of Indus Deltaic Flood Plain: a case study of Tando Ghulam Hyder Taluka, Sindh, Pakistan

Tando Ghulam Hyder Taluka is part of Tando Muhammad Khan district which is reported as worst arsenic (As) affected part of Indus deltaic plain. Study area is an agricultural land where wheat, rice, cotton, sugarcane and banana plantations are common. Twenty four groundwater samples were randomly collected at very shallow depth (4.5-24 meters) from hand pump wells. All samples were analyzed to determine their physicochemical and microbiological constituents including arsenic. Groundwater is mostly saline (mean TDS: 1192 mg/L) containing arsenic or microbial contaminants as major source of pollution. Seven out of total 24 samples are contaminated with arsenic (10 to 300 μg/L). About one fifth of total collected samples were found sewage impacted but arsenic free. The pH of all arsenic contaminated samples is alkaline (pH: 7.1 to 7.7) coupled with elevated bicarbonate contents (140-370 mg/L) indicating organic matter as a source of arsenic which is being decomposed under local reducing conditions. Arsenic shows strong correlation with phosphate (r2 = 0.8) suggesting fertilizer as other source of arsenic.