48. Arsenic III, V and total in canal irrigation water and transported load to rice fields of district Tando Muhammad Khan, Sindh-Pakistan

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Muhammad Chohan, Mehrunisa Memon, Inayatullah Rajpar Muhammad Saleem Akhtar


Canal irrigation water coupled with city and industrial waste can increase the arsenic levels in sub-distributary canals and transfer arsenic into associated fields, rice grain and ultimately the human food chain. The trivalent arsenite [AsO3]3− and pentavalent arsenate [AsO4]3−  (As-III and As-V) are the dominant and most toxic species in water. We investigated total and inorganic arsenic i.e. (As-III and As-V) in the irrigation water of District Tando Muhammad Khan, Sindh-Pakistan that was contaminated by different effluents and applied to rice fields. We also assessed total arsenic load transported to associated rice fields with the passage of time.  Atomic Absorption Spectrometer equipped with Hydride Vapor Generation Assembly was employed to determine arsenic in water. The inorganic As-III fraction (4.21-51.47 µg L-1) was dominant over As-V (3.03-36.68 µg L-1). Three out of twenty four rice irrigation sites were above the prescribed limits of 50 µg L-1 for irrigation by World Health Organization (WHO).  High concentration of total arsenic (102.18 µg L-1) was due to arsenic coming from city (28.78 µg L-1), animal (26.76 µg L-1), cement factory,  textile mills (31.42 µg L-1) and sugar industries (36.24 µg L-1) entering at Hyderabad and Tando Muhammad Khan. The water usage of 1000-1300 mm a-1 will transport 0.065-0.085 mg kg-1 of As-III, 0.045-0.058 mg kg-1 of As-V and 0.12-0.16 mg kg-1 of total arsenic per year in rice fields. Currently, these values are below the prescribed limit of 50 mg kg-1 for soils, however, can accumulate more in coming decades.

Keywords: Akram; As-III; As-V; Fuleli; Indus river



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