Codeposition of Organic Carbon and Arsenic in Bengal Delta Aquifers

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• 作者：Andrew A. Meharg ; Charlie Scrimgeour ; Shahid A. Hossain ; Kenneth Fuller ; Kenneth Cruickshank ; Paul. N. Williams ; David G. Kinniburgh
• 刊名：Environmental Science & Technology
• 出版年：2006
• 出版时间：August 15, 2006
• 年：2006
• 卷：40
• 期：16
• 页码：4928 - 4935
• 全文大小：641K
• 年卷期：v.40,no.16(August 15, 2006)
• ISSN：1520-5851

文摘

We present data showing that arsenic (As) was codepositedwith organic carbon (OC) in Bengal Delta sediments asAs and OC concentrations are highly (p < 0.001) positivelycorrelated in core profiles collected from widely dispersedgeographical sites with different sedimentary depositionalhistories. Analysis of modern day depositional environmentsrevealed that the As-OC correlations observed in coresare due to As retention and high OC inputs in vegetated zonesof the deltaic environment. We hypothesize that elevatedconcentrations of As occur in vegetated wetland sedimentsdue to concentration and retention of arsenate in aeratedroot zones and animal burrows where copious iron(III)oxides are deposited. On burial of the sediment, degradationof organic carbon from plant and animal biomass detritusprovides the reducing conditions to dissolve iron(III)oxides and release arsenite into the porewater. As tubewellabstracted aquifer water is an invaluable resource onwhich much of Southeast Asia is now dependent, thisincreased understanding of the processes responsible forAs buildup and release will identify, through knowledgeof the palaeosedimentary environment, which sediments areat most risk of having high arsenic concentrations inporewater. Our data allow the development of a new unifyinghypothesis of how As is mobilized into groundwaters inriver flood plains and deltas of Southeast Asia, namely thatin these highly biologically productive environments, Asand OC are codeposited, and the codeposited OC drives Asrelease from the sediments.