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Flushing history as a hydrogeological control on the regional distribution of arsenic in shallow groundwater of the Bengal Basin.

Van Geen A, Zheng Y, Goodbred S, Horneman A, Aziz Z, Cheng Z, Stute M, Mailloux B, Weinman B, Hoque MA, Seddique AA, Hossain MS, Chowdhury SH, Ahmed KM - Environ. Sci. Technol. (2008)

Bottom Line: Whereas serious health consequences of widespread consumption of groundwater elevated in As have been documented in several South Asian countries, the mechanisms responsible for As mobilization in reducing aquifers remain poorly understood.We document here a previously unrecognized and consistent relationship between dissolved As concentrations in reducing groundwater and the phosphate-mobilizable As content of aquifer sediment for a set of precisely depth-matched samples from across Bangladesh.The relationship holds across nearly 3 orders of magnitude in As concentrations and suggests that regional as well as local patterns of dissolved As in shallow groundwater are set by the solid phase according to a remarkably constant ratio of approximately 250 microg/L dissolved As per 1 mg/kg P-mobilizable As.

View Article: PubMed Central - PubMed

Affiliation: Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA. avangeen@ldeo.columbia.edu

ABSTRACT
Whereas serious health consequences of widespread consumption of groundwater elevated in As have been documented in several South Asian countries, the mechanisms responsible for As mobilization in reducing aquifers remain poorly understood. We document here a previously unrecognized and consistent relationship between dissolved As concentrations in reducing groundwater and the phosphate-mobilizable As content of aquifer sediment for a set of precisely depth-matched samples from across Bangladesh. The relationship holds across nearly 3 orders of magnitude in As concentrations and suggests that regional as well as local patterns of dissolved As in shallow groundwater are set by the solid phase according to a remarkably constant ratio of approximately 250 microg/L dissolved As per 1 mg/kg P-mobilizable As. We use this relationship in a simple model of groundwater recharge to propose that the distribution of groundwater As in shallow aquifers of the Bengal Basin could primarily reflect the different flushing histories of sand formations deposited in the region over the past several thousand years.

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Predicteddecrease in groundwater As concentrations according to the analyticalsolution of the advection-dispersion transport model (28). The various scenarios corresponding to a range of flushingtimes, advection velocities, dispersion coefficients, and retardationfactors are described in the text. Note the logarithmic scale of distancealong the flow path.
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fig4: Predicteddecrease in groundwater As concentrations according to the analyticalsolution of the advection-dispersion transport model (28). The various scenarios corresponding to a range of flushingtimes, advection velocities, dispersion coefficients, and retardationfactors are described in the text. Note the logarithmic scale of distancealong the flow path.

Mentions: A dissolved As concentration of 1000 μg/L was selected torepresent the upper limit in Bangladesh groundwater today. The correspondingconcentration of P-mobilizable As dictated by the model is 4 mg/kgalong the entire flow path. We start by comparing the predicted distributionsof As along the flow path under the central scenario after 50, 500,and 5000 years of flushing (Figure 4). Themodel suggests that only the shallowest layers of the aquifer in anarea of recharge are significantly flushed of a portion of their Ascontent after 50 years. After 500 and 5000 years, however, As concentrationsare reduced to <10 ug/L within the first 100 and 2000 m of theflowpath, respectively. The implication is that flow-paths at thelow end of the 50−500 m range corresponding to shallow aquiferscould be significantly depleted of As by 500 years and almost entirelyso by 5000 years.


Flushing history as a hydrogeological control on the regional distribution of arsenic in shallow groundwater of the Bengal Basin.

Van Geen A, Zheng Y, Goodbred S, Horneman A, Aziz Z, Cheng Z, Stute M, Mailloux B, Weinman B, Hoque MA, Seddique AA, Hossain MS, Chowdhury SH, Ahmed KM - Environ. Sci. Technol. (2008)

Predicteddecrease in groundwater As concentrations according to the analyticalsolution of the advection-dispersion transport model (28). The various scenarios corresponding to a range of flushingtimes, advection velocities, dispersion coefficients, and retardationfactors are described in the text. Note the logarithmic scale of distancealong the flow path.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3050603&req=5

fig4: Predicteddecrease in groundwater As concentrations according to the analyticalsolution of the advection-dispersion transport model (28). The various scenarios corresponding to a range of flushingtimes, advection velocities, dispersion coefficients, and retardationfactors are described in the text. Note the logarithmic scale of distancealong the flow path.
Mentions: A dissolved As concentration of 1000 μg/L was selected torepresent the upper limit in Bangladesh groundwater today. The correspondingconcentration of P-mobilizable As dictated by the model is 4 mg/kgalong the entire flow path. We start by comparing the predicted distributionsof As along the flow path under the central scenario after 50, 500,and 5000 years of flushing (Figure 4). Themodel suggests that only the shallowest layers of the aquifer in anarea of recharge are significantly flushed of a portion of their Ascontent after 50 years. After 500 and 5000 years, however, As concentrationsare reduced to <10 ug/L within the first 100 and 2000 m of theflowpath, respectively. The implication is that flow-paths at thelow end of the 50−500 m range corresponding to shallow aquiferscould be significantly depleted of As by 500 years and almost entirelyso by 5000 years.

Bottom Line: Whereas serious health consequences of widespread consumption of groundwater elevated in As have been documented in several South Asian countries, the mechanisms responsible for As mobilization in reducing aquifers remain poorly understood.We document here a previously unrecognized and consistent relationship between dissolved As concentrations in reducing groundwater and the phosphate-mobilizable As content of aquifer sediment for a set of precisely depth-matched samples from across Bangladesh.The relationship holds across nearly 3 orders of magnitude in As concentrations and suggests that regional as well as local patterns of dissolved As in shallow groundwater are set by the solid phase according to a remarkably constant ratio of approximately 250 microg/L dissolved As per 1 mg/kg P-mobilizable As.

View Article: PubMed Central - PubMed

Affiliation: Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA. avangeen@ldeo.columbia.edu

ABSTRACT
Whereas serious health consequences of widespread consumption of groundwater elevated in As have been documented in several South Asian countries, the mechanisms responsible for As mobilization in reducing aquifers remain poorly understood. We document here a previously unrecognized and consistent relationship between dissolved As concentrations in reducing groundwater and the phosphate-mobilizable As content of aquifer sediment for a set of precisely depth-matched samples from across Bangladesh. The relationship holds across nearly 3 orders of magnitude in As concentrations and suggests that regional as well as local patterns of dissolved As in shallow groundwater are set by the solid phase according to a remarkably constant ratio of approximately 250 microg/L dissolved As per 1 mg/kg P-mobilizable As. We use this relationship in a simple model of groundwater recharge to propose that the distribution of groundwater As in shallow aquifers of the Bengal Basin could primarily reflect the different flushing histories of sand formations deposited in the region over the past several thousand years.

Show MeSH
Related in: MedlinePlus