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Fecal contamination of shallow tubewells in Bangladesh inversely related to arsenic.

van Geen A, Ahmed KM, Akita Y, Alam MJ, Culligan PJ, Emch M, Escamilla V, Feighery J, Ferguson AS, Knappett P, Layton AC, Mailloux BJ, McKay LD, Mey JL, Serre ML, Streatfield PK, Wu J, Yunus M - Environ. Sci. Technol. (2011)

Bottom Line: In this study, 125 tubewells 6-36 m deep were sampled in duplicate for 18 months to quantify the presence of the fecal indicator Escherichia coli.On any given month, E. coli was detected at levels exceeding 1 most probable number per 100 mL in 19-64% of all shallow tubewells, with a higher proportion typically following periods of heavy rainfall.The frequency of E. coli detection averaged over a year was found to increase with population surrounding a well and decrease with the As content of a well, most likely because of downward transport of E. coli associated with local recharge.

View Article: PubMed Central - PubMed

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

ABSTRACT
The health risks of As exposure due to the installation of millions of shallow tubewells in the Bengal Basin are known, but fecal contamination of shallow aquifers has not systematically been examined. This could be a source of concern in densely populated areas with poor sanitation because the hydraulic travel time from surface water bodies to shallow wells that are low in As was previously shown to be considerably shorter than for shallow wells that are high in As. In this study, 125 tubewells 6-36 m deep were sampled in duplicate for 18 months to quantify the presence of the fecal indicator Escherichia coli. On any given month, E. coli was detected at levels exceeding 1 most probable number per 100 mL in 19-64% of all shallow tubewells, with a higher proportion typically following periods of heavy rainfall. The frequency of E. coli detection averaged over a year was found to increase with population surrounding a well and decrease with the As content of a well, most likely because of downward transport of E. coli associated with local recharge. The health implications of higher fecal contamination of shallow tubewells, to which millions of households in Bangladesh have switched in order to reduce their exposure to As, need to be evaluated.

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Related in: MedlinePlus

Distribution of monitored wells including (a) a country map showing location of the two study areas, with close-ups at the same scale of (b) Char Par and small local stream and (c) six villages in Matlab and the Meghna River. Maps in (b) and (c) are on the same scale. The colored circles in the two study areas indicate the location of a total of 125 shallow (6−36 m) wells with at least 10 months of data, color-coded according to the frequency of E. coli detection in January−November. White circles show the location of households surrounding around each monitored well whose population was enumerated by surveys conducted in 2008 and 2009. In Char Para, black dots indicate the location of all wells surveyed in 2009; in Matlab, black dots correspond to wells blanket-tested for As in Matlab in 2002−2003.(18) Wells are concentrated in the villages; surrounding areas without wells typically correspond to cultivated fields. Also shown by a double black line in (c) is a flood-control embankment bisecting the study area in Matlab. Additional maps are included in the Supporting Information.
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fig1: Distribution of monitored wells including (a) a country map showing location of the two study areas, with close-ups at the same scale of (b) Char Par and small local stream and (c) six villages in Matlab and the Meghna River. Maps in (b) and (c) are on the same scale. The colored circles in the two study areas indicate the location of a total of 125 shallow (6−36 m) wells with at least 10 months of data, color-coded according to the frequency of E. coli detection in January−November. White circles show the location of households surrounding around each monitored well whose population was enumerated by surveys conducted in 2008 and 2009. In Char Para, black dots indicate the location of all wells surveyed in 2009; in Matlab, black dots correspond to wells blanket-tested for As in Matlab in 2002−2003.(18) Wells are concentrated in the villages; surrounding areas without wells typically correspond to cultivated fields. Also shown by a double black line in (c) is a flood-control embankment bisecting the study area in Matlab. Additional maps are included in the Supporting Information.

Mentions: Two densely populated and geologically comparable rural areas of Bangladesh were selected for this study (Figure 1a). The village of Char Para (23.796° N, 90.629° E) in Araihazar upazilla is located on a sand bar rising 1−3 m above surrounding fields and the meander of a small stream to the south (Figure 1b). Local recharge is likely an important factor that maintains As concentrations in shallow groundwater at generally low levels in the center of Char Para, with As concentrations increasing toward the periphery of the village.(17) Several hundred latrines scattered throughout the villages and approximately fifty ponds, many of which receive discharge from latrines, are potential sources of fecal pollution to the shallow aquifer of Char Para. In Matlab upazilla (Figure 1c), the six villages of Barahaldia (23.370° N, 90.646° E), Sardarkandi (23.352° N; 90.656° E), Shakharipara (23.356° N, 90.646° E), Farazikandi (23.360° N, 90.637° E), Namapara (23.361° N, 90.628° E), and Shankibhanga (23.370° N, 90.623° E) cover a range of depositional environments and groundwater As concentrations.(18) The rural sanitation infrastructure in the region ranges from simple septic tanks built of concrete rings to defecation directly into ponds and does not differ markedly between Araihazar and Matlab. The location of each household within the study areas was recorded with hand-held GPS units to calculate the population residing within a given distance from each monitored well (Supporting Information).


Fecal contamination of shallow tubewells in Bangladesh inversely related to arsenic.

van Geen A, Ahmed KM, Akita Y, Alam MJ, Culligan PJ, Emch M, Escamilla V, Feighery J, Ferguson AS, Knappett P, Layton AC, Mailloux BJ, McKay LD, Mey JL, Serre ML, Streatfield PK, Wu J, Yunus M - Environ. Sci. Technol. (2011)

Distribution of monitored wells including (a) a country map showing location of the two study areas, with close-ups at the same scale of (b) Char Par and small local stream and (c) six villages in Matlab and the Meghna River. Maps in (b) and (c) are on the same scale. The colored circles in the two study areas indicate the location of a total of 125 shallow (6−36 m) wells with at least 10 months of data, color-coded according to the frequency of E. coli detection in January−November. White circles show the location of households surrounding around each monitored well whose population was enumerated by surveys conducted in 2008 and 2009. In Char Para, black dots indicate the location of all wells surveyed in 2009; in Matlab, black dots correspond to wells blanket-tested for As in Matlab in 2002−2003.(18) Wells are concentrated in the villages; surrounding areas without wells typically correspond to cultivated fields. Also shown by a double black line in (c) is a flood-control embankment bisecting the study area in Matlab. Additional maps are included in the Supporting Information.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3037737&req=5

fig1: Distribution of monitored wells including (a) a country map showing location of the two study areas, with close-ups at the same scale of (b) Char Par and small local stream and (c) six villages in Matlab and the Meghna River. Maps in (b) and (c) are on the same scale. The colored circles in the two study areas indicate the location of a total of 125 shallow (6−36 m) wells with at least 10 months of data, color-coded according to the frequency of E. coli detection in January−November. White circles show the location of households surrounding around each monitored well whose population was enumerated by surveys conducted in 2008 and 2009. In Char Para, black dots indicate the location of all wells surveyed in 2009; in Matlab, black dots correspond to wells blanket-tested for As in Matlab in 2002−2003.(18) Wells are concentrated in the villages; surrounding areas without wells typically correspond to cultivated fields. Also shown by a double black line in (c) is a flood-control embankment bisecting the study area in Matlab. Additional maps are included in the Supporting Information.
Mentions: Two densely populated and geologically comparable rural areas of Bangladesh were selected for this study (Figure 1a). The village of Char Para (23.796° N, 90.629° E) in Araihazar upazilla is located on a sand bar rising 1−3 m above surrounding fields and the meander of a small stream to the south (Figure 1b). Local recharge is likely an important factor that maintains As concentrations in shallow groundwater at generally low levels in the center of Char Para, with As concentrations increasing toward the periphery of the village.(17) Several hundred latrines scattered throughout the villages and approximately fifty ponds, many of which receive discharge from latrines, are potential sources of fecal pollution to the shallow aquifer of Char Para. In Matlab upazilla (Figure 1c), the six villages of Barahaldia (23.370° N, 90.646° E), Sardarkandi (23.352° N; 90.656° E), Shakharipara (23.356° N, 90.646° E), Farazikandi (23.360° N, 90.637° E), Namapara (23.361° N, 90.628° E), and Shankibhanga (23.370° N, 90.623° E) cover a range of depositional environments and groundwater As concentrations.(18) The rural sanitation infrastructure in the region ranges from simple septic tanks built of concrete rings to defecation directly into ponds and does not differ markedly between Araihazar and Matlab. The location of each household within the study areas was recorded with hand-held GPS units to calculate the population residing within a given distance from each monitored well (Supporting Information).

Bottom Line: In this study, 125 tubewells 6-36 m deep were sampled in duplicate for 18 months to quantify the presence of the fecal indicator Escherichia coli.On any given month, E. coli was detected at levels exceeding 1 most probable number per 100 mL in 19-64% of all shallow tubewells, with a higher proportion typically following periods of heavy rainfall.The frequency of E. coli detection averaged over a year was found to increase with population surrounding a well and decrease with the As content of a well, most likely because of downward transport of E. coli associated with local recharge.

View Article: PubMed Central - PubMed

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

ABSTRACT
The health risks of As exposure due to the installation of millions of shallow tubewells in the Bengal Basin are known, but fecal contamination of shallow aquifers has not systematically been examined. This could be a source of concern in densely populated areas with poor sanitation because the hydraulic travel time from surface water bodies to shallow wells that are low in As was previously shown to be considerably shorter than for shallow wells that are high in As. In this study, 125 tubewells 6-36 m deep were sampled in duplicate for 18 months to quantify the presence of the fecal indicator Escherichia coli. On any given month, E. coli was detected at levels exceeding 1 most probable number per 100 mL in 19-64% of all shallow tubewells, with a higher proportion typically following periods of heavy rainfall. The frequency of E. coli detection averaged over a year was found to increase with population surrounding a well and decrease with the As content of a well, most likely because of downward transport of E. coli associated with local recharge. The health implications of higher fecal contamination of shallow tubewells, to which millions of households in Bangladesh have switched in order to reduce their exposure to As, need to be evaluated.

Show MeSH
Related in: MedlinePlus