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Abstract
Temporal and seasonal variability of As concentrations in groundwater were evaluated in As-affected areas of Matlab, southeastern Bangladesh. Groundwater samples from 61 randomly selected tubewells were analyzed for As concentrations over a period of three years and four months (from July 2002 to November 2005) and monitored seasonally (three times a year). The mean As concentrations in the sampled tubewells decreased from 153 to 123 μg/L during July 2002 to November 2005. Such changes were pronounced in tubewells with As concentration >50 μg/L than those with As concentrations <50 μg/L. Similarly, individual wells revealed temporal variability, for example some wells indicated a decreasing trend, while some other wells indicated stable As concentration during the monitoring period. The mean As concentrations were significantly higher in Matlab North compared with Matlab South. The spatial variations in the mean As concentrations may be due to the differences in local geological conditions and groundwater flow patterns. The variations in mean As concentrations were also observed in shallow (<40 m) and deep (>40 m) wells. However, to adequately evaluate temporal and seasonal variability of As concentration, it is imperative to monitor As concentrations in tubewells over a longer period of time. Such long-term monitoring will provide important information for the assessment of human health risk and the sustainability of safe drinking water supplies.
Acknowledgments
This study was conducted at the ICDDR, B: Centre for Health and Population Research in collaboration with Bangladesh Rural Advancement Committee (BRAC) with the support of Swedish International Development Cooperation Agency (Sida) through the financial support for the AsMat project (dnr: U11 BB/1.5.5-3, 1998-05440 and U11 BB/1.5.5-3/A) and subsequently evaluation of the database was carried out under the action research project Sustainable Arsenic Mitigation (SASMIT) (Sida Contribution 73000854). The authors also thank field workers for their assistance with the seasonal water sampling program. We deeply appreciate the constructive comments of M. Alauddin, Wagner College, Staten Island, USA and three anonymous reviewers on the earlier drafts of this manuscript.
