Arsenic removal efficiencies of 43 household sand filters were studied in rural areas of the Red
River Delta in Vietnam. Simultaneously, raw groundwater from the same households and additional 31
tubewells was sampled to investigate arsenic coprecipitation with hydrous ferric iron from solution, i.e.,
without contact to sand surfaces. From the groundwaters containing 10-382 ?g/L As, 99%, 90%, and 71%,
respectively. The concentration of dissolved iron in groundwater was the decisive factor for the removal of
arsenic. Residual arsenic levels below 50 ?g/L were achieved by 90% of the studied sand filters, and 40%
were even below 10 ?g/L. Fe/As ratios of ?50 or ?250 were required to ensure arsenic removal to levels
below 50 or 10 ?g/L, respectively. Phosphate concentrations >2.5 mg P/L slightly hampered the sand filter
and coprecipitation efficiencies. Interestingly, the overall arsenic elimination was higher than predicted from
model calculations based on sorption constants determined from coprecipitation experiments with artificial
groundwater. This observation is assumed to result from As(III) oxidation involving Mn, microorganisms,
and possibly dissolved organic matter present in the natural groundwaters. Clear evidence of lowered arsenic
burden for people consuming sand-filtered water is demonstrated from hair analyses. The investigated sand
filters proved to operate fast and robust for a broad range of groundwater composition and are thus also a
viable option for mitigation in other arsenic affected regions. An estimation conducted for Bangladesh
indicates that a median residual level of 25 ?g/L arsenic could be reached in 84% of the polluted
groundwater. The easily observable removal of iron from the pumped water makes the effect of a sand filter
immediately recognizable even to people who are not aware of the arsenic problem. ?? 2006 American
Chemical Society.
