Since the late 20th century most people in rural Bangladesh use hand pumped tube wells to extract groundwater as their primary source of water. In 1993 it was officially recognized that many of the Holocene groundwater aquifers contain elevated levels of arsenic (As) and that millions of people in Bangladesh are exposed and at risk for mass poisoning.
The need to focus efforts to areas with scarce supply of safe drinking water has raised the need to quickly locate and identify these areas. Mitigation options evaluated in this study focus on 1) how to target As safe aquifers and 2) how to identify As safe tube wells.
An attempt to target As safe shallow aquifers based on sediment color was evaluated. The majority of 30 new tube wells screened in off-white sand sediments have As safe water with respect to both the WHO and the national guideline, but including the failed attempts to target off-white sediments at shallow depths, the success rate of the method was considered to be too low.
This study also attempt to validate platform color as a rapid low-cost screening tool for As by relating platform color to water chemistry in 103 tube wells. Different classification methods were tested to develop recommendations for the future use of this method. The results showed that a simplified color classification was better than a detailed classification at predicting water chemistry of iron (Fe), manganese (Mn) and As.
Recently, Mn has also emerged as a possible widespread problem in the Bengal Basin. Although not thoroughly investigated, present evidence indicates that a high concentration of Mn in drinking water affects the intellectual function in children. The occurrence of both low As and low Mn concentrations in shallow aquifers was found to be very unlikely since only one out of 133 tested wells had this water chemistry composition.
Instead it was showed that the highest Mn concentrations occur in As-safe aquifers. Therefore WHO should consider reintroducing their previous health based guideline value for Mn to highlight the potential risk of excessive exposure, since more people risk being exposed to Mn when As-safe shallow aquifers are targeted.
Author: Gingborn, Nicklas | Wåhlén, Hanna