Arsenic in tubewell water of Bangladesh and approaches for sustainable mitigation

Sammanfattning: There is an urgent need for Bangladesh to identify the arsenic (As) contaminated tubewells (TWs) in order to assess the health risks and initiate appropriate mitigation measures. This involves testing water in millions of TWs and raising community awareness about the health problems related to chronic As exposure from drinking water, and providing alternative safe water option for the exposed population of the country. The use of spatial maps in a participatory context emerged as an important tool for an effective and rational distribution of alternative safe water options for the exposed population of the country. Field test kit offers the only practical tool available to screen all the TW water considering the time frame and financial resources of the country.A comparison of the field test kit results and laboratory measurements by atomic absorption spectrometry (AAS) as “gold standard” for As in water of 12,532 TWs in Matlab upazila (sub-district) in Bangladesh, indicates that the field test kit correctly determined the status of 87% of the As levels compared to the Bangladesh Drinking Water Standard (BDWS) of 50 ?g/L, and 91% of the World Health Organization (WHO) drinking water guideline value of 10 ?g/L.In order to identify the sustainable alternative safe water options, different type of safe water options were distributed in Sonargaon and Jhikargachha upazilas (sub-district) in 2001 and later revisited the options in 2004 to identify the sustainable ones. It was observed that community acceptability of the distributed options was not encouraging; less than 2% of the provided options were found to be in use. However, two new approaches emerged from people’s initiatives, which were making rapid and positive contributions to safe water coverage: switching to the existing As-safe TWs and reinstalling TWs at 50-100 m depths by looking at particular type of sediment colours.A study was conducted in Matlab upazila to validate the concept of installation/reinstallation of TWs at certain depths, a new concept promoted by local drillers (masons). The study revealed that locally a thick layer of black to grey sediments overlies an oxidized unit of yellowish-grey to reddish-brown sediments. The correlation between the colour of both units and the groundwater redox conditions was investigated to provide an easy tool for targeting low-arsenic groundwater. The water abstracted from black sediments contained high amount of As concentration but the concentration decreased towards the yeallowish to red sediments. Three boreholes verified the driller's perception of the subsurface lithologic conditions. Discrepancies between the driller's and the research team description of the sediment colours were insignificant. This study shows that sediment colour is a reliable indicator of high and low As-concentrations in TW water and can be used by local drillers to install TW.Lack of financial resources and identification of an appropriate distribution tools are some of the major obstacles to provide sustainable solution to the exposed population of the country. Spatial mapping exercise along with community participation can help maximize the safe water coverage of different alternative safe water options by reducing financial involvement. Combining people’s voice with that of spatial information gave better results and the method is already been proved useful in targeting non-served areas. Participatory Rural Appraisal (PRA) methods along with geographical information system (GIS) used in the study to obtain relevant information. Participants from different focus groups were asked to determine their ‘own priorities’ for spatial planning of alternative arsenic-safe water options. The study discusses community perspectives on demand-based safe water options and reveals the suitability of using participatory geographic information system (PGIS) technique to target non-served areas for rational distribution of safe water options.