Arsenic contamination in groundwaters in Bangladesh and options of sustainable drinking water supplies

Groundwater sources used for drinking in many parts of the world contain geogenic arsenic (As) with levels of concentrations above the drinking water guideline value of the World Health Organisation (WHO, 10 iJg L-1). Occurrence of arsenic in groundwater has been known a century ago from Argentina, where the toxic effects on public health were described already in the year 1917. However, it was not before half a century later, that the As problem achieved world interest. This was the consequence of a UNICEF program to provide the rural population of Bangladesh with microbe-free drinking water by changing the drinking water resource from surface- and rainwater to groundwater exploited from shallow aquifers. However, the quality of the groundwater was not tested for As and caused, after 10 years of exposure of large parts of the population, toxicological effects. This became the beginning of extended international aid efforts to mitigate the As problem in Bangladesh and adjacent West-Bengal, India, where many treatment methods have been developed and tested, and brought the groundwater As topic to wide scientific and public interest. Since several decades, the contamination of groundwater and to less extent of surface water by geogenic As is well known from countries such as Mexico, Chile, Peru, Taiwan and some small regions in European countries such as Hungary. Until recently, it was thought that the problem is limited to these countries. However, there were many new discoveries all over the world such as in several regions of the People's Republic of China (1993- 1996), Nicaragua (1996), Chhattisgarh, India (1999), Nepal (2000), Bolivia (2001) , Thailand (2001), Vietnam (2001), Australia (2001); Bihar, India (2002), Uttar Pradesh, India (2003), Jharkhand, India (2004), Assam, India (2004) , Myanmar (2004), Cambodia (2004), Pakistan (2005), El Salvador (2005), Ecuador (2005), Honduras (2006), Baja California State, Mexico (2006), Lao People's Democratic Republic (2006), Cambodia (2007), Manipur, India (2007), and more recently in Sumatra, Indonesia (2009) and Izmir province, Turkey (2009) (Fig. 1.1 in chapter 1 of this book)

Sediment color tool for targeting arsenic-safe aquifers for the installation of shallow drinking water tubewells

In rural Bangladesh, drinking water supply mostly comes from shallow hand tubewells installed manually by the local drillers, the main driving force in tubewell installation. This study was aimed at developing a sediment color tool on the basis of local driller's perception of sediment color, arsenic (As) concentration of tubewell waters and respective color of aquifer sediments. Laboratory analysis of 521 groundwater samples collected from 144 wells during 2009 to 2011 indicate that As concentrations in groundwater were generally higher in the black colored sediments with an average of 239μg/L. All 39 wells producing water from red sediments provide safe water following the Bangladesh drinking water standard for As (50μg/L) where mean and median values were less than the WHO guideline value of 10μg/L. Observations for off-white sediments were also quite similar. White sediments were rare and seemed to be less important for well installations at shallow depths. A total of 2240 sediment samples were collected at intervals of 1.5m down to depths of 100m at 15 locations spread over a 410km2 area in Matlab, Bangladesh and compared with the Munsell Color Chart with the purpose of direct comparison of sediment color in a consistent manner. All samples were assigned with Munsell Color and Munsell Code, which eventually led to identify 60 color shade varieties which were narrowed to four colors (black, white, off-white and red) as perceived and used by the local drillers. During the process of color grouping, participatory approach was considered taking the opinions of local drillers, technicians, and geologists into account. This simplified sediment color tool can be used conveniently during shallow tubewell installation and thus shows the potential for educating local drillers to target safe aquifers on the basis of the color characteristics of the sediments