Serious Arsenic Problem in Groundwater: Bangladesh

An example of a very serious arsenic problem in groundwater is that of Bangladesh. The issue there is related to high rates of groundwater extraction through shallow wells in conjunction with shallow groundwater pollution that caused anoxia at shallow depth (see Fig. 5). The arsenic is associated with the anoxic zone which has been tapped by hundreds of thousands of shallow "tube wells" since the 1980s (Fig. 4), an innovation that saved millions from potential disease, including death by cholera, associated with getting their water from shallow pits. Ultimately, the new deeper water source began poisoning them with arsenic (Bhattacharjee, et al., 2007, Science 315, p.1659) liberated from iron oxides that were "reduced" under anoxic conditions, thereby liberating adsorbed As into dissolved form in the groundwater.

Pipe spewing water into a stone basin with a child standing in it

Figure 4. Tube well emptying into an open reservoir. Replacement of shallow tube wells in the 1980s with wells that draw from deeper reservoirs reduced the risk of disease, but unintentionally tapped into arsenic-contaminated anoxic deep aquifers.

Source: Wikipedia

A pit with people in it. Clay on the top half of pit is red (oxidation) and the bottom half is grey (reduction)

Figure 5. A pit in Bangladesh illustrating the oxidation (red)/reduction (gray) front in the subsurface. Note that As concentrations in water>10ppm are considered toxic to humans.

Source: USGS International Program.