However, the cause of carbon in the silt, which led to the release of arsenic, was still unknown until now. Another research team from Massachusetts Institute of Technology has now found that the likely cause are man-made ponds. These man-made ponds are excavations which have filled with rainwater.
Scientific American reports: "Using a six-square-mile test plot, they found that the organic carbon comes from shallow ponds that were dug to provide soil for flood protection. The carbon compounds sink in the pondwater and seep underground where bacteria digest them, setting up the perfect chemical conditions to free up the soil’s arsenic. Groundwater flow then brings the arsenic-rich water to the wells."
The team also suggested two methods which might help in reducing the problem — digging deeper wells that go below the influence of the ponds, and using wells that retrieve water from beneath rice paddies, which the team found to be less toxic than other wells.
The cause of arsenic poisoning has been a puzzle for many years now. While solving the problem of arsenic poisoning in Bangladesh is complex and will take a lot of resources and effort, these findings will go a long way in finding a permanent solution to this calamity that is affecting an entire nation.