Millions of people around the world, particularly in southern and southeastern Asia, are exposed to drinking and irrigation water contaminated with arsenic. Now, it appears that the poison gets into groundwater largely through the action of bacteria residing in aquifer sediments.
Jonathan Lloyd at the University of Manchester in England and his colleagues discovered that mechanism while analyzing sediments collected from a contaminated aquifer in West Bengal, India. The researchers mixed the sediments with arsenic free water and incubated the samples for several weeks. Over that period, the team detected a rising concentration of arsenic in the water.
Further analyses revealed that bacteria in the sediments caused the change. As the bacteria respire, they obtain energy by transferring electrons to arsenic attached to sedimentary grains. In its changed chemical state, arsenic detaches from the sediments and enters the groundwater.
The researchers report in the July 1 Nature that they have also simulated the influence of organic compounds on the process. They found that acetate added to the sediments enhanced the release of arsenic. Lloyd’s group is now investigating how to reverse or even halt the arsenic-releasing mechanisms.