Human-made ponds drive the arsenic contamination of groundwater in Bangladesh, according to a study published online this week in Nature Geoscience.

It is known that organic carbon triggers arsenic release from sediments into groundwater, but the source of this carbon has remained uncertain. Charles Harvey and colleagues modelled groundwater flow in a typical agricultural area in Bangladesh and found that human-made ponds are a key source of organic carbon. The scientists report that groundwater pumping for agriculture carries organic carbon underground, where it can trigger arsenic release.

To prevent this, they suggest that the development of artificial ponds above the wells that supply drinking water should be avoided.