U.S. scientists including researchers from the Lawrence Livermore National Laboratory say those natural processes predate any recent human activity such as intensive pumping of groundwater.
Bacterial respiration of organic carbon releases naturally occurring arsenic from sediment into groundwater, they report in the Proceedings of the National Academy of Sciences.
For their study, the scientists developed a method to filter, extract and purify DNA from groundwater aquifers for radiocarbon analysis to determine the organic carbon sources fueling microbial reduction.
The radiocarbon signature of DNA is a direct measure of the carbon used during microbial respiration and growth, they said.
The carbon has flowed into the aquifer over hundreds to thousands of years, suggesting recent human activities, such as intensive groundwater pumping, have not yet significantly affected the release of arsenic into the groundwater, the researchers said.
Millions of people in Bangladesh and neighboring countries are continually exposed to arsenic-contaminated groundwater, which can cause skin lesions and increase the risk of certain cancers.
The study results may help explain the causes of arsenic contamination in the region help in the development of potential mitigation strategies, the researchers said.