It's only natural: Researchers find link to arsenic-contaminated groundwater

Mar 04, 2013 by Anne M Stark
Lawrence Livermore helps find link to arsenic-contaminated groundwater
Hand pump at a community well of a sampling site in Bangladesh.

(Phys.org) —Human activities are not the primary cause of arsenic found in groundwater in Bangladesh.

Instead, a team of researchers from Lawrence Livermore National Laboratory, Barnard College, Columbia University, University of Dhaka, Desert Research Institute and University of Tennessee found that the arsenic in groundwater in the region is part of a natural process that predates any recent , such as intensive pumping.

The results appear in the March 4 edition of the .

Millions of people in Bangladesh and neighboring countries are chronically exposed to arsenic-contaminated groundwater, which causes and increases the risk of certain cancers. Bacterial respiration of organic carbon releases naturally-occurring arsenic from sediment into groundwater, but the source of this organic carbon remains unclear.

Lawrence Livermore helps find link to arsenic-contaminated groundwater
Sampling site in Bangladesh where thousands of liters of ground water were passed through filters to collect bacteria for DNA dating.

Brian Mailloux of Barnard College and his team isolated from several depth intervals in arsenic-contaminated in Bangladesh and analyzed the DNA's radiocarbon signature, which reflects whether the organic carbon used by the microbes derives primarily from younger, surface-derived sources that are transported by groundwater into the aquifers, or older, sediment-derived sources.

Using "bomb pulse" radiocarbon analysis, Lawrence Livermore scientist Bruce Buchholz dated the DNA of groundwater bacteria. He found that the were consistently younger than the sediment, suggesting that the microbes favor using surface-derived carbon.

The surface-derived carbon has flowed into the aquifer over hundreds to thousands of years—a rate that is approximately 100 times slower than groundwater flow. The results suggest that recent human activities, such as intensive groundwater pumping, have not yet significantly affected the release of arsenic into the groundwater at this site.

Above-ground testing of nuclear weapons during the Cold War (1955-1963) caused a surge in global levels of carbon-14 (14C), and remains in all living things. Carbon-14 or radiocarbon is naturally produced by cosmic ray interactions with air and is present at low levels in the atmosphere and food. Although nuclear weapon testing was conducted at only a few locations, excess levels of 14C in the atmosphere rapidly dispersed and equalized around the globe.

According to Buchholz, "The bomb curve forms a chronometer of the past 60 years."

The radiocarbon signature of DNA is a direct measure of the carbon used during microbial respiration and growth. In this study, the team developed a method to filter, extract and purify DNA from aquifers for radiocarbon analysis to determine the pools fueling microbial reduction.

"We were able to separate the recent bomb pulse from the natural carbon signature and found the arsenic levels are now directly tied to a natural process as opposed to being driven by human activities," Buchholz said.

The results may help scientists understand the causes of arsenic contamination in the region, and the development of potential mitigation strategies.

Explore further: US delays decision on Keystone pipeline project

More information: "Advection of surface-derived organic carbon fuels microbial reduction in Bangladesh groundwater," by Brian J. Mailloux et al. PNAS, 2013.

Related Stories

Putting teeth into forensic science

May 19, 2010

In a large natural disaster, such as the Haitian earthquake earlier this year, or in an unsolved homicide case, knowing the birth date of an individual can guide forensic investigators to the correct identity ...

Tracing arsenic threat to groundwater

Mar 29, 2012

In the driest inhabited continent on earth, underground water accounts for a large portion of Australia’s most precious resource – freshwater.

Recommended for you

US delays decision on Keystone pipeline project

Apr 18, 2014

The United States announced Friday a fresh delay on a final decision regarding a controversial Canada to US oil pipeline, saying more time was needed to carry out a review.

New research on Earth's carbon budget

Apr 18, 2014

(Phys.org) —Results from a research project involving scientists from the Desert Research Institute have generated new findings surrounding some of the unknowns of changes in climate and the degree to which ...

User comments : 0

More news stories

China says massive area of its soil polluted

A huge area of China's soil covering more than twice the size of Spain is estimated to be polluted, the government said Thursday, announcing findings of a survey previously kept secret.

UN weather agency warns of 'El Nino' this year

The UN weather agency Tuesday warned there was a good chance of an "El Nino" climate phenomenon in the Pacific Ocean this year, bringing droughts and heavy rainfall to the rest of the world.

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...