An international team of researchers has used cutting-edge computer modelling to investigate how different types of bacterial activities can influence the rate at which arsenic moves in groundwater systems.  

"Our research showed that, instead, the bacteria supported the formation of highly-mobile forms of arsenic."

Dr James Jamieson

Professor Henning Prommer, from The University of Western Australia ’s School of Earth Sciences, said that on a global scale arsenic was widely considered as the main groundwater pollutant threatening drinking water resources and therefore the health of hundreds of millions of people.

This is particularly the case in the lowlands of the large river systems in South and Southeast Asia.

“Since the magnitude of the arsenic problem was discovered two decades ago, many of the world’s leading groundwater scientists have collaborated to uncover the mysterious origin of the problem and how it could possibly be mitigated,” Professor Prommer said.

The study’s lead author, Dr Athena Nghiem, from Columbia University in the US, said most previous research suggested that understanding the behaviour of iron oxide minerals could be key to establishing how fast arsenic could move in groundwater systems used for drinking water supplies in countries such as Bangladesh, Vietnam and Cambodia.

“In a bid to lower exposure to arsenic contamination in groundwater, people started to use ‘safer’ aquifers that contained more oxidized iron minerals, as these were thought to absorb the arsenic and prevent its release into the groundwater,” Dr Nghiem said.

However, after conducting novel field experiments in Bangladesh that provided a comprehensive and unique data set, the research team was surprised to find that sulphate-reducing bacteria could play a previously unrecognised role in arsenic mobility.

Dr James Jamieson from UWA’s School of Earth Sciences said the team used process-based computer modelling as a forensic tool to test a wide range of hypothesis on what could explain the field observations, until all the pieces of the puzzle fitted together.

“While sulphate-reducing bacteria had been suggested as a way to slow down the migration of arsenic in polluted aquifers and had even been presented as a groundwater remediation strategy, our research showed that, instead, the bacteria supported the formation of highly mobile forms of arsenic,” he said.

The study found that while water managers in affected regions had shifted to install wells for drinking and irrigation water supply in deeper aquifer zones, which were typically rich in iron-oxides and therefore thought to be protected from the intrusion of arsenic polluted water, innovative new solutions were required to safeguard population health.

The results of the study have been published in the latest edition of Nature Water.