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Microbes release arsenic in groundwater



A team of international researchers, including a Bangladeshi, has made a breakthrough in identifying the process responsible for arsenic contamination of groundwater in Bangladesh. They came to the conclusion that microscopic organisms that get their energy by inhaling metals under the ground play a key role in the arsenic poisoning of drinking water, a phenomenon that endangers the health of tens of millions of people throughout the country.

The research summary has been published in the current issue of the international science magazine Nature under the title ‘Role of metal-reducing bacteria in arsenic release from Bengal delta sediments’. John Lloyd, a microbiologist of the University of Manchester, led the seven-member research team, which includes Farhana S Islam, a Bangladeshi PhD student.

Dr. MA Aziz, a member of the Bangladesh Atomic Energy Commission, who carried out extensive research on “absorption of arsenic by azola plant”, thanked the researchers for their contribution and hoped that their efforts might help to reduce arsenic contamination in the country’s groundwater. The researchers described the result of their research as a breakthrough and said it can help identify areas that are at risk and could eventually lead to ways of cleaning up contaminated water. According to the research, bacteria are responsible for the release of arsenic into water from the surrounding earth. The microbes gain energy by changing the chemistry of minerals containing both iron and arsenic and release the arsenic into the water as a by-product of the reaction.

Without such bacterial activity, the arsenic would remain in an insoluble form and thus be unable to contaminate the water. “This research means we now have a much better idea of how arsenic is released into drinking water and aquifers in the region,” says Farhana, who is the leading author of the study.

“When we found maximum rates of arsenic mobilisation, we found signs of known metal-reducing bacteria including a commonly found iron-reducing bacterium,” said John Lloyd. Metal-reducing bacteria “breathe” metals such as iron to get energy from their food, in the same way that humans breathe oxygen to break down our food. The bacteria breathe by passing electrons onto metals, which changes the characteristics of the metals. Scientists refer to this as metal reduction. The researchers collected earth samples at a depth of 13 metres from a site in West Bengal known to have relatively high concentrations of arsenic in the water. The samples were mixed with groundwater in a laboratory and exposed to a range of biological, geological and chemical factors. The scientists found that arsenic was only released from the earth samples in the absence of oxygen, and that the presence of organic matter — derived from decaying animal and plant life — enhanced this process.

This is because the bacteria’s ability to gain energy from surrounding minerals is influenced by the quantity of carbon (which all organic matter contains) present. This conclusion reinforces speculation that human activities that increase the amount of organic matter underground — such as irrigation pumping, during which water drawn from below the ground is replaced by water containing organic matter seeping down from above — may promote the release of arsenic into groundwater.

According to the researchers, the suggested link between iron and arsenic means that some of the processes at work could be reversed. For example, one way of treating contaminated water could be to add air to it for a suitable period of time prior to drinking. This could reverse the release of arsenic and reform an insoluble mineral that could be removed by a simple filter.

So far the researchers have estimated that about two-thirds of the population in the country are at risk of chronic arsenic poisoning. For the past decade, research teams from around the world have tried to determine why arsenic is present in such high concentrations in the aquifers in Bangladesh and West Bengal. The researchers now have started to believe that the latest research would help them identify areas of high risk and develop appropriate remedial strategies.

Source: Kazi Shamsul Amin, Weekly Holiday, February 2005

Kalyani scientists trace arsenic roots

The cause has been traced. Scientists and researchers from the state’s Kalyani University and Manchester University in the UK claim to have identified the process responsible for contaminating groundwater with the deadly toxic chemical, arsenic. The toxic agent has been solely responsible for killing millions, which the WHO states is the worst mass poisoning in history. A team of scientists from Kalyani University and Manchester University has discovered the cause of one of the biggest humanitarian disasters to hit the Third World and also discovered probable method of cleansing it. The breakthrough research was done in a joint collaboration between the Earth Science Department of the University of Manchester and the Chemistry department of Kalyani University and samples were collected from Lalpur in West Bengal. The research was named as “Role of Metal Reducing Bacteria in Arsenic Release from Bengal Delta Sediment” . According to the research which was published in the 1 July issue of Nature, bacteria are responsible for the release of arsenic into water from surrounding earth. The microbes gain energy by changing the chemistry of minerals containing both iron and arsenic, and release the arsenic into the water as a by-product of the reaction. Without such bacterial activity, the arsenic would remain in an insoluble form, and thus be unable to contaminate the water.

“This research means we now have a much better idea of how arsenic is released into drinking water and aquifers in the region. We used the microcosm (micro organism) based approach in the investigation. Micro biologists and molecular ecologists were involved in the study,” says Prof. Debashish Chatterjee of Chemistry department of KU who was a part of the research. “The results will help to inform ways of (detoxifying) the water, leading to a healthier supply for thousands of people,” Prof Chatterjee added. The researchers collected earth samples at a depth of 13 metres from Lalpur village in Chakdah, Nadia. During the two-year study, largely conducted in a university laboratory in Oxford Road, Manchester, samples were mixed with groundwater in a laboratory and exposed to a range of biological, geological and chemical factors.

The scientists found that arsenic was only released from the earth samples in the absence of oxygen, and that the presence of organic matter — derived from decaying animal and plant life — enhanced this process. This is because the bacteria’s ability to gain energy from surrounding minerals is influenced by the quantity of carbon (which all organic matter contains) present. This conclusion reinforces speculation that human activities that increase the amount of organic matter underground — such as irrigation pumping, during which water drawn from below ground is replaced by water containing organic matter seeping down from above — may promote the release of arsenic into groundwater.

According to the researchers, the suggested link between iron and arsenic would mean that some of the processes at work could be reversed. For example, one way of treating contaminated water could be to add air to it for a suitable period of time prior to drinking. This could reverse the release of arsenic and reform an insoluble mineral that could be removed by a simple filter. Following the study, out today, the team believes reversing the process could control pollution and one simple way of doing this is by bubbling air through the water.

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