Study detects Bangladesh’s
mass arsenic poisoning source
Agence France-Presse . Paris
Researchers have pinpointed the source of what is probably the worst mass poisoning in history, according to a study published Sunday.
For nearly three decades scientists have struggled to figure out exactly how arsenic was getting into the drinking water of millions of people in rural Bangladesh.
The culprit, says the new study, are tens of thousands of man-made ponds excavated to provide soil for flood protection.
An estimated two million people in Bangladesh suffer from arsenic poisoning, and health experts suspect the toxic, metal-like element has caused – and will continue to cause – many deaths as well.
Symptoms include violent stomach pains and vomiting, diarrhoea, convulsions and cramps. A large dose can kill outright, while chronic ingestion of small doses has been linked to a large range of cancers.
It has long been known that the arsenic comes from water drawn from millions of low-tech ‘tube wells’ scattered across the country.
Ironically the wells were dug – often with the help of international aid agencies – to protect villages from unclean and disease-ridden surface water.
Tragically, millions of people continue to knowingly poison themselves for lack of an alternative source of water.
Earlier studies succeeded in filling in a few pieces of the deadly puzzle.
They showed that water with the highest concentrations of arsenic is roughly 50 years old, and that the organic carbon which, once metabolised by microbes causes the poison to leach from sediment, does not take long to filter down from the surface.
But the source of both the contaminated water and the organic carbon remained unknown until a team of researchers led by Charles Harvey of MIT in Boston, Massachusetts cracked the secret.
Working in the Munshiganj, the researchers analysed the flow patterns of surface and underground water in a six square-mile area.
They used natural tracers and a 3-D computer model to track water from rice fields and ponds, and tested the capacity of organic carbon in both settings to free up arsenic from soil and sediments.
‘We saw that water with high arsenic content originates from the human-built ponds, and water with lower arsenic content originates from the rice fields,’ said Rebecca Neumann, a co-author and postdoctoral associate at Harvard.
Chemical analysis showed that the organic compound that unleashes the poison first settles on the bottom of the ponds and then slowly seeps into the ground.
The findings, published in Nature Geoscience, ‘suggest that the problem could be alleviated by digging deeper drinking water wells below the influence of the ponds, or by locating shallow drinking wells under rice fields,’ Neumann said in a communique.
The same team of researchers plan to dig such wells in different region to see whether it leads to improved health for villages.
Scott Fendorf, a professor at Stanford University who studies arsenic content in soils and sediments along the Mekong River in Cambodia, said the new study was clearly a breakthrough.
‘It shows that human modifications are impacting the arsenic content in the groundwater,’ he said in a statement. ‘The ponds … are having a negative impact on the release of arsenic.’
I think the interpretation of the research outcome in your post is misleading. I didn’t have a chance to read the article but the abstract clearly depicts the findings.
You can read the abstract here: http://www.nature. com/ngeo/ journal/vaop/ ncurrent/ pdf/ngeo685. pdf
The source of arsenic in Bangladesh and many other parts of the world is the minerals in our soil. Arsenic was bound to the minerals and those mineral containing sediments were carried down through the rivers and build this delta. Therefore, we have been living on this arsenic containing ground for thousands of years!
Arsenic was strongly bound to the minerals, but in recent past due to some anthropogenic reasons the chemical composition of those minerals has been changed, leading to a release of those arsenic to groundwater. This article points out the new findings about the reasons that trigger that chemical changes.
There were several hypothesis to explain this trigger. The first one is the oxidation theory by Prof. Dipankar Chakrabarty of Jadhabpur university, which says that due to increased irrigation, the groundwater table falls exposing the minerals to atmospheric oxygen leading to oxidation and release of arsenic from minerals.
But research in Bangladesh (by DPHE, BGS; the mentioned team of Prof. Charles Harvey; Me) shows that in almost all the cases, polluted groundwater has negative ORP values, which indicates a reducing condition. The question was the source of the reducing condition and they have found a source.
But in this connection my favorite hypothesis is the green revolution theory. Arsenic is removed from mine wastes by running phosphate containing water through it. Arsenic and phosphate have similar properties (being in the same column in periodic table) but P is more active than arsenic and it easily replaces arsenic from a compound, making it (As) mobile. Now, if we look to our situation, we use TSP (Triple Super Phosphate) fertilizer in our fields. The application rate of fertilizer for rice production is much higher in Bangladesh than from the same in Japan. To my judgment, a considerable part of that phosphate may leach into the ground and can trigger arsenic release, though I have no data in this regard.
Your mentioned research finding is interesting, and I really would like to know about the phosphate situation in the Munshigonj site. Fortunately, I had a chance to visit the site, used for this research, and my teachers (Prof. Badruzzaman and Prof. Ashraf Ali) are a part of that research team.
Miah M. Hussainuzzaman
The following study shows the role of organic carbon originating fom ponds to mobilize arsenic. However, it is already known that the organic carbon, mostly dissolved organic carbon (DOC, mostly humic and fulvic acids), is polyelectrolytic with negative charges and can bind postively charged metal cations like arsenic. The pumping of water from underground sources by any means, e.g. shallow and deep tube wells, or slow infiltration of organic carbon from ponds, can increase the movement of DOC from surface water (ponds, channels, irrigated rice fields) to the underground to mobilize arsenic. The increased utilization of river water for irrigation and drinking water preparation can help to reduce the underground suction pressure and thus decrease the mobilization of DOC from surface to undergorund water and the accompanied arsenic from underground. Instead of rice field shallow tube wells, the another interesting option is to install shallow wells with a water pump in the dense bamboos bushes, the roots of which will stop the movement of dissolved organic matter alongwith positively charged metal ions like arsenic, iron, etc. In this way, the mobilization of arsenic via DOC can be reduced and the contamination of drinking water with metal ions in bamboos bush wells can be avoided to a large extent. The regulation of general use of infiltration- stop foils (impervious thin durable high-density polyethylene) in enriched DOC-sources by Bangladesh Government is also highly recommended to reduce slow infiltration of DOC from ponds, channels, drains, etc. to stop mobilization of arsenic in groundwater.
Best wishes and regards
Enamul Hoque PhD, Dr. rer. silv. et rer. nat. habil. (DSc)
Senior Scientist (Anaerobic Microbial Degradation) , Priv.-Doz. of Plant Physiology (TUD) & Professor of Biotechnology (USTC)
Helmholtz Zentrum Muenchen
Deutsches Forschungszentrum fuer Gesundheit und Umwelt (GmbH)
Institute of Groundwater Ecology
Ingolstaedter Landstr. 1
Fon: +49 (89) 3187 – 2579
Fax: +49 (89) 3187 – 3361
Mail: hoque@helmholtz- muenchen. de
http://www.helmholt z-muenchen. de/igoe