SURREY, United Kingdom -- Mercury pollution is poisoning many Latin American rivers. The Argentinean, Brazilian, Peruvian, British, Swedish and Spanish researchers working on the Mercury project are now tackling this specific problem with the aid of some remarkable supramolecules.
"Latin America could experience a disaster comparable to that of Minamata, given the degree of mercury pollution in certain regions and rivers,” believes Angela Danil de Namor, a chemist at the University of Surrey (UK), coordinator of the Mercury project. The famous garimperos or gold diggers of the Amazon Basin are not the only culprits. Forest fires and, above all, untreated urban and industrial waste are major contributors to this mercury pollution that has reached alarming levels in Brazil’s Amazon Basin and certain rivers in Peru and Argentina. The highly toxic heavy metal builds up in the flesh of fish to the point where it contaminates predators, including man. The effects can include neurological disorders and retarded development.
Supported by the European Union, the Mercury project is getting to grips with the problem by means of supramolecular chemistry and the phenomenon known as chelation by which certain compounds are able to attach themselves selectively to others and literally ‘encapsulate’ them. This is true of calixarenes, a family of cyclical molecules discovered accidentally – as by-products of bakelite production – and which are currently the subject of intensive research worldwide. Danil de Namor’s team synthesised specific calixarenes that bind themselves to the soluble forms of metals such as mercury, cadmium, lead and copper. If incorporated in solid recyclable matrixes they could be used in depollution devices.
What is more, as Angela Danil de Namor explains, "present depollution methods are inefficient due to a lack of selectivity, and the analysis techniques for mercury content measurement are too expensive for these countries and little used as a result”.
Mercury trap Between 1997 and 2000, an initial European INCO project(2) was devoted to developing molecules and their support matrixes. Launched in 2002 for a three-year period, the Mercury project is the next stage during which tools will be developed and tested in the field. The selected sites are the River Chili in Peru, the port of Bahia Blanca (Argentina) with its effluent from the petrochemical industry, and the Rio Negro (Argentina).
Portable detectors have been developed which are equipped with electrodes boosted with calixarenes – and thus rendered sensitive to mercury. But the depollution exercise itself presents a major challenge. A new material, silica with added calixarenes, which was developed and tested successfully in the United Kingdom, could make it possible to create extracting membranes that filter out industrial effluent. An initial market study has shown that farmers, industrialists and environmental protection agencies could be interested in these measurement and filtering tools.
At the same time, Barcelona University’s plant biology laboratory – Spain is also affected by mercury pollution – is testing the ability of certain native South American plants to fix mercury in their tissue and which could therefore be of potential use as depolluters. A crucifer of the turnip and colza family is currently showing the best results.
The project’s third line of inquiry involves a team of Peruvian pharmacologists who are engaged in a preliminary study with much longer term potential: the possibility of using calixarenes as therapeutic agents to clean the bodies of people who have been contaminated with mercury.
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