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September 11, 2008 12:13 am

Super microscope helps land clean-up

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The UK's newest synchrotron is contributing to the treatment of contaminated land, an audience at the BA Festival of Science heard on Wednesday.

The vast, Oxfordshire-based facility generates intense light beams to probe matter down to the atomic scale, and can be used in areas as diverse as medical research and arts restoration.

There is increasing pressure to reclaim brownfield sites for housing, leisure and industrial use. Currently, contaminated soil is either dug up to be treated or buried, or is capped in order to contain the toxins. The cost of these methods can be as high as £250 per tonne. The new results from the Diamond Light Source synchrotron suggest cheaper, less disruptive ways of dealing with the problem.

Earthworms eat about 30 times their own body weight per day, but the most common types of worms struggle to survive in soils contaminated with lead, arsenic and copper.

However, Mark Hodson, reader in environmental geochemistry at the University of Reading, has discovered that several varieties of worm thrive in soils contaminated by these metals.

The worms are able to digest the metals, changing them into a form that plants are able to use. These plants can then be removed from the site and the contaminants dealt with in a variety of ways, leaving the soil behind.

Until now, Dr Hodson’s group did not understand the way in which the worms altered the chemistry of the soil. “The differences we are looking for are very subtle,” he said, “The narrowly focused beam-line at Diamond gives us the ability to look at the differences in soil at a very fine resolution, so it allows us to find a needle in a haystack.”

The results were published earlier this year in Mineralogical Magazine.

Paul Schofield, researcher in mineral sciences at the Natural History Museum, London, is investigating an alternative method using bonemeal. The phosphates in bonemeal react with the toxic metals in the soil to form stable compounds that lock away the contaminants.

Analyses performed at Diamond showed that the method is capable of treating lead, zinc, copper, nickel and cadmium. Results of successful field trials of the treatment were published in the August issue of Applied Geochemistry.

The two methods are likely to be complementary. “The soil texture will be very different in different contaminated sites, and they will require different approaches,” said Dr Schofield, “It’s a matter of choosing the right technology for each individual site.”

The methods will be developed over the next five to 10 years.

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