Page last updated at 10:40 GMT, Friday, 12 September 2008 11:40 UK

Earthworms to aid soil clean-up

By Elizabeth Mitchell
Science reporter, BBC News

Worms munching polluted and non-polluted soils showed different colours

Scientists have discovered how metal-munching earthworms can help plants to clean up contaminated soils.

Researchers at Reading University found that subtle changes occurred in metals as worms ingested and excreted soil.

These changes make it easier for plants to take up potentially toxic metals from contaminated land.

Earthworms could be the future "21st Century eco-warriors", scientists suggested at the British Association Science Festival in Liverpool.

There are many sites across the UK with contaminated soil due to previous industrial activities, including mines, engineering works and lead smelters.

The dream scenario is that the plants become so efficient at extracting the metals that you can take them off to a smelting plant
Mark Hodson

Earthworms are ideal "soil detectives": their presence can act as a reliable indicator to the general health of the soil.

They have evolved a mechanism that allows them to survive in soils contaminated with toxic metals including arsenic, lead, copper and zinc.

"Earthworms produce metallothinein - a protein that is specifically designed to wrap around particular metals and keep them safe," explained Mark Hodson from the University of Reading.

"In broad terms, if an earthworm can cope with one type of metal, it can often cope with a suite of metals," he added.

Metal harvest

A key piece of equipment in the study was the Diamond Light Source in Oxfordshire, the UK's newest synchrotron.

Schematic of Diamond facility (BBC)
Electrons fired into straight accelerator, or linac
Boosted in small synchrotron and injected into storage ring
Magnets in large ring bend and focus electrons accelerated to near light-speeds
Energy lost emerges down beamlines as highly focused light at X-ray wavelengths

The X-ray technology there allowed scientists to examine metal samples that were, in Dr Hodson's words, "around 1,000 times smaller than a grain of salt".

They found that properties of metals in the material excreted from earthworms were slightly different from those found in the rest of the soil.

Some plants can pull out toxic metals from the soil, incorporate them into their tissues, and then be harvested and removed.

This whole process offers a sustainable and non-intrusive way to decontaminate land.

But it can take a very long time.

Earthworms make the metals more readily available to plants, speeding up the process and making it more efficient.

"The dream scenario is that the plants become so wonderfully efficient at extracting the metals that you can then take them off to a smelting plant," said Dr Hodson.

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