One of the gardener's best friends, the worm, will face the formidable challenge next spring of converting a mixture of sewage sludge and colliery soil into relatively fertile soil.

The task for the worms has been formulated by Kevin Butt, a researcher at the University of Central Lancashire, who believes that worms could play an important role in reclaiming land that has been ruined by industrial pollution.

Armed with Pounds 2,000 from the Nuffield Foundation, he intends to put the idea to the test at a disused steelworks at Hallside just outside Glasgow. The 30-hectare site has just been covered with the sludge and colliery soil.

Dr Butt said there are three main types of worms. The surface worms live at depths of just a few centimetres, munching away at soil to produce casts which are high in organic content. Such worms - often sold as fish bait - are commonly found in compost heaps and although relatively short lived, reproduce rapidly.

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The second type of worm is found at sub-surface levels, typically five to ten centimetres. These worms burrow away horizontally and their activity in the region of the plant root zone creates valuable aeration channels and concentrations of nutrients for the roots.

The most dramatic effect on soils, however, is created by deep-burrowing worms which can operate at depths of one to two metres. These tend to have vertical burrows which help with drainage and aeration of the soil. Deep-burrowing worms live longer and are bigger than the other types but they tend to reproduce slowly. In addition to producing soil-nourishing casts, they take organic matter from the surface deep into the soil, burying it there. Dr Butt said: "They are very important because they effectively mix the soil layers together."

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At Hallside, the worms will be expected to chump their way through a horrible mix of sludge and colliery leftovers covering an area the size of 60 football pitches. Funds are tight, so Dr Butt intends to breed and set loose only the deep-burrowing worms at first. He hopes they will ameliorate the soil sufficiently to allow trees to grow. He stresses that because of the slow pace at which earthworms perform their good work, it will be several years before the work can be fully evaluated.

Monitoring will be carried out at six-month intervals, and data collected will include measurements of how far the worms have moved from their initial positions and the condition of the soil, including measurements of texture, bulk density and porosity.