SOME of Britain鈥檚 rarest plants have been poisoned by the fallout from slag blasted onto the Clifton Suspension Bridge in Bristol last summer to remove paint. About 20 tonnes of slag laced with heavy metals has fallen onto a site of special scientific interest in the Avon Gorge, beneath the bridge. Tim Rich, a leading consultant biologist, calls it 鈥渙ne of the biggest disasters in the botanical world for decades鈥�.
鈥淭housands of plants are affected,鈥� says Mike Martin of the University of Bristol. 鈥淪ome are 2 centimetres deep in slag dust, which is leaching copper, zinc, lead and cadmium into the soil. We won鈥檛 know if any plants will survive until the spring.鈥�
The sheltered Avon Gorge SSSI is one of the country鈥檚 most spectacular homes for rare plants. According to Martin, 80 per cent of the British population of the round-headed leek is now spattered with the heavy metals. Also badly hit is the Bristol rock-cress, a species found only in the gorge, and one of the country鈥檚 largest populations of spiked speedwell. At least 12 species in the contaminated zone are protected under the Wildlife and Countryside Act.
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The Clifton Suspension Bridge is outside the SSSI. Last summer, contractors renovating the bridge blasted the paintwork with 100 tonnes of slag 鈥� waste from a Swedish copper smelting works. The contractors recovered 80 tonnes of the slag, leaving the rest spread over a half-kilometre length of the gorge on either side of the bridge, with drifts up to 8 centimetres deep.
English Nature, the government鈥檚 guardian of SSSIs, did not object to the blasting, despite protests from local botanists, because technical data sheets provided by the importers, Scangrit of Huddersfield, said the slag was 鈥渋nert鈥�, with metals held in a glassy matrix.
But English Nature has changed its mind after seeing analyses commissioned by Rich and Martin, which show that the 20 tonnes of fallout contains around half a tonne of zinc and 80 kilograms of copper as well as some cadmium and lead 鈥� possibly from the bridge鈥檚 paint. This is leaching into the soil.
鈥淭he slag is highly toxic,鈥� says Rich. 鈥淚t is likely to contaminate the gorge for thousands of years. The metals will probably get through the food chain, perhaps even to the peregrines for which the gorge is also famous.鈥�
Earlier this month, the bridge鈥檚 trustees met English Nature, local botanists and the contractors, Ferrous Protection of Oldham in Lancashire. The trustees provisionally agreed that either they or their contractors would pay for cleaning up the mess and removing some plants to improve their chances of recovery. The contractors decline to comment on the fallout. Scangrit says that 100 000 tonnes of copper slag are used every year for cleaning metal in Britain.
Martin, Rich and local botanist Libby Houston, who first raised the alarm, are now trying to remove the slag from plants and soils using hand-held vacuum cleaners and toothbrushes. 鈥淏ut it鈥檚 an almost impossible task,鈥� says Rich.