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by Steve Connor, Science Editor
11 May 2000
Radioactive pollution from the accident at the Chernobyl nuclear power plant in 1986 will continue to contaminate British sheep for up to another 15 years.
Scientists have revised their estimates for how long it will take to eradicate contamination from the upland regions of Wales, Cumbria and Scotland after new evidence showed that radioactivity from Chernobyl was more persistent than originally thought.
The most significant pollutant is radiocaesium, which is absorbed by plants and can enter the human food chain through grazing livestock, notably sheep on upland farms.
Scientists had initially estimated that the radiocaesium fallout from Chernobyl -- washed out in rainfall -- would eventually bind tightly to the clay matrix of the soil, preventing further uptake. But work by a team of scientists has revealed that there is a limit to how much radiocaesium can be "lost" in this way. This has enabled them to formulate new predictions on how long current restrictions on farm livestock in affected areas need to remain in place.
Jim Smith, from the the Centre for Ecology and Hydrology in Dorchester, said: "Restrictions in the United Kingdom, for example, may need to be retained for a further 10-15 years, more than 100 times longer than originally estimated."
In a report in the journal Nature, Dr Smith said the rate at which radiocaesium is being "removed" from the environment has slowed down, increasing the effective time it will continue to pose a potential threat. "At the time of the accident we didn't have the same knowledge that we have now. The decontamination of foodstuffs was thought to be more rapid," Dr Smith said.
The scientists say that 389 upland farms responsible for about 232, 000 sheep are still subject to restrictions because of the Chernobyl accident.
Tests on three of these farms show that some sheep have levels of radiocaesium that are nearly twice the limit deemed to be safe for human consumption.
Sheep found to have high levels of radiocaesium are moved to decontaminated pastures where the animals can rid themselves of the pollutant.
As bad as the problem is in parts of Britain, it is far worse in Belarus and western Russia, where livestock restrictions are likely to remain in place for another 50 years.
Chernobyl was the site of the worst nuclear accident in history, killing 31 people from radiation sickness.