Cutting Edge

December 10, 1999

Well into the next century, thousands will

still be suffering Chernobyl's legacy: contaminated soil poisoning the food chain 'It was estimated that radiocaesium concentrations in fish in Lake Kozhanovskoe, Russia, will remain

above the recommended maximum

limit for consumption for 50 years or more from now' Chernobyl's radioactive legacy still affects the lives of hundreds of thousands of people living in and around the contaminated zones 13 years after the accident in reactor No 4.

I have been working on long-term mobility of Chernobyl radionuclides since doing an applied mathematics PhD in this field. In joint studies with teams from the former Soviet Union (FSU) countries, I and other scientists at the Centre for Ecology and Hydrology have found that some food products from these affected areas will remain contaminated well into the next century.

Many of the radioactive elements released by the accident have long since decayed, but their effects are still seen in the children being treated for thyroid cancer caused by their early exposure to radioactive iodine. At present, and for the foreseeable future, most of the radiation in the Chernobyl area comes from radiocaesium (Cs-137). This has a physical half-life of 30 years: in 2016 half of the Cs-137 released by Chernobyl will still be in the environment. Because of its chemical similarity to potassium, Cs-137 is strongly accumulated by plants and animals.

No increase in cancer rates has so far been observed in the Chernobyl-affected populations as a result of exposure to Cs-137, but the contamination has had a devastating effect. Thousands of square kilometres of land in Belarus, Russia and Ukraine still cannot be used for agriculture and have been defined as areas of strict radiation control. Populations of towns have been relocated. Studies have shown that contamination of land and foodstuffs by Cs-137 will be a long-term problem.

After a nuclear accident, ecosystems have a self-cleaning capacity: radiocaesium becomes immobilised in the soil so that it becomes less easily accumulated. Before Chernobyl, most scientists believed that the soil immobilisation process was so strong that contamination of foodstuffs would not be long-lived.

In joint studies, projects funded by the European Commission, UK and FSU scientists have found that radiocaesium is not completely immobilised by the soil. In a project I coordinated, it was estimated that Cs-137 activity concentrations in fish in Lake Kozhanovskoe, Russia, will remain above the recommended maximum limit for consumption for 50 years or more from now. Similar studies by CEH's Merlewood laboratory have shown that restrictions on mushroom consumption will need to continue until 2150.

It comes as a surprise to many people to find that the current exposure to radiation of people living in and around the affected areas is relatively low. Radiation experts expect only a very small increase in people's cancer risk. In most cases, radioactive doses are less than many people in Europe receive from natural "background" radiation. But small health risks can have enormous social and economic consequences. A major problem in dealing with the long-term effects of the accident is the public's overestimation of the radiation risk. An International Atomic Energy Agency study found the psychological effects of Chernobyl to be wholly disproportionate to the biological significance of the radiation. Populations in the contaminated areas have been shown to have higher levels of stress, worse perceived health and greater use of medical facilities than similar unaffected populations.

The challenge for scientists now is to determine how best to manage these contaminated areas in the decades to come. A key element of this management strategy is an information and education programme for the people who have to live with Chernobyl's radioactive legacy. Jim Smith, Centre for Ecology and Hydrology,

Natural Environment Research Council, East Stoke, Wareham, Dorset.

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