Important factors governing exposure of the population and countermeasure application in rural settlements of the Russian Federation in the long termafter the Chernobyl accident

Rural settlements located in areas of the Russian Federation contaminated a fter the Chernobyl accident and exceeding an annual dose of 1 mSv a(-1) hav e been classified according to Cs-137 contamination density, internal dose and the neighbourhood of forests. It has been shown that, with the exceptio n of the most contaminated areas, the internal doses decreased in accordanc e with a decline in Cs-137 availability for plant root uptake. An inverse t endency was observed in areas with Cs-137 contamination above 555 kBq m(-2) which can be explained by a reduction or even termination of countermeasur e application and by an increasing consumption of forest products in areas where restrictive countermeasures are still implemented. Twenty-seven settl ements have been studied to estimate the effectiveness of countermeasures a pplied previously and to identify the most important factors governing the radiation exposure to the population and its change with time, It has been shown that the effectiveness of countermeasures which resulted in a decreas e of up to 40% of doses has a tendency to decline in the long term. The nee d for continuation of remediation in rural settlements was evaluated both f or selected settlements and extrapolated to the whole contaminated area and it has been shown that the application of countermeasures will be of impor tance at least up to the year 2045. Rather high effectiveness in terms of i nternal dose reduction (factor of 2-2.5) of radical improvement (disking, p loughing and reseeding) and administration of Cs binders to animals (Ferroc yn) was demonstrated for the selected settlements. It could be demonstrated that for forest-remote settlements there is a linear dependence between in ternal dose normalised to the density of contamination and the proportion o f peat soils around settlements. For neat-forest settlements. this dependen ce was less pronounced which can be explained by the high contribution of f orest food products to the internal dose. Milk is still the major dose-form ing product in rural Russian settlements (its contribution to internal dose in forest-remote settlements is above 70%); however, in near-forest settle ments, the contribution of mushrooms to the internal dose is comparable to the contribution from milk. (C) 2001 Elsevier Science Ltd. All rights reser ved.