EcoDoses - Improving radiological assessment of doses to man from terrestrial ecosystems. A status report for the NKS-B project 2005

Considerable variations in activity concentrations in milk of 137Cs and 90Sr were observed between countries or regions due to precipitation patterns, soil types and inhomogeneity of Chernobyl fallout. Time trends indicate that factors influencing ecological half-lives for 90Sr are not the same as for 137Cs in the pasture–milk system.

Internal doses to Faroese people derive mainly from dairy products, lamb and potatoes. The largest doses were received from nuclear weapons fallout in the early 1960’s. 137Cs causes higher doses than 90Sr, and the regional variability is larger for 137Cs than for 90Sr. 137Cs deposition maps were made of Sweden.

Values of 137Cs deposition and precipitation were used in the calculations of Nuclear Weapons Fallout (NWF). The deposition of 137Cs from the Chernobyl accident was calculated for western Sweden. Lowest levels of NWF 137Cs deposition density were noted in the north-eastern and eastern Sweden and the highest levels in the western parts.

The Chernobyl 137Cs deposition is highest along the coast and lowest in the south-eastern part and along the middle. The calculated deposition from NWF and Chernobyl in western Sweden was compared to observed deposition and showed good agreement. Ecological halftimes of 137Cs in perch in Finnish lakes vary by a factor of three.

The longest halftime of 137Cs in perch was 9 y and the shortest 3 y. Norwegian lakes differ from each other with respect to the rates of decrease of 137Cs in fish. Ecological halftimes of 137Cs in trout and Arctic char varied from 1 to 5 y. A more rapid reduction of 137Cs in fish is found in certain Norwegian lakes compared to Finnish lakes.

In two Norwegian lakes the 137Cs concentrations in trout remain at about 100 Bq/kg since 1990. The European decision support systems, ARGOS and RODOS, include foodchain modules with default parameters derived from southern Germany. Many parameters describing foodchain transfer are subject to considerable variation according to local conditions.

Such parameters include soil type, sowing and harvesting times, feeding regimes for animals, human consumption habits, and dependence of plant development on season. Model features and parameter values need adjustment for the model to produce reliable predictions for Nordic areas. Further generic inadequacies of the modelling system relate to dry deposition processes.