Field studies on the behaviour of radiocaesium in agricultural environments after the Chernobyl accident

This thesis deals with the occurrence of Chernobyl 137Cs and 134Cs in cultivated, semi-natural and natural agricultural areas of five Swedish counties. The investigations were carried out under field conditions 1986 to 1995 on farms where transfer to grass and milk during the first years were high. Vertical migration rate in soil profiles, the practical value of countermeasures to reduce transfer to feed and food and the impact of passing time were important aims for the study. The transfer of Cs was higher on permanent pasture than on temporary grassland and much lower to barley grain. Stubble and grass swards kept Cs available for transfer to grass. High organic matter contents in the surface soil also caused high transfer during a lag period of some years. Soil texture, grass sward, K-fertilization and growth dilution explained the variation in Cs transfer and its reduction rate. A case study on transfer of Cs to vegetation and to grazing lambs was made on a mountain farm. High transfer to vegetation was found, 510-2260 Bq/kg d.w.. Mean transfer soil to plant (TFg,m2/kg) was 67 and plant to muscle 0.7 during 1990-1993. The effect of K-fertilization on soil-plant transfer was studied on 15 soils. A dose of 100 to 200 kg/ha K decreased the transfer on sandy soils with a factor of up to 10. Liming was effective on soils that were originally low in pH. Adding zeolite on the surface of pastures did not reduce the root uptake of Cs. Ploughing down the contaminated surface was effective in reducing the transfer. Downward migration of Cs was usually less on mineral soils than or organic or podsolized soils. 68 refs, 9 figs, 13 tabs