Transfer of radiocaesium deposited after the Chernobyl accident to agricultural plants

The behaviour of radiocaesium deposited by the Chernobyl fall-out was investigated in a permanent pasture. Samples of grass, mat and subjacent soil at various depths were regularly collected and analysed for their caesium content. The results show that most of the activity is located in the mat horizon. No significant amounts of Chernobyl radiocaesium could be detected in the soil layers below the mat. The comparison of the transfer factors to maize and potatoes observed yearly from 1982 in plants grown on a soil homogeneously contaminated with 134CsCl shows a decrease by a factor 3 between the year of contamination (1982) and 1986 due to a progressive sequestration of Cs by the clay fraction. The activity ratio between plant and soil calculated in 1986 for plants grown on control plots contaminated by the Chernobyl fall-out are 10 times higher than the transfer factors estimated for the same species grown during the same year on artificially contaminated plots. Samples of various crops and vegetables grown in the region of Mol (Belgium) were collected at maturity between August and October in 1986 and 1987. In parallel, soil samples from the 20 cm layer on which the crops and vegetables had been grown were also taken. The 137Cs activity deposited in the region of Mol after the Chernobyl accident was calculated to be approximately equal to the 137Cs remaining from the activity deposited in the soil plough layer by the weapon tests fall-out. Based on the 137Cs content in soils of the region of Mol collected and measured in 1967 and the data from the sampling campaigns in 1986 and 1987, effective half-lives for 137Cs in these soils were estimated to 9 to 19 y