Iodine-129 and Caesium-137 in Chernobyl contaminated soil and their chemical fractionation

Soil samples from areas in Belarus, Russia and Sweden contaminated by the Chernobyl accident were analysed for 129I by radiochemical neutron activation analysis, as well as for 137Cs by gamma-spectrometry. The atomic ratio of 129I/137Cs in the upper layer of the examined soil cores ranged from 0.10 to 0.30, with an average of 0.18, and no correlation between 129I/137Cs ratio and the distance from Chernobyl reactor to sampling location was observed. It seems feasible to use the 129I/137Cs ratio to reconstruct the deposition pattern of 131I in these areas. The association of 129I and 137Cs in the Chernobyl soil and Irish Sea sediment was investigated by a sequential extraction method. Similar speciation of 129I in the Chernobyl soil and Irish Sea sediment was found. Approximately 70% of 129I is bound to oxides and organic matter, and 10–20% is in the readily available phase, while most of the 137Cs (73%) in Chernobyl soil remains in the extraction residue.