Plutonium distribution in sequentially extracted phases of arable and uncultivated soils

Abstract

The aim of this study was to determine the distribution of alpha-emitting plutonium isotopes from arable and uncultivated soils. The effect of soils cultivation on plutonium fractionation and mobility was studied using the sequential extraction technique (modified Tessier’s method). Soil samples were collected from the surface layer in the selected points. By means of reagents with increasing leaching power, the fractions were separated: readily available, carbonate bound, sesquioxide (Fe/Mn) bound and organically bound as well as residual. The content of 239+240Pu in the fractions was determined by alpha spectrometry. The sequential analysis showed that in the case of uncultivated soils, 67% of Pu was combined with organic matter, 15% was permanently bound to the matrix, but only 4% was associated with the available fraction, and 2% with the carbonate one. Arable soils revealed a different distribution: 36% of Pu was combined with the organic fraction, only 7% was bound permanently but as much as 9% was bound with the available fraction, and 11% with the carbonate one. It was proved that plutonium is bound mostly by organic matter (67% Pu—uncultivated and 36%—arable soils), however, the amounts of Pu combined with the labile fractions (ion-exchange and carbonate) are approximately 4 times higher for the arable soils than for uncultivated ones. This proves that soil cultivation can lead to the launch of plutonium in soil and its transition to more accessible forms which can cause a radiological risk.