Detailed study of post-Chernobyl Cs-137 redistribution in the soils of a small agricultural catchment (Tula region, Russia)

A detailed study of Cs-137 redistribution was conducted within a small agricultural catchment in the highly contaminated Plavsk radioactive hotspot in the Tula region of Central Russia, 32 years after the Chernobyl nuclear power plant (NPP) accident, which occurred on April 26,1986. Although more than three decades have passed since the Chernobyl NPP incident, Cs-137 contamination is high. The Cs-137 inventory varies from 67 to 306 kBq.m(-2), which is 2-6 times higher than the radiation safety standard; however, the soils remain suitable for crop cultivation. The initial Cs-137 fallout within the Plavsk radioactive hotspot was extremely heterogeneous, with a trend of decreasing Cs-137 inventories from the NW to the SE directions within the studied territory. Contemporary Cs-137 inventories are also very heterogeneous in the studied catchment. However, the trend of the initial Cs-137 fallout does not appear in the contemporary Cs-137 inventories on the slopes. Two methods of interpolation (expert-visual and automatic) were used to calculate the Cs-137 budget, revealing high similarity in their Cs-137 loss estimates; however, a large discrepancy was observed in their (137)Css gain estimates. A detailed analysis of Cs-137 redistribution revealed the importance of hollows and "plow ramparts" (positive topographic forms on the boundaries of cultivated fields) in the transport and deposition of sediments. A quarter of the total Cs-137 gain was deposited within the arable land, whereas a quarter was deposited within the non-plowing sides of the dry valley; the other half was deposited in the valley bottom. About 7-8 x 10(6) kBq of the Cs-137 inventory flowed out of the catchment area, which was only about 2% of the Cs-137 fallout after the Chernobyl NPP accident. About 89% of the total Cs-137 reserve is concentrated in the top (0-25 cm) layer of soils, regardless of land use or location within the catchment.