Sediment tracing using environmental radionuclides; the distribution and behaviour of 137Cs and natural radioisotopes in a small loess agricultural watershed

The concentrations of 137Cs, 226Ra, 232Th and 40K in loessial soil from cultivated field located on a gentle slope on the Proboszczowicki tableland (near Ujazd village, SW Poland) were measured using gamma-ray spectrometry with the aim of investigating the behaviour of those radionuclides in soil in the eroded area. These concentrations were also determined in soil after citrate-dithonite extraction treatment, as well as in the remaining liquid. The 137Cs concentrations in soil profiles suggest that soil movement for the study area is considerable. The 137Cs inventories were 10–63% lower on the slopes than on the plateau and were 66% higher at the bottom of the valley. The calculated values of soil erosion range between 1.3 and 59.8. tons ha−1·a−1 whereas in the deposition area the calculated soil accumulation rate is about 89.6 tons ha−1·a−1. Activity concentration measurements using the chemical extraction solutions suggest that 137Cs is not retained by the iron oxide layers in these soils, in contrast to a significant fraction of the natural radionuclides 226Ra and 232Th. The relative standard deviations (RSD) of the activity concentration ratios of 137Cs/226Ra, 137Cs/232Th and 137Cs/40K are comparable with the RSD of caesium activity and thus cannot be used to minimize particle size effects at this location.