Sediment-associated transport and redistribution of Chernobyl fallout radionuclides

Fallout of Chernobyl-derived radionuclides over the United Kingdom evidenced marked spatial variation. Relatively high levels were recorded in central Wales, but they declined rapidly to the east. As a result the headwaters of the River Severn received significant inputs of fallout, whereas only low levels were recorded over the middle and lower reaches. Measurements of the caesium-137 content of suspended sediment transported by the River Severn and of channel and floodplain sediments collected from various locations within the basin have been used to assess the importance of fluvial transport and redistribution of Chernobyl-derived radionuclides. High concentrations of caesium-137 (up to 1450 mBqg-1) were recorded in suspended sediment collected from the lower reaches of the river shortly after the Chernobyl incident and substantial accumulations of Chernobyl-derived radionuclides have been detected in floodplain and channel sediments collected from areas which received only low levels of fallout directly. (author)