Inventories and fluxes of Pb-210, Cs-137 and Am-241 determined from the soils of three small catchments in Cumbria, UK

Inventories and vertical profiles of fall-out Pb-210, Cs-137 (both weapons test and Chernobyl) and Am-241 (a decay product of Pu-241) have been measured in the soils of three catchments in Cumbria, UK. Soil types varied from mineral soils to highly organic peat bog. The Pb-210 inventor ies in different cores from the same catchment were relatively uniform, the standard deviation of measurements being around 30%. Mean annual fluxes of Pb-210 calculated from the soil inventories were 63 Bq m(-2) year(-1) (Brotherswater catchment), 63 Bq m(-2) year(-1) (Blelham Tarn catchment, and 97 Bq m(-2) year(-1) (Devoke Water catchment) per metre of rainfall. From these and earlier data published in the literature, the mean UK Pb-210 flux is estimated to be 77 +/- 14 Bq m(-2) year(-1) per metre of rainfall. Inventor ies of Cs-137 (weapons test and Chernobyl) were more variable, but mean values for each of the catchments were in agreement with independent studies. The mean weapons test deposition (decay corrected to 1986) was 2790 Bq m(-2) per metre of rainfall, con?par ed to a UK aver age of 3160 Bg m(-2) derived from extensive national surveys. Although Am-241 levels in Brotherswater soils were comparable with those expected from weapons test fall-out, significantly higher values were recorded at Blelham Tarn and Devoke Water. Well-resolved peaks in Am-241 activity some distance below the present surface suggest that this radionuclide is relatively immobile within the soil column. The depth of penetration of 75% of the inventory into the soil column was similar for Pb-210, Cs-137 (weapons) and Am-241, all being significantly greater than Chernobyl(137)Cs. The vertical profiles of Cs-137 (weapons) suggest that there has been little mobility during the 15 years since a previous study (Cawse 1983). (C) 1997 Elsevier Science Ltd.