INVENTORIES AND FLUXES OF PB-210, CS-137 AND AM-241 DETERMINED FROM THE SOILS OF 3 SMALL CATCHMENTS IN CUMBRIA, UK

Inventories and vertical profiles of fall-out Pb-210, Cs-137 (both wea pons test and Chernobyl) and Am-241 (a decay product of Pu-241) have b een measured in the soils of three catchments in Cumbria, UK. Soil typ es varied from mineral soils to highly organic peat bog. The Pb-210 in ventor 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) (Ble lham Tarn catchment, and 97 Bq m(-2) year(-1) (Devoke Water catchment) per metre of rainfall. From these and earlier data published in the l iterature, 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 tes t and Chernobyl) were more variable, but mean values for each of the c atchments 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 fro m 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 W ater. Well-resolved peaks in Am-241 activity some distance below the p resent surface suggest that this radionuclide is relatively immobile w ithin the soil column. The depth of penetration of 75% of the inventor y into the soil column was similar for Pb-210, Cs-137 (weapons) and Am -241, all being significantly greater than Chernobyl(137)Cs. The verti cal profiles of Cs-137 (weapons) suggest that there has been little mo bility during the 15 years since a previous study (Cawse 1983). (C) 19 97 Elsevier Science Ltd.