Long-term studies on transfer of Cs-137 from soil to vegetation and to grazing lambs in a mountain area in Northern Sweden

Studies were made during 1990-1997 on the transfer of Cs-137 from soil to v egetation (herbage) and to glazing lambs on a mountain farm with an unculti vated grazing area of about 10 km(2). The farm is situated in an area in No rthern Sweden which was contaminated by the Chernobyl fallout in 1986, The mean concentration of Cs-137 in the soil to a depth of 10 cm for eight samp ling sites observed in the 8-year period was 14.51 kBq/m(2), while in the c ut herbage the average concentration was 859 Bq/kg d.w, and in lamb meat 68 2 Bq/kg w.w. A slow vertical migration of Cs-137 in the 0-10 cm soil layer was indicated, Although the Cs-137 concentration in herbage gradually decre ased, the concentration in lamb meat varied from year to year. Soil ingesti on by the lambs as a pathway for activity transfer was shown to be negligib le, while ingestion of fungi with high concentrations of Cs-137 was demonst rated to occur, as large numbers of fungi spores were counted in samples of the lambs' faeces. Fungi ingestion might therefore partly explain the vary ing mean yearly Cs-137 concentrations in lamb muscle, The mean transfer par ameters were as follows: for "soil to herbage" 61.3 Bq/kg d.w. herbage per kBq/m2 soil, for "herbage to lamb meat" 0.81 Bq/kg w,w, meat per Bq/kg d.w. herbage, and for "soil to lamb meat" 47.1 Bq/kg w.w. meat per kBq/m(2) soi l. A trend of decreasing values of the transfer parameter for "soil to herb age" indicated that 137Cs was becoming less available for root-uptake with time, The effective ecological half-life of Cs-137 in, soil, herbage and la mb meat was calculated to be 19, 7 and 10 years, respectively. It can be co ncluded that natural areas are vulnerable to Cs-137 contamination, resultin g in high concentrations in plants, fungi and lamb meat for a long time. (C ) 2000 Elsevier Science Ltd. All rights reserved.