Migration of Cs-137 and Sr-90 in undisturbed soil profiles under controlled and close-to-real conditions

Migration of Cs-137 and Sr-90 in undisturbed soil was studied in large lysi meters three and four years after contamination, as part of a larger Europe an project studying radionuclide soil-plant interactions. The lysimeters we re installed in greenhouses with climate control and contaminated with radi onuclides in an aerosol mixture, simulating fallout from a nuclear accident . The soil types studied were loam, silt loam, sandy loam and loamy sand. T he soils were sampled to 30-40 cm depth in 1997 and 1998. The total deposit ion of Cs-137 ranged from 24 to 45 MBq/m(2), and of Sr-90 from 23 to 52 MBq /m(2). It was shown that migration of Cs-137 was fastest in sandy loam, and of 90Sr fastest in sandy loam and loam. The slowest migration of both nucl ides was found in loamy sand. Retention within the upper 5 cm was 60% for b oth C-137 and Sr-90 in sandy loam, while in loamy sand it was 97 and 96%, r espectively. In 1998, migration rates, calculated as radionuclide weighted median depth (migration centre) divided by time since deposition were 1.1 c m/year for both Cs-137 and Sr-90 in sandy loam, 0.8 and 1.0 cm/year, respec tively, in loam, 0.6 and 0.8 cm/year in silt loam, and 0.4 and 0.6 cm/year for Cs-137 and Sr-90, respectively, in loamy sand. A distinction is made be tween short-term migration, caused by events soon after deposition and less affected by soil type, and long-term migration, more affected by e.g. soil texture. Three to four years after deposition, effects of short-term migra tion is still dominant in the studied soils. (C) 2000 Elsevier Science Ltd. All rights reserved.