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

Migration of ¹³⁷Cs and ⁹⁰Sr in undisturbed soil was studied in large lysimeters three and four years after contamination, as part of a larger European project studying radionuclide soil–plant interactions. The lysimeters were installed in greenhouses with climate control and contaminated with radionuclides in an aerosol mixture, simulating fallout from a nuclear accident. The soil types studied were loam, silt loam, sandy loam and loamy sand. The soils were sampled to 30–40 cm depth in 1997 and 1998. The total deposition of ¹³⁷Cs ranged from 24 to 45 MBq/m², and of ⁹⁰Sr from 23 to 52 MBq/m². It was shown that migration of ¹³⁷Cs was fastest in sandy loam, and of ⁹⁰Sr fastest in sandy loam and loam. The slowest migration of both nuclides was found in loamy sand. Retention within the upper 5 cm was 60% for both ¹³⁷Cs and ⁹⁰Sr in sandy loam, while in loamy sand it was 97 and 96%, respectively. In 1998, migration rates, calculated as radionuclide weighted median depth (migration centre) divided by time since deposition were 1.1 cm/year for both ¹³⁷Cs and ⁹⁰Sr in sandy loam, 0.8 and 1.0 cm/year, respectively, in loam, 0.6 and 0.8 cm/year in silt loam, and 0.4 and 0.6 cm/year for ¹³⁷Cs and ⁹⁰Sr, respectively, in loamy sand. A distinction is made between 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 migration is still dominant in the studied soils.