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TECHNICAL REPORTS

Ecological Risk Assessment

Prediction of Radionuclide Aging in Soils from the Chernobyl and Mediterranean Areas

^a Institut de Tècniques Energètiques, Universitat Politècnica de Catalunya, Av. Diagonal 647, 08028 Barcelona, Spain
^b Departament de Química Analítica, Universitat de Barcelona, Martí i Franqués 1-11, 3^a Planta, 08028 Barcelona, Spain

^* Corresponding author (miquel.vidal{at}ub.edu)

Received for publication September 26, 2006. The aging of soil-pollutant interaction, which may lead to an increase in pollutant fixation, is the main driving force in the natural attenuation of contaminated soils. Here a test was evaluated to predict the aging of radiostrontium and radiocesium in soils from the Chernobyl and Mediterranean areas. After contamination, soils were maintained at various temperatures for up to 12 mo, with or without drying–wetting (DW) cycles. Changes in the quantity of radionuclide reversibly sorbed over time were monitored using an extraction test (1 mol L^–1 NH₄Cl; 10 mL g^–1; 16 h). The fixed fraction could not be predicted from soil properties controlling the sorption step. Aging was not as relevant for Sr as for Cs. The time elapsed since contamination was the main factor responsible for the slight (up to 1.3-fold) decreases in Sr extraction yields. The additional effect of DW cycles was negligible. Instead, all factors accelerated Cs aging due to the enhancement of Cs trapping by clay interlayer collapse, with up to 20-fold increases in Cs fixation. The DW cycles also caused secondary effects on the Cs-specific sorption pool, which were beneficial or detrimental depending on the soil type. Extraction yields from laboratory aged samples agreed with those from field samples taken a few years after the Chernobyl accident. These results confirm the prediction capacity of the laboratory test and its usefulness in risk assessment exercises and in the design of intervention actions, particularly because neither fixation nor aging were related to the soil properties, such as clay content.

Abbreviations: DW cycles, drying–wetting cycles • RIP, radiocesium interception potential • FES, frayed edge sites • REC, regular exchange complex • HAS, high selectivity sites