Long-term behavior of 90Sr and 137Cs in the environment: Case studies in Switzerland

We present long-term records of the 137Cs and 90Sr activity concentrations in soil, grass and milk from two lowland and two alpine pastures of Switzerland. The data is used for better understanding the long-term behavior of these radionuclides in the environment. Transfer factors between compartments are used as qualitative indicators of the magnitude of transfer and as a way to compare different elements (e.g. Cs and Sr) in similar conditions. The long-term behavior was quantified by means of the effective half-life which integrates all processes that cause a decrease of activity in a given medium such as leaching, fixation, erosion and radioactive decay. Our study shows that 90Sr is more likely transferred from alpine soil to grass than 137Cs. This is explained by a stronger fixation of Cs in the soils. We observed higher transfers of 90Sr to grass in soils with lower Ca concentrations, and vice versa. In contrast, the transfer of 137Cs to grass was not affected by the variations of the K content in the soil. We provide evidence that shows that 137Cs, after intake by dairy cattle, is more likely transferred to milk than 90Sr. However, as the 90Sr and Ca transfers to milk are influenced by parameters/processes that were not taken into account in our study, our result cannot be entirely validated. The effective half-lives of 137Cs and 90Sr in soil, grass and milk corresponded with previous estimates in alpine soils. We have found that processes other than radioactive decay are responsible for a major decrease of the 90Sr activity in soil. For 137Cs, on the other hand, radioactive decay is among the most relevant process. Our data shows to be of interest in studying the trends of behavior of radionuclides in alpine regions.