High plant uptake of radiocesium from organic soils due to Cs mobility and low soil K content

Post-Chernobyl experience has demonstrated that persistently high plant transfer of 137Cs occurs from organic soils in upland and seminatural ecosystems. The soil properties influencing this transfer have been known for some time but have not been quantified. A pot experiment was conducted using 23 soils collected from selected areas of Great Britain, which were spiked with 134Cs, and Agrostis capillaris grown for 19−45 days. The plant-to-soil 134Cs concentration ratio (CR) varied from 0.06 to 44; log CR positively correlated to soil organic matter content (R 2 = 0.84), and CR values were highest for soils with low distribution coefficients (Kd) of 134Cs. Soils with high organic matter contents and high concentrations of NH4+ in solution showed high 134Cs mobility (low Kd). The plant-to-soil solution 134Cs ratio decreased sharply with increasing soil solution K+. A two parameter linear model, used to predict log CR from soil solution K+ and Kd, explained 94% of the variability in CR values. In conclusion, the high transfer of 134Cs in organic soils is related to both the high 134Cs mobility (low clay content and high NH4+ concentra tions) and low K availability.