An evaluation of ratio systems in radioecological studies

Replicate samples of soil, Juncus squarrosus and Calluna vulgaris were taken within a grid system on an organic peatland soil site in Ireland. A similar sampling survey was carried out on an organic rich forest soil site in Sweden, where Vaccinium myrtillus and Vaccinium vitis-idaea with corresponding soil samples were taken within a Picea abies stand. The data were used to investigate the relationship between soil and plant 137Cs content and to examine the validity of using ratios to describe this relationship. Findings from both countries were in agreement. There were no significant changes in plant 137Cs concentration associated with increasing soil content. When data from both countries were merged and treated as a single data set, a significant overall positive correlation (95% confidence level) between soil and plant 137Cs levels was observed. Concentration ratios and transfer factors were calculated for 137Cs and 40K uptake from soils to plants. Both ratio types exhibited a clearly defined decrease associated with increasing soil concentrations for both radionuclides. Findings demonstrate serious problems with the use of ratios for the evaluation of radionuclide transfer.