A new method for determining the bioavailability of radionuclides in the soil solution

A new method for determining the pool of radionuclides in the soil solution, available for root uptake, has been compared to existing methods. The new method is based on extracting the soil solution at a soil moisture below saturation. It uses the soaking capacity of a polyacrylamide resin deposited on a cellulose acetate membrane laid on the soil surface. The new method exhibited the best reproductibility amongst the methods tested. It allowed us to extract more 134Cs and a similar amount of 85Sr relative to the other methods. The correlation between the observed ratio of radionuclide concentrations in soil and plants and the radionuclide concentration of the soil solution using the new method was better than using the existing methods. Using the measurement of 134Cs and natural potassium in the soil solution by the new method, based on a multiple regression equation involving an exponential form, the uptake of 134Cs by bean and wheat was predicted with a 0.9 determination coefficient. As far as the uptake of 85Sr is considered, this method was not very successful since the equation with a linear form involved a large number of parameters.