Natural Sr Concentrations and Kd Determinations

Strontium distribution coefficients were determined on samples of glacial till from two sites in Southern Ontario to investigate the effect of natural strontium concentrations on measured distribution coefficient (Kd) values. The distribution coefficients were determined by the ‘batch’ method using synthetic ground water solutions prepared on the basis of 1:1 soluble soil extract analysis. A regression analysis of Sr Kd versus soluble strontium content of the soil materials indicated a strong relationship between decreasing Sr Kd and increasing natural strontium concentrations with a correlation coefficient of $-0.8511\text{.}$ Batch tests performed using stable strontium showed that the horizontal section of the distribution curve observed using the conventional radiometric method of analysis is not representative of varying Sr concentrations but is a result of Kd values determined at one Sr concentration, due to the natural Sr content of the soil material. Removal of the natural Sr caused an increase in the measured Kd value. This increase in Kd, coupled with the previous observations, provides evidence that the Sr Kd values for the soils studied are significantly affected by the natural Sr content of the soils. The effect on Kd values by background isotopes has important implications with respect to both the measurement of Kd values and with respect to their field application in as much as Kd values could be altered by any changes in the natural concentration of stable isotopes of the radionuclides of interest.