Determination of labile cadmium in lime-amended soils by isotope dilution plasma mass spectrometry

We examined the effect of pH on isotopically exchangeable Cd in lime-amended and upland soils using an IEK technique. In all the soils, an increase in pH from 5 to 7 decreased the concentrations of water-soluble Cd. In contrast, the isotopically exchangeable Cd (E-value) was not influenced by the soil's pH value. The calculated IEK parameters r(1)/R and n from isotopic kinetics were successful in predicting E-value during 15 d of exchange. In the lime-amended soils, as the pH increased, E(1) decreased, and the IEK parameters r(1)/R and n increased. These results indicate that, as the soil's pH increased, the instantaneous isotopically exchangeable Cd in the soil reduced and exchange velocity increased. Accordingly, the increase in soil pH should reduce water-soluble Cd in soil, but should not affect the labile Cd pool. Thus, the IEK technique can evaluate both the instantaneous isotopically exchangeable Cd and E-value, and will be a useful tool for assessing the Cd hazard risk in soils. (author)