Interaction and fractionation of added cadmium in some typical soils of the Danubian Lowland

This study was conducted to investigate the effect of time on cadmium (109Cd) availability in four typical soils of the Danubian Lowland through the modified Tessier's sequential extraction procedure as well as its short-term sorption in the bulk soils and their two grain-size fractions. Results of the fractionation study showed that there were significant changes in the proportional distribution of cadmium in all studied soils during 180 days of incubation with spiked cadmium. Generally, the proportions of cadmium associated with the most weakly bound fractions (water soluble and exchangeable) tended to decrease with corresponding increases in the residual fraction during the incubation. The extent of cadmium sorption in all studied soils was high, exceeding 95% of the spiked amount after 60 min of incubation, likely due to slightly alkaline character of the soils. The finding that soil particles less than 10 μm sorbed up to 51% of the spiked cadmium in soils is of great importance since they could play a role in colloid-facilitated transport of cadmium through preferential pathways, as previously observed in the region. Addition of 1 M ammonium nitrate into the soil solution generally decreased cadmium sorption in all four soils. The lowest extractabilities of Cd were obtained using 1 M ammonium nitrate as a single extractant, whereas 0.025 M ammonium ethylenediaminetetraacetate solution extracted the highest proportions of cadmium from the studied soils. (author)