Retention of cadmium by soils and humic acids

The problem of anthropogenic contamination of soils by cadmium is highly topical also in Slovak soils utilized for agriculture. The main issue is: the proportion of different soil properties in the range of sorption of this microelement in soils. For this reason seven different soil types were chosen for retention experiments with cadmium under laboratory conditions. Sorption and desorption of cadmium were performed on humic acids. Retention experiments confirmed the fact that different soil types have different retention abilities against cadmium. Sorption and desorption of this element was profoundly affected by soil pH and sorptive capacity of the soil. No correlation was found between total amount of organic matter in soil and sorption of cadmium. Significant linear correlation was measured between the size of sorption of cadmium by soil and amount of carboxyl groups in humic acids. Sorption of cadmium on isolated humic acids was approximately seven times greater than in the case of soils from which humic acids were isolated. Significant differences in retention abilities of humic acids were also found. The size of sorption and desorption of cadmium on humic acids was markedly affected by their chemical structure, particularly by the number of carboxyl groups and degree of humification.