Measuring and simulating effect of organic residues on the transport of cadmium, nickel, and zinc in a calcareous soil

Abstract

Knowledge of heavy metal movement from organically-rich soils is important for assessing heavy metal mobility and developing methods for predicting such losses. Laboratory soil column study and sequential extraction analysis were conducted to evaluate the effect of eight organic residues (sewage sludge, municipal solid waste compost (MSWC), poultry manure, sheep manure, mushroom compost, and residues of wheat, potato, and rape) on retention and leaching of cadmium (Cd), nickel (Ni), and zinc (Zn) in a sandy loam soil. Cadmium, Ni, and Zn were monitored in the leachate of soil column by passing a mixture of 50mgL−1 CdCl2, 50mgL−1 NiCl2, and 50mgL−1 ZnCl2 solutions through the soil column. The addition of all amendments to the soil caused to an increase in leachate pH in the initial stage of leaching. Movement of Cd, Ni, and Zn ions in control soil was retarded due to adsorption. The retardation factor (Rf) decreased due to the addition of organic residues, enhancing heavy metal movement. Soil treated with wheat residue, MSWC, and mushroom compost had the highest Rf for heavy metals, followed by sheep manure, rape residue, sewage sludge, potato residue and poultry manure. Potato residues and poultry manure enhanced heavy metals transport to the greatest degree. For most organic residues studied, Rf showed the trend Ni>Zn>Cd, indicating the rate of heavy metals transport in this calcareous soil was: Cd>Zn>Ni. The above trend was confirmed by sequential extractions of soil columns, indicating 44% (average of all amended soil columns) of total Cd was in the exchangeable form (EXCH), while EXCH fraction was 26% and 19% for Zn and Ni, respectively. The risk of groundwater contamination will increase after applying organic resides and it needed to be used very carefully. An integrated modeling approach employing a surface complexation and an ion exchange model has been developed in PHREEQC. The similarity between measured and simulated data indicated that the model was successful to predict Cd, Ni, and Zn movement in control and organically-amended soils.