| The disposal of municipal sewage sludge has become a big problem to the scientific community and the governments in countries around the world. With the inherent advantage, land utilization of sewage sludge became the reasonable and effective one of all disposal measures. In the application of sewage sludge to soil, the migration of heavy metals was the focus issue of the scientific community. For this study, an adsorption-desorption experiment and a pot experiment were carried out investigating the migration of copper and the biological effect of cadmium in the municipal sludge compost-amended soil, respectively. The results showed:1. With the increase of compost proportions, the adsorption amounts and the potential adsorption amounts of copper on loess amended compost increased. The adsorption amount of copper on the soil sample with the compost content of 48.8% rose 32.6% than that on loess, and the potential adsorption amount of copper on the soil samples with the compost content of 48.8% rose 49.6% than that on loess.2. With the increase of compost proportions, the retention amounts of copper on loess amended compost increased. The retention amount of copper on the soil samples with the compost content of 48.8% rose 537% than that on loess. The retention capacity was influenced by organic matter content, pH and EC, but organic matter content was the important impact factor, and the correlation coefficient between retention amounts and organic matter contents was 0.9423.3. pH of the soil amended with compost of 0.5% content was 0.24 less than that of loess, but pH of two soil samples was more than 8. Organic matter content, nitrogen content of the soil amended with compost of 0.5% content rose 116%,21.6% than that on loess, respectively. EC of the soil amended with compost of 0.5% content was 837 μs/cm, but the EC was less than the threshold (1500 μs/cm). Contents of copper, zinc, nickel, lead, cadmium in the soil amended with compost were 25.5 mg/kg,73.8 mg/kg,26.2 mg/kg,17.6 mg/kg,0.07 mg/kg, which were less than the threshold of soil contamination.4. The 0.5% content of compost may promote wheat growth. Dry weights of root, dry weights of stem and leaf, dry weights of ear, dry weights of grain, grain numbers, plant heights rose 52.6%,109.6%,258.7%,3.4%,521.7%,35.1% than that of loess, respectively. A low rate of cadmium, may promote wheat growth, but after the rate reached the threshold of 1.6 mg/kg and 2.4 mg/kg, cadmium toxicity in loess and soil amended with compost become obvious, respectively.5. As the application of compost, exchangeable cadmium content and carbonate-bonded cadmium content decreased of 0.05 mg/kg and 0.04 mg/kg, respectively; but organic cadmium content and residual cadmium content increased of 0.008 mg/kg and 0.1 mg/kg, respectively. The proportions of forms also displayed the same trend. As the application of compost, exchangeable cadmium proportion and carbonate-bonded cadmium proportion decreased of 1.26% and 1.23%, respectively; but organic cadmium proportion and residual cadmium proportion increased of 0.77% and 4.80%, respectively.6. As the application of compost, cadmium contents in root, stem and leaf, shell, grain decreased of 0.94 mg/kg,0.58 mg/kg,3.35 mg/kg,0.67 mg/kg; and the biological enrichment factors of root, stem and leaf, shell, grain decreased of 0.37,0.48,1.61,0.31; and the transfer factor decreased of 0.44.7. Cadmium contents in various organs followed the sequence:root>stem and leaf>shell> grain. The biological enrichment factors of various organs followed the sequence:root>stem and leaf≈shell>grain. With rising cadmium application rate, the transfer factors decreased.8. As the application of compost, the bioavailability of cadmium became weak. The threshold of plant toxicity in loess was 2.4425 mg/kg, and the threshold of food contamination in loess was 0.4425 mg/kg. The threshold of plant toxicity in soil amended with compost was 4.4725 mg/kg, and the threshold of food contamination in soil amended with compost was 0.8725 mg/kg. |
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