Relation between heavy metal fraction in soils and plants enrichment in pilot scale experiment on land application of sewage sludge

In order to understand the heavy metals accumulation and transfer in a plant-soil system in sewage sludge applied soils, 15 familiar garden plants (including 7 herbages, 5 shrubs and 3 arbor species) were planted in soil with sewage land application at the experimental site in Shanghai, China. The experiment measured the changes in 7 heavy metals (Zn, Cu, Ni, Cd, Pb, Cr and As) fractions and concentrations in the soils and the distribution of heavy metals in plants during a growth season. The results showed that the physical and chemical properties of the soil were much changed after the sewage land application. The heavy metal concentrations and fractions changed after the sewage sludge was applied on the land. The planting experiment indicated that the capability of plants to accumulate heavy metals was mainly related to the plant species. The distributions of heavy metals in plant were different. For most plants in the experiment, the element concentrations of roots were higher than those of the above-ground parts of plants. The order of ability to accumulate the heavy metals was herbages > shrubs > arbor in both above-ground and below-ground parts of these garden plants. The results also showed that the absorption of heavy metals in soil into the plants was determined by the fractions, contents of the heavy metals, and the selective absorption of plants. With respect to the absorption of heavy metals in plants, a 30% application rate was probably the optimum application rate for the experimental land.