Giant Reed (Arundo Donax L.) Remediation With Amendments For Metal-contaminated Soils From The Typical Mining And Smelting Areas

It is a concerned environmental problem for the soil metal contamination and its ecoremediation in the vicinity of non-ferrous mining and smelting area. Heavy metal contaminated soil samples, which are from the vicinity of the typical non-ferrous mining and smelting areas located in Changsha, Zhuzhou, Hengyang and Chenzhou regions, were investigated. The metals contamination and fertilities characteristics of soil were also analyzed. The pot experiments based on the abondanded agricultural surface soil from the vicinity of a smelter in Zhuzhou region, the tolerance and accumulation for heavy metals, and growth biophysiological characteristics of giant reed (Arundo donax L.) in soil polluted by As, Cd and Pb were determined. The growth physiological characteristics and accumulation of As, Cd and Pb in aerial parts of giant reed grown in soil amended with sepiolite, phosphogypsum, EDTA, citric acid and acetic acid were also studied, respectively.The results show that the soils from the vicinity of the typical mining and smelting areas are the multi-pollution of As, Cd, Pb and Zn. Concentrations of As, Cd, Cr, Cu, Pb and Zn in wasteland are significantly higher than those in vegetable soils and paddy soils, respectively. The tested soils are mainly acidic and the soil texture is viscous. Concentration ranges of soil organic matter are 0.18-143 g kg-1 and those of available N, available P and available K are 14.7-372,7.82-202 and 0.00-782 mg kg-1, respectively. Compared with the second levels of the Soil Fertility Standard (NY/T 1749-2009), the over-standard rates of organic matter, available N, available P and available K in the soil samples from the studied areas are 93.7%,95.4%,100% and 89.1%, respectively. The results show that the soil fertility is very well and can meet the demand of ecological restoration for the metal contaminated soils.The transferring ability of As, Cd and Pb in giant reed is weak while these heavy metals mainly accumulated in the roots. When the concentrations of As, Cd and Pb in tested soils are less than 93.7,26.1 and 552 mg kg-1, respectively, the contents of chlorophyll, malondialdehyde and the activities of catalase are significantly higher than the contents of the controlled treatment. The shoot height and biomass of giant reed, however, are slightly changed. Giant reed demonstrated strong endurance when the concentrations of As, Cd and Pb in tested soils are less than 254,76.1 and 1552 mg kg"1, respectively. When the concentrations of As, Cd and Pb in soils reach or exceed 334,101 and 2052 mg kg-1, respectively, the shoot height and biomass of giant reed reduce significantly (P<0.05). Using SEM analysis, the vascular bundles in the stem exhibit stress response obviously. The stem tissues have slightly change and show obviously tolerance when the concentrations of As, Cd and Pb in the soil are 93.7,26.1,552 mg kg-1, respectively.When the concentration of As, Cd and Pb in the soil are 334,101,2052 mg kg-1, respectively, the amendments significantly improve the biomass of giant reed and the biomass of giant reed of the treated amendments has increased 6.15-141.5% compared to the control, especially the treatments with 4 g kg-1 sepiolite and 5 mmol kg-1 citric acid, respectively. The content of chlorophyll in giant reed is not decreased obviously when adding low concentration of EDTA (1.25 mmol kg-1) and high concentration of citric acid (5.0 mmol kg-1). All amendments improve the activities of superoxide dismutase and catalase and concentrations of heavy metals in giant reed. The accumulation of As, Cd and Pb in aerial parts of giant reed has obviously improved under the treatments with moderate concentration of organic acids, light concentrations of sepiolite and phosphogypsum, respectively.