Research On The Continuous Field Phytoremediation Of Zinc And Cadmium Contaminated Soil

Phytoremediation of heavy metal contaminated soil had wide range of applications because of its inherent potential advantages. However, application of this technology often requires multiple hyperaccumulators to continuous remediation. The change of heavy metals in soil and plant uptake will significantly affect the remediation efficiency, and the long-time phytoextraction had a contradiction with the use of farmland. In this paper, we took metal smelting contaminated soil and the long-term sewage sludge manure application contaminated soil as tested soils, the field experiments with Sedum plumbizincicola and field crop, then another water simulations experiment were conducted. The aim was to find the changes of soil heavy metals after repeated phytoextraction and the relationship between metals in the soil and metal uptake by plants, as well as appropriate production and remediation at the same time. It will provide a theoretical basis for the safety production of zinc and cadmium contaminated soil at the same time to achieve efficient extraction and remediation. The main findings are as follows:1. One field plot experiment, S. plumbizincicola intercropped with Zea mays were conducted to find the changes of soil heavy metals after repeated phytoextraction and the relationship between metals in the soil and metal uptake by the hyperaccumulator S. plumbizincicola. The results showed that soil Zn and Cd concentrations decreased markedly after long-term phytoextraction. In the present study, the soil Zn and Cd concentrations occurred in the maize/Sedum intercropping treatment after eight crops of phytoextraction declined from 3.75±0.57 to 0.55±0.44 mg kg-1, and reached the third level of the National Soil Environmental Quality Standard (Cd 1 mg kg-1). Compared to the metal concentration in year 2006, after eight crops of repeated remediation the Zn concentrations in the maize monocropping, Sedum monocropping and maize/Sedum intercropping in year 2014 decreased by 1.5, 13.4 and 24.9%, respectively; and the Cd concentration decreased by 33.8,70.7 and 85.5%, respectively. The phytoremediation efficiency of Zn and Cd by S. plumbizincicola intercropped with maize was higher than by the S. plumbizincicola monoculture. So, S. plumbizincicola intercropped with maize can improve heavy metal phytoextraction without affecting the cereal crop production, so as to achieve the purpose of simultaneous’safe agricultural production’and’heavy metal phytoextraction’2. S. plumbizincicola as well as conventional maize-wheat-carrot crop rotation in field experiment was carried out to study the safe agricultural production and continuous phytoremediation efficiency after the long-term application of sewage sludge. Sludge conducted on soil planted with of field experiments to explore the long-term application of sewage sludge heavy metal contaminated soil contamination. The results showed that crops and S. plumbizincicola grew well in soil under the long-term application of sewage sludge. Compared with the control, the Zn and Cd concentration in corn-wheat-carrots crop rotation system has increased, but the grain Cd concentrations of wheat and carrots in the experiment were over the National Food Quality Standard. The Zn and Cd concentrations in soil under S. plumbizincicola treatments decreased markedly. The phytoremediation efficiency of Cd by S. plumbizincicola’was 56%. While the treatment for "continuous application of sewage sludge manure", the phytoremediation efficiency was still up to 48%. So under conditions of application of sewage sludge, planted with S. plumbizincicola and corn could achieve the triple objective of the safe handling of sludge, promote crop growth and high phytoextraction efficiency.3. Soil moisture changes can significantly affect soil properties and lead to the change of soil heavy metal availability. In this study, the effects of moisture and drying process on soil heavy metal availability by investigating Zn, Cd concentrations represented by DGT and in soil solution. The results showed that Zn, Cd availability evaluated by DGT with the soil water contend decreasing during soil drying processes; In agricultural production, appropriate water management can be used to reduce the availability of heavy metal, thus alleviate the toxicity of heavy metal.