Phytoremediation Of Pb-Cd-As Contaminated Soil By Different Plant Species Composition

With the development of mineral resources, random emission of environmental pollutants and so on, heavy metal contamination has been received a closed attention. The purposes of using phytoremediation to control farmland soil pollution are how to improve the efficiency of phytoremediation and how to make better use of the land. Selected plants that have different heavy metals accumulation intercropping, added different enhancement measures, such as fertilizers and organic acids, and increasing seedling growth, heavy metal uptake and accumulation. So the phytoremediation efficiency could be improved and the Pb-Cd-As contaminated soil could be repaired and used. It is recognized to be a promising approach for phytoremediation.This thesis was divided into two parts, greenhouse pot experiment and field trials. (1) Determine the phytoextraction efficiency of several plants, including hyperaccumulators and high biomass, accumulator in the contaminated soil with Pb, Cd and As; (2) evaluate the effects of fertilizers and organic acids on heavy metal uptake and accumulation of plants; (3) conducted a field experiment, explore the effect of situ remediation, and determined the contents of Pb, Cd and As in corn grain. To getting some agricultural products which conform certain health standards while conducting phytoremediation. The results indicated as follows:1. Corns had the largest above-ground biomass (6.93 g-plant-1) in the treatment of corn/Solanum nigrum intercropping. Compared with the other two intercropping modes, the aboveground biomass increased 1.7 and 1.9 times. The heavy metal contents in maize shoots were much lower than the roots under any intercropping modes. Although corn/S. nigrum intercropping could not significantly increase Pb, Cd and As concentrations better than other configurations, it could markedly enhance dry biomass of maize, thus it was the most effective treatment in increased heavy metals accumulation.2. NH4CI could significantly increase the aboveground biomass of plants, the max value of maize is 10.36 g-plant-1, and Solanum nigrum is 4.11 g·plant-1. Compared with the control, it increased 49.5%and 31.7%respectively. The extractability contents of Pb, Cd and As with the application of NH4Cl was increased 2.4,1.0 and 1.3 times, respectively. could reduce Pb concentration in root tissues of maize. Potassium and compound fertilizers could reduce Cd concentration in aboveground tissues of S. nigrum. Nitrogen fertilizer was the most effective fertilizer in enhancing phytoremediation of Pb-Cd-As contaminated soil by plants.3. The imposition of organic acids brought a general decline of plant biomass, but the effects were insignificant. What's more, its inhibitory effect to S. nigrum was relatively more intense than that of maize. For Pb accumulation in the aboveground of maize, the order follows citric acid> tartaric acid> oxalic acid, while for Cd and As, it's citric acid> oxalic acid> tartaric acid. Citric acid could significantly increase As accumulation at high concentration. Compared with the control, it could increase Cd extraction for 1.1 folds, and As extraction for 69.2%. It also could increase Pb extraction for 1.8 folds in aboveground tissues of S. nigrum at medium concentration. Due to the inhibiting effect of organic acids on the growth of plants, it did not to improve the extraction of heavy metals by plants very well.4. Different plant configurations were not affected the growth of maize markedly, but inhibited Pteris cretica significantly. For the concentration of Pb, Cd and As in different organs of maize, the results showed that leaf> root> stem> grain. Corn/S. nigrum intercropping was the most effective mode in enhancing phytoremediation, and the total migration contents of Pb, Cd and As were 0.203,0.029 and 0.316 kg-ha-1. In addition, the concentration of Pb in grain was obviously lower than the national standard of feed hygiene. Except corn/Pteris cretica intercropping, the concentrations of Cd, As in maize grain harvested in other configuration modes were lower than the national standard of food hygiene, and maize grain is safe as animal feed. Therefore, corn/S. nigrum intercropping is feasible to repair the Pb-Cd-As contaminated farmland.