| Soils contaminated with metals pose a major environmental and human health problem, which is still in need of an effective and affordable technological solution. The phytoremediation is a cost-effective"green"technology based on the use of metal-accumulating plants to remove toxic metals. In phytoremediation process, Pb mobility and the change of Pb fractionations were controlled by the physio-chemical properties of the soils, and Pb fractionations impacted on the toxic levels of heavy metal. The success of reclamation schemes is dependent greatly upon the choice of plant species and their methods of establishment. Mixed substrate of EDTA and NPK fertilizer has been used to restore contaminated soil in recent years, however, little is known about the effect of both major nutrient elements and EDTA on various forms and mobility of Pb and metal extraction. Plant growth and lead accumulation of accumulating and non-accumulating ecotypes of Sedum Spinacia oleracea, Sonchus arvensis, Portulaca olerace, and Helianthus annuus were studied with greenhouse pot experiments. To elucidate the characteristics of Pb tolerance and accumulation in the accumulating ecotype of plants, a series of chemical, biochemical analytic techniques were used to study the absorption, distribution of Pb at tissue and unit in plant, as well its application to phytoremediation. The major results were summarized as follows:1. In the greenhouse pot experiments, we studied influences of major nutrient elements on Pb phytoextraction of two crops (S. oleracea and S. arvensis) from a Pb-contaminated soil. Results indicated that the Pb concentrations in both shoots and roots of two crops ascended with increasing nutrient elements, and the highest nutrient treatment had the best effect as compared with other treatments in which the Pb concentrations in shoots of S. arvensis increased 23.4% (P=0.0202), and nitrogenous nutrient treatment had the best effect in which the Pb concentrations in roots of S. oleracea and S. arvensis increased 49.4% and 57.7% respectively (P=0.0106, P=0.0329), as compared with the control treatment. The potassic and phosphorus nutrient treatments had little effect on the Pb concentrations in plant tissues for S. oleracea. Pb concentration in S. oleracea was lower than S. arvensis. Because of the higher total biomass in S. oleracea than S. arvensis, the ability to Pb phytoextraction in S. oleracea was better than S. arvensis. Sequential extraction results indicated that the addition of soil amendments transform soil Pb from nonresidual fractions to residual fraction substantially. The results suggested that nitrogen and phosphorus amendments can effectively increase Pb uptake by two crops, and phosphorus fertilizer is the best amendment to remediate Pb-contaminated soil with low organic matter.2. We examined biomass accumulation, tissue concentrations of Pb, and net uptake of Pb in S. oleracea, S. arvensis, and P. olerace grown under greenhouse conditions in soil of middle Pb concentrations. Some physiological differences between S. oleracea, S. arvensis, and P. olerace include photosynthetic pathways (C3, C3, and C4, respectively). The transpiration rates and salt tolerance of C4 plants were greater than C3 plants. Whole plant biomass of P. olerace was significantly greatest on initial period August 25, but the greatest biomass of both S. oleracea and S. arvensis was on harvest period September 26. This difference in allocation was more profound at the middle Pb contaminated soil. In S. oleracea, significantly more of Pb concentration was allocated to belowground biomass (roots) than to aboveground biomass (leaves and stems), but S. arvensis was in reverse. No difference between aboveground and belowground of Pb concentration was in P. olerace. The highest pool of Pb was allocated to aboveground biomass in S. oleracea, so S. oleracea was a potential plant for remediation in middle Pb-contaminated soils. The grown period of tissues in P. olerace was short, so if the time of phytoremediation process was not abundant, the replacement of C4 plants with C3 plants may increase times and efficiency of remediation.3. Soil amendment application frequency contributes to phytoextraction of lead by sunflower at different nutrient levels. The main aims of this paper were to investigate whether a combination of nutrients and ethylenediaminetetraacetic acid (EDTA) enhanced Pb uptake of sunflower (Helianthus annuus) plants, and if timing of EDTA application altered Pb uptake and environmental persistence. Plants were grown in greenhouse pot experiments. Pb distributions and uptake of the whole plant were studied using chemical and flame atomic absorption spectrometry analyses. Pb mobilization by EDTA appeared to be dose dependent (P<0.001), with more mobilization for the high than the low dose. There were distinct differences in mobilization patterns of various nutrient amendments. EDTA mobilized Pb more in the medium than the highest and lowest nutrient levels. Heterogeneous soil humus components exerted mobilizing and stabilizing effects, so the medium nutrition was most effective for phytoextraction (P=0.002). At low nutrient levels, Pb concentration in the shoot with one low EDTA application was less than two applications to the same total EDTA dosage. So in the poor soil, two applications of EDTA was more effective than once. The half-life of two low EDTA treatment applications was longer than for one application, to the same total dosage (P<0.001). In general, sunflower was suited to phytoremediation of moderately Pb-contaminated soil by phytoextraction.The result mentioned above showed that the main reasons that nutrient and EDTA could impact on phytoremediation efficiency was these as below: firstly, the addition of soil amendments (N, P, and K) transform soil Pb from nonresidual fractions to residual fraction substantially. Secondly, the grown period of tissues in C4 plants was short, so the replacement of C4 plants with C3 plants may increase times and efficiency of remediation. Finally, two applications of low dose EDTA were more effective than once, and decreased secondary pollution. The innovative points of the study were that the phytoremediation efficiency with twice addition of low dose EDTA and nutrients (N, P, and K) were studied for the first time, the interaction of soil characters and EDTA addition and the affection of nutrients (N, P, and K) on soil Pb fractions were concerned emphatically, secondary environmental risk of ecological invasion was avoided, and scientific basis and theoretical foundation were supplied for non-point source phytoremediation. Addition of low cost nutrients and low dose EDTA in the process of phytoremediation was adopted in order to achieve goal to better control cost, hence which had important significance to wide application of phytoremediation on large area middling Pb polluted soil.
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