| Soil contamination with heavy metals has toxic effects on plants and soil organisms, and it also presents a serious threat to ecosystem and human health. As the contaminated area is larger, the in situ remediation technologies are considered. The culturing experiment in water or salt solution, pot experiment and semi-field experiment were carried out to study the effect of insoluble polyacrylate polymers or polymers from diappers on adsorption of heavy metals in the solutions and remediation of artificially and long-term contaminated soil with heavy metals. Meanwhile, the effect of compost solely or together with polymers on remediation of contaminated mine soil was also presented in this thesis. The results got from following studies supply a gap for the application of polyacrylate polymers on remediation of heavy metal contaminated soil. Moreover, they also provide the experimental information about application of municipal waste such as the compost and used diapers. The results showed that:(一) The adsorption of metals by polyacrylate polymer and the effects of polyacrylate polymer on artificially contaminated soil with Cd were studied. At the temperature of 25℃,The heavy metals in the solutions were adsorbed rapidly by the polyacrylate polymer and very stable during 120d’s soaping. The amount of absorption to the heavy metal was highest and stable at the pH 4.5-6.5. The bond of polyacrylate polymer with ions of heavy metals was much more stronger than ammonium acetate, slightly higherer than citric acid, and was similar to EDTA. In the soil pot experiment, the growth of ryegrass was enhanced even in the highest Cd level by application of polyacrylate polymer as compared with that of control, and the concentration of Cd in ryegrass shoot was decreased significantly, the water soluble Cd of soil was reduced remarkably as well. The results also indicated the 0.1% of polyacrylate polmers in this experiment should be reasonable.(二) The effects of polyacrylate polymer on remediation of artificially contaminated soil with Zn, Cu and Cd solely or together were studied. The application of polymer resulted in greater growth of ryegrass, significant reduction of concentration of heavy metals in ryegrass and soil in the contaminated soil with metals solely or together. The competition between metals caused differences in the concentration of metals in ryegrass and soil in the muti-metal contaminated soil.(三) We investigated the application of insoluble polyacrylate polymers to improve soil and plant health. Sorghum was grown in a Cd-contaminated sandy soil. Polyacrylate polymers at 0.2% (w/w) were added to half of the soil. Control soil without plants was also included in the experiment. Growth of sorghum was stimulated in the polymer-amended soil. The concentration of Cd in the shoots, and the activities of catalase and ascorbate peroxidase decreased in plants from polymer-amended soil compared with unamended control. The amount of CaCl2-extractable Cd in the polymer-amended soil was 55% of that in the unamended soil. The activities of soil acid phosphatase,β-glucosidase, urease, protease and cellulase were greatest in polymer-amended soil with sorghum. In conclusion, the application of polyacrylate polymers to reduce the bioavailable Cd pool seems a promising method to enhance productivity and health of plants grown on Cd-contaminated soils. The plant of sorghum could be used for the phytoextraction of Cd in this experiment.(四) We investigated the effects of different application rates of insoluble hydrophilic polyacrylate polymers on plant growth and soil quality from a Pb-contaminated mine soil. The polymer increased the waterholding capacity of the soil from about 250 g/kg in unamended soil to almost 1000 g/kg in soil with 0.6% polymer. However, the capacity of the polymer to retain water decreased progressively, presumably as the polymer sorbed Pb. Growth of orchardgrass (Dactylis glomerata L. cv. Amba) was stimulated in the polymer-amended soil. The greatest accumulated biomass over four cuts was obtained in soil amended with 0.4% of polymer. After orchardgrass had been growing for 101 days, the amounts of CaC12-extractable Pb present in the polymer-amended soil were 15-66% of those in the unamended soil, depending on polymer application rate. The number of bacteria culturable on agar enriched with ’Nutrient’ and yeast extract, and the activities of dehydrogenase, phosphatase, b-glucosidase, protease and cellulase increased following polymer application. In contrast, urease activity was impaired by polymer application, presumably due to the presence of ammonium as a counter ion. Principal component analysis was used to compare the effects of the different rates of polymer application. Overall, the application of 0.2 or 0.4% polymer resulted in closer values for the indicators of soil quality used than the treatment with 0.6% polymer.(五) We evaluated the use of polyacrylate polymers to aid phytostabilization of mine soil. In a pot experiment, perennial ryegrass was grown in a mine soil and in uncontaminated soil.Growth was stimulated in the polymer-amended mine soil compared with an unamended control, and water-extractable levels of soil Cu and Zn decreased after polymer application.In an experiment performed in six 60-cm-diameter cylinders filled with fertilized mine soil, polymers were applied to three cylinders, with the remainder used as unamended control. Total biomass produced by indigenous plant species sown in polymer-amended soil was 1.8 (Spring-Summer) or 2.4 times (Fall-Winter) greater than that of plants from unamended soil. The application of polymers to the mine soil led to the greatest activity of soil enzymes. Soil pH, biomass of Spergularia purpurea and Chaetopogon fasciculatus, and activities of protease and cellulase had large loadings on principal component (PC)1, whereas growth of Briza maxima and the activities of urease, acid phosphatase, andβ-glucosidase had large loadings on PC2. The treatments corresponding to controls were located on the negative side of PC1 and PC2. Amended treatments were on the positive side of PC2 (Spring-Summer) or on the positive side of PC1 (Fall-Winter), demonstrating differential responses of plants and soil parameters in the two growth cycles.(六) We used hydrophilic polymers from diapers to aid establishment of an indigenous plant(Spergularia Purpurea) in a soil from a pyrite mine. The establishment of a plant cover was faster in soil amended with polymer from diapers, and at the end of the experiment (85 days after sowing) the soil was completely covered in all treatments except unamended control. Total biomass in polymer-amended soil was about four to five times greater than that of plants from unamended soil. The concentrations of trace elements in plant shoots decreased in amended soil. The activities of soil acid phosphatase, -glucosidase, protease and cellulase were greatest in soil amended with the polyacrylate polymer or with polymer removed from diapers, while the application of shredded diapers lead to values that were in general intermediate between these treatments and unamended control. Basal and substrate-induced respirations, and dehydrogenase (related to microbial activity) were greatest in soil amended with polymers, but the presence of a plastic film and fibrous materials from shredded diapers prevented any improvement in these parameters compared with unamended soil. In conclusion, hydrophilic polymers from diapers can be used to promote a vegetation cover in pyrite mine soils and improve soil hydrolytic enzymatic activities, although studies are still 39 needed to treat diapers and decrease the toxicity towards soil microorganisms associated with some of the materials present in disposable diapers.(七) We applied three doses of compost from mixed municipal solid waste (0、15、30 g kg-1 of soil) to a soil developed from pyrite mine wastes. Compost application to bare soil increased pH, provided plant nutrients, and enhanced the activity of soil enzymes tested. Growth of D. glomerata and E. australis was stimulated in compost-amended soil compared with unamended controls. The presence of D. glomerata led to the greatest activities of soil acid phosphatase,β-glucosidase and cellulase compared with bare soil or with soil with E. australis. The presence of E. australis increased the activities of protease and cellulase in amended soil, compared with control, but it impaired dehydrogenase,β-glucosidase and acid phosphatase activities. These negative impacts probably derived from phenolic compounds known to be released from roots of this species. The survival strategy of this species seems to include a small need for P in the shoots and the release of exudates that impair microbial activity and P cycling.(八) We tested the application of compost and polyacrylate polymers to promote the growth of indigenous plant species present in the mine area. In the absence of plants, the greatest improvements in soil conditions were obtained by the application of both polymer and compost, which was associated with the greatest values of protease, acid phosphatase, andβ-glucosidase, whereas the activity of cellulase and microbial respiration were similar in soil amended with compost or polymer. Dehydrogenase activity was greatest in soil with compost (with or without polymer), whereas urease activity was impaired by both amendments. In the presence of plants, the application of both amendments led to the greatest activities of protease, urease,β-glucosidase, cellulase, and microbial respiration, but acid phosphatase was mainly enhanced by polymer and dehydrogenase was increased by compost. Plant growth was stimulated in all treatments compared with unamended soil, but the greatest value for total accumulated biomass was obtained in fertilized soil receiving both amendments. However, species responded differently to treatment: while the growth of B. maxima was greatest in soil with compost and polymer, the growth of C. fasciculatus responded better to soil with compost, and S. purpurea grew better in polymer-amended soil. The amendments tested improved the quality of a mine soil and stimulated plant growth. However, botanical composition likely changes over time with amendments, and this needs to be considered when a large scale application of amendments is projected.(九) The risk of downward movement of polymers in columns of a sandy soil was studied. Hydrophilic polymers from diapers with or without Cu were placed at a 10 cm-depth in the soil. Five leaching cycles with artificial rain took place and leachates were analyzed for organic matter (OM) and Cu. At the end of the experiment, the soil columns were sliced and each layer analyzed separately. The results showed that leaching of OM and Cu took place, albeit from mobile fractions in the soil. Some repacking of soil and polymer particles took place, but there was no indication that polymers moved to any great depth in soil columns. |
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