الفهرس 
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Abstract
The extent of the current work dealt with bioremediation of toxic heavy metals in agricultural soil ecosystem.
The first chapter included biological and chemical characterization of three soil ecosystems irrigated with sole or mixed diversified low quality water, i.e., sewage effluent, drainage water or industrial effluent for varied extended periods. The first sample is a surface sandy soil irrigated with sewage effluent for more than 35 year from El-Lebeny drain collected from Abou-Rawash (Giza Governorate), the second one is an alluvial soil irrigated with mixed sewage, industrial effluents and agricultural drainage for more than 80 year from Branch 62 - main canal pronged from Kitchener drain collected from Kafr-el-Sheikh Governorate and the third one is surface alluvial soil irrigated with sewage effluent for more than 30 year collected from Kafr-Shokr (Qalubya governorate). Two samples were collected from each site, i.e., cultivated with corn or un-cultivated, all types of irrigation water were also sampled.
• Biological and chemical characteristics were estimated to investigate the effect of long term irrigation with low quality water on the soil ecosystem. The biological characterization included counting the numbers of the major microbial groups, i.e., bacteria, Actinomycetes and fungi as well as measuring the enzyme activities in each soil ecosystem (dehydrogenase, urease and alkaline phosphatase).
• The chemical characteristics of the soil ecosystems included pH, EC and heavy metal contents. The soil quality was assessed through different parameters such as WHO and FAO limits and geoaccumlation index. A speciation for the heavy metals Zn, Cu, Ni, Cd and Cr in the different soil fractions was carried out to get reliable information about the potential toxicity of heavy metals in the soil ecosystem.
• Results of the chemical and biological characteristics of the different tested soil ecosystems confirmed risky impacts on the investigated soil ecosystem. Results indicated that Kafr-el-Sheikh soil ecosystem exhibited the highest concentrations of Cd, Cr, Ni (13 and 14 ppm), (215 and 280 ppm) and (65.4 and 72ppm) in cultivated and un-cultivated soil ecosystems respectively, which exceeded the permissible limits set by FAO and WHO. It had lower microbial activity compared to other tested soil ecosystem and the highest degree of contamination according to geo-accumlation index, hence was selected for further trails on heavy metals decontamination to restore a healthy soil ecosystem.
• Different microorganisms were isolated from the selected soil ecosystems capable for heavy metals decontamination. Based on their morphological and microscopic characteristics as well as their 16S rRNA genes sequence analysis, the isolates were identified as Pseudomonas aeruginosa, Enterobacter cloacae and Saccharomyces cerevisiae; all are habitually used as bioremediation tools.
• The second chapter deals with the results of the greenhouse experiment that was carried out at the National Research Centre using a high contaminated soil ecosystem with heavy metals collected from Kafr-el-Sheikh
• The efficiency of some remediative treatments on heavy metals decontamination (Cd, Cr, Ni, Cu, and Zn) in highly contaminated soil ecosystems using the hyper-accumulator radish plant as a test plant were evaluated. The tested treatments were Pseudomonas aeruginosa, Saccharomyces cerevisiae, Enterobacter cloacae + Rock Phosphate, Mixed culture consortium of Pseudomonas aeruginosa, Saccharomyces cerevisiae and Enterobacter cloacae (MCC) , mixture of kaolinite and bentonite + mixed culture consortium and soluble organic matter + mixed Culture consortium.
• Effect of different treatments on soil microbial activities, total biomass of radish and pH were also followed. The maximum dehydrogenase activities were attained under the action of a mixture of tested microorganisms, 41.67 µg TPF/g soil/24h. Application of soluble organic matter + MCC and KB+MCC increased the dehydrogenase activity by (48 and 30%) compared to un-cultivated control soil ecosystem. Single amendments such as Saccharomyces cerevisiae, Pseudomonas aeruginosa and Enterobacter cloacae + Rock phosphate raised the dehydrogenase activities by 8, 25 and 11% compared to control un-cultivated soil ecosystem.
• The mixed culture consortium (MCC) resulted in the highest reduction in total concentration of all tested heavy metals in the soil ecosystem and lowered Ni, Cd and Cr to 36,1.96, 96 ppm, under permissible limits set by FAO and WHO (50, 3,100 ppm) and increased the uptake of these heavy metals in radish. These, however, were promising treatments in the phyto-extraction of heavy metals from the soil ecosystem. The application of soluble organic matter + MCC led to reduction in total concentration of all tested heavy metals compared to the cultivated control soil ecosystem, the maximum reduction was recorded for Cd and Cr it lowered total Cr and Cd under the permissible limits and showed a little reduction in Ni (10.4%). Application of a mixture of kaolinite and bentonite + Pseudomonas aeruginosa and Saccharomyces cerevisiae proved to be a promising technology for the immobilization of tested heavy metals in the soil ecosystem, as they exhibited the highest reduction in availability and uptake of tested heavy metals. They lowered total concentrations of Zn, Cu, Ni in radish under the permissible limits given by FAO and WHO for plant (50, 10 and10 ppm). Application of a mixture of kaolinite and bentonite + Pseudomonas aeruginosa inhibited the uptake of Cd completely, while Saccharomyces cerevisiae, exhibited higher reduction in Cd uptake compared to control plant, yet radish content of Cd was still above permissible limits (0.02ppm). They also gave the highest reduction in uptake of Cr, despite the radish content of Cr was above safe limits in plant (1.36 ppm). Application of Pseudomonas aeruginosa and Enterobacter cloacae + Rock phosphate and a mixture of kaolinite and bentonite +MCC led to a significant reduction in total concentration of all tested heavy metals, but doesn’t lowered them to the permissible limits given by in FAO and WHO in the soil ecosystem, and the total concentration of all tested heavy metals was still higher than the permissible levels gave by FAO and WHO for plants except for Ni.
• Regarding to soil pH, all tested remediative amendments decreased soil pH, the highest reduction was measured under the application of Pseudomonas aeruginosa and Enterobacter cloacae+RP (7.5 and 7.4) compared to control soil ecosystem (8.08). It is worthy to state that all tested remediative amendments led to a growth promotion and increased the total vegetative biomass of radish and mixed treatments were more efficient than the single ones, the maximum growth promotion was observed by application of soluble organic matter + MCC, it increased total vegetative biomass by 117 %.
• In the third chapter, MCC and soluble organic matter + MCC were selected to phyto-extract the tested heavy metals, because they exhibited the highest reduction in total concentrations of studied heavy metals in soil and the highest uptake by plant.
• Application of Saccharomyces cerevisiae and KB + Pseudomonas aeruginosa was a promising technology in fixing the tested heavy metals, because they resulted in a significant reduction in availability and uptake of the tested heavy metals and led to safe food production and this method was so effective in the heavily contaminated soil ecosystem and caused rapid decontamination of heavy metals for safe food production. Gained results in the field experiment confirmed those of the greenhouse one.
• The rhizosphere effect was so obvious enhancing dehydrogenase activity, it increased dehydrogenase activity by 17.4% compared to control soil ecosystem. Application of MCC and tea compost + MCC led to the maximum dehydrogenase activities; they increased dehydrogenase activities by 108 and 73% compared to un-cultivated control ecosystem.
• Application of MCC and tea compost + MCC showed also the highest reduction of all tested elements (57, 47, 48, 65and 2.0 ppm), (101, 58, 62.6, 46 and 2.9 ppm) and they enhanced phyto-extraction of these elements. In contrast application of Saccharomyces cerevisiae and KB + Pseudomonas caused a higher reduction in availability and uptake of all tested heavy metals.
• The rhizosphere had a clear effect in lowering pH from 8.01 to 7.85. The maximum depression in pH value was recorded under the application of MCC and Saccharomyces cerevisiae reaching (7.65, 7.7).
• Results displayed that all treatments improved total fresh biomass of radish compared to control. The highest increase in total fresh biomass was recorded under application of MCC and tea compost + MCC (56.7, 58.8%) compared to control, the lowest increase was recorded under application of Saccharomyces cerevisiae (15.4%).