Traditional remediation techniques in removing toxic metal contaminants using physical and chemical methods are expensive and may cause other forms of damage to the environment, comparing with these techniques bioremediation can serve as an inexpensive, effective and environmental friendly remediation method. This thesis mainly discusses different bioremediation techniques and identifies possible areas in Hong Kong for bioremediation and suggests bioremediation methods for each potential area. Bioremediation of toxic metals is the use of microorganisms, plants, or even larger sized organisms to decontaminate sites with toxic metals. Bioremediation includes phytoremediation, microremediation and vermiremediation which use plants, microorganisms and earthworms to remediate contaminated environments respectively. The 4 most common mechanisms in phytoremediation of toxic metals are phytoextraction, phytofiltration, phytovolatilization and phytostabilization. Phytoremediation are used frequently for remediation around the world and its development includes using well-understood technology and genetic engineering to increase its effectiveness. Microremediation is another promising technology in bioremediation of toxic metals and consists of 6 major mechanisms which are biosorption, bioaccumulation, biotransformation, bioleaching, biomineralization and microbially-enhanced chemisorption of metals. Microremediation is mainly in research phase and its development includes identifying new species, combining with phytoremediation and genetic engineering. Vermiremediation is another rapidly developing technique in bioremediation of toxic metals, assisting other bioremediation by burrowing actions of earthworms and its excretion, and accumulating toxic metals inside their bodies. Vermiremediation is also in research phase but it is rapidly developing. Generally, bioremediation is around 60% cheaper than traditional remediation methods and no pollutants are emitted during the process. However the remediation process is slow and generally takes longer than a year. Sources of toxic metals in contaminated areas in Hong Kong are mainly due to historic industrial discharge although present activities also contribute. Potential areas include sites for electronic waste activities, sediments of Kwun Tong typhoon shelter and sediments of Tolo Harbour. / published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

In fracture management with open reduction and internal fixation with metallic implant, secondary procedure of removal of implant is often required. Such procedure causes additional surgical risks to patients, including anaesthetic risks, wound infection, bone infection, soft tissue adhesion and joint stiffness. The procedure is also costly to the patient and society. If the fixation implant is self-resorbable, the need for secondary surgery will be completely eliminated and the social resources can be saved. Making use of the corrosion process, metals can be developed into new generation of resorbable (or biocorrodible, biodegradable) implants. An ideal bioresorbable orthopaedic implant should provide adequate mechanical support that matches the bone healing process. The implant should resorb progressively as the bone heals. Many current resorbable materials are biomechanically inferior to conventional metallic implants. Magnesium based alloys are popularly studied because of their mechanical properties and biocompatibility. Implants made of magnesium based alloy are expected to resorb in the human body with no harmful effect. The major research challenge is to identify an alloy that performs satisfactorily in the following aspects: biocompatibility, degradation rate, hydrogen gas formation (gas product from the reaction between Mg and water), and mechanical strength. In addition, there is no standard evaluation method for the biodegradable alloys. It is because the interaction between the degradable implants and the physiological environment is too complicated to mimic. The in vitro and the in vivo results often mismatch. This research involved the design and the tests of three Mg based alloys. Zinc (Zn) and manganese (Mn) were chosen as the alloying elements for corrosion resistance and mechanical enhancement. Mg-1Zn-1Mn, Mg-3Zn-1Mn, Mg-5Zn-1Mn (in wt.%) were developed and compared. The study was divided into three parts: material characterization, in vitro studies, and in vivo (animal) studies. The SEM/EDX confirmed that the surface properties of the alloys were consistent after the surface treatment. From the mechanical test, the yield strengths and the densities of the alloys were found to be close to that of the natural bones. The theoretical calculation showed that the amount of Mn determined the threshold implant mass of the test alloys. The hydrogen evolution test showed that the Mg-1Zn-1Mn was the least corrodible. The elution test showed that the Mg-1Zn-1Mn was the least cytotoxic and the cytotoxicity was affected by the pH changes brought by the alloys. The live cell imaging captured the interaction between the alloys and the cells. The subcutaneous implantation showed that the Mg-3Zn-1Mn formed the smallest gas pocket. In the six-month femoral implantation study (Mg-3Zn-1Mn excluded), the Mg-1Zn-1Mn showed the least volume loss and the steadiest degradation behaviour. It was also found to associate with better bone responses. Concluding from all the results, the Mg-1Zn-1Mn demonstrated better potential to become biodegradable orthopaedic products. This work evaluated the potentials of the new alloys and proposed some suggestions for the mismatch results. Moreover, quantitative investigation of biomechanical properties, long term degradation behaviour, and toxicity are recommended to be carried out in the future. / published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy

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