This thesis is directed towards the development of the diffusive gradients in thin films (DGT) technique for the measurement of total dissolved As, and for As speciation measurements. In addition, a preliminary investigation of a novel laboratory-based method for measuring labile metal species was carried out; this method involved the coupling of a microcolumn of adsorbent with a standard electrothermal atomic absorption spectrometer. An iron-oxide adsorbent was utilized for As measurements by DGT. The diffusion coefficients of inorganic Asv and AsIII> were measured through the polyacrylamide diffusive gel using both a diffusion cell and DGT devices. A variety of factors that may affect the measurement of total As by DGT were investigated. These factors, which included pH, anions, cations, fulvic acid, FeIII-fulvic acid complexes, and colloidal Fe, may affect the adsorption of the As species to the iron-oxide, or may affect the diffusion coefficients of the individual As species. The DGT method was further developed to selectively accumulate the AsIII species in the presence of Asv. This was achieved by the placement of a negatively charged Nafion membrane at the front of the DGT device which slowed the diffusion of the negatively charged Asv species (H₂AsO₄₂ ⁻) considerably, relative to the uncharged AsIII species (H₃AsO₃). The effect that pH, anions, and cations may have on the selective accumulation of AsIII, in the presence of Asv, was investigated. DGT devices without a Nafion membrane and with a Nafion membrane were deployed in natural waters to determine the total inorganic As and AsIII> concentrations, and to evaluate its performance. A preliminary investigation of the coupling of a microcolumn of Chelex-100 resin with a standard electrothermal atomic absorption spectrometer was undertaken to establish its value as a laboratory-based speciation method. This involved the examination of various microcolumn materials to accommodate the Chelex-100 resin, and finding an appropriate buffer that could be used to buffer the Chelex-100 resin without interfering with the ETAAS measurement. Furthermore, factors that may affect the uptake of metal by the Chelex-100 resin, such as concentration of buffer in solution, ionic strength, and conditioning of the Chelex-100 resin, were investigated.

Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Michael Saunders; Committee Member: Ching-Hua Huang; Committee Member: Marc Frischer.

Universiẗat, Diss., 2001--Dortmund.

Iodine-129 is a high-yield fission product of 235U and 239Pu; is produced in nuclear power plants and is therefore present in substantial quantities in radioactive wastes. In the environment, iodine exists as a range of species: iodate (IO3-), iodide (I-), elemental iodine (I2), HOI and organic species are the most common. The behaviour of iodine in the environment is linked to its speciation which can be affected by different factors such as pH, redox potential and enzymatic reduction. Previous research has shown that iodine speciation can determine its fate in the environment; however the mechanisms of redox cycling amongst the different species are not yet fully understood. This research project has focused on improving the understanding of the changes on speciation of iodine in sediment and mineral systems undergoing redox cycling reactions. The fate and changes in iodine speciation were studied under reducing and oxidising conditions, with all experiments conducted under circumneutral pH conditions. Overall the results showed that when microbial activity is promoted in a sediment system, iodate is reduced to iodide with the reduction occurring during manganese reduction. Further, when nitrate is present at high concentrations the reduction of iodate is retarded. A net release of native iodine from sediments was observed in all experiments conducted with sediments; confirming previous observations that sediment bound iodine is released from sediments under reducing conditions. Modest abiotic reduction of iodate was observed under manganese and iron reduction; and iodate reduction happened faster in a mixed system with iron and pure culture bacteria than solely by the pure culture alone or via abiotic reduction with Fe(II). When reduced experiments were exposed to air, concentrations of iodide decreased with no iodate ingrowth or losses in total iodine in solution. This suggested that iodide had been oxidised to intermediate species (I2, HOI) that were not detected, although this reaction has been described in past research. Finally, when no microbial activity is promoted, iodine remains as iodate which showed modest sorption onto sediment systems and Fe(III) oxide. Overall, these results highlight the important role that bacteria play in the reduction of iodate. This research also confirms that iodine speciation impacts on the fate of 129I throughout the environment, where it may be less mobile in an oxic environment than under reducing conditions. Moreover, some techniques of bioremediation (e.g. promoting metal reducing conditions) may cause the release of radioactive iodine to solution.

Chemical speciation has become increasingly important in environmental and industrial systems, because of the difference in properties of the different physico-chemical forms of an element. In modern environmental and industrial analysis the determination of these individual species are required over and above total elemental analysis. In particular, oxidation state speciation has become a focus area of modern analytical chemistry. Hyphenated techniques where two or more analytical techniques are coupled, have been widely used in chemical speciation analysis. In particular, chromatographic techniques coupled with suitable detection systems have been proved to be very useful in trace element speciation. In this study, modified hyphenated techniques have been proposed for vanadium and thallium speciation. Two main species of vanadium, V(IV) and V(V) as a redox couple are widely used in petrochemical industries for the removal of sulphur. The effectiveness of vanadium as a catalyst is dependent on the ratio of the two species. Ion chromatography with an anion exchange column as the separation system, followed by ICP-OES detection at the wavelength of 309.311 nm has been proposed for the determination of the two species. In this method, EDTA was used for the stabilization of V(IV) and for the formation of V(IV) and V(V) EDTA complexes, which can be separated readily by means of a Dionex anion exchange column (AG5 guard column). The detection limits were 0.02 mg/L for V(IV), and 0.05 mg/L for V(V). The use of an ultrasonic nebulizer can enhance the sensitivity and therefore improve detection limits to as low as 2 ƒÝg/L for both species. The method is fast, cost-effective and interference free and was successfully used in the analysis of complex industrial samples. Thallium speciation is important because thallium species have accumulative toxicity to humans. No methods for the simultaneous separation and determination of thallium species could be found in the chemical literature. In this research, a new hyphenated method, namely HPLC coupled with ICP-OES was developed for the simultaneous separation and determination of the two thallium species, Tl(I) and Tl(III). DTPA was used in this method for stabilizing Tl(III) by formation of an anionic Tl(III)-DTPA complex. After stabilization, the two species were separated by using a Dionex cation exchange column, CG12A guard column, followed by ICP-OES detection at the wavelength of 351.924 nm. The detection limits were 0.8 mg/L and 0.1 mg/L for both species when using a V-groove nebulizer and ultrasonic nebulizer, respectively. No spectral interferences were observed. Only iodide can cause a chemical interference by forming a precipitate with Tl(I). / Prof. P.P. Coetzee

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Excessive metal deposition in soil is of major concern to the environment due to the toxicity of metals to animals and plants. Since metals do not degrade, reducing risk of exposure relies in either removing the metals from soil, or changing their speciation which leads to changes in bioavailability, mobility and toxicity. Plants have been shown to provide a cheap alternative to chemical methods for both removing and changing metal speciation, particularly when augmented with plant growth promoting bacteria. The focus of this thesis was to investigate whether the form (speciation) in which a metal contaminant is introduced to soil affects both plant health and the efficiency of metal remediation by the plant, using the well-known hyperaccumulator Brassica juncea (L.) Czern and zinc (Zn) as the metal contaminant. This study also examined the role of plant growth promoting bacteria in changing metal speciation, impact on metal toxicity and phytoremediation efficiency. Brassica juncea was grown in pots containing soil spiked with equal amounts (600 mg Zn kg-1) of soluble Zn (ZnSO4) and nanoparticulate ZnS and ZnO. Plant height, number of leaves, root length, plant biomass and chlorophyll content of Brassica juncea were used to assess Zn toxicity. Zn localisation and speciation in soil and plant tissues was studied using transmission electron microscopy (TEM), synchrotron micro-X-ray fluorescence elemental mapping (μXRF) and synchrotron X-ray absorption spectroscopy (XAS). Growth parameters showed that ZnSO4 was the most toxic form of Zn whilst ZnS and ZnO effects were not statistically different. These differences were linked to differences in Zn content in root and shoot biomass, which was higher in ZnSO4 treatments. Inoculation with Rhizobium leguminosarum and Pseudomonas brassicacearum enhanced plant growth, Zn concentration in plant biomass and translocation of Zn in all Zn treatments. XAS analysis showed that Zn speciation was altered in roots of plants inoculated with bacteria, with Zn cysteine as the most dominant form of Zn in all inoculated Zn treatments, suggesting a role for cysteine in ameliorating Zn toxicity. By also assessing Zn speciation changes across the soilrhizosphere- plant interface, this study established that Rhizobium leguminosarum modified Zn speciation at the rhizosphere. Through this thesis work, metal speciation is a major factor in determining the efficiency of metal phytoremediation and plant tolerance. Hence, this research provides useful information on Zn speciation which will contribute to effective implementation of Zn phytoremediation.

Graduation date: 1991

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