Elevated concentrations of mercury (Hg) in aquatic systems can be a threat to ecosystems and human health. Mercury-bearing sediment particles from eroding riverbanks can be an ongoing source of bioavailable Hg to aquatic ecosystems. Hyporheic zones in particular can be important sources of both inorganic and organic-complexed Hg, which can be rapidly transported to adjacent surface waters. The objective of this study was to investigate the release and treatment of dissolved and particle-bound Hg in water derived from the riverbank sediments of the South River, Virginia. The solid-phase forms of Hg in riverbank sediment samples were characterized by sequential extraction and synchrotron based techniques. The analyses suggest that 79-93% of Hg in the sediment samples is in the form of insoluble sulfides (βHgS metacinnabar); however significant masses of more-soluble Hg phases (0.4-33 μg/g) are also present. Simulated erosion events resulted in elevated concentrations of Hg in the river water up to 80 μg/L. There was no correlation between the mass of water-soluble Hg in the sediment and the concentrations of Hg released in the river water following sediment suspension. Column transport experiments were conducted to assess Hg release from the sediment under water:sediment ratios typical of those that might occur at the bottom or in the banks of the river. Concentrations of Hg in the 0.45 μm-filtered fraction of the effluent varied from 0.15 μg/L for samples collected from the base of the riverbank to 8 μg/L for samples collected from the top of the riverbank. Filter size-fractionation of water column effluent suggested approximately 50% of the leached Hg was present in the dissolved phase, with the remainder in particulate form. Riverbank sediments were amended with various types of reactive material including complexing agents, reductants and charcoals. Batch experiments indicate that the mass of Hg released from the sediment could be lessened by 64-99% with the addition of reactive media, and that aerating and re-wetting the sediment amendments resulted in equal or greater removal of Hg from the water. The greatest removal of Hg was observed when more amendment was added to the sediment, however the greatest Hg uptake capacity (Hg captured per mass of material) was observed for the lowest doses of reactive media. The Hg uptake capacities ranged from 35-500 ng/g and were greatest for treatment of water with elevated concentrations of Hg. The Hg uptake capacities were a function of the Hg concentrations in the untreated water, and were generally lower relative to values reported in the literature. Column studies were used to simulate the flow of river water containing elevated concentrations of Hg through a reactive zone containing a charred hardwood material. The concentration of filtered Hg was < 120 ng/L for treated effluent from columns, resulting in > 98% removal of Hg from the water. Assuming that the majority of removal occurred within the initial 2-3 cm along the length of the column, the calculated uptake of Hg2+ ranged from 1.2-7.7 μg/g. The uptake capacity for charred hardwood material was much greater for the column experiments relative to the batch experiments, suggesting that the uptake capacity is limited by Hg loading. The chemical composition of the treated column effluent was similar to the South River water, and suggests the material did not add or remove significant constituents during the course of these experiments.

The technical feasibility of producing sulphur-impregnated activated carbons (SIACs) from high-sulphur fluid coke by chemical activation was investigated. Using KOH and SO2, the activation process was able to produce SIACs with controllable specific surface area (SBET), pore size distribution and sulphur content. The highest SBET was over 2500 m2/g and the highest sulphur content was 8.1 wt%. K-edge X-ray Absorption Near Edge Structure (XANES) spectroscopy was employed to characterize the sulphur in fluid cokes and SIACs. The results revealed that the sulphur on fluid coke surface was mainly in the form of organic sulphide and thiophene (total 91-95 %), in addition to some sulphate (5 - 9%). The study of KOH-treated fluid coke suggested that KOH was effective in converting organic sulphide and thiophene to water soluble inorganic species which were readily removed by acid and water washing. SO2 treatment of fluid coke added sulphur to fluid coke through SO2-carbon reaction. Elemental sulphur was the main product, while part of the thiophene, sulphide and sulphate in the raw coke remained in the product. In KOH-SO2 activation, disulphide, sulphide, sulphonate and sulphate were identified on SIAC surface; no thiophene was found, suggesting a complete removal of thiophene. Sulphur content in specific forms in SIACs was therefore controllable by varying the ratio of KOH, SO2 and fluid coke. SIACs produced from KOH-SO2 activation showed a comparable Hg2+ adsorption capacity (43 – 72 mg/g) with those reported in the literature (35-100 mg/g) and that of a commercial SIAC (41 mg/g). Although a larger SBET often resulted in a greater Hg2+ adsorption capacity, the benefit started to diminish when SBET was greater than about 1000 m2/g. A statistically significant and positive correlation was found between Hg2+ adsorption capacity and total sulphur content. Elemental sulphur and reduced sulphur were largely responsible for the enhanced Hg2+ adsorption.

Elevated concentrations of mercury (Hg) in aquatic systems can be a threat to ecosystems and human health. Mercury-bearing sediment particles from eroding riverbanks can be an ongoing source of bioavailable Hg to aquatic ecosystems. Hyporheic zones in particular can be important sources of both inorganic and organic-complexed Hg, which can be rapidly transported to adjacent surface waters. The objective of this study was to investigate the release and treatment of dissolved and particle-bound Hg in water derived from the riverbank sediments of the South River, Virginia. The solid-phase forms of Hg in riverbank sediment samples were characterized by sequential extraction and synchrotron based techniques. The analyses suggest that 79-93% of Hg in the sediment samples is in the form of insoluble sulfides (βHgS metacinnabar); however significant masses of more-soluble Hg phases (0.4-33 μg/g) are also present. Simulated erosion events resulted in elevated concentrations of Hg in the river water up to 80 μg/L. There was no correlation between the mass of water-soluble Hg in the sediment and the concentrations of Hg released in the river water following sediment suspension. Column transport experiments were conducted to assess Hg release from the sediment under water:sediment ratios typical of those that might occur at the bottom or in the banks of the river. Concentrations of Hg in the 0.45 μm-filtered fraction of the effluent varied from 0.15 μg/L for samples collected from the base of the riverbank to 8 μg/L for samples collected from the top of the riverbank. Filter size-fractionation of water column effluent suggested approximately 50% of the leached Hg was present in the dissolved phase, with the remainder in particulate form. Riverbank sediments were amended with various types of reactive material including complexing agents, reductants and charcoals. Batch experiments indicate that the mass of Hg released from the sediment could be lessened by 64-99% with the addition of reactive media, and that aerating and re-wetting the sediment amendments resulted in equal or greater removal of Hg from the water. The greatest removal of Hg was observed when more amendment was added to the sediment, however the greatest Hg uptake capacity (Hg captured per mass of material) was observed for the lowest doses of reactive media. The Hg uptake capacities ranged from 35-500 ng/g and were greatest for treatment of water with elevated concentrations of Hg. The Hg uptake capacities were a function of the Hg concentrations in the untreated water, and were generally lower relative to values reported in the literature. Column studies were used to simulate the flow of river water containing elevated concentrations of Hg through a reactive zone containing a charred hardwood material. The concentration of filtered Hg was < 120 ng/L for treated effluent from columns, resulting in > 98% removal of Hg from the water. Assuming that the majority of removal occurred within the initial 2-3 cm along the length of the column, the calculated uptake of Hg2+ ranged from 1.2-7.7 μg/g. The uptake capacity for charred hardwood material was much greater for the column experiments relative to the batch experiments, suggesting that the uptake capacity is limited by Hg loading. The chemical composition of the treated column effluent was similar to the South River water, and suggests the material did not add or remove significant constituents during the course of these experiments.

This study sought to characterize the risk to human health from dietary mercury (Hg) exposure in two Inuit communities, Repulse Bay and lgloolik. Hg exposure was estimated using food frequency questionnaires. Body burden was determined by measuring Hg in hair samples. Estimated average daily Hg exposures for women of child-bearing age were 21.3 mug in Repulse Bay, and 6.0 mug in lgloolik; the general population exposures were 43.1 mug in Repulse Bay and 23.2 mug in lgloolik. Average hair concentrations were 2.1 mg/kg and 2.8 mg/kg in Repulse Bay, 2.1 mg/kg and 6.2 mg/kg in lgloolik for women of child-bearing age and the general population respectively. No participants had concentrations above the "at risk" concentration of 30 mg/kg. Significant correlations were observed between hair Hg concentration and traditional food intake. These results do not necessitate direct intervention, but validate continued monitoring of Hg exposure in Nunavut.

Upland environments are important sources of mercury (Hg) to downstream wetlands and water bodies. Hydrology is instrumental in facilitating Hg transport within, and export from watersheds. Two complementary studies were conducted to assess the role hydrological processes play in controlling Hg mobility and transport in forested uplands. A field study compared runoff and Hg fluxes from three, replicate hillslope plots during two contrasting spring snowmelt periods, in terms of snowpack depth and timing. Hillslope Hg fluxes were predominately flow-driven. The melting of soil frost significantly delayed a large portion of the Hg flux later into the spring following a winter with minimal snow accumulation. A microcosm laboratory study using a stable Hg isotope tracer applied to intact soil cores investigated the relative controls of soil moisture and precipitation on Hg mobility. Both hydrologic factors control the mobility of contemporary Hg; with greatest Hg flushing from dry soils under high-flow conditions.

This thesis reports the fabrication and characterization of long wavelength infrared mercury cadmium telluride (Hg1-xCdxTe) photodiodes and 128x128 focal plane arrays grown on lattice matched cadmium zinc telluride (Cd1-yZnyTe) substrates by metal organic vapor phase epitaxy (MOVPE). The dark current modeling of 33x33 mm2 Hg1-xCdxTe photodiodes has shown the dark current is dominated by trap assisted tunneling under small reverse bias voltages typically used to bias these detectors. The dominant dark current mechanisms under high reverse bias and low forward bias are band&ndash / to&ndash / band tunneling and generation&ndash / recombination, respectively. The photodiodes have yielded a peak 77 K detectivity of 3.2x1010 cm&amp / #8730 / Hz/W with a cut-off wavelength (50%) of 10.92 mm. It has also been found that the 1/f noise current of the detectors at 1 Hz is related to the trap-assisted tunneling current through the empirical relation in=&amp / #945 / TAT(ITAT)&amp / #946 / with &amp / #945 / TAT=7.0 x 10-5 and &amp / #946 / =0.65. In the course of the focal plane array (FPA) fabrication process development work, ohmic contact formation on p-type Hg1-xCdxTe and mesa wet etch were studied in detail. Contacts with chromium, gold, platinum and copper on p-type Hg1-xCdxTe resulted in bad ohmic contacts, which did not seem to improve with annealing. On the other hand a HgTe cap layer on p-type Hg1-xCdxTe resulted in good ohmic contact with acceptably low resistance. Among the etchants studied for mesa etching of the diode structures, Br2/HBr solution yielded the best performance. After developing all of the steps of FPA processing, 128x128 Hg1-xCdxTe FPAs were successfully fabricated and tested in a thermal imager. While thermal imaging was performed with the FPAs, high nonuniformity of the material and low R0A product of the pixels did not allow high sensitivity imaging.

Thesis (Ph.D.) -- McMaster University, 1999. / Includes bibliographical references (leaves 212-219). Also available via World Wide Web.

Thesis (Ph. D.)--McMaster University (Canada), 1989. / Source: Dissertation Abstracts International, Volume: 62-13, Section: A, page: 0000.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 6 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 5 uppsatser.