Elevated mercury levels have been observed in a wide variety of aquatic systems. A mass balance non-steady state model was developed to examine mercury cycling in lakes and reservoirs. Hg(ll), methylmercury, Hg° , dimethylmercury and solid phase HgS cycles were interconnected. Compartments included air, water, sediment, suspended solids, plankton, benthos, and two generic fish categories based on diet. Bioenergetics equations for individual fish were extended to consider mercury dynamics for entire fish populations. Biota represented large methylmercury fluxes in the water column and were found to be important methylmercury repositories. In a simulation of a generic well-mixed shield lake in Ontario, the fish population contained about 4 times as much methylmercury as water. Uptake of methylmercury by individual walleye and yellow perch was predicted to be dominated by the food pathway (eg. 99% of total uptake). Based on simulations for the generic shield lake, the watershed has the potential to be an important source of methylmercury in some shield lakes (exceeding in-situ methylation in the generic simulation). Methylation in the water column and sediments were both simulated to be significant. Simulated net production of methylmercury in the generic shield lake was on the order of 0.05 to 0.15 ug methylmercury m⁻² year⁻¹ in the water column, with similar rates in sediments. Simulated rates of net methylation in polluted sytems were higher. Fractions of total dissolved Hg(II) or methylmercury available for methylation and demethylation in aerobic waters were thermodynamically predicted to be small (e.g. <1%). Dissolved organic carbon and sulphides (if present) were thermodynamically predicted to dominate Hg(II) and methylmercury complexation in freshwaters. Hg(II) burial and outflows represented about 85-90% of total mercury losses for the generic shield lake (2 year hydraulic retention time). Volatilization of Hg° , produced by demethylation and Hg(II) reduction, represented the remaining 10-15% of losses. Considerable system to system variability is expected for sources and sinks of total mercury and methylmercury in shield lakes. In simulations of two mercury contaminated environments, Lake St. Clair and Clay Lake, Ontario, sediment return of Hg(II) caused the lakes to be net sources of mercury to downstream areas. Sediment return of mercury could partially explain observed two-phase recoveries of fish methylmercury levels in some polluted systems. The time required for Hg(II) and methylmercury concentrations in various compartments to respond to changes in loads was simulated. There was a tendency towards relatively rapid internal cycling of Hg(II) and methylmercury, but slower overall system response times (eg. years to decades to respond to recover from flooding or pollution episodes). / Thesis / Master of Engineering (ME)

The present study focused on methylmercury (MeHg) in emergent aquatic insects and spiders from human-made ponds. This dissertation addresses two main topics: (1) factors affecting variation in spider MeHg concentrations around human-made ponds and (2) the magnitude of MeHg transported out of human-made ponds by emergent aquatic insects (insect-mediated MeHg flux). Spiders were specifically targeted in this study because they have been proposed as sentinels of MeHg contamination (organism whose tissue concentrations reflect the level of MeHg in the environment). Spider MeHg concentrations were related to spider diet, size, and proximity to waterbody, but affected individual spider taxa differently. In a second study, I found that only "large" spiders within a taxa had tissue concentrations positively related to prey MeHg concentrations. These results indicate that the relationship between spider and prey MeHg could be size-dependent and that "large" spiders within a taxa may better reflect ambient MeHg contamination. Finally, I tested a conceptual model hypothesizing insect-mediated MeHg flux from human-made ponds is controlled by pond permanence and fish presence. In agreement with the conceptual model, insect-mediated MeHg flux from ponds was suppressed by the presence of fish, likely due to fish predation on emergent insect larvae. I found the mean aggregate MeHg flux was approximately 6 times higher from ponds without fish than from ponds with fish. The suppression of insect flux by fish was stronger for large insect taxa than small insect taxa. Results of this study indicate that community structure can influence the cross-system transport of contaminants, like MeHg, from ponds to terrestrial food webs.

From the 1960s to the 1980s, many schools throughout the country installed synthetic flooring in indoor gymnasiums that contained mercury which was used as a catalyst in the polyurethane formulation. Many of these floors now have been found to be releasing mercury vapors into the school gymnasiums, leading to a concern that these mercury concentrations might be elevated enough to cause harmful effects. This paper examines data that have been collected from 57 different school gymnasiums using portable devices, such as the Lumex RA-915+ Portable Mercury Vapor Analyzer, and aggregated for analyses, then compares this data to that obtained in chamber tests performed on samples obtained directly from a gymnasium with mercury-containing floors. The overall objective of this paper is to determine if the chamber tests can adequately emulate mercury emissions in school gymnasiums, and using the results of the laboratory experiments, successfully analyze the emissions curve to determine what factors drive the profile. The laboratory testing was successful in emulating the condition of a school gymnasium, as data collected from the laboratory setting was comparable to the measured field data. The average mercury concentration in the gymnasium yielded an emission rate 3.1E-05 ug/m2s, while the calculated laboratory emission rate was 3.2E-05 ug/m2s, a negligible difference. The overall objective was met, as it was determined that floor samples taken from a gymnasium could be measured in the laboratory with similar results to those screened in the actual gym with handheld devices. Additionally, using the data collected in the chamber experiments, the emissions profile was characterized. / Master of Science

No description available.

Call number: LD2668 .T4 1957 T82 / Master of Science

Aquatic mercury (Hg) contamination caused by industrial Hg emissions, atmospheric transport and deposition to sensitive ecosystems is an ongoing concern in many parts of the world. Boreal ecosystems are particularly sensitive to Hg deposition, and large soil-Hg burdens in these regions may prolong recovery of Hg impacted surface waters for many decades. Four studies were undertaken to examine interactions between watershed characteristics, hydro-climatic variability and terrestrial-aquatic export of key chemical parameters linked to watershed Hg sensitivity. Two new quantitative techniques, hydrogeomorphic edge detection and characteristic morphology analysis, were developed to explicitly map and characterize the spatial distribution, geomorphic form and hydro-biogeochemical function of forested wetlands using airborne Light Detection and Ranging (LiDAR) surveys. The results demonstrate the critical contribution of forested wetlands and upland-wetland interactions to the production and mobilization of dissolved organic carbon (DOC) and methyl-mercury (MeHg) - respectively - to downstream surface waters. Results of strategic, event-based hydrochemical sampling also demonstrate the critical contribution of summer high-flow periods to terrestrial-aquatic MeHg export. Finally, an analysis of historical monitoring databases of streamflow volume, hydrochemistry and Hg concentrations in yearling perch in two contrasting headwater lake basins was conducted. The results indicate strong potential for short-term, hydrologically-driven shifts in terrestrial-aquatic coupling and watershed Hg sensitivity, but only for the wetland-dominated, humic lake that exhibited consistent, summertime hypolimnetic anoxia. These various findings suggest that accurate characterization of watershed structure can help researchers identify first-order limitations on whole-watershed methylation efficiency, particularly in relation to hydro-climatic drivers of terrestrial-aquatic coupling in Boreal headwater regions.

Aquatic mercury (Hg) contamination caused by industrial Hg emissions, atmospheric transport and deposition to sensitive ecosystems is an ongoing concern in many parts of the world. Boreal ecosystems are particularly sensitive to Hg deposition, and large soil-Hg burdens in these regions may prolong recovery of Hg impacted surface waters for many decades. Four studies were undertaken to examine interactions between watershed characteristics, hydro-climatic variability and terrestrial-aquatic export of key chemical parameters linked to watershed Hg sensitivity. Two new quantitative techniques, hydrogeomorphic edge detection and characteristic morphology analysis, were developed to explicitly map and characterize the spatial distribution, geomorphic form and hydro-biogeochemical function of forested wetlands using airborne Light Detection and Ranging (LiDAR) surveys. The results demonstrate the critical contribution of forested wetlands and upland-wetland interactions to the production and mobilization of dissolved organic carbon (DOC) and methyl-mercury (MeHg) - respectively - to downstream surface waters. Results of strategic, event-based hydrochemical sampling also demonstrate the critical contribution of summer high-flow periods to terrestrial-aquatic MeHg export. Finally, an analysis of historical monitoring databases of streamflow volume, hydrochemistry and Hg concentrations in yearling perch in two contrasting headwater lake basins was conducted. The results indicate strong potential for short-term, hydrologically-driven shifts in terrestrial-aquatic coupling and watershed Hg sensitivity, but only for the wetland-dominated, humic lake that exhibited consistent, summertime hypolimnetic anoxia. These various findings suggest that accurate characterization of watershed structure can help researchers identify first-order limitations on whole-watershed methylation efficiency, particularly in relation to hydro-climatic drivers of terrestrial-aquatic coupling in Boreal headwater regions.

Mercury amalgam microelectrodes, typically fabricated by electrodeposition of mercury onto metal (platinum, gold, silver) inlaid disks, possess certain advantageous properties for scanning electrochemical microscopy (SECM) and electroanalysis. But as applications require more and more precision, fundamental questions concerning the exact shape and constitution of the amalgam can become important for interpreting SECM experimental data. The purpose of this study is to analyze in depth the formation of the amalgam, in order to provide a better understanding of the key physical processes, and so be able to judge of the accuracy of the currently used models and refine them when necessary. The amalgam formation is the result of several processes that occur roughly at two different scales: the global scale, which is microscopic, and the local scale, of the order of few nanometers. On the global scale, the dominant physical process is the mass transport, driven almost entirely by diffusion, which determines the rate of mercury deposition. Other phenomena occur at the smaller local scale. Their understanding is essential to predict precisely the volume and shape of the amalgam at shorter times. Among these local phenomena, nucleation and droplet interactions appear critical. The former sets the formation rate and the size of the isolated mercury droplets that are initially formed at the surface of the electrode. An understanding of the latter is necessary to determine the droplet coalescence process. Among the specific accomplishments of this Master thesis work, a time scale analysis of the global phenomena has been performed leading to the conclusion that quasi-steady state diffusion of mercury ions in the bulk mainly defines the electrodeposition rate. Then, a series of analytical formulations for diffusion-limited electrodeposition current available in the literature has been quickly analyzed, leading to development of analytical/numerical models. These latter have been implemented, and results were critically compared with experimental data, leading to the conclusion that the early electrodeposition was not enough finely modeled. Mercury droplets nucleation and surface interaction have been identified as relevant processes of this period. They have next been investigated in detail, leading to the characterization of the nucleation process, and the derivation of two complimentary approaches on charged droplet stability. Regime maps have been developed, providing first explanations and quantitative information on charged droplet stability dependence on potential applied, electrolyte and droplet size. Finally, through analysis of theoretical predictions, a series of electroanalytical experiments have been proposed for the future validation of the suggested theoretical models.

Exposure to environmental toxins is a major contributing factor to the expected increase in chronic disease within developing countries in the next 20 years. Due to its ubiquitous distribution and persistent nature, mercury (Hg) is an example of a toxic substance that has garnered global concern because of its known detrimental effects on human and ecosystem health. Although fish consumption is the predominant source of Hg exposure to humans in developed nations, studies in developing countries have shown that high Hg concentrations in humans cannot be explained by fish consumption alone. The estimated daily intake (EDI) and the relative contribution of various sources of Hg to humans differ significantly between individuals, ethnic groups, and across continents. Health Canada is currently attempting to regulate the anthropogenic release and exposure dose of Hg to its citizens based on known EDIs, however the greatest sources of Hg exposure across sub-Saharan Africa (SSA) are still unknown, thus impeding the regulatory process. This thesis focuses on four major sources of Hg exposure in SSA: skin-lightening cosmetics, soil geophagy, small-scale gold mining, and fish consumption. An exposure assessment model has been developed to identify the sources of greatest concern for various age groups in Ghana and Uganda and is presented using published and unpublished data, as well as experimental Hg bioaccessibility data. The results indicate that occupational exposure and lifestyle choices (mining and use of skin-lightening cosmetics) have the greatest contribution to overall increases in Hg toxicity in adults. The health of infants, however, is most likely to be compromised before birth and in the first few days of life due to maternal consumption of fish with elevated Hg concentrations and the use of Hg-containing cosmetics. It is imperative that further research of these sources be carried out to prevent the possible long-term negative social and economic consequences of chronic illness in SSA. / Thesis (Master, Environmental Studies) -- Queen's University, 2008-09-25 20:05:32.606

Thesis (doctoral)--Lund University, 1995. / Added t.p. with thesis statement inserted.