Call number: LD2668 .T4 1958 W49

North American beavers (Castor canadensis) build dams in stream channels, thus creating impoundments that flood surrounding riparian areas. Due to the widely circulating global pool of mercury in the atmosphere, mercury is deposited onto the landscape both near and far from point sources, including areas occupied by beavers. The organic form of mercury, methylmercury, is a potent neurotoxin with potential to cause harm to both humans and wildlife due to its ability to biomagnify up food chains. Recently flooded areas, such as those resulting from beaver impoundments, create ideal environments for the methylation of mercury. These impoundments can release methylmercury to downstream food webs where there is potential for it to be transferred to higher trophic level organisms. Beaver impoundments can also boost productivity in aquatic systems, so increases in mercury may be accompanied by an increase in nutrients and algal and invertebrate biomass. The findings here describe increased concentrations of methylmercury in water, algae, and invertebrates downstream from in-channel beaver dams in the southern Canadian Rockies. There was, however, no significant increase in nutrients or algal and invertebrate biomass downstream from impoundments. An examination of trophic transfer of mercury in these stream systems reveals that uptake is enhanced at low concentrations. The uptake pathway from water to algae is especially important but is attenuated in higher trophic levels due to a small relative difference in trophic level between predators and prey. The overall rate of trophic transfer in these systems falls within the low end of the typical range, and low baseline concentrations mean that methylmercury is not biomagnifying to dangerous levels in these low-productivity mountain systems. Beavers can provide important ecosystem services such as improving landscape heterogeneity, creation of new habitat for invertebrates and fish and improved angling opportunities, but they also enhance mercury export. Therefore, in systems that are mercury-sensitive such as those with low pH or long-lived, slow-growing predatory fish species, beaver influence should be considered as an important source of methylmercury.

Mercury has been an element of great industrial importance since early times.This wide utilization of the element has led to pervasive mercury contamination in theglobal environment. Due to mercury's high toxicity, this is a matter of great concern. Anumber of methods, includ ing phytoremediation, filtration, and precipitation/chelation,have been investigated to remove mercury from the environment. Unfortunately, thesemethods are not entirely satisfactory for the in-situ remediation of mercury from aqueousenvironments.The hypothesis of this dissertation is that this can best be accomplished by theaddition of a large and flexible sulfur-based chelate, that will bind mercury in atetracoordinate and presumably tetrahedral environment, to mercury-contaminatedwaters. Although this proved difficult due to the tendency of these ligands to decomposeinto smaller, sulfur-containing rings, the synthesis and characterization of such a chelatewas achieved. Several potential mercury-binding ligands were eventually synthesizedsignificant amounts of mercury (91-100%) from the contaminated solutions, in one caselowering the mercury levels in the water to below the CVAF detection limits. Theresulting solids lost little (andlt;15 ppb) of their mercury during leaching studies.This work demonstrates the use of tetradentate chelates in precipating Hg2+ fromwater to produce stable mercury- ligand precipitates. A calculation for the quantification ofthe geometry of a four-coordinate compound was also developed and applied to aluminum,gallium, and mercury compounds. This calculation could also be applied to the mercurycompounds described in this thesis once X-ray structures become available

No description available.

Environmental conditions can lead to mercury accumulations in fish that are highly variability among spatially close lakes in Ontario, Canada. Mercury methylation caused by sulfate reduction can influence total mercury concentrations in fish (THgfish). Kahshe and Mountain lakes were chosen to assess temporal trends of THgfish and using paleolimnological tools described the lake environment in terms of total mercury (THgsed), total sulfur (TSsed), chromium-reducible sulfur (CRSsed), and chrysophyte-inferred lake-water pH (CI-pH). THgfish were standardized by length (LS-THgfish) to identify trends and make comparisons with archived fish from the Royal Ontario Museum. In Kahshe Lake, LS-THgfish for 30-cm smallmouth bass and 40-cm walleye displayed peak concentrations in the early 1980s (0.74 +/- 0.17 µg/g d.w; n=41 and 1.40 +/- 0.42 µg/g d.w; n=16, respectively) with clear declines starting in 1999 (0.33 µg/g d.w +/- 0.13, n=12). At Mountain Lake, LS-THgfish in smallmouth bass (0.31 – 0.45 µg/g) and walleye (0.30 – 0.49 µg/g) were low and stable through the period of observation. Peak concentrations at Kahshe Lake were over 300% higher than the 1926 archival sample (0.22 µg/g d.w, 22.1 cm total length), while the 1948 Mountain Lake sample (0.28 µg/g, 24.4 cm total length) is consistent with modern concentrations. As expected from LS-THgfish , THgsed was higher in Kahshe Lake, although enrichment was seen at both sites. Temporal trends for TSsed and CRSsed diverged with enrichment in Kahshe Lake and depletion in Mountain Lake. CI-pH showed minimal temporal changes. Although trends of CRSsed indicate sulfate is processed differently among the lakes, geochronology highlighted a consistent spatio-temporal relationship between THgfish and CRSsed. This strongly supports a relationship between sulfate reduction rates and Hg methylation, independent of THgsed and pH. Therefore, if THgfish is used as an indicator of aquatic health CRSsed may be a useful tool for rapid assessment. / Thesis (Master, Biology) -- Queen's University, 2013-01-11 15:48:02.718

The Common tern (Sterna hirundo) is considered a sentinel wildlife species for monitoring mercury (Hg) and other contaminants within the St. Lawrence River Cornwall/Massena Areas of Concern (AOC). Here, I investigate the relationship between Hg bioaccumulation and diet using stable isotopes of carbon (δ13C) and nitrogen (δ15N) in adult and chick Common terns from three colonies along a 160 km transect of the upper St. Lawrence River. The foraging range of the colony furthest downstream (EMC) includes both the Massena and Cornwall AOC’s while the two upstream colonies (213 and Ice) are more removed from known point sources of Hg. I also sampled winter- and summer-grown breast feathers to compare diet and Hg exposure on the terns’ breeding ground vs. the terns’ wintering grounds. Hg exposure in summer-grown feathers was significantly higher than Hg exposure in winter grown feathers. Stable carbon (δ13C) and nitrogen (δ15N) isotopes revealed a switch from a marine-based diet during the winter months to a freshwater-based diet on the breeding grounds. Among colonies in summer-grown and chick feathers, the only significant difference in total mercury (THg) exposure was found in chick feathers where Hg was significantly lower at 213 than Ice – both of which are upstream from the AOC’s. However, THg was negatively correlated with δ13C in both winter and summer feathers, and the most parsimonious multi-regression model for winter and summer feathers indicated that δ13C explains 24 and 25% of the variation in Hg exposure, respectively. This suggests terns foraging offshore bioaccumulate more Hg than individuals foraging inshore or in freshwater (winter feathers), and that during the breeding period, terns foraging in pelagic habitats bioaccumulate more Hg than terns foraging in littoral habitats (summer feathers). For the upper St. Lawrence River, these results provide strong evidence that foraging habitat is more important than colony location in determining Hg exposure in a top trophic consumer. / Thesis (Master, Biology) -- Queen's University, 2013-06-01 19:35:59.665

Projections of the World Energy Council indicate a significant increase in global energy consumption in the medium and long term due to a growing world population and rising prosperity whilst global fossil fuel reserves are in decline. Eighty percent of the world’s energy consumption is generated from fossil fuels and this is unlikely to change in the short and medium term inevitably leading to energy shortfalls. The CO2-less energy of nuclear fuel shows strong potential to meet the future energy demands. However economic, politic and environmental requirements mean that the nuclear industry must adapt its current technology and present fuel usage. A pyroelectrochemical reprocessing system utilising liquid cathode technology could provide an efficient and secure reprocessing cycle essential for reduction in volume and toxicity of nuclear waste and extension of natural nuclear resources. The electrochemistry of aqueous copper(II) and zinc(II) chloride was studied upon a liquid mercury cathode using cyclic voltammetry. Bulk deposition of the Cu upon the liquid mercury cathode was studied using both amperometry and Electrochemical Impedance Spectroscopy. The surface deposits formed by copper deposition upon the mercury liquid cathode were analysed using x-ray powder diffraction and determined to be the rare naturally occurring mineral Belendorffite, Cu7Hg6. Electrochemical diagnostics for surface deposition upon the mercury liquid cathode surface were investigated as a potential analogue system for high temperature liquid cathode systems. Bulk deposition investigation of lanthanum upon the high temperature bismuth system demonstrated transfer of EIS diagnostics for surface growth, with the system demonstrating a similarity to the zinc-mercury ambient system. An electrochemical technique for purifying LiCl/KCl molten salt using an electrolysis technique was demonstrated. The electrochemical cleaning method forgoes the standard chemical treatments that can leave contaminants within the treated salt and results in a cleaner less oxidising molten salt eutectic.

Methylmercury (MeHg) is a ubiquitous environmental toxin. Exposure to MeHg in humans occurs primarily through the consumption of contaminated seafood. MeHg has been shown to act most strongly during neural development. Epidemiological data on the effect MeHg exposure through seafood has on children and fetuses is conflicted, with large cohort studies showing both presence and absence of MeHg-induced deficits in achieving developmental milestones. Because of this uncertainty in the literature it is important that we come to understand the mechanisms of MeHg toxicity so that we might advise the public more accurately on the risks of MeHg exposure. Research into the mechanisms of MeHg toxicity has found a number of cellular and molecular effects including disruptions of microtubule formation, Ca2+ homeostasis, and glutamate signaling. However, none of these effects of MeHg fully explains its neurodevelopmental specificity. Previous work in Drosophila neural-derived cell lines has shown that MeHg causes upregulation of the canonical Notch response gene E(spl)m . The Notch pathway is crucial to neural development and perturbation of a Notch target may explain the developmental specificity of MeHg. In this dissertation I describe experiments I performed to test the hypothesis that the observed upregulation of E(spl)m plays an important role in MeHg toxicity in Drosophila. I first describe experimental evidence that E(spl)m is upregulated by MeHg treatment in vivo in Drosophila embryos in addition to cells, as has previously been shown. By contrasting the effects of the toxic inorganic mercurial HgCl2 with MeHg I show that the E(spl)m expression response to MeHg is not simply a stress response and is a likely specific activity of MeHg. I also show that the effect of MeHg on E(spl)m expression is not simply due to a developmental delay induced by the toxin. I also identify two neural phenotypes of MeHg toxicity in Drosophila embryos, in the outgrowth of the intersegmental and segmental motor nerves. Genetic manipulation causing overactivity of the Notch pathway in neurons can mimic these phenotypes. However, induced expression of E(spl)m in neurons does not cause a failure of motor nerve outgrowth. Upon further examination I demonstrate that endogenous expression of E(spl)m occurs in the muscle. Induced E(spl)m expression in the muscle causes a segmental nerve phenotype similar to MeHg treatment, indicating a role for E(spl)m in MeHg toxicity in this system. MeHg treatment and E(spl)m overexpression in the muscle causes a failure of normal muscle development. Yet, this gross developmental abnormality only partially explains the observed motor nerve phenotype. E(spl)m is unique among the E(spl) genes in its ability to cause these muscle and motor nerve phenotypes as shown by contrasting genetic manipulation of the closely related E(spl)m . Overall my findings support the hypothesis that MeHg toxicity in Drosophila is mediated in part by E(spl)m . They also suggest that E(spl)m plays an important role in the formation of the muscle during embryonic development, contributing to the literature describing disparate functions for E(spl) genes despite structural similarities. Finally, my findings suggest that MeHg may be able to impact neural development through toxicity in supporting tissues rather than neurons themselves. This final finding has implications for the study of MeHg toxicity in humans, and is supported by previous findings that describe a role of glia in modulating MeHg neurotoxicity.

The use of algae as heavy metal bioindicators in aquatic environments has received much attention. In this study, the performance of a common freshwater living green alga, Cladophora sp. as a mercury bioindicator and its potential for phytoremediation applications was assessed by various parameters which included the influence of contact time, pH, initial mercury concentration and the presence of competing metal cations. A rapid uptake of mercury by Cladophora sp. was displayed. More than 99% of mercury in solution was removed within the first 5 min of contact and equilibrium was attained after 10 min. High adsorption capacities of 800 mg kg-1, 530 mg kg-1 and 590 mg kg-1 at pH 3, 6.5 and 8.5 respectively were obtained at the optimum mercury concentration of 1.0 mg l-1. Competitive adsorption studies showed that the selectivity of heavy metal cations by Cladophora sp. was in the following order: Hg2+ ˃Fe2+˃Cu2+˃ Zn2+ ˃ Co2+. These results indicate that living Cladophora sp. algae are suitable for use as mercury bioindicators in AMD waters and are also suitable for the removal of mercury in AMD conditions.

Cheung Ching Ying. / Bibliography: leaf 126 / Thesis (M.Phil.)--Chinese University of Hong Kong