Thesis(M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references.

Dissertation (Ph.D.)--Auburn University, 2005. / Abstract. Includes bibliographic references.

This dissertation summarizes three investigations in which immunosuppressive effects of environmentally relevant concentrations of dietary methylmercury (MeHg) were assessed in adult non-breeding male kestrels, female kestrels during egg laying, and nestling kestrels. Immunological endpoints included cell-mediated immunity (CMI) using the phytohemagglutinin (PHA) skin-swelling assay and antibody-mediated immune function using the sheep red blood cell (SRBC) hemagglutination assay. Hematology profiles were evaluated over time in adult males and nestlings to monitor immunological and physiological status of kestrels. Primary and secondary immune system organs were examined histopathologically to identify T and B cell-dependent structural changes related to immunosuppressive effects of MeHg. Male kestrels dosed with 3.9 µg/g MeHg in the diet for 13 weeks exhibited suppression of CMI (p = 0.019), elevation in the proportion of heterophils (p < 0.001) and total white blood cell counts (p < 0.001), and a decline in the proportion of peripheral blood lymphocytes (p < 0.001). Primary antibody-mediated immune response was suppressed at 0.6 µg/g MeHg (p = 0.014), but secondary immune function was not adversely effected. Female kestrels were dosed with 2.8 µg/g MeHg in the diet for 13 weeks prior to egg laying and exhibited a higher primary immune response to sheep red blood cells (SRBC) than controls (p = 0.013). Subtle reproductive effects were also apparent including a 4.3-day delay in egg laying (p < 0.001) and depletion of egg mass (p = 0.037), egg volume (p = 0.050), and eggshell thickness (p = 0.004). The quantity of antibody production during egg laying, as measured by anti-SRBC antibody concentrations in egg yolk, did not differ from controls. However, the duration of antibody production was significantly longer for MeHg dosed females (p = 0.007), suggesting immunomodulation occurred among dosed kestrels during egg laying. Nestlings dosed with 0.6 and 3.9 µg/g in the diet for 25 days post-hatch also exhibited suppression of CMI at 11 days of age (p = 0.004) and lymphoid depletion in spleen (p < 0.001) and thymus tissue (p = 0.017). Antibody-mediated immune function was not adversely affected in nestling kestrels. Results from these three investigations suggested suppression of CMI and lymphoid depletion occurred at a dose concentration of 3.9 µg/g MeHg in adult, non-breeding male kestrels and at both 0.6 and 3.9 µg/g MeHg dose concentrations in nestlings. Immunosuppressive effects and immune dysfunction with respect to antibody-mediated immune function occurred at a dose concentration of 2.8 µg/g in female kestrels during egg laying; estrogen-disrupting characteristics of MeHg during avian reproduction cannot be excluded as a potential influence on this response. Immunotoxic effects of dietary MeHg in female kestrels during egg laying were primarily immunosuppressive and targeted T cell-mediated immune function. Cell-mediated immunity was highly sensitive to the immunosuppressive effects of dietary MeHg at low, environmentally relevant exposure concentrations, and at comparatively high doses (> 3 ppm) at which reproductive effects have been demonstrated in kestrels in other investigations.

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No description available.

The bath-to-cell transport, cytosolic concentration, and tubular content of methylmercury (Me203Hg+) and the sulfhydryl-amino acids and sulfhydryl-amino acid derivatives conjugated to Me203Hg+ were studied in the non-perfused S2 segments of the proximal tubule of the rabbit kidney. Active transport of Me203Hg+ was established by a temperature dependent (greater than 100% reduction in bath-to-cell transport, 99% decrease in cytosolic concentration, 63% decline in the tubular contents at 12°C when compared to 37°C). Conjugates of Me203Hg+ showed mixed results, with L-cysteine and L-taurine demonstrating the most significant increase in uptake. Transport of Me203Hg+-L-cysteine was also temperature dependent with a 77% reduction in bath-to-cell transport, 76% decrease in cytosolic concentration, and 86% decline in tubular contents at 12°C when compared to 37°C. A significant decrease in transport was seen with the classic organic anion transport (OAT) inhibitors of PAH (71% and 67%) and probenicid (48% and 38%), as well as, the dicarboxylates, adepate (over 100%) and glutarate (69% and 52%) in both bath-to-cell and cytosolic concentration respectively. The addition of L-methionine to the Me203Hg+-L-cysteine conjugate significantly reduced the bath-to-cell transport by 64% and the cytosolic contents by 47%. The Me203Hg+-L-taurine conjugate also demonstrated temperature dependence (99% reduction and 91% decrease in bath-to-cell and cytosolic concentration respectively, at 12°C when compared to 37°C). Inhibition with PAH was also seen (77% reduction) in bath-to-cell transport and 67% decline in cytosolic concentration giving further evidence to the transport of the Me203Hg+-L-taurine conjugate via OAT. When Me203Hg+ was conjugated to L-methionine a 55% reduction in bath-to-cell transport was seen which was also temperature dependent (59% decrease at 12°C when compared to 37°), although no significant decrease in transport was noted with the addition of PAH. Analysis of the methylmercury conjugates via mass spectrometry demonstrated that L-cysteine, L-taurine, and L-methionine all are binding with methylmercury in the same unknown common configuration (MW=409). These results indicate the mercuric conjugate is gaining entry into the renal epithelial cells via the OAT and the amino acid transport system in the basolateral membrane of the proximal tubule.

Benthic uptake of mercury (Hg) governs bioavailability to fish yet there are still large gaps in our knowledge of what mediates this process. Without this information it is difficult to ascertain where Hg accumulation in the foodweb will be greatest. In the St. Lawrence River Area of Concern (AOC) at Cornwall, one contaminated zone (Zone 1) shows elevated Hg in yellow perch (Perca flavescens) and their prey items compared to those from other zones in the AOC. Greater availability of Hg to benthos due to unique physical features (large deposition of woodfibre deposits) of Zone 1 is hypothesized to account for this observation. In this study, amphipods (Gammarus fasciatus) and (Echinogammarus ischnus) were collected in Zone 1 using artificial substrates between June-September 2007, and Hg concentrations compared to those obtained in sediments and porewaters of surficial sediments, as well as methane gas evasion rates. Methylmercury (MeHg) concentrations in amphipods were significantly related to porewater total Hg (THg) and MeHg concentrations. No parallel relationship was found for sediment Hg concentrations or methane bubbling rates from sediments. Spatial and temporal trends in Hg bioavailability were evident from significant relationships with water column depth and temperature. Water column depth was associated with higher MeHg concentrations in amphipods and porewaters. Concentrations of porewater MeHg were above the detection limit in all of the June samples, the month which also coincided with highest amphipod MeHg concentrations. Finally, sediment organic matter may be influencing patterns of MeHg availability in Zone 1, and displayed a negative relationship to amphipod MeHg. Although bubbling from contaminated sediments did not directly correlate with amphipod Hg uptake, future studies should look at the influence of bubbling on the redistribution of contaminated sediment particles within the zone. / Thesis (Master, Biology) -- Queen's University, 2008-12-30 23:34:20.287

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Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (leaves [148]-164).

Thesis (M.S.)--University of North Carolina Wilmington, 2008. / Title from PDF title page (viewed May 27, 2009) Includes bibliographical references (p. 56-61)