| A new analytical method using genetically engineered bacteria that produce light when Hg(II) enters their cells has provided a way to gain insight into the fraction of Hg(II) that is bioavailable and into factors controlling its bioavaiIability. Part of the research in this thesis contributed to the methods development for the analyses of bioavailable Hg in environmental samples; the remainder used the method to quantify and characterize bioavailable Hg in the environment.; Measurements were made for the first time on a variety of aquatic samples as a preliminary assessment of source strengths of bioavailable Hg entering lakes at the Experimental Lakes Area (ELA) in northwestern Ontario. With the exception of snow, all input sources had detectable but low concentrations of bioavailable Hg representing on average 1 to 2.5% of the total Hg concentration. Bioavailable Hg in snow was surprisingly high representing ∼50% of the total Hg. Conversely, in lakes, bioavailable was never detectable.; The mer-lux bioreporter was also used to examine the behaviour of Hg(II) in four distinctly different lakes at the ELA by conducting trace level Hg(II) addition experiments and measuring subsequent changes in its bioavailability. The dissolved phase dominated the complexation of Hg(II) and it seems likely that much of the Hg(II) entering lakes rapidly becomes bound (and unavailable for uptake) by a functional group or ligand class that has a high affinity for Hg(II), such as reduced sulfur.; To further characterize the dissolved phase in relation to its effects on bioavailability, the mer-lux bioreporter was used in conjunction with trace level ultrafiltration methods and XAD-8 chromatography for the characterization of dissolved organic carbon (DOC). There was a natural preference for Hg(II) to bind or partition to the higher molecular weight DOC (>10 kDa). Consequently, the bioavailability of Hg(II) increased with decreasing molecular weight of DOC. The low absorptivity and percent aromaticity of the lower molecular weight fraction suggested an autochthonous origin. Weak correlations were observed between bioavailable Hg and parameters such as DOC concentration (R2 = 0.48) and SUVA or molar absorptivity (R2 = 0.66) suggesting that a much more specific parameter than carbon is needed to characterize the bioavailable reactivity of DOC. In attempts to understand and model the implications of environmental change on the biological fate of Hg(II), the character of the DOC rather than the quantity should be considered. (Abstract shortened by UMI.)... |
