Dissolved Organic Matter Kinetically Controls Mercury Bioavailability to Bacteria in Lake Water from the Canadian Arctic

• Main Author: Chiasson-Gould, Sophie
• Format: Thesis
• Language: English
• Published: Université d'Ottawa / University of Ottawa 2015
• Subjects: Mercury; Dissolved Organic Matter; Arctic; Bacteria; Climate change; Subarctic; Tundra
• Online Access: https://dx.doi.org/10.20381/ruor-2746; http://www.ruor.uottawa.ca/handle/10393/32024

The repercussions of rapid climate-change are felt worldwide, but particularly in Arctic and Subarctic regions. Evidence of recent changes in water chemistry is being recorded in Arctic aquatic ecosystems, bringing further attention to contaminant dynamics in these environments. I assessed the role of dissolved organic matter (DOM) in controlling the bioavailability of mercury (Hg), a top priority among Arctic contaminants, to aquatic food webs using a bacterial bioreporter under oxic conditions. Experiments were performed under pseudo- and non-equilibrium conditions, in both defined media and water samples from tundra lakes with a large gradient in DOM. Inorganic HgII was considerably more bioavailable under non-equilibrium conditions than when DOM was absent or when HgII and DOM had reached pseudoequilibrium (24h). Under these enhanced uptake conditions, HgII bioavailability followed a bell shaped curve as DOM concentrations increased, both for defined media and field samples, suggesting that complexation kinetics and binding thresholds on DOM determine HgII bioavailability to methylating bacteria, and likely MeHg concentrations, the bioaccumulative neurotoxic form of Hg. Experiments also suggest that DOM may alter cell wall properties to facilitate the first steps toward HgII internalization via facilitated or active transport, and yet without altering overall cell wall permeability. While further research on ternary (HgII-cell-DOM) interaction is warranted, I propose a molecular shuttle model for DOM in facilitating bacterial HgII uptake, and the existence of a short-lived yet critical time window (<24h) during which DOM facilitates the entry of newly deposited HgII from the atmosphere into aquatic food webs.