QUANTIFICATION OF MERCURY BIOAVAILABILITY AND METHYLATION POTENTIAL IN CONTAMINATED AQUATIC ECOSYSTEMS

Mercury (Hg) contamination persists in numerous sediment sites worldwide, and this contamination becomes a problem if the metal is converted to monomethylmercury (MeHg), the highly bioaccumulative form that can impart neurotoxic effects to humans and wildlife. Strategies for remediation generally aim to minimize MeHg production by benthic microorganisms native to the sediments. However, the factors that influence MeHg production in sediments have been poorly understood and difficult to quantify. Moreover, these processes that control Hg methylation can differ between sites. Therefore, methylation potential of Hg at a site needs to be quantified prior to the selection of a remediation strategy.

This presentation will summarize the challenges of mercury contamination in the aquatic environment and offer strategies for assessing risk and appropriate remediation methods. These strategies are based on research to delineate the two major factors that control the net production of MeHg in sediments: the activity of the methylating microbial community and the bioavailability of inorganic Hg for these microorganisms. Genetic-based methods to quantify mercury methylating microorganisms have been combined with chemical leaching methods to quantify Hg bioavailability in sediments. These methods were applied to sediment slurry microcosm experiments in which the type of Hg and the growth of methylating microorganisms were carefully controlled. The results demonstrate that under conditions of low microbial growth, Hg methylation is limited by the productivity of these organisms. While under conditions of high microbial growth, MeHg production is sensitive to the speciation and bioavailability of Hg. The use of these indicators will be discussed in the context of management and in-situ remediation of contaminated sediments.