Citation:

RANDALL, P. M. Evaluation Of Selected Sorption Materials For Capping Mercury-Contaminated Fresh Water Sediments. Presented at The 10th International Conference on Mercury as a Global Pollutant (ICMGP), Halifax, NS, CANADA, July 24 - 29, 2011.

Impact/Purpose:

To characterize the extent of mercry methylation under conditions simulating those at a mercury-contaminated superfund site in Alabama, both during baseline (non-reactive capping) conditions and with the implementation of reactive capping materials.

Description:

Fate and transport of mercury (Hg) and methylmercury (MeHg) within the aquatic environment involves many complex and interconnected pathways. MeHg is formed mainly at the sediment-water interface, just below which there is a transition from oxic to anoxic conditions. The formation of MeHg is mediated by the complex interaction of inorganic Hg and microorganisms. Transport of Hg and MeHg into the overlying water, particularly in lacustrine environments, can be mitigated by the placement of a sediment cap. Traditional caps are used as physical isolation barriers between the source sediments and the sensitive ecological receptors of the overlying aquatic ecosystem. Contaminant transport from source sediments through a sediment cap and into the overlying water is promoted by groundwater upwelling and processes that contribute to sediment re-suspension, such as bioturbation and gas ebullition. The function, capacity and longevity of traditional isolation caps can be augmented through the strategic use of both permeability control and reactive materials. Reactive capping materials, in metals-impacted sediments, typically have high sorptive capacities, hypothetically rendering the metals non-bioavailable and limiting the transport of contaminants into overlying surface water. In the case of Hg, a reactive cap with requisite sorptive characteristics can also render the Hg non-bioavailable and thereby mitigate the rate and extent of methylation. The aim of this project is to characterize the extent of mercury methylation under conditions simulating those at a mercury-contaminated superfund site in Alabama, both during baseline (non-reactive capping) conditions and with the implementation of reactive capping materials. In order to evaluate the performance of each reactive capping material, a three-stage experimental study was developed. The adsorption of Hg and MeHg onto the five materials (bauxite, AquaBlok^®, local soil, local dredged sediment, and Ottawa sand as a control) was evaluated in Stage 1 (Sorption Study). The ability of two candidate capping materials (local soil and local dredge material) to inhibit the methylation of Hg relative to the quantity of MeHg produced during the incubation conditions was evaluated in Stage 2 (Incubation Study). The capacity of one candidate capping material (local soil) to inhibit translocation of Hg and MeHg with respect to ebullition-facilitated contaminant transport was evaluted in Stage 3 (Column Study). This presentation will report the results of this study.

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