State Water Resources Research Institute Program (WRRI)
Start Date: 2010-03-01 End Date: 2011-02-28
Total Federal Funds: $15,992 Total Non-Federal Funds: $36,654
Principal Investigators: K.T. Valsaraj, Ronald DeLaune
Abstract: The presence of mercury in Louisiana lakes has become a pervasive problem with fish consumption advisories having been issued for several of them in the last several years. The Louisiana Department of Environmental Quality (LDEQ) has listed in the 2000 Annual Mercury Report nineteen areas under fish consumption advisory spread along the State. The sediments in these areas were contaminated, with several showing sediment with high mercury concentration. In-situ capping (ISC) is one of the remediation methods that have been shown to be effective in reducing mercury transport from contaminated sediments to overlying water (Liu et al, 2007, 2008; Liu, 2008). In-situ capping consists of placing a layer of proper isolating material between the layers of contaminated sediment and overlying water. This method is useful in reducing the transport of the contaminant, and requires fewer infrastructures associated with the handling, dewatering, treatment and disposal process. Methyl mercury is the predominant form in anaerobic sediments that bioaccumulate up the food chain and move to the upper trophic levels. The first step in preventing mercury from migrating from sediment to water is to control the mercury methylation process and transport in the porewater. To this end, a control strategy is to cap the contaminated sediment and engineer the cap to be reactive towards Hg so that it is converted to sulfides of mercury thereby preventing the methylation process. The use of Mackinawite as a mercury stabilizer in sediments has been proven by us in laboratory studies (Liu et al, 2009; Chaves et al, 2009). This project is to study the mechanism of this process so that a possible control strategy for an “active cap” can be explored in sedimentary microcosms. This research will demonstrate the optimum methodology for the production of modified Mackinawite that can be added within sediment cap and prevent the methylation of mercury in freshwater lakes in Louisiana. Pure Mackinawite is a good inhibitor of mercury methylation in anoxic sediments; however, it is easily transformed when applied to natural sediments. A series of experiments will be conducted to allow us to see how adding a modifier to the synthetic Mackinawite will substantially alter the stability of the sediment cap and help in selecting appropriate capping materials for Louisiana lake sediments. The preliminary experiments on Mackinawite modification promoted a high mercury sequestration capacity and made the mackinawite more resistant to oxidation. The next step is to demonstrate the mercury sequestration capacity of modified mackinawite in field sediments, to evaluate the efficiency and feasibility of the solid to use as an isolating material in capping. Thus, this proposal seeks to continue the research by evaluating mercury sequestration in contaminated sediments of Henderson Lake, La, Pearl River, La, and/or Devil’s Swamp, La using modified mackinawite. This evaluation comprises the following tasks: a) To determine the mercury contamination level of sediments from the selected areas in Louisiana; b) To evaluate the capping technology to prevent and minimize the transport of mercury from contaminated sediment to water column in sediment microcosms in the laboratory.