Superfund Research Program
Biogeochemical Framework to Evaluate Mercury Methylation Potential During in-situ Remediation of Contaminated Sediments
Project Leader: Heileen Hsu-Kim
Co-Investigators: Marc Deshusses, Dwayne A. Elias (Oak Ridge National Laboratory)
Grant Number: R01ES024344
Funding Period: 2014-2021
This project is establishing biogeochemical indicators for methylmercury production that will be used to improve the effectiveness of in situ remediation of mercury-contaminated sediments. Methylmercury (MeHg) is a potent neurotoxin that is produced by anaerobic microorganisms and biomagnifies in the aquatic food web. In situ remediation methods such as sediment amendments have not been widely implemented, mainly because the effects on MeHg production are unknown. Moreover, the processes that control mercury methylation can differ between sites, and this uncertainty is a barrier for effective implementation of in situ remediation.
The research team is addressing this knowledge gap by establishing indicators of mercury methylation potential and using them to assess the effectiveness of sediment amendments for remediation. The research is focusing on two critical drivers of methylmercury production: the environmental conditions that promote the growth of sediment microorganisms that produce MeHg and the processes that influence the bioavailability of mercury for these microorganisms. The balance between these two drivers will determine the success of in situ sediment treatments. In this respect, the central hypothesis of this work is that the identification of the primary controls to methylmercury production at the field site will improve the efficacy of sediment treatments. To test this hypothesis, the research team is applying fundamental knowledge regarding mercury biogeochemistry to improve the determination of mercury methylation potential in sediments and compare in situ techniques for sediment remediation.
The researchers are:
- Developing relationships between the activity of methylating microorganisms and MeHg production in sediments
- Refining methods to quantify mercury bioavailability in sediments
- Identifying factors that control methylation potential and formulate guidelines for characterization of sites
- Determining how sediment amendment techniques influence methylmercury production potential
The research is being implemented with laboratory sediment microcosm experiments that simulate a range of conditions relevant to mercury-contaminated Superfund sites. A variety of molecular biological and geochemical tools will be used to quantify the activity of methylating microorganisms and the reactivity of mercury as related to biouptake into anaerobic microorganism.
The researchers apply recent discoveries to develop new tools to quantify mercury methylation potential. These discoveries include the genetic basis of mercury methylation in microorganisms and the geochemical processes controlling mercury speciation in sediments. The researchers also work with managers of Superfund sites in the implementation of the research, interpretation of the results, and in the establishment of a guiding framework for assessments at specific field sites and the selection of remediation strategies.