The Biogeochemical Cycling of Mercury in the EnvironmentEPA Grant Number: F5B71267
Title: The Biogeochemical Cycling of Mercury in the Environment
Investigators: Stetson, Sarah J.
Institution: Colorado School of Mines
EPA Project Officer: Zambrana, Jose
Project Period: July 1, 2005 through July 1, 2008
Project Amount: $94,272
RFA: GRO Fellowships for Graduate Environmental Study (2005) RFA Text | Recipients Lists
Research Category: Academic Fellowships
The principle objective is to create the analytical and conceptual framework needed to integrate isotopic analyses into investigations of the cycling of mercury (Hg) both locally and globally. This framework will be created by developing a model for the biogeochemical cycling of Hg in the environment that integrates total Hg levels, speciation, and isotope ratios. The study will explore the likelihood that transport of Hg from an ore deposit having a specific and known isotopic signature can be understood in terms of small but measurable changes in the isotopic ratios with weathering and biological processes that occur within the mining area, waste dump, and watershed.
The focus will be on characterizing major processes in the cycling of Hg in the environment by characterizing Hg mining areas and the associated waste dumps and watersheds in the system. By determining the total concentration, Hg species, and isotope ratios of Hg in various compartments of the system, the overall fate of Hg can be modeled and better understood.
Total Hg levels and speciation will be determined by Atomic Fluorescence Hg analysis. Isotope ratios will be determined by Multicollector Inductively Coupled Plasma Mass Spectrometry. An IRMM Hg isotopic spike standard will be used in the determination of the Hg isotopes. Where necessary, carefully controlled experiments may be performed to mimic natural processes such as dissolution and microbial transformation to determine isotopic fractionation. The total concentration, speciation, and isotope data will be compiled to create a model for the cycling of Hg using a computer modeling program such as Stella, which is designed to quantitatively evaluate complex relationships between multiple sources and sinks, with multiple flux vectors.
Gathering and analyzing data in a Hg mining area will allow the creation of a model for the cycling of Hg in that system through mass balances and isotopic signatures. By evaluating the concentrations and isotopic signatures of all of the different components of the system and comparing them, insight into the cycling, transport processes, and fractionating activities in the system will be attained.
The differences among the isotope ratios of the samples may give information on Hg fractionation processes occurring in the environment. Specifically, Hg that has been transformed biotically will be expected to be enriched in the lighter isotopes. Hg that has gone through dissolution and equilibrium reactions may have different isotopic signatures from that of the orebody as well.