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Mercury Stable Isotope Fractionation to Elucidate Biogeochemical Transformations in the Environment

EPA Grant Number: F07B20465
Title: Mercury Stable Isotope Fractionation to Elucidate Biogeochemical Transformations in the Environment
Investigators: Gehrke, Gretchen E.
Institution: University of Michigan
EPA Project Officer: Cobbs, Gladys M.
Project Period: September 1, 2007 through June 1, 2010
RFA: STAR Graduate Fellowships (2007)
Research Category: Mercury , Fellowship - Geology/Geochemistry , Academic Fellowships

Description:

Objective:

Mercury is a globally distributed and severely toxic pollutant, the mobility and bioaccumulation of which is highly dependent on its biogeochemical transformations in the environment. Stable isotope fractionation is a powerful tool for identifying reaction pathways, and recent analytical advancements in mass spectrometry have enabled precise measurements of the mercury stable isotope system. This project investigates the natural fractionation of mercury stable isotopes in order to understand and quantify mercury sources, sinks and transformations in the environment.

Approach:

Ore samples, mine tailings, and streambed sediments will be collected at the New Idria mercury mine and along the San Carlos Creek downstream of the mine. Stream water, soil, and foliage samples will also be collected from the surrounding areas. Mercury concentrations will be measured by gold-trap mercury atomic absorption spectroscopy (AAS). The mercury stable isotope composition of samples will be determined by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS). Coupling mercury concentrations and isotopic compositions, a mercury mass-balance for the study site will be calculated.

Expected Results:

It is anticipated that the mercury leached from the unprocessed ore and mine tailings will be isotopically distinct from mercury released from the ore processing mill. In addition, it is expected that the isotopic composition of mercury in San Carlos Creek will change as it moves downstream from the New Idria Mine, reflecting the processes transforming mercury in this environment. Mercury can be removed from the water column either through scavenging by particulate matter or reduction to a gas (Hg0) leading to evasion to the atmosphere. It is expected that particulate scavenging and mercury volatilization will lead to different mercury isotope fractionations, and isotopic mass-balance calculations will allow estimation of the relative dominance of each process in the mercury cycle. Mercury released to the atmosphere from ore processing may also be traceable into soils and vegetation using its distinct isotopic composition. This project will be the first major application of mercury isotopes to explore the biogeochemical controls on mercury, and will help us to understand how past, present, and future mercury pollution will affect ecosystems and the environment.

Supplemental Keywords:

mercury, stable isotopes, isotope fractionation, contamination, mass-balance, toxins, , Scientific Discipline

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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