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Some samples on the shaker. |
Samples about to be preserved with 5% BrCl. It's such a pretty orange color! |
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The mercury analyzer used to determine the Hg in my samples. Detection limit ~1 ng/L. That's crazy! |
abstract |
This is the abstract that I wrote for the SURE Symposium. It does a lovely job of summing up my summer research.
Sarah Steely, Dr. Stefan Grimberg
Atmospheric deposition of mercury is a problem in otherwise pristine areas of northeastern North America, such as the Adirondacks. This deposition leads ultimately to elevated levels of methyl mercury (MeHg) in fish. Methyl mercury is a neurotoxin that bioaccumulates in muscle tissue. Many of the steps in the cycle of how mercury gets from the atmosphere into the food chain are not well understood and are currently being studied. One such area of interest is how mercury interacts under differing redox conditions with soil. Sulfate reducing microorganisms found in anoxic soils and sediments such as wetland peats produce MeHg in a detoxification pathway to protect themselves from ionic mercury, Hg(II). The availability of mercury to sulfate reducing microorganisms may be affected by the interactions of Hg(II) with soil. These sorption interactions may vary depending on a number of properties such as pH, organic matter content, mineral composition (Lyon et al 1997), and redox potential.
It has been shown that as soil organic carbon content increases there is a higher fraction of Hg(II) that is resistant to desorption (Yin et al 1997). This is presumably due to the strong interactions of Hg(II) with soil organic matter. Although studies have been done involving the sorption kinetics and equilibrium reactions between Hg(II) and soils, little has been done under varying redox conditions. The aim of this project was to see if sorption of Hg(II) to soil is a function of redox conditions. Soil was collected from two areas of the Adirondack Park and Forest Preserve: the Sunday Lake watershed and Huntington Forest. Three different redox couple solutions were used, aerobic (~ +150 mV), denitrifying (~ +100 mV) and sulfate reducing (~ -200 mV), and the concentration of mercury desorbed into solution was measured over time. The samples were kept at a constant temperature of 20 ºC and shaken at 130 rpm.
Preliminary results from the Sunday Lake soil indicate that the systems reach a steady state quickly in regards to mercury desorption, with the sulfate reducing treatment releasing significantly more mercury into the aqueous phase than the aerobic or denitrifying treatments.
The dissolution of organic carbon from the soil under these conditions is currently being investigated as well, and its release is expected to mirror that of mercury. Preliminary data supports this hypothesis. At the writing of this abstract the results from the Huntington Forest soil experiment are not yet available; however, they will be compared to the Sunday Lake soil and should follow the same trends.
A partition coefficient will also be calculated using data from the equilibrium state of the desorption experiments. The partition coefficient is the ratio of the amount of mercury sorbed onto soil particles to the amount present in the aqueous solution when the system is at equilibrium. Therefore, with the analysis of the soil bound mercury and the liquid phase mercury values, the partition coefficient can be calculated for each redox condition and soil. Results will be presented at the SURE Symposium on July 28th, 2005.
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Some samples on the shaker. |
Samples about to be preserved with 5% BrCl. It's such a pretty orange color! |
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The mercury analyzer used to determine the Hg in my samples. Detection limit ~1 ng/L. That's crazy! |
Lyon et al (1997) Calculation of soil-water and benthic sediment partition coefficients for mercury. Chemosphere. 35(4):791-808.
Yin, Allen, and Huang. (1997) Kinetics of Mercury(II) Adsorption and Desorption on Soil. Environ. Sci. Technol. 31(2):496-503.