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Scientific Investigations Report 2014–5234

Prepared in cooperation with the National Park Service

Assessment of the Use of Sorbent Amendments for Reduction of Mercury Methylation in Wetland Sediments at Acadia National Park, Maine

By Thomas G. Huntington, Ariel Lewis, Aria Amirbahman, Mark Marvin-DiPasquale, and Charles W. Culbertson

Thumbnail of and link to report PDF (2.76 MB)Abstract

Mercury is a contaminant of ecological concern because of its ubiquity and toxicity to fish and wildlife, and is considered a severe and ongoing threat to biota at Acadia National Park in Maine. The formation and biomagnification of methylmercury is the primary concern of resource managers at Acadia, and information is needed to develop strategies for remediation or mitigation of this contaminant. The U.S. Geological Survey in cooperation with Acadia National Park, National Park Service carried out a series of laboratory and field experiments to evaluate the potential of zero-valent iron and granular activated carbon to reduce the rate of the bacterially mediated process of mercury methylation and subsequent biological uptake by the great pond snail Lymnaea stagnalis. The addition of zero-valent iron resulted in an increase in ferrous iron that was then further oxidized to poorly crystalline amorphous ferric iron, as was anticipated. Our original hypothesis was that these reactions would reduce methylation by decreasing the concentrations of substrates for bacterial methylation (sulfide and divalent mercury) through sorption to ferric iron surfaces, formation of iron sulfide compounds, or conversion of mercury to gaseous forms and subsequent evasion. The results of our experiments did not consistently support this hypothesis. In one experiment the application of zero-valent iron increased the amount of methylmercury associated with surficial sediment. In another experiment zero-valent iron decreased the amount of methylmercury associated with surficial sediment. The addition of zero-valent iron may have stimulated mercury methylation by iron reducing bacteria and if that effect outweighed the processes that could have decreased methylation then methylation would not be decreased.

The results of field mesocosm experiments indicated that there was a decreasing trend in pore-water methylmercury concentration after application of granular activated carbon but methylation was not affected because there was no corresponding decrease in sediment methylmercury concentration. The application of granular activated carbon resulted in the sorption of methylmercury. The application of granular activated carbon resulted in an increase in the distribution coefficient for methylmercury indicating that this amendment caused a higher proportion of methylmercury to be associated with the sediment than the pore water in comparison to the reference (untreated) condition. Experiments to test whether zero-valent iron or granular activated carbon would reduce the biouptake of methylmercury in snails were inconsistent; zero-valent iron had no effect on uptake in one experiment but resulted in a significant decrease in uptake in a second experiment. Granular activated carbon did not affect biouptake in either experiment.

First posted March 19, 2015

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Suggested citation:

Huntington, T.G., Lewis, Ariel, Amirbahman, Aria, Marvin-DiPasquale, Mark, and Culbertson, C.W., 2015, Assessment of the use of sorbent amendments for reduction of mercury methylation in wetland sediments at Acadia National Park, Maine: U.S. Geological Survey Scientific Investigations Report 2014–5234, 30 p., http://dx.doi.org/10.3133/sir20145234.

ISSN 2328-0328 (online)



Contents

Acknowledgments

Abstract

Introduction and Background

Methods

Laboratory Analytical Procedures for Experiments 1 and 2

Laboratory Analytical Procedures for Pore Water Collected From Experiments 1, 2, 4, and 5 and Sediment From Experiments 4 and 5

Results of the Laboratory and Field Experiments

Discussion of Experimental Results

Limitations of This Study and Potential for Future Research

Summary

References Cited

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