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Influence of dissolved organic matter (DOM) on mercury speciation and reactivity in rainwater

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Sarah D. Manley (Creator)
The University of North Carolina Wilmington (UNCW )
Web Site:
Joan Willey

Abstract: This study focused on determining interactions between dissolved organic matter (DOM) and mercury (Hg) in rainwater, and their significance in affecting the transport and reactivity of mercury in the environment. Photochemical, UV oxidation, and rain - river mixing experiments were also performed to investigate their influences on mercury behavior. Concentrations of total, total dissolved, particulate, labile (reactive), hydrophilic total dissolved and hydrophilic labile mercury were determined in Wilmington, North Carolina rainwater. Volume weighted averages and standard deviations of 32.2 ± 3.3, 24.7 ± 2.5, 5.1 ± 1.1, 14.8 ± 2.0, 13.0 ± 1.6, and 7.8 ± 2.0 pM respectively. Dissolved gaseous mercury was detected at low levels in 40% of samples. Non-labile and hydrophobic fractions of Hg were on average 40 and 53 % respectively, indicating that strong complexes between Hg and DOM exist in rainwater in relatively large percentages. Glutathione did not outcompete Hg in these complexes, suggesting that some Hg-DOM complexes are very strong. Labile mercury concentrations in photochemical experiments increased after 6 hours of irradiation relative to dark controls suggesting light may be contributing to the production of labile Hg complexes. Photochemistry experiments with unfiltered rain yielded inconsistent results that were different from filtered experiments, indicating that particulate mercury plays a variable role in photochemical processes. Labile mercury measured over 6 hours in river water spiked with rain water did not rapidly form strong Hg-DOM complexes with river water DOM suggesting this process does not occur or that it is relatively slow, and light did not influence this. Intense UV oxidation of rain prior to addition of bromine monochloride (BrCl) to ensure total DOC oxidation may result in greater total mercury concentrations and also indicates the presence of organic mercury complexes in rain.

Additional Information

A Thesis Submitted to the University of North Carolina Wilmington in Partial Fulfillment of the Requirements for the Degree of Master of Science
Language: English
Date: 2009
Mercury--Environmental aspects, Rain-water (Water-supply)--North Carolina--Wilmington--Testing, Water--Organic compound content
Mercury -- Environmental aspects
Water -- Organic compound content
Rain-water (Water-supply) -- North Carolina -- Wilmington -- Testing