Mercury concentration and speciation in coastal rainwater

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Nicole Erin Parler (Creator)
The University of North Carolina Wilmington (UNCW )
Web Site:
Robert Kieber

Abstract: Mercury exists in mainly two oxidation states in the atmosphere, Hg0 and Hg(II). Inorganic divalent mercury, Hg(II), has a greater solubility; therefore is in higher concentration in rainwater, than Hg0. The toxic species, methylmercury is an organic form of Hg(II) and is present in low concentration. Mercury is released into the atmosphere by natural and anthropogenic sources. Rainwater is thought to be a main removal mechanism for atmospheric mercury. The concentration and speciation of mercury were determined in rainwater from Wilmington, NC, from September 1, 2003 to September 30, 2005. Volume weighted averages for total Hg in unfiltered rainwater, total dissolved Hg, particulate Hg, dissolved gaseous Hg (Hg0) and methyl-Hg were 52.9 ± 4.7 pM, 40.6 ± 4.0 pM, 13.7± 1.5 pM, 4.3 ± 0.9 pM and 1.1 ± 0.1 pM, respectively. All mercury species were present in all seasons with no significant difference in concentrations between summer and winter, except dissolved gaseous mercury concentration was higher in the winter, with a higher ratio of Hg(II)/Hg(0) in summer relative to winter events. Diurnal variation was seen where Hg(II) decreased during the day into the night, suggesting photochemical reduction of Hg(II). All Hg concentrations were higher in continental storms relative to coastal rain events. Both total mercury species (UFHg and TDHg) were positively correlated with particulate mercury. Total mercury species were washed out of the atmosphere by rainwater with lower concentrations for larger rain events. A weak positive correlation was observed between TDHg and NO3 -, TDHg and SO4 2-, DGHg and Cl-, and Hgpart and DOC. The photochemistry of mercury from Wilmington was also investigated. UFHg, TDHg, and DGHg were generally produced upon irradiation of rainwater samples by simulated sunlight. Particulate Hg concentrations generally declined upon irradiation and MMHg concentrations showed no pattern, in some instances, increasing, decreasing or remaining the same. Positive correlation was observed between, production of UFHg and Hgpart and a negative correlation was observed between production of TDHg and Hgpart. Continental events increased in Hgpart while decreasing in TDHg, whereas coastal events increased in TDHg while decreasing in Hgpart after irradiation. Seasonal differences between Hg species were similar with an increase in TDHg and DGHg, while decreasing in Hgpart and greater changes were observed during the winter. Diurnal variations of Hg(II)/Hg(0) ratio increased during the afternoon and decreased there after. Atmospheric global inputs by natural and anthropogenic sources, 4.1 x 106 kg or 2.0 x 107 mol per year, were in good agreement with calculated total flux of mercury removed via wet deposition, 3.8 x 106 kg or 1.9 x 107 mol per year, suggesting that essentially all mercury released into the atmosphere is removed via rain.

Additional Information

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

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