, Volume 132, Issue 1-2, pp 89-104

Fulvic Acid-Sulfide Ion Competition for Mercury Ion Binding in the Florida Everglades

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Abstract

Negatively charged functional groups of fulvic acid compete with inorganic sulfide ion for mercury ion binding. This competition is evaluated here by using a discrete site-electrostatic model to calculate mercury solution speciation in the presence of fulvic acid. Model calculatedspecies distributions are used to estimate a mercury-fulvicacid apparent binding constant to quantify fulvic acid and sulfide ion competition for dissolved inorganic mercury (Hg(II)) ion binding. Speciation calculations done with PHREEQC,modified to use the estimated mercury-fulvic acid apparent binding constant, suggest that mercury-fulvic acid and mercury-sulfide complex concentrations are equivalent for very low sulfide ion concentrations (about 10-11 M) in Everglades' surface water. Where measurable total sulfide concentration (about 10-7 M or greater) is present inEverglades' surface water, mercury-sulfide complexes shoulddominate dissolved inorganic mercury solution speciation. Inthe absence of sulfide ion (for example, in oxygenated Everglades' surface water), fulvic acid binding should dominateEverglades' dissolved inorganic mercury speciation.