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

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.