Fulvic acid-sulfide ion competition for mercury ion binding in the FloridaEverglades

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 spe ciation in the presence of fulvic acid. Model calculated species distributi ons are used to estimate a mercury-fulvic acid apparent binding constant to quantify fulvic acid and sulfide ion competition for dissolved inorganic m ercury (Hg(II)) ion binding. Speciation calculations done with PHREEQC, mod ified to use the estimated mercury-fulvic acid apparent binding constant, s uggest 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 (a bout 10(-7) M or greater) is present in Everglades' surface water, mercury- sulfide complexes should dominate dissolved inorganic mercury solution spec iation. In the absence of sulfide ion (for example, in oxygenated Everglade s' surface water), fulvic acid binding should dominate Everglades' dissolve d inorganic mercury speciation.