DOM from various locations (F1, 2BS, U3) in northern Everglades, FL, and Suwannee River, GA, was isolated into hydrophobic acids (HPoA), hydrophilic acids (HPiA), hydrophobic neutrals (HPoN), and hydrophilic neutrals (HPiN) (Fig. 1), and into humic (HA) and fulvic (FA) acids. The isolates were characterized in terms of their elemental compositions, specific UV absorbance (SUVA, the ratio between UVA at 254 nm and DOC conc.), carboxyl group content (by titration), and functional group content (by 13C NMR).
Stock solutions of organic matter isolates and model compounds, prepared in distilled water and adjusted for pH (6.0 = 0.1) and ionic strength (0.01 M NaNO3), were added to acid-washed cinnabar. Glass beads were added to each reaction vessel and were shaken in an orbital shaker at 200 rpm. Based on the results of kinetic experiments (data not shown), dissolution was carried out for a period of seven days. Samples were then filtered (0.1 µm) and analyzed for total dissolved Hg concentrations. The detection limit for the Hg-analyzer was 2.5 nM.
Cinnabar was also reacted with filtered water samples collected from the F1 (DOC = 38.9 mg/L) and 2BS (DOC = 17.6 mg/L) sites. To study the effect of polyvalent cations (e.g., Ca+2) on dissolution, these samples were passed through Na-saturated cation exchange resins (CER) and then reacted with cinnabar. Electrophoretic mobility (EM) measurements were made on acid-washed cinnabar (50 mg/L) to determine the surface charge both in the presence and absence of DOM.
