Interaction between Hg(II) and natural dissolved organic matter: a fluorescence spectroscopy based study

Interaction between Hg(II) and dissolved organic matter (DOM) collected from surface water samples of the Florida Everglades was studied using different fluorescence spectroscopic methods. Complexation between Hg(II) and DOM leached from mangrove leaves, sawgrass, and periphyton was investigated. Both fluorescence emission and synchronous fluorescence spectra showed that these dissolved organic materials, whether they are highly degraded or are freshly leached, can “complex” Hg(II) since fluorescence intensity was quenched upon addition of Hg(II) to the DOM samples. Synchronous fluorescence spectra disclosed structural information on the DOM sample, regarding possible binding sites for Hg(II). Chemical parameters on the complexation of Hg(II), including the conditional stability constants and the percentage of fluorophores participating in the complexation, were estimated by the modified Stern–Volmer equation. A detailed investigation under different experimental conditions showed that the complexation of the DOM samples collected from the Everglades was influenced by pH, Cl−(aq) anion, and cations such as Ca2+ and Mg2+. Experimental results suggest that DOM–Hg(II) complexes can be removed from the water column through adsorption on biogenically precipitated CaCO3(s).