Complexation between Hg(II) and dissolved organic matter in stream waters: an application of fluorescence spectroscopy

Complexation between Hg(II) and dissolved organic matter (DOM) collected from streams in Ontario, Canada, was studied using three-dimensional excitation emission matrix (3DEEM) fluorescence spectroscopy. The results show that DOM reacted with Hg(II) rapidly, and the complexation reached pseudo-equilibrium within 20 s. Maximum excitation/emission (Ex/Em) wavelengths shifted towards the longer wavelengths, indicating that DOM structure changed during its interaction with Hg(II). Using fluorescence quenching titrations, complexing parameters, conditional stability constants and the percentage of fluorophores participating in the complexation, were estimated by the modified Stern–Volmer equation. The experimental and field survey results suggest that the Hg–DOM complexation in various streams was related to water quality parameters, e.g. DOC, Cl–, and cation concentrations, and was strongly affected by UV irradiation.