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

Area of Science:

• Environmental Chemistry
• Aquatic Chemistry
• Spectroscopy

Background:

• Mercury (Hg(II)) is a toxic heavy metal pollutant.
• Dissolved organic matter (DOM) plays a crucial role in mercury's fate and transport in aquatic ecosystems.
• Florida Everglades surface waters contain diverse DOM sources, including mangrove leaves, sawgrass, and periphyton.

Purpose of the Study:

• To investigate the complexation interaction between Hg(II) and DOM from Florida Everglades.
• To determine the influence of DOM structure and environmental factors on Hg(II) complexation.
• To explore potential removal mechanisms for DOM-Hg(II) complexes.

Main Methods:

• Fluorescence spectroscopy (emission and synchronous fluorescence) was employed to study Hg(II)-DOM interactions.
• The modified Stern-Volmer equation was used to estimate conditional stability constants and binding site percentages.
• Experimental conditions including pH, chloride concentration, and divalent cations (Ca2+, Mg2+) were varied.

Main Results:

• Fluorescence quenching confirmed complexation between Hg(II) and various DOM types (degraded and fresh).
• Synchronous fluorescence spectra provided insights into DOM structure and potential Hg(II) binding sites.
• Complexation was influenced by pH, chloride, Ca2+, and Mg2+.
• DOM-Hg(II) complexes showed potential for removal via adsorption onto biogenic CaCO3.

Conclusions:

• Everglades DOM effectively complexes Hg(II), influencing its bioavailability and transport.
• Environmental factors significantly modulate mercury complexation with DOM.
• Biogenic calcium carbonate precipitation offers a plausible pathway for removing mercury-DOM complexes from the water column.