Binding characteristics of Hg(II) with extracellular polymeric substances: implications for Hg(II) reactivity within periphyton

Periphyton contains extracellular polymeric substances (EPS), yet little is known about how periphyton EPS affect the speciation and mobility of mercury (Hg(II)) in aquatic systems. This study extracted and characterized EPS from periphyton in Florida Everglades, and explored its role in Hg(II) binding and speciation using multiple approaches. Results from Fourier transform infrared spectroscopy (FTIR) revealed that colloidal and capsular EPS were primarily comprised of proteins, polysaccharides, phospholipids, and nucleic acids. Ultrafiltration experiments demonstrated that 77 +/- 7.7% and 65 +/- 5.5% of Hg(II) in EPS solution could be transformed into colloidal and capsular EPS-bound forms. Three-dimensional excitation emission fluorescence spectra (3D-EEMs) showed that the binding constants (K-b) between colloidal/capsular EPS and Hg(II) were 3.47x10(3) and 2.62x10(3) L center dot mol(-1). Together with 3D-EEMs and FTIR, it was found that the protein-like and polysaccharide-like substances in EPS contributed to Hg(II) binding. For colloidal EPS, COO- was the most preferred Hg(II) binding group, while C-N, C-O-C, and C-OH were the most preferred ones in capsular EPS. Using the stannous-reducible Hg approach, it was found that EPS significantly decreased the reactive Hg(II). Overall, this study demonstrated that EPS from periphyton are important organic ligands for Hg(II) complexation, which may further affect the migration and reactivity of Hg(II) in aquatic environment. These observations could improve our understanding of Hg(II) methylation and accumulation within periphyton in aquatic systems.

Automated summary

This study extracted and characterized extracellular polymeric substances (EPS) from periphyton in Florida Everglades to explore their role in the binding and speciation of mercury (Hg(II)). The results showed that EPS primarily consisted of proteins, polysaccharides, phospholipids, and nucleic acids, and could transform Hg(II) into colloidal and capsular EPS-bound forms. The study found that proteins and polysaccharides in EPS contributed to Hg(II) binding, with different preferred binding groups for colloidal and capsular EPS. EPS also significantly decreased the reactive Hg(II) in the aquatic environment.