Characterizing the Interaction between Trace Metal and Dissolved Organic Matter from the Florida Coastal Everglades

Transcription

1 Characterizing the Interaction between Trace Metal and Dissolved Organic Matter from the Florida Coastal Everglades Rudolf Jaffé and Youhei Yamashita Southeast Environmental Research Center & Department of Chemistry and Biochemistry, Florida International University

2 Dissolved organic matter (DOM) affects the trace metal speciation MX ML (X = Cl, OH, CO3) (L = L1, L2.) + X + L M n+ (H2O) n adsorption M-colloid desorption coagulation disaggregation M-particle solute exchange settling resuspention biological uptake regeneration Soil / Sediment Organisms modified from Santschi et al., 1997

3 Chemical characterization of metal ion binding properties of DOM Evaluation of functional groups of organic ligands Nuclear magnetic resonance (NMR) Extended X-ray absorption fine structure (EXAFS) etc Evaluation of complexing capacities of organic ligands Electrochemical titration Fluorescence quenching titration Ion exchange Competitive ligand exchange with solid-phase extraction etc However, these methods can determine average metal ion binding properties of DOM.

4 Fluorescence quenching titration Fluorescenc ce Intensity at Ex/Em = 320/ Total added metal conc. (10-6 M)

5 Excitation-Emission Matrix (EEM) of surface water at 1 Fluorescence Intensity at Ex/Em = 320/ Total added metal conc. (10-6 M) 0 Excitatio on (nm) Fluores scence Intensity (QSU) Emission (nm)

6 Changes in EEM of water with µm Cu(II) tation (nm) Excit Emission (nm) EEM is useful for determining the binding capacities of each type of the fluorescence components with trace metals. However, peak picking technique is problematic for quantitative estimation. Changes in fluorescence e

7 Parallel factor analysis (PARAFAC) PARAFAC statistically decompose EEMs into independent fluorescent group Observed EEM Modeled EEM

8 Purposes of the present study To test the availability and sensitivity of combination technique of fluorescence quenching titration and EEM-PARAFAC Reproducibility Differences in binding capacities among different fluorescent components / DOM in different sites / different trace metals

9 Materials and Methods Surface water samples 4 FCE-LTER sites Trace metals Cu(II): semi-hard metal Hg(II): soft metal

10 Materials and Methods Modeling of fluorescence quenching curves Fluoresce ence Intensity (QSU) Total added metal conc. (10-6 M) Ryan and Weber Model 1 I = I0 + ( IM I K L 0)( )( 1+ MCL + K 2K C (1 + K M C M L L + K M C M ) 2 4K M 2 M I: fluorescence intensity at the metal conc. C M I 0 : fluorescence intensity without metal I ML : fluorescence intensity which dose not change due to the addition of metal K M : conditional stability constant C L : total ligand concentration ( I 0 I ML ) f = I 0 f: fraction of the initial fluorescence that corresponds to the binding fluorophores C C L M C M )

11 Materials and Methods PARAFACE modeling Excitation (nm) Component 1 Terrestrial humic Component 2 Terrestrial humic Component 3 Terrestrial humic Excitation (nm) Component 4 Microbial humic Component 5 Microbial humic Component 6 Terrestrial humic Emission (nm) Excitation (nm) Component 7 Protein 0 Emission (nm) Component 8 Protein 0 Emission (nm) 1108 surface water samples from Florida Coastal Everglades were used for FCE- PARAFAC model. Source characterization was carried out by comparison to previous PARAFAC studies (Cory and Mcknight, 2005; Stedmon and Markager, 2005; Yamashita et al., 2008).

12 Reproducibility Triplicate titration experiments with Cu(II) for water Component 1 Terrestrial humic Component 4 Microbial humic Component 7 Protein Fluorescence intensity (QSU) logk = 4.83±0.03 f = 46± logk = 5.06±0.04 f = 29± Cu(II) (µm) Cu(II) (µm) Cu(II) (µm) 1 st titration 2 nd titration 3 rd titration The combination of fluorescence quenching titration and EEM- PARAFAC is enough to reproducibly determine the binding capacity of individual humic-like components with trace metals.

13 Differences in quenching among DOM/trace metals Titration experiments with Cu(II) or Hg(II) for 4 different samples Component 2 Terrestrial humic 0 Shark River F/F0 Taylor Cu(II) (µm) Hg(II) (µm)

14 Differences in quenching among fluorescent components Titration experiments with Cu(II) for water F/F F Cu(II) (µm) Comp1 (Terrestrial humic) Comp2 (Terrestrial humic) Comp3 (Terrestrial humic) Comp4 (Microbial humic) Comp5 (Microbial humic) Comp6 (Terrestrial humic) Fluorescence quenching titration with EEM-PARAFAC is a sensitive method to determine the differences in binding capacity of individual fluorescent components with trace metals.

15 The logk and f values of 6 humic-like components Shark River Taylor

16 The logk and f values of 6 humic-like components 24 Shark River Taylor 0

17 The logk and f values of 6 humic-like components Shark River (A) Cu (B) Hg Taylor 0 f (%) not modeled not modeled 0 Comp1 Comp2 Comp3 Comp4 Comp5 Comp6 0 Comp1 Comp2 Comp3 Comp4 Comp5 Comp6

18 The logk and f values of 6 humic-like components Shark River (A) Cu (B) Hg Taylor 0 f (%) not modeled not modeled 0 Comp1 Comp2 Comp3 Comp4 Comp5 Comp6 0 Comp1 Comp2 Comp3 Comp4 Comp5 Comp6

19 The logk and f values of 6 humic-like components Shark River (A) Cu (B) Hg Taylor f (%) not modeled not modeled 0 Comp1 Comp2 Comp3 Comp4 Comp5 Comp6 0 Comp1 Comp2 Comp3 Comp4 Comp5 Comp6

20 Changes in fluorescence of protein-like components Titration experiments with Cu(II) or Hg(II) for 4 different samples Component 7 Protein Shark River Taylor Cu(II) (µm) Hg(II) (µm)

21 Changes in fluorescence of protein-like components Titration experiments with Cu(II) or Hg(II) for 4 different samples Component 7 Protein Shark River Changes in quantum yields by changes in 3D-structure of protein molecules Cu(II) due (µm) to high concentrations Hg(II) (µm) of Cu(II). Increases in fluorescence intensity at the later stage of the Cu(II) addition experiment might be the result of: Changes in quantum yields of protein molecules from a shift of protein-inorganic complexes to protein-cu(ii) complexes. Release of protein molecules due to replacement from DOM-protein interaction to DOM-Cu(II) interactions. Taylor

22 Summary The combination of fluorescence quenching titration and EEM-PARAFAC provides adequate reproducibility and sensitivity for the determination of the binding capacity of individual humic-like components with trace metals. The trace metal binding capacity and behavior was different among humic-like components determined by PARAFAC. The changes in protein-like fluorescence intensity with Cu(II) additions indicate that EEM-PARAFAC is also effective in evaluating the changes in molecular environments of DOM, like as DOM-DOM interactions.

23 Acknowledgements FCE-LTER College of Arts and Science at FIU for financial support The Wetlands Ecosystem Laboratory at SERC for logistic support Geochemistry Group at SERC for support to Lab work