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publications > paper > binding of mercury(II) to aquatic humic substances: influence of pH and source of humic substances
Binding of Mercury(II) to Aquatic Humic Substances: Influence of pH and Source of Humic Substances
Markus Haitzer, * ,
George R. Aiken , and
Joseph N. Ryan
Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, Colorado 80309, and U.S. Geological Survey, Water Resources Division, 3215 Marine Street, Boulder, Colorado 80303
Posted (abstracted/excerpted) with permission from Haitzer, M.; Aiken, G.R.; Ryan, J.N. Environ. Sci. Technol. 2003, 37, 2436-2441. Copyright 2003 American Chemical Society. Note: Entire paper is available from the Environmental Science and Technology Journal website (journal subscription is required) |
Abstract | Figures | Tables | Literature Cited
Abstract
Conditional distribution coefficients (KDOM') for Hg(II) binding to seven dissolved organic matter (DOM) isolates were measured at environmentally relevant ratios of Hg(II) to DOM. The results show that KDOM' values for different types of samples (humic acids, fulvic acids, hydrophobic acids) isolated from diverse aquatic environments were all within 1 order of magnitude (1022.5±1.0 -1023.5±1.0 L kg-1), suggesting similar Hg(II) binding environments, presumably involving thiol groups, for the different isolates. KDOM' values decreased at low pHs (4) compared to values at pH 7, indicating proton competition for the strong Hg(II) binding sites. Chemical modeling of Hg(II)-DOM binding at different pH values was consistent with bidentate binding of Hg(II) by one thiol group (pKa = 10.3) and one other group (pKa = 6.3) in the DOM, which is in agreement with recent results on the structure of Hg(II)-DOM bonds obtained by extended X-ray absorption fine structure spectroscopy (EXAFS).
Figures
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Figure 1. Plot showing the atomic C/S ratio versus atomic C/N ratio for the various DOM isolates. [larger image] |
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Figure 2. Conditional distribution coefficients (log KDOM') measured for the binding of Hg(II) to various DOM isolates. Error bars represent standard deviations calculated from three replicates. [larger image] |
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Figure 3. Binding of Hg(II) to F1 HPOA as a function of solution pH. Binding is given as conditional distribution coefficient log KDOM' (see eq 2) at I = 0.1 M. Circles are the experimental data points (± standard deviation). The solid line represents the model fit to the experimental data using parameters in Table 2. [larger image] |
Tables
Table 1. Site Descriptions for Aquatic Organic Matter Isolates |
sample |
site description |
Suwannee River Humic (SRHA) and Fulvic Acid (SRFA) |
Black water river draining the Okeefenokee Swamp; Sampled at Fargo, GA; Vegetation types: Southern Flood plain Forest (Quercus, Nyassa, Taxodium); International Humic Substances Society Standard Humic and Fulvic Acids. |
Ogeechee River Humic (OGHA) and Fulvic Acid (OGFA) |
Small river draining the piedmont in Eastern Georgia. Sampled at Grange, GA. Vegetation types: Oak-Hickory-Pine Forest (Quercus, Carya, Pinus). |
Coal Creek Fulvic Acid (CCFA) |
Small mountain stream draining the Flattops Wilderness Area, CO. Vegetation type: Spruce-Fir Forest (Picea, Abies). |
F1 Hydrophobic Acid (F1 HPOA) |
Eutrophied marshland located in Water Conservation Area 2A in the northern Everglades. Vegetation dominated by cattails (typha latifolia). |
2BS Hydrophobic Acid (2BS HPOA) |
Relatively pristine marshland located in Water Conservation Area 2B in the northern Everglades. Vegetation dominated by saw grass. |
Table 2. Chemical Characteristics of Isolated Samples |
|
ash-free elemental
composition (wt %) |
|
|
|
|
sample |
C |
H |
O |
N |
S |
relative
% Sred |
relative %
thiol+sulfide |
MW
(daltons) |
% aromatic C |
SRHA |
53.4 |
3.9 |
40.9 |
1.1 |
0.7 |
55 |
14 |
1399a |
35.1 |
SRFA |
54.2 |
3.9 |
38.0 |
0.7 |
0.4 |
48 |
12 |
1360b |
22.9 |
OGHA |
54.6 |
4.9 |
36.8 |
1.6 |
1.8 |
37 |
14 |
1906 |
40.8 |
OGFA |
54.0 |
4.0 |
38.5 |
0.9 |
1.3 |
44 |
18 |
1021 |
24.7 |
CCFA |
52.8 |
4.5 |
38.4 |
1.0 |
0.7 |
47 |
11 |
1180 |
28.0 |
F1 HPOA |
52.2 |
4.6 |
39.9 |
1.5 |
1.7 |
60 |
22 |
103a |
25.4 |
2BS HPOA |
52.3 |
4.8 |
40.2 |
1.6 |
1.2 |
51 |
23 |
953a |
21.3 |
a Ref 6. b Ref 23.
Table 3. Equilibrium Binding Constants Resulting from the Best Fit of the Model to the Experimental Data at Various pH Valuesa |
pKa1
10.3 ± 0.1 |
pKa2
6.3 ± 0.1 |
log KHgsite
28.7 ± 0.1 |
site concentration
5 x 10-9 mol mg-1 |
apKa1 and pKa2 are deprotonation constants for the two different functional groups of the bidentate Hg(II) binding site. log KHgsite is the equilibrium binding constant for the reaction of Hg2+ with the fully deprotonated binding site. Errors in binding constants were calculated as a variation in binding constant resulting in a 5% variation of the sum of fit errors. Note that errors reported here only relate to the fitting procedure. Overall errors for absolute binding constants are significantly higher (see ref 12).
Literature Cited
- Zillioux, E. J.; Porcella, D. B.; Benoit, J. M. Environ. Toxicol. Chem. 1993, 12, 2245-2264.
- Wolfe, M. F.; Schwarzbach, S.; Sulaiman, R. A. Environ. Toxicol. Chem. 1998, 17, 146-160.
- Watras, C. J.; Bloom, N. S.; Hudson, R. J. M.; Gherini, S. A.; Munson, R.; Claas, S. A.; Morrison, K. A.; Hurley, J. P.; Wiener, J. G.; Fitzgerald, W. F.; Mason, R. P.; Vandal, G.; Powell, D.; Rada, R. G.; Rislov, L.; Winfrey, M. R.; Elder, J.; Krabbenhoft, D. P.; Andren, A. W.; Babiarz, C. L.; Porcella, D. B. In Mercury pollution: integration and synthesis; Watras, C. J., Huckabee, J. W., Eds.; CRC Press: Boca Raton, FL, 1994; pp 153-185.
- Stordal, M. C.; Gill, G. A.; Wen, L.-S.; Santschi, P. H. Limnol. Oceanogr. 1996, 41, 52-61.
- Hurley, J. P.; Benoit, J. M.; Babiarz, C. L.; Shafer, M. M.; Andren, A. W.; Sullivan, J. R.; Hammond, R.; Webb, D. A. Environ. Sci. Technol. 1995, 29, 1867-1875.
- Ravichandran, M.; Aiken, G. R.; Reddy, M.M.; Ryan, J. N. Environ. Sci. Technol. 1998, 32, 3305-3311.
- Ravichandran, M.; Aiken, G. R.; Ryan, J. N.; Reddy, M.M. Environ. Sci. Technol. 1999, 33, 1418-1423.
- Mason, R. P.; Lawrence, A. L. Environ. Toxicol. Chem. 1999, 18, 2438-2447.
- Sjöblom, Å.; Meili, M.; Sundbohm, M. Sci. Total Environ. 2000, 261, 115-124.
- Miskimmin, B. M.; Rudd, J. W. M.; Kelly, C. A. Can. J. Fish. Aquat. Sci. 1992, 49, 17-22.
- Barkay, T.; Gillman, M.; Turner, R. R. Appl. Environ. Microbiol. 1997, 63, 4267-4271.
- Haitzer, M.; Aiken, G. R.; Ryan, J. N. Environ. Sci. Technol. 2002, 36, 3564-3570.
- Lövgren, L.; Sjöberg, S. Water Res. 1989, 23, 327-332.
- Lu, X.; Jaffe, R. Water Res. 2001, 35, 1793-1803.
- Xia, K.; Skyllberg, U. L.; Bleam, W. F.; Bloom, P. R.; Nater, E. A.; Helmke, P. A. Environ. Sci. Technol. 1999, 33, 257-261.
- Skyllberg, U. L.; Xia, K.; Bloom, P. R.; Nater, E. A.; Bleam, W. F. J. Environ. Qual. 2000, 29, 855-865.
- Hesterberg, D.; Chou, J. W.; Hutchinson, K. J.; Sayers, D. E. Environ. Sci. Technol. 2001, 35, 2741-2745.
- Drexel, T. R.; Haitzer, M.; Ryan, J. N.; Aiken, G. R.; Nagy, K. L. Environ. Sci. Technol. 2002, 36, 4058-4064.
- Aiken, G. R.; McKnight, D. M.; Thorn, K. A.; Thurman, E. M. Org. Geochem. 1992, 18, 567-573.
- Huffman, E. W. D.; Stuber, H. A. In Humic Substances in Soil Sediment and Water - Geochemistry, Isolation and Charakterisation; Aiken, G. R., Wershaw, D. M., MacCarthy, P., Eds.; John Wiley & Sons: New York, U.S.A., 1985; pp 433-456.
- Vairavamurthy, M. A.; Maletic, D.; Wang, S.; Manowitz, B.; Eglinton, D.; Lyons, T. Energy Fuels 1997, 11, 546-553.
- Wershaw, R. L. In Humic Substances in Soil Sediment and Water - Geochemistry, Isolation and Charakterisation; Aiken, G. R.; Wershaw, D. M.; MacCarthy, P., Eds.; John Wiley & Sons: New York, U.S.A., 1985; pp 561-582.
- Chin, Y.-P.; Aiken, G. R.; OLoughlin, E. Environ. Sci. Technol. 1994, 28, 1853-1858.
- Van Loon, L. R.; Granacher, S.; Harduf, H. Anal. Chim. Acta 1992, 268, 235-246.
- Glaus, M. A.; Hummel, W.; Van Loon, L. R. Environ. Sci. Technol. 1995, 29, 2150-2153.
- Glaus, M. A.; Hummel, W.; Van Loon, L. R. Anal. Chim. Acta 1995, 303, 321-331.
- Glaus, M. A.; Hummel, W.; Van Loon, L. R. Appl. Geochem. 2000, 15, 953-973.
- Anderegg, G. Critical survey of stability constants of EDTA complexes, IUPAC Chemical Data Series - No. 14; Pergamon Press: Oxford, UK, 1978.
- Westall, J. C.; Jones, J. D.; Turner, G. D.; Zachara, J. M. Environ. Sci. Technol. 1995, 29, 951-959.
- Amirbahman, A.; Reid, A. L.; Haines, T. A.; Kahl, J. S.; Arnold, C. Environ. Sci. Technol. 2002, 36, 690-695.
- McKnight, D. M.; Feder, G. L.; Thurman, E. M.; Wershaw, R. L.; Westall, J. C. Sci. Total Environ. 1983, 28, 65-76.
- Cotton, F. A.; Wilkinson, G. In Advanced Inorganic Chemistry; Cotton, F. A.; Wilkinson, G., Eds.; John Wiley & Sons: New York, U.S.A., 1980; pp 589-616.
- Pettit, L. D.; Powell, K. J. IUPAC Stability Constants Database, version 4.11; Academic Software: Yorks, U.K., 1999.
- Schwarzenbach, G.; Schellenberg, M. Helv. Chim. Acta 1965, 48, 28-46.
- Tipping, E. Aquat. Geochem. 1998, 4, 3-47.
- DiToro, D. M.; Allen, H. E.; Bergman, H. L.; Meyer, J. S.; Paquin, P. R.; Santore, R. C. Environ. Toxicol. Chem. 2001, 20, 2383-2396.
- Leonard, D.; Reash, R.; Porcella, D. B.; Paralkar, A.; Summers, K.; Gherini, S. A. Water, Air, Soil Pollut. 1995, 80, 519-528.
- Morel, F. M. M.; Kraepiel, A. M. L.; Amyot, M. Annu. Rev. Ecol. Syst. 1998, 29, 543-566.
- Thurman, E. M. In Organic geochemistry of natural waters; Thurman, E. M., Ed.; Martinus Nijhof/Dr. W. Junk Publishers: Dordrecht, The Netherlands, 1985; pp 273-361.
- Schecher, W. D.; McAvoy, D. C. MINEQL+ A chemical equilibrium modeling system: version 4.0 for Windows user's manual; Environmental Research Software: Hallowell, ME, 1998.
- Benoit, J. M.; Gilmour, C. C.; Mason, R. P.; Heyes, A. Environ. Sci. Technol. 1999, 33, 951-957.
* Corresponding author phone: (303)492-0772; fax: (413)702-4196;
e-mail: mhaitzer@usgs.gov.
University of Colorado.
U.S. Geological Survey.
Related information:
SOFIA Project: Interactions of Mercury with Dissolved Organic Carbon in the Florida Everglades
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