Interactions of hydrophobic metal complexes and their constituents with aquatic humic substances

Amiel Boullemant; Jean-Pierre Gagné; Claude Fortin; Peter G. C. Campbell

doi:10.1071/EN07046

RESEARCH ARTICLE

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Interactions of hydrophobic metal complexes and their constituents with aquatic humic substances

Amiel Boullemant ^A ^B , Jean-Pierre Gagné ^C , Claude Fortin ^A and Peter G. C. Campbell ^A ^D

+ Author Affiliations

- Author Affiliations

^A INRS-Eau, Terre et Environnement, Université du Québec, 490 de la Couronne, Québec, QC, G1K 9A9, Canada.

^B Present address: Alcan Research and Development Centre, Jonquière, QC, G7S 4K8, Canada.

^C Institut des Sciences de la Mer, 310 allée des Ursulines, Rimouski, QC, G5L 3A1, Canada.

^D Corresponding author. Email: campbell@ete.inrs.ca

Environmental Chemistry 4(5) 323-333 https://doi.org/10.1071/EN07046
Submitted: 4 July 2007 Accepted: 1 October 2007 Published: 2 November 2007

Environmental context. Lipophilic metal complexes, because they can readily cross biological membranes, are especially bioavailable. However, in natural waters these complexes do not necessarily exist in a free state, i.e. they may bind to the organic matter (humic substances) that is present in natural waters. It follows that the in situ bioavailability of lipophilic metal complexes will tend to be less than that measured in simple laboratory experiments.

Abstract. The ability of dissolved humic substances (HS: fulvic and humic acids) to complex cationic metals is well known, but their interactions with neutral lipophilic metal complexes are little understood. In the present study, we have examined the behaviour of two such complexes (Cd L⁰₂: L = DDC = diethyldithiocarbamate, or L = XANT = ethylxanthate) in the presence of Suwannee River Humic and Fulvic acids. Interactions between the neutral complexes and the humic substances were assessed by excitation-emission matrix (EEM) fluorescence spectroscopy at pH 5.5 and 7.0, and by equilibrium dialysis experiments (500 Da cut-off). The EEM measurements were carried out by titrating the humic substances (6.5 mg C L^–1) with Cd, in the absence or presence of ligand L (1 µM DDC or 100 µM XANT). Given the very high stability constants for the complexation of cadmium by DDC and XANT and the excess ligand concentration, virtually all (>96%) of the Cd added to the L + HS matrix was calculated to be present as the neutral CdL²₀ complex over the entire pH range tested. For both humic substances, addition of DDC or XANT alone led to shifts in the fluorescence spectra at both pH values, indicating that the DDC^– and XANT^– anions likely interact by electrostatic or hydrogen bonding within the humic molecules. The subsequent addition of Cd to these L + HS systems resulted in a disproportionately large enhancement of the fluorescence intensities of individual EEM peaks, this fluorescence enhancement being only slightly decreased by the shift from pH 7.0 to 5.5. We interpret this enhancement as evidence that the two neutral complexes associate with the humic substances, presumably by forming ternary complexes (L_n-Cd-HS). Hydrophobic interactions between the humic substances and the neutral complexes may also contribute, but to a lesser extent, as demonstrated by partitioning calculations based on the lipophilicity of the neutral complexes. The association of the neutral complexes with Suwannee River Humic Acid was confirmed by dialysis experiments.

Additional keywords: Cd, equilibrium dialysis, fluorescence, lipophilic metal complexes, ternary complexes.

Acknowledgements

The present work was supported by grants from the Canadian Network of Toxicology Centres (Environment Canada) and from the Natural Sciences and Engineering Research Council of Canada (NSERC). Rob Cook (Louisiana State University) and Scott Smith (Wilfrid Laurier University) read draft versions of the manuscript and provided useful insights into the fluorescence behaviour of humic substances. The constructive comments from three anonymous referees are gratefully acknowledged. P. G. C. Campbell is supported by the Canada Research Chair Program.

References

[1] S. Niyogi , C. M. Wood , Biotic ligand model, a flexible tool for developing site-specific water quality guidelines for metals. Environ. Sci. Technol. 2004 , 38, 6177.
        | Crossref | GoogleScholarGoogle Scholar | PubMed |

[2] J. W. Gorsuch , C. R. Janssen , C. M. Lee , M. C. Reiley , Special issue: the biotic ligand model for metals – current research, future directions, regulatory implications. Comp. Biochem. Physiol. 2002 , 133C, 1.


[3] V. I. Slaveykova , K. J. Wilkinson , Predicting the bioavailability of metals and metal complexes: critical review of the biotic ligand model. Environ. Chem. 2005 , 2, 9.
        | Crossref | GoogleScholarGoogle Scholar |

[4] J. T. Phinney , K. W. Bruland , Uptake of lipophilic organic Cu, Cd and Pb complexes in the coastal diatom, Thalassiosira weissflogii. Environ. Sci. Technol. 1994 , 28, 1781.
        | Crossref | GoogleScholarGoogle Scholar |

[5] Handy R. D., Eddy F. B., in Physicochemical Kinetics and Transport at Biointerfaces (Eds H. P. van Leeuwen, W. Köster) 2004, Vol. 9, Ch. 7, pp. 337–356 (Wiley: Chichester, UK).

[6] Köster W., in Physicochemical Kinetics and Transport at Biointerfaces (Eds H. P. van Leeuwen, W. Köster) 2004, Vol. 9, Ch. 6, pp. 271–335 (Wiley: Chichester, UK).

[7] M. Haitzer , S. Höss , W. Traunspurger , C. Steinberg , Effects of dissolved organic matter (DOM) on the bioconcentration of organic chemicals in aquatic organisms – a review. Chemosphere 1998 , 37, 1335.
        | Crossref | GoogleScholarGoogle Scholar | PubMed |

[8] P. G. C. Campbell , M. R. Twiss , K. J. Wilkinson , Accumulation of natural organic matter on the surfaces of living cells: implications for the interaction of toxic solutes with aquatic biota. Can. J. Fish. Aquat. Sci. 1997 , 54, 2543.
        | Crossref | GoogleScholarGoogle Scholar |

[9] B. Vigneault , A. Percot , M. Lafleur , P. G. C. Campbell , Permeability changes in model and phytoplankton membranes in the presence of aquatic humic substances. Environ. Sci. Technol. 2000 , 34, 3907.
        | Crossref | GoogleScholarGoogle Scholar |

[10] A. Boullemant , B. Vigneault , C. Fortin , P. G. C. Campbell , Uptake of neutral metal complexes by a green alga: influence of pH and humic substances. Aust. J. Chem. 2004 , 57, 931.
        | Crossref | GoogleScholarGoogle Scholar |

[11] H. K. J. Powell , R. M. Town , Interaction of humic substances with hydrophobic metal complexes: a study by anodic stripping voltammetry and spectrophotometry. Anal. Chim. Acta 1991 , 248, 95.
        | Crossref | GoogleScholarGoogle Scholar |

[12] R. R. Scharfe , V. S. Sastri , C. L. Chakrabarti , Stability of metal dithiocarbamate complexes. Anal. Chem. 1973 , 45, 413.
        | Crossref | GoogleScholarGoogle Scholar |

[13] E. Bardez , I. Devol , B. Larrey , B. Valeur , Excited-state processes in 8-hydroxyquinoline: photoinduced tautomerization and solvation effects. J. Phys. Chem. B 1997 , 101, 7786.
        | Crossref | GoogleScholarGoogle Scholar |

[14] H. M. V. M. Soares , P. C. F. L. Conde , A. A. N. Almeida , M. T. S. D. Vasconcelos , Evaluation of N-substituted aminosulfonic acid pH buffers with a morpholinic ring for cadmium and lead speciation studies by electroanalytical techniques. Anal. Chim. Acta 1999 , 394, 325.
        | Crossref | GoogleScholarGoogle Scholar |

[15] H. M. V. M. Soares , P. C. F. L. Conde , Electrochemical investigations of the effect of N-substituted aminosulfonic acids with a piperazinic ring pH buffers on heavy metal processes which may have implications on speciation studies. Anal. Chim. Acta 2000 , 421, 103.
        | Crossref | GoogleScholarGoogle Scholar |

[16] A. Finizio , M. Vighi , D. Sandroni , Determination of n-octanol/water partition coefficient (K_ow) of pesticide. Critical review and comparison of methods. Chemosphere 1997 , 34, 131.
        | Crossref | GoogleScholarGoogle Scholar |

[17] A. Paschke , P. L. Neitzel , W. Walther , G. Schüürmann , Octanol/water partition coefficient of selected herbicides: determination using shake-flask method and reverse-phase high-performance liquid chromatography. J. Chem. Eng. Data 2004 , 49, 1639.
        | Crossref | GoogleScholarGoogle Scholar |

[18] C. A. Stedmon , S. Markager , R. Bro , Tracing dissolved organic matter in aquatic environments using a new approach to fluorescence spectroscopy. Mar. Chem. 2003 , 82, 239.
        | Crossref | GoogleScholarGoogle Scholar |

[19] J. S. Tucker , V. L. Amszi , W. E. Acree , Primary and secondary inner filtering. J. Chem. Educ. 1992 , 69, A8.


[20] U. Zimmermann , T. Skrivanek , H.-G. Löhmannsröben , Fluorescence quenching of polycyclic aromatic compounds by humic substances. Part 1. Methodology for the determination of sorption coefficients. J. Environ. Monit. 1999 , 1, 525.
        | Crossref | GoogleScholarGoogle Scholar | PubMed |

[21] D. M. McKnight , E. W. Boyer , P. K. Westerhoff , P. T. Doran , T. Kulbe , D. T. Andersen , Spectrofluorometric characterization of dissolved organic matter for indication of precursor organic material and aromaticity. Limnol. Oceanogr. 2001 , 46, 38.


[22] MINEQL+: A Chemical Equilibrium Modeling System 2001 (Environmental Research Software: Hallowell, ME, USA).

[23] NIST Critically Selected Stability Constants of Metal Complexes v. 8.0 2004 (National Institute of Standards and Technology: Gaithersburg, MD, USA).

[24] E. Tipping , Humic ion-binding model VI: an improved description of the interactions of protons and metal ions with humic substances. Aquat. Geochem. 1998 , 4, 3.
        | Crossref | GoogleScholarGoogle Scholar |

[25] R. G. Zepp , W. M. Sheldon , M. A. Moran , Dissolved organic fluorophores in South-eastern US coastal waters: correction method for eliminating Rayleigh and Raman scattering peaks in excitation-emission matrices. Mar. Chem. 2004 , 89, 15.
        | Crossref | GoogleScholarGoogle Scholar |

[26] J. J. Alberts , M. Takacs , Comparison of the natural fluorescence distribution among size fractions of terrestrial fulvic and humic acids and aquatic natural organic matter. Org. Geochem. 2004 , 35, 1141.
        | Crossref | GoogleScholarGoogle Scholar |

[27] N. Patel-Sorrentino , S. Mounier , J. Y. Benaim , Excitation-emission fluorescence matrix to study pH influence on organic matter fluorescence in the Amazon Basin rivers. Water Res. 2002 , 36, 2571.
        | Crossref | GoogleScholarGoogle Scholar | PubMed |

[28] M. J. Pullin , S. E. Cabaniss , Rank analysis of the pH-dependent synchronous fluorescence spectra of six standard humic substances. Environ. Sci. Technol. 1995 , 29, 1460.
        | Crossref | GoogleScholarGoogle Scholar |

[29] M. M. Sierra , M. Giovanela , E. Parlanti , E. J. Soriano-Sierra , Fluorescence fingerprint of fulvic and humic acids from varied origins as viewed by single-scan and excitation/emission matrix techniques. Chemosphere 2005 , 58, 715.
        | Crossref | GoogleScholarGoogle Scholar | PubMed |

[30] S. E. Cabaniss , Synchronous fluorescence spectra of metal–fulvic acid complexes. Environ. Sci. Technol. 1992 , 26, 1133.
        | Crossref | GoogleScholarGoogle Scholar |

[31] R. M. Cory , D. M. McKnight , Fluorescence spectroscopy reveals ubiquitous presence of oxidized and reduced quinones in dissolved organic matter. Environ. Sci. Technol. 2005 , 39, 8142.
        | Crossref | GoogleScholarGoogle Scholar | PubMed |

[32] K. M. Elkins , D. J. Nelson , Spectroscopic approaches to the study of the interaction of aluminum with humic substances. Coord. Chem. Rev. 2002 , 228, 205.
        | Crossref | GoogleScholarGoogle Scholar |

[33] E. M. Larrivee , K. M. Elkins , S. E. Andrews , D. J. Nelson , Fluorescence characterization of the interaction of Al³⁺ and Pd²⁺ with Suwannee River Fulvic Acid in the absence and presence of the herbicide 2,4-dichlorophenoxyacetic acid. J. Inorg. Biochem. 2003 , 97, 32.
        | Crossref | GoogleScholarGoogle Scholar | PubMed |

[34] Cook R. L., Langford C. H., in Understanding Humic Substances: Advanced Methods, Properties and Applications (Eds E. A. Ghabbour, G. Davies) 1999, pp. 31–48 (Royal Society of Chemistry: Cambridge, UK).

[35] M. Schilling , W. T. Cooper , Identification of copper binding sites in soil organic matter through chemical modifications and (CP)-C-13-MAS NMR Spectroscopy. Environ. Sci. Technol. 2004 , 38, 5059.
        | Crossref | GoogleScholarGoogle Scholar | PubMed |

[36] C. Plaza , G. Brunetti , N. Senesi , A. Polo , Molecular and quantitative analysis of metal ion binding to humic acids from sewage sludge and sludge-amended soils by fluorescence spectroscopy. Environ. Sci. Technol. 2006 , 40, 917.
        | Crossref | GoogleScholarGoogle Scholar | PubMed |

[37] M. Grassi , V. Daquino , Cd-113 NMR and fluorescence studies of multiple binding mechanisms of Cd(II) by the Suwannee River Fulvic Acid. Ann. Chim. Rome 2005 , 95, 579.
        | Crossref | GoogleScholarGoogle Scholar |

[38] J. R. Lead , K. J. Wilkinson , E. Balnois , B. J. Cutak , C. K. Larive , S. Assemi , R. Beckett , Diffusion coefficients and polydispersities of the Suwannee River Fulvic Acid: comparison of fluorescence correlation spectroscopy, pulsed-field gradient nuclear magnetic resonance, and flow field-flow fractionation. Environ. Sci. Technol. 2000 , 34, 3508.
        | Crossref | GoogleScholarGoogle Scholar |

[39] Stevenson F. J., Humus Chemistry. Genesis, Composition, Reactions 1994 (Wiley: New York).

[40] M. L. Pacheco , E. M. Peña-Méndez , J. Havel , Supramolecular interactions of humic acids with organic and inorganic xenobiotics studied by capillary electrophoresis. Chemosphere 2003 , 51, 95.
        | Crossref | GoogleScholarGoogle Scholar | PubMed |

[41] E. M. Perdue , J. D. Ritchie , Dissolved organic matter in freshwaters. Treatise on Geochemistry 2003 , 5, 273.


[42] Schwarzenbach R. P., Gschwend P. M., Imboden D. M., Environmental Organic Chemistry 1993 (Wiley: New York).

[43] J. T. Phinney , K. W. Bruland , Effects of dithiocarbamate and 8-hydroxyquinoline additions on algal uptake of ambient copper and nickel in south San Francisco Bay water. Estuaries 1997 , 20, 66.
        | Crossref | GoogleScholarGoogle Scholar |

[44] P. L. Croot , B. Karlson , J. T. Elteren , J. J. Kroon , Uptake of ⁶⁴Cu–oxine by marine phytoplankton. Environ. Sci. Technol. 1999 , 33, 3615.
        | Crossref | GoogleScholarGoogle Scholar |

[45] A. Turner , I. Williamson , Octanol–water partitioning of chemical constituents in river water and treated sewage effluent. Water Res. 2005 , 39, 4325.
        | Crossref | GoogleScholarGoogle Scholar | PubMed |

[46] S. M. Macfie , Y. Tarmohamed , P. M. Welbourn , Effects of cadmium, cobalt, copper, and nickel on growth of the green alga Chlamydomonas reinhardtii: the influences of the cell wall and pH. Arch. Environ. Contam. Toxicol. 1994 , 27, 454.
        | Crossref | GoogleScholarGoogle Scholar |

[47] J. Labuda , M. Skatulokova , M. Nmeth , S. Gergely , Formation and stability of diethyldithiocarbamate complexes. Chem. Zvesti 1984 , 38, 597.


[48] M. Block , Distribution of cadmium in an octanol–water system in the presence of xanthates and diethyldithiocarbamate. Environ. Toxicol. Chem. 1991 , 10, 1267.
        | Crossref | GoogleScholarGoogle Scholar |