Cadmium Isotope Fractionation during Complexation with Humic Acid

Cadmium (Cd) isotopes are known to fractionate during complexation with various environmentally relevant surfaces and ligands. Our results, which were obtained using (i) batch experiments at different Cd concentrations, ionic strengths, and pH values, (ii) modeling, and (iii) infrared and X-ray abso...

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Bibliographic Details
Published in:Environmental science & technology 2021-06, Vol.55 (11), p.7430-7444
Main Authors: Ratié, Gildas, Chrastný, Vladislav, Guinoiseau, Damien, Marsac, Rémi, Vaňková, Zuzana, Komárek, Michael
Format: Article
Language:English
Subjects:
Cadmium
Cadmium isotopes
Chemical analysis
Complexation
Contaminants in Aquatic and Terrestrial Environments
Coordination compounds
Earth Sciences
Fingerprinting
Fractionation
Geochemistry
Humic acids
Isotope fractionation
Isotopes
Ligands
Organic matter
Phytoplankton
Plankton
Sciences of the Universe
Seawater
Soil solution
Water analysis
X ray absorption
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Summary:Cadmium (Cd) isotopes are known to fractionate during complexation with various environmentally relevant surfaces and ligands. Our results, which were obtained using (i) batch experiments at different Cd concentrations, ionic strengths, and pH values, (ii) modeling, and (iii) infrared and X-ray absorption spectroscopies, highlight the preferential enrichment of light Cd isotopes bound to humic acid (HA), leaving the heavier Cd pool preferentially in solution (Δ114/110CdHA–Cd(aq) of −0.15 ± 0.01‰). At high ionic strengths, Cd isotope fractionation mainly depends on its complexation with carboxylic sites. Outer-sphere complexation occurs at equilibrium together with inner-sphere complexation as well as with the change of the first Cd coordination and its hydration complexes in solution. At low ionic strengths, nonspecific Cd binding induced by electrostatic attractions plays a dominant role and promotes Cd isotope fractionation during complexation. This significant outcome elucidates the mechanisms involved in HA–Cd interactions. The results can be used during (i) fingerprinting the available Cd in soil solution after its complexation with solid or soluble natural organic matter and (ii) evaluating the contribution of Cd complexation with organic ligands and phytoplankton-derived debris versus Cd assimilation by phytoplankton in seawater.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.1c00646