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| Titel |
The effect of Dunaliella tertiolecta organic exudates on the Fe(II) oxidation kinetic in seawater |
| VerfasserIn |
Aridane G. Gonzalez, J. Magdalena Santana-Casiano, Melchor González-Dávila, Norma Pérez |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250052146
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| Zusammenfassung |
| The Fe(II) oxidation was studied in seawater and in seawater enriched with organic exudates
collected from Dunaliella tertiolecta, in order to demonstrate the role of the group of ligands
excreted by this type of phytoplankton on the Fe(II) oxidation rate. The Fe(II) oxidation
kinetic was studied as a function of cell density (1•107-5.04•108 cell/L), pH (7.2-8.2),
temperature (5-35ºC) and salinity (10-36.72). The effect of the exudates on the apparent
Fe(II) rate constant was computed as a function of all the parameters studied, in order to
quantify the contribution of the organic ligands excreted by Dunaliella tertiolecta to the
Fe(II) oxidation rate in seawater. A kinetic modelling approach was carried out in order to
describe the Fe(II) speciation and the contribution of each Fe(II) species to the overall rate
constant. This model considered the presence of two types of ligands, carboxyl and
amino/phosphoryl groups.
The Fe(II) oxidation rate constant described a lineal dependence with the cell
concentrations, suggesting that the type of ligands capable to complex Fe(II) in seawater
either are the same or have a similar properties to bind Fe(II). The pH, temperature and
salinity dependence was function of the cell concentration in the culture, where the
exudates were extracted and the Fe(II) rate was always retarded respect to the seawater
control (with f/2 nutrients). All parameters studied in this work where fitted to a
polynomial function in order to compute the log kapp in the presence of organic
exudates of Dunaliella tertiolecta in seawater as a function of pH, temperature and
salinity.
The kinetic modelling approach described the presence of ligands, both carboxyl-like
groups and phosphoryl- amino-like groups in the Fe(II) speciation and on the contribution to
the overall rate constant. The equilibrium constants were accounted to KFe(II)-LH=
9•108-1•109 and KFe(II)-L= 9•106-1.5•107, for carboxyl- and phosphory/amine-like
groups, respectively. The Fe(II)-organic ligands rate constant were estimated as
kFe(II)-LH = 68±9 M-1min-1 (carboxyl) and kFe(II)-L = 54±6 M-1min-1
(phosphoryl/amine). The model explains the role played by the Fe(II)-organic complexes,
as Fe(II)-LH (carboxyl-like) or Fe(II)-L (phosphoryl or amino-like) in the Fe(II)
speciation in natural waters. The individual contributions to the overall Fe(II) rate
constant demonstrated that Fe(II)-LH (carboxyl-like complexes) controlled the Fe(II)
oxidation process at low pH, even at low ligand concentrations, and it must be
considered in kinetic studies of Fe(II) in natural waters due to its key role in the Fe(II)
oxidation.
The results presented in this work can be applied to other natural and artificial
media where ligand exudates behave as those excreted by Dunaliella tertiolecta. |
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