Superoxide-mediated Fe(II) formation from organically complexed Fe(III) in coastal waters

Access & Terms of Use
metadata only access
Fe(III) complexed by organic ligands (Fe(III)L) is the primary form of dissolved Fe in marine and coastal environments. Superoxide, typically produced in biological and photochemical processes, is one of the reducing agents that contributes to transformation of Fe(III)L to bioavailable, free dissolved Fe(II) (Fe(II)`). In this work, the kinetics of superoxide-mediated Fe(Il)` formation from Fe(III)L in a simulated coastal water system were investigated and a comprehensive kinetic model was developed using citrate and fulvic acid as exemplar Fe-binding ligands. To simulate a coastal environment in laboratory experiments, Fe(III)L samples with various ligand/Fe ratios were incubated for 5 min to 1 week in seawater medium. At each ratio and incubation time, the rate Of superoxide-mediated Fe(II)` formation was determined in the presence of the strong Fe(II) binding ligand ferrozine by spectrophotometrically measuring the ferrous-ferrozine complex generated at a constant concentration of superoxide. The Fe(II)` formation rate generally decreased with incubation time, as Fe(III)L gradually dissociated to form less reactive Fe(III) oxyhydroxide. However, when the ligand/Fe ratio was sufficiently high, the dissociation of Fe(III)L (and subsequent Fe precipitation) was suppressed and Fe(II)` was formed at a higher rate. The rate of Fe(III)` produced during the experiment was explained by the kinetic model. The model confirmed that both the ligand/Fe ratio and incubation time have a significant effect on the pathway via which Fe(II)` is formed from Fe(III)-fulvic acid complexes. (c) 2008 Elsevier Ltd. All rights reserved.
Persistent link to this record
Link to Publisher Version
Link to Open Access Version
Additional Link
Fujii, Manabu
Ito, H
Rose, Andrew
Waite, T
Omura, T
Conference Proceedings Editor(s)
Other Contributor(s)
Corporate/Industry Contributor(s)
Publication Year
Resource Type
Journal Article
Degree Type
UNSW Faculty