Mechanism of Superoxide-Mediated Fe(II) Production from Organically Complexed Fe(III) in Coastal Seawater: Kinetic Model of Fe(II) Production Developed Using Fe(III)-Citrate Complex

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  • FUJII Manabu
    Department of Civil and Environmental Engineering, Graduate School of Engineering, Tohoku University
  • FUCHIGAMI Yosuke
    Department of Civil and Environmental Engineering, Graduate School of Engineering, Tohoku University
  • ITO Hiroaki
    Department of Civil and Environmental Engineering, Graduate School of Engineering, Tohoku University
  • WAITE T. David
    School of Civil and Environmental Engineering, The University of New South Wales
  • OMURA Tatsuo
    Department of Civil and Environmental Engineering, Graduate School of Engineering, Tohoku University

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Other Title
  • 沿岸域でのスーパーオキシドを介した有機鉄からのＦｅ（ＩＩ）生成機構―クエン酸鉄錯体を用いて構築したＦｅ（ＩＩ）生成速度論モデル―
  • 沿岸域でのスーパーオキシドを介した有機鉄からのFe(2)生成機構--クエン酸鉄錯体を用いて構築したFe(2)生成速度論モデル
  • エンガンイキ デノ スーパーオキシド オ カイシタ ユウキテツ カラノ Fe 2 セイセイ キコウ クエンサン テツ サクタイ オ モチイテ コウチクシタ Fe 2 セイセイ ソクド ロン モデル

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Abstract

Superoxide radical produced during algal metabolism is one of the most important agents that contribute to the transformation of the Fe(III)-organic ligand complex to more bioavailable Fe(II). In this work, we investigated the kinetics of superoxide-mediated Fe(II) production from Fe(III) complexed by citrate (Fe(III)Cit) in coastal seawater on the basis of a laboratory experiment and a kinetic model. To simulate a coastal environment, Fe(III)Cit samples with various ratios of citrate concentration to iron concentration (ligand/Fe ratio) were incubated for five minutes to one week in seawater medium. Then, Fe(II) production rate was spectrophotometrically measured by detecting the ferrous-ferrozine complex. During the measurement, superoxide was constantly generated by oxidizing xanthine. Fe(II) production rate generally decreased with incubation time, since Fe(III)Cit as a source of Fe(II) gradually dissociated to form less reactive iron oxyhydroxide in coastal seawater. However, when the ligand/Fe ratio was sufficiently high, the dissociation of Fe(III)Cit was suppressed and Fe(II) was formed at a relatively higher rate over one week. These results demonstrated that Fe(II) production rate is largely influenced by ligand/Fe ratio and incubation time. The kinetic model developed was in good agreement with the experimentally determined Fe(II) production rates.

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