The autoxidation of Fe(II) is known to produce a suite of reactive oxygen species, including superoxide, hydrogen peroxide and hydroxyl radical. Therefore, Fe(II) oxidation enables the concurrent oxidation of other materials through the intermediacy of reactive oxygen species. Here we report the production of reactive halogen species, particularly Br<sup>+</sup> and I<sup>+</sup> (as their hypohalites) as a consequence of the oxidation of Fe(II) at the surface of sediments. Fe(II) is generated biotically at sediment surfaces through its use as a terminal electron acceptor by facultative anaerobes and abiotically through its reaction with diagenetically-produced reductants such as hydrogen sulfide. Experiments in this study examined the relationship between the kinetics and yield of hypohalite formation in solution and heterogeneous suspensions of sediment as a function of the initial concentration of Fe(II), Fe(III), hydrogen sulfide and dissolved organic matter. Experiments followed both single-factor and multifactorial designs to explore the effects of single factors and interaction terms, such as the Fe(III)-hydrogen sulfide interaction. Hypohalite production and lifetimes were quantified by probes based on the oxidation of aniline, Celestine blue, and monochlorodimedone, followed by spectroscopy and mass spectrometry. Fe(II) and Fe(III) were quantified by Ferrozine in the presence or absence of added hydroxylamine. Hydrogen peroxide was quantified by the Amplex Red technique. Superoxide was quantified via chemiluminometric technique based on the luciferin assay. The production of 4-iodoaniline was observed and verified against a standard reference material and the iodination of Celestine blue was also observed. The net stoichiometry of the process indicated a yield of well under unity for incidental HOX production with respect to Fe(II) oxidation although it was higher in the presence of hydrogen sulfide, presumably because the rapid reduction of Fe(III) by hydrogen sulfide allowed Fe(II) to recycle quickly.

Generation of reactive halogen species from autoxidation of Fe(II) in seawater

254th National Meeting (2017)

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