Determination of Labile Fe(II) Species Complexed with Seawater Extractable Organic Matter Under Seawater Conditions Based on the Kinetics of Ligand-exchange Reactions with Ferrozine

Abstract

Barren ground is a phenomenon associated with the depletion of seaweed in coastal areas. The development of barren ground has been attributed to a lack of soluble Fe (<1 nM), 1 which is an essential micronutrient for the growth of algae. 2,3 In macroalgae, the uptake of soluble iron is required for the gametophyte to produce an oogonium or an antheridium, 4-7 and a sporophyte is formed from the matured gametophyte. 3 Thus, a lack of dissolved Fe in coastal area seawater can lead to seaweed depletion. It is known that natural organic matter plays an important role in the mobility, solubility and bioavailability of trace metals in terrestrial and aquatic environments. 2,[8][9][10][11][12] In seawater, the majority of dissolved ferric (Fe(III)) and ferrous (Fe(II)) species are present in the form of complexes with dissolved organic matter. 2,[13][14][15] Based on this, a fertilizer comprised of a steel slag and compost was tested for its ability to supply dissolved Fe to barren coastal areas, and this attempt was successful and resulted in the restoration of seaweed beds. 16 In this technique, seawater extractable organic matter (SWEOM) from the compost serves as a chelator of Fe and allows for its elution from the steel slag. 17,18 Fe(III)-oxides are found on the surface of the steel slag, 19 and can be reduced to soluble Fe(II) species in the presence of dissolved organic matter. 20 It has been reported that all of the reduced Fe(II) species are complexed with dissolved organic matter. 21 Therefore, the nature of the complex produced between SWEOM and Fe(II) need to be evaluated to better understand the performance of such fertilizers.On the other hand, estimating the bioavailability of a metal to aquatic biota is an important approach. 22,23 The kinetic stability of complexes is a key factor in determining the bioavailability of metal species. 2,3,22,24,25 Readily dissociable complexes (labile species) are the likely primary source of soluble iron for algae. 2,19,[26][27][28] A key factor in the uptake of Fe(II) involves ligand-exchange reactions between dissolved organic matter and receptor proteins on the cell-membrane. 2 The kinetics of ligand-exchange reactions of Fe(II)-humic acid complexes have been investigated using ortho-phenanthroline or ferrozine (FZ) as models of receptor proteins, 17,29 although the conditions (pH 3.6 or 5, I = 0.02) were far from those for seawater (pH 8, I = 0.7). To investigate the contribution of SWEOM as a chelator of Fe, it should be examined that the complexation ability under the conditions of seawater. However, it is difficult to determine both free and complex species of Fe(II) at higher pH and ionic strength levels because Fe(II) is readily oxidized to insoluble Fe(III)-hydroxides, which precipitates from the solution. 30 Indeed, pH and ionic strength both have a dramatic 2013 © The Japan Society for Analytical Chemistry † To whom correspondence should be addressed. Experimental MaterialsAmmonium iron(II) sulfate hexahydrate (Fe(SO4)2(NH4)2·6H2O), tris(hydroxymethyl)ami...

Roles of Microbial Activity and Anthraquinone-2,7-disulfonate as a Model of Humic Substances in Leaching of Iron from Hematite into Seawater

“…This result could be attributed to Fe(II) being immediately re-oxidized and converted to inactive ferrozine under oxic and weak alkaline conditions. 20 Although the dissolved iron concentration for S4 was negligible, the maximum concentration of dissolved iron for S5 (38 mg L -1 ) was 1.7-times larger than that for S3 (23 mg L -1 ) (Fig. 2).…”

“…The concentrations of a Fe(II) species in the media were colorimetrically determined with ferrozine as an indicator of Fe(II). 20,25 A 50-µL aliquot of 50 µM ferrozine was added to a 1-mL aliquot of media, which and then centrifuged and filtrated (0.45 µm). After 30 min of incubation, the concentration of Fe(II) species was determined from the concentration of Fe(II)-ferrozine complexes from their absorbance at 562 nm.…”

Evaluation of the Effect of Humic Acids on the Reductive Elution of Fe from Fe₂O₃ in a Saline, Seawater-like Medium

“…ASC is a suitable reducing agent under seawater conditions. 5) In our experimental condition, soluble Fe(II) species can be detected in the following equilibria:…”

“…Ascorbic acid can also perform a well-reducing agent in seawater condition. 5) In this study, to provide the simple evaluation process, we used ascorbic acid as a model of reducing agent. The capability of HA to participate in this process would largely depend on the chemical structures.…”

Changes in the Structural Features of Organic Matter Extracted from Compost by the Seawater during a 90-day Period under Anaerobic Conditions, and Its Effect on Oogenesis of Brown Macroalga

“…6 However, in these previous reports, the SWEOM fraction that had been extracted after an incubation period of only 3 days was investigated. 6,[10][11][12] Regarding developing an understanding of the role for compost in the fertilization of coastal water, the elution characteristics and structural alterations of SWEOM from compost during a longer extraction period under anaerobic seawater conditions should also be investigated.…”