Determination of the contribution of humic substances to iron complexation in seawater by catalytic cathodic stripping voltammetry

Sukekava, Camila; Downes, Javier; Slagter, Hans A.; Gerringa, Loes J. A.; Laglera, Luis M.

doi:10.1016/j.talanta.2018.07.021

Cited by 35 publications

(84 citation statements)

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“…However, relative contributions by groups like humic substances (HS; Laglera & van den Berg, ) and exopolymeric substances (Hassler et al, ) may be considerable. We know from a previous study on one station in the Arctic Ocean, also described in this paper, that the Fe‐binding organic binding sites consist for 62% of HS (Sukekava et al, ).…”

Section: Introductionmentioning

confidence: 70%

“…of the averages are calculated for each property and increments divided by ∆[HS] for DFe and [L t ] per mg SRFA across the TPD border. A conversion to equivalent [L t ] HS has been added using the conversion factor of 14.6 nM/mg after Sukekava et al (). DFe = dissolved Fe; CLE‐AdCSV = Competitive Ligand Exchange Adsorptive Stripping Voltammetry; HS = humic substance; TPD = TransPolar Drift; FDOM = fluorescent DOM.…”

Section: Resultsmentioning

confidence: 99%

“…A subset of separately filled bottles stored frozen until analysis in the laboratories of the University of the Balearic Islands (UIB lab) was analyzed after the cruise with a voltammetric system identical to the system used onboard. In this case the original voltammetric method (Laglera et al, ) was slightly modified to ensure the saturation with iron of the HS binding groups of both the sample and the reference standard (Sukekava et al, ). In the presence of 20‐nM KBrO 3 and 5‐mM POPSO buffer (from a mixed solution cleaned with MnO 2 as in Laglera et al, ) the sample was saturated with iron (20–60 nM depending on the DFe concentration) and was continually measured until the voltammetric signal decreased to a constant value.…”

Section: Methodsmentioning

confidence: 99%

“…HS were therefore expressed as milligrams of SRFA per liter. The data sets for [HS] from both labs (on board and UIB lab) showed good correlation and could therefore safely be combined into one (Sukekava et al, ) and are from here on reported after conversion to [L t ] HS for most purposes. A complexing capacity of 14.6 ± 0.7 mg of SRFA per liter measured using the same batch of SRFA by Sukekava et al () was used to convert HS concentrations into HS derived ligand concentrations ([L t ] HS ).…”

Section: Methodsmentioning

confidence: 99%

“…The data sets for [HS] from both labs (on board and UIB lab) showed good correlation and could therefore safely be combined into one (Sukekava et al, ) and are from here on reported after conversion to [L t ] HS for most purposes. A complexing capacity of 14.6 ± 0.7 mg of SRFA per liter measured using the same batch of SRFA by Sukekava et al () was used to convert HS concentrations into HS derived ligand concentrations ([L t ] HS ). The complexing capacity was obtained by titration with iron of the SRFA standard dissolved in UV‐digested seawater as suggested by Laglera and van den Berg ().…”

Section: Methodsmentioning

confidence: 99%

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Fe‐Binding Organic Ligands in the Humic‐Rich TransPolar Drift in the Surface Arctic Ocean Using Multiple Voltammetric Methods

et al. 2019

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Samples inside and outside the Arctic Ocean's TransPolar Drift (TPD) have been analyzed for Fe‐binding organic ligands (Lt) with Competitive Ligand Exchange Adsorptive Stripping Voltammetry (CLE‐AdCSV) using salicylaldoxime (SA). This analysis is compared to prior analyses with CLE‐AdCSV using 2‐(2‐thiazolylazo)‐p‐cresol (TAC). The TPD's strong terrestrial influence is used to compare the performance of both CLE‐AdCSV methods in representing the nature of natural organic ligands. These measurements are compared against direct voltammetric determination of humic substances (HS) and spectral properties of dissolved organic matter. The relationship between the two CLE‐AdCSV derived [Lt] versus HS in the TPD has a comparable slope, with a 40% offset toward higher values obtained with SA. Higher [Lt] values inside the TPD, most probably due to HS, explain high dissolved Fe concentrations transported over the Arctic Ocean by the TPD. Outside of the TPD in the surface Arctic Ocean HS occur as well but at lower concentrations. Here changes in HS relate to changes in dissolved Fe concentration and to [Lt] obtained with SA, whereas [Lt] obtained with TAC remain constant. Moreover, with decreasing HS the offset between the methods using TAC and SA decreases. We surmise that in the presence of HS, the TAC method detects HS only either at higher concentrations or of specific composition. On the other hand, the SA method might overestimate [Lt], as an offset with the TAC method that remains constant where HS are not detected. Regardless, HS are the dominant type of Fe‐binding organic ligand in the surface of the Arctic Ocean.

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Section: Introductionmentioning

confidence: 70%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Fe‐Binding Organic Ligands in the Humic‐Rich TransPolar Drift in the Surface Arctic Ocean Using Multiple Voltammetric Methods

et al. 2019

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Electrochemical Characterization of Fe(II) Complexation Reactions at an Electrified Micro Liquid‐Liquid Interface

2021

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Dedicated to Prof. Marcin Opallo on the occasion of his 65th birthday!Phytoplankton growth in the open ocean is critical to carbon fixation and often limited by low iron concentrations. Owing to its low solubility, phytoplankton employ ligands for iron uptake; therefore, ligand binding characterization is important. Herein, a micro immiscible liquid/liquid interface was employed with four ligands through an electrochemically induced facilitated ion-transfer process. Ligands 1,10-phenathroline (phen), 1nitroso-2-naphthol (N2N), 2-(2-thiazolylazo)-p-cresol (TAC), and salicylaldoxime (SAL), where tested using established facilitated ion-transfer thermodynamics combined with differential pulse voltammetry. Three metal ion/ligand binding stoichiometries were observed for Fe 2 + :phen, whereas only one was observed with Fe 2 + with SAL, N2N, and TAC. Overall binding constants were calculated such that binding strengths can be ranked highest to lowest as phen > N2N > TAC > SAL. Additionally, the formal ion transfer for Fe 2 + (0.66 V) for an aqueous/1,2-dichloroethane interface was also determined.

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Coastal waters contamination by mining tailings: What triggers the stability of iron in the dissolved and soluble fractions?

Longhini

Mahieu

Sá

et al. 2020

Limnology & Oceanography

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The solubility of iron (Fe) in seawater is greatly enhanced by complexation with organic ligands, predominantly occurring as humic substances (HS) in coastal areas. Mining exploitation is believed to change the natural biogeochemical cycle of Fe in coastal waters, even though its impacts on the physical and chemical speciation of the Fe fractions are not known. Here we show that dissolved and soluble Fe concentrations in coastal waters affected by a mining catastrophe (Fundão dam, Southeast Brazil) remain very high, even almost 3 years later, with concentrations of dissolved Fe up to 2.8 μM (0.45 μm filtration) or 700 nM (0.22 μm filtration), and soluble Fe (0.02 μm) up to 40 nM. Levels of humic substances can only explain the binding of 2% and 10% (median values) of dissolved Fe (0.22 μm) and soluble Fe concentrations, respectively, which shows that processes other than complexation with humic substances are at play to maintain such high dissolved Fe concentrations. We hypothesize that the colloidal phase that dominates the dissolved Fe fraction occurs as Fe(III) oxyhydroxides while the soluble fraction is comprised of Fe(III) complexes with amine compounds (widely used in the ore extraction process). Mass balance of dissolved Fe in the water column suggests that sediment resuspension on the continental shelf is by far the dominant process delivering dissolved Fe to coastal and shelf waters. Estimates of dissolved Fe yearly fluxes highlight the sheer magnitude of this catastrophe that might provide a non-negligible amount of dissolved Fe to the open ocean.

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Determination of the contribution of humic substances to iron complexation in seawater by catalytic cathodic stripping voltammetry

Cited by 35 publications

References 21 publications

Fe‐Binding Organic Ligands in the Humic‐Rich TransPolar Drift in the Surface Arctic Ocean Using Multiple Voltammetric Methods

Fe‐Binding Organic Ligands in the Humic‐Rich TransPolar Drift in the Surface Arctic Ocean Using Multiple Voltammetric Methods

Electrochemical Characterization of Fe(II) Complexation Reactions at an Electrified Micro Liquid‐Liquid Interface

Coastal waters contamination by mining tailings: What triggers the stability of iron in the dissolved and soluble fractions?

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