Formation, Aggregation, and Deposition Dynamics of NOM-Iron Colloids at Anoxic–Oxic Interfaces

Liao, Peng; Li, Wenlu; Jiang, Yi; Wu, Jiewei; Yuan, Songhu; Fortner, John D.; Giammar, Daniel E.

doi:10.1021/acs.est.7b02356

Cited by 112 publications

(129 citation statements)

References 91 publications

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“…Similar differences between Ca 2þ and Mg 2þ have also been reported, e.g. for the aggregation of humic acid-Fe colloids and citrate-coated gold nanoparticles (Liao et al 2017;Liu et al 2013). Considering the levels of total calcium and magnesium in soil solution amount up to ,5 mM and ,1 mM , respectively, higher magnesium to calcium ratios are expected to result in an enhanced dispersion and thus in an increased mobility of NOM.…”

Section: Environmental Implicationsupporting

confidence: 75%

Magnesium binding by terrestrial humic acids

Christl¹

2018

Environ. Chem.

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Environmental contextThe behaviour of magnesium, which is an essential element for all living organisms, in terrestrial environments is influenced by natural organic matter. This study shows that magnesium binding by terrestrial humic acids exhibits a pronounced ionic strength-dependence indicating a strong preference for electrostatic binding to humic acids. This interaction is expected to influence the mobility of humic substances and their associated trace elements. AbstractMagnesium binding by three terrestrial humic acids was investigated at pH 8 and 25 °C as a function of Mg2+ activity and ionic strength using NaCl as the background electrolyte. The Mg2+ activity in solution was directly measured with an Mg2+-selective electrode in the titration experiments. In addition, coagulation experiments using Ca2+ and Mg2+ as the coagulants were carried out at pH 8. For the titration data, the NICA–Donnan model was used to quantitatively describe Mg2+ binding to the humic acids considering electrostatic and specific Mg2+ binding. Mg2+ binding to humic acids was found to be strongly affected by ionic strength variations indicating that Mg2+ binding largely arose from electrostatic (nonspecific) interactions with negatively charged functional groups of the humic acids. Data modelling suggested that the relative contribution of specific binding increased with decreasing Mg2+ activity and was related to functional groups with low proton affinities. For all three humic acids studied, the fitted Mg2+ affinity constants for specific binding were lower than the respective Ca2+ affinities. Corresponding to the observed differences in cation binding and the known differences in ion hydration, Ca2+ was observed to be the stronger coagulant as compared with Mg2+. The results suggest that Mg2+ may influence the mobility of trace elements that are strongly bound to humic acids such as mercury, although Mg2+ is not expected to directly compete with strongly sorbing elements for specific binding.

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Section: Environmental Implicationsupporting

confidence: 75%

Magnesium binding by terrestrial humic acids

Christl¹

2018

Environ. Chem.

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“…This is interesting because strain SW2 was proposed to oxidize Fe(II) intracellularly with a putative iron oxidase FoxE embedded in the periplasm of the cell (43,45). The observed oxidation of large Fe(II)-OM complexes, such as the Fe(II)-PPHA and Fe(II)-SRFA complexes, which were determined to be in the colloidal size range (46), suggests that strain SW2 may also be able to oxidize Fe(II) extracellularly, similar to many other bacteria with enzymatic Fe(II) oxidation pathways (47), since the large Fe(II)-PPHA and Fe(II)-SRFA complexes may not be easily transported into the periplasm.…”

Section: Discussionmentioning

confidence: 93%

Cryptic Cycling of Complexes Containing Fe(III) and Organic Matter by Phototrophic Fe(II)-Oxidizing Bacteria

Peng

Bryce

Sundman

et al. 2019

Appl Environ Microbiol

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Fe-organic matter (Fe-OM) complexes are abundant in the environment and, due to their mobility, reactivity, and bioavailability, play a significant role in the biogeochemical Fe cycle. In photic zones of aquatic environments, Fe-OM complexes can potentially be reduced and oxidized, and thus cycled, by light-dependent processes, including abiotic photoreduction of Fe(III)-OM complexes and microbial oxidation of Fe(II)-OM complexes, by anoxygenic phototrophic bacteria. This could lead to a cryptic iron cycle in which continuous oxidation and rereduction of Fe could result in a low and steady-state Fe(II) concentration despite rapid Fe turnover. However, the coupling of these processes has never been demonstrated experimentally. In this study, we grew a model anoxygenic phototrophic Fe(II) oxidizer,Rhodobacter ferrooxidansSW2, with either citrate, Fe(II)-citrate, or Fe(III)-citrate. We found that strain SW2 was capable of reoxidizing Fe(II)-citrate produced by photochemical reduction of Fe(III)-citrate, which kept the dissolved Fe(II)-citrate concentration at low (<10 μM) and stable concentrations, with a concomitant increase in cell numbers. Cell suspension incubations with strain SW2 showed that it can also oxidize Fe(II)-EDTA, Fe(II)-humic acid, and Fe(II)-fulvic acid complexes. This work demonstrates the potential for active cryptic Fe cycling in the photic zone of anoxic aquatic environments, despite low measurable Fe(II) concentrations which are controlled by the rate of microbial Fe(II) oxidation and the identity of the Fe-OM complexes.IMPORTANCEIron cycling, including reduction of Fe(III) and oxidation of Fe(II), involves the formation, transformation, and dissolution of minerals and dissolved iron-organic matter compounds. It has been shown previously that Fe can be cycled so rapidly that no measurable changes in Fe(II) and Fe(III) concentrations occur, leading to a so-called cryptic cycle. Cryptic Fe cycles have been shown to be driven either abiotically by a combination of photochemical reduction of Fe(III)-OM complexes and reoxidation of Fe(II) by O2, or microbially by a combination of Fe(III)-reducing and Fe(II)-oxidizing bacteria. Our study demonstrates a new type of light-driven cryptic Fe cycle that is relevant for the photic zone of aquatic habitats involving abiotic photochemical reduction of Fe(III)-OM complexes and microbial phototrophic Fe(II) oxidation. This new type of cryptic Fe cycle has important implications for biogeochemical cycling of iron, carbon, nutrients, and heavy metals and can also influence the composition and activity of microbial communities.

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“…These trends are facilitated by ubiquitous interactions with organic matter that serve as a bridge between mineral particles and produce thin coatings on mineral surfaces in both the dissolved and particulate phases (Baas Becking et al 1960;Hunter and Liss 1979;Filella et al 1993;Turner 1995;Buffle et al 1998;Mosley et al 2003;Doucet et al 2007;Filella 2007;Aiken et al 2011;Philippe and Schaumann 2014;Peijnenburg et al 2015;Louie et al 2016). These "macromolecular coronas" are especially prevalent at anoxicoxic interfaces, and they can help to stabilize dissolved Fe oxyhydroxide nanoparticles in the water column by producing a uniformly negative charge on particle surfaces (Lynch et al 2014;Liao et al 2017). These coatings may also induce sedimentation by creating aggregates or may create larger mixed organic-inorganic particles that fall into the particulate phase (i.e., >0.45 m).…”

Section: Colloids and Colloidal Systemsmentioning

confidence: 99%

Geochemical and biological controls on the ecological relevance of total, dissolved, and colloidal forms of trace elements in large boreal rivers: review and case studies

et al. 2020

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The concentrations of trace elements (TEs) in large boreal rivers can fluctuate markedly due to changing water levels and flow rates associated with spring melt and variable contributions from tributaries and groundwaters, themselves having different compositions. These fluctuating and frequently high concentrations create regulatory challenges for protecting aquatic life. For example, water quality criteria do not account for changes in flow regimes that can result in TE levels that may exceed regulatory limits, and neither do they account for the markedly different lability and bioaccessibility of suspended solids. This review addresses the geochemical and biological processes that govern the lability and bioaccessibility of TEs in boreal rivers, with an emphasis on the challenges posed by the colloidal behaviour of many TEs, and their relationship to the dissolved fraction (i.e., <0.45 μm in size). After reviewing the processes and dynamics that give rise to the forms and behaviour of TEs in large boreal rivers, their relevance for aquatic organisms and the associated relationships between size and lability and bioaccessibility are discussed. The importance of biological variables and different forms of TEs for limiting lability and bioaccessibility are also addressed. Two case studies emphasize seasonal fluctuations and accompanying changes in the distribution of TE amongst different size fractions and associated colloidal species in large boreal rivers: the Northern Dvina and one of its tributaries, the Pinega River, both in Russia, and the Athabasca River in Alberta, Canada. Water quality in the Athabasca River is briefly discussed with respect to Canadian guidelines.

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Formation, Aggregation, and Deposition Dynamics of NOM-Iron Colloids at Anoxic–Oxic Interfaces

Cited by 112 publications

References 91 publications

Magnesium binding by terrestrial humic acids

Magnesium binding by terrestrial humic acids

Cryptic Cycling of Complexes Containing Fe(III) and Organic Matter by Phototrophic Fe(II)-Oxidizing Bacteria

Geochemical and biological controls on the ecological relevance of total, dissolved, and colloidal forms of trace elements in large boreal rivers: review and case studies

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