Search

Interaction with natural organic matter (NOM) is hypothesized to impact the fate and bioavailability of enzymes and some hazardous proteins in terrestrial and aquatic environments. By using saturated column transport experiments the transport and deposition of the model enzyme lysozyme (LSZ), in the absence and presence of purified Aldrich humic acid (PAHA), was investigated at a series of mass ratios PAHA/LSZ at pH 5 and 8 and two ionic strength values (0.5 mM and 50 mM KCl solution). PAHA decreased LSZ transport under all conditions. The shapes of breakthrough curves (BTCs) and retention profiles (RPs) during cotransport of both colloids evolved from symmetrical to blocking with time and from flat to hyper-exponential with depth, respectively, in response to increases in mass ratio PAHA/LSZ. The results indicated that the “size-selective retention” and concurrent homo- and hetero-aggregation induced straining, which resulted in preferential retention of relatively large PAHA-LSZ aggregates in the column and elution of relatively small ones. Due to differences in aggregate size, in general, the enzyme activity of LSZ in the effluent was larger and that of the retained LSZ was smaller than that of the influent. Therefore, protein transport process could partially increase the enzyme activity and bring potential environmental hazards. [ABSTRACT FROM AUTHOR]

Abstract: The humic substances (HS) have a high reactivity with other components in the natural environment. An important factor for the reactivity of HS is their negative charge. Cationic surfactants bind strongly to HS by electrostatic and specific interaction. Therefore, a surfactant binding model is developed that takes both the specific and electrostatic interactions explicitly into account. The model is analogous to that of ion binding to HS with the NICA-Donnan model, but competition for the binding sites is not taken into account and the NICA-Donnan model reduces to the Langmuir–Freundlich–Hill–Donnan (LFH-D) model. The parameters of the LFH equation are the maximum binding, the affinity constant and the non-ideality constant. The non-ideality parameter accounts for both the site heterogeneity and the cooperativity due to hydrophobic interaction between surfactant molecules. The affinity constant incorporates the specific (e.g., hydrophobic) interactions between surfactant and HS. The Donnan part of the model accounts in a simple way for the electrostatic interactions by assuming that for a given set of conditions there is only one electrostatic potential that governs the behavior in the Donnan phase. The separation between the specific interactions (LHF) and the electrostatic interactions (D) is based on the so-called master curve (MC) procedure in which the binding is replotted as a function of the “free” surfactant concentration in the Donnan phase. The MC depends only on the specific interactions. Once the MC is obtained it can be fitted to the LFH equation to obtain the model parameters. Subsequently, the surfactant isotherms can be calculated with the LFH-D model. The model is tested using previously obtained data on dodecyl pyridinium chloride (DPC) and cetyl pyridinium chloride (CPC) binding to some purified humic and fulvic acids at pH about 5. The LFH-D model is well suited to describe the surfactant binding to HAs from very low concentrations up to the iso-electric point (IEP). The affinity of DPC for the different HAs allows ranking of the HAs according to their hydrophobicity. Prediction of DPC binding at other pH values also leads to good results for HA. For FAs the model can only describe the surfactant binding up to an adsorbed amount of 0.5mol/kg. For higher binding values the LFH-D model underestimates the binding. [Copyright &y& Elsevier]

Abstract: Interactions of calcium and fulvic acid (Strichen) with the surface of goethite were studied with batch and titration experiments. The mutual influence of the interactions on the adsorption of fulvic acid, calcium ions and protons were examined. Adsorption of the fulvic acid to goethite decreased with increase in pH (pH range 3–11). Addition of Ca (1.0 mM) at intermediate and high pH significantly enhanced the adsorption of fulvic acid. Compared to the adsorption to pure goethite, the presence of fulvic acid enhanced the adsorption of Ca significantly. In comparison to the simple linear sum of Ca bound to fulvic acid and goethite, the interactions between goethite and fulvic acid led to a reduced adsorption of Ca at low pH and an enhanced adsorption at high pH. With the adsorption of fulvic acid, protons were released at low pH and coadsorbed at high pH. When Ca was added, fewer protons were released at low pH and fewer coadsorbed at high pH. The experimental results can be adequately described using a surface complexation model, the Ligand and Charge Distribution (LCD) model, in which the CD-MUSIC model for ion adsorption to mineral oxides and the NICA model for ion binding to humics are integrated. In the model calculations, adequate descriptions of the ternary system data (Ca-fulvic acid-goethite) were obtained with parameters derived from three binary systems (fulvic acid-goethite, Ca-goethite and Ca-fulvic acid) without further adjustment. The model calculations suggest that the interactions between Ca and fulvic acid at the surface of goethite are mainly due to the electrostatic effects. [Copyright &y& Elsevier]

Modification of enzyme/protein conformation will affect the activities and functionality of enzymes. Previous studies have shown that the activity of lysozyme (LSZ) in the presence of humic acid (HA) is largely determined by the mass ratio of HA/LSZ (f = m HA/ m LSZ), pH and ionic strength. Here the interaction and conformation of LSZ in HA/LSZ-complex/aggregate (HA/LSZ-c/a) were investigated by spectroscopic techniques at (initial) pH 5 and 8 and ionic strength 5 mmol/L. The results indicated a strong interaction between HA and LSZ. Circular dichroism (CD), and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy showed that the helix content reached a minimum at the mass ratio of its iso electric point (IEP) at given initial pH, f IEP,pHi. The changes in β-sheet and random coil of HA/LSZ-c/a were opposite with increasing f. The minimum of helix content at f IEP,pHi corresponded with the minimum LSZ activity and maximum aggregate size of HA/LSZ-c/a. UV–vis spectra and fluorescence measurements indicated that the amino acid residues (especially for tyrosine) in LSZ were in a more hydrophobic microenvironment before f IEP,pHi due to the formation of HA/LSZ-c/a, while were gradually exposed to a more polar microenvironment beyond f IEP,pHi with the disaggregation of HA/LSZ-c/a. HA and LSZ interaction caused a more hydrophobic microenvironment for the amino acid residues at initial pH 8. This study improves our understanding of enzyme/protein behavior in the natural environment. Unlabelled Image • Conformation of lysozyme(LSZ) bound with HA depends on the mass ratio f HA/LSZ and pH. • LSZ conformation was closely related to its encapsulated degree and complexation size. • Helix in LSZ reached the minimum around f IEP , opposite to β-sheet and random coils. • Amino acid residues in LSZ were in a more hydrophobic micro-environment before f IEP. [ABSTRACT FROM AUTHOR]

Abstract: The anionic charge of humic substances (HS) plays a major role in the interaction of HS with other components. Therefore, the potential of the polyelectrolyte titration technique to obtain the charge density of HS in simple 1–1 electrolyte solutions has been investigated. Titrations are carried out with an automatic titrator combined with the “Mütek particle charge detector” which allows determination of the Mütek potential and the pH as a function of the added amount of titrant which is a solution of poly-diallyldimethylammonium chloride (polyDADMAC), a cationic strong polyelectrolyte. When the Mütek potential reverses its sign the iso-electric point (IEP) of the polyDADMAC–HS complex is reached. The polyDADMAC/HS mass ratio at the IEP gives information on the HS charge density and from the pH changes in solution an estimate of the charge regulation in the HS–polyDADMAC complex can be obtained. In general, for polyDADMAC–HS complexes an increase in the dissociation of the acid groups of HS is found (charge regulation). The charge regulation decreases with increasing concentration of 1–1 background electrolyte. Cation incorporation can be neglected at 1–1 electrolyte concentrations⩽1mmolL−1 and a 1–1 stoichiometry exists between the polyDADMAC and HS charge. However, at these low salt concentrations the charge regulation is substantial. A detailed analysis of purified Aldrich humic acid (PAHA) at pH 5 and a range of KCl concentrations reveals that the anionic charge of PAHA in the complex increases at 5mmolL−1 KCl by 30% and at 150mmolL−1 KCl by 12%. On the other hand, increasing amounts of K+ become incorporated in the complex: at 5mmolL−1 KCl 5% and at 150mmolL−1 KCl 24% of the PAHA charge is balanced by K+. By comparing at pH 5 the mass ratios polyDADMAC/PAHA in the complex at the IEP with the theoretical mass ratios of polyDADMAC/PAHA required to neutralize PAHA in the absence of charge regulation and K+ incorporation, it is found that at 50mmolL−1 KCl the extra negative charge due to the interaction between polyDADMAC and PAHA is just compensated by K+ incorporation in the complex. Therefore, a pseudo 1–1 stoichiometry exists at about 50mmolL−1 1–1 electrolyte concentration and only at this salt concentration polyDADMAC titrations and conventional proton titrations give identical results. Most likely this is also true for other HA samples and other pH values. For FA further study is required to reveal the conditions for which polyDADMAC and proton titrations give identical results. [Copyright &y& Elsevier]

Zn is a common heavy metal in soils and sediments. In this study, the release behaviors of octahedral ( VI Zn) and tetrahedral ( IV Zn) Zn complexes on synthesized hexagonal birnessite were explored by solution chemistry method in combination with spectroscopic analysis. In acidic dissolution processes, the release of adsorbed Zn 2+ from birnessite occurred into two stages: in the first stage, ~60% of Zn 2+ was desorbed rapidly, with only 8% of Mn being released, and the ratio of VI Zn/ IV Zn increased with time; in the second stage, the residual Zn 2+ was mostly VI Zn and released slowly at a nearly constant rate until complete dissolution of the matrix mineral was observed. During desorption of Zn 2+ by Pb 2+ , the ratio of VI Zn/ IV Zn on birnessite also increased, while the residual percentage of VI Zn remained nearly constant. However, it is known that IV Zn-triple corner-sharing (TCS) is more stable than VI Zn-TCS, suggesting that part of the remaining IV Zn-TCS on birnessite might transform to VI Zn-TCS immediately when VI Zn-TCS is replaced by H + or Pb 2+ . Additionally, the possible distribution of Mn 3+ and IV Zn or the partial charge compensation by protons can lead to the preferential retention of VI Zn on birnessite or the preferential re-adsorption of VI Zn at the new edge sites. These results can provide new insights into the geochemical behavior of Zn 2+ contaminant in soil and aquatic environments. [ABSTRACT FROM AUTHOR]

The presence and formation of hydroxy-interlayered minerals in the Holocene paleosol at the Wugong profile on the southernmost Chinese Loess Plateau were investigated by examining the < 1 μm and 1–2 μm clay fractions of the 50–150 cm horizon by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Prior to the analyses free Al and Fe phases were removed by dithionite-citric-bicarbonate (DCB) extraction. XRD patterns were obtained with air-dried, Mg-saturated, Mg-saturated with glycerol solvation (Mg-glycerol) and K-saturated and heated at 110, 250, 350, 450 and 550 °C samples both before and after hydroxy-interlayered materials removal by sodium citrate extraction. The absorption bands at 3699 and 3430 cm − 1 in the FTIR spectra of both sub-fractions indicated the presence of hydroxy-interlayered minerals. The K-saturated and heated XRD patterns confirmed this by the progressive collapse of the 1.4 nm reflection to a 1.0 nm reflection. After removal of the hydroxy-interlayered materials no obvious increase of the relative XRD intensity of the 1.8 nm reflection in Mg-glycerol pattern was observed and the 1.4 nm reflection exhibited a stronger collapse to 1.0 nm after K-saturation and increasing temperature treatment. This indicated that the hydroxy-interlayered minerals in the Holocene paleosol were mainly composed of hydroxyl-interlayer vermiculite. The hydroxyl-interlayer vermiculite was formed by the polymerization of Al/Fe-hydroxy materials within the interlayer space of vermiculite. Shoulder-like reflection at 1.2 nm in the K-550 °C pattern of the 1–2 μm fraction indicated a higher degree of Al/Fe-hydroxylation in the coarse fraction than in the fine fraction, which was consistent with the lower extractable Al and Fe in the coarse fraction. The reflection at 1.38 nm in the K-550 °C pattern could be interpreted as pedogenic chlorite. Thus, transformation of vermiculite into hydroxy-interlayered vermiculite and finally into a chlorite-like mineral (pedogenic chlorite) has occurred in the Holocene paleosol on the southernmost Chinese Loess Plateau. [ABSTRACT FROM AUTHOR]

Hydroxycarbonate green rust (GR1(CO 3 2− )) was prepared by oxidation of aerated aqueous suspensions of Fe(II) hydroxide, and the presence of light promoted the transformation of GR1(CO 3 2− ) by dissolved O 2 at pH 7.8 and 25 °C. Further transformation of GR1(CO 3 2− ) in the light was conducted in the presence of orthophosphate (P) or silicate (Si) anions, followed by solution analysis and solid product characterization using X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). Results show that both P and Si anions significantly affect the transformation of GR1(CO 3 2− ) through adsorption on the intermediate products. The time required for complete GR1(CO 3 2− ) transformation and the phases, crystallinity and morphology of the transformation products all depend on the Fe/anion molar ratio. When compared to the control, the transformation can be promoted by low Si concentrations but retarded by P. With decreasing Fe/P ratio, the products change from acicular goethite (absence of P) to tabular lepidocrocite (Fe/P: 120-48) and to mixed phases of platelets of ferric GR1(CO 3 2− ) (EX-GR1) and minor ferrihydrite (Fe/P: 24-3). In terms of Si, the products are goethites when the Fe/Si ratio of 48-12, and with increasing ratio, the goethite crystallinity and particle size decrease and the morphology changes from acicular (absence of Si) to plate-like or isodimensional particles. The goethite morphology at low Fe/Si ratios is comparable to natural goethite samples commonly found in soils. At Fe/Si = 3, the products are EX-GR1 platelets with minor ferrihydrite coexisting. The likely pathway of the oxidative GR1(CO 3 2− ) transformation in the control system and in the presence of low concentrations of Si (Fe/Si ⩾ 12) is GR1(CO 3 2− ) → amorphous γ-FeOOH-like phase → α-FeOOH via a dissolution–oxidation–precipitation mechanism. In addition, Fe(II) released during dissolution of GR1(CO 3 2− ) is adsorbed on the products and the transformation of the γ-FeOOH-like phase to goethite is catalyzed by the adsorbed Fe(II). For the P system, the released Fe(II) forms ternary surface complexes with P on the mineral surfaces without any catalytic role, leading to the formation of lepidocrocite at low P concentrations. Clearly, the oxidative transformation of green rust to various crystalline iron oxyhydroxides depends on the type and concentration (Fe/anion molar ratio) of co-existing anions. This study also suggests that the natural goethite formed by Fe(II) oxidation in the form of plate-like or isodimensional particles is most likely related to the ubiquitous presence of silicates in soil environments. [ABSTRACT FROM AUTHOR]

The most prominent paleosol unit in the Chinese Loess Plateau (CLP) is the fifth paleosol complex (S5) with its well-developed very thick and dark colored pedons. To provide more insight in the formation of S5 and its environmental significance, the pedogenesis and clay mineral transformation in the S5 of the Wugong section (Shaanxi Province) on the southernmost CLP are analyzed. S5 at the Wugong section is essentially composed of three well-developed reddish pedons (i.e., S5 -1, S5 -2, S5 -3) which signify three glacial-interglacial climatic fluctuations during its formation. Complete decalcification in each pedon and a calcic horizon of only 30-50 cm in thickness beneath each of the three pedons suggests that after deposition the pedons developed with a relatively stable surface in a sustained warm and humid climate. Clay formation in the S5 includes neogenesis of clay materials by in situ post-depositional weathering and mechanical migration of the fine fraction after complete decalcification. Complete leaching of CaCO3, intensive clay formation (with 60-100% higher clay content than that in the overlying and underlying loess (L5 and L6)) and extremely high magnetic susceptibility in the S5 pedons reflected a warmer, more humid climate and soil environment for pedogenesis than in the 'optimum' Holocene. However, the chemical alteration of the phyllosilicate minerals was weak and restrained by the hard calcic horizon, the compact argillic horizon and the flat terrain. The major clay mineral weathering processes during the formation of the S5 pedons at the Wugong section were depotassication, hydrolysis of primary minerals and degradation of chlorite. The pedogenesis in a loess-paleosol sequence and its pedogenic environment can best be deduced from combined data on pedogenic properties, and geochemical and mineralogical characteristics. [ABSTRACT FROM AUTHOR]

The soil carbon reservoir is the largest carbon reservoir in terrestrial ecosystems and consists of soil organic and inorganic carbon stocks. Previous studies have mainly focused on the soil organic carbon (SOC) stock, and limited information is available about the soil inorganic carbon (SIC) stock. The Chinese Loess Plateau (CLP), which is located in the arid and semi-arid region of China, is an important inorganic carbon reservoir, with a thick soil layer that is rich in calcium carbonate. However, there are few reports on the SIC stock and its spatial distribution in this region. In the current study, the SIC densities and stocks for various soil types and land use patterns were evaluated based on 495 profiles with 2470 soil samples across the CLP, which were collected from the Chinese Second National Soil Survey. The results showed that in the top 1m of soil across the CLP, the average SIC density is 17.04kg/m², and the total SIC stock is approximately 10.20 Pg C (1 Pg=1015g). The SIC stock of the CLP accounts for approximately 18.4% of the total SIC stock throughout China. The average values of the SIC stock in the 0-20, 20-50 and 50-100cm depths of the CLP are 2.39, 2.92 and 4.89 Pg, respectively. Under different land use patterns, the order of the average SIC density is farmland≈grassland > forest in all soil layers. For the various soil types, the SIC density in the 0-100cm layer is the highest in alkaline soil and lowest in subalpine meadow soil, whereas the SIC stock is highest in loessial soil, eolian sandy soil and sierozem, and the lowest in subalpine meadow soil. These differences are largely a result of the area occupied by each soil type and the climate conditions. The results of this study provide basic information about carbon reservoir in China and contribute to our understanding of the SIC stock on the CLP as it relates to the carbon balance of terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Highlights: [•] NICA-Donnan with material-specific values can well describe H+ binding to soil HS. [•] H+ binding to soil HS deviates in non-systematic way from generic prediction. [•] Q max,H1 is the key parameter to improve the prediction. [•] The Lenoir-method provides a convenient way to obtain material-specific Q max,H1. [ABSTRACT FROM AUTHOR]

Abstract: Fe-doped hexagonal birnessite was synthesized by adding Fe3+ to the initial reactants, and the effects of Fe doping on the structures and properties of birnessite were investigated and compared with the effects of Co and Ni doping. The underlying mechanisms controlling the incorporation of transition metals (TMs) into the birnessite structure were proposed. Compared to the un-doped control, Fe-doped birnessite has weaker crystallinity, i.e., less stacking of the phyllomanganate sheets in the c direction, and larger surface area. Combination of X-ray photoelectron spectroscopy (XPS) and Mn K-edge XANES and EXAFS spectra demonstrates that Fe doping decreases the Mn average oxidation state (AOS) but has little effect on the basic layer structure and local Mn environments. Fe(III) located in the birnessite layers exhibits high-spin (HS) configuration whereas layer Mn(III) and Co(III) plausibly adopt low-spin (LS) state. The TMs decrease the thickness of birnessite plate crystals along the c axis and affect the unit cell parameter b in the order Fe>Ni>Co. Co and Fe incorporate into the birnessite layers by substitution for Mn(IV) while Ni substitutes for Mn(III). The substitution of TMs into the birnessite layers is governed by the coordination radius (CR), crystal field stabilization energy (CFSE) and oxidation state of the TMs. The variations in potassium contents in doped birnessites together with TM K-edge EXAFS data indicate that most of the Fe (∼81–82%) or Ni (∼66–76%) incorporated into the birnessite structure exists in the interlayer regions, while most of the Co (∼71–80%) occurs in the manganese layers. The compatibility of these TM ions in the birnessite layers is in the order Co>Ni>Fe. The smaller the difference between the CR of Fe, Co or Ni and Mn(IV) or Mn(III), the more dopants are compatible within the Mn layers. [Copyright &y& Elsevier]

A good understanding of mineral evolution and soil properties in the context of agricultural activities is important for soil utilization and management. To investigate the effect various forms of intensive agriculture in different climate regions on the evolution of phyllosilicate minerals and iron (hydr)oxides, three zonal soils were studied under various long-term agriculture with different fertilizers and using fallow soil as reference state. The phyllosilicate composition and Fe species of the clay fractions (<2 μm) were determined, and the detailed mineralogical differences together with selected soil specific properties were analyzed. The results were used to unravel the most likely reasons for the distinctive mineral weathering differences caused by the different conditions. The variation of the extent of mineral weathering of the soils was mainly controlled by climate conditions. The relatively arid climate restrained the chemical weathering in Orthic Entisols. In subtropic humid area, intensive agriculture promoted the decilication of Udic Ferrisols, resulting in a slignt increase in kaolinite content by <5%. However, in the temperate humid area the phyllosilicate mineral assemblage of Udic Isohumosols was sensitive to tillage and fertilization practices. This was mainly reflected by the mutual transformation between non-expandable illite and expandable vermiculite or smectite depending on the variation of K pool. This conclusion was supported by the significant positive correlations between illite and available K (P = 0.005) and between illite and slow-available K (P = 0.047). Compared with phyllosilicate minerals, the iron species and crystallinity indicated by Fe o /Fe d ratio were more susceptible to intensive agriculture. This could be inferred from the one order of magnitude larger variation coefficients of the Fe o /Fe d ratio in the three soils under different agriculture/fertilization than the variation of the Fe d /Fe t ratio. The key factor affecting the Fe o /Fe d ratio was the OC/Fe d molar ratio. Highest values of the Fe o /Fe d ratio and its variation coefficients in Udic Isohumosols also illustrated that iron (hydr)oxides were more vulnerable to agricultural activities in the temperate monsoon climate region. It can conclude that it is necessary to manage the agricultural utilization of arable soils in temperate humid areas with more by specifically regarding the K and OC content for a good soil quality. • Effect of intensive agriculture on phyllosilicate minerals is controlled by regional climate. • Mutual transformation of 2:1 type mineral in temperate humid areas depends on K pool. • Iron (hydr)oxides are more susceptible to tillage and fertilization. • The OC/Fe d molar ratio is the key factor affecting the Fe o /Fe d ratio. [ABSTRACT FROM AUTHOR]

Abstract: Among several types of manganese oxides α-MnO2 is the most active due to its good catalytic, adsorption and ion exchange properties. Sea urchin-like α-MnO2 particles were synthesized by a one-step chemistry route at room temperature using MnSO4 in combination with KIO4 as oxidant. The obtained α-MnO2 was characterized using X-ray powder diffraction (XRD), structure refinement, electron microscopy and N2 gas adsorption and used to investigate the property of the As (III) oxidation. Results revealed that the space group of the prepared product is I 4 /m with lattice constants a =9.840Å and c =2.856Å, and the average grain diameter is around 6.7nm. The BET surface area is 201m2·g−1. Its maximum oxidation capacity of arsenite is up to 1086mmol·kg−1. [Copyright &y& Elsevier]