Influence of thermal treatment applied to Fe(III) polyhydroxy cation intercalated vermiculite on the adsorption of atrazine

Intercalation of vermiculite with Fe(III) polyhydroxy cations at 1:1 and 2:1 [OH-]/[Fe(III)] molar ratios increases the affinity of the clay mineral toward atrazine in comparison with potassium saturated vermiculite. The present paper describes the effects of thermal treatments applied to Fe(III) polyhydroxy cations modified vermiculite on the adsorption properties of the clay mineral. Only small changes in the textural characteristics were observed for the materials intercalated with either 1:1 or 2:1 [OH-]/[Fe(III)] molar ratios treated at 100 and 250 degrees C. In comparison with potassium saturated vermiculite, or intercalated vermiculite treated at 100 degrees C, a significant enhancement in the adsorption of atrazine was observed for the materials treated at 250 and 400 degrees C, which removed more than 95.8 and 99.5% of the herbicide initially present in a 50.0 microg L-1 aqueous solution, respectively. In comparison with potassium saturated vermiculite and intercalated vermiculite treated at 100 degrees C, a lower desorption degree of preadsorbed atrazine was observed for both intercalated materials treated at 250 and 400 degrees C. These findings suggest that the thermal treatment produced modified vermiculite materials with a high adsorption capacity and high affinity toward atrazine, with potential application in the removal of this herbicide, as well as other triazines, from aqueous medium.     

Influence of humic acid on adsorption and desorption of atrazine, hydroxyatrazine, deethylatrazine, and deisopropylatrazine onto a clay-rich soil sample

Adsorption and desorption properties of atrazine and some of its metabolites, hydroxyatrazine (AT-OH), deethylatrazine (DEA), and deisopropylatrazine (DIA), were studied with a clay-rich soil sample (clay content of 53%). A part of this soil was treated with humic acid (Soil-HA) to assess the influence of this important component of natural organic matter on adsorption and desorption processes. This study was performed using the batch approach with 1.0 g of soil, or Soil-HA, in 5.0 mL of 0.010 mol L(-)(1) CaCl(2) solution containing the herbicide and the metabolites in a concentration range between 0.010 and 5.0 mg L(-)(1). After 24 h of contact time, the suspensions were centrifuged and the four compounds were quantified in the supernatant phases by high-performance liquid chromatography. The adsorption and desorption data of both Soil and Soil-HA were properly fitted by the linearized Freundlich equation. For the untreated soil, the adsorption affinity order evaluated as a function of the K(f) values was AT-OH > AT > DIA > DEA, while desorption followed the order DEA > DIA approximately AT > AT-OH. The presence of humic acid increased significantly the adsorption of all compounds, following the same affinity order observed for the untreated soil. Increase in adsorption was especially high for AT-OH and AT. On the other hand, the dealkylated metabolites, DEA and DIA, were more easily desorbed from the Soil-HA sample, suggesting that natural organic matter facilitates the leaching of these compounds. Desorption order in the presence of humic acid was DEA > DIA > AT > AT-OH.     

Kinetics and adsorption of metolachlor and atrazine and the conversion products (deethylatrazine, deisopropylatrazine, hydroxyatrazine) in the soil profile of a river basin

The adsorption kinetics and adsorption parameters of metolachlor, atrazine, deethylatrazine (DEA), deisopropylatrazine (DIA) and hydroxyatrazine (HA) were investigated in a soil profile in a maize field formed from recent alluvial deposits in a river basin in Greece. We used the batch equilibrium method modified to simulate field conditions as closely as possible for the use and practices related to soil applied pre‐emergence herbicides. Pseudo‐equilibrium times, determined by kinetic studies, were achieved after 16, 16, 24, 24 and 48 hours for metolachlor, DIA, DEA, HA and atrazine, respectively. At pseudo‐equilibrium the percentage of the adsorbed amount increased in the order of DEA (10%) < DIA (14%) < atrazine (27%) < metolachlor (43%) ≪ HA (94%) which indicates that more than 57% of all compounds except for HA are in solution and available for transport to deeper soil layers when conditions similar to those simulated in the laboratory exist in the field. Adsorption isotherms of all compounds and in most of the cases correlated well with the Freundlich model and adsorption coefficients (K_f) decreased with increased soil depth. Principal component and multiple regression analyses confirmed the importance of the soil organic carbon content on the adsorption capacity of soils for all compounds except HA in the plough layers (0–40 cm). In the subsurface soils (40–110 cm) variables such as clay content and pH were more important. For HA, the K_f values determined for the plough and subsurface soil layers were better correlated with clay content and pH. Also in the subsurface soils, the variation in organic carbon content was not correlated with the variation of K_f values. Thus calculated K_oc‐f‐values misrepresent the adsorptive capacity of these soils towards the compounds studied.     

Adsorption and desorption of atrazine, desethylatrazine, deisopropylatrazine, and hydroxyatrazine in vegetated filter strip and cultivated soil

Adsorption and desorption of atrazine and its metabolites in vegetated filter strip soil (VFS) has not been evaluated, yet these data are needed to predict the transport of these compounds through the VFS. Adsorption and desorption parameters for atrazine, desethylatrazine (DEA), deisopropylatrazine (DIA), and hydroxyatrazine (HA) were compared between a cultivated Houston Black clay (CS) and an adjacent 12-year-old VFS established in a mixed stand of bermudagrass [Cynodon dactylon (L.) Pers.] and buffalograss [Buchloe dactyloides (Nutt. Engelm)]. Adsorption and desorption isotherms were determined by batch equilibrium. The evaluated chemical and physical properties of the VFS and CS were similar with the exception of a 1.7-fold increase in the organic carbon content of the VFS. Adsorption and desorption coefficients for atrazine were at least 59% higher in VFS than in CS. The adsorption coefficient for HA was 48% higher in VFS compared with CS, but desorption was not statistically different between soils. Adsorption and desorption coefficients for DEA and DIA were not statistically different between soils. The predicted order of mobility in CS is HA < atrazine = DIA = DEA. In VFS, the predicted order of mobility is HA < atrazine = DIA < DEA. These data indicate that the higher organic carbon in VFS will likely retard the transport of atrazine and HA to surface and ground waters; however, the transport rates of DEA and DIA will be similar between soils.     

几种吸附剂对阿特拉津的吸附及其 Zeta 电位特性研究

通过振荡吸附平衡试验,研究了蒙脱石、凹凸棒石、竹炭、木炭对阿特拉津的吸附行为,讨论了pH值、离子强度对吸附的影响,并考察了吸附剂表面的Zeta电位变化。结果表明,几种吸附剂对阿特拉津的吸附均符合Freundlich方程;竹炭、木炭的吸附能力明显高于蒙脱石和凹凸棒石。吸附剂对阿特拉津的吸附量随着悬液离子强度的增加而增加,在悬液pH一定(pH=6),离子强度为10-3mol/L NaNO3时,蒙脱石、凹凸棒石对阿特拉津的吸附量分别为538.30、609.68 mg/kg,当离子强度增加为10-2mol/L时,吸附量分别增至611.26、731.63 mg/kg;当离子强度由10-3增至10-1mol/L NaNO3时,竹炭、木炭对阿特拉津的吸附量有较多增加。当悬液pH在3~8范围时,几种吸附剂表面均带负电荷,其Zeta电位值随着pH的增加而增加,随离子强度的增加而减小。悬液离子强度一定时,随着pH的增加,吸附阿特拉津后吸附剂表面Zeta电位变化不显著。研究结果有助于从机理上解析吸附剂对有机污染物的吸附行为。     

Lactic acid decreases Fe(II) and Fe(III) retention but increases Fe(III) transepithelial transfer by Caco-2 cells

Lactic acid (LA) has been proposed to be an enhancer for dietary iron absorption, but contradictory results have also been reported. In the present study, fully differentiated Caco-2 cell monolayers were used to evaluate the effects of LA (1-50 mmol/L) on the cellular retention and transepithelial transport of soluble non-heme iron (as ferric nitrilotriacetate). Our data revealed a linear decline in Fe(III) retention with respect to the concentration of LA added. In the presence of 50 mmol/L LA, retention of Fe(III) and Fe(II) decreased 57% and 58%, respectively. In contrast, transfer of Fe(III) across the cell monolayer was doubled, while Fe(II) transfer across the cell monolayer decreased 35%. We conclude that LA reduces cellular retention and transepithelial transport of Fe(II) by Caco-2 cells in a dose-dependent manner. However, while LA also reduces retention of Fe(III) by Caco-2 cells, the transfer of Fe(III) across cell monolayers is enhanced, possibly due to effects on paracellular transport.     

Interaction of Oxidation Products from Caffeic Acid with Fe(III) and Fe(II)

Abstract

Phenolic substances in the soil–plant system can be oxidized by metal ions, inorganic components, molecular oxygen as well as by phenoloxidases, giving rise to the formation of products of low or high molecular weight. Interactions of these products with iron, in both reduced and oxidized form, can affect the iron mobility in soil and rhizosphere, and thus its availability to plants. Here we report the results of a study on the complexing and reducing activity of the oxidation products from caffeic acid (CAF), obtained via electrochemical means, towards Fe(III) and Fe(II) in aqueous solution in the 3.0–6.0 pH range. The HPLC analysis of the filtered solutions after the CAF oxidation showed the formation of two main groups of products: (i) CAF oligomers formed through radicalic reactions which do not involve the double bond of the CAF lateral chain and (ii) products where this bond is involved. These oxidation products (COP) were found to interact with both Fe(III) and Fe(II) with formation of soluble and insoluble Fe(III)‐, and Fe(II)‐COP complexes. The COP were found to be able to reduce Fe(III) to Fe(II) mainly at pH < 4.0. A low redox activity was observed at pH ≥ 4.5 due to Fe(III) hydrolysis reactions as well as to the decrease in the redox potential of the Fe(III)/Fe(II) couple. Formation of hydroxy Fe(III)‐COP polymers occurs at pH > 3.5.     

Preparation, Characterization, and Adsorption Behavior of Cu(II) Ions onto Alkali-Treated Weed (Imperata cylindrica) Leaf Powder

The adsorption of Cu(II) ions by sodium-hydroxide-treated Imperata cylindrica (SoHIC) leaf powder was investigated under batch mode. The influence of solution pH, adsorbent dosage, shaking rate, copper concentration, contact time, and temperature was studied. Copper adsorption was considered fast as the time to reach equilibrium was 40–90 min. Several kinetic models were applied and it was found that pseudo-second-order fitted well the adsorption data. In order to understand the mechanism of adsorption, spectroscopic analyses involving scanning electron microscope (SEM) coupled with energy-dispersive spectroscopy (EDS) and Fourier transform infrared (FTIR) spectrophotometer were carried out. Ion exchange was proven the main mechanism involved as indicated by EDS spectra and as there was a release of light metal ions (K⁺, Na⁺, Mg²⁺, and Ca²⁺) during copper adsorption. Complexation also occurred as demonstrated by FTIR spectra involving hydroxyl, carboxylate, phosphate, ether, and amino functional groups. The equilibrium data were correlated with Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models. Based on Langmuir model, the maximum adsorption capacity was recorded at the highest temperature of 310 K, which was 11.64 mg g^?1.     

Fe(III)-EDDHA and -EDDHMA sorption on Ca-montmorillonite, ferrihydrite, and peat.

The effectiveness of Fe chelates as Fe sources and carriers in soil can be severely limited by the adsorption of Fe chelates or chelating agents in the solid phase. To study this phenomenon, well-characterized peat, Ca-montmorillonite, and ferrihydrite were used as model compounds, and the adsorption of Fe-EDDHA and Fe-EDDHMA chelates were studied. Sorption isotherms for the meso and racemic isomers of these chelates on the soil materials are described. The variability of sorption with pH in peat and ferrihydrite was also determined because both have variable surface charge at different pH values. In montmorillonite, at low concentrations, the retention of Fe from the Fe-EDDHMA chelate is greater than the one of the Fe-EDDHA chelate. As well as the concentration increased, the inverse situation occurs. The behavior of both meso and racemic isomers of chelates in contact with Ca-montmorillonite is similar. The Fe-meso-EDDHA isomer was highly adsorbed on ferrihydrite, but the racemic isomer is not significantly retained by this oxide. For Fe-EDDHMA isomers, the racemic isomer was more retained by the oxide, but a small sorption of the racemic isomer was also observed. Results suggest that Fe-EDDHA chelates were more retained in peat than Fe-EDDHMA chelates. The most retained isomer of Fe-EDDHA was the meso isomer. For Fe-EDDHMA, the adsorption was very low for both racemic and meso isomers.     

Resistance of mineral soils to Fe(III) reduction

Gleying and enhancement of hydromorphism in wetland soils due to Fe(III) reduction entail a series of degradation processes. The resistance of wetlands to degradation can be calculated from the content of potentially reducible iron, Fe(III)_pr, which is found from the van Bodegom equation taking into account the contents of oxalate-soluble iron Fe_ox and dithionite-soluble iron Fe_dit in the soil. In addition, this makes it possible to distinguish relict and actual gleysols. The van Bodegom equation is applicable to soils from which the oxalate solution extracts only amorphous and poorly crystallized iron compounds, which are quickly reduced by Fe-reducing bacteria. These soils have a low proportion of Fe(II) (no more that 15% of the total iron), as well as an accumulative profile distribution of Fe_ox. The van Bodegom equation is unsuitable for calculating the Fe(III)_pr content in soils with a high proportion of Fe(II) and a nonaccumulative profile distribution of Fe_ox.     

Kinetic Speciation of Ni(II) in Model Solutions and Freshwaters: Competition of Al(III) and Fe(III)

The competing ligand exchange method was used to investigate the competitive binding of Ni(II) by Al(III) and Fe(III) in model aqueous solutions and freshwaters. Graphite furnace atomic absorption spectrometry and adsorptive cathodic stripping voltammetry were used to monitor the rate of uptake of the Ni by Chelex 100 chelating resin and dimethylglyoxime as the competing ligands, respectively. The results have revealed that Ni(II)–humate complexes were more labile in presence of the mixture of Al(III) and Fe(III), compared to the lability of the Ni(II)–humate complexes when only one of the two, Al(III) or Fe(III), was present. The environmental significance of this work is that in model solutions simulating freshwater containing humic substances and the target trace metal Ni(II) and cations, Al(III) and Fe(III), the competitive binding of Ni(II), Al(III) and Fe(III) by humic substances makes Ni(II)–humate complexes labile, releasing free Ni²⁺–aqua complex, which reported to be toxic.     

Heavy metal sorption on soil minerals affected by the siderophore desferrioxamine B: the role of Fe(III) (hydr)oxides and dissolved Fe(III)

Phytoextraction of heavy metals from polluted soils has often been found to be limited by the bioavailability of the pollutants. Inorganic or organic ligands are occasionally used as complexing agents to enhance the mobility of the heavy metals. However, the opposite effect is also possible. We studied the influence of the hydroxamate siderophore desferrioxamine B (DFOB) on the sorption of Cu, Zn and Cd to clay minerals, with the emphasis on the role of dissolved Fe(III) and Fe(III) minerals. Depending on the surface charge of the minerals and on pH, sorption of heavy metals can be either enhanced or diminished. We show here that this effect of DFOB disappears if dissolved Fe(III) is added to suspensions of clay minerals in excess to DFOB. We found that the solid Fe(III) phases ferrihydrite and goethite did not impede the effect of DFOB on the sorption of heavy metal, however. Between pH 4 and 10, DFOB completely prevented Cu sorption on ferrihydrite. A strong mobilizing effect was also observed for Zn, but not for Cd. In presence of goethite, concentrations of dissolved Cu, Zn and Cd were enhanced only above approximately pH 5, 7 and 8, respectively. Below these pH values the binding of these metals to goethite was even stronger with than without DFOB. In the absence of heavy metals, DFOB‐promoted dissolution of ferrihydrite was much faster than that of goethite due to the larger surface area of ferrihydrite. In the alkaline pH range, where sorption of DFOB on the surfaces of the iron oxides was greater, dissolution of both minerals was reduced.     

Specific sorption of antimony (III) by the hydrous oxides of Mn,Fe, and Al

The hydrous oxides of Mn, Fe, and Al avidly sorbed Sb from μM Sb(OH), solutions, with uptake levelling off as initial Sb concentration increased. Capacity values decreased along the sequence MnOOH > Al(OH)₃ > FeOOH. The amount sorbed by each substrate decreased gradually at pH values > 6. Addition of 0.4M CH₃COONa to the aqueous phase (to minimise retention of weakly bound Sb) had little effect on MnOOH uptake capacity (～160 mmol, kg^?1 at pH < 7) but retention dropped rapidly at higher pH. With the other two substrates (pH 6–7) the calculated capacity values for specific Sb sorption were ～ 45 mmol kg^?1 FeOOH and ～ 33 mmol kg^? Al(OH)₃; about a third of the total capacity values. On these substrates specific Sb sorption tended to peak in the pH 7 to 8 region. The pH response pattern was modified using Sb tartrate sorbate solutions. Factors influencing Sb sorption included substrate surface charge, chemical form of Sb and surface interactions. Formation of a sparingly soluble metal coating was indicated by the uptake plateaus observed when increasing amounts of solid were added to Sb solutions containing acetate.     

The adsorption of polycationic Fe (III) species on Na-illite

The adsorption of polymeric ferric species from hydrolysed Fe (III) solutions on Naillite at pH 2.5 has been examined. The bulk of the adsorption appears to be due to polycationic species of high molecular weight (> 10,000). Electrophoretic and cation exchange data indicated that the net charge on the clay surface became strongly positive at low pH values as a result of adsorption of the polycations. The adsorbed material was apparently amorphous to x-rays and did not affect the BET nitrogen surface area of the clay. Significant increases in the resistance of the dried clay to redispersion were observed, however, even at quite low Fe contents (< 1% by weight). These have been attributed to cementation effects.     

Reductive biogenic transformation of Fe(III)-containing phyllosilicates (review of publications)

Microorganisms are capable of reducing the structural Fe(III) of some phyllosilicates, i.e., montmorillonite, nontronite, and illite. Two reduction results are possible. For the low-ferruginous minerals, the solid-phase partial reduction of the structural Fe(III) does not cause any decay of particles. In this case, reduction leads to a partial dehydroxylation of the lattice and magnetic disordering of the mineral, as well as to changes in the layer packaging, the crystallization degree, the texture, the color, the surface charge, and the cation-exchange capacity. Except for dehydroxylation and the changing Fe oxidation status, the transformations of minerals’ properties are irreversible for the most part. In highly ferruginous phyllosilicates, the structural Fe(III) reduction leads to the particle dissolution. As a result of microbial reductive dissolution of crystallized nontronite, new amorphous minerals are formed, i.e., aluminosilicates with an elevated Al/Si ratio, Si globules, and Fe hydroxides. Another biogenically crystallized Si mineral (tridymite βSiO₂) is formed in light-textured soils and sediments after smectite decomposition. The bacterial reduction of highly ferruginous illite leads to transformation of the shape of some particles: initially acicular illite crystals were transformed into plates. The amorphous structure is formed in illite particles contacting with bacterial cells. The solid-phase reduction of structural Fe(III) does not lead to particle dissolution in the case of low-ferruginous illite.     

Adsorption of emerging sodium p-perfluorous nonenoxybenzene sulfonate (OBS) onto soils: Kinetics, isotherms and mechanisms

The widespread use of sodium p-perfluorous nonenoxybenzene sulfonate(OBS), a typical alternative to perfluorooctane sulfonate, has resulted in potential threats to the environment, but the adsorption behavior of OBS in soils has not yet been reported. In this study, the adsorption behaviors of OBS on five soils with different physicochemical properties were investigated. The rate of OBS adsorption was fast, and most of the OBS uptake was completed within 12 h. The good model fit of OBS adsorption to the pseudo-second-order and Elovich models indicated the occurrence of chemical adsorption. The adsorption isotherms of OBS on the soils were better described by the Freundlich model than by the Langmuir model, suggesting that the OBS adsorption sites on the soils were heterogeneous. This is possibly associated with various adsorption mechanisms including hydrophobic, π-π, hydrogen bonding, and electrostatic interactions,further confirmed by the good model fit to the D-R isotherm. Adsorption of OBS occurred on the soils, and the adsorption process was spontaneous and endothermic. In addition, the soils were more suitable for OBS adsorption at lower pH values due to the stronger electrostatic adsorption. The OBS adsorption on the soils decreased with the increase of soil depth from 0 to 30 cm. Moreover, the presence of organic matter and ammonia nitrogen in the soils was favorable for OBS adsorption, and these parameters decreased with increasing soil depth, making OBS adsorption less prominent in the deeper soil. This study indicates that OBS is easily enriched in surface soils, and that soil organic matter and ammonia nitrogen significantly affect OBS migration in soil.     

Adsorption of atrazine and metolachlor in three soils from Blue Creek wetlands, Waterville, Ohio

Atrazine and metolachlor are extensively used pesticides in agricultural activities in northwest Ohio. Adsorption coefficients are often used to model pesticide fate and transport. Many physical-chemical parameters, such as organic matter, clay content, pH, and ionic strength, affect pesticide adsorption. Adsorption kinetics and adsorption isotherms were studied by batch experiment. Effects of humic acid, solution pH, and ionic strength on atrazine and metolachlor adsorption were also approached. After 24 h, both atrazine and metolachlor reached adsorption equilibrium in three local soils. Adsorption isotherms were described by Freundlich equations. The Freundlich coefficient (Kf) ranged from 0.14 to 4.47 (L kg^–1) for atrazine, and 0.04 to 5.30 (L kg^–1) for metolachlor. Adsorption capacity decreased in the order Sloan loam > Del Rey loam > Ottokee fine sand. Koc values varied considerably for both pesticides: metolachlor > in Sloan loam, atrazine metolachlor in Del Rey loam, and atrazine > metolachlor in Ottokee fine sand. In addition to organic matter content, clay played a key role in adsorption in the Del Rey loam and Ottokee fine sand. Higher adsorption was observed at pH 5 for both pesticides. As pH decreased to 3 and increased to 11, adsorption decreased. Adsorption increased as ionic strength increased.     

Adsorption and desorption of monomeric Bt (Bacillus thuringiensis) Cry1Aa toxin on montmorillonite and kaolinite

Genetically modified crops, which produce pesticidal proteins from Bacillus thuringiensis, release the toxins into soils through root exudates and upon decomposition of crop residues. Although the phenomena of gene transfer and emergence of resistance have been well documented, the fate of these toxins in soil has not yet been clearly elucidated. The aim of this study was to elucidate the adsorption and the desorbability of the Cry1Aa Bt insecticidal protein in contact with two sodium-saturated clays: montmorillonite and kaolinite. Because the toxin is released into soil in small quantities, it was assumed that it will be in a monomeric state in solution until it oligomerized on cell membranes. The originality of this study was to focus on the monomeric form of the protein. Specific sample conditions were required to avoid polymerisation. A pH above 6.5 and an ionic strength of at least 150 mM (NaCl) were necessary to keep the protein in solution and in a monomeric state. The adsorption isotherms obtained were of the L-type (low affinity) for both clays and fitted the Langmuir equation. The adsorption maximum of the toxin, calculated by the Langmuir nonlinear regression, decreased with increasing pH from 6.5, which was close to the isoelectric point, to 9. At pH 6.5, the calculated adsorption was 1.7 g g⁻¹ on montmorillonite and 0.04 g g⁻¹ on kaolinite. Desorbability measurements showed that a small fraction of toxin could be desorbed by water (up to 14%) and more by alkaline pH buffers (36 ± 7%), indicating that it was not tightly bound. Numerous surfactants were evaluated and the toxin was found to be easily desorbed from both clays when using zwitterionic and nonionic surfactants such as CHAPS, Triton-X-100, and Tween 20. This finding has important implications for the optimization of detection methods for Bt toxin in soil.