Adsorption of chloroacetanilide herbicides on soil and its components Ⅲ. Influence of clay acidity, humic acid coating and herbicide structure on acetanilide herbicide adsorption on homoionic clays

Adsorption of chloroacetanilide herbicides on homoionic montmorillonite, soil humic acid, and their mixtures was studied by coupling batch equilibration and FT-IR analysis. Adsorption isotherms of acetochlor, alachlor, metolachlor and propachlor on Ca2 + -, Mg2 + -. Al3 + -and Fe3 + -saturated clays were well described by the Freundlich equation. Regardless of the type of exchange cations, Kf decreased in the order of metolachlor ＞ acetolachlor ＞ alachlor ＞ propachlor on the same clay. FT-IR spectra showed that the carbonyl group of the herbicide molecule was involved in binding, probably via H-bond with water molecules in the clay interlayer. The type and position of substitutions around the carbonyl group may have affected the electronegativity of oxygen, thus influencing the relative adsorption of these herbicides. For the same herbicide, adsorption on clay increased in the order of Mg2+ ＜ Ca2+ ＜ Al3+ ≤ Fe3+ which coincided with the iucreasing aciditv of homoionic clays. Acidity of cations may have affected the protonation of water, and thus the strength of H-bond between the clay water and herbicide. Complexation of clay and humic acid resulted in less adsorption than that expected from independent adsorption by the individual constituents. The effect varied with herbicides, but the greatest decrease in adsorption occurred at a 60:40 clay-to-humic acid ratio for all the herbicides. Causes for the decreased adsorption need to be characterized to better understand adsorption mechanisms and predict adsorption from soil compositions.     

Adsorption of chloroacetanilide herbicides on soil (I). Structural influence of chloroacetanilide herbicide for their adsorption on soils and its components

Adsorption of chloroacetanilide herbicide acetochlor,alachlor, metolachlor and propachlor on soils and soil components was determined, and the structural differences of these herbicides were used to explain the order of sorptivity. Adsorption isotherms for all herbicide-soil combinations conformed to the Freundlich equation, and Kf increased with increasing soil organic carbon content. Kd on soil humic acid was greater than that on clay, but association of humic acid with clay reduced the overall adsorption. On all soils and soil humic acids, herbicide adsorption decreased in the order: metolachlor > acetochlor > propachlor > alachlor. On Ca²⁺-montmorrilonite, the order changed to metolachlor > acetochlor > alachlor > propachlor. FT-IR spectra of herbicide-clay or herbicide-humic acid-clay mixtures showed that H-bonding and charge transfer were the primary interaction pathways between these compounds and the surface of clay or humic acids. The different moieties attached to 2-chloro-acetanilide and their unique arrangement may have influenced the binding mechanisms and thus the sorptivity of these herbicides. This study indicates that the structural difference of pesticides in the same classes may be used as a molecular probe to obtain a better understanding of sorption mechanisms of pesticides on soil.     

Adsorption of acetanilide herbicides on soil and its components. II. Adsorption and catalytic hydrolysis of diethatyl-ethyl on saturated Na(+)-, K(+)-, Ca(2+)-, and Mg(2+)-montmorillonite

Adsorption and catalytic hydrolysis of the herbicide diethatyl-ethyl [N-chloroacetyl-N-(2,6-diethylphenyl)glycine ethyl ester] on homoionic Na⁺-, K⁺-, Ca²⁺-, and Mg²⁺-montmorillonite clays were investigated in water solution. The Freundlich adsorption coefficient, Kf, got from isotherms on clay followed the order of Na⁺ K⁺ > Mg²⁺ Ca²⁺. Analysis of FT-IR spectra of diethatyl-ethyl adsorbed on clay suggests probable bonding at the carboxyl and amide carbonyl groups of the herbicide. The rate of herbicide hydrolysis in homoionic clay suspensions followed the same order as that for adsorption, indicating that adsorption may have preceded and thus caused hydrolysis. Preliminary product identification showed that hydrolysis occurred via nucleophilic substitution at the carboxyl carbon, causing the cleavage of the ester bond and formation of diethatyl and its dechlorinated derivative, and at the amide carbon, yielding an ethyl ester derivative and its acid.These pathways also suggest that hydrolysis of diethatyl-ethyl was catalyzed by adsorption on the clay surface.     

Sorption and cosorption of the nonionic herbicide mefenacet and heavy metals on soil and its components

Sorption and cosorption of the nonionic herbicide mefenacet and two typical metals (copper and silver) on black soil and its components (kaolinite and humic acid) were investigated. It was found that because of their different valences and properties, Cu²⁺and Ag⁺ presented different effects on the sorption of mefenacet. Due to the competition of Cu²⁺, along with the shells of dense water formed by its surface complexation, for sorption surface area with mefenacet, the addition of Cu²⁺ decreased the sorption amount of mefenacet on soil and its components, especially on humic acid. However, the addition of Ag⁺ significantly enhanced the sorption of mefenacet, which was attributed to the softness of the cation that weakened the hydrophilicity of the local region around Ag⁺-complexed functionalities, and thus mitigated the competitive sorption of water. In addition, the sorption of mefenacet on soil with or without the two metals was generally decreased with increasing pH, which was caused by the hydrolysis of carbonyl and carboxyl groups on the surface of the sorbents, π-π interaction between mefenacet and the soil organic matter, and so on. On the other hand, the presence of mefenacet seemed to have little effect on the sorption of Cu²⁺ and Ag⁺, indicating that Cu²⁺ and Ag⁺ might be sorbed strongly on the tested sorbents and the mefenacet added was too low in concentration to affect the sorption of the metals.     

Adsorption kinetics of the herbicide safeners, benoxacor and furilazole, to activated carbon and agricultural soils

Chloroacetamide herbicides, namely acetochlor and metolachlor, are common herbicides used on corn and soybean fields. Dichloroacetamide safeners, namely benoxacor and furilazole, are commonly used in formulations containing chloroacetamide herbicides. Extensive reports on adsorption of chloroacetamide herbicides are available, yet little information exists regarding adsorption potential of co-applied safeners. Herein, the adsorption and desorption characteristics of selected herbicide safeners to granular activated carbon (GAC) and in agricultural soils are reported. Further, soil column studies were performed to understand the leaching behaviour of the herbicide Dual II Magnum. Equilibrium sorption experiments of safeners to three agricultural soils and one GAC showed that adsorption was best fitted by the Freundlich isotherm. The Freundlich adsorption constant, K_f, for benoxacor and furilazole sorption onto three agricultural soils ranged from 0.1 to 0.27 and 0.1 to 0.13 (mg/g) × (mg/L)?(1/n), respectively. The K_f for benoxacor and furilazole to GAC was 6.4 and 3.4 (mg/g) × (mg/L)?(1/n), respectively, suggesting more favorable sorption of benoxacor to GAC than furilazole to GAC. The sorption to soils was reversible as almost 40%–90% of both safeners was desorbed from three soils. These results were validated in four replicated soil column studies, where S-metolachlor was shown to leach similarly to the safener benoxacor, originating from the herbicide formulation. The leaching of S-metolachlor and benoxacor was influenced by soil texture. Cumulatively, these results show that safeners will move through the environment to surface waters similarly to the active ingredients in herbicides, but may be removed during drinking water treatment via GAC.     

Freeze–dried synthesized bifunctional biopolymer nanocomposite for efficient fluoride removal and antibacterial activity

Local fluoride contamination and bacterial infections in potable water have dangerous effects on the human body and are today a global concern. In this study, we have synthesized a pH-responsive bifunctional biopolymer nanocomposite (HAZ) of humic acid with incorporating aluminum zirconium bimetallic oxide by deep freeze–drying method. Fast nucleation and interconnection of nanoparticles form a highly porous network because of sublimation of frozen HAZ. This duo nanocomposite has efficiently worked for fluoride removal and showed potent antibacterial activity against the Escherichia coli Gram-negative and Staphylococcus aureus Gram-positive bacteria. The X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the hydroxyl groups act as a pivot in the ion exchange process of adsorption, each element of bimetallic oxide primarily takes part in the adsorption mechanism. The maximum adsorption capacity of the adsorbent was 180.62 mg/g at pH seven. Thermodynamic parameters like Gibbs free energy change (ΔG⁰), entropy (ΔS⁰), and enthalpy (ΔH⁰) indicate that the process was endothermic, feasible, and taken place by a chemisorption mechanism. This is the first novel freeze–dried bifunctional biopolymer nanocomposite composed of humic acid natural polymer incorporated with Al–Zr metal oxide, and it exhibited three times higher adsorption efficacy with excellent antibacterial action at a concentration of 5 µg/mL of the nanocomposite.     

Redox potential EH [Se(VI)/Se(IV)] of aqueous extractof soils from Yongshou Kaschin-Beck diseaseregion and the influence by humic acid

The relation between E_H [Se(VI)/Se(IV)] and pH of soil aqueous extract in Kaschin-Beck disease region and the effects of natural redox agents, namely humic substances, MnO₂ and Fe²⁺, on the redox property of the system were studied. The results indicated that both humic acid and Fe²⁺ could enhance the reducibility of Se(VI) and MnO₂, a limited oxidizability for Se(IV). Fe²⁺ showed a weak reducibility only at low pH value. The reducibilities of three sulfur-containing compounds for Se(VI) were in following order:thioglycollic acid > L-cysteine > sulfide     

Fate of the herbicide metolachlor in aerobic and anaerobic soils

The fate of the herbicide metolachlor in aerobic and anaerobic soils with repeated applications of the metolachlor over a period of 5 years was studied. After 12 weeks incubation, cumulative 14CO2 evolution from the soil accounts for 8.01% in aerobic condition versus 1.5% of 14CO2 in the soil had not been treated with metolachlor. The total 14C recovery in the methanol-water extract and in the non-extractable portion of this aerobic soil accounted for 73.1% and the total metolachlor recovery in the methanol-water extract was 46.7% but 86.9% of 14C was accounted for in the γ-irradiated control soil. There axe no differences in the recovery of 14C between non-sterile and γ-irradiated control soil under anaerobic conditions. The results show that there was some active metolachlor-degrading population in the Virginia soil which had been previously received repeated applications of the metolachlor but only under aerobic condition.     

Effect of calcium on adsorption capacity of powdered activated carbon

We investigated the effect of calcium ion on the adsorption of humic acid (HA) (as a target pollutant) by powered activated carbon. The HA adsorption isotherms at different pH and kinetics of two different solutions including HA alone and HA doped Ca²⁺, were performed. It was showed that the adsorption capacity of powdered activated carbon (PAC) for HA was markedly enhanced when Ca²⁺ was doped into HA. Also, HA and Ca²⁺ taken as nitrate were tested on the uptake of each other respectively and it was showed that the adsorbed amounts of both of them were significantly promoted when HA and calcium co-existed. Furthermore, the adsorbed amount of HA slightly decreased with the increasing of Ca²⁺ concentration, whereas the amount of calcium increased with the increasing of HA concentration, but all above the amounts without addition. Finally, the change of pH before and after adsorption process is studied. In the two different solutions including HA alone and HA doped Ca²⁺, pH had a small rise, but the extent of pH of later solution was bigger.     

Effect of sorbed and desorbed Zn（II） on the growth of a green alga （ Chlorella pyrenoidosa）

Toxic effect of Zn（II） on a green alga （Chlorella pyrenoidosa） in the presence of sepiolite and kaolinite was investigated. The Zn-free clays were found to have a negative impact on the growth of C. pyrenoidosa in comparison with control samples （without adding any clay or Zn（II））. When Zn（II） was added, the algae in the presence of clays could be better survived than the control samples, which was actually caused by a decrease in Zn（II） concentration in the solution owing to the adsorption of Zn（II） on the clays. When the solution system was diluted, the growth of algae could be further inhibited as compared to that in a system which had the same initial Zn（II） concentration as in the diluted system. This in fact resulted from desorption of Zn（II） from the zinc-contaminated clays, although the effect varied according to the different desorption capabilities of sepiolite and kaolinite. Therefore the adsorption and desorption processes of Zn（H） played an important part in its toxicity, and adsorption and desorption of pollutants on soils/sediments should be well considered in natural eco-environmental systems before their risk of toxicity to aquatic organisms was assessed objectively.     

Behavior of the herbicide dimepiperate with homoionic clays in aqueous solution

Ｂｅｈａｖｉｏｒｏｆｔｈｅｈｅｒｂｉｃｉｄｅｄｉｍｅｐｉｐｅｒａｔｅｗｉｔｈｈｏｍｏｉｏｎｉｃｃｌａｙｓｉｎａｑｕｅｏｕｓｓｏｌｕｔｉｏｎ￥ＬｉｕＷｅｉｐｉｎｇ；ＷａｎｇＱｉｑｕａｎ；ＳｈａｏＹｉｎｇ；ＪｉＪｉｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉ...     

Adsorption of herbicide triclopyr on homoionic clays

ＡｄｓｏｒｐｔｉｏｎｏｆｈｅｒｂｉｃｉｄｅｔｒｉｃｌｏｐｙｒｏｎｈｏｍｏｉｏｎｉｃｃｌａｙｓＬｉｕＷｅｉｐｉｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉｓｔｒｙ，ＺｈｅｊｉａｎｇＵｎｉｖｅｒｓｉｔｙ，Ｈａｎｇｚｈｏｕ３１００２７，Ｃｈｉｎａ）ＡｌｂａＰｕ...     

Adsorption and desorption of herbicide monosulfuron-ester in Chinese soils

Monosulfuron-ester is a new, low rate, sulfonylurea herbicide that is being promoted for annual broadleaf and gramineal weed control; however, there is a lack of published information on its behavior in soils. The adsorption and desorption of monosulfuronester by seven type soils were measured using a batch equilibrium technique. The results showed that the Freundlich equation fitted its adsorption and desorption well, and the Freundlich constant values (Kf-ads) ranged from 0.88 to 5.66. Adsorption isotherms were nonlinear with 1/nf-ads values < 1. Soil pH, organic matter (OM), and clay content were the main factors influencing its adsorption and desorption. Adsorption and desorption were negatively correlated with pH 4.0–8.0 while positively correlated with OM and clay content. The adsorption of monosulfuron-ester was mainly a physical process, because its free energy (ΔG) in seven soils was less than 40 kJ/mol. Monosulfuron-ester adsorption by three soils increased with increasing CaCl2 concentration using CaCl2 as a background electrolyte. Monosulfuron-ester desorption was hysteretic in all tested soils.     

新农药HW-02在土壤中的吸附

采用振荡平衡法研究了新型除草剂HW-02在5种不同土壤中的吸附特性. 结果表明:土壤对HW-02的吸附性强;HW-02在黑钙土、白浆土、草甸土、砂性土和黏壤土等5种土壤中的吸附可用Freundlich等温式较好地描述,其吸附系数(K_F)分别为332.65,103.32,672.97,577.96和289.60,吸附自由能变绝对值(ΔG)分别为16.55,22.73,18.32,18.48和22.86 kJ/mol,说明HW-02在土壤中的吸附以物理吸附为主;HW-02在5种土壤中的有机质吸附常数(K_OM)为796.57～10 197.18,说明其在土壤中迁移性很弱. HW-02在土壤中的吸附系数与土壤w(有机质),pH和w(黏粒)相关性较好,而与阳离子交换量(CEC)的相关性差,说明土壤w(有机质),w(黏粒)和pH是影响HW-02在土壤中吸附的主要因素.      

灭草松在腐殖酸上的吸附及其机理

通过吸附动力学、吸附等温线和IR，ESR技术，研究了腐殖酸对灭草松的吸附及吸附机理，并且对pH、离子强度对吸附过程的影响进行了探讨。结果表明灭草松在腐殖酸上经过大约4h的初始快速阶段，此后进入慢速吸附过程。溶液pH可能会影响腐殖酸的构型。高pH时，吸附量随溶液离子强度增加稍有增加。灭草松在腐殖酸上的吸附过程中存在氢键、电荷转移作用，疏水分配也是可能存在的机理。