Effect of the simultaneous addition of beta-cyclodextrin and the herbicide norflurazon on its adsorption and movement in soils

The effects of beta-cyclodextrin (BCD) on the sorption-desorption and transport processes of the herbicide norflurazon (NFL) in soils of different characteristics when both are applied simultaneously have been investigated. Adsorption-desorption studies of NFL on six soils of very different characteristics in the presence of BCD have been performed using a batch equilibration method and correlated to its mobility in homogeneous hand-packed soil columns. NFL determinations were undertaken by HPLC equipped with a diode array detector at a wavelength of 220 nm. BCD was also analyzed by HPLC with fluorimetric detection using a postcolumn reaction. The interaction of NFL with BCD yielded the formation of an inclusion complex in solution. When this complex is applied to soils, a large decrease in NFL adsorption capacity and an increase in its desorption were observed, due to the higher tendency of NFL-BCD complexes to remain in solution. The results obtained in adsorption and soil column experiments indicated that the influence of BCD on NFL mobility and availability depends on the different affinities of BCD to be sorbed on soils of different characteristics and on the concentration of BCD used. The lower the concentration of BCD added, the more tenaciously it adheres to the soil, and most of the BCD molecules would be adsorbed, providing a coating to soil particles that acts as a bridge between NFL and the soil surface, acting as an adsorbent and retarding the mobility of the herbicide. At higher concentrations of BCD, or in soils where its adsorption is very low, most of the BCD molecules are in the aqueous phase and NFL molecules tend to be complexed with BCD in solution, acting then as a solubilizing agent.     

Influence of pH and soil copper on adsorption of metalaxyl and penconazole by the surface layer of vineyard soils

The upper horizons of old vineyard soils have substantial copper contents due to the traditional use of copper-based fungicides. Total copper levels in eight vineyard soils in the Rías Baixas area of Galicia (northwestern Spain) ranged from 60 to 560 mg kg(-1) (mean +/- SD = 206 +/- 170 mg kg(-1)). The adsorption of the fungicides metalaxyl (pK(a) = 1.41) and penconazole (pK(a) = 2.83) by these soils was determined using fungicide solutions of pH 2.5 and 5.5, and desorption of fungicide adsorbed at pH 5.5 was also determined. In all cases, Freundlich equations were fitted to the data with R (2) > 0.96. Penconazole was adsorbed and retained more strongly than metalaxyl, with K(F) values more than an order of magnitude greater. In the desorption experiments, both fungicides exhibited hysteresis. Soil copper content hardly affected the adsorption of metalaxyl, but K(F) values for adsorption of penconazole increased at a rate of about 0.1 mL(n) (microg of penconazole)(1-n) (microg of Cu)(-1), which is attributed to the formation of Cu(2+)-penconazole complexes with greater affinity for soil colloids than penconazole itself. Because the dependence of K(F) for penconazole adsorption on copper content was the same at both pH values, complex formation appears not to have been affected by the solubilization of 6-17% of soil copper at pH 2.5. A similar copper dependence, or lack of dependence, was observed when 100-1000 mg kg(-1) of copper was added as Cu(NO(3))(2).2H(2)O to the solutions from which the fungicides were adsorbed.     

Adsorption und Desorption von Methabenzthiazuron in verschiedenen Böden

Adsorption and desorption of methabenzthiazuron in various soils A method investigating adsorption and desorption of pesticides using radioactive tracers and a computer programme is described. The adsorption and desorption of the herbicidal substance methabenzthiazuron in 7 soil samples is investigated. The adsorption of methabenzthiazuron decreases from the A_p- to the C-horizons. A good correlation exists between the adsorbed amount of the herbicidal substance and the C- and N-content of the soils. The relatively highest desorption was found with nearly humusfree soils. The amount of adsorbed herbicide residues, not desorbable by water in 5 desorption cycles, is much higher in the humic soils than in the nearly humusfree soils. From the relationship found between adsorption and corresponding herbicide concentrations proper adsorption values can be predicted for any herbicide concentration within the investigated concentration range by using one single adsorption measurement as a basis of calculation.     

甲硫嘧磺隆在土壤中的吸附和解吸特性研究

Methiopyrsulfuron is a new low-rate sulfonylurea herbicide for weed control in wheat; however, there is a lack of published information on its behavior in soils. In this study, methiopyrsulfuron adsorption and desorption were measured in seven soils sampled from Heilongjiang, Shandong, Jiangxi, Sichuan, Anhui, and Chongqing provinces of China using a batch equilibrium method. The Freundlich equation was used to described its adsorption and desorption. Adsorption isotherms were nonlinear with the values of Kf-ads, the Freundlich empirical constant indicative of the adsorption capacity, ranging from 0.75 to 2.46, suggesting that little of this herbicide was adsorbed by any of the seven soils. Soil pH and organic matter content (OM) were the main factors influencing adsorption; adsorption was negatively correlated with pH and positively correlated with OM. Methiopyrsulfuron desorption was hysteretic on the soils with high OM content and low pH.     

Adsorption-desorption of atrazine on four soils of Hyderabad

The adsorption-desorption equilibrium of atrazine (2-chloro, 4-ethylamino, 6-isopropyl amino-1, 3, 5 triazine) was studied by the batch equilibration method at 27 ± 1 °C on four soils of Hyderabad. Adsorption isotherms conformed to the Freundlich equation (A = KC^1/n ). K increased in the same order as the organic C content of the soils. Desorption studies were conducted by repeated replacement of 5 mL of the supernatant equilibrium solutions after adsorption, with 0.01 M CaCl₂. Desorption isotherms showed considerable hysteresis which was more prominent when the desorption was carried out with higher adsorbed concentration of atrazine. Desorption from the lowest level of adsorbed atrazine (3 to 5 μg g^?1 soil) was close to the adsorption isotherm. The cumulative desorption after four desorption steps covering five days was significantly different at the 1% level, for different initial adsorbed concentrations of atrazine. Desorption was significantly higher at the lowest adsorbed level of atrazine. The soils differed significantly at 6% level for desorption and the amount desorbed decreased in the inverse order of organic C. Desorption isotherms also conformed to Freundlich equation but K andn values were both higher than that for adsorption and increased with increase in initially adsorbed concentration of atrazine. Desorption thus confirmed the irreversible nature of the adsorption of atrazine on these soils. The quantitative factors and reasons for desorption are discussed.     

恒电荷土壤及可变电荷土壤与离子间相互作用的研究 I.共存离子对NO_3~-吸附的影响

研究了我国典型３种可变电荷土壤和４种恒电荷土壤在陪伴阳离子分别为Ｋ十、Ｎａ十、Ｃａ２＋时和１ｍｍｏｌＬ－１ＫＣ１、Ｋ２ＳＯ４支持电解质中ＮＯ３－的吸附。结果表明，ＮＯ３－吸附量随ｐＨ的增加而减小。在添加相同浓度ＮＯ３－时，３种可变电荷土壤对ＮＯ３－的吸附量顺序为Ｃａ（ＮＯ３）２＞ ＫＮＯ３＞ＮａＮＯ３＞ＫＮＯ３十ＫＣＩ＞ＫＮＯ３＋Ｋ２ＳＯ４；在初始ＮＯ３－浓度０．５－５ｍｍｏｌＬ－１的范围内，吸附量随浓度变化的关系符合Ｌａｎｇｍｕｉｒ等温吸附式．由此求出与ＮＯ３－吸附结合能有关的常数（Ｋ）在不同共存离子存在下数值较小且差异不大，因此认为不同陪伴阳离子和不同伴随阴离子对ＮＯ３－吸附的电性机理影响不大，只是改变了土壤表面的正电荷数量从而使吸附量发生变化。４种恒电荷土壤对ＮＯ３－的吸附量通常很小，其中在Ｃａ（ＮＯ３）２介质中较在其他介质中稍大，最大吸附量仅为１．５～ｍｍｏｌ ｋｇ－１左右，约为可变电荷土壤的１／１０，且在浓度较低时常观察到负吸附。     

Mutual Influence of Cu and a Cationic Herbicide on Their Adsorption-Desorption Processes on Two Selected Soils

Adsorption of Cu and the cationic herbicide chlordimeformwas carried out on two acidic soils (S-48 and LM).Chlordimeform adsorption occurred by cationic exchange andwas higher on LM soil due to its higher CEC, partlyassociated to the presence of vermiculite. Cu adsorptionwas also higher on LM soil and was related to its higheriron and manganese oxides content. The presence of theherbicide in solution always decreased Cu adsorption on S-48 soil, but on LM soil the amount of Cu adsorbed onlydecreased at the highest concentrations used. This togetherwith the lower amounts of Cu desorbed from LM soil afterfive successive desorptions in comparison to S-48 soil,indicates that Cu was being mostly adsorbed on oxides whichexhibit a very high affinity for the heavy metal. Themaximal amount of Cu desorbed on both soils only reached upto 13% of the amount adsorbed. Chlordimeform adsorption decreased in the presence of Cu as aresult of its competition for the adsorption sites on bothsoils. Cu competition on LM soil was not so strong as on S-48 soil due to the higher adsorption of the heavy metal onoxides, for which the herbicide’s affinity is not so high. Thelower the amounts of chlordimeform adsorbed on both soilsthe higher its desorption percentage. This was attributedto steric impediment of chlordimeform molecule itself forthe desorption from lamellar silicates.     

Adsorption and desorption of triasulfuron by soil

The adsorption and desorption of the herbicide triasulfuron [2-(2-chloroethoxy)-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide] by three soils, soil organic matter (H(+) and Ca(2+)-saturated), and an amorphous iron oxide were studied. Adsorption isotherms conformed to the Freundlich equation. It was found that pH is the main factor influencing the adsorption in all of the systems. Indeed, the adsorption on soils was negatively correlated with pH. The highest level of adsorption was measured on soils with low pH and high organic carbon content. Moreover, it was found that humic acid is more effective in the adsorption compared with calcium humate (the pH values of the suspensions being 3.5 and 6, respectively). Experiments on amorphous iron oxide confirmed the pH dependence. Desorption was hysteretic on soils having high organic carbon content.     

Adsorption and desorption of imazosulfuron by soil

Understanding and quantifying the adsorption and desorption of herbicides by soil is important for predicting their fate and transport in the environment. Here we report a study concerning the adsorption and desorption, by four different soils, of imazosulfuron, 1-(2-chloroimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4, 6-dimethoxypyrimidin-2-yl)urea, a new sulfonylurea herbicide. Both phenomena are well-described by the Freundlich equation, which shows this herbicide to be little adsorbed by each of the four soils investigated. The Freundlich adsorption constants, K(f-ads), ranged from 1.46 to 3.02. Distribution coefficients between soil and water, Kd, measured on soils of different organic matter contents and pH values showed an important effect of these two parameters on imazosulfuron retention. The Freundlich desorption data indicated that a significant amount of the imazosulfuron sorbed is not easily desorbed. The desorption process showed an evident hysteresis phenomenon, which may contribute to the persistence of imazosulfuron in soil.     

Estimation of buffering capacity of mangrove soils by using hydrophobic organic compounds,atrazine and linuron

Samples of two soils and two sediments collected at sites originating from mangrove forests in Thailand, were examined in terms of buffering capacity to organic compounds. Atrazine and linuron were used as representative hydrophobic organic compounds for estimating the buffering capacity by observing their adsorptive and desorptive behavior. The buffering capacity could be represented by the distribution of the adsorption ratio (AR) and desorption ratio (DR) as follows: AR (%) = (amount of herbicide adsorbed per unit weight of soil)/(initial amount of herbicide) x 100, and DR (%) = (amount of herbicide desorbed per unit weight of soil after herbicide desorption experiments) / (initial amount of adsorbed herbicide on soil) x 100. The soil under mangrove forests displayed a larger buffering capacity to atrazine and linuron. Compared with 42 soils from Japan, in terms of the adsorption proparty of atrazine and linuron, the mangrove soil ranked in a higher category on the classification of the Japanese soils. Thus, the importance of maintaining or recovering the mangrove forests to promote environmental conservation was emphasized.     

Influence of copper on the adsorption and desorption of paraquat, diquat, and difenzoquat in vineyard acid soils

Retention of the cationic herbicides paraquat (PQ), diquat (DQ), and difenzoquat (DFQ) in two vineyard soils with a different management history and retention capacity was examined. The influence of copper on the ability of the soils to retain the herbicides was determined by comparing the results of adsorption and desorption tests on untreated and Cu-enriched soil samples, and also on soils that were previously treated with EDTA to extract native copper. The three herbicides were strongly adsorbed by both soils. Soil 1 exhibited linear adsorption isotherms for PQ and DFQ with partition coefficients, KD, of 1.28 x 103 and 1.37 x 103 L kg-1, respectively, and a Freundlich-type isotherm for DQ with a linearized partition coefficient, KD*, of 1.01 x 103 L kg-1. On the other hand, soil 2 exhibited curved isotherms and smaller KD* values (viz. 106, 418, and 28 L kg-1 for PQ, DQ, and DFQ, respectively). Using EDTA to extract copper from the soils released new sites for the herbicides to bind. The three herbicides exhibited strong hysteresis in the adsorption-desorption process. Extracting copper decreased the percent desorption of PQ and DQ; on the other hand, it decreased the affinity of DFQ for the resulting vacant adsorption sites. Similarly, competitive adsorption tests with copper and the herbicides revealed that the metal was only capable of displacing DFQ from adsorption sites. The behavior of this herbicide in the soils was consistent with a specific adsorption model. The disparate behavior of the two soils toward the herbicides was a result of the adsorption sites in soil 1 being less extensively occupied than those of soil 2 in the adsorption tests. The effect of copper on the adsorption of DFQ in the two soils was acceptably reproduced by an adsorption model involving Coulombic and specific sorption with competition from the metal.     

Effect of soil type on adsorption-desorption, mobility, and activity of the herbicide norflurazon

Adsorption-desorption studies of norflurazon on 17 soils of very different characteristics have been performed using a batch equilibration method and correlated to its mobility, activity, and persistence in soils. The influence of different soil properties and components on norflurazon adsorption was determined. The significant variables were organic matter (OM) content and iron and aluminum oxides, which accounted for 85 and 11% of the variability, respectively. Norflurazon desorption from soils was hysteretic in all cases, being more irreversible at the lowest herbicide concentrations adsorbed. The percentage of norflurazon eluted from columns of selected soils reached almost 100% in soils with sand content >80% and OM <1%, but in the soil which gave the highest sorption, herbicide residues were not detected at depths >16 cm. The herbicidal activity of norflurazon was followed by measuring its bleaching effect on soybean plants, and the herbicide concentration required to give 50% chlorophyll inhibition (CI(50)) was calculated. CI(50) was achieved on a sandy soil with 0.08 mg x kg(-)(1), whereas 1.98 mg x kg(-)(1) was necessary for the soil that presented maximum norflurazon adsorption.     

Adsorption,desorption and extractability of Zn in some Algerian soils under orange cultivation

The Zn adsorption/desorption in some Algerian soils, which are under orange cultivation, was studied and the results obtained were analyzed using Langmuir equation. The maximum amount of Zn adsorbed, in majority of cases, varies between 60 and 80 % of the cation exchange capacity. As regards sequential desorption, the EDTA desorbed about 80 %of the Zn adsorbed, whereas, the desorption through 1 N KCI averaged about 15 % only. The adsorption maximum (Sm) and desorption maximum (Rm) correlate significantly with various soils properties, like clay content, cation exchange capacity and pH. The calculation of distribution coefficient (Kd) and adsorption density of Zn (r) indicates that the metal above 2.5 · 10 ions/m2 is adsorbed through ion exchange, whereas below this value, the ion is most possibly adsorbed due to specific adsorption mechanisms.     

菜园土壤锌的吸附——解吸特性研究

本文研究了菜园土壤锌的吸附 -解吸特性。实验结果表明 ,三种菜园土壤吸附Zn2 + 均随平衡液中Zn2 + 浓度的增加而增大 ,且均可用Langmuir方程和Freundlich方程来描述 ,相关系数均大于 0 .9,达极显著水平。由Langmuir方程求得的菜园土壤对Zn2 + 的最大吸附量的大小顺序为 :黄松土 >粉泥土 >江涂砂 ,但对Zn2 + 的吸附作用力强度和最大缓冲容量的顺序则相反 ,以江涂砂 >粉泥土 >黄松土。菜园土壤对Zn2 + 的解吸量随其吸附量的增加而增加 ,两者之间呈显著线性正相关。     

Adsorption and desorption of organotin compounds in organic and mineral soils

Organotin compounds (OTC) are deposited from the atmosphere into terrestrial ecosystems and can accumulate in soils. We studied the adsorption and desorption of methyltin and butyltin compounds in organic and mineral soils in batch experiments. The adsorption and desorption isotherms for all species and soils were linear over the concentration range of 10–100 ng Sn ml^?1. The strength of OTC adsorption correlated well with the carbon content and cation exchange capacity of the soil and was in the order mono‐ > di‐ > tri‐substituted OTCs and butyltin > methyltin compounds. The OTC adsorption coefficients were much larger in organic soils (K_d > 10⁴) than in mineral soils. The adsorption and desorption showed a pronounced hysteresis. Trimethyltin adsorption was partly reversible in all soils (desorption 2–12% of the adsorbed amounts). Dimethyltin, tributyltin and dibutyltin exhibited reversible adsorption only in mineral soils (desorption 4–33% of the adsorbed amounts). Mono‐substituted OTCs adsorbed almost irreversibly in all soils (desorption < 1% of adsorbed amounts). Trimethyltin was more mobile and more bioavailable in soils than other OTCs. It might therefore be leached from soils and accumulate in aquatic ecosystems. The other OTCs are scarcely mobile and are strongly retained in soils.     

不同磷浓度处理暗棕壤对Zn2+吸附解吸行为的研究

通过等温吸附试验,研究不同磷含量处理暗棕壤对Zn2+的吸附解吸行为,结果表明:(1)随平衡液中Zn2+浓度的增加,3种处理暗棕壤对Zn2+的吸附作用均表现为:低浓度下(0～100 mg/L),吸附量增加迅速,随着浓度升高(100～150 mg/L),吸附量变缓并渐趋平衡,含磷量高的土壤吸附Zn2+的量较高。(2)Freundlich、Langmuir和Temkin方程均能很好描述Zn2+在3种不同磷含量暗棕壤上的吸附等温线,拟合效果依次为Freundlich>Langmuir>Temkin。经参数计算,较高磷含量有利于提高暗棕壤的最大吸附量和土壤对Zn2+的缓冲容量,而磷含量不同对Zn2+在暗棕壤上的吸附力没有太大影响。(3)3种不同磷含量处理暗棕壤吸附量与解吸量关系图形状相似,呈高度线性相关,均表现为暗棕壤对Zn2+的解吸量随吸附量的增加而增加,磷含量较高土壤有利于Zn2+的固定且不易解吸。     

Adsorption of Acrylonitrile on Some Soils and Minerals from Aqueous Solutions

Equilibrium and kinetic studies have been made on the adsorption of acrylonitrile(CH2=CHCN) on three soils and four minerals from aqueous solutions.It was shown that the organic matter was the major factor affecting the adsorption process in the soils.The conformity of the equilibrium data to linear type(one soil) and Langmuir type(two soils) isotherms indicated that different mechanisms were involved in the adsorption.This behavior appears bo be related to the hydrophobicity of soil organic matter due to their composition and E4/E6 ratio of humic acids.The adsorption kinetics were also different among the soils,indicating the difference in porosity of organic matter among the soils,and the kinetics strongly affected the adsorption capacity of soils for acrylonitrile.Acrylonitrile was slightly adsorbed from aqueous solutions on pyrophyllite with electrically neutral and hydrophobic nature,and practically not on montmorillonite and kaolinite saturated with Ca.However,much higher adsorption occurred on the zeolitized coal ash,probably caused by high organic carbon content(107g/kg).     

甘草根瘤菌CCNWGX035的抗逆特性及结瘤特征研究

Thirty-nine rhizobial isolates were isolated from the root nodules of Glycyrrhiza uralensis and Glyeyrrhiza glabra, growing in the arid and semiarid regions of northwestern China, to test their taxonomic position and stress tolerance and to select one promising putative inoeulant strain for further studies. On the basis of 113 physiological and biochemical characteristics, the isolates were clustered into three groups. One isolate CCNWGX035 was found to have high tolerance to NaC1, pH, and temperature. By sequencing the 16S rDNA, isolate CCNWGX035 was placed in genus Mesorhizobium. Nodulation tests demonstrated that the isolate not only formed nitrogen-fixing nodules on its original host plant Glyeyrrhiza glabra, but also on Sophora vieiifolia, Lotus cornieulatus, Trifolium repens, Melilotus suaveolens, and Sophora alopecuroides. On the basis of sequence analysis of the nodA gene, isolate CCNWGX035 was closely related to strains of the genus Mesorhizobium, exhibiting some novel characteristics of root nodule bacteria.     

Ionic-strength and pH effects on the sorption of cadmium and the surface charge of soils

Two Oxisols (Mena and Malanda), a Xeralf and a Xerert from Australia and an Andept (Patua) and a Fragiaqualf (Tokomaru) from New Zealand were used to examine the effect of pH and ionic strength on the surface charge of soil and sorption of cadmium. Adsorption of Cd was measured using water, 0.01 mol dmp^?3 Ca(NO₃)₂, and various concentrations of NaNO₃ (0.01–1.5 mol dm^?3) as background solutions at a range of pH values (3–8). In all soils, the net surface charge decreased with an increase in pH. The pH at which the net surface charge was zero (point of net zero charge, PZC) differed between the soils. The PZC was higher for soils dominated by variable-charge components (Oxisols and Andept) than soils dominated by permanent charge (Xeralf, Xerert and Fragiaqualf). For all soils, the adsorption of Cd increased with an increase in pH and most of the variation in adsorption with pH was explained by the variation in negative surface charge. The effect of ionic strength on Cd adsorption varied between the soils and with the pH. In Oxisols, which are dominated by variable-charge components, there was a characteristic pH below which increasing ionic strength of NaNO₃ increased Cd adsorption and above which the reverse occurred. In all the soils in the normal pH range (i.e. pH>PZC), the adsorption of Cd always decreased with an increase in ionic strength irrespective of pH. If increasing ionic strength decreases cation adsorption, then the potential in the plane of adsorption is negative. Also, if increasing ionic strength increases adsorption below the PZC, then the potential in the plane of adsorption must be positive. These observations suggest that, depending upon the pH and PZC, Cd is adsorbed when potential in the plane of adsorption is either positive or negative providing evidence for both specific and non-specific adsorption of Cd. Adsorption of Cd was approximately doubled when Na rather than Ca was used as the index cation.