Improvement of the desorption of the herbicide norflurazon from soils via complexation with beta-cyclodextrin

The effect of beta-cyclodextrin (beta-CD) on the removal of the herbicide norflurazon (NFL) from soils has been investigated. The interaction of NFL with beta-CD in solution yielded the formation of a water-soluble inclusion complex at 1:1 stoichiometric ratio, which gave an increase in NFL solubility. Desorption studies of NFL previously adsorbed on six soils of different characteristics have been performed in the presence of 0.01 M beta-CD or 0.01 M Ca(NO(3))(2) as extractant solutions. Positive hysteresis was observed in all soils when 0.01 M Ca(NO(3))(2) solution was used, indicating that desorption of NFL from these soils was not completely reversible. On the contrary, the application of beta-CD solutions to soils where NFL had been previously adsorbed increased very much its desorption, and a negative hysteresis was obtained for all soils studied; that is, more NFL was desorbed with respect to NFL adsorption isotherm. A clear relationship was observed between the physicochemical characteristics of the soils and the beta-CD concentration necessary to remove the herbicide, the percentages of desorption observed for each soil being inversely related to the values obtained for the Freundlich sorption capacity parameter of the herbicide, K(f). In general, high desorption yields can be obtained with very low beta-CD concentrations, which is an important advantage from an economic point of view, although in those soils that present an extremely high NFL adsorption, higher amounts of beta-CD should be used. The results obtained indicate the high extracting power of beta-CD toward the herbicide previously adsorbed on the soils and the potential use of beta-CD for in situ remediation of pesticide-contaminated soils.     

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.     

Influence of soil properties on the adsorption and mobility of metamitron

Abstract

The adsorption and mobility of herbicide, metamitron, in 41 soils samples from the province of Salamanca (Spain) was studied. Thirty‐four of the samples assayed were from irrigated soils and seven were from natural, uncultivated soils with organic matter contents above 3%. The correlations between the Freundlich K constants, Kd distribution coefficients, and Rf mobility parameters and the soils parameters were determined. Considering all the soils, the soils with organic matter contents above 2% or the soils with organic matter contents below 2%, significant correlations (p<0.001 to p<0.05) were found between K and Kd and the organic matter content of the soils. There were also a significant correlations (p<0.05) of K and Kd with clay+silt and clay contents of soils with organic matter contents below 2%. The adsorption of the herbicide by isolated soil components confirmed the results obtained with the soils and point to the importance of the exchangeable cation nature of the samples in the adsorption process. Based on Rf values obtained by TLC, the herbicide was found to be moderately mobile in 74% and mobile in 26% of the soils studied. The results of metamitron leaching by thin layer chromatography (TLC) and in undisturbed soil columns indicated the influence of organic matter content and of soil texture on the mobility of this herbicide.     

Adsorption density,mobility and limit values of Cd,Zn, Cu and Pb in acid forest soils

To investigate Cd, Zn, Cu and Pb adsorption in acidified forest soils, six soil samples of the aluminium buffer range were selected and analyzed for their physical and chemical properties. Determination of the specific surface area using ethylene glycol monoethyl ether (EGME) adsorption yielded a characteristic value of the solid phases, which can parameterize the major properties of the various soil constituents with sufficient accuracy.

Traditional adsorption isotherms reveal the relation between the amount of a heavy metal adsorbed and the heavy metal concentration in the soil solution only for the soil under study and can therefore not be applied to other soils. To meet the aim of modelling heavy metal adsorption and mobility also for soils differing greatly in their properties, it was attempted to establish a generalizing adsorption isotherm for soils of entirely different composition of the solid phase. The generalizing adsorption density isotherms introduced in the following provide a useful mathematical model for the quantity/intensity relation of heavy metals in soils that differ greatly in their specific surface area and their composition.

It is also shown that limit values which take into account the major quantities influencing heavy metal adsorption and mobility in acid soils can be established from the regression equation between the adsorption density of a heavy metal (ions/m² specific surface area) and its concentration in the soil solution. In particular in view of the groundwater contamination to be expected if acid rain and, as a result, soil acidification continues, these limit values seem to provide considerably more information than the European limit values, given in mg heavy metal /kg soil, which are presently valid for any soil condition and property.     

Effect of organic amendments on the retention and mobility of imazaquin in soils

The influence of two organic amendments consisting of an urban waste compost (SUW) and a commercial amendment from olive mill wastes (OW) was assessed on the sorption properties and leaching of the ionizable herbicide imazaquin on four soils with different physicochemical characteristics. A loamy sand soil (CR), a loam soil (P44), a silt loam soil (AL), and a clay soil (TM), with low-medium organic matter contents, were chosen. Sorption-desorption experiments were performed on the original soils and on a mixture of these soils with the organic amendments at a rate of 6.25% (w/w). These mixtures were used just after preparation and after aging for 3 months. Imazaquin adsorption was higher on AL soil because of its high content of amorphous iron oxides, whereas it was related to the soils' organic matter (OM) contents on TM and CR soils and to acid pH on P44 soil. Addition of exogenous OM to soils caused a decrease in the adsorption of the herbicide with the only exception of CR soil, due to blocking of adsorptive surfaces and/or equilibrium pH rise. The extent of this decrease was dependent only on the nature of the added amendment on AL soil. The adsorbed amounts of imazaquin on aged organic fertilized soils were usually fairly close to that on original soils. Results of soil column experiments indicate that addition of exogenous organic matter cannot be considered as a regular practice for retarded movement of imazaquin.     

Ethylcellulose formulations for controlled release of the herbicide alachlor in a sandy soil

The development of controlled-release formulations of alachlor to diminish its leaching in sandy soils, avoiding groundwater contamination and maintaining its efficacy, was studied. For this purpose, ethylcellulose (EC) microencapsulated formulations (MEFs) of alachlor were prepared under different conditions and applied to soil columns to study their mobility. The results show that in all cases the release into water of alachlor from MEFs was retarded when compared with commercial formulation. Total leaching losses in soil columns were reduced to 59% from 98%. The mobility of alachlor from EC microspheres into soil columns has been greatly diminished in comparison with its current commercial formulation (CF), above all with increasing EC/herbicide ratios. Distribution of alachlor applied as MEFs at different depths in the soil was higher in the soil surface (66.3-81.3% of herbicide applied at the first 12 cm). In contrast, the residues from CF along the complete soil column were only 20.4%. From the results of bioassays, MEFs showed a higher efficacy than CF at 30 days after the treatment. The use of ME formulations could provide an advantage in minimizing the risk of groundwater contamination by alachlor and reducing the application rates, as a result of maintaining the desired concentration of the herbicide in the top soil layer, obtaining longer periods of weed control.     

动物粪液中可溶性磷在土壤中的吸附和迁移特性研究

农田土壤施用动物粪肥引入了大量的可溶性有机物、有机磷和无机磷,了解这些可溶性物质在土壤中的相对移动性及它们之间的相互作用有助于指导农田养分管理。本研究从粪液中分离获得含水溶性无机磷、有机磷和有机物（碳）的溶液,选择了具不同质地和有机质含量的4个土壤（含高量有机质的黄筋泥、含低量有机质的黄筋泥、淡涂泥和清水沙）,应用等温吸附和土柱模拟淋洗方法研究了可溶性有机碳、无机磷和有机磷共存条件下,粪液中可溶性有机态磷和无机态磷在土壤中的吸附和迁移特性。吸附试验表明,可溶性有机物（碳）的存在大大降低了土壤对有机态磷和无机态磷的吸附,表明施用液态有机肥比施用化肥具有更大的磷流失风险。供试土壤对无机态磷的吸附强度高于有机态磷,但对二者的吸附量大小为:黄筋泥>淡涂泥>清水沙;并与粘粒含量、氧化铁含量呈正相关。有机质较高的土壤对有机磷的吸附明显低于有机质低的土壤。淋洗试验表明,在供试土壤中,这3种可溶性物质在土壤中吸持(包括生物吸持)的顺序为:可溶性无机磷>可溶性有机碳>可溶性有机磷;有机态磷比无机态磷更易在土壤中迁移。     

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.     

Soil moisture and the rates of biodegradation of diallate and triallate

Degradation experiments were combined with biomass measurements and adsorption tests to determine how soil moisture content influences the rates of degradation of ⁴¹C-labelled diallate and triallate. In soils treated with 1 μg^?1 herbicide and incubated at constant temperature and moisture, degradation rates were regulated by two variables: the quantity of microbial biomass in the soil; and the quantity of herbicide dissolved in the soil solution. The quantity of biomass was influenced by soil water content and the duration of incubation. The amounts of herbicide in solution were determined by the amount of water present and the total quantity of herbicide in the soil. In all soil samples, the rates of degradation increased with increasing water content but decreased with prolonged incubation. The factors responsible for decrease with time were the loss of biomass during incubation and the decline in herbicide concentration in the soils as degradation proceeded.     

新农药哌虫啶在三种典型土壤中的吸附与淋溶研究

应用振荡平衡法和柱淋洗法研究了哌虫啶在红壤、棕壤和黑土3种典型土壤中的吸附和淋溶特性,并探讨了3种土壤改良剂对其淋溶的影响。结果表明:哌虫啶在黑土、红壤和棕壤中的吸附平衡时间分别为12、12和9 h,分配系数Kd分别为23.16、11.24和4.68,吸附常数Kf分别为22.03、11.69和5.05,KOC值分别为1 619、2 094和495,吸附自由能值分别为-16.96、-17.59和-14.02 k J mol-1,Freundlich和线性等温吸附模型均能较好地描述哌虫啶在土壤中的吸附过程,其吸附能力顺序分别为黑龙江黑土福建红壤山东棕壤。哌虫啶在3种供试土壤中淋溶性存在差异,在棕壤中迁移性最强,随着施药量的增加,其淋出率也略有提高,但3个不同水平施药量差异不显著。在黑土中迁移性最弱,红壤和黑土中的哌虫啶残留量随着土壤深度的增加逐渐降低。土壤中添加0.5%的活性炭、腐殖酸和草炭能显著地降低农药哌虫啶在土壤中的淋溶性,减少对地下水的污染风险。     

Effect of acid deposition on the displacement of Al(III) in soils

This study represents an assessment of some of the key factors influencing the mobility of Al(III) and its displacement in acid soils. This assessment is based on the effect of pH and other solution variables on the solubility of Al(III) and its complex formation with OH^?, F^? and organic ligands (fulvates and humates). Above all, the adsorption behavior of Al(III) on iron(III) (hydr)oxides and on SiO₂ on one hand, and the adsorption of organic acids and of humic substances on mineral surfaces on the other hand was investigated. Adsorption is interpreted in terms of surface complex formation equilibria; the mass law constants derived permit the modeling of adsorption as a function of solution variables. It is illustrated that the distribution of oxides and hydroxides in the soil profile affects the pH buffering, determines the mobility of the organic acids while the mobility of Al(III) is primarily governed by the formation and dissolution of Al(III) (hydr)oxides.     

不同添加剂对土壤中乙草胺吸附／解吸的影响

采用批处理恒温振荡法,利用气相色谱一质谱联用仪研究了人工添加不同吸附物质对土壤中乙草胺的吸附／解吸作用。结果表明,人工添加不同吸附物质对土壤中乙草胺的吸附强度和吸附容量不同,不同的添加剂对土壤中乙草胺的吸附／解吸作用均呈现明显的非线性关系,可用Freundlich模型描述。并且随着土壤中添加量的增大,吸附强度增大、吸附容量增大、所得吸附等温线的非线性也逐步增大;另外,添加剂对乙草胺的解吸迟滞作用也随添加剂含量的增高而更加明显。但是不同添加剂对土壤中乙草胺的吸附能力有明显差异,其中煤粉的吸附能力最大,其次是壳聚糖,沸石最小。     

Adsorption,Desorption And Mobility of Fomesafen in Chinese Soils

Fomesafen, 5-[2-chloro-4-(trifluoromethyl)phenoxy]-N-(methylsulfonyl)-2-nitrobenzamide, is used widely for weed control in soybeans since its introduction to China. Little information is available on its adsorption, desorption and movement in Chinese soils. The adsorption, desorption and mobility of fomesafen in six Chinese soils was studied. Adsorption isotherms agreed with the Freundlich equation very well. The results of regressionanalysis indicated that soil pH was more important than organic matter for fomesafen adsorption. Fomesafen was more readily desorbed from soils with 0.01 M CaSO₄ solution. Soil TLC and column leaching studies showed that fomesafen and its metabolites was less mobile in Chinese soils. About 89.82% of applied fomesafen and its metabolites still remained in upper 5 cm layer 60 days after treatment under field conditions.     

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.     

Comparative sorption and leaching study of the herbicides fluometuron and 4-chloro-2-methylphenoxyacetic acid (MCPA) in a soil amended with biochars and other sorbents

Biochar, the solid residual remaining after the thermochemical transformation of biomass for carbon sequestration, has been proposed to be used as a soil amendment, because of its agronomic benefits. The effect of amending soil with six biochars made from different feedstocks on the sorption and leaching of fluometuron and 4-chloro-2-methylphenoxyacetic acid (MCPA) was compared to the effect of other sorbents: an activated carbon, a Ca-rich Arizona montmorillonite modified with hexadecyltrimethylammonium organic cation (SA-HDTMA), and an agricultural organic residue from olive oil production (OOW). Soil was amended at 2% (w/w), and studies were performed following a batch equilibration procedure. Sorption of both herbicides increased in all amended soils, but decreased in soil amended with a biochar produced from macadamia nut shells made with fast pyrolysis. Lower leaching of the herbicides was observed in the soils amended with the biochars with higher surface areas BC5 and BC6 and the organoclay (OCl). Despite the increase in herbicide sorption in soils amended with two hardwood biochars (BC1 and BC3) and OOW, leaching of fluometuron and MCPA was enhanced with the addition of these amendments as compared to the unamended soil. The increased leaching is due to some amendments' soluble organic compounds, which compete or associate with herbicide molecules, enhancing their soil mobility. Thus, the results indicate that not all biochar amendments will increase sorption and decrease leaching of fluometuron and MCPA. Furthermore, the amount and composition of the organic carbon (OC) content of the amendment, especially the soluble part (DOC), can play an important role in the sorption and leaching of these herbicides.     

Leaching of imidazolinones in soils under a clearfield system

Herbicides with high mobility can leach to deeper layers of the soil and to contaminate underground aquifers. The potential of herbicide leaching in soil can be monitored by chromatography or bioassay methods. This study evaluated the leaching of imazethapyr, imazapic and its commercial mixture (imazethapyr + imazapic) in three tropical soils via a bioassay method. The herbicides were applied in a polyvinyl chloride column and an 80 mm rainfall was simulated. The bioindicator species sorghum (Sorghum vulgare) BRS 655 was sown. Imazethapyr, imazapic and the commercial herbicide mixture showed high leaching in the soils. The presence of imazethapyr and the commercial mixture was detected up to 25 cm deep in Haplic Plinthosol and Oxisol. Imazapic showed less leaching to tree soil, being found at depth 10–15 cm. The pH, texture and iron oxide amount levels affected herbicide leaching. The mobility of the herbicides imazethapyr and imazapic in the Haplic Plinthosol and the Oxisol at depth 25 cm indicates a high risk of groundwater contamination.     

Studies on the Complexes of Montmorines with Urea and its Derivatives

It is considered that the study of the complex formation of soil colloids with urea and its derivatives is important not only to reveal the adsorption mechanisms of those compounds, but also to give valuable suggestions for the synthesis of organic fertilizers. Montmorine, on the other hand, is one of major clay constituents of soil colloids from arable soil in Japan, and that gives greater influence to the physical and chemical properties of the soils than other clay minerals do. The complex formation of montmorine with organic substances have been intensively studied by soil scientists, mineralogists and colloid scientists. From the data reported up to now, it is presumed that there are four different mechanisms in the complex formation of montmorine with organic substances. The first is a Van der Waals adsorption, the second the ion exchange reaction of adsorbed cations with organic molecules, the third the polar bonding of exchangeabe cations with polaar organic molecules, and the last the covalent bond of clays and organic substances. In the complex formation of montmorine with urea and its derivatives, two or more mechanisms are expected at a time, in accordance with their structural characters.     

Effect of undesalted dissolved organic matter from composts on persistence, adsorption, and mobility of cyhalofop herbicide in soils

The effect of undesalted dissolved organic matter (DOM) extracted from composts on the degradation, adsorption, and mobility of cyhalofop herbicide in soils was studied. A paddy-field sediment poor in organic matter (OM), an OM-rich forest soil, and DOM from agroindustrial or municipal waste compost were used. DOM increased the cyhalofop-acid but not the cyhalofop-butyl solubility in water. The degradation of cyhalofop-butyl in the sediment was slow, giving cyhalofop-acid as the only metabolite, whereas in forest soil, the process was faster, and three byproducts were detected. Soil pretreatment with DOM did not modify the degradation pattern but only reduced the adsorption of cyhalofop-butyl by soil, whereas it increased the adsorption of cyhalofop-acid. Among the cationic components of DOM solutions, the potassium ion seems to be related to the increased adsorption of the cyhalofop-acid in both OM-poor and OM-rich soils, yielding reversible complexes with the former and favoring hydrophobic interactions with the latter.     

Sorption-desorption of indaziflam in selected agricultural soils

Indaziflam, a new alkylazine herbicide that inhibits cellulose biosynthesis, is under current development for soil applications in perennial crops and nonagricultural areas. Sorption and desorption of indaziflam in six soils from Brazil and three soils from the United States, with different physical chemical properties, were investigated using the batch equilibration method. Sorption kinetics demonstrated that soil-solution equilibrium was attained in <24 h. The Freundlich equation described the sorption behavior of the herbicide for all soils (R(2) > 0.99). K(f) values of the Brazilian oxisols ranged from 4.66 to 29.3, and 1/n values were ≥ 0.95. Sorption was positively correlated to %OC and clay contents. U.S. mollisol K(f) values ranged from 6.62 to 14.3; 1/n values for sorption were ≥ 0.92. K(f) values from mollisols were also positively correlated with %OC. These results suggest that indaziflam potential mobility, based solely on its sorption coefficients, would range from moderate to low in soil. Desorption was hysteretic on all soils, further decreasing its potential mobility for offsite transport.