Organic amendments affecting sorption, leaching and dissipation of fungicides in soils

Metalaxyl and tricyclazole are two fungicides widely used in Spain in vineyard and rice crops respectively. In this study an investigation has been made of the effect of three organic amendments [two commercial amendments, solid fertiormont (SF) and liquid fertiormont (LF), and a residue from the olive oil production industry, alperujo (OW)] on fungicide fate in soils. Changes in soil porosity on amendment were studied by mercury intrusion porosimetry, sorption-desorption studies were performed by the batch equilibration method, dissipation of metalaxyl and tricyclazole in the soil was studied at - 33 kPa moisture content and 20 degrees C and leaching was studied in hand-packed soil columns. Amendments with SF and LF reduced soil porosity, while OW increased porosity through an increase in pore volume in the highest range studied. Tricyclazole sorbed to soils to a much higher extent than metalaxyl. With some exceptions, sorption of both fungicides increased on amendment, especially in the case of SF-amended soils, which rendered the highest K(oc) values. In soils amended with the liquid amendment LF, sorption either remained unaffected or decreased, and this decrease was much higher in the case of metalaxyl and a soil with 70% clay. In this clay soil, amendment with OW, of very high soluble organic matter content, also decreased metalaxyl sorption. Tricyclazole is more persistent in soil than metalaxyl, and both fungicides were found to be more persistent in amended soils than in unamended soils. Leaching of metalaxyl and tricyclazole in soil columns was inversely related to sorption capacity. The low recoveries of tricyclazole in leachates and in soil columns when compared with metalaxyl, a less persistent fungicide, were attributed to diffusion into micropores and to increase in sorption with residence time in the soil, both processes favoured by the low mobility of tricyclazole.     

Sorption of low levels of nonionic and anionic surfactants on soil: effects on sorption of triticonazole fungicide

The sorption of two anionic surfactants and a series of seven nonionic alkylphenolethoxylate surfactants of increasing hydrophilic/lipophilic balance (HLB) in a loamy clay soil was evaluated. The effect of low doses of these surfactants on the sorption characteristics of the fungicide triticonazole was investigated. The critical micellar concentration (CMC) of the surfactants in pure water and soil–water systems, and surfactant sorption were estimated by surface tension measurements using a batch equilibration technique. Triticonazole sorption, alone and in the presence of low doses of surfactants, was also measured by batch equilibration. CMC of the alkylphenol surfactants increased with their HLB. The sorption of surfactants increased with their lipophilicity. CMC in the soil–water systems were considerably higher than in pure water. Sorption of the most lipophilic alkylphenol surfactants at the higher doses significantly increased triticonazole sorption. Proposed mechanisms are modifications of soil surface properties, and increase of soil organic carbon content. Sorption of the other nonionic and anionic surfactants only resulted in monomeric surfactant concentrations in pore water, and did not affect triticonazole sorption. © 1998 Society of Chemical Industry     

绿洲区土壤镍的吸附解吸特性

土壤重金属的移动性和生物有效性与重金属的吸附解吸及形态分布密切相关.通过序批试验、单步提取和连续提取的方法,研究绿洲区土壤镍(Ni)的吸附解吸特性.结果发现:①所研究的土壤呈现碱性,具低有机质含量和高碳酸盐含量特征,土壤未被镍所污染;②Freundlich可以用来模拟绿洲区土壤对镍的吸附行为.吸附能力与土壤粉粒、黏粒、全磷、有机质、CEC成显著正相关,而与砂粒成显著负相关,土壤pH并不是影响绿洲区土壤吸附镍的重要因子,绿洲区土壤对镍的吸附不是哪一个土壤理化参数所控制,而可能是土壤理化参数的联合控制;③绿洲区土壤镍的解吸量随土壤中镍吸附量的增加而增加,土壤镍解吸量与解吸前吸附量的关系可以用幂函数进行模拟;④在添加50 mg/L镍的条件下,绿洲区土壤吸附的镍主要以铁-锰结合态、碳酸盐结合态和可交换态为主.     

Characterization of the sorption of an anthranilate fungicide in soil using thermal analytical and mineralogical techniques

The sorption of pesticides to soil particles has implications for their distribution and fate in the soil environment. A batch equilibrium technique was used to investigate sorption of the fungicide AEC623892 to intact and hydrogen-peroxide-treated whole soils and several particle-size fractions isolated from them. Sorption of AEC623892 to the soil as a whole was low. K(f oc) values measured in the whole soils were 169.2 and 41.9 ml g(-1) for Soil A and Soil B respectively. The highest values of K(f oc) were measured in soil particle-size fractions <53 microm (266.5 ml g(-1) in the 2-20 microm fraction of Soil A; 471.9 ml g(-1) in the 20-53 microm fraction of Soil B). Sorption was most irreversible in the 2-20 microm fractions. Overall, treatment of soil particle-size fractions with hydrogen peroxide resulted in lower values of K(f oc) (112.3 ml g(-1) in Soil A whole soil and 30.9 ml g(-1) in Soil B whole soil). In both soils, the maximum sorption among hydrogen-peroxide-treated samples was observed in the <2 microm fraction (166.6 and 311.0 ml g(-1) for Soil A and Soil B, respectively). Investigation of the mineralogical composition of the soils suggested that the clay mineralogy (dominated by kaolinite and illite) is less likely to account for the differences in sorption observed than differences in the characteristics of the soil organic matter. Thermal analysis of the different soil fractions indicated that hydrogen peroxide treatment preferentially removed aliphatic fractions of organic matter, but had less effect on lignin-like, aromatic fractions.     

Adsorption and degradation of four acidic herbicides in soils from southern Spain

BACKGROUND: Pesticide degradation and adsorption in soils are key processes determining whether pesticide use will have any impact on environmental quality. Pesticide degradation in soil generally results in a reduction in toxicity, but some pesticides have breakdown products that are more toxic than the parent compound. Adsorption to soil particles ensures that herbicide is retained in the place where its biological activity is expressed and also determines potential for transportation away from the site of action. Degradation and adsorption are complex processes, and shortcomings in understanding them still restrict the ability to predict the fate and behaviour of ionisable pesticides. This paper reports the sorption and degradation behaviour of four acidic pesticides in five soils from southern Spain. Results are used to investigate the influence of soil and pesticide properties on adsorption and degradation as well as the potential link between the two processes. RESULTS: Adsorption and degradation of four acidic pesticides were measured in four soils from Spain characterised by small organic matter (OM) contents (0.3-1.0%) and varying clay contents (3-66%). In general, sorption increased in the order dicamba < metsulfuron-methyl < 2,4-D < flupyrsulfuron-methyl-sodium. Both OM and clay content were found to be important in determining adsorption, but relative differences in clay content between soils were much larger than those in OM content, and therefore clay content was the main property determining the extent of herbicide adsorption for these soils. pH was negatively correlated with adsorption for all compounds apart from metsulfuron-methyl. A clear positive correlation was observed for degradation rate with clay and OM content (P < 0.01), and a negative correlation was observed with pH (P < 0.01). The exception was metsulfuron-methyl, for which degradation was found to be significantly correlated only with soil bioactivity (P < 0.05). CONCLUSIONS: Both OM and clay content were found to be important in determining adsorption, but relative differences in clay content between soils were much larger than those in OM content, and therefore clay content was the main property determining the extent of herbicide adsorption for soils of this type. pH was negatively correlated with adsorption for all compounds apart from metsulfuron-methyl. The contrasting behaviour shown for these four acidic pesticides indicates that chemical degradation in soil is more difficult to predict than adsorption. Most of the variables measured were interrelated, and different behaviours were observed even for compounds from the same chemical class and with similar structures.     

Influence of Dissolved Organic Carbon and Initial Moisture on Zinc Sorption by Two Arid Soils

Sorption of added zinc to irrigated soils in arid regions is an important process that may control the availability of zinc to growing plants . Two soil surface samples varying in clay , organic matter , and calcium carbonate content were selected from central and southwestern regions of Saudi Arabia and prepared in order to give different initial moisture contents ranging from air dried to 100 % of field capacity . The sorption experiment was conducted using Zn concentrations ranging from 5 to 25 mg L 1, prepared from ZnSO4 either in distilled water or in solutions containing 75 mg L 1 dissolved organic carbon (DOC). Results indicate that the amount of Zn sorbed in the presence of DOC was relatively high compared with the absence of DOC and Zn retention was strongly affected by the initial soil moisture content . Also , equilibrium Zn concentrations were quite low , while Zn retentions were high in all treatments . Data of Zn sorption were described by the Freundlich isotherm , and two linear portions were found in most cases . In the absence of DOC , retentions of added Zn were controlled by the available exchange sites and / or the precipitation of Zn as sparingly soluble forms. Zn ions in the presence of DOC were able to form soluble - Zn organic complexes that adsorb on the soil surfaces . The extent of such behavior was related to the variations in clay , organic matter , and calcium carbonate contents as well as the initial moisture of the soil . Results indicate that addition of DOC reduces the amount of extractable Zn from either soil Zn or the sorbed Zn by ammonium bicarbonate diethylenetriamine pentaacetic acid ( AB DTPA ). More than 80 % of the sorbed Zn was extracted by AB-DTPA , and the percentage of extracted / sorbed Zn decreased with the increase in sorbed Zn . The obtained results give evidence that initial moisture content and addition of DOC reduce the extractability of applied inorganic Zn by AB-DTPA extract in arid soils.     

Variability of retention process of isoxaflutole and its diketonitrile metabolite in soil under conventional and conservation tillage

BACKGROUND: Sorption largely controls pesticide fate in soils because it influences its availability for biodegradation or transport in the soil water. In this study, variability of sorption and desorption of isoxaflutole (IFT) and its active metabolite diketonitrile (DKN) was investigated under conventional and conservation tillage. RESULTS: According to soil samples, IFT K_D values ranged from 1.4 to 3.2 L kg^?1 and DKN K_D values ranged from 0.02 to 0.17 L kg^?1. Positive correlations were found between organic carbon content and IFT and DKN sorption. IFT and DKN sorption was higher under conservation than under conventional tillage owing to higher organic carbon content. Under conservation tillage, measurements on maize and oat residues collected from the soil surface showed a greater sorption of IFT on plant residues than on soil samples, with the highest sorbed quantities measured on maize residues (K_D ≈ 45 L kg^?1). Desorption of IFT was hysteretic, and, after five consecutive desorptions, between 72 and 89% of the sorbed IFT was desorbed from soil samples. For maize residues, desorption was weak (<50% of the sorbed IFT), but, after two complementary desorptions allowing for IFT hydrolysis, DKN was released from maize residues. CONCLUSION: Owing to an increase in organic carbon in topsoil layers, sorption of IFT and DKN was enhanced under conservation tillage. Greater sorption capacities under conservation tillage could help in decreasing DKN leaching to groundwater. Copyright © 2012 Society of Chemical Industry     

The behavior of clomazone in the soil environment

BACKGROUND: Clomazone is a herbicide used to control broadleaf weeds and grasses. Clomazone use in agriculturally important crops and forests for weed control has increased and is a potential water contaminant given its high water solubility (1100 µg mL^?1). Soil sorption is an environmental fate parameter that may limit its movement to water systems. The authors used model rice and forest soils of California to test clomazone sorption affinity, capacity, desorption, interaction with soil organic matter and behavior with black carbon. RESULTS: Sorption of clomazone to the major organic matter fraction of soil, humic acid (HA) (K_d = 29–87 L kg^?1), was greater than to whole soils (K_d = 2.3–11 L kg^?1). Increased isotherm non‐linearity was observed for the whole soils (N = 0.831–0.893) when compared with the humic acids (N = 0.954–0.999). Desorption isotherm results showed hysteresis, which was greatest at the lowest solution concentration of 0.067 µg mL^?1 for all whole soils and HA extracts. Aliphatic carbon content appeared to contribute to increased isotherm linearity. CONCLUSION: The results indicate that clomazone does not sorb appreciably to sandy or clay soils. Its sorption affinity and capacity is greater in humic acid, and consequently clomazone has difficulty desorbing from soil organic matter. Sorption appears to follow processes explained by the dual‐mode model, the presence of fire residues (black carbon) and a recently proposed sorption mechanism. Copyright © 2009 Society of Chemical Industry     

Aminocyclopyrachlor sorption–desorption and leaching in soil amended with organic materials from sugar cane cultivation

The correct application of a new herbicide depends on knowledge concerning its behaviour within the cultivation system. The objective of this study was to evaluate the sorption–desorption process of aminocyclopyrachlor in soils with the addition of three aged organic materials from sugar cane and their transport via leaching. Sugar cane straw (12 t/ha), filter cake (90 t/ha) and vinasse (200 m³/ha) were added to a clayey soil 15, 30 and 60 days before herbicide application. Sorption and desorption were evaluated by the batch equilibrium method. For leaching assessments, the materials were applied to the soil surface. Sorption was relatively low in all treatments (K_d = 0.17–0.41 L/kg), although significantly higher in soil without organic material addition. A negative correlation between herbicide sorption and increased soil base saturation was observed, indicating competition for sorption sites. With the addition of vinasse, 71% of the herbicide reached the leachate, while <50% reached the leachate in the other treatments. Aminocyclopyrachlor availability was not reduced with organic material addition to the soil, which may be favourable for weed control. However, the presence of vinasse leads to the risk of leaching to deeper soil layers than the seed bank.     

Sorption of ionisable organic compounds by field soils. Part 1: Acids

Sorption of different classes of weak organic acids was measured using soils with a range of pH values, taken from long-term field experiments that had received different amounts of lime. Non-ionisable compounds were used to demonstrate that the soils of different pH used in the experiments have similar sorptive properties. Values of the sorption coefficients for chloride ion were negative at all pHs except one. Sorption of moderately polar, monobasic, weak acids was weak in acidic soils and very weak in neutral and alkaline soils where they were predominantly dissociated. A lipophilic weak acid was strongly sorbed even at high pH. A model is presented which estimates soil/water distribution coefficients, at any soil pH, from lipophilicity and pK_a of the acid and organic matter content of the soil. The model was derived using sorption measured for substituted phenoxyacetic acids. Sorption values calculated using the model were compared with values measured for chlorsulfur on and showed useful agreement. Dibasic acids were strongly sorbed, probably by the mechanism of ligand exchange, if they were chelating agents with potential to form 5- or 6-membered rings with an acceptor atom. Phenylphosphonic acid was strongly sorbed, being a strong monodentate ligand.     

Mobility of imidacloprid from alginate-bentonite controlled-release formulations in greenhouse soils

The mobility of imidacloprid [1-(6-chloro-3-pyridinyl)methyl]-N-nitro-2-imidazolidinimine] from alginate-based controlled-release (CR) formulations was investigated in two different soil profiles. In one, a layered bed system simulating the typical arrangement under a plastic greenhouse, which is composed of sand, peat, amended soil and native soil, was used. In the other, the layer containing amended soil was used in order to determine the mobility of the insecticide in a soil system with a low content of organic matter and a high content of clay. Two CR formulations based on sodium alginate (1.87% wt/wt), imidacloprid (1.21%), natural or acid-treated bentonite (3.28%), and water (93.64%) were compared to technical grade imidacloprid. The use of alginate CR formulations produced less vertical mobility of the active ingredient as compared to the technical product. With the technical grade product treatment, the total amount of imidacloprid leached from columns packed with amended soil was 82.3% of that applied, whereas for the alginate-based CR formulations containing natural or acid-treated bentonite, the leached percentages were 44.7% and 37.1%, respectively. In the column experiments simulating the layered bed system, no insecticide was found in the leachate when the alginate-based CR formulations containing natural bentonite were used. However, 3% of the applied imidacloprid appeared when the treatment was carried out with technical grade material. Sorption-desorption capacities of the various soil layers for imidacloprid molecules were also calculated using batch experiments. © 1999 Society of Chemical Industry     

Role of sorption and degradation in the herbicidal function of isoxaflutole

BACKGROUND: The fate of isoxaflutole (IFT) in soil is closely related to soil sorption. Sorption and transformation of IFT were investigated in laboratory incubations with four soils, and these results were used to interpret greenhouse studies using IFT to control several weed species. RESULTS: Degradation proceeded by previously observed pathways to form diketonitrile (DKN) and benzoic acid (BA) derivatives, as well as traces of unidentified products. Over the course of the incubation, DKN was the dominant active form of the herbicide present in the experimental system, and was thus critical to the soil activity of the herbicide for weed control. CONCLUSION: Control of most weed species appeared to be a function of both sorption and biodegradation of DKN, with greatest weed control being observed in soils in which a significant portion of the DKN that was formed persisted and remained bioavailable over the course of the incubation. Copyright © 2009 Society of Chemical Industry     

Adsorption-desorption behaviour of flufenacet in five different soils of India

Adsorption-desorption of the herbicide flufenacet (FOE 5043) has been studied in five soils from different locations in India (Delhi, Ranchi, Nagpur, Kerala and Assam) varying in their physicochemical properties. The organic matter (OM) content varied from 0.072 to 0.864%, clay content from 2.5 to 43.7% and pH from 4.45 to 8.35. The adsorption studies were carried out using a batch equilibration technique. Ten grams of soil were equilibrated with 20 ml of aqueous 0.01 M CaCl2 solution containing different concentrations (0-30 mg litre-1) of flufenacet. After equilibration, an aliquot of supernatant was taken out for analysis. During desorption, the amount withdrawn for analysis was replenished with fresh 0.01 M CaCl2 solution and further equilibrated. Desorption studies were carried out with the 30 mg litre-1 concentration of flufenacet only. The adsorption studies revealed that there was moderate to high adsorption of flufenacet considering the comparatively low organic carbon content in the five test soils. Average Kd values ranged from 0.77 to 4.52 and Freundlich KF values from 0.76 to 4.39. The highest adsorption was observed in Kerala soil (OM 0.786%; clay 25%; pH 4.45) followed by Ranchi, Nagpur and Delhi soils, and the lowest in Assam soil (OM 0.553%; clay 2.5%; pH 6.87). The trend in adsorption could be attributed to the chemical nature of flufenacet and the physicochemical properties of the soil such as pH, OM and clay contents. OM and clay contents were positively correlated whereas pH was negatively correlated. Soils having low pH, high OM and high clay contents showed higher adsorption. Desorption studies revealed that there was a hysteresis effect in all the soils. Hysteresis coefficient values (ratio of n(ad) and n(des)) varied from 0.09 to 0.45. The study implies that, because of its moderate to high adsorption, flufenacet is likely to persist in soil for some time. However, the possibility of its movement by leaching or surface run off is less.     

Characterization of triadimefon sorption in soils using supercritical fluid (SFE) and accelerated solvent (ASE) extraction techniques

Sorption–desorption of the fungicide triadimefon in field‐moist silt loam and sandy loam soils were determined using low‐density supercritical fluid extraction (SFE). The selectivity of SFE enables extraction of triadimefon from the soil water phase only, thus allowing calculation of sorption coefficients (K_d) at field‐moist or unsaturated conditions. Triadimefon sorption was influenced by factors such as soil moisture content and temperature; sorption increased with increased moisture content up to saturation, and decreased with increased temperature. For instance, K_d values for triadimefon on the silt loam and the sandy loam soils at 40 °C and 10% water content were 1.9 and 2.5 ml g⁻¹, respectively, and at 18% water content, 3.3 and 6.4 ml g⁻¹, respectively. Isosteric heats of sorption (ΔH_i) were −42 and −7 kJ mol⁻¹ for the silt loam and sandy loam soils, respectively. Sorption–desorption was also determined using an automated accelerated solvent extraction system (ASE), in which triadimefon was extracted from silt loam soil by 0.01 M CaCl₂. Using the ASE system, which is basically a fast alternative to the batch equilibration system, gave a similar ΔH_i value (−29 kJ mol⁻¹) for the silt loam soil (K_f = 27 µg^{1 − 1/n} ml^1/n g⁻¹). In order to predict transport of pesticides through the soil profile more accurately on the basis of these data, information is needed on sorption as a function of soil water content. © 2000 Society of Chemical Industry     

Sorption of isoxaflutole by five different soils varying in physical and chemical properties

Isoxaflutole is a new pre-emergence corn herbicide which controls both grass and broadleaf weeds. Experiments were performed in the laboratory to study the sorption of isoxaflutole in five different soils (Moorhead, MN; East Monroe, CO; Ellendale, MN; South Deerfield, MA; and Chelsea, MI) using the batch equilibration technique. Total initial isoxaflutole solution concentrations for each soil were 0.05, 0.15, 0.3. 0.8, 1.5, 2.0 and 4.0 mg litre⁻¹. Analysis of [ring-¹⁴C] isoxaflutole was performed using liquid scintillation counting, and sorption data were fitted with the Freundlich model. Isotherms of isoxaflutole in all the soils were non-linear as depicted by the exponent (n < 1.0), indicating differential distribution of sorption site energies in various soils. Since the isotherms were non-linear the data fit Freundlich's isotherm well, as was indicated by high values of the regression coefficient (r²). The Freundlich sorption coefficient ranged from 0.555 to 50.0 (litre ⁿmg ^l−nkg⁻¹). Multiple regression of the sorption constant, K_F against selected soil properties indicated that organic matter content was the best single predictor of isoxaflutole sorption (r² = 0.999) followed by soil pH (r² = 0.954). Clay content of the soils did not have a high correlation with K_F values (r² = 0.453), while the sorption of isoxaflutole was not influenced by the Ca²⁺ concentration in the soil solution. Isoxaflutole sorption increased with an increase in organic matter content of soils. Sorption of isoxaflutole decreased as the soil pH increased from 4.5 to 8.5, which was depicted by the reduction of K_F values. Sorption of isoxaflutole to the soils varied with differences in binding energies. At a particular net energy value (E*), the corresponding site energy distribution [F(E*)] values followed the order, Chelsea, MI > Moorhead, MN > East Monroe, CO > South Deerfield, MA > Ellendale, MN. The negative magnitude of Gibbs free energy of sorption (ΔG ^x) indicates the spontaneity of the given sorption process in the soils from Moorhead, MN; East Monroe, CO and Chelsea, MI. © 1999 Society of Chemical Industry     

Mobility of four triazole fungicides in two Indian soils

The sorption and downward mobility of four triazole fungicides, triadimefon, hexaconazole, penconazole and propiconazole, were studied in two Indian soils (New Delhi and Punjab). Punjab soil (organic carbon 0.4%) showed greater sorption capability for triazole fungicides than New Delhi soil (organic carbon 0.5%) and the order of sorption of triazoles in both soils was: penconazole > hexaconazole > propiconazole > triadimefon. Fungicides were more mobile in New Delhi soil columns than Punjab soil columns, and increasing the total water flux from 1 pore volume to 3 pore volumes further increased the transport to lower down in the column. Triadimefon showed maximum mobility while penconazole was the least mobile triazole fungicide. After percolating 3 pore volumes of water, triadimefon leached down to 25-30 cm depth in New Delhi soil and 15-20 cm in Punjab soil columns. Downward mobility of triazole fungicides was in order of their sorption results.     

毒死蜱和氰戊菊酯在土壤中的吸附与迁移

为评估被用作白蚁预防药剂的毒死蜱和氰戊菊酯在土壤中的移动性,采用平衡吸附法和薄层层析法分别测定了两种农药在浙江宁波地区的东钱湖土(粉砂质壤土)、青岭土(粉砂质壤土)和象山土(粉砂质黏壤土)3种土壤中的吸附常数(Kd)和迁移率(Rf)。结果表明,两种供试药剂在东钱湖土中的吸附等温线线性化程度均较高,而在青岭土和象山土中的吸附等温线均近似于 "L"型。从Kd和有机质吸附常数Koc的数值看,氰戊菊酯在土壤中的吸附作用主要受土壤有机质因素影响,而毒死蜱的吸附并非只受土壤有机质因素的影响。毒死蜱在3种供试土壤中的Kd和Rf值均高于氰戊菊酯。这表明由Kd值推测不同农药在土壤中的相对移动性可能会存在一定偏差。毒死蜱和氰戊菊酯在3种土壤中的Rf值由大到小的顺序为:东钱湖土>青岭土>象山土;而Kd值由大到小顺序为象山土>青岭土>东钱湖土。对Kd和Rf值与土壤理化性质的多元线性回归分析表明:1)土壤有机质含量和阳离子代换量在决定Kd和Rf值中所起的作用相互重叠;2)土壤有机质含量(或土壤阳离子代换量)和土壤黏粒含量是影响Kd和Rf值的关键因素,而土壤pH值对于Kd和Rf值无决定性影响。     

原油污染对土壤吸附水中二溴甲烷的影响

通过分析水中二溴甲烷在原油开采区土壤中的吸附作用,探讨其在土壤中的吸附机理及原油污染的影响。结果表明：水中二溴甲烷在原土及原油污染土壤中的吸附等温线均符合线性方程,土壤有机相（包括土壤有机质和原油单独相）的分配作用在吸附机制中占主导地位。当原油含量较低时,水中二溴甲烷在油污土壤中的吸附系数值小于未污染土壤,原油污染增大...     

Sorption and desorption of flumioxazin to soil, clay minerals and ion-exchange resin

Flumioxazin adsorption kinetics were described using a Greenville sandy clay loam soil. Adsorption kinetics experiments showed that 72% of total herbicide was absorbed after 1 h of continuous shaking and continued to increase to 78% after 72 h. Flumioxazin adsorption was then tested on seven agriculturally important soils throughout the southern USA. Adsorption isotherms for all soils had K(f) (Freundlich distribution coefficient) values that ranged from 8.8 to 0.4, with many near 1.5. Soil organic matter content was the parameter most highly correlated with flumioxazin adsorption (r(2) = 0.95, P < 0.001). Sorption to clay minerals had K(f) values ranging from 50 for bentonite to 4.7 for kaolinite. However, normalizing K(f) for sorbent surface area revealed that aluminum hydroxide (gibbsite) possessed the greatest flumioxazin sorption per unit area. Sorption to anionic exchange resin (K(f) 676) was greater than cationic exchange resin (K(f) 42). Molecular model calculations were performed to elucidate why sorption was greater to anionic exchangers. These calculations indicated that a region of dense electronegativity exists on the 3-dione moiety of the molecule. This would lead to greater flumioxazin sorption by positively charged surface sites. Desorption isotherms from soil exhibited no effect of hysteresis. Desorption from clay minerals was very rapid and flumioxazin in solution was undetectable after three desorption steps. From these data it was concluded that flumioxazin can become readily available in soil solution with increase in soil water content.