Sorption-desorption of aminocyclopyrachlor in selected Brazilian soils

Aminocyclopyrachlor sorption/desorption was investigated in 14 soils from Brazil, representing a range of pH, and organic carbon (OC) and clay contents. The Freundlich equation adequately described behavior of aminocyclopyrachlor in soil. Freundlich sorption coefficient (K(f)) values ranged from 0.06 to 1.64 and 1/n values for ranged from 0.9 to 1.0. Sorption was correlated to OC (K(f,oc) ranged from 11 to 64) and clay contents. The lowest sorption was found for soils with very low OC contents (0.50-0.65%) and loamy-sand to sand textures. The 1/n values for desorption were lower than those observed for sorption, suggesting that aminocyclopyrachlor sorption by soil was not reversible; hysteresis coefficients ranged from 0.13 to 0.74. The results suggest that although aminocyclopyrachlor would be very mobile based on its sorption coefficients, its potential depth of leaching may be overestimated due to the hysteretic desorption.     

Sorption and desorption of triadimefon by soils and model soil colloids

Sorption-desorption of the azole fungicide triadimefon [1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2, 4-triazol-1-yl)-2-butanone] on eight soils and a series of single, binary, and ternary model soil colloids was determined using the batch equilibration technique. Regression analysis between Freundlich sorption coefficients (K(f)) and soil properties suggested that both clay and organic C (OC) were important in triadimefon sorption by soils, with increasing importance of clay for soils with high clay and relatively low OC contents. Triadimefon sorption coefficients on soil were not significantly affected by the concentration of electrolyte or the presence of soluble soil material in solution, but they were highly dependent on the soil:solution ratio due to the nonlinearity of triadimefon sorption on soil. Freundlich sorption isotherms slopes were very similar for all soils (0.75 +/- 0.02). Desorption did not greatly depend on the concentration at which it was determined and showed higher hysteresis for more sorptive soils. Results of triadimefon sorption on model sorbents supported that both humic acid and montmorillonite-type clay constituents contribute to triadimefon retention by soil colloids.     

Sorption of pesticides in tropical and temperate soils from Australia and the Philippines

The sorption behavior of diuron, imidacloprid, and thiacloprid was investigated using 22 soils collected in triplicate from temperate environments in Australia and tropical environments in Australia and the Philippines. Within the temperate environment in Australia, the soils were selected from a range of land uses. The average KOC values (L/kg) for imidacloprid were 326, 322, and 336; for thiacloprid, the values were 915, 743, and 842; and for diuron, the values were 579, 536, and 618 for the Ord (tropical), Mt. Lofty (temperate), and Philippines (tropical) soils, respectively. For all soils, the sorption coefficients decreased in the following order: thiacloprid > diuron > imidacloprid. There were no significant differences in sorption behavior between the tropical soils from the Philippines and the temperate soils from Australia. Sorption was also not significantly related with soil characteristics, namely, organic carbon (OC) content, clay content, and pH, for any of the three chemicals studied. When the data were sorted into separate land uses, the sorption of all three chemicals was highly correlated (P < 0.001) with OC for the rice soils from the Philippines. Sorption coefficients for all three chemicals were highly correlated with OC in temperate, native soils only when one extreme value was removed. The relationships between sorption of all three chemicals and OC in temperate, pasture soils were best described by a polynomial. Sorption coefficients for imidacloprid and thiacloprid determined in the temperate pasture soils remained fairly consistent as the OC content increased from 3.3 to 5.3%, indicating that, although the total OC in the pasture soils was increasing, the component of OC involved with sorption of these two compounds may have been remaining constant. This study demonstrated that the origin of the soils (i.e., temperate vs tropical) had no significant effect on the sorption behavior, but in some cases, land use significantly affected the sorption behavior of the three pesticides studied. The impact of land use on the nature of soil OC will be further investigated by NMR analysis.     

Azimsulfuron sorption--desorption on soil

The sorption and desorption of the herbicide azimsulfuron, N-[[(4-dimethoxypyrimidin-2-yl)amino]carbonyl]1-methyl-4-(2-methyl-2H-tetrazole-5-yl)1H-pyrazole-5-sulfonamide, were studied using five soils. Sorption isotherms conformed to the Freundlich equation. It was found that pH is the main factor influencing the sorption and that the sorption on soils was negatively correlated with pH. The highest level of sorption was measured on soils with low pH and high organic carbon content. Moreover, inorganic soil colloids, for example, smectite clay minerals and iron oxides, contributed to the sorption of azimsulfuron. Desorption was hysteretic on soils with high organic and inorganic colloid contents.     

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.     

Sorption and mobility of 14C-labeled imazaquin and metolachlor in four soils as influenced by soil properties

Aqueous batch-type sorption-desorption studies and soil column leaching studies were conducted to determine the influence of soil properties, soil and suspension pH, and ionic concentration on the retention, release, and mobility of [14C]imazaquin in Cape Fear sandy clay loam, Norfolk loamy sand, Rion sandy loam, and Webster clay loam. Sorption of [14C]metolachlor was also included as a reference standard. L-type sorption isotherms, which were well described by the Freundlich equation, were observed for both compounds on all soils. Metolachlor was sorbed to soils in amounts 2-8 times that of imazaquin, and retention of both herbicides was related to soil organic matter (OM) and humic matter (HM) contents and to herbicide concentration. Metolachlor retention was also related to soil clay content. Imazaquin sorption to one soil (Cape Fear) increased as concentration increased and as suspension pH decreased, with maximum sorption occurring in the vicinity of pK(a1) = (1.8). At pH levels below pK(a1) imazaquin sorption decreased as hydronium ions (H3O+) increased and competed for sites. NaCl was more effective than water in desorption of imazaquin at pH levels near the pK(a1). Mechanisms of bonding are postulated and discussed. The mobility of imazaquin through soil columns was in the order Rion > or = Norfolk > Cape Fear > or = Webster, whereas for metolachlor it was Rion > or = Norfolk > Webster > or = Cape Fear. Imazaquin was from 2 to 10 times as mobile as metolachlor.     

Sorption and leaching of atrazine and MCPA in natural and peat-amended calcareous soils from Spain.

The sorption and leaching of atrazine and MCPA (0.02 M CaCl(2) aqueous solution at 25 degrees C) by a calcareous soil from Southeastern Spain, after organic carbon (OC) amendment with a commercial peat (from 0.18% to 4.61% OC), were studied in batch and soil column experiments. Adsorption capacity (K(f)) values, obtained by fitting the experimental data to the Freundlich equation, ranged from 0.24 mg kg(-)(1) for MCPA sorption on the original soil to 5.47 mg kg(-)(1) for atrazine sorption on the peat-amended soil containing 4.61% OC. The breakthrough curves obtained from the step-function soil column experiments indicated that the amount of herbicide adsorbed ranged from 17.5 mg kg(-)(1) for MCPA in the original soil to 331 mg kg(-)(1) for atrazine in the peat-amended soil containing 1.67% OC. The results obtained from the pulse experiments indicate that the mobility of MCPA is much greater than that corresponding to atrazine.     

Sorption and desorption of endosulfan sulfate and diuron to composted cotton gin trash

This paper investigates the potential use of composted cotton gin trash (CCGT) as a pesticide sorption medium in remediation of contaminated tailwater. CCGT was found to contain a large organic matter fraction (25.22%). Sorption of endosulfan sulfate and diuron, using the batch equilibrium method, was rapid but not limited for the range of applied concentrations, with diuron failing to reach equilibrium after two days. The partition K d and organic carbon partition K(OC) coefficients determined diuron ( Kd = 78; K(OC) = 526) and endosulfan sulfate ( Kd = 1500; K(OC) = 10,111) to reside in the solid phase. Limited desorption of diuron and higher range concentrations of endosulfan sulfate (50-100 microg L(-1)) were quantified. Sorption and desorption resulted from hydrophobic and hydrophilic interactions with the humic components of the compost. CCGT was concluded to have a superior sorption capacity to other sorbents reported in the literature, an assessment that requires field substantiation.     

Effect of soil properties on the degradation of isoxaflutole and the sorption-desorption of isoxaflutole and its diketonitrile degradate

The transformation of isoxaflutole (ISOX) to its herbicidally active diketonitrile degradate (DKN) was significantly enhanced in the presence of soil and occurred more rapidly in systems containing soil with a greater soil pH. Sorption-desorption of ISOX and DKN in five soils collected within a field revealed both ISOX and DKN were more readily sorbed to soils with greater organic matter, clay content, and lower soil pH. Sorption of ISOX residues occurred within 2 h, and extracts contained similar concentrations of ISOX and DKN at 24 h, suggesting the 24-h sorption coefficients for ISOX-treated systems were actually for mixed ISOX residues. Freundlich sorption coefficients were 3 and 4 times greater for ISOX than for DKN. On the basis of the Freundlich organic carbon sorption constants, ISOX and DKN can be categorized in the very high and high mobility classes, suggesting their potential to leach in the soils needs to be evaluated.     

Sorption and aging of corn and soybean pesticides in tropical soils of Brazil

The efficacy and fate of pesticides in soil strongly depend on sorption reversibility that is known to decrease with increasing contact time (aging). We elucidated the aging dynamics of eight different pesticides in two contrasting agricultural soils of tropical Brazil (Ustox and Psamments), using batch equilibrium experiments and sequential extractions of field samples. Adsorption was best described by Langmuir isotherms for the entire and by Freundlich equations for the lower concentration range. In field samples, water extractable pesticide fractions mostly dissipated at least twice as fast as did the solvent extractable fractions. Hence, in comparison to 0 days K(OC) values, measured field K(OC) values were higher by a factor of 2.6-38 for the clayey Ustox and 2.1-72 for the sandy Psamments toward the end of the experimental period at 80 days after application. The extent of such aging basically increased with increasing polarity of the pesticide. An absolute enrichment of polar pesticides within the final exhaustive acetone--ethyl acetate--water extracts was observed during the experimental period, so that we may deduce that pesticides had redistributed into stronger sorption sites. The time course of the K(OC) development was well-described using a semiempirical equation, which had been employed for temperate soils before.     

COPPER SORPTION BY SOILS AT LOW CONCENTRATIONS AND RELATION TO UPTAKE BY PLANTS

Copper sorption was measured in 14 agricultural soils from England and Wales with a wide range of properties. Sorption from 0.01 M CaCl₂ was described by the Freundlich adsorption isotherm when Cu in solution was initially at 200 HM and greater, but at lower initial concentrations (i. e. 100 fiM and less) there was a steep rise in the gradients of the isotherms. At initial concentrations of 100 JIM and less, sorption was linearly correlated to the concentration of Cu remaining in solution; the gradients of these relationships varied considerably amongst the soils and were highly correlated to soil pH. There was no correlation between either the gradients or the extrapolated values of final solution concentration at which there was no sorption of added Cu by the soils (an ‘equilibrium’ concentration), and other determined soil properties. The effect of pH adjustment on sorption varied between the 5 soils examined although, in general, there was increasing sorption with increasing pH. Extrapolated values for ‘equilibrium’ concentrations for an individual soil were higher at pH 6.0 or greater, than at pH 5.5. A large proportion of the Cu in the final solutions was apparently complexed but this varied between soils and was dependent on both pH and total concentration. There was little effect of varying pH of the final solution on these proportions in most soils. Neither extractable Cu in the soils, nor the sorption characteristics were related to availability as measured by uptake by perennial ryegrass.     

Affinity constants and behavior of Cd sorption in some acid soils

Cadmium sorption was studied in several acidic soils in a pH range from 4.5 to 6.5. The soils had two classes of surfaces with acidity constants (pKa₁ = 4.09 and pKa₂ = 6.39) similar to those for weakly and very weakly cidic carboxyls, and N-containing groups in fulvic acid. Titratable H and acidity constants were used to estimate the number of exchange sites at each pH level. Sorption of Cd was closely related to Cd concentration, pH, and soil type. Although the inclusion of pH and organic C contents in a regression accounted for some variations in the Cd distribution coefficient defined as the ratio of the quantity of Cd sorbed to the solution Cd concentration, the number of sorption sites was a more appropriate factor to explain the variability. Because of a negligible contribution to the number of exchange sites from Fe oxides, the sorption of Cd at pH = 4.5 was considered to be of a one-surface Langmuir type. A two-surface Langmuir equation was considered to model sorption at higher pH values. The average affinity constants (log K) were 3.61 and 4.89 for Cd sorption by the two classes of surfaces.     

Zinc sorption–desorption by two Andepts: effect of pH and support medium

Laboratory experiments were carried out to evaluate the effect of pH, ionic strength and electrolyte composition on zinc sorption–desorption by two Andepts from the Canary Islands (Spain). At the natural soil pH, the soils exhibited little net negative surface charge and small Zn sorption capacities. More than 75% of the sorbed Zn was apparently strongly bonded. The pH greatly influenced the sorption–desorption reactions. Sorption increased with increasing pH, and retention increased abruptly at pH > 6.0. Sorption also occurred at pH values below the point of zero charge (PZC) of the soils, when most of the surface sites are positively charged. Desorption decreased continuously with rising pH and became a trace at pH > 6.0. An increase in the ionic strength of the background electrolyte decreased Zn sorption and enhanced the amount of sorbed metal that could be subsequently released. In the two soils, Zn sorption diminished somewhat in the K and Ca electrolytes as compared with the Na electrolyte. However, this did not happen at small Zn loadings. Desorption was not affected by the type of electrolyte and cation used. The results are consistent with chemisorption being responsible for most of the sorption. The results also suggested a strong affinity sorption or even precipitation at high pHs.     

Linuron sorption-desorption in field-moist soils

Pesticide sorption or binding to soil is traditionally characterized using batch slurry techniques. The objective of this study was to determine linuron sorption in field-moist or unsaturated soils. Experiments were performed using low-density (i.e., 0.25 g mL(-)(1)) supercritical carbon dioxide to remove linuron from the soil water phase, thus allowing calculation of sorption coefficients (K(d)) at low water contents. Both soil water content and temperature influenced sorption. K(d) values increased with increased water content, if less than saturated. K(d) values decreased with increased temperature. K(d) values for linuron sorption on silty clay and sandy loam soils at 12% water content and 40 degrees C were 3.9 and 7.0 mL g(-)(1), respectively. Isosteric heats of sorption (DeltaH(i)) were -41 and -35 kJ mol(-)(1) for the silty clay and sandy loam soils, respectively. The sorption coefficient obtained using the batch method was comparable (K(f) for sandy loam soil = 7. 9 microg(1)(-)(1/)(n)() mL(1/)(n)() g(-)(1)) to that obtained using the SFE technique. On the basis of these results, pesticide sorption as a function of water content must be known to more accurately predict pesticide transport through soils.     

Metsulfuron methyl sorption-desorption in field-moist soils

Pesticide sorption coefficients (K(d)) are generally obtained using batch slurry methods. As a consequence, the results may not adequately reflect sorption processes in field-moist or unsaturated soil. The objective of this study was to determine sorption of metsulfuron methyl, a weak acid, in field-moist soils. Experiments were performed using low density (i.e., 0.3 g mL(-)(1)) supercritical fluid carbon dioxide (SF-CO(2)) to convert anionic metsulfuron methyl to the molecular species and remove it from the soil water phase only, thus allowing calculation of sorption coefficients (K(d)) at low water contents. K(d) values for sorption of the metsulfuron methyl molecular species on sandy loam, silt loam, and clay loam soil at 11% water content were 120, 180, and 320 mL g(-)(1), respectively. Using neutral species K(d) values, the pK(a) of metsulfuron methyl, and the pH of the soil, we could successfully predict the K(d) values obtained using the batch slurry technique, which typically has a predominance of anionic species in solution during the sorption characterization. This application of supercritical fluid extraction to determine sorption coefficients, combined with sulfonylureas' pK(a) values and the soil pH, will provide an easy method to predict sorption in soil at different pH levels.     

干旱区绿洲灌漠土对铜的吸附解吸特性研究

土壤对重金属的吸附解吸是影响土壤系统中重金属的移动性和归宿的主要过程.本文使用序批实验方法、单步提取方法、连续提取方法等研究了干旱区绿洲灌漠土Cu的吸附解吸特性.结果表明,灌漠土对Cu的吸附等温线可很好地用Freundlich等温方程拟合,灌漠土的Cu吸附可能受土壤理化综合因素影响,而不仅是某个土壤理化指标所控制;二次...     

Effects of sorbate speciation on sorption of selected sulfonamides in three loamy soils

Sorption of sulfamethazine (SMN) and sulfathiazole (STZ) was investigated in three soils, a North Carolina loamy sand, an Iowa sandy loam, and a Missouri loam, under various pH conditions. A significant increase in the sorption coefficient (KD) was observed in all three soils, as the sulfonamides converted from an anionic form at higher pH to a neutral/cationic form at lower pH. Above pH 7.5, sulfonamides exist primarily in anionic form and have higher aqueous solubility and no cationic character, thereby consequently leading to lower sorption to soils. The effect of speciation on sorption is not the same for all sulfonamides; it is a function of the pH of the soil and the pKa of the sulfonamides. The results indicate that, for the soils under investigation, SMN has comparatively lower KD values than STZ. The pH-dependent sorption of sulfonamides was observed to be consistent in all three soils investigated. The KD values for each speciated form-cationic, neutral, and anionic-were calculated using an empirical model in which the species-specific sorption coefficients (KD0, KD1, and KD2) were weighted with their respective fractions present at any given pH.     

Effect of zeolite application and soil pH on cadmium sorption in soils

Abstract

In this study the influence of zeolite application and soil liming on cadmium (Cd) sorption by soils in Greece was investigated. The zeolite was natural and consisted mainly of clinoptilolite. The soil samples were strongly acid surface horizons of an Alfisol limed from a pH of 4.0 to 8.5, and a neutral Bt horizon. The result showed that liming and zeolite application substantially increased sorption of Cd in the soils. Cadmium sorption was described adequately by the Freundlich equation whereas the Langmuir model failed to describe Cd sorption in the soils. The Freundlich constant K increased in value by zeolite application as well as by soil liming. A strong relationship was observed between this parameter and soil pH. A high percentage of cadmium sorbed was released in the desorption procedure. The amount of Cd released was reduced by zeolite application as well as by soil liming. It is concluded that zeolite application as well as soil liming increased Cd sorption by the soils.     

Phosphate sorption by red mediterranean soils from Greece

Abstract

In nineteen surface horizons of red Mediterranean soils from various locations of Greece, phosphorus (P) sorption experiments were conducted and the sorption characteristics were studied in relation to soil properties. Phosphate sorption data were fitted both to the Langmuir and Freundlich equations. From these equations, the following P sorption parameters were determined from the Freundlich equation, X = ACⁿ, the parameters A (the phosphate sorbed at C = 1 mg P/L), n (the P sorption intensity), the P sorption index (PS = X/log C) and maximum P sorption (Xmfr). From the Langmuir equation, C/X = 1/KXm + C/Xm, the parameters K (showing the bonding energy), maximum P sorption (Xmla), the quantity of P adsorbed at a standard concentration of 0.2 mg P/L (P0.2), and P maximum buffering capacity (PMBC). The Freundlich parameter A was strongly correlated to the clay and sesquioxides ("free”; iron and aluminum oxides and amorphous iron oxides) content. Seventy‐four percent of the variance of this parameter was explained by clay and “free”; iron (Fe) content. The Freundlich parameter n was significantly correlated with pH and amorphous iron oxides content, while 52% of its variance was explained by amorphous Fe and dithionite extrac‐table aluminum (Al). The P sorption maxima calculated from the Freundlich equation were in general lower than those calculated by the Langmuir equation. Both these parameters were strongly correlated with clay and more slightly with sesquioxides content. About 50% of their variance was explained by clay content of the soils. The P sorption index was strongly correlated with the clay content and less strongly with dithionite‐extractable Fe and Al. The P‐buffering capacity calculated from the data of Langmuir equation was also strongly correlated with these two parameters. In addition, clay content and dithionite‐extractable Fe and Al were well correlated to the amounts of P required to obtain an equilibrium concentration of 0.2 mg P/L while 61% of the variation of this parameter was explained by the clay and the dithionite‐extractable Fe content. From these findings, it seems that for the red Mediterranean soils from Greece, P sorption is affected by clay content and iron and aluminum oxide contents.