Sorptive Behavior of Sorgoleone in Ultisol in Two Solvent Systems and Determination of Its Lipophilicity

Sorgoleone (SGL) exuded by sorghum roots inhibits the development of some weeds. Due to its high hydrophobicity, it is expected that SGL presents low soil mobility and limited allelopathic activity in the field. This work aims to evaluate the sorptivity of sorgoleone in octanol-water and in soil under two solvent systems. The two solvent systems were methanol:water (60:40) (MeOH:H₂O) and pure methanol (MeOH). These two solvent systems promote different conditions for SGL solubility. Treatments were arranged in a 2 × 6 factorial (solvent systems × equilibrium concentrations in the solution (EC)). For each solvent, the sorption was achieved by shaking 500 mg of soil with 10 ml of 0, 5, 10, 15, 25, 40, and 60 mg L^?1 of SGL solution, during 24 h. After centrifugation, the supernatant was filtered and the SGL concentration was determined by high performance liquid chromatography (HPLC). Data of sorbed amount of SGL were submitted to variance analysis, using a hierarchic factorial model. The data of sorbed amount (x/m) and equilibrium concentration (C) were fitted to the linear (x/m = a + K _d C) and to the Freundlich (x/m = K _f C ^1/n ) models. The isotherm obtained for the MeOH:H₂O system presented linear shape, whereas for the MeOH system a two subsequent linear isotherm was fitted. Sorgoleone is a highly hydrophobic compound, presenting a log K _ow of 6.1. The sorption of sorgoleone to the soil was very high. The organic environment stimulated the sorgoleone sorption to the soil.     

Sorption and desorption behavior of benzidine in different solvent-sediment systems

The sorption and desorption behavior of benzidine in eight solvent-sediment systems were studied using a batch method. The solvents tested included deionized water (DI), calcium chloride solution (CaCl2), sodium hydroxide solution (NaOH), acetonitrile (ACN), a mixture of acetonitrile and ammonium acetate solution (ACN-NH4OAc), methanol (MeOH), ammonium acetate solution (NH4OAc) and hydrochloric acid solution (HCl). Three sets of sorption isotherm experiments were conducted separately in these eight solvents with seven days, three weeks, and two months of contact times, respectively. The results demonstrated nonlinear benzidine sorption phenomena in all eight solvents with higher sorption affinities for sediment sites in the aqueous solvents than in the organic solvents. The results from the desorption experiments revealed that the benzidine desorption efficiencies in the solvents decreased in an order, which was approximately the reverse order of its sorption affinity. Results also suggested that hydrophobic partitioning and covalent binding processes dominated in the desorption experiments, while cation exchange process had little effect on desorption of benzidine. A three-stage model was subsequently applied to simulate the desorption data in the selected solvents of ACN, ACN-NH4OAc and NaOH, respectively. The rapidly desorbing initial fractions were about 0.13-0.20, 0.15-0.26, and 0.18-0.25 for ACN, ACN-NH4OAc and NaOH, respectively. Finally, the sorbed concentrations of benzidine in slowly and very slowly desorbing domains in the selected solvents were correlated with the maximum sorption capacities obtained from the Langmuir sorption isotherm model. The maximum sorption capacities of benzidine were found to be comparable to the amount of benzidine residing in the slowly and very slowly desorbing domains.     

Cosolvent effects on sorption isotherm linearity

Sorption-desorption hysteresis, slow desorption kinetics, and other nonideal phenomena have been attributed to the differing sorptive characteristics of the natural organic polymers associated with soils and sediments. In this study, aqueous and mixed solvent systems were used to investigate the effects of a cosolvent, methanol, on sorption isotherm linearity with natural organic matter (NOM), and to evaluate whether these results support, or weaken, the rubbery/glassy polymer conceptualization of NOM. All of the sorption isotherms displayed some nonlinear character. Our data indicates that all of the phenanthrene and atrazine isotherms were nonlinear up to the highest equilibrium solution concentration to solute solubility in water or cosolvent ratios (Ce/Sw,c) used, approximately 0.018 and 0.070, respectively. Isotherm linearity was also observed to increase with volumetric methanol content (fc). This observation is consistent with the NOM rubbery/glassy polymer conceptualization: the presence of methanol in NOM increased isotherm linearity as do solvents in synthetic polymers, and suggests that methanol is interacting with the NOM, enhancing its homogeneity as a sorptive phase so that sorption is less bimodal as fc increases. When the equilibrium solution concentration was normalized for solute solubility in water or methanol-water solutions, greater relative sorption magnitude was observed for the methanol-water treatments. This observation, in conjunction with the faster sorption kinetics observed in the methanol-water sediment column systems, indicates that the increase in relative sorption magnitude with fc may be attributed to the faster sorption kinetics in the methanol-water systems, and hence, greater relative sorptive uptake for the rubbery polymer fraction of NOM at similar time scales.     

不同粒级黑土胶体对铅的等温吸附特征

采集了黑土样品并从中提取了3种粒级(5~10、2~5和1~2 μm)的胶体,测试了胶体的比表面积、颗粒粒径分布和颗粒矿物质组成等特征参数.在不同温度(25、35、45和55℃)、不同pH(2、4和6)条件下,使用黑土胶体对铅离子作等温吸附实验,并用Langmuir、Freundlich和Dubinin-Redushkevich (D-R)吸附等温方程对实验数据进行了拟合.结果显示,黑土胶体对铅具有较强的吸附能力;不同温度下黑土胶体对铅的吸附等温式能很好地符合Freundlich模式(R2=0.94~0.98)和D-R模式(R2=0.91~0.98),随温度的升高,黑土胶体对铅离子的吸附能力增加;不同pH条件下,不同粒径黑土胶体对铅的吸附等温式较好地符合Freundlich模式,而当粒径小于5 μm时,胶体对铅的吸附等温式能很好地符合Langmuir、Freundlich和D-R模式;随pH的升高,黑土胶体对铅离子的吸附能力增加;小粒径的胶体对铅具有更强的吸附能力;黑土胶体对铅的吸附属于化学吸附.     

The impact of contact time on pyrene sorptive behavior by a sandy-loam soil

Batch experiments with pyrene (PYR) were conducted to quantify the effect of contact time on its sorption and desorption behavior by a sandy-loam soil. Twenty-four and 48 h contact times were chosen for the nonequilibrium conditions and 240 h for the pseudoequilibrium study. All times was selected based on the kinetic results. The nonlinear, pseudoequilibrium sorption isotherm was fit to a two-stage Freundlich model: 3-7 mg/l for the first stage and 7-15 mg/l for the second stage. A substantial fraction of the sorbed PYR was not desorbed within the given desorption time. The reason of hysteresis was found to be a sorption enhancement due to soil hydration which provided more sorption sites. A desorption enhancement at 240-h desorption steps was attributed to the increased dissolved organic matter evolution. This study also found that both soil organic matter and clay materials had an equal role in PYR sorption enhancement and desorption resistance.     

Mineralization of aged atrazine and mecoprop in soil and aquifer chalk.

The effect of ageing on the bioavailability and sorption of the herbicides atrazine and mecoprop was studied in soil and aquifer chalk sampled at an agricultural field near Aalborg, Denmark. The herbicides were incubated in sterile soil or chalk up to 3 months prior to inoculation with 5 x 10(7) cells g(-1) (dry weight) of a mecoprop degrading highly enriched culture (PM) or 1 x 10(9) cells g(-1) (dry weight) of the atrazine degrading Pseudomonas sp. strain ADP. As a measure of the bioavailable residues accumulated 14CO2 was measured for 2 months. In both soil and chalk ageing limited the rate of atrazine mineralization, and in chalk the extent of mineralization was reduced as well. The fraction of sorbed atrazine in the soil ranged between 50% and 62%, whereas a maximum of 12% was sorbed in chalk. No impact on the mineralization of aged mecoprop was seen as no sorption of this herbicide on either soil or chalk was measured.     

Application of a mechanistic desorption-biodegradation model to describe the behavior of polycyclic aromatic hydrocarbons in peat soil aggregates

A procedure was developed to obtain three size fractions (2360 < d(p) < 1000, 1000 < d(p) < 710, and 710 < d(p) < 425 microm) of stable aggregates from Koopveen peat soil by application of an intense mixing regime prior to sieving of the soil material. The organic matter content, aggregation structure and the microstructure of these aggregates were determined and the particles were artificially contaminated with naphthalene and phenanthrene via a solvent phase. A nonlinear Freundlich sorption isotherm was determined for the naphthalene contaminated soil aggregates (n = 0.39; K(F) = 1.13 x 10(-2) m(1.17) kg(-0.39)). The applicability of a mathematical model, that describes sorption equilibrium, intraparticle mass-transfer, and nonlinear bacterial degradation kinetics, was tested by fitting results of dynamic desorption and biodegradation experiments, generated in this study and earlier work on the peat soil aggregates. The experimental data were described adequately although strong variations in the values of the fit parameter, the intra-particle porosity (0.30 < epsilon < 0.88), were found. This indicates the necessity of further investigations.     

Sorption of cobalt and nickel on anaerobic granular sludges: isotherms and sequential extraction

The objective of this study was to investigate the sorption capacity and the fractionation of sorbed nickel and cobalt onto anaerobic granular sludges. Two different anaerobic granular sludges (non-fed, pH=7) were loaded with nickel and cobalt in adsorption experiments (monometal and competitive conditions). The combination of sequential extraction with the sorption isotherm analysis allowed the assessment of the sorption capacity of individual fractions present in the anaerobic granular sludges. The operational fractionation of the sorbed heavy metals was determined using a modified Tessier sequential extraction procedure. The sorption characteristics of each extracted fraction (exchangeable, carbonates, organic matter/sulfides and residual fractions) fitted well to the Langmuir model. The organic matter/sulfides fraction showed the highest affinity for cobalt and nickel in both sludges investigated compared to the other operationally defined fractions. The presence of iron negatively affected cobalt and nickel accumulation in this organic matter/sulfides fraction. The trace metals-iron sulfide interactions are likely to be the key process in controlling the distribution of cobalt and nickel during sorption onto non-fed methanogenic granules due to the high affinity of iron sulfides towards the metals studied.     

Sorption kinetics of atrazine and diuron in soils from southern Brazil

Sorption kinetics of atrazine and diuron was evaluated in soil samples from a typical landscape in Paraná. Samples were collected (0-20 cm) in a no-tillage area from Mamborê, PR, which has been cultivated under a crop rotation for the last six years. Six sampling points of the slope were selected to represent a wide range of soil chemical and physical properties found in this area. Radiolabeled tracers (14C-atrazine and 14C-diuron) were used and the radioactivity was detected by liquid scintillation counting (LSC). Sorption was accomplished for increasing equilibration periods (0.5, 1.5, 3, 6, 12, 24, and 48 h). Kinetics data fitted adequately well to Elovich equation, providing evidences that soil reaction occurs in two distinct stages: a fast, initial one followed by a slower one. During the fast phase, 34-42 and 71-79% of total atrazine and diuron applied were sorbed to soil samples. No important differences were found among combinations of soil and herbicide sorption during the slow phase. The unrealistic conditions under batch experiments should be overestimating sorption in the fast phase and underestimating diffusion in the slow phase. Sorption of both herbicides was positively correlated to organic carbon and clay contents of soils, but atrazine was much less sorbed than diuron, showing its higher potential to contaminate groundwater, specially in sandy, low organic carbon soils.     

Competitive sorption of heavy metal by soils. Isotherms and fractional factorial experiments

Competing ions strongly affect heavy metal sorption onto the solid surfaces of soil. This study evaluated competitive sorption of Cd, Cu, Ni, Pb and Zn on three soils: Calcixerollic Xerochrept, Paralithic Xerorthent and Lithic Haplumbrept. Monometal and competitive sorption isotherms were obtained at 25 degrees C. The individual effect of ions on retention of the others was ascertained by a fractional factorial analysis design. Most of the sorption isotherms belonged to type L subtype 2 in the classification of Giles. In competitive sorption the initial linear part was shorter and the knee sharper when compared with monometal sorption isotherms. Parameters related to sorptive capacity, such as Point B, Langmuir monolayer and Freundlich distribution coefficient, were higher in monometal than in competitive sorption, and in basic soils than in acidic soil. Calcium desorbed at different points of the sorption isotherms indicated that cationic exchange with Ca was the main retention mechanism in calcareous soils. For Pb, the ratio Ca desorbed/Pb sorbed was close to one; for Cu, Ni and Zn the ratio ranged from 1.20 to 1.37, probably due to partial dissolution of calcium carbonates by hydrolytic processes during retention. On the other hand, Cd had a ratio around 0.6 reflecting another additional retention mechanism, probably surface complexation. Fractional factorial design confirmed that the presence of the cations investigated reduced the amount of the five metals retained, but the presence of Cu and Pb in the system depressed Ni, Cd and Zn sorption more than the inverse. Cation mobility was enhanced when equilibrium concentration increased and the effect was higher in Ca-saturated soils.     

Abiotic reductive dechlorination of chlorinated ethylenes by soil

Abiotic reductive dechlorination of chlorinated ethylenes by soil in anaerobic environments was characterized to improve knowledge of the behavior of chlorinated ethylenes in natural systems, including systems modified to promote attenuation of contaminants. Target organics in the soil suspension reached sorption equilibrium in 2 days and the sorption isotherm of target organics was properly described by the linear sorption model. A modified Langmuir-Hinshelwood model was developed to describe the kinetics of reductive dechlorination of target organics by soil. The rate constants for the reductive dechlorination of chlorinated ethylenes at the reactive surfaces of reduced soils were found in the range between 0.055 (+/- 8.9%) and 2.60 (+/- 3.2%) day(-1). The main transformation products in reduced soil suspensions were C2 hydrocarbons. No chlorinated intermediates were observed at concentrations above detection limits. Five cycles of reduction of the soil followed by oxidation of the soil with trichloroethylene (TCE) did not affect the removal of TCE. The removal was affected by the reductants used and increased in the order: Fe(II) < dithionite < Fe(II) + dithionite.     

Impact of vegetated filter strips on sorbed herbicide concentrations and sorption equilibrium in agricultural plots

The objective was to investigate the impact of vegetated filter strips on exported atrazine and deethylatrazine concentrations [dissolved and sorbed to eroded sediments (>1.5 μm)], the deethylatrazine to atrazine ratio in water and sediments, the ratio of sorbed to dissolved herbicides in runoff and subsurface infiltration as well as field equilibrium state under natural climate during two seasons. We hypothesize that sorption equilibrium was not achieved in 2004 because of the short delay (<24 h) between herbicide application and the first rain event. In 2005, observations suggest that possible changing sorption equilibrium conditions were reached (20 days after atrazine application), especially for eroded sediments submitted to changing environmental conditions in subsurface. If confirmed by other experiments, this will raise the question of the representativeness of laboratory-determined soil sorption coefficients to predict the fate of pesticides.     

Impact of vegetated filter strips on sorbed herbicide concentrations and sorption equilibrium in agricultural plots

The objective was to investigate the impact of vegetated filter strips on exported atrazine and deethylatrazine concentrations [dissolved and sorbed to eroded sediments (>1.5?μm)], the deethylatrazine to atrazine ratio in water and sediments, the ratio of sorbed to dissolved herbicides in runoff and subsurface infiltration as well as field equilibrium state under natural climate during two seasons. We hypothesize that sorption equilibrium was not achieved in 2004 because of the short delay (<24?h) between herbicide application and the first rain event. In 2005, observations suggest that possible changing sorption equilibrium conditions were reached (20?days after atrazine application), especially for eroded sediments submitted to changing environmental conditions in subsurface. If confirmed by other experiments, this will raise the question of the representativeness of laboratory-determined soil sorption coefficients to predict the fate of pesticides.     

Sorption Kinetics of Atrazine and Diuron in Soils from Southern Brazil

Abstract

Sorption kinetics of atrazine and diuron was evaluated in soil samples from a typical landscape in Paraná. Samples were collected (0–20 cm) in a no-tillage area from Mamborê, PR, which has been cultivated under a crop rotation for the last six years. Six sampling points of the slope were selected to represent a wide range of soil chemical and physical properties found in this area. Radiolabeled tracers (¹⁴C-atrazine and ¹⁴C-diuron) were used and the radioactivity was detected by liquid scintillation counting (LSC). Sorption was accomplished for increasing equilibration periods (0.5, 1.5, 3, 6, 12, 24, and 48 h). Kinetics data fitted adequately well to Elovich equation, providing evidences that soil reaction occurs in two distinct stages: a fast, initial one followed by a slower one. During the fast phase, 34–42 and 71–79% of total atrazine and diuron applied were sorbed to soil samples. No important differences were found among combinations of soil and herbicide sorption during the slow phase. The unrealistic conditions under batch experiments should be overestimating sorption in the fast phase and underestimating diffusion in the slow phase. Sorption of both herbicides was positively correlated to organic carbon and clay contents of soils, but atrazine was much less sorbed than diuron, showing its higher potential to contaminate groundwater, specially in sandy, low organic carbon soils.     

Natural phillipsite as a matrix for a slow-release formulation of oxamyl

The performance of phillipsite as a matrix for slow-release formulation of oxamyl [N,N-dimethyl-2-methylcarbamoyl-oxymino-2-(methylthio)acetamide] was tested. The adsorption kinetics followed a first-order law, and the adsorption isotherm fitted well in a two-surface Langmuir model, suggesting a double mechanism of interaction between oxamyl and the sorbent. The sorption mechanism, studied by FTIR, provided two fractions of oxamyl. The first one is sorbed on the mineral surface, linked by H-bonding, and the second one is constituted by a multilayer of oxamyl molecules linked by a water bridge between them. The release kinetics of oxamyl from a substratum zeolite-oxamyl also follows a first-order law, with two stages that correspond to both fractions of oxamyl previously detected.     

Sorption of heterocyclic compounds from a complex mixture of coal-tar compounds on natural clayey till

The sorption and desorption of heterocyclic organic compounds in a complex multisolute system to a natural clayey till was investigated. The composition of the solutes reflect a simplified composition of an aqueous phase in contact with coal tar. Sorption was studied for two ratios (s:l) of clayey till (solid) to aqueous phase (liquid). The effect of the complex mixture of solutes on sorption of the four heterocyclic compounds: benzofuran, dibenzofuran, benzothiophene, and dibenzothiophene is evaluated by comparison with their sorption measured in single-solute systems. Sorption of the four compounds is affected by the complex mixture, with sorption decreases for all four compounds at high s:l ratio indicating competitive sorption. The effect on sorption of the individual compounds is not related to solubility or hydrophobicity of the compounds. Freundlich-type isotherms are observed for all compounds in the high s:l-ratio experiments, but for the most hydrophobic compounds isotherms are close to linear. The sorption of N-compounds and benzofuran is apparently influenced by cation exchange and dipole–dipole attraction to clay minerals. At high concentrations a dramatic increase in the sorption of the most strongly sorbing compounds is observed in the low s:l-ratio experiment. The dramatic increase in sorption appears to be a result of multimolecular layer sorption or condensation on surfaces in the clayey till at high surface density of organic compounds, and the data are fitted by BET (Brunauer, Emmet, and Teller) type 2 isotherms. The increase may or may not be induced by the presence of N-heterocyclic compounds sorbed by cation exchange and dipole–dipole attraction. The desorption of the compounds was studied for the low s:l ratio where multimolecular layer formation apparently had occurred. Partially irreversible sorption, hysteric Langmuir type desorption with isotherms of very high K_l coefficient, or behaviour reflecting dissolution of a condensed phase is observed.     

Adsorption and transport of arsenate in carbonate-rich soils: coupled effects of nonlinear and rate-limited sorption

The transport and fate of arsenate in carbonate-rich soil under alkaline conditions was investigated with multiple approaches combining batch, sequential extraction and column experiments as well as transport modeling studies. Batch experiments indicated that sorption isotherm was nonlinear over a wide range of concentration (0.1-200 mg L(-1)) examined. As(V) adsorption to the calcareous soil was initially fast but then continued at a slower rate, indicating the potential effect of rate-limited sorption on transport. Column experiments illustrated that transport of As(V) was significantly retarded compared to a non-reactive tracer. The degree of retardation decreased with increasing As(V) concentration. As(V) breakthrough curves exhibited nonideal transport behavior due to the coupled effects of nonlinear and rate-limited sorption on arsenate transport, which is consistent with the results of modeling studies. The contribution of nonlinear sorption to the arsenate retardation was negligible at low concentration but increased with increasing As(V) concentration. Sequential extraction results showed that nonspecifically sorbed (easily exchangeable, outer sphere complexes) fraction of arsenate is dominant with respect to the inner-sphere surface bound complexes of arsenate in the carbonate soil fraction, indicating high bioavailability and transport for arsenate in the carbonate-rich soils of which Fe and Al oxyhydroxide fractions are limited.     

Tylosin sorption to silty clay loam soils, swine manure, and sand

The objectives of this study were to assess sorption and desorption of tylosin, a macrolide antimicrobial chemical used in swine, cattle, and poultry production, in three silty clay loam soils of South Dakota and compare soil sorption to sand and manure sorption. The silty clay loam soils, from a toposequence in eastern South Dakota, standardized sand samples, and swine manure were used in 24-h batch sorption studies with tylosin concentrations ranging from 25 to 232 micro mole/L. Desorption from soil was conducted over a four-day period. Partition coefficients, based on the Freundlich isotherm (K(f)) or K(d) values, were calculated. K(f) values for the silty clay loams were similar, not influenced by landscape position, and averaged 1,350 with isotherm slopes ranging from 0.85 to 0.93. K(f) values for sand were dependent on solution/sand ratios and pH, ranging from 1.4 to 25.1. K(d) values of manure were dependent on the solution type and ranged from 840 L/kg with urine to about 175 L/kg when sorbed from water. Desorption of tylosin from each soil over the four-day period was < 0.2% of the amount added. The soils' high K(f) values and low desorption amounts suggest that once tylosin is in these soils, leaching to lower depths may not occur. However, this does not preclude runoff with soil eroded particles. If tylosin reaches a sand aquifer, through bypass flow or other mechanism(s), movement in the aquifer most likely would occur.     

Effects of lipids on the sorption of hydrophobic organic compounds on geosorbents: a case study using phenanthrene

The impact of the lipid fraction of natural geosorbents on the sorption of a polycyclic aromatic hydrocarbon was assessed using several experiments. In the first set of experiments phenanthrene was sorbed on a coastal sediment as well as on its humin and humic acid fractions before and after lipid extraction. Before lipid extraction, sorption shows dominantly partitioning characteristics. However, the extraction of lipids from sediment and humin drastically increases, by up to one order of magnitude, their sorption affinity for phenanthrene at low sorbate concentrations, resulting in increased isotherm nonlinearity. This effect is less pronounced for humic acids. One mechanism proposed for the increasing sorption is that lipids, despite their very low relative abundance in the sediments, can compete with phenanthrene for specific high affinity sorption sites (e.g., matrix pores and adsorption sites). This competition is not surprising considering the similar hydrophobic nature of lipids and phenanthrene. Lipids, or any non-polar molecules, could also act like plasticizers by swelling rigid domains and disrupting high affinity sites. In both cases, the removal of lipids (and extraction solvents) makes those sites available for phenanthrene. These provide alternative explanations to the previously proposed “solvent conditioning effect” believed to occur when geosorbents are treated with non-polar solvents modifying the matrix structure, an effect yet to be proven at molecular scale. To further investigate the impact of lipids on sorption, other independent experiments were performed. In a second experiment, re-addition of lipids to the extracted sediment restored the sorption isotherm linearity observed in the native material supporting the absence of irreversible extraction artifacts. However, high addition of lipids (i.e., after saturation of high affinity sites) seems to also enlarge the low affinity partitioning domain. These results are consistent with dual-mode, hole-filling, sorption models involving diffusion. In the final set of experiments, solid-state ¹⁹F-NMR using F-labeled lipids sorbed onto the sediments confirmed that lipids may be in different domains (mobile or rigid) that interact or not with phenanthrene. The possible effects of lipid removal on sorption have been overlooked and should be considered when geosorbents are pretreated.