Progress 10/01/00 to 09/30/05
Outputs
Commercial atrazine formulations commonly contain nonionic surfactants that serve as solubilizing and wetting agents for enhancing the stability and efficacy of the herbicide. The fate of atrazine in soils has been extensively investigated, yet few studies have considered the effects of formulation components on the fate of atrazine in soils. In this study, we investigated the influence of the nonionic surfactant, Brij 35 (Brij), on the sorption of atrazine on Ca- and K-saturated samples of a reference smectite, Panther Creek (PC). In general, Brij concentrations of 50 and 200 mg/L had little effect on atrazine sorption, but sorption was substantially inhibited by Brij concentrations of 2100 mg/L. For Brij concentrations of 6300 mg/L, atrazine sorption was intermediate between that observed for the 200 and 2100 mg/L Brij systems. Brij molecules themselves were very strongly sorbed by PC, with sorption maxima exceeding 200 g/kg. X-ray diffraction analysis of Brij-treated
PC indicated that the sorbed Brij was intercalated into interlayers of the smectite. At Brij concentrations of 2100 mg/L, Brij competed with atrazine for interlayer sorption sites. In contrast, at the initial Brij concentration of 6300 mg/L, the clay interlayers were largely filled with Brij, and excess Brij probably accumulated on external surfaces of the clay as surface micelles. We hypothesize that atrazine partitioning into surfactant micelles on external surfaces of the clay led to enhanced retention by the solid phase.
Impacts
Studies of a model clay, a model surfactant, and atrazine, suggest that surfactants applied to soil as herbicide carriers may either enhance or diminish the retention of the herbicide by the soil. The impact of the surfactant on herbicide retention depends on its concentration as well as on characteristics of the clay. Surfactant molecules can compete with atrazine for sorption sites.
Publications
- Chappell, M.A., Laird, D.A., Thompson, M.L., Li, H., Teppen, B.J., Aggarwal, V., Johnston, C.T. and Boyd, S.A. 2005. Influence of smectite hydration and swelling on atrazine sorption behavior. Environ. Sci. Technol. 39:3150-3156.
- Chappell, M.A., Laird, D.A., Thompson, M.L. and Evangelou, V.P. 2006. Co-sorption of atrazine and a lauryl polyoxyethylene oxide nonionic surfactant on smectite. J. Agric. Food Chem. In press.
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Progress 01/01/04 to 12/31/04
Outputs
The herbicide atrazine is commercially available in a number of different formulations. One of the main components in these formulations is nonionic polyoxyethylene oxide (PEO) alcohols. PEO surfactants serve as solubilizing agents for concentrating the atrazine and as wetting agents to promote the pesticide's distribution when applied to soil. We investigated the influence of the PEO surfactant Brij 35 on atrazine sorption by soil. Samples of three air-dried soils with varying organic C and clay contents were rehydrated in CaCl2 or KCl for 24 h. Aliquots of prepared atrazine-Brij 35 emulsions were added and the suspensions were equilibrated for another 24 h. Atrazine sorption was evaluated in the presence of 0, 50, 200, and 2100 mg L-1 Brij 35. In general, the surfactant inhibited atrazine sorption, but in some cases, high additions of Brij 35 (2100 mg L-1) enhanced atrazine sorption. In separate experiments, sorption of atrazine originating from the commercial
formulation, Aatrex 4L, was measured. Some of the sorption isotherms appeared convex, suggesting cooperative atrazine sorption. We identified the nonionic surfactant in Aatrex 4L as Brij 30, a smaller, less hydrophilic polymer than Brij 35. We speculated that favorable interactions between atrazine and Brij 30 might have promoted cooperative atrazine sorption.
Impacts
We determined that sorption of atrazine by clay and by soil materials when the atrazine is emulsified with a surfactant was considerably different and more complicated than when pure atrazine was used in sorption experiments. This observation may help us to predict better the fate of atrazine and other similar pesticides that are applied to soils in the presence of a surfactant.
Publications
- Chappell, M.A. 2004. Confounding factors and tertiary-phase control by a surfactive agent on the sorption of atrazine. PhD. Dissertation. Iowa State Univ., Ames. 121 pages.
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Progress 01/01/03 to 12/31/03
Outputs
Sampling handling and atrazine sorption by soils and reference clay. The influence of sample handling (air-drying) on atrazine sorption by a reference smectite and three smectite-dominated soils was investigated. Samples of Na-saturated Panther Creek (PC) smectite (less than 2 micrometers) were K- or Ca-saturated by dialysis, first against 0.2 eq/L KCl and CaCl2 solutions and then against 10 meq/L KCl and CaCl2 solutions, respectively. Sample handling effects were tested either by keeping the homoionic PC in the 10 meq/L suspension (moist) or by air-drying and then resuspending the homoionic PC samples in 10 meq/L KCl or CaCl2 solutions (dry) for seven days. Air-drying the clays increased the atrazine distribution coefficient, Kd, by approximately one order of magnitude for both K- and Ca-PC. Surface horizon samples of three soils (Sparta, an Entic Hapludoll; Sperry, a Typic Argialboll; and Zook, a Cumulic Vertic Endoaquoll) with clay fractions dominated by smectite
were collected and stored in sealed containers at 4 C without drying. Portions of these soil samples were air-dried. A batch equilibration technique was used to determine atrazine sorption affinity. Both the moist and air-dry samples were suspended in 10 mM CaCl2 for 24 hrs. Afterwards, atrazine was added and the suspensions were allowed to equilibrate for another 24 hrs. Freundlich sorption constants, K'F (adjusted for the water solubility of atrazine), were less for the air-dry Sparta and Zook samples than for the moist Sparta and Zook samples. The air-drying treatment had no effect on KF values for the Sperry samples. Our results suggest that hysteresis induced by air-drying regulates the physical organization (hydrated phase) of smectites, which in turn influences atrazine sorption affinity. A similar sample-handling effect also appeared to alter the affinity of the soil samples for atrazine. However, the physical state of soil organic matter could also be affected by air-drying.
Thus, there may be multiple causes for the effect of air-drying on atrazine sorption by soil materials. Sorption of atrazine and surfactant by reference clay. We have also investigated the sorption behavior of emulsified atrazine in commercial and lab-simulated formulations. We investigated three smectitic soils and the reference smectite Panther Creek bentonite. Different lab-simulated formulations were prepared by varying the concentration of the polydisperse nonionic surfactant, lauryl polyoxyethylene alcohol (Brij 35) above and below its critical micelle concentration (80 mg/L). For the soils, atrazine sorption isotherms (in general) shifted in shape from nearly linear without Brij 35, to concave with 50 mg/L Brij 35, to convex with 200 mg/L Brij 35, indicative of cooperative sorption. With 2000 mg/L Brij 35 (approaching surface saturation with surfactant), sorption isotherms ranged in appearance from concave to hyperbolic. Cooperative atrazine sorption seemed to occur at initial
atrazine concentrations <5 mg/L, while higher initial atrazine concentrations (10 mg/L) appeared to promote self-desorption of the atrazine-Brij 35 solloids.
Impacts
We determined that sorption of emulsified atrazine to clay and to soil was considerably different and more complicated from that of neat atrazine sorption. This observation may help us understand better and predict the fate of other pesticides that are applied to soils in the presence of a surfactant.
Publications
- Chappell, M.A., Laird, D.A. and Thompson, M.L. 2003. Effects of sample handling (air-drying) on sorption of atrazine by soils and clays. Abstracts for Clay Minerals Society Annual Meeting, Athens, GA.
- Chappell, M.A., Laird, D.A. and Thompson, M.L. 2003. Sorption of atrazine from commercial and laboratory-simulated formulations to smectites. Abstracts for Soil Science Society of America Annual Meeting, Denver, CO.
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Progress 01/01/02 to 12/31/02
Outputs
While atrazine sorption studies commonly employ only the pure chemical, atrazine is commercially distributed as part of a formulation. Commercial atrazine formulations contain polyoxyethylene (POE) alcohol nonionic surfactants, such as Brij 35 (CH3(CH2)11(EO)23OH, where EO = CH2CH2O), which emulsify atrazine to increase its solubility and uniformity of application. We investigated whether a surfactant added to the herbicide could influence the sorption of atrazine by soil materials and by clays. For most of the soil materials, we observed a decrease in atrazine sorption (as measured by the solid-liquid distribution coefficient, Kd) with the addition of Brij 35 (both above and below the critical micelle concentration of the surfactant). In contrast, we observed larger Kd values when atrazine was added as part of the commercial formulation Aatrex 4L, suggesting that there are important differences in the formulation (e.g., such as shorter POE chain) that are not
simulated by Brij 35. We also investigated how cation saturation and sample handling of smectitic clays may modify their affinity for atrazine. Using the low-charge, Panther Creek (PC) bentonite, we found that air-drying PC after cation saturation, followed by rehydrating and sonicating the clays (as opposed to never drying the clay) before adding atrazine, gave larger Kd values. The effect was much greater in the K-saturated PC compared with the Ca-saturated PC. We propose that both the type of saturating cation and sample handling, separately and in combination, produced unique PC interlayer phases and quasicrystal sizes that had differing affinities for atrazine.
Impacts
By understanding the role that surfactants play in retention of herbicides by soil we will be able to better predict the efficiacy and movement of herbicides that are applied to soils. Our current data indicate that rather than making atrazine more mobile, the surfactant in atrazine makes it more likely to be sorbed and retained by soils, especially those with high organic matter contents.
Publications
- Chappell MA, VP Evangelou, DA Laird and ML Thompson. 2002. Impact of cation saturation and the nonionic surfactant Brij 35 on atrazine sorption by panther creek smectite. Soil Sci. Soc. Am. Annual Meeting Abstracts.
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Progress 01/01/01 to 12/31/01
Outputs
Many studies have confirmed that atrazine (bio-active form) is hydrolyzed to hydroxy-atrazine (bio-inactive form). This transformation represents chemical degradation since atrazine is relatively resistant to microbial degradation at the concentrations commonly encountered in normal agricultural soils. Atrazine hydrolysis occurs under acid or basic conditions. The relative rates of hydroxylation of atrazine with Ca-montmorillonite in the presence of Brij 35 were studied in our laboratory by observing the increase of the C=O band as a function time. Infrared spectroscopic data strongly suggested that there was a synergistic hydrolysis effect between the surfactant epoxide and atrazine on the clay surface. A possible mechanism is the oxidation of ethylene oxide and production of carboxylic acid. The presence of carboxylic acid leads to the hydrolysis of atrazine. The pathway from the ethylene oxide to carboxylic acid is as follows: First the epoxide (ethylene oxide) is
hydrolyzed. Our preliminary data showed that the polyether epoxide appeared stable under atmospheric conditions, even under strong acid conditions, e.g., pH=0. However, when the polyethylene oxide entered the clay interlayer, hydrolysis occurred. We propose to investigate how clay carries out this apparent catalysis and what are the variables in the 2:1 clay that are responsible for this catalysis, e.g., tetrahedral vs. octahedral substitutions, high charge density vs. low charge density, exchangeable cations with high electronegativity vs. low electronegativity. Our data also indicated that the glycol group underwent oxidation and the carbon-carbon bond was cleaved. Oxidation of the glycol group generally requires concentrated periodic acid or strong oxidizing agents, e.g., KMnO4, K2Cr2O7 and heat. We showed that clay interlayer under standard pressure and temperature catalyzes this reaction as well. Our current data suggested that oxidation of the epoxide group produces relatively
low pKa organic acids. Assuming that the organic acids produced exhibit a pKa of 4, when fully protonated they are producing an equilibrium solution pH of approximately 2. Atrazine rapidly hydrolyzes at pH 2.
Impacts
It is important that atrazine, used for weed control in soils, does not accumulate in soil and/or move to the groundwater. The results of this study open the door for the design of pesticide-additives that may effectively control the fate of pesticides in the soil environment.
Publications
- Evangelou VP. 2001. Pyrite microencapsulation technologies: Principles and potential field application. J. Ecol. Engin. 17:165-178.
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Progress 01/01/00 to 12/31/00
Outputs
Degradation Mechanisms of Nonionic Surfactants Confined in 2:1 Expanding Clays. Many studies have confirmed that atrazine (bio-active form) is hydrolyzed to hydroxy-atrazine (bio-inactive form). This transformation represents chemical degradation since atrazine is relatively resistant to microbial degradation at the concentrations commonly encountered in normal agricultural soils. Atrazine hydrolysis occurs under acid or basic conditions. The relative rates of hydroxylation of atrazine with Ca-montmorillonite in the presence of Brij 35 were studied in our laboratory by observing the increase of the C=O band as a function time. Infrared spectroscopic data strongly suggested that there was a synergistic hydrolysis effect between the surfactant epoxide and atrazine on the clay surface. A possible mechanism is the oxidation of ethylene oxide and production of carboxylic acid. The presence of carboxylic acid leads to the hydrolysis of atrazine. The pathway from the
ethylene oxide to carboxylic acid is as follows: First the epoxide (ethylene oxide) is hydrolyzed. Our preliminary data showed that the polyether epoxide appeared stable under atmospheric conditions, even under strong acid conditions, e.g., pH = 0. However, when the polyethylene oxide entered the clay interlayer, hydrolysis occurred. We propose to investigate how clay carries out this apparent catalysis and what are the variables in the 2:1 clay that are responsible for this catalysis, e.g., tetrahedral vs. octahedral substitutions, high charge density vs. low charge density, exchangeable cations with high electronegativity vs. low electronegativity. Our FTIR data also indicated that the glycol group underwent oxidation and the carbon-carbon bond was cleaved. Oxidation of the glycol group generally requires concentrated periodic acid or strong oxidizing agents, e.g., KMnO4, K2Cr2O7 and heat. Using FTIR spectroscopy we showed that clay interlayer catalyzes this reaction as well. Our
current data suggest that oxidation of the epoxide group produces relatively low pKa organic acids. Assuming that the organic acids produced exhibit a pKa of 4, when fully protonated they are producing an equilibrium solution pH of approximately 2. Atrazine rapidly hydrolyzes at pH 2.
Impacts
It is important that herbicides, used for weed control in soils, do not accumulate in soil and/or in the groundwater. In our study we demonstrated that herbicide additives, e.g., surfactants, undergo abiotic oxidation. This oxidation produces easily biodegradable simple organic acids which aid in the degradation process of herbicides.
Publications
- Pils JP and Evangelou VP. 2000. Spectroscopic and wet chemistry techniques for elucidating ammonium fixation in smectites. 92nd Annual Agronomy Meetings Abstracts. Minneapolis, MN. Nov. 5-9, 2000.
- Chappell MA and Evangelou VP. 2000. Influence of added K on NH4 selectivity/mobility in soil. Soil Sci. (In Press).
- Evangelou VP and McDonald L. 1999. Influence of Sodium on Soils of Humid Regions. In: M Passarakli (ed.) Handbook of Plant Stress. Marcel Dekker, New York, NY.
- Evangelou VP and Marsi M. 2000. Composition and metal-ion complexation behavior of humic fractions derived from corn tissue. Plant and Soil (In Press).
- Chappell MA and Evangelou VP. 2000. Influence of added K on inducing ammonium fixation and inhibiting nitrification. Soil Sci. 165:421-426.
- Evangelou VP. 2000. Pyrite microencapsulation technologies: Principles and potential field application. J. Ecolog. Eng. (In Press).
- Evangelou VP. 1999. Pyrite microencapsulation technologies: Principles and potential field application. pp. 147-156. In: I Gaballah, J Hager, and R Solozabal (eds.) Proc. of the Global Symp. on Recycling, Waste Treatment and Clean Technology. San Sebastian, Spain. Sep. 5-9, 1999.
- Fytas K, Bousquet P and Evangelou B. 1999. Application of silicate coatings on pyrite to prevent acid mine drainage. pp. 1199-1207. In: Proc. of the Sudbury'99 - Mining and the Environment II Conference, Ontario. Sep. 13-15, 1999.
- Fytas K, Bousquet P and Evangelou B. 1999. Silicate coating on pyrite to prevent acid drainage. Proceedings of the 101st CIM Annual Meeting. Org. by CIM, Calgary, Alberta. May 2-5, 1999. CD-Rom.
- Chappell MA and Evangelou VP. 1999. Influence of added potassium on ammonium mobility and nitrification in soil. 91st Annual Agronomy Meetings Abstracts, Salt Lake City, UT. Oct. 31-Nov. 4, 1999.
- Evangelou VP and Marsi M. 1999. Stability of Ca2+, Cd2+, and Cu2+-[illite-humic] complexes. 91st Annual Agronomy Meetings Abstracts, Salt Lake City, UT. Oct. 31-Nov. 4, 1999.
- Evangelou VP. 2000. Mechanisms of interactions between a hydrophilic surfactant (polyether-Brij-35) atrazine complex and 2:1 clay interlayers. Bouyoucos Conference on Environmental Chemistry at the Clay-Water Interphase. Honolulu, HI. March 6-9, 2000.
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Progress 01/01/99 to 12/31/99
Outputs
We hypothesized that the surface amino-group of chloro-atrazine particles protonates when exposed to atmospheric moisture and therefore an outer layer of chloro-atrazine colloids was expected to transform to hydroxy-atrazine. To test the hypothesis we compared transmittance infrared (FT-IR) spectra with diffuse reflectance spectra of pure atrazine and hydroxy-atrazine under various treatments and a commercial form of atrazine, AATREX-90. These spectra comparisons indicated that a certain number of chloro-atrazine molecules in the outer-layer of chloro-atrazine crystals transformed to protonated hydroxy-atrazine molecules. This is believed to have practical implications on the fate and mobility of atrazine in the field.
Impacts
It is important that atrazine, used for weed control in soils, does not accumulate in soil and/or move to the groundwater. The limiting step in the decomposition reaction of atrazine in soil is the replacement of the chlorine molecule with hydroxyl (OH), a process refered to as hydrolysis. The resulting molecule, hydroxy-atrazine, is readily decomposed microbiologically.
Publications
- Evangelou, V.P. and Marsi, M. 1999. Stability of Ca2+-, Cd2+-, and Cu2+-Illite-humic complexes. Agron. Abstr. pp. 209.
- Chappel, M.A. and Evangelou, V.P. 2000. Influence of added K on nitrification. Soil Sci. Accepted for publication.
- Chappel, M.A. and Evangelou, V.P 1999. Influence of added potassium on ammonium mobility and nitrification in soil. Agron. Abstr. pp. 204.
- Evangelou, V.P., Marsi, M. and Vandiviere, M.M. 1999. Stability of Ca2+-, Cd2+-, Cu2+-[illite-humic] complexes and pH influence. Plant and Soil 213:63-74.
- Evangelou, V.P. 1999. Pyrite microencapsulation technologies: Principles and potential field application. J. Ecol. Eng. In press.
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Progress 01/01/98 to 12/31/98
Outputs
IMPACTS OF RESEARCH. Pesticides are often required for insect and weed control in production agriculture. Without these chemicals, total yields would no doubt be lower. A potential problem clearly exists, however, when these compounds survive and move in the environment to impact nontarget hosts, including humans. ACCENT (nicosulfuron) is a new sulfonyluras herbicide that can be used at low rates to control weeds in corn. An understanding of the sorption of this chemical onto soil colloids and the subsequent movement through a soil may be important to reduce the impact on groundwater contamination. For nicosulfuron transport, breakthrough curves (BTCs) were measured using soil columns for eight Iowa sols and four Oxisols from Brazil. For nonsandy Iowa soils, BTCs were asymmetrical, indicative of nonequilibrium during transport. Conversely, BTCs for sandy Iowa soils and Brazilian soils were symmetrical, indicative of equilibrium transport. Measured asymmetrical BTCs
were well fitted by using the two-site/two-region nonequilibrium model. Both the equilibrium and nonequilibrium models were good estimators for nicosulfuron BTCs when the measured BTCs were symmetrical. The BTCs of nonreactive tracers were symmetrical and their shape was not affected by the size of the tracer, suggesting that transport-related nonequilibrium was not important in the soil columns in this study. Therefore, the observed nonequilibrium for nicosulfuron transport in nonsandy Iowa soils was likely caused by rate-limited sorption. For nonsandy Iowa soils, linear sorption coefficients obtained from miscible displacement experiments were close to those obtained from the batch equilibrium experiments reported in an earlier study. This might be due to the fast or instantaneous sorption of nicosulfuron and the high proportion of sites where instantaneous adsorption occurs. On the contrary for Brazilian soils and sandy Iowa soils, column values calculated from the miscible
displacement experiments were lower than those obtained from the batch equilibrium experiments.
Impacts
(N/A)
Publications
- Gonzalez, J.M. and Ukrainczyk, L. 1999. Transport of nicosulfuron in soil columns. J. Environ. Qual. 28:101-107.
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Progress 01/01/97 to 12/31/97
Outputs
Nicosulfuron is a relatively new sulfonylurea promoted for weed control in corn. In this study breakthrough curves (BTCs) were measured using soil columns for eight Iowa soils and four Oxisols from Brazil. Chloride (Cl-) and pentafluorobenzoic acid (PFBA) were used as non-reactive tracers. For the sandy Iowa soils and the Brazilian soils BTCs were symmetrical, while for the non-sandy Iowa soils BTCs were asymmetrical. Breakthrough curves were interpreted using convection-dispersion equation and equilibrium and non-equilibrium transport models. In Brazilian soils and sandy Iowa soils equilibrium models described the BTCs well. In non-sandy Iowa soils, where tailing was observed, the data were better described by a two-site/two-region model, indicative of non-equilibrium processes. A comparison with the Cl- and PFBA BTCs suggests that the non-equilibrium is not transport-related. This is also supported by the low correlation between the mass transfer parameters and the
partition coefficients. Kd values obtained by batch equilibrium experiments and by miscible displacement experiments were similar for non-sandy Iowa soils which suggests rapid sorption processes in those soils whereas Kd values obtained from the miscible displacement experiments for Brazilian soils and sandy Iowa soils were significantly lower than those obtained from the batch equilibrium experiments. It is proposed that the observed non-equilibrium in non-sandy Iowa soils is most likely due to nicosulfuron chemisorption on smectites.
Impacts
(N/A)
Publications
- GONZALEZ, J.M. 1997. Sorption and mobility of nicosulfuron in soils. M.S. Thesis, Iowa State Univ., Ames. 134 p.
- GONZALEZ, J.M. and UKRAINCZYK, L. 1997. Transport of nicosulfuron in soil columns. J. Environ. Qual. (accepted for publication).
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Progress 01/01/96 to 12/30/96
Outputs
Nicosulfuron (ACCENT) is a new, low-rate, sulfonylurea herbicide that is being promoted for weed control in corn. The kinetics of sorption and transport of nicosulfuron in soil columns were examined in miscible displacement experiments. This study is a continuation of our previous study of sorption of nicosulfuron in soils using batch-equilibrium method. Objectives of the column study were to (i) measure nicosulfuron Kd values in soil column experiments and to compare those values to Kd values measured in batch experiments, (ii) characterize the dynamics of nicosulfuron adsorption-desorption in soil columns by determining sorption rate coefficients and (iii) evaluate whether incomplete desorption of nicosulfuron in Iowa soils is due to physical or chemical nonequilibrium. 8 Iowa soils and 4 Brazilian soils were packed in glass columns of 11-15 cm length and 2.9 cm diameter. Chloride and PFBA were used as nonreactive tracers. BTCs were interpreted using convection-
dispersion equation and equilibrium and non-equilibrium transport models. The results indicate that Kd batch values are similar to Kd values obtained from BTCs. In Oxisols and in sandy soils from Iowa equilibrium models described the BTCs well. In Iowa soils high in smectite content, tailing was observed and the data were better described by a two-site/two region model, indicative of non-equilibrium processes. A comparison with the Cl and PFBA BTCs suggests that the non-equilibrium is due to adsorption rather than to slow diffusion.
Impacts
(N/A)
Publications
- GONZALEZ, J.M and UKRAINCZYK, L. 1996. Adsorption and desorption of nicosulfuronin soils. J. Environ. Qual. 25:1186-1192.
- GONZALEZ, J.M and UKRAINCZYK, L. 1996. Adsorption and desorption of nicosulfuronin soils. Agronomy Abstracts. ASA Annual Meetings, Indianapolis, IN, p.333.
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Progress 01/01/95 to 12/30/95
Outputs
Nicosulfuron (ACCENT) is a new, low-rate, sulfonylurea herbicide that is being promoted for weed control in corn. There is a lack of information on its sorption and mobility in soils. In this study nicosulfuron sorption in soils was quantified in batch experiments at a 2:1 soil/solution ratio, for 10 Iowa soils and 4 Oxisols from Brazil. Adsorption isotherms were nonlinear. Freundlich Kf values ranged from 0.21 to 8.78 with the highest values obtained for Iowa soils. Nicosulfuron K values in Iowa soils were correlated with clay content (Kf=-0.08+0.15%clay; r=0.92), while in Oxisols the K values were correlated with organic C content (Kf=0.11+0.89%organic C; r=0.97). These differences are interpreted in terms of different clay mineralogy of Iowa soils (expandable 2:1 clay minerals) and Oxisols (kaolinite, Al and Fe oxides). The results are consistent with a previous study on nicosulfuron adsorption on minerals, where it was found that unlike other sulfonylureas,
nicosulfuron exhibits high and irreversible sorption on the 2:1 clay minerals. Nicosulfuron desorption isotherms, obtained using one-step extraction with 0.005 M CaCl2, were nearly single valued with adsorption isotherms in soils with pH>5.5, while hysteresis was observed in soils with pH<5.5. Up to 100% nicosulfuron could be desorbed in one desorption step with a 2:1 acetonitrile/water mixture from Oxisols, which all had pH<5.5. Only 50-70% of adsorbed nicosulfuron could be desorbed with the same extractant from Iowa soils.
Impacts
(N/A)
Publications
- NO PUBLICATIONS REPORTED THIS PERIOD.
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