Atrazine in mineral soil: chemical species and catalysed hydrolysis

Gamble, Donald S.; Khan, Shahamat U.

doi:10.1139/v92-197

Cited by 25 publications

(33 citation statements)

References 13 publications

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“…Therefore we conclude that one set of parameters can be successfully used to describe atrazine behavior over this C i range. Table 1 is one order of magnitude greater than the hydrolysis constant for a mineral soil (1.72 x 10 -4 hours-i), as reported by Gamble and Khan [1992]. The reason for this discrepancy may be due to the assumption that this irreversible coefficient is a "lumped" constant which accounts for both chemical degradation as well as possible irreversible reac-…”

Section: Resultsmentioning

confidence: 81%

“…Therefore it is not easy from our data base to achieve a set of model parameters which can fully describe atrazine adsorptiondeso•tion over a wide concentration range. In fact, Gamble and Khan [1992] found that values for atrazine adsorptiondesorption rate coefficients decreased as the amount of the atrazine adsorption sites approached saturation. They also found that a mass balance loss, referred to as bound residue, increased as atrazine concentration decreased.…”

Section: Attempts To Describe Atrazine Adsorption and Desorption Isotmentioning

confidence: 99%

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Predicting atrazine adsorption‐desorption in soils: A modified second‐order kinetic model

Li¹,

Selim²

1994

Water Resources Research

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Atrazine retention on a Sharkey clay soil was quantified using a kinetic batch method for different soil to solution ratios. Time‐dependent adsorption‐desorption was also measured using a batch method with successive dilution steps. Adsorption was found to be highly kinetic in nature. In addition, adsorption‐desorption isotherms exhibited a strong hysteretic behavior. The extent of observed hysteresis increased with retention time. Attempts were made to describe atrazine retention based on a modified second‐order approach where heterogeneity of adsorption sites was assumed. Two retention sites were considered: type 1 (Se) represented that retained on noncatalytic sites with low binding energy, and type 2 (Sk) was that retained on catalytic sites and form strong interactions with matrix surfaces. A third type (Si) represented irreversible sites occupied by hydroxyatrazine following hydrolysis or other physical/chemical transformations. The rates of reactions were assumed as a function of vacant or available sites which were equally accessible to either Se or Sk. A direct method to quantify the adsorption capacity (ϕm) as a measure of the total retention sites by maintaining high atrazine concentrations in soil solution was not successful. However, the use of an indirectly estimated ϕm along with nonlinear least squares adequately described kinetic retention results. Based on least square best fit, model parameters were independent of initial concentrations (Ci) and an overall set of parameters was capable of describing an entire data set for all Ci. The model was also successful in predicting atrazine retention for a different data set and for all Ci using one set of model parameters which were obtained independently from another data set. Further application of the model was to test whether these independently estimated model parameters can predict the kinetics of adsorption‐desorption hysteresis. Unlike other approaches where adsorption and desorption isotherms were separately described, the second‐order model was capable of describing both adsorption and desorption kinetics. Improved hysteresis predictions were observed when model parameters were derived from experiments of simuar conditions.

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Section: Resultsmentioning

confidence: 81%

Section: Attempts To Describe Atrazine Adsorption and Desorption Isotmentioning

confidence: 99%

Predicting atrazine adsorption‐desorption in soils: A modified second‐order kinetic model

Li¹,

Selim²

1994

Water Resources Research

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“…In addition, prefiltered solutions are injected for simple analysis of the soluble pesticide. Details of the method and equipment have been described elsewhere (Gamble and Khan 1992).…”

Section: The Rp-hplc On-line Microfiltration Methodsmentioning

confidence: 99%

Kinetics and equilibria of Metribuzin sorption on model soil components

Sha’Ato¹,

Buncel²,

Gamble³

et al. 2000

Can. J. Soil. Sci.

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Sha'ato, R., Buncel, E., Gamble, D. G. and vanLoon, G. W. 2000. Kinetics and equilibria of Metribuzin sorption on model soil components. Can. J. Soil Sci. 80: 301-307. Sorption to solid phase materials is known to significantly affect the transport, bioavailability and ultimate fate of organic contaminants in soils and sediments. In order to develop a complete description of the fate of these compounds, it is necessary to understand both equilibrium interactions and rates and mechanisms of the sorption processes. The object of the present study was to investigate both these factors with respect to the sorption of metribuzin on model soil components, including the clay minerals kaolinite and montmorillonite, amorphous iron and aluminum hydrous oxides and humic acid. In all cases, uptake followed a similar course; there was a very rapid initial sorption process followed by continued uptake at a much slower rate. Rate constants for the slow sorption were smallest for the clay minerals, intermediate for the hydrous oxides and greatest for humic acid. Labile sorption capacities for metribuzin on the humic acid and clay minerals were also determined; the organic material had the largest capacity, and montmorillonite had a greater capacity than kaolinite.Key words: Metribuzin, sorption, clay minerals, humic material Sha'ato, R., Buncel, E., Gamble, D. G. et vanLoon, G. W. 2000. Cinétique et équilibre de la sorption du métribuzin sur les composantes du sol modélisées. Can. J. Soil Sci. 80: 301-307. Il est connu que la sorption sur des matières solides influe sur la migration, sur la biodisponiblité et sur le devenir ultime des contaminants organiques présents dans le sol et dans les sédiments. Mais pour obtenir une description complète du sort de ces substances, nous devons au préalable élucider à la fois les interactions d'équilibre et les rythmes et les mécanismes des processus de sorption. Ce sont ces deux facteurs que nous examinons ici relativement à la sorption du métribuzin sur des composantes du sol modélisées, notamment les minéraux argileux kaolinite et montmorillonite, le fer amorphe, les hydroxydes d'aluminium et l'acide humique. Sur tous ces matériaux, la sorption comportait une phase initiale de sorption très rapide puis une phase beaucoup plus lente d'absorption. Les constantes de rythme pour cette phase étaient basses pour les minéraux argileux, intermédiaires pour les hydroxydes et produisaient les valeurs les plus hautes pour les substances humiques. Nous mesurions aussi la capacité de sorption sous forme labile du métribuzin sur les substances humiques et sur les minéraux argileux. Ce sont les matières humiques qui démontraient le pouvoir de sorption le plus grand, suivies de la montmorillonite puis de la kaolinite.

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“…Proof of concept has been published for the experimentally supported theory that reveals the kinetics and mechanisms of pesticides in soil and water [1][2][3][4][5][6][7][8][9]. For a soil immersed in a pesticide solution, the starting point was the answer to a critical question.…”

Section: What Has Been Donementioning

confidence: 99%

The Physical Chemistry of Pesticides in Soil and Water

Gamble

2017

Agriculture

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Soils are the ultimate examples of physically and chemically irregular mixtures. They are also dynamic. Early investigators consequently did not understand the physical chemistry of pesticides in soil and water. By taking shortcuts instead of trying to understand the physical chemistry, they measured the wrong variables, used the wrong units, calculated the wrong parameters, and totally ignored chemical stoichiometry. Theoretical concepts for the physical chemistry of pesticides in soil have been published during the last quarter century. They are experimentally supported. Yet, chemically incorrect descriptions persist in the literature to this day. That has serious environmental and economic consequences. In particular, government regulators make legally binding pesticide decisions based on computer predictions that are wrong by 1 to 3 orders of magnitude. This needs the attention of scientists, governments, and multinational corporations.

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Atrazine in mineral soil: chemical species and catalysed hydrolysis

Cited by 25 publications

References 13 publications

Predicting atrazine adsorption‐desorption in soils: A modified second‐order kinetic model

Predicting atrazine adsorption‐desorption in soils: A modified second‐order kinetic model

Kinetics and equilibria of Metribuzin sorption on model soil components

The Physical Chemistry of Pesticides in Soil and Water

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