Humic substances reactions involving bipyridylium herbicides in soil and aquatic environments

Khan, Shahamat U.

doi:10.1007/978-1-4615-8504-6_1

Cited by 12 publications

(11 citation statements)

References 56 publications

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“…A review of Stevenson for example (2), presents evidence for this accumulated since 1962 (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). A number of authors have consequently investigated the interactions of organic pesticides with humic materials (5,7,(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33). The acidic functional groups of humic materials are an important factor (32,(34)(35)(36)(37)(38), 'Contribution NO.…”

Section: Introductionmentioning

confidence: 99%

Atrazine hydrolysis in aqueous suspensions of humic acid at 25.0 °C

Gamble¹,

Khan²

1988

Can. J. Chem.

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. J. Chem. 66,2605Chem. 66, (1988.The acidic properties of a Chemozemic humic acid were determined by equilibrium titration. The number of carboxyl groups is 2.828 (mmol/g) ? 0.5%. The results were used for an investigation of Bronsted acid catalysis of atrazine hydrolysis by a suspension of the humic acid. There is sufficient sorption so that the rates of change of atrazine and product hydroxyatrazine in solution differ both from each other and form the rate of atrazine conversion on the catalytic sites. An important objective of this work was the separate determination of the sorption equilibrium constants for atrazine and hydroxyatrazine, and the rate constant for atrazine conversion on the catalytic sites. All three constants are relevant to environmental research. The apparent rate constants for changes in solution are experimental artifacts however, not useful for such research. calculated-in terms of carboxyl sorption sites in the free acid form, the sorption equilibrium constants were 1.74 X lo2, CJ = 0.03 X 10' and 8.5 x lo2, a = 2.3 X lo2, for atrazine and hydroxyatrazine, respectively. The rate constant for conversion on catalytic sites ranges from 1.8 X lo-' day-' k 20% to 2.9 X lo-' day-' r 20%, for atrazine coverage of sites from 9.0 ( p,mol/g) to 1.0 ( p,mol/g).

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Section: Introductionmentioning

confidence: 99%

Atrazine hydrolysis in aqueous suspensions of humic acid at 25.0 °C

Gamble¹,

Khan²

1988

Can. J. Chem.

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“…The pore sizes of the gel should allow retention of the adsorptive, but should exclude the adsorbent molecules. Burchill et al (I 981) have outlined applications of the procedure for studies of the binding of small molecules by humic substances (see also Burns et al, 1973a;Khan, 1974).…”

Section: Continuous Flow Procedures For Measuring Adsorption From Solmentioning

confidence: 97%

Interactions between Small Organic Chemicals and Soil Colloidal Constituents

Hayes

Mingelgrin²

1991

Interactions at the Soil Colloid — Soil Solution Interface

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“…The organic anion presumably does not displace polar water molecules (or other inorganic cations) bound to surface adsorption sites inasmuch as particle surfaces, like the organic anion, generally are negatively charged (Khan, 1974a(Khan, , 1980Hayes and others, 1975;Jackson, 1975;Wang, 1975;Mulholland, 1981;Davis, 1982;Olsen and others, 1982). Therefore, since increased dissociation of the organic acid will not cause increased adsorption and since increased solute solubility will reduce solute partitioning into the sediment organic matter, the sorption of organic acids will be reduced at elevated pH.…”

Section: Orsanic Acidsmentioning

confidence: 99%

“…The a. dsorption process is, therefore, sensitive to both the charge and atomic radius of the saturating cation associated with the sediment. Khan (1974a) stated that the sediment-associated cations that enhanced adsorption of both diquat and paraquat to a humic acid followed the sequence: A1+ 3 < Fe+ 3 < Cu+ 2 < Ni+ 2 < Zn+ 2 < Co+ 2 < Mn + 2 < H+ < Ca+ 2 < Mg+ 2 . The above relation is inversely related to the stability of the element when complexed with humic acid (Khan, 1974a).…”

Section: Organic Basesmentioning

confidence: 99%

“…Distribution coefficients were greater than 1,000 for the clay fraction of one of the sediments. Khan (1974a) noted that paraquat and diquat sorb by ion exchange, and that their magnitudes of sorption are comparable. LaFleur (1979) noted that sorption of trifluralin to several model soils was extensive and rapid, with practically 100 percent of the applied herbicide being sorbed to the soil within 100 minutes of batch mixing.…”

Section: Diquatmentioning

confidence: 99%

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