Abstract--Adsorption studies indicate that paraquat, diquat, and thionine are bound on bentonite by amounts greater than the measured cation-exchange capacity (CEC) of the clay. Methylene blue, new methylene blue, and malachite green are bound by amounts equal to the CEC. The unipositive organocations form aggregates on the clay surface. Aggregation increases with ionic strength and increases the apparent adsorption capacity by 25%. The aggregates are removed by washing with distilled water. Desorption studies show that the dyes are irreversibly bound, whereas the dipositive organocations are reversibly bound. Ionic strength variation reduces adsorption by 15 and 36% in the monovalent and divalent organocation-clay systems, respectively. In the clay-divalent organocation systems adsorption is greater on Na-saturated clay than on K-saturated clay. Adsorption is unchanged over the pH range 4.5-8.5 and decreases steadily below pH 4.0. Changes in adsorption due to changes in temperature are small. The study indicates that ionic strength is the most important variable in clay-organocation interactions.

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E S I L V A . Can. J. Chem. 58, 547 (1980). A model system composed of bentonite, humic acid (HA), polystyrene sulphonic acid (PSSA), methylene blue (MB), and paraquat was used to characterize the possible interactions of organocations in natural waters. The adsorption and desorption studies with bentonite indicated that the clay had a strong preference for the organocations over alkali and alkaline earth cations. Paraquat saturated the bentonite up to the cation exchange capacity whereas methylene blue did not completely saturate the clay but did form methy!ene blue aggregates on the clay surface. The aggregates could be readily removed by washing with distilled water. The organocation interactions with the anionic polyelectrolytes were more susceptible to changes in pH or ionic strength. Paraquat could be completely desorbed from HA and PSSA by raising the solution ionic strength to 0.1. Methyiene blue could not be completely removed from the humic acid bat could be removed from PSSA by raising the ionic strength to 0.1. The studies indicate that a combination of dialysis separations. variation of ionic strength, and spectrophotometric analysis could be used to determine the free paraquat and the bound paraquat susceptible to changes in environmental levels of pH and ionic strength. Can. J. Chem. 58,547 (1980) Nous avons utilise un systeme compose de bentonite, d'acide humique (AH), d'acide polystyrene sulfonique (APSS), de bleu de methylene (BM) et de paraquat afin de caracteriser les interactions possibles des organocations dans les eaux naturelles. Les Ctudes d'adsorption et de desorption avec la bentonite indiquent que I'argile prefere de beaucoup les organocations aux cations des terres alcalines. Le paraquat sature la bentonite jusqu'a la capacite d'ichange des cations alors que le bleu de methylene ne le sature pas completement mais forme des agregats de bleu de methylene Bla surface de I'argile. Les agregats peuvent itre faciiement enlevis par lavage B I'eau distillee. Les interactions entre les organocations et les polyelectrolytes anioniques sont plus susceptibles de varier selon la force ionique ou le pH. Le paraquat peut itre completement desorbe du AM ou du APSS en augmentant la force ionique de la solution a 0.1. Le bleu de methylene ne peut Ctre enleve completement de l'acide humique; dans le cas du AQSS on peut toutefois I'enlever en augmentant la force ionique aO.l. Les etudes indiquent qu'onpeut utiliserune combinaison de separation par dialyse, de variation de la force ionique et d'analyse spectrophotometrique, pour determiner le paraquat sous forme libre ou combinee susceptible de changer dans des milieux de differents pH ou de force ionique.[Traduit par le journal] Introduction soluble, colloidal, and particulate species plays a ~h~ interactions of organic compounds vital role in the toxicity of organic herbicides. Gilin the environment play an important role in the lott et al. (1) have shown that the presence of seditransport and persistence of the chemicals. The ment in test systems si...

Can. J. Chem. 58.555 (1980). A chemical model that employs the photosensitization properties of methylene blue to mimic herbicide toxicity is used to test size separation as a method of chemical speciation. A spectrophotometric study of the dye interactions with the humic colloid indicated that the dye -humic acid complex has a weaker absorption spectrum than the free dye. The absorption spectra suggested that the binding sites on the humic acid are sufficiently isolated to prevent dye-dye interactions on the colloid su~-fxe. The dye photosensitization of tryptophan degradation indicated that only the free methylene blue was active in the presence of humic acid. clay. and polystyrene sulphonic acid. The model suggests that if the pollutant must be in true solution to be biologically active then a size separation by dialysis would be a satisfactory speciation procedure.ROBERT D. GUY et DEORAJ R, NARINE. Can. J. Chem. 58,555 (1980). On a utilisk un modeie chimique qui fait appel aux proprietes photosensibilisatrices du bleu de methylkne dans ia toxicit6 de I'herbicide mimique, pour verifier la separation dimensionnelle comme une methode de determination de i'esptces chimique. Une etude spectrophotornetrique des interactions entre le colorant et le colloide humique icdique que le complexe colorant -acide humique a un spectre d'absorption plus faible que le colorant B l'ltat libre. Les spectres d'absorption suggkrent que les sites de liaison dans l'acide humique sont suffisamment isoles pour prevenir les interactions colorant-colorant a L a surface du colloide. La degradation du tryptophane phoiosensibilisee par le colorant indique que seu! le bleu de methyl&ne est actif en presence d'acide humique, d'argile et de l'acide polystyrene sulfonique. Le modele suggere que si le polluant doib se trouver rkellement en solution pour itre biologiquement actif la separation par dialyse peut &re satisfaisante commr mcthode de determination de I'espece.[Traduit par le journal]

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