BINDING OF DIQUAT AND PARAQUAT TO HUMIC ACID IN AQUATIC ENVIRONMENTS

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Abstract
Binding of diquat and paraquat to humic acid, at low concentrations of adsorbates and adsorbents, is described under various conditions. Ionic strength and variations in size and change indicated that binding interaction was mainly electrostatic in nature. Scatchard plots indicated that 2 binding sites were involved. The stability constants in all cases were of the order of 105 to 104, and the number of binding sites per 100 equivalent weights was in the range of 3-23. The nature of the binding sites did not correlate well with the known functional groups on humic acid. Variation in pH suggested that H ions competed strongly with the herbicides for the binding sites on humic acid. Temperature exerted a small influence on the binding of diquat and paraquat.

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