Adsorption of Ametryne and Atrazine on an Oxisol, Montmorillonite, and Charcoal in Relation to pH and Solubility Effects

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Abstract
Adsorption of ametryne exceeded that of atrazine on soil and montmorillonite at both low and high pH. Ametryne (pKa ≅ 4.0) showed a greater increase in adsorption with decrease in pH than atrazine (pKa = 1.68). Addition of charcoal to soil masked the effect of soil pH on ametryne adsorption. Adsorption of ametryne on charcoal decreased at the low pH values conducive to ametryne protonation, demonstrating the effect of pH on triazine‐water affinity in the absence of specific triazine‐adsorbent interactions which are responsive to triazine protonation. Adsorption isotherms were adjusted by use of “relative solution concentrations” to examine the influence of pH and temperature on the relative affinities of water and adsorbent for triazine herbicides. A wetting agent used in the commercial ametryne product had no effect on the adsorption of ametryne.