Submitted to: Agronomy Abstracts
Publication Type: Abstract only
Publication Acceptance Date: 10/31/1997
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Interactions between pesticides and soil minerals depend on the chemical nature of the pesticide and the nature and properties of the mineral surfaces. Anionic chlorophenoxy acids are electrostatically repulsed from the predominantly negatively charged surfaces of soil minerals and are only weekly sorbed by anion exchange on positively charged sites. However, other anionic pesticides, such as glyphosate, interact strongly with positive charge sites on variable charge mineral surfaces. Glyphosate has a phosphonate group which forms strong complexes with non-bridging aluminol sites. Weak bases, such as the s-triazines, are retained on negatively charged surfaces by cation exchange when the pH of the system is within one or two pH units of the pKa of the base. For systems with pHs substantially higher than the pKa, weak bases are retained by hydrophobic interactions between non-polar moieties of the pesticide and hydrophobic microsites on mineral surfaces.