The effect of Cu and Cu-humic acids on the adsorption of imazethapyr herbicide by montmorillonite clay.

Adsorption of imazethapyr, an imidazolinone herbicide, was measured from dilute suspensions onto montmorillonite clay and complexes of montmorillonite with Cu and humic acid. Adsorption of imazethapyr was found to be greater for the Cu-montmorillonite and Cu-humic acid-montmorillonite complexes than by montmorillonite alone. Isotherm shape was similar for all supports studied. Adsorption of imazethapyr varied with pH for montmorillonite and for Cu-humic acid-montmorillonite complex. The pH had no apparent effect on imazethapyr adsorption to the Cu-montmorillonite complex. This might be due to imazethapyr retention at high pH by Cu ions linked to the clay. Imazethapyr adsorption kinetics was faster for Cu-montmorillonite (15 min) and Cu-humic acid-montmorillonite (30 min) than for montmorillonite (240 min). The copper-humic acid complexes with montmorillonite might be used to detoxify water contaminated with imazethapyr.