Adsorption of Buthidazole, VEL 3510, Tebuthiuron, and Fluridone by Organic Matter, Montmorillonite Clay, Exchange Resins, and a Sandy Loam Soil

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Abstract
Adsorption isotherms were obtained for buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone}, VEL 3510 {1-β,β-dimethoxy-1-methyl-3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]urea}, tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4 (1H)-pyridinone} on soil organic matter (H- and Ca-saturated), Ca-montmorillonite, and Cape Fear sandy loam soil. Prometryn [2,4-bis (isopropylamino)-6-(methylthio)-s-triazine] was included as a reference. The order of adsorption on all adsorbents was fluridone ≥ prometryn > > tebuthiuron ≥ VEL 3510 > buthidazole. Fluridone adsorption on the various adsorbents was: H-organic matter > Ca-montmorillonite > Ca-organic matter > > Cape Fear sandy loam. Tebuthiuron, VEL 3510, and buthidazole adsorption on the various adsorbents was in the order: H-organic matter > Ca-organic matter = Ca-montmorillonite > Cape Fear sandy loam. Adsorption of all herbicides increased with decreasing pH, suggesting that the adsorption mechanism was molecular under neutral pH conditions and ionic under acidic conditions. All of the herbicides were adsorbed in high amounts as protonated species on IR-120-H cation exchange resin and in low amounts as molecular species on IR-400-Cl anion exchange resin. Buthidazole and VEL 3510 were adsorbed in high amounts as anionic species by the IR-400-Cl exchange resin at high pH levels.