Chlorsulfuron Dissociation and Adsorption on Selected Adsorbents and Soils

The dissociation constant for chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} in aqueous solution measured by spectrophotometric titration is 3.58 ± 0.05. Chlorsulfuron was more strongly adsorbed on IRA-400-Cl strong anion exchange resin than on IR-4B-OH weak anion exchange resin or Al2O3 anionotropic adsorbent. Hydrogen bonding was probably responsible for the adsorption observed on IR-120-Na(H) cation exchange resin. No chlorsulfuron was adsorbed on Al2O3 cationotropic absorbent, technical montmorillonite, illite, or kaolinite. Adsorption did occur on organic matter derived from a histosol. Chlorsulfuron was strongly adsorbed on activated charcoal but had little affinity for α-cellulose. Adsorption onto hydrophobic polymeric XAD-2 adsorbent at pH 5.2 was not significant for chlorsulfuron concentrations below 30 μM. No significant adsorption occurred on a variety of mineral soils low in organic matter. Adsorption on a Sharpsburg silty clay loam was inversely related to solution pH. Hydrogen bonding and charge transfer bonds were postulated as the major mechanisms responsible for chlorsulfuron adsorption in soil.