The adsorption and desorption of imazapyr, (()-2- [4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-pyridinecarboxylic acid, by six soils were studied. Adsorption isotherms conformed to the Freundlich equation. A multiple regression analysis indicated that K f(ads) values were better correlated if cation exchange capacity and pH (r ) 0.984) were simultaneously taken into account. The results show that the herbicide adsorption is strongly affected by the pH and the charge of the adsorbing component. The organic matter is effective in imazapyr retention, but only at pH <5. Enhanced adsorption was observed in amorphous iron oxide, most likely because of a ligand exchange process.

bstract : Triasulfuron was degraded in aqueous solution by ultraviolet irradiation to yield 2chloroethoxybenzene and (4-methoxy-6-methyl-1,3,5-triazin-2-yl)urea. The reaction followed ürstorder kinetics. In sunlight, the reaction was slower and aþ orded these two photoproducts together with 2-amino-4-methoxy-6-methyltriazine and 2-(2-chloroethoxy)benzenesulfonamide. The latter compounds arise from hydrolytic cleavage of the sulfonylurea bridge of triasulfuron because of the acidity of the reaction medium due to the loss of sulfur dioxide. A mechanism which accounts for the formation of the photoproducts is proposed.

Summary Inorganic and organic soil colloids are responsible for the sorption of many pesticides. We studied the sorption of the herbicide primisulfuron [methyl 2 N‐[[[[[4,6‐bis(difluoromethoxy)‐2‐pyrimidinyl]amino]carbonyl]amino]sulfonyl]benzoate] on Fe3+‐, Al3+‐, Ca2+‐ and Na+‐exchanged montmorillonite, soil organic matter (H+‐ and Ca2+‐saturated), amorphous iron oxide, and three soils in aqueous media. The sorption on soils was negatively correlated with pH. Ca2+‐ and Na+‐exchanged montmorillonites are ineffective in the sorption of primisulfuron. The sorption on Fe3+‐ and Al3+‐exchanged montmorillonite is rapid and follows the Freundlich equation. Fourier transform infrared (FT‐IR) and X‐ray powder diffraction studies of the Fe3+‐ and Al3+‐montmorillonite samples after the interaction with primisulfuron in chloroform solution suggest that primisulfuron is adsorbed and degraded in the interlayer. Humic acid is more effective in the sorption than is Ca humate, suggesting that the pH of the suspension (3.5 for humic acid and 6.0 for Ca humate) has a strong influence on the sorption of primisulfuron. Experiments on amorphous iron oxide indicate similar pH dependence. Infrared spectra indicate that the protonation of the pyrimidine nitrogen moiety of herbicide and subsequent hydrogen bonding with the surface hydroxyls of Fe oxide is the mechanism acting in the primisulfuron sorption.

Abstract--The adsorption from chloroform solution of the herbicide diclofop, (RS)-2-(4-(2,4-dichlorophenoxy)phenoxy)propionic acid, and its methyl ester diclofop-methyl on Cu 2 § A13 § and Fe3+-exchanged bentonite samples was investigated. For comparison, the complexes formed by diclofop were synthesized and studied. Diclofop adsorbed on the clays and formed carboxylate bonds to the interlayer ions. Diclofop-methyl also adsorbed, but its interaction involved the formation of hydrogen bonds with water molecules in the interlayer. Traces of diclofop were observed in both the solution and the clays after adsorption of diclofop-methyl, indicating that some hydrolysis of the ester to the corresponding acid occurred. Thus, pesticides forming neutral complexes with interlayer cations in montmorillonite in soils may be extractable by solvents and therefore released into the environment.