Interaction of Rimsulfuron with Smectites

Luca Calamai1, Ottorino Pantani2, Alba Pusino3, Carlo Gessa4 and Paolo Fusi1
1 Dipartimento di Scienza del Suolo e Nutrizione della Pianta, Università di Firenze, Piazzale Cascine 28, 50144 Firenze, Italy
2 Centro di Studio per i Colloidi del Suolo, CNR, Piazzale Cascine 28, 50144 Firenze, Italy
3 Dipartimento di Scienze Ambientali Agrarie e Biotecnologie Agro-Alimentari, Università di Sassari, Viale Italia 39, 07100 Sassari, Italy
4 Istituto di Chimica Agraria, Università di Bologna, Via Berti Pichat 11, 40127 Bologna, Italy

Abstract: The adsorption of the sulfonylurea herbicide rimsulfuron, [N-((4,6-dimethoxypyrimidin-2-yl)aminocarbonyl)-3-(ethylsulfonyl)-2-pyridinesulfonamide], on clay minerals with different saturating cations was studied. Three smectites with different lattice charge distribution (hectorite, montmorillonite and nontronite) were selected and made homoionic to Ca2+, Cu2+ and Al3+. Because of the instability of rimsulfuron in water, the experiments were carried out in chloroform solution. The interaction mechanism depends on the nature of the saturating cation and the tetrahedral layer charge of the silicate. Among the exchangeable ions studied, only Al3+ is able to produce degradation of the herbicide to N-(4,6-dimethoxypyrimidin-2-yl)-N-[(3-(ethylsulfonyl)-2-pyridinyl]urea. In this case, the lower the tetrahedral charge, the more active the degradation. The Ca2+-saturated clays are ineffective in the degradation. In contrast, the formation of a stable chelate complex with the saturating ion permits rimsulfuron to be adsorbed to a rather high extent into Cu(II)-clays and to be stable against degradation.

Key Words: Adsorption • Infrared Spectroscopy • Pesticides • Rimsulfuron • Smectites

Clays and Clay Minerals; February 1997 v. 45; no. 1; p. 23-27; DOI: 10.1346/CCMN.1997.0450103
© 1997, The Clay Minerals Society
Clay Minerals Society (www.clays.org)