Effects of montmorillonite on the chemical degradation kinetics of metsulfuron methyl in aqueous media

• Published in: Applied clay science Vol. 80-81; pp. 211 - 218
• Main Authors: Brigante, Maximiliano, Zanini, Graciela, Avena, Marcelo
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01.08.2013; Elsevier
• Subjects: Degradation; Earth sciences; Earth, ocean, space; Exact sciences and technology; Herbicide deactivation; Metsulfuron methyl; Mineralogy; Na-montmorillonite; Silicates; UV–VIS spectroscopy; Degradation; Metsulfuron methyl; UV–VIS spectroscopy; Na-montmorillonite; Herbicide deactivation; experimental studies; UV―VIS spectroscopy; adsorption; aqueous solutions; degradation; smectite; montmorillonite; spectroscopy; pH; clay minerals; sheet silicates; silicates; kinetics; desorption; soils; herbicides
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2013.03.018

The degradation kinetics of the sulfonylurea herbicide metsulfuron methyl (MM) has been studied in batch experiments by UV–VIS spectroscopy, and the effects of pH and the presence of a clay mineral (Na-montmorillonite) are reported. The proposed UV–VIS method gives kinetic results that are comparable to those obtained with chromatographic methods. In aqueous solutions, the chemical degradation of MM is undetectable at pH6.5–9.5, but increases about 500 times by decreasing the pH from 6 to 2, and 300 times by increasing pH from 9.5 to 11.5. For example, the half-life of MM is shorter than 1d at pH2 and 11.5, but longer than a year at pH6. Na-montmorillonite has an inhibitory effect on MM degradation. A combination of adsorption–desorption studies and degradation kinetic measurements demonstrates that in the presence of Na-montmorillonite only MM that remains in solution is subject to degradation; adsorbed MM is protected by the clay from being degraded. However, since adsorption only occurs at low pH (around 3) it can be envisaged that montmorillonite and supposedly other phyllosilicate clays do not affect significantly the chemical degradation rate of MM in soils and other natural systems. •Degradation kinetics of metsulfuron methyl (MM) were studied by UV–VIS spectroscopy.•Degradation of MM is strongly dependent on the pH and clay concentration.•Na-montmorillonite protects the adsorbed MM from being degraded.•The adsorption mechanism is related to hydrogen-bond formations.