Interactions of two sulfonylurea herbicides with organoclays

• Published in: Clays and clay minerals Vol. 52; no. 5; pp. 643 - 649
• Main Authors: Carrizosa, María José, Hermosín, María del Carmen, Koskinen, William C, Cornejo, Juan
• Format: Journal Article
• Language: English
• Published: Boulder, CO Clay Minerals Society 01.10.2004; The Clay Minerals Society
• Subjects: clay minerals; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; experimental studies; hectorite; herbicides; Metsulfuron; Mineralogy; Nicosulfuron; organic compounds; Organoclays; pesticides; Pollution, environment geology; sheet silicates; Silicates; smectite; Sorption; Sulfonylureas; United States; Wyoming; Arizona; cation exchange capacity; between organocations was a very important factor. Metsulfuron; ion exchange; isotherms; Organoclays; North America; sorption; smectite; molecular structure; acids; Sulfonylureas; sheet silicates; silicates; clay minerals; hectorite; surface properties; organic carbon; herbicides; Nicosulfuron
• ISSN: 0009-8604; 1552-8367
• DOI: 10.1346/CCMN.2004.0520510

The sorption of two sulfonylurea herbicides (SU), metsulfuron methyl and nicosulfuron, on pure clays and organoclays was investigated. Three clays (Arizona smectite, SAz-1, Wyoming smectite, SWy-2, and hectorite, SHCa-1), were treated with amounts of octadecylammonium (ODA) or dioctadecyldimethylammonium (DODMA) cations equal to ∼50 and 100% of the clays' cation exchange capacity (CEC). Sorption isotherms were fitted to the Freundlich equation. While no measurable sorption was found on the pure clays (Kf = 0), organoclays prepared using both primary and quaternary amines were effective as SU sorbents. The metsulfuron methyl Kf values ranged between 196 and 1498 µmol1-l/n kg-1 L1/n, and Kf values for nicosulfuron, which were lower than those of metsulfuron methyl, ranged from 35 to 198 µmol1-1/n kg-1 L1/n. As shown by sorption coefficients, Kd and KOC, SWy-2 treated with DODMA at ∼100% of the CEC was the most effective sorbent for metsulfuron, Kd = 684 L Kg-1 and KOC = 2138 L Kg-1. For nicosulfuron the most effective sorbent was SAz-1 with ODA at ∼50% of the CEC (Kd = 147 L kg-1 and KOC = 1233 L kg-1). In contrast to other weak-acid herbicides, such as phenoxy and picolinic acids, no clear relationships were found between sorption and layer charge, organic carbon content, and basal spacing of the organoclays for both sulfonylurea herbicides. Sorption of both herbicides on organoclays was assumed to involve hydrophobic and polar interactions for which the availability of interlayer room between organocations was a very important factor.