Slow-Release Formulations of Sulfometuron Incorporated in Micelles Adsorbed on Montmorillonite

Abstract

The design and tests of slow-release formulations of sulfometuron (SFM), an anionic sulfonylurea herbicide, are described. The formulations are based on incorporation of the herbicide in octadecyltrimethylammonium (ODTMA) micelles, which adsorb on a clay mineral, montmorillonite. An optimization of herbicide/micelle clay ratios yielded high adsorption of SFM (95%), and at a 1% (w/ w) water suspension only 0.5% of the adsorbed SFM was released at times varying from hours to 9 days. An analytical test in Seville soil showed that under excessive irrigation (400 mm) 100% of the commercial formulation leached, whereas the micelle-clay formulations showed only 50-65% elution. A plant bioassay in Rehovot soil showed that the commercial dispersible granule formulation (Oust, 75% ai sulfometuron methyl) yielded only 23% root elongation inhibition at the top 5 cm of the soil, whereas complete inhibition was achieved with the micelle-clay formulation. The detected concentration of SFM for the micelle-clay formulation at a depth of 15-20 cm was half of that detected for the commercial one, indicating a reduction in leaching when applying the micelle-clay formulation. A 10-fold reduction in the applied dose of SFM in the micelle-clay formulations resulted in good herbicidal activity of 60-87% inhibition. These characteristics make the new formulation promising from the environmental and economic points of view.

Reduced metribuzin pollution with phosphatidylcholine–clay formulations

“…A new approach in the design of slow‐release formulations has been recently developed. These novel formulations consist of an anionic herbicide in a cationic micelle or vesicle, which is formed in solution by the surfactant and adsorbed onto a negatively charged clay mineral 3–6. Owing to the toxicity of some cationic surfactants, current research is focused on the use of more environmentally friendly substances 7, 8.…”

Reduced Downward Mobility of Metolachlor and Metribuzin from Surfactant-Modified Clays

“…Several workers have successfully demonstrated the potentials of organoclaybased herbicide formulations of alachlor, [1,2] metolachlor, [2,3] fenuron, [4] norflurazon, [5] sulfometuron, [6] and hexazinone [7] in reducing their downward mobility.…”

Clay−Vesicle Interactions: Fluorescence Measurements and Structural Implications for Slow Release Formulations of Herbicides

“…This effect was also observed in the micelle-clay system. [20][21][22] The implication of this effect is that an optimal vesicleclay formulation of anionic herbicides, where a large fraction of the herbicide is adsorbed by the complex, can be obtained for particular vesicle-clay ratios, such that most of the vesicles are adsorbed without undergoing premature decomposition. Vesicle decomposition would result in release to solution of prebound anionic herbicide molecules, which in turn do not adsorb on the negatively charged clay mineral platelets and adsorb inefficiently on clay platelets adsorbed by the positively charged monomers.…”