Organo-clay formulations of pesticides: reduced leaching and photodegradation

Adsorption of organic cations on several clay minerals is reviewed with an emphasis on the effect of ionic strength and modeling. The clay exchanged with suitable organic cations forms a basis for ecologically acceptable formulations of herbicides with reduced leaching, ground water contamination and enhanced weed control efficacy. Incomplete neutralization of the clay surface charge by an organic cation may be advantageous in achieving maximal adsorption of hydrophobic herbicides. One conclusion from these studies is that optimization of clay-based herbicide formulations requires a selection of structurally compatible organic cations preadsorbed on the clay at optimal coverage. New experimental results are presented for alachlor formulations, which significantly reduce herbicide leaching under conditions of heavy irrigation. We were able to demonstrate that organo-clay formulations of alachlor and

Factors affecting the design of slow release formulations of herbicides based on clay-surfactant systems. A methodological approach.

A search for clay-surfactant based formulations with high percentage of the active ingredient, which can yield slow release of active molecules is described. The active ingredients were the herbicides metribuzin (MZ), mesotrione (MS) and flurtamone (FL), whose solubilities were examined in the presence of four commercial surfactants; (i) neutral: two berols (B048, B266) and an alkylpolyglucoside (AG6202); (ii) cationic: an ethoxylated amine (ET/15). Significant percent of active ingredient (a.i.) in the clay/surfactant/herbicide formulations could be achieved only when most of the surfactant was added as micelles. MZ and FL were well solubilized by berols, whereas MS by ET/15. Sorption of surfactants on the clay mineral sepiolite occurred mostly by sorption of micelles, and the loadings exceeded the CEC. Higher loadings were determined for B266 and ET/15. The sorption of surfactants was modeled by using the Langmuir-Scatchard equation which permitted the determination of binding coefficients that could be used for further predictions of the sorbed amounts of surfactants under a wide range of clay/surfactant ratios. A possibility was tested of designing clay-surfactant based formulations of certain herbicides by assuming the same ratio between herbicides and surfactants in the formulations as for herbicides incorporated in micelles in solution. Calculations indicated that satisfactory FL formulations could not be synthesized. The experimental fractions of herbicides in the formulations were in agreement with the predicted ones for MS and MZ. The validity of this approach was confirmed in in vitro release tests that showed a slowing down of the release of a.i. from the designed formulations relative to the technical products. Soil dissipation studies with MS formulations also showed improved bioactivity of the clay-surfactant formulation relative to the commercial one. This methodological approach can be extended to other clay-surfactant systems for encapsulation and slow release of target molecules of interest

Clays, Clay Minerals, and Pesticides

Design and test of clay-based formulations of pesticides for solving environmental and economical problems are described. Organoclays were mainly designed to promote the adsorption of neutral and hydrophobic pesticides and slow their release. Adsorption of organic cations modifies the nature of the clay mineral surface, transforming it from hydrophilic to hydrophobic. The modified clay mineral surface can have enhanced affinity for adsorbing neutral organic molecules of hydrophobic characteristics. The adsorption of the hydrophobic herbicides alachlor, metolachlor norflurazon, and acetochlor, which include a phenyl ring, was maximal for montmorillonite preadsorbed by a small cation, for example, phenyl trimethylammonium at a loading corresponding to 5/8 of the cation-exchange capacity (CEC). Loading of the organic cations above the CEC of the clay can promote the adsorption of certain anionic

Inhibition percents (as measured by reduction in chlorophyll content relative to a control) of MS formulations applied at several rates in pot experiments.^a

<p>The field rate was 100 g ha⁻¹.</p

Sorption isotherms of surfactants on sepiolite at added concentrations below their cmc.

<p>Sorption isotherms of surfactants on sepiolite at added concentrations below their cmc.</p

Clay-surfactant formulations.

<p>Clay-surfactant formulations.</p

Phase solubility diagrams of the herbicides in the presence of surfactants.

<p>Phase solubility diagrams of the herbicides in the presence of surfactants.</p