Montmorillonite-phenyltrimethyl ammonium yields environmentally improved formulations of hydrophobic herbicides

This study aimed to design formulations of hydrophobic herbicides, alachlor and metolachlor, by adsorbing them on the clay mineral montmorillonite pre adsorbed by the small organic cation phenyltrimethylammonium (PTMA). An ads orption model that considers electrostatics and specific binding and the po ssibility of cation adsorption above the cation exchange capacity (CEC) cou ld explain and yield predictions for PTMA adsorption in the presence of NaC l concentrations from 0 to 500 mM. Adsorption of alachlor and metolachlor f rom aqueous solution on a clay mineral preadsorbed by PTMA was determined b y GC and modeled by Langmuir equation. Herbicide interactions with the orga noclay were studied by Fourier transform infrared spectroscopy. Leaching of herbicides was determined by a bioassay using a column technique and Setar ia viridis as a test plant. The adsorbed amounts of alachlor and metolachlo r on montmorillonite preadsorbed by PTMA at a loading of 0.5 mol/kg (Mont-P TME0.5) were higher than at a loading up to the CEC, that is, 0.8 mol/kg, a nd were higher than those obtained by using several other organic cations. Herbicide formulations based on Mont-PTMA0.5 yielded the largest shifts of the infrared peaks of the herbicides. These formulations based on Mont-PTMA 0.5 gave slower release and showed improved weed control in comparison with formulations based on other organoclays. These formulations maintained her bicidal activity in the topsoil and yielded the most significant reduction in herbicide leaching.