Encapsulation of the glyphosate herbicide in mesoporous and soil-affine sorbents for its prolonged release

The increase in herbicide consumption, in particularly glyphosate, is causing considerable health and environmental concerns, due to its possible carcinogenic effects. Indeed, its widespread and intensive use promotes its diffusion in the surrounding environment. Additionally, the operator's exposure to the herbicide is not negligible. In this work the encapsulation of glyphosate into three selected, eco-friendly silica- and clay- based supports, namely SBA-15, montmorillonite (MMT) and Al pillared montmorillonite (Al-MMT) to promote both a punctual application and a prolonged release of glyphosate is innovatively presented. Preliminary, substrates were characterized pre and post encapsulation through XRD and nitrogen adsorption measurements, to assess the incorporation of the herbicide. Release studies were performed in aqueous matrices of different composition, namely ultrapure water, 0.02 M oxalic pH 3 (simulating acid rains) and 0.01 M CaCl2 solution (simulating soil salinity). Within all these media, Al-MMT exhibited a slow-releasing mechanism, with about 10–20% of glyphosate still retained on the support after 7 days, ascribed to complexation and electrostatic interactions. Three different kinetic models usually applied within controlled-releasing processes, i.e. zero order, pseudo-first order and Korsmeyer–Peppas models, were used to describe glyphosate release from Al-MMT in CaCl2 solutions, with Korsmeyer–Peppas model providing the best fit to experimental data (R2 > 0.990). Finally, a water/soil bench-scaled system was efficiently tested, confirming the successfully applicability of Al-MMT in the prolonged release of glyphosate in real systems.