Imazamox-clay complexes with chitosan- and iron(III)-modified smectites and their use in nanoformulations

Imazamox is an ionisable herbicide, weakly retained and with high soil vertical mobility, that is used for the control of the root-parasitic plants Orobanche spp. A natural smectite (SW) modified with the biopolymer chitosan (Ch) or with Fe(3+) cation was assayed as adsorbent or carrier for imazamox controlled-release formulations (CRFs).

The greatest adsorption (74%) was observed for SWFe at high initial concentration (500 µM) and low pH (4.3). The interaction mechanism of imazamox on SWFe implies interlayer polar adsorption, followed by protonation of the imidazolinone ring, whereas ionic, polar and hydrophobic interactions seemed to occur in imazamox adsorption on SWCh. The herbicide release into water was inversely related to the strength of the imazamox-clay interactions and ranged in the first 10 min for imazamox-SWFe and imazamox-SWCh complexes from 27 to 75%, whereas commercial imazamox released 86%. The imazamox-SWCh weak complex (SWCh6 WC) showed similar herbicidal activity to the commercial formulation but produced a reduction of 15% in the total soil leaching losses and a reduction of 40% in the peak maximum concentration in soil column leachates.

The imazamox-clay weak complex (WC) of SWFe and SWCh and the strong complex (SC) with SWCh showed appropriate behaviour as nanopesticides or smart delivery systems to be incorporated in CRFs. © 2015 Society of Chemical Industry.