Controlled Release of Imidacloprid from a Lignin Matrix: Water Release Kinetics and Soil Mobility Study

Abstract

Formulations of the insecticide imidacloprid were made using a commercially available pine kraft lignin. The release kinetics of imidacloprid from granules with variation in the loadings of the insecticide and granule sizes were evaluated in water under dynamic flow conditions. The release data were fitted to the generalized model Mt/Mz = ktn + c, where Mt/Mz is the percentage of insecticide released at time t, k and c are constants, and n is another constant that indicates the mechanism of release. The results indicated that the release of imidacloprid was diffusion-controlled. The time taken for 50% of the active ingredient to be released into water, T50, was also calculated for the comparison of formulations. The results showed that the formulation with the higher loading of imidacloprid had the higher value of T50, which means a slower release of the active ingredient. In a related experiment, it was found that as the size of this formulation decreased, the release of the active ingredient was faster. In addition, mobilities of technical and formulated imidacloprid were compared by using soil columns simulating a layered bed system commonly used under a plastic greenhouse. The use of formulated imidacloprid produced a less vertical distribution of the active ingredient compared to the technical product. Sorption capacities of the various soil constituents for imidacloprid molecules were also calculated by using batch experiments. The results obtained were in agreement with those for sorption in dynamic conditions. Keywords: Controlled release; imidacloprid; lignin; leaching