Mobility of imidacloprid from alginate-bentonite controlled-release formulations in greenhouse soils

The mobility of imidacloprid [1-(6-chloro-3-pyridinyl)methyl]-N-nitro-2-imi dazolidinimine] from alginate-based controlled-release (CR) formulations wa s investigated in two different soil profiles. In one, a layered bed system simulating the typical arrangement under a plastic greenhouse, which is co mposed of sand, peat, amended soil and native soil, was used. In the other, the layer containing amended soil was used in order to determine the mobil ity of the insecticide in a soil system with a low content of organic matte r and a high content of clay. Two CR formulations based on sodium alginate (1.87% wt/wt), imidacloprid (1.21%), natural or acid-treated bentonite (3.2 8%), and water (93.64%) were compared to technical grade imidacloprid. The use of alginate CR formulations produced less vertical mobility of the acti ve ingredient as compared to the technical product. With the technical grad e product treatment, the total amount of imidacloprid leached from columns packed with amended soil was 82.3% of that applied, whereas for the alginat e-based CR formulations containing natural or acid-treated bentonite, the l eached percentages were 44.7% and 37.1%, respectively. In the column experi ments simulating the layered bed system, no insecticide was found in the le achate when the alginate-based CR formulations containing natural bentonite were used. However, 3% of the applied imidacloprid appeared when the treat ment was carried out with technical grade material. Sorption-desorption cap acities of the various soil layers for imidacloprid molecules were also cal culated using batch experiments. (C) 1999 Society of Chemical Industry.