Use of ethylcellulose to control chlorsulfuron leaching in a calcareous soil.

Controlled release formulations (CRFs) have been researched to reduce the water-polluting risk derived from the use of conventional formulations of chlorsulfuron. Coated chlorsulfuron granules were produced in a Wuster-type fluidized-bed equipment using two different amounts of ethylcellulose. The highest one was modified by the addition of a plasticizer such as dibutyl sebacate. The encapsulation efficiency and morphological properties of coated granules having been studied, the chlorsulfuron kinetic release in water was studied. In addition, the mobility of chlorsulfuron in a calcareous soil was finally carried out. High encapsulation efficiency was obtained, being nearly 100% in all cases. SEM pictures show a homogeneous film in coated CRFs; thickness oscillates between 23.32 microm for the system prepared with a 10% of ethylcellulose and 32.61 microm for the system prepared with a 20% ethylcellulose plus plasticizer. The rate of chlorsulfuron release from coated CRFs is diminished in all cases in relation to chlorsulfuron commercial formulation, the latter being completely dissolved in <1 h, but it took at least 50 days to release 90% of chlorsulfuron from the formulation coated with a 20% ethylcellulose plus plasticizer. Using a generic equation, the time taken for 50% of the active ingredient to be released into water (t(50)) was calculated. From the analysis of the t(50) values, it can be deduced that the release rate of chlorsulfuron can be mainly controlled by changing the thickness of the coating film, by modifying the surface properties of the coating film, and by adding a plasticizer. Mobility experiments carried out in calcareous soil show that the use of coated CRFs reduces the presence of chlorsulfuron in the leachate compared to commercial formulation.