Reduction of the environmental impact of pesticides: Waxy microspheres encapsulating the insecticide carbaryl

A controlled-release system with reduced environmental impact was produced by encapsulating the pesticide carbaryl in the waxy lipophilic material Gel ucire 54/02. The microspheres were prepared by a modified hydrophobic conge alable disperse-phase method. The influence of experimental parameters, suc h as the reciprocal ratio between the amounts of pesticide and wax employed , on size, morphology, loading efficiency, and release behavior of the part icles was evaluated. Microspheres were free-flowing and showed a nonporous scaly surface at SEM analysis. The mean particle size ranged from 15.8 to 1 9.8 mum and was independent of the amount of Gelucire used to prepare the m icrospheres. At a fixed Gelucire content, the increase in theoretical carba ryl content yielded up to 72% loading efficiency, whereas at a fixed carbar yl content the increase in Gelucire amount produced a 64% increase in encap sulation efficiency. These data were accounted for by the carbaryl leakage from molten Gelucire toward the dispersing aqueous phase. The release profi les of carbaryl from microspheres showed that the use of increasing amounts of waxy material decreased the carbaryl release rate, whereas at a fixed G elucire content, the release was the slowest when carbaryl was not complete ly dissolved within the matrix. The possibility to achieve different burst effects by simply varying the formulation parameters offers an efficient to ol to ensure the fast release of an active dose of insecticide. The lower v ertical mobility of carbaryl encapsulated in waxy microspheres compared to the vertical mobility of the technical-grade product showed that the contro lled-release system has a lower potential risk for groundwater contaminatio n.