Development of environmentally compatible controlled release formulations of a mosquito larvicide

A new controlled release system of a mosquito larvicide, fenthion has been developed by the chemical modification of sodium carboxymethylcellulose into a hydrophobic gel of copper carboxymethylcellulose. Four formulations having a slab geometry were developed with two concentrations of the larvicide and two extents of cross-linking. The release profile of the larvicide from the formulations was studied under laboratory conditions. The formulation with a cross-linking period for 48 h and a 20 per cent larvicide concentration with respect to the dry weight of the formulation has been found to be stable with a sustained release of the active ingredient for a period of 25 wk. The release profile of the formulation followed zero order release kinetics after three weeks in water. The concentration of fenthion ranged between 0.07 and 0.21 mg/l at the application rate of one slab per five litres of water with an average release rate of 6.38 mg/wk during the period of study.