Increased biodegradability of UltracidTM in aqueous solutions with solar TiO2 photocatalysis

A study of solar TiO2 photocatalytic degradation of the insecticide Ultracid™, a commercial formulation containing methidathion as the active ingredient, is described. Total elimination of methidathion can be achieved in less than 2 h of irradiation, although longer solar exposures are needed for complete mineralisation of the solution (7-8 h). Activated sludge respirometry shows that when methidathion is eliminated, the solution is detoxified, so further irradiation does not seem necessary. A Zahn-Wellens test also indicates improved biodegradability of the treated sample after abatement of the active ingredient. Finally, analysis of the ions formed indicates that the thiophosphate moiety of the molecule is preferentially attacked in the early stages of the reaction, while the thiadiazole ring is more sluggish to the effect of TiO2-photocatalysis.