Catalyzed Photodegradation of the Herbicides Molinate and Thiobencarb

A survey of oxidizing agents capable of supplementing the natural oxidants of field water showed that the rice herbicides molinate (I) and thiobencarb (VIII) were degraded rapidly in sunlight-irradiated suspensions of TiO 2 and ZnO. ZnO served both as a semiconductor photooxidant and as the Zn(II) fertilizer normally applied for plant nutrition. In a flooded rice field, isolated basins were treated with Ordram 10G (molinate); after 3 days, an aqueous ZnO suspension, stable in field water at pH 8 to 9, was applied. The resulting immediate decrease in molinate half-life from 60 h to 1.5 h indicates that applying ZnO before releasing agricultural wastewater may provide an economical means of intentionally degrading persistent chemical residues.