ABSTRACT
16The effect of surfactants on the photodegradation of monuron in aqueous solution was examined using nonionic surfactants of the Tergitol® TMN and the Triton® × series. Surfactant concentrations were in excess of the critical micelle concentration, and samples were examined under oxygenated and nonoxygenated conditions. In these studies, surfactant caused an increase in the photodegradation rate, eliminated the ring hydroxylation reactions, and enhanced the photoreductive dechlorination process. The results indicate that the photoreactions took place in the organic phase of the micelles rather than in the aqueous phase of the solvent.
To obtain an estimation of surfactant effects in general, herbicides of the phenylurea, carbamate, amide, and triazine classes were photolyzed in aqueous solution containing 0.2% heterogeneous Tergitol® TMN-10 or Triton® X-100. With alkyl surfactant (TMN-10), solubilization of herbicide into the micellar region could either increase or decrease the rate of photodegradation depending on the herbicide under investigation. With aryl surfactant (X-100), the chromophoric phenyl group could absorb ultraviolet (UV) light and cause photosensitized degradation of some of the herbicides tested. Conversely, to determine the effect of herbicides on surfactant photolysis, the photosensitized degradation of homogeneous Tergitol® TMN-6 was investigated. The photoproducts identified from TMN-6 degradation were surfactants with successively shorter polyoxyethylene glycol side chains, and polyethylene glycols ranging from hexaethylene glycol down to ethylene glycol.
