Photodegradation of fipronil in natural water by high intensity UV light under laboratory conditions

Abstract

Fipronil is a phenylpyrazole insecticide which is on decomposition produced photoproducts in environment after using in applications such as rice culture, turf grass management and residential pest control. In this study, the photolysis behaviour of fipronil was investigated in natural water of a river in north Iran by high intensity UV light under laboratory conditions. The results showed that fipronil was photodegraded rapidly and its primary product was fipronil-desulfinyl, which was unstable under the condition of this study. The photodegradation could be described by the pseudo first order reaction kinetics equation. The correlation coefficient r2 and the observed pseudo first order rate constant were 0.923 and 0.0205 s-1, respectively. In the presence of humic acid or hydrogen peroxide, the rate of photodegradation was increased, indicating both of them were photosensitizers for the photodegradation of fipronil. The major photoproducts were identified by GC-MS analysis. On the basis of the structurally identified photoproducts a possible degradation pathway is proposed for the photolysis of fipronil in natural water.