The Main Photo-Degradation Intermediates and Pathways of Chlorpyrifos.

Chlorpyrifos (CPF), a type of organophosphorous pesticide, is commonly used in tea-growing regions of Taiwan, and is concerned as a priority pollutant by the European Water Framework Directive (WFD). The organophosphorous pesticides, such as CPF, have a strong inhibitory activity effect to cholinesterase, and these compounds can induce reproductive toxicity, cytotoxicity, immunotoxicity and genotoxicity. Due to its extensive use, the CPF is often found on the crop leaves, soils, and water bodies. Fortunately, the CPF is light-sensitive and may be decomposed with various rates depending on the reactive surfaces and light intensities. In the studies, the photo-transformation of the organophosphorous insecticide CPF was investigated on the leaves of tea trees from Taiwan Tea Experiment Station (TTES No.18) under ultraviolet (UV) light or sunlight as light sources. The differences in the reactive pathways of photo-transformations of CPF on tree leaves and in aqueous solutions were compared by detecting the intermediates of CPF using liquid chromatography/mass spectrometry (LC/MS). LC/MS analyses indicated that the photo-degradations of chlorpyrifos would lead to the production of chloro-2-[pyridinyl-O,O-ethyl] thiophosphate through the de-chlorination reactions, which were indifferent to the reactive media. Besides, the CPF could be transformed to chlorpyrifos-oxon upon the oxidation of P=S to P=O. The chlorpyrifos-oxn was further cleavaged into 3,5,6-trichloropyridinol (TCP) and O,O-diethyl phosphate (DEP) in the aqueous phase due to hydrolysis. However, de-chlorination of diethyl chlorpyrifos oxon (3,5,6-trichloropyridin-2yl phosphate) only occurred on the tea leaves. The transformation pathway and the intermediate of CPF were not found when the reaction was conducted in the solution or in a system involving bio-decompositions. The results demonstrate that the photo-decomposition pathways of CPF rely greatly on the reactive media, which should be accounted for while evaluating correctly CPF transformation and its environmental fate.