Chlorpyrifos Sorption in Tea Tree Soils and Photo-Degradation On Tea Leaves.

Chlorpyrifos [O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl), a phosphorothioate ester, is an efficient and commonly used pesticide in tea-growing regions in Taiwan. Due to its toxicity, the residue and transformation of chlorpyrifos on the leaves of tea trees and in soil planted with tea trees need to be investigated for the safety of tea drinkers and proper functioning of the ecosystems. The research was divides into two parts of (1) sorption of chlorpyritos on goethite and ferrihydrite, representative of the crystal and amorphous forms of Fe oxides, and two types of soils grown with tea trees; (2) a direct photolysis and the possible photo-oxidation pathways of chlorpyrifos on the tender and old leaves of the tea trees irradiated by ultraviolet light (UV) and sunlight. Results showed that chlorpyrifos sorption by ferrihydride was greater than that of goethite, and chlorpyrifos desorption by dissolved organic carbons was significantly increased with higher chlorpyrifos loadings. The red soil, having high iron hydr(o)oxide contents, exhibited a greater sorptive ability of chlorpyrifos even if it contained lower organic matter. Indifferent to the light sources, the rates of photo-decompositions of chlorpyrifos proceeded more rapid on the surface of tender leaves than those of old ones. Photolysis and absorption of chlorpyrifos occurred simultaneously on the surfaces of leaves, and these reactions were enhanced with an increase of leaf temperatures. Our preliminary results of GC/MS analyses indicated that the photo-degradations of chlorpyrifos would lead to the production of intermediate of 3,6-Dichloro-2-[pyridinyl-0,0-ethyl] thiophosphate through the dechlorination or ring cleavage.