Phototransformation of 2,4-D Ethyl Ester on Different Soil Surfaces: Identification of Photoproducts

摘要

Photochemical behaviour of 2,4-D ethyl ester (2,4-DEE) on the surface of alluvial, black and red soils and inert glass under UV light (254 nm) and sunlight is reported. The half-life of 2,4-DEE on glass surface under UV light was 23.60 ± 4.31 minutes. On soil surfaces, the values were 40.72 + 5.08, 104.78+ 11.32 and 159.55 ± 17.52 minutes under UV light, and 6.07 ± 0.35, 3.04 ± 0.32 and 12.37 + 2.63 days under sunlight, on alluvial, black and red soil, respectively. The slower reaction rate on soil surface was due to the quenching effect imparted by humic substances. Major photoproducts from the irradiation of 2,4-DEE on soil surface were 2,4-dichlophenoxyacetic acid (I), 2,4-dichlophenoxyacetylchloride (II), 2,4-dichlorophenol (III), chlorophenoxyacetic acid-2-chloroethyl ester (IV), chlorophenoxyacetic acid-ethyl ester (V), and phenoxyacetic acid-ethyl ester (VI). The photoreaction is slow on soil surfaces where 2,4-D is transformed into less toxic components under sunlight.