Leaf-cutin assisted phototransformation of 2, 4-D ethyl ester

Abstract

The importance of post-emergence foliarly applied pesticides has increased in the last decade with the availability of a greater number of such herbicides. The first reaction environment of those herbicides is the leaf surface made up of polymerised esters of higher fatty acids. In presence of sunlight the fatty substances on leaf surfaces generate reactive radicals or ions which may interact with herbicide molecules leading towards degradation resulting in the loss of bioefficacy of herbicides and the formation of metabolites of unknown toxicity.The present experiment was conducted with the objective to know the photochemical behaviour of 2,4-D on leaf-cutin surface. Epicuticular waxes were extracted from rice, and Echinocloa colona leaf surface by using chloroform as a solvent and further purified with activated charcoal. On rice-cutin coated surface under UV-light, the transformation of the herbicide is very slow as it is evident from its higher half-life (90.85 ± 4.85 min) as compared to that on glass surface (half-life 23.6 ± 4.31 min). It may be due to the quenching or screening effect imparted by the cutin material towards the herbicide. But the cutin material extracted from Echinocloa does not have such effect. The LC-MS/MS analysis of the sunlight-irradiated samples showed the formation of five different photoproducts, among which 2-chlorophenol and 2,6-dichlorophenol are of considerably toxicological significance.