Phototransformation of isoproturon in soil

Abstract

The present experiment was conducted with an objective to reveal the photochemical behaviour of isoproturon on different soil surfaces, viz. red, black and alluvial soil under sunlight. The half-life values of isoproturon on glass surface was found as 25.38 days. But on soil surfaces, the rate of photolysis was changed with half-life values of 20.76, 27.38 and 28.02 days under sunlight for red, black and alluvial soil, respectively. The slower reaction rate on the surfaces of black and alluvial soil was due to the quenching effect imparted by humic substances, which were absent on glass surface and less in red soil. The sunlight-irradiated extracts of isoproturon and its degradation products were analysed by LC-MS/MS using electrospray interfacing technique and the structures of six different photoproducts were characterised by their respective spectra as 3-(4-isopropyl-2/3-hydroxyphenyl)-1-methyl-1- hydroxymethylurea (I), 3-(4-isopropyl-2/3-hydroxyphenyl)-1-methyl-1-(N,N-dimethylcarbamoyl)urea (II), 3-(4-isopropyl-2/3-hydroxyphenyl)-1-methyl-1-(N-methylcarbamoyl)urea (III), 3-(4-isopropyl-2/3- hydroxyphenyl)-1-methyl-1-carbamoyl urea (IV), N-dimethyl-N -methyl urea (V), N-dimethyl-N - dimethyl urea (VI). The products were mainly formed through demethylation, ring oxidation and rearrangement. Thus, sunlight induced photodegradation may contribute in the dissipation of isoproturon in soil minimising the load of environmental hazards.