Metabolism and dissipation kinetics of a novel protoporphyrinogen IX oxidase herbicide [oxadiargyl] in various buffered aqueous system under laboratory-simulated condition

Abstract

Present investigation was carried out using two commercial products Raft (oxadiargyl 6% EC) and Topstar (oxadiargyl 80% WP) of Oxadiargyl {5-tert-butyl-3[2,4-dichloro-5-(prop-2-ynyloxy)phenyl]-1,3,4-oxadiazol-2 (3H)-one} to investigate the persistence behavior and metabolism of the herbicide in various aqueous system under different pH condition. Half-life values revealed that alkaline hydrolysis played a dominant role in hydrolytic degradation of this compound. Q-ToF micromass study with the alkaline fractions of oxadiargyl indicated the formation of five metabolites, which was further characterized from their mass fragmentation data. The nature of metabolites formed indicated that heterocyclic oxadiazoline ring cleavage was found to be the main pathway of hydrolytic transformation of oxadiargyl.

Dissipation Dynamic and Final Residues of Oxadiargyl in Paddy Fields Using High-Performance Liquid Chromatography-Tandem Mass Spectrometry Coupled with Modified QuEChERS Method

“…Considering that the hydrolysis of heterocyclic oxadiazoline is the main mechanism for degradation of oxadiargyl, pH was reported to be a critical factor affecting the dissipation of oxadiargyl. Thus, oxadiargyl was more unstable under alkaline conditions because the t 1/2 in alkaline media was significantly lower than those obtained under acidic and neutral conditions [8]. Hence, the rapid degradation rate for the Heilongjiang samples could be produced by the relatively higher pH of the soil, which can enhance the rate of alkaline hydrolysis.…”

“…The octanol-water partition coefficient (log P) of it is 3.70 and the water solubility is 0.37 g L −1 at 20 °C. The herbicide activity of oxadiargyl lies in binding to the protoporphyrinogen oxidase IX as an inhibitor, preventing light-induced peroxidation and interrupting photosynthesis as a result [7,8]. This herbicide has been mainly used in the prevention of certain perennial broadleaved and grass weeds during the pre-emergence of rice [9,10] and the recommended rate of oxadiargyl in rice in China is 72–96 g a.i.…”

“…Despite the number of detection methods reported, only two studies have studied the dissipation dynamic of oxadiargyl, and studies on the final residues of oxadiargyl have been reported. These two previous articles were mainly focused on the metabolism of oxadiargyl in water samples under laboratory conditions or on studying the association interactions between soil particles and oxadiargyl in calcareous fields [8,23]. The fate and behaviour of oxadiargyl in paddy fields have not been adequately monitored and further studies are required.…”