Degradation Mechanisms of Phoxim in River Water

Abstract

Degradation of phoxim in river water was fully explored in this paper. Effects of pH, temperature, and photoirradiation on the degradation were investigated in detail. The results indicated that the degradation was characterized by a first-order process; UV irradiation and the increase of pH and temperature substantially accelerated the degradation. To fully characterize the degradation mechanism, HPLC-MS/MS was utilized to identify the degradation intermediates. Five intermediates were identified as phoxom, phoxom dimer, O,O,O',O'-tetraethyldithiopyrophosphate, O,O,O'-triethyl-O'-2-hydroxyethyldisulfinylpyrophosphate, and O,O,O'-triethyl-O'-2-hydroxyethyldithiopyrophosphate. On the basis of the results of the intermediate analysis, the degradation pathways of phoxim under the present experimental conditions were proposed. Through conversion of a thiophosphoryl into a phosphoryl group, some phoxim was converted to phoxom, most of which further formed dimer. Another portion of phoxim transformed to O,O,O',O'-tetraethyldithiopyrophosphate via nucleophilic substitution and photolysis. Thereafter, O,O,O',O'-tetraethyldithiopyrophosphate underwent hydroxylation to form O,O,O'-triethyl-O'-2-hydroxyethyldithiopyrophosphate or sulfur oxidation first and then hydroxylation to produce O,O,O'-triethyl-O'-2-hydroxyethyldisulfinylpyrophosphate. The understanding of phoxim's degradation mechanism in this study will be critical to its safety assessment and increase the understanding of the fate of phoxim in environment water.

Hydrolysis and Photolysis of Herbicide Clomazone in Aqueous Solutions and Natural Water Under Abiotic Conditions

“…Therefore, to fully understand pesticides' impact on the environment, there is a need to CAO Jia, E-mail: jiabiyang2006@126.com; Correspondence HU Ji-ye, Tel: +86-10-82376002, E-mail: jyhu@ustb.edu.cn investigate both the parent pesticides' and their corresponding metabolites' impact. Thus, the degradation study of pesticides has become increasingly important in recent years (Lin et al, 2011). Residual pesticides are known to be decomposed by various natural conditions in which hydrolysis and photodegradation are the most important factors involved in the decomposition of pesticides in the environment (Mandal et al, 2011;Chamberlain et al, 2012).…”

Evaluation of the Strain Bacillus amyloliquefaciens YP6 in Phoxim Degradation via Transcriptomic Data and Product Analysis

“…As the ion is the protonated ion, the MW of M1 may be 170. An intermediate of phoxim hydrolyzation with MW of 170 has been previously identified as O, O -diethylthiophosphoric ester [1]. Furthermore, the characteristic ions at m / z 143 and 115 were formed by the loss of -C 2 H 5 and -2C 2 H 5 , respectively.…”

“…Strain YP6 was cultured in LB broth medium with phoxim (an initial concentration of 50 mg L −1 ) under the optimum biodegradation conditions for 48 h. LB broth with phoxim was used as a control. Samples were extracted according to Lin et al [1]. The extracts containing phoxim were analyzed by HPLC-MS.…”

“…Phoxim ( O , O -diethyl O -(alpha-cyanobenzylideneamino) phosphorothioate), a type of organophosphorus pesticide (OP), is widely used in both agriculture and fisheries to control a variety of unwanted insects and underground pests via dipping, spraying, or pour-on applications [1]. Phoxim mainly inhibits the activity of acetylcholinesterase, leading to the accumulation of acetylcholine in the postsynaptic membrane and causing neurological disorders and biological poisoning [2].…”

Investigation of photodegradation and hydrolysis of selected substituted urea and organophosphate pesticides in water

“…4). This was probably due to the fact that molecule's phosphate ester bond is relatively unstable and prone to be hydrolyzed under alkaline conditions (Lin et al 2010). On the contrary, at the other two pH values, the removal of phoxim was improved when the compound was exposed to light.…”