Photodegradation of pesticides and application of bioanalytical methods for their detection

Abstract

Photodegradation of coumaphos and azinphos-methyl in the air, in oxygen, and in nitrogen atmosphere (quartz reactor equipped with six 18-W lamps with the maximum emission intensity at 310 nm) was studied. The fastest reaction occurred with coumaphos in nitrogen atmosphere (complete decomposition in 10 min), where the formation of a new compound was also detected by high-performance liquid chromatography (HPLC). In the case of azinphos-methyl, no additional signals in HPLC chromatogram were observed. The rearrangement mechanism, involving a triplet-state activation complex and the formation of an acetylcholinesterase (AChE)-inhibiting oxo analog of coumaphos was verified and confirmed by laser flash photolysis.The suitability of bioanalytical flow-injection analysis (FIA) systems, based on AChE inhibition and spectrophotometric or thermal lens spectrometric detection for rapid and sensitive screening in food quality control was demonstrated. Owing to the high sensitivity of thermal lens spectrometry (TLS), several steps in sample preparation can be avoided (preconcentration, purification, isolation) and incubation times reduced. High sample throughputs (10 h -1 ) are, however, also achievable for medium toxic oxo organophosphorus (OP) pesticides using spectrophotometric detection providing limits of detection (LODs) at the level of 10 ppb malaoxon equivalents, which is still about 50 times below maximal residue levels. Testing of the method for practical application on a set of 60 samples gave no false negative results and a level of 1.7 % false positives.

Direct photolysis mechanism of pesticides in water

“…43) Although the reaction mechanism is not clear, the LFP of coumaphos at 355 nm proposed T 1 as an intermediate. 44) The aqueous photolysis of fenthion at 300 nm mainly produced the S-phenyl isomer and corresponding phenol; however, it produced 4-chloro-2-methyl-1-(methylthio) benzene instead in the presence of Cl − , indicating σ aryl cation as a reactive intermediate. 43) The heterolytic cleavage of an O-aryl bond from T 1 to form a σ aryl cation is likely, as reported for OP esters that have an electron-rich aromatic group.…”

“…125) The migration of an alkyl group was observed for fenitrothion, 125) profenofos, 150) and quinalophos, 188) while an aryl moiety migrated in coumaphos 44) and fenthion. 43) Although the reaction mechanism is not clear, the LFP of coumaphos at 355 nm proposed T 1 as an intermediate.…”

Fast Screening Techniques for Neurotoxigenic Substances and Other Toxicants and Pollutants Based on Thermal Lensing and Microfluidic Chips

“…FIA-AChE-TLS was also applied for monitoring the toxicity during the photodegradation of OPs and during photocatalytic processes, [53][54][55][56] as well as for the optimization of advanced oxidation methods for treating waters contaminated with OP insecticides. 57 The fast response of FIA-TLS along with actually no sample treatment before the analysis makes it possible to render analyses in 3 -5 min, and therefore provides a quasi-online monitoring of water-treatment processes that take 1 -2 h. The inhibition of AChE activity during such watertreatment processes indicates the formation of toxic degradation products (mainly OP oxons).…”

“…Inhibitions of up to 40% of AChE activity during the photodegradation or photocatalysis of malathion, isomalathion, chlorpyrifos, and azinfos-methyl (initial concentrations 5 -30 ppm) correlated well with the concentrations of the formed oxons, which were detected by GC-MS. 53,56,57 FIA-AChE-TLS also served as a reliable method to determine the endpoint (no AChE inhibition) of the degradation of oxons, such as malaoxon, which were in general found to be more persistent to photodegradation compared to their thio-analogs (phosphorotionates and dithionates). 53,54,56,57 Due to the high sensitivity for oxons and a much faster response, FIA-AChE-TLS offers clear advantages 57 compared to toxicity assays based on the inhibition of Vibrio fischeri fluorescent bacteria, which is threefold less sensitive for the detection of oxo-organophosphates, compared to phosphorothionates, and was most frequently applied in processes for the removal of OPs in the past. 58 AChE is, however, not inhibited by thio-OPs.…”

Fast stopped-flow enzymatic sensing of fenitrothion in grapes and orange juice

“…Several analytical methods, including gas (Hladká and Nosá l, 1967;Alvarez et al, 2008) and liquid chromatography (Itoh et al, 1996;Franko et al, 2005;Sanchez-Ortega et al, 2005), immunoassays (Cho et al, 2004;Kim et al, 2007;Zhang et al, 2008), fluorescence and chemiluminescence spectroscopy (Diaz et al, 1995;Garcia Sanchez et al, 2003;Zhu et al, 2006;Dasary et al, 2008), electrochemical techniques (Navas Diaz and Gonzalez-Garcia, 1994;Fernandez-Sanchez and Costa-García, 1998;Gehring et al, 1999;Pemberton et al, 1999), and biosensors based on cholinesterase or alkaline phosphatase (ALP) inhibition (Garcia Sanchez et al, 2003;Kumaran and Morita, 1995;Navas Diaz and Ramos Peinado, 1997) have been used for the determination of organophosphorus pesticides (OP). More recently, electrochemical detection of FT and other OP pesticides has been described (Cai et al, 2014;Geremedhin et al, 2013).…”