| A novel multi-pesticide residues sample preparation method for the foods of animal origin was developed. Acetonitrile was selected for accelerated solvent extraction (ASE) for effectively extracting the pesticides from the fatty samples. The cleanup was performed with an automated gel permeation chromatography (GPC) cleanup system. It is a simple and reliable pre-treatment method for batch processing of samples with a high degree of automation and less solvent.A new analytical method was developed to simultaneously determine the residues of 109 pesticides (including isomers) in the foods of animal origin, included organochlorines, organophosphates, carbamates and pyrethroids. The prepared samples were analyzed with GC-MS in the selected ion monitoring (SIM) mode using one target and two qualitative ions for each analyte. Chlorpyrifos-d10 was used as an internal standard. The lowest limit of detection (LOD) was 0.1μg·kg-1, the largest LOD was 32.3μg·kg-1. The lowest limit of quantification (LOQ) was 0.3μg·kg-1, the largest LOQ was 108μg·kg-1. The recoveries and relative standard deviations (RSDs) were checked by spiking untreated samples with pesticides at 0.05,0.1 and 0.2 mg·kg-1. The average recoveries of most pesticides were from 64.3±1.7 to 97.4±9.5%. The precision values expressed as RSDs were all≤21.1% (n=6). Good linearity (r≥0.99) was observed between 0.05 and 1.5μg·mL-1.Another analytical method was developed to simultaneously determine residues of 55 organophosphate and carbamate pesticides in the foods of animal origin. The prepared samples were analyzed within 10 min with ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) in the multiple reaction monitoring (MRM) mode using a set of quantitative ions pair and a set of qualitative ions pair for each analyte. The lowest LOD was 0.006μg·kg-1, the largest LOD was 32.3μg·kg-1. The lowest LOQ was 0.019μg·kg-1, the largest LOQ was 0.286μg·kg-1. The recoveries and RSDs were checked by spiking untreated samples with pesticides at 0.05,0.1 and 0.2 mg·kg-1. The average recoveries of most pesticides were from 62.36±5.39 to 102.79±8.34%. The precision values expressed as RSDs were all≤12.76% (n =6). Good linearity (r≥0.90) was observed between 0.01 and 0.1μg·mL-1.Both the two analysis methods were suitable for rapid detection of high-throughput samples with high efficiency and easy operation, less interference of impurities, accurate, reliable and high sensitivity. The LODs of these methods were both lower than the developed maximum residue limits (MRLs) for the pesticide residues in foods of animal origin by European Union (EU), Japan's positive list system, WHO/FAO, Codex Alimentarius Commission (CAC) and other international organizations. Therefore, these methods meet the the lowest LODs and testing requirements of the international standards and China's national standard of GB 2763-2005 and other regulations on pesticide residues in foods of animal origin.Samples of pork, beef, chicken and fish from local markets were prepared and analyzed using the developed sample preparation, cleanup and analysis methods. Pesticide residues were detected in 16% of the total samples (or 8 out of 50 samples). The residues were found in the pork, beef, chicken and fish samples, p, p'-DDE was detected in 6 samples at concentrations ranging from 0.022 to 0.103 mg·kg-1, whileγ-BHC, carbofuran,α-endosulfan, and (β-endosulfan were each found in one fish sample. The most common pesticide residues found were p, p'-DDE and y-BHC. Chlorpyrifos or coumaphos was found in the beef and pork samples. The diversity of pesticide classes, including organochlorine (α-endosulfan,β-endosulfan, p, p'-DDE,γ-BHC), organophosphorus (chlorpyrifos, coumaphos) and carbamate (carbofuran), showed that the proposed method was versatile and sensitive for the determination of multi-residues of pesticides in samples of animal origin.Based upon the results, carbofuran and coumaphos were selected as the research objects. Theγrays radiation-induced degradation of them in aqueous solvent and foods of animal origin were performed. The degradation dynamics of carbofuran and coumaphos in aqueous and foods of animal origin were systematically investigated by using the 14C labeled benzene ring of carbofuran and coumaphos as radioisotope tracer and the modern equipments, included liquid scientillation counting (LSC) and LC-MS/MS. The structures of the degradation products were derived and identified. As a result, theγrays radiation-induced degradation mechanisms of carbofuran and coumaphos in aqueous and foods of animal origin were resolved.The results showed that the degradation rate of pesticides in aqueous solution increased with the increase of irradiation dose. However, in order to achieve the same degradation rate for the different concentrations of the same pesticides, the higher concentration of pesticides often need higher necessary radiation dose than that required for the lower concentrations of pesticide. It was probably due to the y rays radiation-induced degradation of pesticide in aqueous solution induced in most of the performance indirect effects, mainly relying on the cleavage reaction to generate small molecules by the free radicals of'OH,·, and eaq-produced by irradiation of water molecules with the pesticide groups. When the radiation dose keeps constant, the number of active ions in the solution is essentially constant. If the concentration of the solution is increased, the solute molecules will increase, too. Consequently, the degradation rate will decrease.The y rays radiation-induced degradation of pesticide in aqueous solution was different from different pesticides. The contribution to carbofuran degradation by the radicals was in the order as follows, H> OH> eaq-. The rate of degradation rate constant for carbofuran was as follows, kH:k.OH:keaq-=5:7:6. The quantum efficiency ratios of H, OH and eaq- for the degradation of carbofuran were calculated as 12.7:1:2.6. However, the contribution to coumaphos degradation by the radicals was in the order as follows, eaq- >'OH>H. The rate of degradation rate constant for coumaphos was as follows, keaq.:k.OH:k.H=3:2.8:1. The quantum efficiency ratios of eaq-,OH and H for the degradation of coumaphos were calculated as 2.4:1:2.2.The half decay dose (D50) was 72.95 kGy for carbofuran in fish at the initial concentration of 1 mg·kg-1 by 60Co-γrays irradiation, while the D50 of the same concentration of carbofuran in aqueous solution was 6.73 kGy. The D50 was 29.74 kGy for coumaphos in beef at the initial concentration of 1 mg·kg-1 by 60Co-y rays irradiation, while the D50 of the same concentration of coumaphos in aqueous solution was 0.73 kGy.The degradation rate of pesticide in the foods of animal origin was far less than that in aqueous at the same irradiation dose. In order to gain the same degradation rate for the same pesticide in different media, the irradiation dose for pesticide in the foods of animal origin was significantly higher than that in aqueous solution.There are also differences in the products of radiation degradation for the same pesticide. The degradation products in aqueous were much more than those in the foods of animal origin. This may be due to the significant difference of the surrounding medium between the pesticides to cause the different degradation mode.The main products of radiation degradation for carbofuran in aqueous were as follows,3-hydroxy carbofuran (or 2,3-dihydro-2,2-dimethyl-3-hydroxy-7-benzofuranyl N-hydroxymethyl carbamate),2,3-dihydro-2,2-dimethyl-3-oxo-7-benzofuranyl N-hydroxymethyl carbamate,2,3-dihydro-2,2-dimethyl-3-hydroxy-7-benzofuranyl N-al carbamate,3-hydroxy carbofuran (or 2,3-dihydro-2,2-dimethyl-3-hrdroxy-7- benzofuranyl N-methylcarbamate),3-keto-carbofuran (or 2,3-dihydro-2,2-dimethyl-3-oxo-7-benzofuranyl N-methylcarbamate),3-keto-7-phenol (or 2,3-dihydro-2,2-dimethyl-3-oxo-7-benzofuranol), carbofuran-7-phenol (or 2,3-dihydro-2,2-dimethyl-7-benzofuranol) and 2,3-dihydro-benzofuran. Meanwhile, the main products of radiation degradation for carbofuran in fish were as follows,3-hydroxy carbofuran, 2,3-dihydro-2,2-dimethyl-3-oxo-7-benzofuranyl N-hydroxymethyl carbamate, 2,3-dihydro-2,2-dimethyl-3-hydroxy-7-benzofuranyl N-al carbamate and 3-keto-carbofuran. The main products of radiation degradation for carbofuran in fish were also generated in the aqueous solution. However,2,3-dihydro-2,2-Dimethyl-3-hydroxy-7-benzofuranyl N-hydroxymethyl carbamate, and 3-keto-7-phenol, carbofuran-7-phenol and 2,3-dihydro-benzofuran were only produced in the aqueous solution.The main products of radiation degradation for coumaphos in aqueous were as follows,O,O-diethyl-O-(3-chloro-4-methyl-7-hydroxy-coumarin) phosphate,O, O-diethyl-O-(4-methyl-7-hydroxy-coumarin) phosphate, O-ethyl-O-hydroxyl-(3-chloro-4-methyl-7-hydroxy-coumarin) phosphorothioate, O, O-diethyl-O-(3-chloro-4-methyl coumarate-7) phosphate and O, O-diethyl-O-(3-chloro-4-methyl coumarate-7) phosphorothioate. Meanwhile, the main products of radiation degradation for coumaphos in beef were as follows, O, O-diethyl-O-(3-chloro-4-methyl coumarate-7) phosphorothioate,0,0-diethyl-O-(3-chloro-4-methyl-7-hydroxy-coumarin) phosphate and O-ethyl-O-hydroxyl-(3-chloro-4-methyl-7-hydroxy-coumarin) phosphorothioate. However,O, O-diethyl-O-(3-chloro-4-methyl coumarate -7) phosphate and O, O-diethyl-O-(4-methyl-7-hydroxy-coumarin) phosphate were only produced in the aqueous solution rather than in beef byγirridiation. All the products of y rays rays radiation-induced degradation of coumaphos in beef were produced in the aqueous solution, too.The result shows that theγrays radiation-induced degradations of pesticide residues in foods of animal origin may be much more complex. In order to reduce the harmful to humans from the residues of pesticide and veterinary drug, source control should be strengthened to reduce harmful contamination of food at first. At the same time, in order to promote the application of theγrays radiation-induced degradations in food safety, the radiation degradation process, degradation products and their toxicology should be further studied. |
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