Determination of eight pesticides in Lycium barbarum by LC-MS/MS and dietary risk assessment
Introduction
Lycium barbarum, known as goji berry, has been used as a traditional Chinese medicine to nourish the liver and kidney, and to improve vision (Amagase and Farnsworth, 2011, Bo et al., 2016). It has long been favorite in China and Southeast Asia, and is increasingly becoming popular in Western diets due to its potential health benefits (Bondia-Pons et al., 2014, Forino et al., 2016). Lycium barbarum mainly grows in the provinces of Ningxia, Shandong, Liaoning and Qinghai in China. Traditionally, Lycium barbarum has been one of the most important products exported from these provinces and has provided a significant contribution to their economy. As the main producer and important exporter, China exported 12,273 tons of Lycium barbarum in 2014 according to China customs data. In recent years, however, pesticide residues in Lycium barbarum have become a major concern for consumers and has affected its export. Monitoring of pesticide dissipation is likely to be crucial for food safety control. Therefore, this study on the determination and dissipation behavior of the pesticides typically applied to Lycium barbarum is of great significance.
To ensure the production and quality of Lycium barbarum, during cultivation, a substantial amount of fungicides and insecticides are used. Triadimefon, flusilazole, tebuconazole, and difenoconazole belong to the triazole family of chemicals which are widely used for the control of powdery mildew and anthracnose (Salunkhe, Sawant, Banerjee, Wadkar, & Sawant, 2015). Triazoles are known to be stable in the environment due to their high chemical and photochemical stability and low biodegradability (Farajzadeh & Khoshmaram, 2013). Some of the other commonly used fungicides in Lycium barbarum are azoxystrobin and thiophanate-methyl. To protect human health and facilitate international trade, the Europe Union has set the maximum residue limits (MRLs) of these pesticides for Lycium barbarum. In terms of insecticides, sulfoxaflor and amitraz are used in Lycium barbarum plant to ameliorate the increasingly serious problem of insect resistance to neonicotinoids such as imidacloprid (Cutler et al., 2013). The dissipation of these pesticides has been studied in vegetables and fruits. For instance, it was reported that tebuconazole residues were under the determination limit of 0.02 mg/kg in ripe grape berries collected 34 days after the last application (Sakamoto et al., 2004). Xu et al. (2012) found that the half-lives of sulfoxaflor obtained after treatment ranged from 1.6 to 2.9 days in cucumber. In a more recent study, the half-lives of difenoconazole were 3.6 days following one time application and 6.3 days following two separate applications when following good agricultural practices (GAP) (Sun et al., 2015).
So far, only a few studies have investigated the determination and dissipation of pesticides in fruits of Lycium barbarum. Analytical methods were reported by Li et al. (2007) in which 14 organophosphorus pesticide residues in Lycium barbarum were determined. Huang, Xue, Wang, Wu, and Tong (2012) developed a multi-residue method using gas chromatography with an electron capture detector for the determination of 50 organochlorine and pyrethroid pesticides in Lycium barbarum. Whereas pesticides are widely used during Lycium barbarum cultivation, less information is known about their environmental fate in the fruits of Lycium barbarum. Some works investigated the fate of imidacloprid in Lycium barbarum. The results shown that the half-lives of imidacloprid in leaves and fruits were 3.8 and 4.3 days, respectively (Saber & Abedi, 2013). However, no studies have been published on the determination and dissipation of triadimefon, sulfoxaflor, flusilazole, tebuconazole, difenoconazole, amitraz, azoxystrobin and thiophanate-methyl in fruits of Lycium barbarum.
In the present study, eight pesticides (triadimefon, sulfoxaflor, flusilazole, tebuconazole, difenoconazole, amitraz, azoxystrobin, thiophanate-methyl) were analyzed using liquid chromatography tandem mass spectrometry (LC-MS/MS). In addition, the deposition and dissipation of pesticide residues in fruits were explored. Furthermore, the dietary risk was evaluated using the ultimate residues to properly assess potential risk posed by human exposure to these pesticides. The aim of this study was to investigate the residual characteristics of eight pesticides in Lycium barbarum. The results of this study may promote the proper use of these pesticides and protect the consumers from potential health risks associated with pesticide residue in Lycium barbarum.
Section snippets
Materials and reagents
An analytical standard, triadimefon (99%), sulfoxaflor (99%), flusilazole (99%), tebuconazole (99%), difenoconazole (98%), amitraz (99%), N-2,4-dimethylphenyl-N′-methylformamidine (DMPF) (99%), carbendazim (98%), azoxystrobin (98%) and thiophanate-methyl (99%) were purchased from Dr. Ehrenstorfer GmbH (Augsburg, Germany). The formulation of flusilazole (10% aqueous emulsion), tebuconazole (80% water dispersible granule), and difenoconazole (30% water dispersible granule) for the field trials
Method validation
The limit of detection (LOD) and limit of quantification (LOQ) were considered as the concentrations with signal-to-noise ratio greater than 3 and 10, respectively. After being calculated from spiked samples at the lowest level (0.01 mg/kg), the LOD values were 0.001 mg/kg with the exception of amitraz and DMPF (0.005 mg/kg). A mixture of acetonitrile and water was selected as the extraction solvent and then partitioned with inorganic salts. Moreover, the supernatant was further cleaned up with
Conclusions
In the present study, a method for the determination of eight pesticides, namely triadimefon, sulfoxaflor, flusilazole, tebuconazole, difenoconazole, amitraz, azoxystrobin and thiophanate-methyl, in Lycium barbarum was reported by using LC-MS/MS together with modified QuEChERS extraction. The eight pesticides were applied to Lycium barbarum at the recommended dosage. The dissipation study showed that the half-lives of these pesticides were 1.3–5.0 days in fruits of Lycium barbarum. The results
Acknowledgements
This work was financially supported by the Project of Agricultural Sciences and Technological in Ningbo City (Grant No. 2014C10058).
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