JoX, Vol. 13, Pages 2-15: Development of a Modified QuEChERS Method Coupled with LC-MS/MS for Determination of Spinetoram Residue in Soybean (Glycine max) and Cotton (Gossypium hirsutum)

Pesticide degradation is strongly influenced by biotic (micro- and macroflora) and abiotic (environmental) variables (soil, water, temperature, solar energy, etc.). Wide variations in the degradation pattern of the chemicals may result from any modifications to these parameters [29,30,31,32]. In an experiment dealing with six different pesticides, including spinetoram in pak choi, it was reported that dissipation of the compounds was faster in open field conditions than in greenhouse conditions due to several environmental factors, including rainfall and sunlight. A PHI value of 6 d has been determined for spinetoram in pak choi crop in the study [33]. According to the US EPA, spinetoram residues dissipate very rapidly under aquatic field conditions with a reported half value ≤ 1. It is also being reported that spinosyn J in particular is less persistent in the environment due to degradation caused by both biotic and abiotic factors. This particular isomer is stable to hydrolysis at environmental pH (5–9) but undergoes photolysis rapidly, resulting in shorter half-life [34,35]. Biodegradation is also considered as the major driving factor under aerobic conditions for quick dissipation of spinetoram. Both isomers under terrestrial field conditions have very shorter half-life values [34]. In perennial crops such as tea, spinetoram has been found to be less persistent in fresh tea leaves, resulting in shorter half-life values of 0.70 d. The transfer rates of the compound from fresh tea leaves to processed tea and consequently in infusion range between 34.9% and 57.8% and 36.9% and 68.2%, respectively [36]. In another study, half-life values of spinetoram were found to be 2.82 d in soil, 5.77 d in cabbage stem, 4.21 d in roots and 3.57 d in cabbage leaf when applied as seed-palletised coating [37]. An analytical method based on acetonitrile extraction and PSA as adsorbent was found suitable for analyzing spinetoram residues in red bayberry and soil. The calculated half-life values were found to be in the range of 4.4–5.2 and 1.2–1.9 d in the crop and soil, respectively. The recorded amount of terminal residues was lower than the prescribed MRL value (1 mg kg−1) of spinetoram in red bayberry [38]. Similar observations were found in various studies where spinetoram half-life values were reported as 1.29 d in cabbage, 1.95 d in pepper [39], 2.17 d in pear fruits [40], 2.6 d in tomato [41], 4.85 d in cauliflower [42] and 1.1 d in rice straw [16]. Faster dissipation of spinetoram from the plant surface may also be attributed to volatilization of the insecticide from the crop surface [41]. The observation was supported by another study where half-life values of spinetoram were found to be 2.4–3.0 d and 2.8–4.0 d in crown daisy and sweet pepper, respectively [43]. A safe waiting period of 11 d has been recommended before harvesting of tomato after application of spinetoram 12% SC at 240 mL ha−1 in Egypt [44], and the corresponding value is 7 d for sweet cherry in the United States [45].

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