Dissipation of the plant growth regulator hexanoic acid 2-(diethylamino) ethyl ester in pakchoi and soil

A rapid and simple method for determining the plant growth regulator hexanoic acid 2-(diethylamino) ethyl ester (DA-6) in pakchoi and soil using gas chromatography-mass spectrometry (GC-MS) has been developed. For this purpose, a single step was used to extract DA-6 with dichloromethane from aqueous-acetone extracts of vegetables and soil. Average recoveries of DA-6 in pakchoi and soil were between 85% and 104% at both spiking levels 0.01 and 0.1 mg kg^?1. Relative standard deviations (RSD) were less than 11% for all of the recovery tests. The degradation of DA-6 in pakchoi and soil was studied. The results showed that DA-6 degradation in pakchoi and soil coincided with C = 3.9903 e^{?0.0516 t} , C = 0.3476 e^{?0.0224 t} , respectively; the half-lives were 13.43 h and 30.94 h in pakchoi and soil in Beijing, respectively.     

Effects of aqueous extracts from the stems and leaves of Trifolium pratense cv. Minshan on germination and seedling growth of three crops

以岷山红三叶（Trifolium pratense cv.Minshan）的茎、叶为供体植物,用蒸馏水浸泡48h制备水浸液。设0.05、0.10、0.15和0.20g·mL^-1 4个浓度梯度,以蒸馏水为对照,对燕麦（Avena sativa）、小白菜（Brassicachinensis）、披碱草（Elymus dahuricus）3种受体植物种子进行发芽试验和幼苗生长的生物测定。结果表明,不同浓度岷山红三叶茎叶水浸液对不同受体植物种子萌发和幼苗的生长发育有不同的化感效应。各浓度水浸液对种子萌发均没有显著影响（P〉0.05）,但对小白菜幼苗的生长均有显著的抑制作用（P〈0.05）;0.20g.mL-1浓度的水浸液对燕麦、披碱草和小白菜根生长抑制率分别为23.76%、35.73%和62.50%,且抑制作用显著;0.05g.mL-1浓度水浸液对披碱草幼芽的生长促进作用显著;在3种受体植物中,小白菜受到抑制作用较强,燕麦和披碱草则较弱。     

Different transformation of carbosulfan to its higher toxic metabolites in pakchoi (Brassica campestris ssp.) and cucumber (Cucumissativus L.) after field application

Carbosulfan (CAS) is used as an insecticide on vegetables, but its toxicity might increase due to the formation of higher toxic metabolites including carbofuran (CAN), 3-hydroxycarbofuran (3-OH) and 3-ketocarbofuran (3-KETO). In this study, the transformation of CAS to its metabolites in pakchoi (Brassica campestris ssp.) and cucumber (Cucumissativus L.) was investigated in the field in Beijing and Changsha and in a greenhouse in Hangzhou. CAS was metabolised to CAN, 3-OH and 3-KETO in pakchoi but only to CAN and 3-OH in cucumber. In pakchoi, the degradation of CAS (as measured by the DT₅₀ value, the time marking the disappearance of 50% of the pesticide) was the fastest in Hangzhou (0.7 d), followed by Changsha (1.4 d) and Beijing (2.3 d), whereas in cucumber, its degradation was the fastest in Changsha (1.6 d) and Hangzhou (1.6 d), followed by Beijing (2.5 d). These results suggested the monitoring of metabolites should be a prior objective for CAS, and different metabolites should be considered when assessing the risk of CAS in different vegetables.     

Enantioseparation and dissipation of acephate and its highly toxic metabolite methamidophos in pakchoi by supercritical fluid chromatography tandem mass spectrometry

Acephate is widely used in crops as racemate. However, the enantioselective dissipation of acephate enantiomers has not been investigated in pakchoi. A sensitive and effective approach was established for determining residues of acephate and its highly toxic metabolite methamidophos enantiomers by supercritical fluid chromatography tandem mass spectrometry. Baseline separations for their enantiomers were achieved by using a Chiralcel OD-H column. The optimal chromatographic conditions were obtained as follows: CO₂/ethanol (95/5) as mobile phase; flow rate, 3.0 mL/min; column temperature, 40°C. The mean recoveries (RSDs) of analytes were in the range of 77–83.1% (6.1–9.9%), 75.4–87.5% (9.3–13.2%), and 81.5–84.2% (7.1–13.4%) at three fortification levels (0.005, 0.05, and 0.5 mg/kg for each enantiomer) for interday assay (n = 18). The method was used to evaluate the enantioselective dissipation of acephate and methamidophos in pakchoi. S-acephate dissipated faster than R-acephate, while the concentration of R-methamidophos was higher than that of S-methamidophos during the entire study period. The results indicated that the R-enantiomer of acephate and methamidophos was preferentially enriched in pakchoi. The established analysis approach and the study data provided useful information for the rational use of acephate in agriculture.