The aqueous photodegradation of fluopyram was investigated under UV light (λ ≥ 200 nm) and simulated sunlight irradiation (λ ≥ 290 nm). The effect of solution pH, fulvic acids (FA), nitrate (NO3−), Fe (III) ions, and titanium dioxide (TiO2) on direct photolysis of fluopyram was explored. The results showed that fluopyram photodegradation was faster in neutral solution than that in acidic and alkaline solutions. The presence of FA, NO3−, Fe (III), and TiO2 slightly affected the photodegradation of fluopyram under UV irradiation, whereas the photodegradation rates of fluopyram with 5 mg L−1 Fe (III) and 500 mg L−1 TiO2 were about 7-fold and 13-fold faster than that without Fe (III) and TiO2 under simulated sunlight irradiation, respectively. Three typical products for direct photolysis of fluopyram have been isolated and characterized by liquid chromatography tandem mass spectrometry. These products resulted from the intramolecular elimination of HCl, hydroxyl-substitution, and hydrogen extraction. Based on the identified transformation products and evolution profile, a plausible degradation pathway for the direct photolysis of fluopyram in aqueous solution was proposed. In addition, acute toxicity assays using the Vibrio fischeri bacteria test indicated that the transformation products were more toxic than the parent compound.

A simple, quick and efficient approach for simultaneous determination of amidosulfuron and MCPA in wheat field ecosystems was established and validated through rapid resolution liquid chromatography tandem mass spectrometry (RRLC-MS/MS) combined with a modified QuEChERS method with low-temperature cleanup technology. The matrix-matched external calibrations were carried out to eliminate matrix effects. The limits of quantification (LOQs) in soil, wheat grain and wheat straw were 0.002, 0.002 and 0.005 mg kg−1 for amidosulfuron, and 0.02, 0.02 and 0.05 mg kg−1 for MCPA, respectively. The mean recoveries (n = 5) for both amidosulfuron and MCPA in wheat ecosystems varied from 83.14% to 103.83%, from 93.29% to 114.26% with the relative standard deviations (RSDs < 16.45%) at three fortifications. The dissipation kinetics remarkably followed the pseudo-first-order kinetic models. The half-lives of amidosulfuron ranged from 1.30 to 7.99 days in wheat straw and from 2.33 to 18.58 days in soil, whereas those of MCPA ranged from 0.48 to 6.74 days in wheat straw and from 3.10 to 22.22 days in soil at the three representative locations. The terminal residues were much lower than the maximum residue limits (MRLs) of amidosulfuron in triticeae crop recommended by China (0.01 mg kg−1), and the MRLs of MCPA in triticeae registered by the European Union (0.05 mg kg−1), America and Japan (0.1 mg kg−1). These findings were of utmost importance for providing scientific and basic information about the dissipation kinetics and the safety evaluation of amidosulfuron and MCPA in wheat ecosystems.

The dynamic and residues of florasulam and flumetsulam in corn field ecosystem were investigated using quick, easy, cheap, effective, rugged, and safe (QuEChERS) procedure with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The limits of quantification (LOQs) of the proposed method ranged from 0.005 to 0.01 mg/kg. Mean recoveries and relative standard deviations (RSDs) of the two compounds in all samples at three spiking levels ranged 94–110 % and 2.0–9.2 %, respectively. Florasulam and flumetsulam degradation followed first-order kinetics with half-lives 1.7–2.9 and 3.3–8.7 days in soil and 1.3–1.8 and 0.9–1.7 days in plant, respectively. The residues in all the samples were found to be less than the LOQs at preharvest intervals of 53 and 78 days. The results suggest that the combined use of florasulam and flumetsulam on corn is considered to be safe under the recommended conditions and can be utilized for establishing the maximum residue limit (MRL) of florasulam in corn in China.

Residue analysis of emamectin benzoate and lufenuron in cabbage matrices and soil was developed using a quick, easy, cheap, effective, rugged, and safe (QuEChERS) method and ultra high-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). The samples were extracted with 1 % acetic acid in acetonitrile (v/v) or 1 % acetic acid in acetonitrile/water (5:1, v/v) and cleaned up by dispersive solid-phase extraction. Mean recoveries and relative standard deviations (RSDs) in all samples ranged 87.8–100.0 % and 3.6–12.6 % for emamectin benzoate and 87.8–104.8 % and 6.2–11.5 % for lufenuron, respectively. The validated method was used to evaluate the dissipation rate of emamectin benzoate and lufenuron in cabbage and soil as well as the residual levels in harvested cabbage and soil at different preharvest intervals (PHI). The half-lives of emamectin benzoate and lufenuron were 1.08–2.70 and 1.74–5.04 days in cabbage, and 1.42–4.01 and 0.94–6.18 days in soil, respectively. The terminal residues were below the China maximum residue limits (MRLs) at 3 days for emamectin benzoate (0.1 mg kg−1) and European Union MRLs at 5 days for lufenuron (0.5 mg kg−1), which suggested that 5 days could be recommended as the PHI for the commercial formulation of emamectin benzoate and lufenuron application in the Chinese cabbage field.

An integrated method for the simultaneous determination of insecticide fipronil and its three metabolites, desulfinyl, sulfide, and sulfone, in maize grain, maize stem, and soil was developed. This three-step method uses liquid–solid extraction with ultrasound or mechanical grinding, followed by liquid–liquid partitioning and florisil solid-phase extraction (SPE) for cleanup. The quantification was conducted by gas chromatography–electron capture detection in triplicate for each sample. The method was validated with five replicates at three fortification concentrations, 0.002, 0.01, and 0.1 mg kg−1, in each matrix and gave mean recoveries from 83 to 106 % with relative standard deviation ≤8.9 %. The limits of quantification (LOQ) were 0.002 mg kg−1 for the compounds in all matrixes. In the field study in Beijing and Shandong 2012, fipronil-coated maize seeds were planted and the proposed method was applied for checking the possible existence of four compounds in maize and soil samples, but none of them contained residues higher than the LOQs in both application rates. Moreover, the dissipation of fipronil in soil fits first-order kinetics with half-lives 9.90 and 10.34 days in Beijing and Shandong, respectively. Combined with an adequate sample treatment, this technique offers good sensitivity and selectivity in the three complex matrixes. The results could provide guidance for the further research on pesticide distribution and safe use of fipronil as seed coat in cereals.

A convenient method was developed for the determination and validation of fosthiazate in cucumber and soil. The procedure is based on liquid partitioning with acetonitrile followed by dispersive solid phase extraction as the clean-up step, after which samples were analysed by gas chromatography-mass spectrometry (GC-MS). The average recoveries ranged from 91.2 % to 99.0 % with relative standard deviations (RSDs) of less than 6.05 %, at three fortification levels (0.02 mg kg−1, 0.1 mg kg−1, 0.5 mg kg−1) in cucumber and soil, and the limits of quantification (LOQs) for fosthiazate were all established at 0.02 mg kg−1. The proposed method was applied successfully to analyses of the dissipation and residue of fosthiazate in field trials. The dissipation rate of fosthiazate was described using pseudo-first-order kinetics with a half-life of 4.33 days and 4.08 days in soil in Beijing and Shandong, respectively. In the terminal residue experiment, fosthiazate residues in cucumber and soil were clearly below the maximum residue level (MRL, 0.2 mg kg−1) set in China.

Ningnanmycin is a novel biochemical pesticide which was now used extensively in China. A fast and simple method using high-performance liquid chromatography with ultraviolet detection coupled with solid phase extraction was developed and validated for determination of ningnanmycin in cucumber and soil. The recoveries of ningnanmycin from the fortified cucumber and soil samples ranged from 80.7 % to 107.7 % with relative standard deviations less than 6.6 %. Limits of quantification of the method for both cucumber and soil were 0.02 mg kg−1. The proposed method was successfully applied to determine the dissipation and residues of ningnanmycin in cucumber and soil under field conditions. Direct confirmation of the analytes in samples was realized by liquid chromatography–mass spectrometry.

A residue analytical method for the determination of flumetsulam in wheat and soil was developed using gas chromatography with electron capture detector (GC-ECD). The limit of detection of the analytical method was 0.001 ng, and the limit of quantification was 0.005, 0.01 mg/kg for soil and wheat grain, respectively. The mean recoveries from soil and wheat ranged from 83.85 % to 107.2 % with average relative standard deviation ranging from 1.87 % to 8.09 %. The method was successfully applied to determine the residual level and dissipation rate of flumetsulam in the soil and wheat. The half-life in soil was 23.1 days with a dissipation rate of 69 % over 35 days. At harvest time, the residue levels of flumetsulam in wheat grain and soil from high dosage plot were 0.031 and 0.045 mg/kg, respectively. The flumetsulam residues could not be detected from low dosage plot. Direct confirmation of the analyte in real samples was achieved by GC-ECD.

A rapid, sensitive and reliable analytical method for thidiazuron residues in apple and soil was established. The residual levels of the pesticide in apple and soil were determined by high performance liquid chromatography (HPLC) with UV detector. Samples of apple and soil were extracted with acetonitrile–water solutions, and then cleaned up by Florisil or C18 cartridges. The results showed good linearity (r2 = 1.000) over the concentration range of 0.01–5.0 mg/L. Limits of quantification (LOQ) of the method were 0.01 mg/kg for both soil and apple. Recovery from the apple and soil samples were 83.36%–84.08% and 85.27%–89.83%, respectively, and the corresponding relative standard deviations (RSDs) of the recovery data were 0.155%–0.524% and 0.475%–4.79% for the three fortified levels (0.01, 0.1, 0.5 mg/kg). The analyte in the samples were further confirmed by electrospray ionization tandem mass spectrometry (ESI–MS/MS). It was demonstrated that the proposed method was simple and efficient, and particularly suitable for detecting thidiazuron residues in apple and soil.

A simple analysis method to detect clomazone residues in soybean and soil was developed using solid phase extraction coupled with high performance liquid chromatography with diode-array detection. The pesticide residues present in soybean and soil matrices were extracted with methanol–water and extracts purified with Florisil cartridges. The analytes from soybean and soil matrix were eluted with petroleum ether-acetic ether (10 mL, 95:5, v/v) and petroleum ether-acetic ether (2 mL, 95:5, v/v), respectively. The overall recovery of fortified soybean and soil at the levels of 0.01, 0.1 and 0.5 mg/kg ranged from 89.75% to 106.6%, and the coefficients of variation (CV) ranged from 1.68% to 4.93% (n = 3). The limit of quantification (LOQ) is 0.01 mg/kg. This method has been applied to the analysis of clomazone in real samples of soybean and soil. The dissipation of residue over the time in soil coincided with C = 1.189e−0.0926t and the half-lives (T1/2) was 7.48 days. The final residue in soybean was lower than 0.01 mg/kg at harvest time. Direct confirmation of the analyte in real samples was achieved by gas chromatography-mass spectrometry.

A simple and reliable analytical method for fluroxypyr-meptyl residues in wheat and soil was established. The residual levels and dissipation rates of this pesticide in wheat and soil were determined by gas chromatography with electron capture detector (GC–ECD). Samples of wheat grains and soil were extracted with methanol–water, and then liquid–liquid partitioned with dichloromethane. The extracts were further cleaned up by solid-phase extraction (SPE) with Florisil cartridges (500 mg, 3 mL), and eluted with petroleum ether–acetic ether (95/5, v/v). The eluate was collected and concentrated for GC–ECD analysis. The results showed good linearity (r2 = 0.999) over the concentration range of 0.01–1.0 μg mL−1. Limits of quantification (LOQ) of the method were 0.005 mg kg−1 for both soil and wheat grains. Average recoveries for the wheat grains and soil samples were 84.45–108.2% and 95.33–106.6%, respectively, and the corresponding relative standard deviations (RSDs) of the recovery data were 0.819–3.77% and 1.55–5.28% for the three fortified levels (0.005, 0.1, 0.5 mg kg−1). The half-life of fluroxypyr-meptyl in soil from experimental field was 1.93 days (in Beijing) and 3.01 days (in Tianjin). The final residue of the pesticide in wheat and soil was lower than 0.005 mg kg−1, respectively, at harvest time. The analytes in real samples were further confirmed by gas chromatography–mass spectrometry (GC–MS). It was demonstrated that the proposed method was simple and efficient, and particularly suitable for detecting fluroxypyr-meptyl residues in wheat and soil.

The hydrolysis and photolysis of clomazone in aqueous solutions and natural water were assessed under natural and controlled conditions. Kinetics of hydrolysis and photolysis of clomazone were determined by HPLC-DAD. Photoproducts were identified by HPLC-MS. No noticeable hydrolysis occurred in aqueous buffer solutions ((25±2)°C, pH (4.5±0.1), pH (7.4±0.1), pH (9.0±0.1); (50±2)°C, pH (4.5±0.1), pH (7.4±0.1)) or in natural water up to 90 d. At pH (9.0±0.1) and (50±2)°C the half-life of clomazone was 50.2 d. Clomazone photodecomposition rate in aqueous solutions under UV radiation and natural sunlight followed first-order kinetics. Degradation rates were faster under UV light (half-life of 51–59 min) compared to sunlight (half-life of 87–136 d). Under UV light, four major photoproducts were detected and tentatively identified according to HPLC-MS spectral information such as 2-chlorobenzamide, N-hydroxy-(2-benzyl)-2-methylpropan-amide, 2-[2-phenol]-4,4-dimethyl-3-isoxazolidinone and 2-[(4,6-dihydroxyl-2-chlorine phenol)]-4,4-dimethyl-3-isoxazolidinone. These results suggested that clomazone photodegradation proceeds via several reaction pathways: 1) dehalogenation; 2) substitution of chlorine group by hydroxyl; 3) cleavage of the side chain. Photosensitizers, such as H2O2 and riboflavin, could enhance photolysis of clomazone in natural sunlight. In summary, we found that photoreaction is an important dissipation pathway of clomazone in natural water systems.

•A simple QuEChERS coupled with LC–MS/MS method was established.•The method was applied to field samples determination.•The half-lives of metaldehyde and niclosamide ethanolamine were 1.7–9.5 d.•The associated risk of these molluscicides in pakchoi for Chinese people is low.A method using LC–MS/MS after QuEChERS preparation for the simultaneous determination of metaldehyde and niclosamide ethanolamine residues in soil and pakchoi has been developed and validated. The mean recoveries were ranged from 90% to 101% with RSDs (relative standard deviations) less than 9.2%. The dissipation results showed that the half-lives of metaldehyde and niclosamide ethanolamine were 2.3–4.3 d and 1.7–9.5 d, respectively. The terminal residue results indicated that the residues of metaldehyde in pakchoi were lower than the temporary maximum residue limits (MRL) set by China on 1 d after last treatment and the maximum residue of niclosamide ethanolamine in pakchoi was 0.54 mg/kg. The risk quotients of metaldehyde and niclosamide ethanolamine were ranged from 0.015 to 0.033 and from 0.00064 to 0.0014, respectively. This work could provide guidance on reasonable use of these molluscicides and aid in the establishment of MRL in China.

A simple, quick and efficient approach for simultaneous determination of amidosulfuron and MCPA in wheat field ecosystems was established and validated through rapid resolution liquid chromatography tandem mass spectrometry (RRLC-MS/MS) combined with a modified QuEChERS method with low-temperature cleanup technology. The matrix-matched external calibrations were carried out to eliminate matrix effects. The limits of quantification (LOQs) in soil, wheat grain and wheat straw were 0.002, 0.002 and 0.005 mg kg−1 for amidosulfuron, and 0.02, 0.02 and 0.05 mg kg−1 for MCPA, respectively. The mean recoveries (n = 5) for both amidosulfuron and MCPA in wheat ecosystems varied from 83.14% to 103.83%, from 93.29% to 114.26% with the relative standard deviations (RSDs < 16.45%) at three fortifications. The dissipation kinetics remarkably followed the pseudo-first-order kinetic models. The half-lives of amidosulfuron ranged from 1.30 to 7.99 days in wheat straw and from 2.33 to 18.58 days in soil, whereas those of MCPA ranged from 0.48 to 6.74 days in wheat straw and from 3.10 to 22.22 days in soil at the three representative locations. The terminal residues were much lower than the maximum residue limits (MRLs) of amidosulfuron in triticeae crop recommended by China (0.01 mg kg−1), and the MRLs of MCPA in triticeae registered by the European Union (0.05 mg kg−1), America and Japan (0.1 mg kg−1). These findings were of utmost importance for providing scientific and basic information about the dissipation kinetics and the safety evaluation of amidosulfuron and MCPA in wheat ecosystems.