Spatial-temporal distribution and potential risk of pesticides in ambient air in the North China Plain.

The intensive use of pesticides in the North China Plain (NCP) has resulted in widespread contamination of pesticides in the local atmosphere, posing risks to air quality and human health. However, the occurrence and distribution of atmospheric pesticides in the NCP as well as their risk assessment have not been well investigated. In this study, 300 monthly samples were collected using passive air samplers with polyurethane foam at ten rural sites with different crop systems in Quzhou county, the NCP, from June 2021 to May 2022. The pesticides were quantified using mass-spectrometric techniques. Our results revealed that chlorpyrifos, carbendazim, and atrazine were the most frequently found pesticides in the air samples, with detection frequencies of ≥ 87 % across the samples. The average concentrations of atmospheric pesticides during spring (7.47 pg m-3) and summer (16.05 pg m-3) were significantly higher than those during autumn (2.04 pg m-3) and winter (1.71 pg m-3), attributable to the intensified application of pesticides during the warmer seasons. Additionally, cash crop sites exhibited higher concentrations (10.26 pg m-3) of atmospheric pesticides compared to grain crop (5.59 pg m-3) and greenhouse sites (3.81 pg m-3), primarily due to more frequent pesticides spraying events in cash crop fields. These findings indicate a distinct spatial-temporal distribution pattern of atmospheric pesticides influenced by both seasons and crop systems. Furthermore, the model-based inhalation risk assessment indicates that inhalation exposure to atmospheric pesticides is unlikely to pose a significant public concern.

Residues and dietary risk assessment of fluazinam in root mustard after field experiments.

The residue levels of fluazinam in root mustard were investigated by using a quick, easy, cheap, effective, rugged, and safe (QuEChERS) technique with ultra-performance liquid chromatography tandem mass spectrometry. Samples of leaf and root mustard were analyzed. The recoveries of fluazinam were 85.2-110.8% for leaf mustard with the coefficient of variation of 1.0-7.2%, and 88.8-93.3% for root mustard with the coefficient of variation of 1.9-12.4%. The suspension concentrate formulation of fluazinam was applied on root mustard at 262.5 g a.i. ha-1 in accordance with good agricultural practice (GAP), respectively. After the final application, the root mustard samples were collected at 3, 7, and 14 days. Fluazinam residues in root mustard were less than 0.01-0.493 mg kg-1. The dietary risk of fluazinam was predicted by comparing intake amounts with the toxicological data, namely acceptable daily intake (ADI) and acute reference dose (ARfD). The risk quotient (RQ) was 72.2-74.3%, for ordinary consumers, which showed negligible risk. According to the maximum residue limit (MRL) and dietary risk assessment, it is suggested that the pre-harvest interval (PHI) of 3 days; meanwhile, the MRL of 2 mg kg-1 was suggested for fluazinam in root mustard, which indicates that the dietary risk of fluazinam 500 g L-1 suspension concentrate (SC) with the recommended usage on root mustard is negligible. This study provided basic data on the use and safety of fluazinam in root mustard to help the Chinese government formulate a maximum residue level for fluazinam in root mustard.

Residue behavior and risk assessment of pyraclostrobin and tebuconazole in peppers under different growing conditions.

This study evaluates the residue behavior and risks of pyraclostrobin and tebuconazole in peppers. An analytical method for the simultaneous determination of the concentration of these fungicides in peppers was developed using ultra-high performance liquid chromatography-triple quadrupole mass spectrometry. Pepper samples were extracted with acetonitrile and cleaned with primary secondary amine and graphitized carbon black. The average recoveries of pyraclostrobin and tebuconazole under three fortification levels were 86.7-101.4% and 81.7-104.4%, with relative standard deviations of 4.0-7.2% and 3.8-10.9%, respectively. The limit of quantification of both fungicides in peppers was 0.01 mg/kg. The terminal residue trial of 30% pyraclostrobin and tebuconazole suspension concentrate was investigated for samples cultivated in open fields and greenhouses. The results showed that the terminal residues of pyraclostrobin and tebuconazole in peppers were lower than the maximum residue limits established by GB 2763-2021 (0.5 mg/kg for pyraclostrobin and 2 mg/kg for tebuconazole). The results of a statistical t-test indicated that there was no significant difference between samples grown in open fields and greenhouses. According to the international estimate of short-term intake (IESTI) calculation model, provided by the Joint FAO/WHO Meeting on Pesticide Residues, the acute dietary exposure risk of both fungicides in peppers was acceptable for the general population, with an IESTI of 0-3% and 0-5% of the acute reference dose for pyraclostrobin and tebuconazole, respectively.

Efficient degradation of imidacloprid in soil by thermally activated persulfate process: Performance, kinetics, and mechanisms.

Imidacloprid (IMI) as a first-generation commercial neonicotinoid has been frequently detected in the environment in recent years. In this study, the efficient degradation of IMI in soil by a thermally activated persulfate (PS) process was investigated. The degradation efficiencies of IMI were in the range of 82-97% with the PS dosage of 10 mM, when the initial concentrations of IMI were 5-50 mg/kg in the soil. Degradation of the IMI was fitted with a pseudo-first-order kinetic model under different reaction temperatures. Inhibition effects of the common inorganic anions on the IMI degradation in the system followed the order Cl- > HCO3- > H2PO4- > NO3-. Soil pH and soil organic matter were also main factors affecting the degradation of IMI. The degradation efficiencies (64-97%) of three other typical neonicotinoids (acetamiprid, clothianidin, and dinotefuran) indicated that the thermally activated persulfate process could be used for remediation of neonicotinoid-contaminated soil. Quenching experiments indicated that the major reactive species in IMI degradation were SO4•-, O2•-, and •OH. Six degradation intermediates of IMI were inferred in the soil, and degradation pathways of IMI included hydroxylation, denitrification, C-N bond break and further oxidation.

Early evaluation of adjuvant effects on topramezone efficacy under different temperature conditions using chlorophyll fluorescence tests.

Proper selection of adjuvant applications is an important strategy to enhance herbicide efficacy and reduce active ingredient input especially under adverse environmental conditions. In this study, a two-factor split-plot-design experiment was conducted to evaluate the effects of two adjuvants on the efficacy of topramezone on the grassy weed species giant foxtail (Setaria faberi Herrm.) and the broadleaved weed species velvetleaf (Abutilon theophrasti Medik.) under three different temperature conditions. The two tested adjuvants were methylated seed oil (MSO) and organosilicone. Three temperature levels, 35/30°C, 25/20°C, and 15/10°C (day/night), were used in the laboratory and greenhouse experiment. Plant chlorophyll fluorescence measurements shortly after herbicide application and classic whole-plant bioassay methods were used to evaluate the herbicide efficacy among the different treatments. Results indicated that the maximum quantum efficiency (Fv/Fm) of the top leaf of the weeds treated with topramezone mixed with MSO was significantly lower than that of the weeds treated with topramezone mixed with organosilicone and without an adjuvant at 2-3 days after treatment under all three temperature levels. The herbicide response of the plants treated with topramezone mixed with organosilicone and topramezone alone was not significantly different. These results corresponded well with the results of the classic whole-plant test. MSO has been shown to be good at enhancing the efficacy of topramezone on these weed species under all three temperature conditions. The measurement of chlorophyll fluorescence is a promising technique for evaluating the effects of adjuvants on the efficacy of herbicides shortly after herbicide treatment.

Predicting pesticide dissipation half-life intervals in plants with machine learning models.

Pesticide dissipation half-life in plants is an important factor to assessing environmental fate of pesticides and establishing pre-harvest intervals critical to good agriculture practices. However, empirically measured pesticide dissipation half-lives are highly variable and the accurate prediction with models is challenging. This study utilized a dataset of pesticide dissipation half-lives containing 1363 datapoints, 311 pesticides, 10 plant types, and 4 plant component classes. Novel dissipation half-life intervals were proposed and predicted to account for high variations in empirical data. Four machine learning models (i.e., gradient boosting regression tree [GBRT], random forest [RF], supporting vector classifier [SVC], and logistic regression [LR]) were developed to predict dissipation half-life intervals using extended connectivity fingerprints (ECFP), temperature, plant type, and plant component class as model inputs. GBRT-ECFP had the best model performance with F1-microbinary score of 0.698 ± 0.010 for the binary classification compared with other machine learning models (e.g., LR-ECFP, F1-microbinary= 0.662 ± 0.009). Feature importance analysis of molecular structures in the binary classification identified aromatic rings, carbonyl group, organophosphate, =C-H, and N-containing heterocyclic groups as important substructures related to pesticide dissipation half-lives. This study suggests the utility of machine learning models in assessing the environmental fate of pesticides in agricultural crops.

Insight into the uptake, accumulation, and metabolism of the fungicide phenamacril in lettuce (Lactuca sativa L.) and radish (Raphanus sativus L.).

The fungal species Fusarium can cause devastating disease in agricultural crops. Phenamacril is an extremely specific cyanoacrylate fungicide and a strobilurine analog that has excellent efficacy against Fusarium. To date, information on the mechanisms involved in the uptake, accumulation, and metabolism of phenamacril in plants is scarce. In this study, lettuce and radish were chosen as model plants for a comparative analysis of the absorption, accumulation, and metabolic characteristics of phenamacril from a polluted environment. We determined the total amount of phenamacril in the plant-water system by measuring the concentrations in the solution and plant tissues at frequent intervals over the exposure period. Phenamacril was readily taken up by the plant roots with average root concentration factor ranges of 60.8-172.7 and 16.4-26.9 mL/g for lettuce and radish, respectively. However, it showed limited root-to-shoot translocation. The lettuce roots had a 2.8-12.4-fold higher phenamacril content than the shoots; whereas the radish plants demonstrated the opposite, with the shoots having 1.5 to 10.0 times more phenamacril than the roots. By the end of the exposure period, the mass losses from the plant-water systems reached 72.0% and 66.3% for phenamacril in lettuce and radish, respectively, suggesting evidence of phenamacril biotransformation. Further analysis confirmed that phenamacril was metabolized via hydroxylation, hydrolysis of esters, demethylation, and desaturation reactions, and formed multiple transformation products. This study furthers our understanding of the fate of phenamacril when it passes from the environment to plants and provides an important reference for its scientific use and risk assessment.

Uptake, Translocation, and Biotransformation of Neonicotinoid Imidaclothiz in Hydroponic Vegetables: Implications for Potential Intake Risks.

Imidaclothiz is a novel and systemic neonicotinoid pesticide with excellent insecticidal efficacy. However, knowledge of its uptake, translocation, and biotransformation within plants is still largely unknown, restricting work on its accurate and comprehensive risk assessment. Here, we systematically investigated the behavior of imidaclothiz in three plant-water systems via hydroponic experiments. The results showed that imidaclothiz was readily taken up by plant roots and translocated upward, resulting in relative enrichment in leaves. The recoveries of imidaclothiz in plant-water systems decreased with increasing exposure time, and approximately 31.8-45.6% mass loss was measured at the end of exposure. Ultimately, imidaclothiz yielded five products in celery leaves, three products in lettuce leaves, and two products in radish leaves. Multiple metabolic reactions including hydroxylation, hydrolysis of nitrate ester, and methylation occurred within plants. This is the first report on the fate of imidaclothiz within plants and suggests increasing concerns about the risk assessment of imidaclothiz.

Occurrence and dietary risk assessment of 37 pesticides in wheat fields in the suburbs of Beijing, China.

The co-occurrence of multiple pesticides in wheat fields adversely affects human health and the environment. Herein, 206 pairs of wheat and soil samples were collected from wheat fields in Beijing, China from 2018 to 2020. One or multiple pesticide residues were detected, and carbendazim (maximum: 38511.5 µg/kg) and tebuconazole (maximum: 45.4 µg/kg) had heavy occurrence in the wheat samples. Carbendazim, triazoles, and neonicotinoids were frequently detected in the soil samples. HCHs and DDTs were detected, with p,p'-DDE in 100.0% of the soil samples at a maximum concentration of 546.0 µg/kg in 2020. Concentrations of carbendazim, tebuconazole, hexaconazole, and cyhalothrin in the paired soil and wheat samples exhibited significant positive correlations. Pesticides that exceeded the maximum residue limits do not pose non-carcinogenic risks, with one exception. The results provide important references towards risk monitoring and control in wheat fields, as well as facilitating the scientific and reasonable use of these pesticides.

Determination of thiamethoxam and its metabolite clothianidin residue and dissipation in cowpea by QuEChERS combining with ultrahigh-performance liquid chromatography-tandem mass spectrometry.

The dissipation and residue levels of thiamethoxam and its metabolite clothianidin in cowpea were investigated under field conditions. Samples of cowpea were analyzed using a QuEChERS technique with ultra-performance liquid chromatography tandem mass spectrometry. The recoveries were 86.5-118.9% for thiamethoxam and 75.6-104.1% for clothianidin, with the coefficient of variation of < 13%. The water dispersible granule formulation of thiamethoxam was applied on cowpea at 30 and 45 g active ingredient ha-1 in accordance with good agricultural practice. The half-life of thiamethoxam in cowpea was 0.8-1.6 days. The cowpea samples were gathered at 3, 7, and 10 days after the last application, and the residues of thiamethoxam in cowpea were < 0.005-0.054 mg kg-1, while those of clothianidin were < 0.005-0.008 mg kg-1. The final residues of thiamethoxam and clothianidin were below the European Union (EU) maximum residue level (0.3 mg kg-1 for thiamethoxam; 0.2 mg kg-1 for clothianidin) in cowpea after a preharvest interval (PHI) of 7 days. This study provided basic data on the use and safety of thiamethoxam and clothianidin in cowpea to help the Chinese government formulate a maximum residue level for thiamethoxam in cowpea.

Dispersive solid-phase extraction combined with dispersive liquid-liquid microextraction for simultaneous determination of seven succinate dehydrogenase inhibitor fungicides in watermelon by ultra high performance liquid chromatography with tandem mass spectrometry.

In this study, a simple and accurate sample preparation method based on dispersive solid-phase extraction and dispersive liquid-liquid microextraction has been developed for the determination of seven novel succinate dehydrogenase inhibitor fungicides (isopyrazam, fluopyram, pydiflumetofen, boscalid, penthiopyrad, fluxapyroxad, and thifluzamide) in watermelon. The watermelon samples were extracted with acetonitrile, cleaned up by dispersive solid-phase extraction procedure using primary secondary amine, extracted and concentrated by the dispersive liquid-liquid microextraction procedure with 1,1,2,2-tetrachloroethane, and then analyzed by ultra high performance liquid chromatography with tandem mass spectrometry. The main experimental factors affecting the performance of dispersive solid-phase extraction and dispersive liquid-liquid microextraction procedure on extraction efficiency were investigated. The proposed method had a good linearity in the range of 0.1-100 µg/kg with correlation coefficients (r) of 0.9979-0.9999. The limit of quantification of seven fungicides was 0.1 µg/kg in the method. The fortified recoveries of seven succinate dehydrogenase inhibitor fungicides at three levels ranged from 72.0 to 111.6% with relative standard deviations of 3.4-14.1% (n = 5). The proposed method was successfully used for the rapid determination of seven succinate dehydrogenase inhibitor fungicides in watermelon.

Dissipation and residues of fluazinam and dimethomorph in potatoes, potato plants, and soil, determined by QuEChERS ultra-performance liquid chromatography tandem mass spectrometry.

Fluazinam and dimethomorph 35% suspension concentrate (SC) is a new combined fungicide formulation introduced in China to improve fungicidal efficacy and decrease the risk of resistance in potatoes. Fluazinam and dimethomorph dissipation and residues in potatoes, potato plants, and soil under field conditions were determined by ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Fluazinam and dimethomorph 35% SC was applied at two doses to potatoes and soil in Ningxia Autonomous Region and Anhui Province, China. Fluazinam and dimethomorph dissipation fitted first-order kinetics, and the fluazinam half-lives in potato plants and soil were 3.3-5.4 and 9.4-9.5 days, respectively. The dimethomorph half-lives in potato plants and soil were 2.1-2.6 and 5.9-8.6 days, respectively. Fluazinam and dimethomorph 35% SC was sprayed onto potato plants three or four times at application rates of 420 and 630 g a.i. ha-1 with 7 days between applications. Potato and soil samples were collected at 3, 7, and 14 days after the last application. Potatoes and soil had fluazinam concentrations of < 0.01 and < 0.05-0.183 mg kg-1, respectively, and dimethomorph concentrations of < 0.01 and 0.129-0.677 mg kg-1, respectively. The final fluazinam and dimethomorph concentrations in potatoes were below the EU maximum residue limits (0.02 and 0.05 mg kg-1, respectively) 3 days after application. Fluazinam and dimethomorph can therefore be applied to potatoes at the recommended doses.

Residue behavior and dietary intake risk assessment of carbosulfan and its metabolites in cucumber.

The residue behavior and dietary intake risks of carbosulfan and its metabolites in cucumbers were investigated. A quick and reliable method for determining carbosulfan and its metabolite residues in cucumbers was established using ultrahigh performance liquid chromatography-tandem mass spectrometry. The fortified recoveries ranged from 87.2% to 91.0% with relative standard deviations of 3.2%-8.1%. The dissipation results showed that carbosulfan was transformed into carbofuran and 3-hydroxy carbofuran in cucumbers. The half-life of carbosulfan was 1.5 days, and the half-life of carbofuran was 45 days. The final residues of carbosulfan varied from 0.245 to 0.005 mg/kg and carbofuran varied from 0.123 to 0.008 mg/kg. After a 5-day application period the residues of carbosulfan was 0.113 mg/kg that was below the maximum residue limit set by China (0.2 mg/kg), and the residues of carbofuran was 0.055 mg/kg that was higher than the maximum residue limit set by China (0.02 mg/kg). The risk assessment results indicated that the dietary intake risks of carbosulfan and carbofuran from cucumber consumption were safe for Chinese consumers, but pre-harvest intervals should be strictly recommended for 7 days at the recommended dose to ensure that food quality conforms to the MRL standard. This study provides a method and data for scientifically evaluating dietary intake risks of carbosulfan and its more toxic metabolites.

Determination of oxathiapiprolin concentration and dissipation in grapes and soil by ultrahigh-performance liquid chromatography-tandem mass spectrometry.

BACKGROUND: The residue concentrations and dissipation rate of a new oxathiapiprolin fungicide in grapes and soil were investigated to provide an evaluation for the safe use of oxathiapiprolin in grapes. Pesticide residue was extracted by acetonitrile, then purified by solid-phase extraction with an Envi-Carb cartridge and determined by ultrahigh-performance liquid chromatography-tandem mass spectrometry. RESULTS: The fortified recoveries ranged from 85.2% to 99.0%, with relative standard deviations of 1.7-4.5%. The limit of quantitation for oxathiapiprolin in grapes and soil was 0.002 mg kg-1 . The mean initial deposits of oxathiapiprolin in grapes were 0.345-0.565 mg kg-1 , with half-lives of 8.6-9.2 days. The mean initial deposits of oxathiapiprolin in soil were 0.078-0.273 mg kg-1 , with half-lives of 7.6-12.0 days. The oxathiapiprolin residue in grapes and soil was 0.002-0.022 mg kg-1 and 0.002-0.123 mg kg-1 when sampling 14 days after application, respectively. CONCLUSION: The residue in the grapes was less than 0.01 mg kg-1 when sampling 28 days after application, which suggested that the application rate of 20 mg a.i. kg-1 for this fungicide should be used to ensure that treated grapes can be considered safe for humans to consume when sampling 28 days after the final application. © 2016 Society of Chemical Industry.

Solid-phase extraction combined with dispersive liquid-liquid microextraction for the determination of pyrethroid pesticides in wheat and maize samples.

A rapid, selective and sensitive sample preparation method based on solid-phase extraction combined with the dispersive liquid-liquid microextration was developed for the determination of pyrethroid pesticides in wheat and maize samples. Initially, the samples were extracted with acetonitrile and water solution followed phase separation with the salt addition. The following sample preparation involves a solid-phase extraction and dispersive liquid-liquid microextraction step, which effectively provide cleanup and enrichment effects. The main experimental factors affecting the performance both of solid-phase extraction and dispersive liquid-liquid microextration were investigated. The validation results indicated the suitability of the proposed method for routine analyze of pyrethroid pesticides in wheat and maize samples. The fortified recoveries at three levels ranged between 76.4 and 109.8% with relative standard deviations of less than 10.7%. The limit of quantification of the proposed method was below 0.0125 mg/kg for the pyrethoroid pesticides. The proposed method was successfully used for the rapid determination of pyrethroid residues in real wheat and maize samples from crop field in Beijing, China.

Residue behavior and dietary intake risk assessment of three fungicides in tomatoes (Lycopersicon esculentum Mill.) under greenhouse conditions.

The residue behavior and dietary intake risk of three fungicides (pyrimethanil, iprodione, kresoxim-methyl) in tomatoes (Lycopersicon esculentum Mill.) grown in greenhouse were investigated. A simple, rapid analytical method for the quantification of fungicide residues in tomatoes was developed using gas chromatography coupled with mass spectrum detection (GC-MSD). The fortified recoveries were ranged from 87% to 103% with relative standard deviations (RSDs) varied from 4.7% to 12.1%. The results indicated that the dissipation rate of the studied fungicides in tomatoes followed first order kinetics with half lives in the range of 8.6-11.5 days. The final residues of all the fungicides in tomatoes were varied from 0.241 to 0.944 mg/kg. The results of dietary intake assessment indicated that the dietary intake of the three fungicides from tomatoes consumption for Chinese consumers were acceptable. This study would provide more understanding of residue behavior and dietary intake risk by these fungicides used under greenhouse conditions.

Concentrations and dissipation of difenoconazole and fluxapyroxad residues in apples and soil, determined by ultrahigh-performance liquid chromatography electrospray ionization tandem mass spectrometry.

A new combined difenoconazole and fluxapyroxad fungicide formulation, as an 11.7 % suspension concentrate (SC), has been introduced as part of a resistance management strategy. The dissipation of difenoconazole and fluxapyroxad applied to apples and the residues remaining in the apples were determined. The 11.7 % SC was sprayed onto apple trees and soil in Beijing, Shandong, and Anhui provinces, China, at an application rate of 118 g a.i. ha(-1), then the dissipation of difenoconazole and fluxapyroxad was monitored. The residual difenoconazole and fluxapyroxad concentrations were determined by ultrahigh-performance liquid chromatography tandem mass spectrometry. The difenoconazole half-lives in apples and soil were 6.2-9.5 and 21.0-27.7 days, respectively. The fluxapyroxad half-lives in apples and soil were 9.4-12.6 and 10.3-36.5 days, respectively. Difenoconazole and fluxapyroxad residues in apples and soil after the 11.7 % SC had been sprayed twice and three times, with 10 days between applications, at 78 and 118 g a.i. ha(-1) were measured. Representative apple and soil samples were collected after the last treatment, at preharvest intervals of 14, 21, and 28 days. The difenoconazole residue concentrations in apples and soil were 0.002-0.052 and 0.002-0.298 mg kg(-1), respectively. The fluxapyroxad residue concentrations in apples and soil were 0.002-0.093 and 0.008-1.219 mg kg(-1), respectively. The difenoconazole and fluxapyroxad residue concentrations in apples were lower than the maximum residue limits (0.5 and 0.8 mg kg(-1), respectively). An application rate of 78 g a.i. ha(-1) is therefore recommended to ensure that treated apples can be considered safe for humans to consume.

[Determination of hexachlorocyclohexane and dichlorodiphenyltrichloroethen residues in honey by gas chromatography-mass spectrometry combined with dispersive liquid-liquid microextraction].

A gas chromatography-mass spectrometry (GC-MS) method for the determination of hexachlorocyclohexane (BHC) and dichlorodiphenyltrichloroethane (DDT) residues in honey was developed using dispersive liquid-liquid microextraction (DLLME) as sample preparation method. The samples were extracted with chloroform, and concentrated into chloroform by vortex and centrifuging. The analytes were analyzed by GC-MS. The factors affecting the extraction efficiency were investigated, such as the type and volume of extraction and dispersive solvent, extraction time, etc. The matrix effects and method performance were evaluated at the same time. The results indicated that all the eight BHC and DDT pesticides displayed the enhancement of signals due to the matrix effects. The calibration curves were linear in the range of 2-500 microg/L and the correlation coefficients were 0.991-0.998 for the eight BHC and DDT pesticides. The enrichment factors (EF) were 74-96 for the eight pesticides. The recoveries of the eight BHC and DDT pesticides at three spiked levels of 20, 50 and 100 microg/kg were 61.0%-100.1%, while the RSDs were 2.2%-19.5%. The limits of quantification for the eight pesticides were 20 microg/kg, and the limits of detection were 1.0 ng. The developed method is easy, quick and with high performance. It is applicable for the determination of BHC and DDT residues in honey.

[Preparation of nicosulfuron molecularly imprinted microspheres and research of adsorption characteristics].

Molecularly imprinted microspheres (MIPMs) for binding and recognition of nicosulfuron (NS) (NS-MIPMs) were prepared by precipitation polymerization. Methacrylic acid (MAA) was used as the functional monomer, trimethylolpropane trimethacrylate (TRIM) as the linking agent, 2,2-azobisisobutyronitrile (AIBN) as the initiator and chloroform as the porogenic solvent. The preparation conditions were optimized, and MIPMs exhibited the best adsorption capacity when the molar ratio of NS/MAA/TRIM/AIBN was 1:4:4:1 and the volume of the porogenic solvent was 90 mL. An ultraviolet-visible (UV-Vis) spectrophotometer was employed to study the mechanism of the interaction between NS and MAA, and the results showed that the NS-MAA complexes of 1:1 molar ratio were obtained in the pre-polymerization phase. The rebinding capacity of MIPMs was evaluated according to adsorption kinetics and adsorption isotherm of the imprinted microspheres. The Scatchard plot revealed that the template polymer system has a two-site binding behavior and the MIPMs exhibited the maximum rebinding to NS at 11,370.5 microg/g. The MIPMs were then used as adsorbents in a solid phase extraction (SPE) column and the optimum loading, washing and eluting conditions for the MIPMs were established. Additionally, a rapid method for the determination of NS residues in soil was developed using an NS-MIPMs SPE column. The analyte was extracted using acetonitrile and phosphate buffer, cleaned-up by an NS-MIPMs SPE column and analyzed by HPLC. The results showed that good linearity was observed in the range of 0.01-1 mg/L for NS, with a correlation coefficient of 0. 998 6. The recovery tests were performed at the spiked levels of 0.02-1 mg/kg, and the recoveries were in the range of 82.2%-86.3% with the relative standard deviations of 1.9%-4.3%. The advantages of the proposed method are that it is easy to operate, reliable and applicable to analyze the NS residues in soil samples.

Combination of dispersive solid-phase extraction and salting-out homogeneous liquid-liquid extraction for the determination of organophosphorus pesticides in cereal grains.

A new analytical method for the determination of organophosphorus pesticides in cereal samples was developed by combining dispersive SPE (d-SPE) and salting-out homogeneous liquid-liquid extraction (SHLLE). The pesticides were first extracted from cereal grains with acetonitrile, followed by d-SPE cleanup. A 2 mL aliquot of the extract was then added to a centrifuge tube containing 9.2 mL water and 3.3 g NaCl for SHLLE. Analysis of the extract was carried out by gas chromatography coupled with flame photometric detection. The d-SPE procedure effectively provides the necessary cleanup of the extract while SHLLE is used as an efficient concentration technique. Experimental parameters influencing the extraction efficiency including amounts of added water and salt were investigated. Recovery studies were carried out at three fortification levels, yielding recoveries in the range of 57.7-98.1% with the RSD from 3.7 to 10.9%. The reported limits of determination obtained from this study were 1 µg/kg, which is better than the conventional methods. In the analysis of 40 wheat and corn samples taken from Beijing suburbs, only two wheat samples have chlorpyrifos residue over the limits of determination.