Simultaneous determination of residues of metalaxyl, cyazofamid and a cyazofamid metabolite in tobacco leaves and soil by liquid chromatography with tandem mass spectrometry

Long-term leaching through clayey till of N,N-dimethylsulfamide, a Persistent and Mobile Organic Compound (PMOC)

Environmental pollution with Persistent and Mobile Organic Compounds (PMOC) from anthropogenic activities is an increasing cause for concern. These compounds are readily leached to groundwater aquifers and are likely to resist degradation, putting pressure on groundwater resources. Pesticides can form PMOCs upon degradation in the environment. The PMOC N,N-dimethylsulfamide (DMS) was the most frequently detected pesticide metabolite in Danish drinking water wells in 2020, although the pesticidal use of the last parent compound (tolylfluanid) ended in 2007. This study aimed to improve the understanding of the leaching of the PMOC DMS from clayey tills by combining a review of compound properties, sources and use, comprehensive field observations and numerical flow and solute transport modeling. The modeling explored the mechanisms of DMS retention during vertical transport in clayey till and the fingerprint in the underlying aquifer. The results were supported by detailed field observations at an agricultural site with strawberry production. Porewater samples were collected from clayey till to a depth of 12 m bgs by a custom designed installation method of suction cups. Groundwater sampling (249 samples) was designed to provide vertical concentration profiles at various distances from the presumed sources. The review of properties showed that the parent compounds and intermediates degrade quickly in topsoil, releasing the highly persistent and mobile DMS. We tested the effect of fractures on transport with different hydraulic apertures and a scenario without fractures by numerical modeling. The results showed that the presence of fractures can smooth the breakthrough curve below the clayey till, leading to faster breakthrough, lower maximum concentration, and several decades of prolonged leaching in simulations with the largest aperture (20 μm). The fracture-matrix interaction is a possible explanation for the observed delay of leaching from clayey till. The vertical concentration profiles in groundwater were used for identifying the sources at the field site and testing source strengths. Assigning one point source (200 μg/L) and two diffuse sources (40-50 μg/L) to the model produced vertical concentration profiles that compared well with observed field data in clayey till and the aquifer. All results were integrated into a conceptual model for the environmental fate of PMOCs in soil and groundwater. The findings of this study imply that the presence of fractures in clayey till should be considered in conceptual site models, since they can substantially prolong the leaching of PMOCs to groundwater. The integration of comprehensive field investigations and numerical modeling is key to understand the fate of PMOCs in complex field systems with different source types. Together with widespread occurrences of PMOCs in groundwater systems, the results highlight the need for improved approval procedures for pesticides and biocides which considers their persistent and mobile metabolites.

Determination of Commonly Used Multiclass Pesticide Residues in Tobacco and Cigarette Smoke by Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry

A novel method has been developed for the simultaneous determination of multiclass pesticide residues in tobacco and cigarette smoke, using a modified QuEChERS (quick, easy, cheap, effective, rugged and safe) procedure and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Cigarette mainstream smoke particulate was collected on a Cambridge filter pad. Pesticide residues was extracted with an aqueous solution, back extracted into acetonitrile after freezing, purified by dispersive solid phase extraction with primary-secondary amine adsorbents and analyzed by UPLC-MS/MS. The obtained mean recoveries of 16 pesticides commonly used on tobacco at three fortification levels (5.9, 94.1 and 352.9 ng g-1) ranged from 69.3 to 115.9% with relative standard deviations between 2.4 and 11.3%. The limits of detection ranged from 0.14 to 13.28 ng g-1. Finally, the proposed method was applied to study the pesticide smoke transfer ratio in 2 cigarettes with pesticide standard spiked and 51 cigarettes with one or more pesticide residues. The transfer ratio of pesticides residue in tobacco into the smoke might be much less than that from artificially spiked tobacco (<25%) with spiking levels varied from 1.88 to 9.41 μg g-1. The transfer ratio of pesticide from artificially spiked tobacco into cigarette mainstream smoke was from 0.0 to 56.5%, and pesticide residues from tobacco into cigarette smoke were from 0.0 to 26.1% using the ISO smoking method (ISO 3308 2012).

Enantiomer/stereoisomer-specific residues of metalaxyl, napropamide, triticonazole, and metconazole in agricultural soils across China

In this study, the residual status of four chiral pesticides including metalaxyl, napropamide, triticonazole, metconazole, and their enantiomers/stereoisomers were investigated in agricultural soils across China. The levels in the soils were detected as non-detected (n.d.)-16.67 ng/g for metalaxyl with a median of 0.14 ng/g; 0.004-32.99 ng/g for napropamide with a median of 0.29 ng/g; n.d.-207.39 ng/g for triticonazole with a median of 1.29 ng/g; and n.d.-71.83 ng/g for metconazole with a median of 1.03 ng/g, respectively. Enantiomer/stereoisomer-specific residues were observed for metalaxyl and triticonazole. R-Metalaxyl and R-triticonazole were identified as the major enantiomers in the soils for the two pesticides. There was no obvious enantioselective residue for napropamide in most of the soils. As for metconazole, metconazole-1 and metconazole-4 were identified as the major stereoisomers in the soils. These results suggest that enantiomer/stereoisomer-specific risk should be considered when assessing the ecological safety of these pesticides in soils.

The Study of the Kinetics of Metalaxyl Accumulation and Dissipation in Durian (Durio zibethinus L.) Leaf Using High-Performance Liquid Chromatography (HPLC) Technique

Metalaxyl is an effective approach to control Phytophthora palmivora infection in durian plantation. However, inappropriate metalaxyl usage may increase production cost, pathogen with fungicide resistance, and environmental toxicity. This study established and validated a simple and reproducible procedure to measure metalaxyl concentration in the durian leaf using HPLC. Linearity of the detection ranged from 1–100 µg/mL. The limits of detection (LOD) and quantification (LOQ) were 0.27 and 0.91 µg/mL, respectively. The extraction method gave recovery rates ranging from 88% to 103%. Durian seedlings were treated with 4 g/L metalaxyl either by foliar spray or soil drench. The highest metalaxyl accumulation in durian leaf was found between 6–24 h after treatment and persisted above its effective concentration at least 60 days after foliar application. The dissipation pattern fit to a first-order kinetics equation showed a half-life of 16.50 days. Soil drenching led to eight times higher metalaxyl concentrations in plants than foliar spraying and caused plant death within 15 days after application. These results suggest that foliar spraying of 4 g/L metalaxyl or soil drenching at a lower concentration every two months is sufficient in controlling P. palmivora infection in durian seedlings.

Residue Monitoring and Risk Assessment of Cyazofamid and Its Metabolite in Korean Cabbage Under Greenhouse Conditions

The residual characteristics and risk assessment with respect to cyazofamid and its metabolite 4-chloro-5-p-tolylimidazole-2-carbonitrile were monitored in case of Korean cabbage at different preharvest intervals during a greenhouse trial. The 0.02 kg a.i/ha of cyazofamid was sprayed twice on seven-day intervals (i.e., on day 0, 7, 14, and 21 before harvest). The liquid chromatography-tandem mass spectrometry analysis was used to monitor the residual amount of fungicide. The matrix-matched calibration curves with respect to the cyazofamid in Korean cabbage exhibited good linearity (R² ≥ 0.999) and acceptable recoveries of 84.1%-114.9%. The biological half-life of cyazofamid in Korean cabbage was 3.18 days. During the treatment, the preharvest residue of cyazofamid in Korean cabbage 14 days before harvest (0.80 mg/kg) was lower than that specified by the MFDS-MRL (Ministry of Food and Drug Safety-Maximum Residue Limit, 2.0 mg/kg) and should be recommended as the safe preharvest-interval application limit. The hazard quotient showed low toxicity (70.58%) during the risk assessment study of cyazofamid.

Rapid and Sensitive Immunochromatographic Method-Based Monoclonal Antibody for the Quantitative Detection of Metalaxyl in Tobacco

In this study, we prepared a monoclonal antibody (mAb) against metalaxyl (Met) with a half-maximum inhibitory concentration (IC₅₀) of 0.54 ng/mL based on a new hapten, and a gold nanoparticle-based immunochromatographic assay (GICA) was developed for the rapid detection of Met residues in tobacco. Under optimal conditions, even with the naked eye, one can see the semiquantitative analysis results. The naked eye detection limit of Met in tobacco is 25 μg/kg, and the detection threshold is 100 μg/kg. In addition, the cross-reactivity test shows that the mAb has good specificity for Met, and the GICA results have a good correlation with the indirect competitive enzyme-linked immunosorbent assay and liquid chromatography with tandem mass spectrometry test results, which show that the method is feasible and reliable and are more convenient and quicker than the methods using instrumentation for detection. Therefore, GICA may provide a useful tool for the rapid screening and detection of Met residues in tobacco.

Dissipation and Risk Assessment of Multiresidual Fungicides in Grapes under Field Conditions

Grapes are among the most popular fruits globally, and various fungicides are widely applied to grape crops. As such, the presence of multiple fungicide residues and dietary risks in grapes has become the focus of significant attention. In this study, an easy-to-implement and sensitive UPLC-MS/MS approach was developed to simultaneously determine pyraclostrobin, dimethomorph, cymoxanil, cyazofamid and its metabolite CCIM in grapes via QuEChERS. This approach achieved 78.1-106.0% recovery and a 0.01 mg kg^-1 limit of quantitation (LOQ). Field trials revealed that these compounds had degradation half-lives ranging from 0.9 to 13.3 days. And their terminal residues ranging from < LOQ to 1.36 mg kg^-1 were below the official maximum residue limit (MRL) in China. The short-term risk for each tested fungicide was below 54%. The long-term risk of individual chemicals ranged from 0.0086% to 3.1%, and their cumulative risk was 4.4%. Results indicated that the dietary risk of these fungicides in grapes was minor.

Residue behaviours, dissipation kinetics and dietary risk assessment of pyaclostrobin, cyazofamid and its metabolite in grape

BACKGROUND

Grape is an important fruit consumed either fresh or processed, therefore, fungicide misuse of grape has become an issue of global food safety and human health. Pyraclostrobin, and cyazofamid have been applied to grape frequently.

RESULTS

Here a simple QuEChERS (quick, easy, cheap, effective, rugged, and safe) liquid chromatography mass spectrometry technique has been developed and validated for the determination of pyraclostrobin, cyazofamid and its metabolite CCIM in open field grape samples. The recoveries of these three in the range of 0.01 to 5 mg kg^-1 (n = 5) ranged from 73.1% to 97.9%. The relative standard deviations (RSDs) were below 12% for all cases. The limits of quantitation of each analyte was 0.005 mg kg^-1 , which was lower than maximum residue limits of not only pyraclostrobin but also cyazofamid. Not only dissipation kinetics but also residue determination was obtained in grape for those three pesticides. Furthermore, their half-lives in grapes were 10.7-30.1 days, recommending the pre-harvest intervals for these three of 14 days. The calculated hazard quotient and acute hazard index lower than 100% illustrated the safety of intake of grape for the Chinese population for not only long-term but also short-term dietary risk assessment.

CONSLUSIONS

The less than 30 day half-life illustrated that pyraclostrobin and cyazofamid could degrade relatively easily in the environment. The long-term and short-term dietary risk assessment also illustrated the intake safety of these three. Thus, a 14 day pre-harvest interval was safe and recommended. The results of this study contributed to environmental protection, food safety and human health. © 2019 Society of Chemical Industry.

Determination, residue and risk assessment of trifloxystrobin, trifloxystrobin acid and tebuconazole in Chinese rice consumption

A simple and rapid analytical method for the detection of trifloxystrobin, trifloxystrobin acid and tebuconazole in soil, brown rice, paddy plants and rice hulls was established and validated by liquid chromatography with tandem mass spectrometry. Acceptable linearity (R²  > 0.99), accuracy (average recoveries of 74.3-108.5%) and precision (intra- and inter-day relative standard deviations of 0.9-8.8%) were obtained using the developed determination approach. In the field trial, the half-lives of trifloxystrobin and tebuconazole in paddy plants were 5.7-8.3 days in three locations throughout China, and the terminal residue concentrations of trifloxystrobin and tebuconazole were <100 and 500 μg/kg (maximum residue limits set by China), respectively, at harvest, which indicated that, based on the recommended application procedure, trifloxystrobin and tebuconazole are safe for use on rice. The risk assessment results demonstrated that, owing to risk quotient values of both fungicides being <100%, the potential risk of trifloxystrobin and tebuconazole on rice was acceptable for Chinese consumers. These data could provide supporting information for the proper use and safety evaluation of trifloxystrobin and tebuconazole in rice.