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A simple pretreatment method with liquid chromatography–tandem mass spectrometry (LC–MS/MS) was developed and validated to simultaneously determine dichlorvos and phoxim in tobacco and soil matrices. Satisfactory linearity (R2 ≥ 0.9991) of the method was obtained for both analytes. The limits of detection and limits of quantification for dichlorvos and phoxim in three matrices were 0.0015–0.006 and 0.005–0.02 mg/kg, respectively. Average recoveries were 78.24–92.21% for dichlorvos and 76.62–100.51% for phoxim in soil, green tobacco leaves and cured tobacco leaves. The intra‐ and inter‐day relative standard deviations were <6%. The established method was successfully applied for the residual analysis of dichlorvos and phoxim in real soil and tobacco samples. The results indicated that the established method could be used to detect trace amounts of dichlorvos and phoxim in tobacco. The data could also help the Chinese government establish maximum residue limits of dichlorvos and phoxim on tobacco and establish proper and safe use of dichlorvos and phoxim on tobacco plants in China.

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BACKGROUND: Thiophanate-methyl and its metabolite carbendazim are broad-spectrum fungicides used on many crops. The residues of these chemicals could result in potential environmental and human health problems. Therefore, investigations of the dissipation and residue behaviors of thiophanate-methyl and its metabolite carbendazim on cowpeas and associated dietary risk assessments are essential for the safety of agricultural products. RESULTS: A simple analytical approach using liquid chromatography with tandem mass spectrometry was developed and validated for the determination of thiophanate-methyl and carbendazim concentrations in cowpeas. Good linearity (R 2 > 0.998) was obtained, and the recoveries and relative standard deviations were 80.0-104.7% and 1.4-5.2%, respectively. The dissipation rates of thiophanatemethyl, carbendazim and total carbendazim were high (half-lives of 1.61-2.46 days) and varied in the field cowpea samples because of the different weather conditions and planting patterns. Based on the definition of thiophanate-methyl, the terminal residues of total carbendazim in cowpea samples were below the maximum residue limits set by Japan for other legumes. The acute and chronic risk quotients of three analytes were 0.0-27.6% in cowpea samples gathered from all terminal residue treatments, which were below 100%.CONCLUSION: An optimized approach for detecting thiophanate-methyl and carbendazim in cowpeas was applied for the investigation of field-trial samples. The potential acute and chronic dietary risks of thiophanate-methyl, carbendazim and total carbendazim to the health of Chinese consumers were low. These results could guide the safe and proper use of thiophanatemethyl in cowpeas and offer data for the dietary risk assessment of thiophanate-methyl in cowpeas.

Enantioselective degradation behavior of mandipropamid, and factors affecting its degradation and metabolites in four types of Chinese soil were investigated in this work. The results showed that the enantiomeric selectivity values ranged from 0.025 to 0.170, indicating that enantioselectivity was found in the degradation process of the racemate in all of the soil samples and that the R-(−)-enantiomer was preferentially degraded. The degradation compounds formed faster in native alkaline soils (half-lives = 35.5-39.80 d) than in native acidic soils (half-lives = 51.3-77.90 d). The half-lives of the R-(−)-enantiomer and S-(+)-enantiomer were 35.5-73.7 and 37.5-77.9 d, 66.6-97.6 and 70.0-103.5 d, and 52.5-110.0 and 66.0-144.4 d in the fourtypes of soil under native, sterilized, and organic matter-removed conditions, respectively, which indicated that mandipropamid degradation can be attributed to microbial activity and the organic matter content in the soil. Furthermore, the half-lives of the R-(−)-enantiomer and S-(+)-enantiomer decreased 1.07-1.95 and 1.08-1.79 times with each 10˚C increase in incubation temperature, and the half-lives of the R-(−)-enantiomer and S-(+)-enantiomer decreased 1.09-1.43 and 1.06-1.50 times with increasing moisture content. However, the incubation temperature and soil moisture did not change the enantioselectivity. Mandipropamid enantiomers were observed to be configurationally stable in the selected soil, and no interconversion was found during the incubation of enantiopure R-(−)-mandipropamid or S-(+)-mandipropamid in native or sterilized soil. During the degradation process, four major metabolites were detected. In comprehensive consideration of the environmental behavior, the enantioselective degradation results should be considered to more accurately assess the risk of this chiral pesticide in a real environment.

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Soil moisture is a vital factor affecting the hydrological cycle and the evolution of soil and geomorphology, determining the formation and development of the vegetation ecosystem. The previous studies mainly focused on the effects of different land use patterns and vegetation types on soil hydrological changes worldwide. However, the spatial heterogeneity and driving factors of soil gravimetric water content in alpine regions are seldom studied. On the basis of soil sample collection, combined with geostatistical analysis and the geographical detector method, this study examines the spatial heterogeneity and driving factors of soil gravimetric water content in the typical alpine valley desert of the Qinghai–Tibet Plateau. Results show that the average value of soil gravimetric water content at different depths ranges from 3.68% to 7.84%. The optimal theoretical models of soil gravimetric water content in 0–50 cm layers of the dune are different. The nugget coefficient shows that the soil gravimetric water content in the dune has a strong spatial correlation at different depths, and the range of the optimal theoretical model of semi-variance function is 31.23–63.38 m, which is much larger than the 15 m spacing used for sampling. The ranking of the influence of each evaluation factor on the alpine dune is elevation > slope > location > vegetation > aspect. The interaction detection of factors indicates that an interaction exists among evaluation factors, and no factors are independent of one another. In each soil layer of 0–50 cm, the interaction among evaluation factors has a two-factor enhancement and a nonlinear enhancement effect on soil gravimetric water content. This study contributes to the understanding of spatial heterogeneity and driving factors of soil moisture in alpine deserts, and guidance of artificial vegetation restoration and soil structure analysis of different desert types in alpine cold desert regions.

Soil quality evaluation is the foundation for understanding the current situation of soil quality and promoting the sustainable utilization of land resources. However, the evaluation of the impacts of the different long-term afforestation timescales on the soil quality in a typical watershed valley area is still insufficient. Here, based on the soil samples collected from different afforestation years of 2, 5, 11, 15, and 31 years and natural sample plots with similar site conditions in the same region, the gray target model and criteria importance through intercriteria correlation (CRITIC) method are used in this study to evaluate the soil quality of the sample plots with different afforestation years and the corresponding natural sample plots in the Tibet Plateau. Results show that: (1) The most positive soil physical and chemical indexes increase with the increase in afforestation years based on the analysis of the characteristics, variation, and fertility grade of 13 soil physical and chemical indexes in different areas. The content of most soil physical and chemical indexes is greater than that in the corresponding natural sample plots in 31 years of afforestation. (2) The bullseye degree of the soil quality in the study area is divided into five grades according to the principle of equal division and integration. The soil quality grade of the corresponding sample plot after 15 years of afforestation is grade 4. The other plots are grade 5. (3) The soil quality index (SQI) generally increases with the increase of in forestation years. The different afforestation years indicate SQI (0.709) of 15 years &gt; SQI (0.662) of 31 years &gt; SQI (0.426) of 11 years &gt; SQI (0.348) of 2 years &gt; SQI (0.309) of 5 years. (4) The full data set method verifies the effectiveness of the gray target model. The two soil quality evaluation methodologies are consistent and can verify each other’s accuracy. The correlation coefficient of the two results reaches 0.957. This study finds that the long-term afforestation timescales have improved the soil quality of watershed valley. Available phosphorus, silt, soil water content are the main factors impacting the soil quality in the afforestation timescales.