Climate warming inhibits neonicotinoid photodegradation on vegetable leaves: Important role of the olefin group in leaf wax.

Neonicotinoid photodegradation is seldom considered in different vegetable leaves after spraying under climate warming. This study investigated the effect of elevated cultivated temperature from 15/10 °C to 21/16 °C on the photodegradation of dinotefuran, thiamethoxam, acetamiprid, and thiacloprid on four vegetable leaves under simulated sunlight irradiation. The photodegradation rates of neonicotinoids on spinach leaves were 1.1-1.6, 1.1-2.0, and 1.4-2.4 times higher than those on pak choi, Chinese cabbage, and radish leaves, respectively. The higher production concentrations of hydroxyl radicals (•OH) and superoxide radicals in spinach leaf wax may contribute to the fastest photodegradation among four vegetables. When the cultivated temperature increased from 15/10 °C to 21/16 °C, neonicotinoid photodegradation rates decreased by 1.4-2.8 times on the four vegetables. Elevated cultivated temperature decreased the polarity of wax, which reduced the contact probability of neonicotinoids with reactive species on vegetable leaves and photodegradation rates. A positive linear correlation was found between the content of CHCH groups in wax determining •OH generation and the neonicotinoid photodegradation rates on four vegetable leaves cultivated at three temperatures (R2 = 0.67-0.94). Insights into neonicotinoid photodegradation on edible vegetables under climate warming are of great significance for better evaluating human exposure to neonicotinoids through the dietary pathway.

Derivation and validation of soil cadmium thresholds for the safe farmland production of vegetables in high geological background area.

Excessive dietary intake of cadmium (Cd) poses toxicity risks to human health, and it is therefore essential to establish accurate and regionally appropriate soil Cd thresholds that ensure the safety of agricultural products grown in different areas. This study investigated the differences in the Cd accumulation in 32 vegetable varieties and found that the Cd content ranged from 0.01 to 0.24 mg·kg-1, and decreased in the order of stem and bulb vegetables > leafy vegetables > solanaceous crops > bean cultivars. A correlation analysis and structural equation model showed that pH, soil organic matter, and the cation exchange capacity had significant effects on Cd accumulation in the vegetables and explained 72.1 % of the variance. In addition, species sensitivity distribution (SSD) curves showed that stem and bulb vegetables were more sensitive to Cd than other types of vegetables. Using the Burr Type III function for curve fitting, we derived Cd thresholds of 6.66, 4.15, and 1.57 mg·kg-1 for vegetable soils. These thresholds will ensure that 20 %, 50 %, and 95 % of these vegetable varieties were risk-free, respectively. The predicted threshold of soil Cd was more than twice that of China's current National Soil Quality Standard (GB 15618-2018) for Cd values. Therefore, soil scenarios and cultivars should be considered comprehensively when determining farmland soil thresholds. The present results provide a new model for setting soil Cd criteria in high geological background areas.

Correlation and the concentrations of Pb, Cd, Hg and As in vegetables and soils of Chongqing, China.

This paper studies the concentration of Pb, Cd, Hg and As in vegetable and soil of 13 main vegetable base, Chongqing, China, as well as the correlation between them. Results show that the concentrations of heavy metals in different vegetables from 13 main vegetable bases of Chongqing are also significantly different. The order of Pb concentration is root vegetable (the average value is 0.203 mg/kg) > leaf vegetable (the average value is 0.065 mg/kg) > solanaceous vegetable (the average value is 0.004 mg/kg); the order of Cd concentration is leaf vegetable (the average value is 0.090 mg/kg) > solanaceous vegetable (the average value is 0.061 mg/kg) > root vegetable (the average value is 0.049 mg/kg); the order of Hg concentration is leaf vegetable (the average value is 0.004 mg/kg) > root vegetable (the average value is 0.003 mg/kg) > solanaceous vegetable (the average value is 0.001 mg/kg); the order of As concentration is root vegetable (the average value is 0.116 mg/kg) > solanaceous vegetable (the average value is 0.057 mg/kg) > leaf vegetable (the average value is 0.026 mg/kg). Significant positive correlation was found between the Cd concentration in vegetables and the Cd concentration in soil, and the linear equation was y = 0.065 + 0.012x. There was no significant correlation between the concentrations of Pb, Hg and As in vegetables and Pb, Hg and As in soil.

[Greenhouse Gas Emissions for Typical Open-Field Vegetable Production in China].

To quantify the net greenhouse gas emissions (NGHGE) of typical open-field vegetables production in China and analyze potential mitigation measures, the life cycle assessment (LCA) method was used to calculate the agricultural inputs, carbon sequestration, and greenhouse gas emissions of open-field tomato, cucumber, Chinese cabbage, and radish production in China based on national statistical data. The results showed that greenhouse gas emissions of typical vegetable production in China were much higher than the associated carbon sequestration, suggesting that they were net greenhouse gas emitters. The weighted average net greenhouse gas emissions of open-field tomato, cucumber, Chinese cabbage, and radish production when expressed on an area basis were 4149, 3718, 3780, and 2427 kg·hm-2(CO2-eq), respectively. The results from this study also indicated significant differences in the spatial distribution of greenhouse gas emissions for open-field vegetable production in China, and open-field tomato, cucumber, Chinese cabbage, and radish had higher greenhouse gas emissions in Hainan, Yunnan, Shaanxi, and Shandong, respectively, than in the other provinces. Fertilizer production, transportation, and application were the most significant contributors to the greenhouse gas emissions, contributing 86.8%-90.8% of the total emissions. This is significant for improving industry technology during fertilizer production and optimizing fertilizer management in open-field vegetable production based on different vegetables and provinces, which could achieve a double-win strategy in terms of increasing open-field vegetable yield and minimizing greenhouse gas emissions simultaneously.