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.

[Safety Production Threshold and Land Quality Classification of Vegetable Pb in High Geological Background Area of Southwest China].

In order to ensure the safe production of vegetables in Pb-contaminated farmland under the complex interactions of an extreme geological background area and human activities in Southwest China, 32 types of widely planted vegetable varieties in the southwest region were collected. Correlation analysis, multiple linear regression analysis, and other methods were used to study the accumulation of Pb in soil-vegetables and the key constraints. The threshold of soil Pb ecological security in farmland in southwest China was determined by the method of species sensitivity distribution. The results showed that ω(Pb) of the soils was 47.59-462.38 mg·kg-1, which was 1.88 times higher than that of the background value of soil Pb in Yunnan Province (90 mg·kg-1), and 68.40% of the soil samples exceeded the screening value of the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Management Standard" (GB 15618-2018). The content of Pb in the edible parts of vegetable crops ranged from 0.02 to 0.49 mg·kg-1, and the exceeding rate reached 20.49%. Pb concentration in the vegetables was in the decreasing sequence of leafy vegetables > roots and stems vegetables > eggplant vegetables > edible bean vegetables > pepper vegetables. Based on soil pH, OM, and CEC, the model of Pb accumulation in vegetables was constructed, in which pH was the first critical factor affecting Pb accumulation in vegetables. The sensitivity index of vegetable Pb species showed that leafy vegetables, eggplant vegetables, and a small number of frame bean vegetables were less sensitive to Pb. The soil Pb classification thresholds of the three types (priority protection, safe use, and strict control) of areas for vegetable safety production was ≤ 100, 100-353, and ≥ 353 mg·kg-1, respectively.