崇明岛芦笋种植区土壤盐碱化和重金属污染风险评估

Chongming Island is located at the mouth of the Yangtze River, with fertile soil, and is one of Shanghai's vegetable production bases. Asparagus, a nutritious and crisp vegetable, has become a featured vegetable grown on Chongming Island. With the rapid development of science and technology, industrialization and urbanization are accelerating. Agriculture has encountered many problems in production development, including the discharge of large amounts of industrial waste and unscientific land use, leading to a decline in soil utilization efficiency. Soil salinization and heavy metal pollution have become serious problems in agricultural environments. This article focuses on the risk assessment of soil salinization and heavy metal pollution characteristics in the asparagus planting area, as well as the safety of asparagus agricultural products. Therefore, this study selected soil and asparagus samples from Chongming Island farmland as the research object, and conducted sampling research to detect soil salinization and heavy metal pollution characteristics and evaluate health risks using appropriate methods. The study aimed to provide basic data on soil salinity and heavy metal pollution content for the layout of the asparagus base industry.

The research results showed that:

The cations detected in the soil of the asparagus planting area were K+, Na+, Ca2+, and Mg2+, with average contents of 0.109, 0.174, 0.441, and 0.134 g/kg, respectively. The content of K+ and Mg2+ were low, and Mg2+ had the largest variation coefficient of 0.748. Ca2+ had the highest content, accounting for 51% of the total water-soluble cations. The main anions in the soil of the asparagus planting area were HCO-3, SO2-4, and Cl-, with CO2-3 present in small amounts. The average contents of HCO-3, Cl-, and SO2-4 in the soil were 0.013 g/kg, 0.176 g/kg, and 0.592 g/kg, respectively, with a relatively high content of SO2-4. The variation coefficient of Cl- was the largest among the anions, reaching 0.761. The soil salinization types were sulfate-chloride type, chloride-sulfate type, and sulfate type. Part B showed mild saline soil.

The average contents of As, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Zn, and Hg in the surface soil of Chongming Island were 11.726, 5219.766, 0.192, 52.686, 65.298, 29608.889, 4215.255, 474.241, 23.902, 21.11, 116.038, and 0.214 mg/kg, respectively. None of the element contents exceeded the risk control values set by the GB15618-2018 standard. Compared with the background values, there was different degrees of accumulation of Mg, Zn, Cu, As, Hg, and Cd in the soil, while Mn, Ni, and Pb decreased. As had a low coefficient of variation, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Zn, and Hg had a moderate variation, and Hg had a high variation. From the geological accumulation index, the average value of As was slightly polluted, while Cd was unpolluted but had some local slight pollution. Cr was unpolluted, Cu was unpolluted but had some local slight pollution, Mn was unpolluted, Ni was unpolluted, Pb was unpolluted, and Zn was unpolluted but had some local slight pollution. Hg was unpolluted, but had some local slight pollution.

In the edible part of the asparagus, the content of Cr exceeded the limit set by the national food safety standard (GB 2762-2022), while the contents of other elements were below the limit. The enrichment coefficient of Zn in asparagus was the largest, while that of Pb was the smallest. The trend of bioaccumulation coefficient was: Zn > As > Ca > Cd > Cr > Cu > Fe > Hg > Mg > Mn > Ni > Pb. For both adults and children, the non-carcinogenic risk of the five metals was highest for Cr, and for the five metal carcinogens, the risk was also highest for Cr. The carcinogenic risk, regardless of adults or children, was highest for Cr through asparagus intake, exceeding 1×10-4.

The main conclusions are as follows: The soil salinization in the asparagus planting area of Chongming Island has begun to appear slightly, and the average concentration of Cr in asparagus is higher than the national standard limit. The spatial variability coefficient of Hg in the soil of the asparagus base is the highest, which may be due to human activities causing a large variation coefficient and significantly affecting the distribution of soil heavy metals. Children ingest more heavy metals through dietary pathways than adults, and their health risks are higher. The carcinogenic risk values of heavy metals Cd and Cr exceed the safety line, indicating a certain health risk.