Abstract:

Investigating the characteristics of Hg content in farmland soil-agricultural products and the associated health risks and formulating more realistic soil environmental benchmarks provides a scientific basis for regional farmland protection and pollution control. This study focused on the Ningxia section of the Yellow River Basin. A total of 859 paired soil-crop samples were synchronously collected, comprising 505 cornfield samples, 78 wheat field samples, 52 paddy field samples, 20 potato field samples, 28 orchard samples (including watermelon, apple, apricot, grape, and melon), 156 vegetable field samples (including rapeseed, pak choi, broccoli, celery, eggplant, pumpkin, leek, and pepper), and 20 other grain field samples (including buckwheat, sorghum, soybean, broomcorn millet, and oat). The Hg content in major farmland soils and agricultural products in Ningxia was determined, its potential health risks to humans were assessed, and soil environmental benchmark values were derived. The results indicated that soil Hg concentrations ranged from 2.00×10⁻³ to 4.01×10⁻¹ mg·kg⁻¹, with a mean value of 3.40×10⁻² mg·kg⁻¹, exceeding the background value of Ningxia soil. The Monitoring points with maximum Hg concentrations in corn, wheat, rice, potato, fruit, vegetables, and other grain fields all surpassed the background level, suggesting some accumulation of Hg in soils at specific sampling sites within the studied area, albeit without posing a regulatory risk. The geo-accumulation index (I_geo) revealed varying degrees of Hg pollution in the soil across all agricultural product types. The non-carcinogenic risk index for children (1.51×10⁻³) exposed to soil Hg in different agricultural production areas was higher than that for adults (2.40×10⁻⁴), but neither indicated a non-carcinogenic risk. The mean Hg content in agricultural products was 3.37×10⁻³ mg·kg⁻¹, exhibiting moderate to high variability, and was below the national food safety limit. However, Hg levels exceeded the national standard limit (GB 2762—2017) in four corn, one fruit, and six vegetable samples. Coupled with a certain degree of bioaccumulation, this warrants further attention. The health risk index associated with Hg intake via agricultural products was low, indicating no risk of foodborne diseases. The derived HC₅ (hazard concentration for 5% of species) values for soil Hg were 6.73×10⁻¹ mg·kg⁻¹ for corn fields, 1.82 mg·kg⁻¹ for wheat fields, 5.10×10⁻¹ mg·kg⁻¹ for potato fields, 1.16 mg·kg^-¹ for orchards, 1.25 mg·kg⁻¹ for vegetable fields, and 1.22 mg·kg⁻¹ for other grain fields. All these values are lower than the national risk screening value (3.40 mg·kg⁻¹, GB 15618—2018), indicating that the national standard threshold for Hg in soils supporting these crop is relatively high. In contrast, the critical value for paddy soil was 1.35 mg·kg⁻¹, which is higher than the national risk screening value (1.00 mg·kg⁻¹), suggesting that the national standard imposes a stricter threshold for Hg in rice-growing soils within the studied area. Future efforts should strengthen Hg monitoring in the studied area, particularly focusing on the impact of anthropogenic activities such as pesticide/fertilizer application and irrigation water use. Soil environmental benchmark values for Hg should be adjusted according to the type of agricultural products.

Key words: soil, crop, Hg concentration, concentration factor, distribution of species sensitivity

摘要：

探究农田土壤-农产品Hg含量特征及其健康风险，制定更符合实际的土壤环境基准，可为区域农田保护及污染防治提供科学依据。通过协同采集859对土壤-农产品样品，测定宁夏农田Hg含量，评价其对人体健康的潜在风险，并推导土壤环境基准值。 结果表明，宁夏农田土壤Hg含量分布在2.00×10⁻³－4.01×10⁻¹ mg·kg⁻¹，平均值为3.40×10⁻² mg·kg⁻¹，玉米、小麦、水稻、马铃薯、水果、蔬菜和其他谷物地最大含量均有超过宁夏土壤背景值的点位，说明部分样点土壤Hg具有累积性。所有农产品类型土壤中Hg均有不同程度的污染，但对儿童和成人均无非致癌风险。农产品中Hg平均含量3.37×10⁻³ mg·kg⁻¹，处于中等及以上变异程度，低于国家限量值。从摄入农产品途径来看，Hg含量对人体的健康风险指数较低，无食源性危害风险。推导出玉米、小麦、马铃薯、水果、蔬菜和其他谷物地土壤Hg的HC₅值分别为6.73×10⁻¹、1.82、5.10×10⁻¹、1.16、1.25、1.22 mg·kg⁻¹，均小于国家标准（GB 15618—2018）中的风险筛选值（3.40 mg·kg⁻¹），说明标准对以上农产品类型土壤Hg的阈值要求宽松；而水稻地土壤临界值为1.35 mg·kg⁻¹，相比标准的风险筛选值（1.00 mg·kg⁻¹）大，说明国家标准较为严格。今后应加强研究区Hg含量的监测，并根据不同农产品对土壤Hg环境基准值进行修订。

关键词: 土壤, 农产品, 汞含量, 富集系数, 物种敏感性分布