安顺市耕地土壤重金属元素地球化学特征及富硒资源评价

Geochemical characteristics of heavy metal elements in cultivated soil and evaluation of selenium-rich resources in Anshun City

关键词:  硒元素  富硒资源  农产品安全  地球化学

Key words:  selenium element  selenium-rich resources  agricultural product safety  geochemistry

摘要:

为研究耕地土壤中硒（Se）元素地球化学特征及清洁富硒耕地与农产品资源的空间分布关系，在贵州省安顺市内采集了表层土壤样品28003件（基本样27448件+重复样555件），农产品及根系土壤样品各475件，采用X射线荧光光谱法（XRF）、电感耦合等离子体质谱法（ICP-MS）等多种分析方法，测定了土壤及农产品中的硒及重金属元素含量，并基于SPSS、ArcGIS、MapGIS等软件绘制了统计分析、地球化学图、空间分布图。结果显示：安顺市表层土壤硒元素平均含量为0.51 mg/kg，高于富硒土壤标准 （0.4 mg/kg），含量与成土母岩类型密切相关，玄武岩及辉绿岩成土母岩背景下的土壤硒含量最高；全市富硒耕地面积达2275.33 km² ，占耕地面积的76.53%，且重金属元素含量超标率低，清洁富硒耕地主要集中分布在平坝区 − 西秀区 − 镇宁县北部一线，呈带状展布，面积较广。整体来看，普定县、西秀区、平坝区采样农产品富硒率达39.08%；其余地区富硒率达20.25%，且受土壤中重金属元素影响，局部区域存在农产品铅（Pb）、镉（Cd）、汞（Hg）元素超标。对此，建议加强对特色农产品研究，更大规模发展富硒产业；同时，局部重金属超标区域，应调整农业种植结构，以种植非食用的经济作物或者观赏类作物为主，或者采取相应的技术修复土壤。该研究可为安顺市富硒资源的合理开发和利用提供科学依据，对推动地方特色富硒农业高质量发展具有重要指导意义。

Abstract:

Background, aim, and scope As a key development city in western China, Anshun City boasts prominent potential in selenium (Se)-rich resource endowment. However, existing research remains insufficient regarding the distribution characteristics and concentration levels of selenium in regional agricultural soils, as well as its correlations with natural controlling factors including geological background, climatic conditions, and soil types. To a certain extent, this research gap has restricted the scientific planning, rational development, and efficient utilization of local selenium-rich resources. In view of this, this study implemented detailed geochemical surveys and large-scale field sampling, combined with advanced analytical testing techniques and modern information technology, to systematically reveal the selenium concentration, spatial distribution patterns, and key influencing factors of selenium in agricultural soils across Anshun City. Furthermore, this study aimed to evaluate the resource status of clean selenium-rich farmland and selenium-rich agricultural products, with the core objective of providing robust theoretical support and practical guidance for the sustainable utilization of selenium-rich resources in the region, as well as promoting the sound development of selenium-enriched agriculture in western China. Materials and Methods Extensive field sampling was conducted to collect surface soil samples 28003 and corresponding agricultural product samples across the study area. Selenium and heavy metal concentrations in both soil 475 and agricultural 475 product samples were determined using advanced analytical techniques, including X-ray Fluorescence Spectrometry (XRF) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Subsequent data processing and spatial analysis were performed using professional geostatistical and geographic information software, namely SPSS, ArcGIS, and MapGIS, to conduct statistical analysis, geochemical mapping, and spatial distribution visualization of selenium and heavy metals. Results The average selenium content in the surface soil of Anshun City is 0.51 mg/kg, which is higher than the selenium-rich soil standard (0.4 mg/kg). The selenium content is closely related to the types of soil-forming parent rocks, with the highest selenium content found in soils derived from basalt and diabase. The cultivated land with selenium-rich soil in the city totals 2275.33 km² , accounting for 76.53% of the total cultivated land area. The selenium-rich cultivated land is mainly concentrated in a strip along the northern line of Pingba District, Xixiu District, and Zhenning County, with a relatively low rate of heavy metal content exceeding standards. Overall, the seleniumrich rate of agricultural products sampled in Puding County, Xixiu District, and Pingba District is 39.08%, while in other regions, it is 20.25%. The selenium-rich rate of agricultural products from selenium-rich cultivated land is generally moderate, and due to the influence of heavy metal elements in the soil, there are localized areas where the heavy metal content in agricultural products exceeds standards. Discussion (1) The selenium content in the cultivated soil of Anshun City is abundant but unevenly distributed. Selenium is ubiquitous in the surface soil, with an average content higher than the selenium-rich soil standard. The selenium-rich cultivated land resources are vast, and the spatial distribution of selenium is mainly influenced by soil-forming parent rocks, especially those derived from basalt, diabase, and black shale (coal-bearing strata), which have the highest selenium content, reaching 0.78 mg/kg and 0.72 mg/kg, respectively. (2) The overall heavy metal content in the cultivated soil of Anshun City is relatively low, but there are localized areas where arsenic and cadmium content exceed standards. In particular, cadmium content is mainly affected by the weathering of soil-forming parent rocks. Due to its immobility, cadmium accumulates in place during the weathering process, potentially leading to increasing cadmium content in weathering products over time. Therefore, heavy metal pollution prevention should be considered in future cultivated land utilization and planning to avoid risks to agricultural product safety and human health in areas exceeding standards. (3) Anshun City is rich in selenium-rich cultivated land resources, accounting for 76.53% of the total cultivated land area. The clean selenium-rich areas are mainly distributed along the northern line of Pingba District, Xixiu District, and Zhenning County. The selenium-rich rate of agricultural products varies depending on crop types and selenium content distribution in the soil. In the development of selenium-rich agricultural products, it is urgent to strengthen regional planning and prioritize the development of planting in areas with high selenium content. Conclusions Surface soils in Anshun City are characterized by favorable selenium enrichment, with a large proportion of selenium-rich farmland concentrated in contiguous high-quality zones, laying a solid foundation for the large-scale development of local selenium-rich agriculture. Although the overall soil heavy metal concentration is low, localized exceedance phenomena require close attention and effective prevention during resource development. Findings regarding the selenium enrichment rate of agricultural products provide a scientific basis for optimized regional planting layout. Recommendations and Perspectives In the future, Anshun City should further strengthen the protection and rational development of selenium-rich resources, formulate scientific selenium-rich industry development plans, and promote the large-scale, standardized, and branded development of selenium-rich agricultural industries. Meanwhile, research on the formation mechanism, enrichment patterns, and development and utilization technologies of selenium-rich resources should be intensified to provide scientific and technological support for the sustainable development of selenium-rich industries. In addition, for localized areas severely affected by arsenic and cadmium and where the heavy metal content in agricultural products exceeds standards, the agricultural planting structure should be adjusted to prioritize the cultivation of non-edible economic or ornamental crops. Alternatively, corresponding soil remediation technologies should be adopted to promote the sustainable and high-quality development of local characteristic agricultural industries.