Geochemical characteristics, geological genesis and ecological environment evaluation of soil selenium in Chengde, Hebei Province

This paper is the result of agricultural geological survey engineering.

Objective The study aims to delineate the distribution characteristics and geological origins of selenium in the soil of the Chengde area, providing a scientific foundation for the exploration and effective utilization of selenium in the region's soils.

Methods Geological surveys were conducted to identify the types of soil parent materials in the area. The content of selenium and multiple elements in 553 soil samples and 66 rock/ore samples were determined using X−ray fluorescence spectrometry, inductively coupled plasma emission spectrometry, and the Kjeldahl nitrogen method. Data analysis was performed using SPSS software, with geological genesis being interpreted in conjunction with geological processes.

Results The soil parent materials in the Chengde area are categorized into nine distinct groups. The selenium content in surface soils ranges from a minimum of 0.016 mg/kg to a maximum of 0.743 mg/kg, with an average value of 0.17 mg/kg. This average selenium content is half of the national average, indicating a state of deficiency. The average selenium content in iron ore, gold ore, and lead−zinc ore are 0.860 mg/kg, 1.233 mg/kg, and 3.365 mg/kg, respectively, significantly higher than those in the tailings and wall rocks associated with various ores.

Conclusions The overall selenium content in the soils of Chengde is very low, primarily determined by the soil parent materials, with distribution patterns influenced by geological formations. Selenium−rich soil areas are notably concentrated in the south of Longhua County (Area A), the southern parts of Chengde City (Area B) including Shuangluan and Shuangqiao districts, and the eastern part of Kuancheng County (Area C). Area C is characterized as “rock weathering type”, associated with the presence of selenium−enriched primary carbonate rocks and carbonaceous mudstones. Area B is classified as “mineralization associated type”, linked to the symbiotic relationship between selenium and metal sulfides during lead−zinc mineralization, as well as the substitution relationship between selenium and sulfur. Area A is defined as “river sedimentary type”, relating to the dynamics of river and lake sedimentation and the adsorption by organic matter. The selenium−rich region in southern Chengde possesses a natural advantage for developing a forest and fruit economy. Weichang County, situated in a low selenium environment, is identified as a contributing factor in the prevalence of Keshan disease and other endemic conditions.