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

Objective To find out the distribution characteristics and geological genesis of soil selenium in Chengde area, so as to provide scientific basis for the exploration and effective utilization of local soil selenium.Method The types of soil parent materials in this area were identified by geological survey. The contents of selenium and multiple elements in 553 soil samples and 66 rock/ore samples were obtained by X-ray fluorescence spectrometry, inductively coupled plasma emission spectrometry and Kjeldahl nitrogen. The data were analyzed by SPSS software and the geological genesis was analyzed combined with geological process.Results the soil parent materials in Chengde area are roughly divided into nine categories. The minimum value of selenium content in surface soil is 0.016 mg/kg, the maximum value is 0.743 mg/kg, and the average value is 0.17 mg/kg. The average soil selenium content is only 1/2 of the national average selenium content, which is in a lack level. The average selenium contents in iron ore, gold ore and lead-zinc ore were 0.860, 1.233 and 3.365 mg/kg, respectively, which were significantly higher than those in tailings and surrounding rocks of various ores.Conclusions The overall content of soil selenium in Chengde is very low, which is mainly determined by the parent material, and its distribution characteristics are controlled by geological formation. Selenium-rich soil areas are concentrated in the south of Longhua County (Area A), the south of Chengde City (Area B) (Shuangluan District, Shuangqiao District) and the eastern Kuancheng County (Area C). Area C belongs to the 'rock weathering type', which is related to the combination of primary carbonate rock and carbonaceous mudstone with high selenium content. Area B belongs to ' mineralization associated type ', which is related to the associated relationship between selenium and metal sulfide and the substitution relationship between selenium and sulfur in the process of lead-zinc mineralization. Area A belongs to the ' river sedimentary type ', which is related to the driving force of rivers and lakes and the adsorption of organic matter in the process of channel deposition. The selenium-rich region in southern Chengde has the natural advantage of developing forest and fruit economy. Weichang County is in a low selenium environment, which is one of the factors leading to the epidemic of Keshan disease and other local diseases.