Geochemical Characteristics and Influencing Factors of Selenium in the Xichang Area, Southwest China

Taking the Xichang area of China as an example, this study investigated factors affecting the geochemical characteristics of Se element by analyzing and comparing the environmental geochemical characteristics and temporal and spatial changes of Se in different rock formations, soil types, parent material layers, and soil layers. Analytical and statistical tests revealed that the content of Se in the soil of the study area ranged from 0.01 to 0.57 mg·kg-1, with an average value of 0.12 mg·kg-1, corresponding to a relatively low content. The orders of Se content in different materials are as follows: soil layer > soil parent material layer > rock layer in terms of the profile; Triassic continental clastic > Neogene-Quaternary continental clastic > Mesozoic intermediate-acid > Proterozoic intermediate-acid > Jurassic-Cretaceous continental clastic > Permian basic-ultrabasic = Sinian marine carbonate = Proterozoic volcanic clastic in terms of rock formations (parent rocks); and brown soil > yellow brown soil > dark brown soil > black felt soil > red soil > purple soil. The spatial distribution of Se exhibits distinct zoning and a good spatial coupling relationship with geological formations, rivers, topography, and geomorphology. The selenium content is mainly controlled by geological factors such as parent rock and parent material under different geological tectonic units, followed by clay minerals, organic matter such as Corg, S, N and element adsorption and fixation.