Migration and Enrichment Mechanisms of Selenium, Zinc, and Iodine in the Soil–Plant–Animal Continuum of Yushu, Qinghai– Tibet Plateau: Insights from Environmental Geochemical Factors

Selenium (Se), zinc (Zn), and iodine (I) are essential micronutrients for human health, yet their bioavailability is governed by environmental geochemical cycling. This study investigates the distribution, migration, and health risks of Se, Zn, and I in the soil–plant–animal continuum of the Yushu region on the Qinghai–Tibet Plateau. A total of 1,706 topsoil, 505 biological, and 100 water/sediment samples were collected and analyzed. Spatial interpolation, geographically weighted regression (GWR), bioconcentration/biomagnification factors, and scenario‑based dietary exposure models were employed. Results show that soil Se background (0.22 mg·kg⁻¹) is 21% lower than the national average, classifying Yushu as an inherently Se‑deficient area. Zn is moderately enriched (background: 83.7 mg·kg⁻¹), while I levels are comparable to national values. GWR modeling revealed that Fe/Al oxide adsorption–desorption processes are key factors controlling the spatial distribution of these elements, surpassing the influence of soil pH and organic matter. Food‑chain transfer efficiency diverges between grassland and farmland systems: forages strongly enrich Se and Zn, with further biomagnification in animal viscera, whereas crop systems exhibit extremely low Se transfer (BCF = 0.157). Dietary risk assessment indicates severe Se and I deficiency in farmers, while herders face I deficiency alongside potential Zn excess. Targeted interventions are proposed, including agronomic fortification in farmland, dietary guidance in pastoral areas, and sustained iodized‑salt supply. This study provides an integrated geochemical‑ecological‑health perspective for managing trace‑element nutrition in alpine regions.