Regional geochemical background values and upper geochemical thresholds in surface soils of Golmud, Qinghai: a...

Regional geochemical background values are needed to interpret soil screening values in geologically enriched areas. This study aimed to derive regional background values and upper geochemical thresholds for 15 soil elements in the alpine and geologically heterogeneous Golmud area on the northern Tibetan Plateau. We analysed 3319 surface-soil samples using a multifractal accumulated concentration-area frequency approach and compared the resulting thresholds for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn with the agricultural-soil screening values specified in GB 15618-2018. The upper geochemical thresholds for Pb, Zn, Cr, and Ni differed by less than 15% from the corresponding national values, whereas the threshold was higher for As and lower for Cu and Hg. Regional thresholds were also derived for Co, U, Th, Mn, V, B, and P, for which element-specific screening values are unavailable in the evaluated standard. Lower D₂ values (< 2), indicating slower spatial decay within the second fitted concentration segment, characterized Co, Ni, V, and Cu, whereas Cr showed a higher D₂ of 2.86. The multifractal results provide regional geochemical reference information for soil assessment, monitoring prioritization, and mineral-exploration screening. Because these thresholds are derived from concentration distributions and do not incorporate toxicity, exposure pathways, land use, or bioavailability, they should complement rather than replace regulatory soil screening values.