Multifractal-based soil elemental standards extrapolation and pollution risk assessment in Qinghai-Tibetan...

As an essential ecological barrier in China, the soil environmental health of the Tibetan Plateau is crucial for ecological balance and sustainable development. However, the risk of soil elemental contamination in the region shows spatial heterogeneity due to geological and anthropogenic influences. Existing studies focusing on a single land use type have failed to provide risk screening values for elements lacking evaluation criteria in soils in agro-pastoral combination areas (e.g., Sb, Sr, and nutrients such as B, P, S, and N), resulting in an insufficient assessment of relevance. This study targets the Qingshizui area in Menyuan County, a typical agro-pastoral region on the Qinghai-Tibet Plateau, to address these gaps. Using multifractal analysis, we systematically characterized the distribution of 20 elements, including heavy metals (e.g., As, Cd, Pb, Sb, Cr) and nutrients, and established risk screening values for all elements being studied, notably those without national standards, for the first time. The rationality of the model was validated by comparing it with existing standards, confirming that the method can provide a scientific reference for elements without evaluation standards. The results showed that elements such as As, Ni, and Mn were significantly affected by human activities, and the high S (D₂ = 2.20) content was concentrated and slowly transformed, with a serious pollution trend. This study fills a critical gap in soil risk assessment for high-altitude agro-pastoral ecosystems, providing a scientific basis for precision ecological agriculture and sustainable soil management.