Spatial distribution of surface soil selenium and its influencing factors in China: A literature-based analysis

A national assessment of the distribution of surface soil selenium (Se) and its key influencing factors across 1047 locations in China, was conducted based on 448 studies published in the past 40 years (1980-2024). The distribution of Se varied widely across the country, with concentrations ranging from 0.007 to 25.42 mg/kg. The Se richness threshold was exceeded at 39.92 % of all sampling sites, and the Se toxicity screening level was surpassed at 2.48 % of sites. Based on precipitation patterns, we classified the sampling locations into three regions, with mean soil Se content decreasing as follows: humid southeastern region (0.7294 mg/kg) > arid northwestern region (0.2785 mg/kg) > semi-humid central region (0.2745 mg/kg). The key factors influencing Se distribution varied across these three regions. Se-rich parent materials and the southeastern monsoon were identified as important factors in the humid eastern region. In the semi-humid central region, the lack of Se-rich parent material and the monsoon climate limited the distribution of Se-rich soils, and steep terrain further exacerbated Se deficiency. In contrast, low soil organic matter content and temperature in the arid northwestern region contributed to the formation of Se-deficient soils. However, Se-rich soils were found in small areas of the latter region, likely due to the influence of the northwestern monsoon and Se-rich parent materials. Our findings reveal the spatial distribution and key influencing factors of Se in topsoil across China, and provide a scientific basis for the formulation and revision of regional environmental health benchmarks and the development of Se-enriched agriculture.