Vertical distributions of toxic elements in agricultural soils around coal mining areas as influenced by soil...

Coal mining has led to widespread accumulation of potentially toxic elements (PTEs) in surrounding agricultural soils, posing serious threats to ecosystems. While numerous studies have documented metal contamination in mining-impacted regions, the vertical distribution patterns of PTEs in soil profiles and their associated biological characteristics remain poorly understood. In this study, vertical soil profiles (0-100 cm) were collected from agricultural fields surrounding coal mining areas in China to investigate the depth-dependent distributions of six PTEs (Zn, Pb, Cd, Cr, As, and Hg) and their associations with soil physicochemical properties and microbial community features. Results showed that the concentrations of Pb and Hg exceeded background levels across all soil layers, whereas Zn, Cd, Cr, and As showed layer-specific exceedances of up to 67%. Most elements (Zn, Pb, Cd, Hg, and As) exhibited decreasing concentrations with depth, while Cr was significantly enriched in the subsoil. Moreover, microbial community composition changed significantly along soil depth, and random forest analyses indicated that several bacterial taxa (e.g., Steroidobacteraceae, Hyphomicrobiales_unclassified and Methylophilaceae) were identified as microbial predictors statistically associated with PTE distribution patterns. In addition, soil organic carbon (SOC), total nitrogen (TN) and microbial composition (PC1) were dominant predictors of Zn, Cd and Hg accumulation (explaining 25-42% of their variance), while soil texture and cation exchange capacity primarily governed Pb, Cr and As. These findings demonstrate that integrating potential bioindicators with physicochemical parameters provides a biologically informed framework for interpreting vertical contamination patterns in mining-impacted agricultural soils.