From risk to response: Causal effects of soil heavy metal ecological risk on microbial community assembly in mining...

Accurate ecological risk assessment is essential for pollution prevention and risk control of heavy metals (HMs) in mining areas. Herein, a hierarchical ecological risk assessment framework integrating source apportionment, risk characterization, and bacterial community analysis was proposed, and causal pathways between HM risk and bacterial diversity was established using Mantel analysis and structural equation modeling. Source apportionment revealed As, Cd, Cu, Pb and Zn in industrial land and nearby agricultural soils were primarily influenced by mining activities, whereas those in distant agricultural soils were governed by agricultural and mining activities. Unlike traditional indices, site-specific risk quotient provided more realistic ecological risks. The potentially affected fractions (PAFs) for As, Cd, Cu, Pb, and Zn were 25.44%, 2.42%, 39.76%, 13.42%, and 18.06%, respectively, while multi-substance PAF (msPAF) for HMs ranged from 27.34% to 98.98%. The distributions of both PAF and msPAF decreased outward from mining area, exhibiting a concentric circular pattern. Chloroflexota was the most dominant phylum, followed by Pseudomonadota, Bacillota, Actinomycetota, and Acidobacteriota. Causal inference revealed that indirect soil degradation contributed more to alterations in bacterial α-diversity compared with direct effects of msPAF-based risks. Collectively, these findings provide an effective hierarchical risk assessment methodology applicable to similar mining areas.