A novel tiered ecological risk framework linking metal-driven pollution to soil microbial dynamics in a fragile ecosystem.

Widespread soil heavy metal (HM) pollution has caused great concerns worldwide. A refined and cost-effective ecological risk assessment (ERA) is critical for managing these risks. Herein, we propose a novel tiered ERA framework to evaluate indigenous pollution-effect associations in contaminated soils. This framework progressively applies source apportionment, spatial regression, deterministic and probabilistic risk characterization, ecological surveys of soil phospholipid fatty acids (PLFAs), and successive multivariable statistics to provide comprehensive ERA evidence, as demonstrated in an ecologically fragile mining area. The risk screening phase identified Zn, Pb, Cd, Cu, and Hg as priority contaminants, and mining activities contributed 86.5 % (Zn), 87.2 % (Pb), 83.3 % (Cd), 64.6 % (Cu), and 52.3 % (Hg) of the total soil concentrations in the study area determined by the positive matrix factorization (PMF) model. The risk quotient of ecological criteria tailored to different land uses exhibited ecologically relevant risk grading. The risk quantification phase determined the overall risk probabilities to be 53.98 %, 11.12 %, 9.69 %, 5.03 % and 1.34 % for Zn, Pb, Cu, Cd and Hg, respectively, and provided adaptive HM priority lists with different risk grades. The risk causeeffect attribution phase confirmed that HMs significantly reduced soil fungal PLFA abundance and indirectly altered the PLFA structure by decreasing the soil pH. The proposed framework offers a cost-effective, refined and feasible technical support for ecological risk management in contaminated areas.