Remediation of antimony-arsenic co-contaminated soils in mining areas: Synergistic interaction of amendments and plants affects soil Sb and As bioavailability, nutrient and enzyme activity

Antimony (Sb) and arsenic (As) released from Sb mining activities accumulate in the soil, resulting in complex co-contamination that threatens agricultural ecosystems, food safety and human health. However, most of the existing studies are based on indoor pot experiments, exploring the remediation of contaminated soil by using a single remediation technology or amendment. Currently, there is a lack of research on the combined application of amendments and phytoremediation technology to the actual Sb-As co-contaminated soil, as well as determining the driving factors affecting the remediation effect. In the present study, a field experiment was conducted in combination with Structural Equation Modelling (SEM) and Random Forest (RF) algorithm to investigate the synergistic effects of four amendments—lime (CA), polyferric sulfate (PFS), biochar (BC), and potassium humate (HA)—along with two plant species, bermudagrass ( Cynodon dactylon L. ) and plantain ( Plantago asiatica L.), on the remediation of Sb- and As-co-contaminated soil. Furthermore, the key influencing factors and potential mechanisms underlying the remediation effectiveness were analysis. The results demonstrated that the combined application of amendments and plants increased soil nutrient content, including organic matter (OM), total nitrogen (TN), total phosphorus (TP), total potassium (TK) and alkaline nitrogen (AN), while also enhancing soil enzyme activity. Additionally, the combined use of amendments and plants reduced the bioavailable fractions of Sb and As – water-soluble fraction (F1) and surface adsorption fraction (F2) – by 27.17 % and 20.95 %, respectively, while increasing the residual fraction (F5) by 42.45 % and 70.49 %, thereby enhancing Sb and As stabilisation. The integration of SEM and RF models indicated that soil pH, OM, available phosphorus (AP), F1 and F2 are key factors influencing the remediation effectiveness of Sb- and As-co-contaminated soils. As the most active fractions of soil Sb and As, the proportions of F1 and F2 are directly determined to influence the remediation effectiveness. In environments with low pH, high OM, and high AP, Sb and As in the soil are more likely to be immobilized and stabilized, resulting in lower bioavailability. A comprehensive analysis of soil nutrient improvements, enzyme activity and reductions in Sb and As bioavailability revealed that 1 % HA combined with bermudagrass has strong potential for remediating Sb- and As-co-contaminated soils. These findings provide feasible strategies for the ecological restoration of Sb- and As-co-contaminated soil in mining areas and have significant application value in ensuring the safety of agricultural ecosystems. Future research should focus on the evaluation of long-term remediation effects and further explore the remediation mechanisms and influencing factors. • Amendments application improved nutrient and enzyme activities in mining soils. • Amendments and phytoremediation reduced the bioavailability of Sb and As in the soil by 27.17 % and 20.95 %. • pH, organic matter, bioavailability, water-soluble forms, and surface adsorption states are key influencing factors. • 1 % Potassium humate combined with bermudagrass shows significant potential for ecological restoration in mining areas.