## 2 Materials and Methods
### Analysis Method of Soil and Plant Samples  
(1) Bioavailable Heavy Metal Content Analysis in Soil:  
This study used NaHCO\({}_{3}\) as an extractant to extract arsenic from soil, and calculated the bioavailability of arsenic through ICP-MS (NEXION 2000, PerkinElmer, Waltham, MA, USA) analysis [38]. A 10 g of the sample, sieved through a 2 mm screen, were taken in a 250 mL conical flask. Then, 150 mL of 0.5 mol/L NaHCO\({}_{3}\) solution was added. The mixture was shaken at the magnetic stirrer (Cimarec+, Thermo Scientific, Waltham, MA, USA) with 25 \({}^{\circ}\)C and 200 r/min for 2 h and filtered through a 0.45 \(\upmu\)m microporous membrane (MF-Millipore(tm) Filter membrane, pore size 0.45 \(\upmu\)m) for subsequent ICP-MS (Nexlon 300\(\times\), Perkin Elmer, USA) analysis. We repeated each test three times and took the average.  
Bioavailable Cd and Pb were extracted using a diethylene-triamine-penta-acetic acid (DTPA) solution (0.005 mol/L DTPA(AR, Shanghai Macklin Biochemical Technology Co., Ltd.), 0.01 mol/L CaCl\({}_{2}\) (AR, Shanghai Macklin Biochemical Technology Co., Ltd.), and 0.1 mol/L triethylamine (TEA, AR, Shanghai Macklin Biochemical Technology Co., Ltd.)) at a soil-to-water ratio of 1:5 (_w/v_), and the results were obtained via ICP analysis [39; 40]. We repeated each test three times and took the average. The reduction rate (\(\upeta\)) of the bioavailable heavy metal [41; 42] in the soil after material remediation was calculated using the following formula:  
\[\eta\ (\%)=\frac{\upeta_{\text{Before}}-\upeta_{\text{After}}}{\upeta_{ \text{Before}}}\times 100 \tag{2}\]  
where \(\upeta_{\text{Before}}\) measures the bioavailable heavy metal concentrations in the soil before combined remediation, and \(\upeta_{\text{After}}\) measures them after combined remediation.  
(2) Heavy Metal Speciation Distribution Analysis in Soil:  
Arsenic speciation was determined using the Tessier method, and cadmium speciation was analyzed using the BCR sequential extraction method [43]. Repeated each test three times and taken the average.  
(3) Total Heavy Metal Content Analysis in Plants:  
The test samples (0.04 g of the plant under investigation) were digested in a polytetrafluoroethylene (PTFE) crucible [44]. The sample was treated with a mixture of HCl and HNO\({}_{3}\) (AR, Shanghai Macklin Biochemical Technology Co., Ltd.) in a 3:1 volume ratio, heated until the volume reduced to approximately 3 mL, and then allowed to digest at low temperatures until clear. The solution was transferred into a pre-labeled container, and the crucible was washed with 1% nitric acid. The filtrate was obtained by filtering the wash solution through a filter membrane (0.22 \(\upmu\)m) and was then used for ICP-MS analysis. We repeated each test three times and took the average.  
(4) Plant Extraction Indices:  
The bioconcentration factor (BCF) and translocation factor (TF) [45] indicated the vegetal potential to absorb and distribute metals.  
BCF was the comparative level of heavy metal concentrations in plant tissue (\(C_{Plant}\)) versus soil (\(C_{Soil}\)) [46]. The formula for calculating BCF is as follows:  
\[\text{BCF}=\frac{C_{Plant}}{C_{Soil}} \tag{3}\]  
TF measured the comparison of metal concentrations from the shoot (\(C_{Plant\ shoot}\)) versus the roots (\(C_{Plant\ root}\)) [47]. The formula for calculating TF is as follows:  
\[\text{TF}=\frac{C_{Plant\ shoot}}{C_{Plant\ root}} \tag{4}\]Statistical analysis  
The data were subjected to one-way ANOVA using SPSS 29.0.2 software. At least three independent replicates of each sample and determination were tested, and mean values and respective standard deviations were calculated.