Stabilization remediation of atrazine and cadmium co-contaminated soil using zinc-modified biochar loaded Mg-Fe layered double hydroxide: Performance, plant responses and mechanism

The application of herbicides, along with human activities such as mining and metal smelting, results in the release of organic pollutants and heavy metals into the environment, thereby posing significant risks to both human health and ecosystems. There is a pressing demand for efficient technologies to remediate soil contaminated with organic pollutants and heavy metals. In this paper, a novel zinc-modified biochar supported Mg-Fe layered double hydroxide (ZnBC/MgFe-LDH) composite was fabricated and characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) techniques. Batch adsorption experiments revealed that the ZnBC/MgFe-LDH exhibited excellent adsorption performance, achieving maximum adsorption capacities of 268.45 mg/g for Cd(II) and 165.04 mg/g for atrazine. Indoor culture, column leaching, and pot experiments demonstrated significant immobilization of atrazine and cadmium in co-contaminated soil. After 28 days, leaching concentrations of atrazine and cadmium decreased by 89.7 % and 90.3 %, respectively. Dynamic leaching experiments showed cumulative losses reduced by 44.55 % for atrazine and 57.70 % for cadmium. Additionally, achieving a non-desorbable state of atrazine at 65.03 % and a stable state of cadmium at 49.34 % in the co-contaminated soil indicates a significant stabilization effect. Pot experiments revealed that using ZnBC/MgFe-LDH notably boosted the biomass of maize seedlings. Compared to the control group, the bioconcentration factor (BCF) and translocation factor (TF) of atrazine decreased by 63.52 % and 59.27 %, respectively, whereas the BCF and TF of cadmium decreased by 71.71 % and 32.48 %, respectively. The ZnBC/MgFe-LDH composite immobilizes cadmium in soil primarily through surface complexation, ion exchange, and co-precipitation mechanisms. However, pore filling, π-π interactions and hydrogen bonding are the main mechanisms by which the composite immobilizes atrazine in soil. These findings provide a potentially effective material for stabilizing soils contaminated with both organic pollutants and heavy metals.