For the removal of Cd(II) and As(III) from water, this study synthesized a nano-zero-valent iron-loaded biochar-zeolite composite material (nZVI-BCZo) using a liquid-phase reduction method, with biochar, zeolite, and FeSO₄·7H₂O as precursors. The successful incorporation of nZVI onto the BCZo was verified through Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and Fourier Transform Infrared Spectroscopy (FTIR) analyses, which revealed significant modifications in the surface oxygen-containing functional groups. Batch adsorption experiments were conducted to evaluate the adsorption characteristics and performance of nZVI-BCZo for Cd(II) and As(III). Under optimal conditions (pH 6.0, temperature of 310 K, and an adsorption time of 360 min), the maximum adsorption capacities for Cd(II) and As(III) were found to be 28.09 mg/g and 186.99 mg/g, respectively. The influence of pH on removal efficiency was more pronounced than that of temperature, with nZVI-BCZo exhibiting a higher affinity for As(III) compared to Cd(II). Kinetic analysis showed that the adsorption process is primarily controlled by chemical adsorption and follows a monolayer adsorption mechanism. Regeneration tests demonstrated that nZVI-BCZo retained good adsorption capacity after three cycles, with adsorption efficiencies of 67.78 % for Cd(II) and 53.04 % for As(III), indicating its potential for repeated use in water treatment applications. The economic evaluation revealed that nZVI-BCZo has a lower processing cost. Therefore, this study established nZVI-BCZo as an efficient, reusable, and cost-effective adsorbent for the treatment of heavy metal-laden water.

Dissolved organic matter (DOM) is a key determinant of heavy metal fate in aquatic environments, influencing their mobility, toxicity, and bioavailability. Derived from natural sources such as soil and vegetation decomposition, natural DOM (N-DOM) typically features humic-like substances with abundant oxygen-containing functional groups that stabilize heavy metals through complexation. However, microplastic-derived DOM (MP-DOM), increasingly prevalent due to plastic degradation, may interact differently with heavy metals, potentially exacerbating environmental risks amid rising plastic pollution. Yet, how heavy metals drive molecular transformations in MP-DOM versus N-DOM remains unclear, hindering accurate pollution assessments. Here, we compare interactions between N-DOM and MP-DOM with cadmium, chromium (Cr), copper, and lead from both fluorescence and molecular perspectives. Our results show that N-DOM, dominated by humic-like substances (46.0-57.3 %), lignin-like (55.0-64.9 %), and tannin-like (10.1-17.6 %) compounds, forms more stable heavy metal complexes via carboxyl, phenolic hydroxyl, and ether groups than MP-DOM. By contrast, MP-DOM-enriched in protein/phenolic-like substances (13.8-24.0 %), condensed aromatic (12.1-28.5 %), and protein/aliphatic-like (8.6-12.4 %) compounds-yields less stable complexes and is highly susceptible to Cr-induced oxidation. Mass-difference network analysis and density functional theory calculations further reveal that both DOM types undergo heavy-metal-triggered decarboxylation and dealkylation, but N-DOM retains complex structures, whereas MP-DOM degrades into smaller, hazardous molecules such as phenol and benzene. This study underscores the potential for heavy metals to exacerbate the ecological risks associated with the transformation of MP-DOM, providing crucial insights to inform global risk assessment and management strategies in contaminated waters where plastic and metal pollution co-occur.

Cadmium contamination inevitably affects the microbially mediated transformation of nitrogen in soils with wheat straw return. The responses of nitrogen functional microorganisms to cadmium in acidic and alkaline soils under wheat straw returned are still unclear. In this study, quantitative polymerase chain reaction (qPCR) and sequencing of nitrifying and denitrifying bacteria were performed to investigate the effects of wheat straw application on nitrogen conversion in different Cd-contaminated soils during an incubation experiment. Results showed that the presence of Cd decreased the abundance of hao gene catalyzing nitrification and norB gene catalyzing denitrification process, resulting the accumulation of NH₄⁺-N and reduction of NO₃^--N in the acidic soils. Additionally, Cd-contamination stimulates the nitrification catalyzed by bacterial amoA gene and thus reduced the NH₄⁺-N content in the alkaline soils. Meanwhile, Cd dominated the decrease of NO₃^--N content by promoting denitrification process catalyzed by nirS gene. Among all nitrifying and denitrifying microorganisms, Nitrosospira are tolerant to Cd stress under alkaline condition but sensitive to acidic condition, which dominantly harbored hao gene in the acidic soils and bacterial amoA gene in the alkaline soils. This study aimed to provide reasonable information for the rational adoption of wheat straw returning strategies to realize nitrogen regulation in Cd-contaminated farmland soil.