Assessment of thin film gradient diffusion technique for precise analysis of soil cadmium passivation and uptake inhibition by different amendments

Abstract

The utilization of the thin film gradient diffusion technique has been on the rise for appraising the efficacy of soil cadmium (Cd). Nonetheless, in contrast to conventional methodologies employed to gauge the efficacy of soil Cd, there exists a dearth of adequate research concerning whether the technique of diffusive gradients in thin films (DGT) can furnish a more precise and all‐encompassing evaluation of soil Cd effectiveness in soil passivation and remediation procedures. Herein, this study selects four popular amendments (i.e., oyster shells, red mud, hydroxyapatite, and biochar) and analyzes the correlations among soil Cd availability, Cd uptake amount, and spinach biomass. Results showed that the following concentration ranges: DGT‐Cd (1.78 ‐ 21.1 μg L‐1), HAc‐Cd (1.84 ‐ 2.22 mg kg‐1), DTPA‐Cd (0.62 ‐ 1.22 mg kg‐1), and CaCl2‐Cd (0.0489 ‐ 0.103 mg kg‐1). Among the methods, CaCl2 extraction had a lower capacity to extract soil Cd compared to the other methods. These amendments improved soil environment, promoted spinach growth, and decreased plant Cd concentrations. Oyster shells and red mud treatments significantly reduced DGT‐Cd levels (by 90.4% and 82.2%, respectively), which led to a reduction in plant Cd concentrations (by 77.1% and 72.4%) and bioconcentration factor (by 75.8% and 68.8%). Furthermore, oyster shells were found to be most effective in reducing soil‐available Cd and inhibiting Cd uptake by spinach. Based on correlation analysis, the DGT method showed the largest measurement range and provided the best prediction of Cd accumulation in spinach compared to chemical extraction methods (R2=0.88, p<0.001). Overall, the use of DGT in combination with plant uptake and chemical extraction data can provide a comprehensive assessment of soil Cd bioavailability. These findings facilitate an accurate and comprehensive evaluation of the bioavailability of Cd after applying amendments. These results also showed that oyster shells can be regarded as a promising eco‐friendly and low‐cost amendment for large‐scale immobilizing Cd and producing plants with lesser Cd concentrations.