Comparison between diffusive gradients in thin film technology (DGT) and traditional methods for prediction of plant available heavy metals in agricultural soil

Purpose: The objectives of this study were to (1) analyze heavy metals (Cr, As, Cu, Zn, Cd, and Pb) in the rhizosphere soil and roots, leaves, stems, and grains of maize and wheat crops using different methods; (2) evaluate the advantages of diffusive gradients in thin films technology (DGT) for predicting the bioavailability of heavy metals; and (3) compare the characteristics of DGT with other methods. Materials and Methods: In this study, we collected maize and wheat samples and their rhizosphere soil over a pollution gradient in Kaifeng City, China. Six heavy metal (Cr, As, Cu, Zn, Cd, and Pb) levels in rhizosphere soil were determined using DGT, EDTA, soil solution, and total amount methods, respectively. The heavy metal content in the roots, leaves, stems, and grains of maize and wheat was also analyzed. The relationships between six heavy metal soils concentrations detected by different methods, and their contents in the different parts of wheat and maize, were analyzed using statistical methods. The characteristics and application scope of the different methods were evaluated. Results and Discussion: The accumulation of heavy metals in maize and wheat was generally higher in the roots than in the above-ground parts (i.e., stems, leaves, and grains). For the soil solution method, only soil As levels showed a significantly positive correlation with its content in different parts of wheat and corn. For the EDTA method and the soil total amount method, only As, Zn, and Pb levels were significantly correlated with their contents in different parts of wheat and corn. Six heavy metal concentrations detected by DGT were all significantly positively correlated with their contents in the different parts of wheat and maize. Furthermore, DGT was less affected by the soil pH than EDTA. Conclusions: DGT was more accurate in simultaneously predicting plant-available Cr, As, Cu, Zn, Cd, and Pb. However, other methods, like EDTA, soil solution, and total amount methods, can also be considered when predicting the bioavailability of a single heavy metal (e.g., As or Zn) in rhizosphere soil.

Automated summary

This study aimed to analyze heavy metals in maize and wheat crops using different methods, evaluate the advantages of DGT in predicting heavy metal bioavailability, and compare it with other methods. Results showed that DGT was more accurate in predicting plant-available heavy metals and less affected by soil pH.