Efficiency of a new allylagarose-assembled DGT in measuring Cd, Zn, and Pb bioavailability in sludge-treated soil

Abstract

The purpose of this study was to assess and validate measures of cadmium (Cd), lead (Pb), and zinc (Zn) bioavailability in a contaminated calcareous soil treated with sewage sludge (0, 10, and 30 g kg −1 ) under peppermint ( Mentha pipertia L.) cultivation using new allylagarose-assembled diffusive gradients in thin-films technique (DGT). To achieve the best gel composition, various diffusive hydrogels were made from different amounts of acrylamide monomer (15, 20, and 25%) and allylagarose cross-linker (0.3, 0.4, and 0.6%). The DGT assembled with 15% acrylamide and 0.3% allylagarose was the best hydrogel based on the obtained swelling rate (3.2) and diffusion coefficients of Cd (5.81 ×10 cm 2 s −1 ), Pb (8.07 cm 2 s −1 ), and Zn (6.13 cm 2 s −1 ). Sewage sludge application increased resupply (R-value) and effective concentration (C E ) of Cd, Pb, and Zn. The highest amounts of C E -Zn (2202 μ g l −1 ), Cd (982.5 μ g l −1 ), and Pb (1847 μ g l −1 ) were observed in soil treated with 30 g kg −1 sewage sludge. Comparison of correlation revealed that 0.3% allylagarose-measured C E -Zn and Pb had a significant logarithmic correlation with the corresponding plant metals concentrations, while C E -Cd was linearly correlated with the plant Cd concentration. These results support the conclusion that the combination of 15% acrylamide and 0.3% allylagarose as a diffusive gel in DGT is a robust gel to predict metal bioavailability and can be reliably used to replace the patented gel cross-linked with agarose. • Increasing percentages of cross-linker led to a reduction in gel pore size. • The high swelling hydrogel facilitated the metals diffusion through the hydrogel. • Increasing sewage sludge level resulted in increasing the re-supply (R) of metals. • 15% acrylamide and 0.3% allylagarose gave the best estimate of bioavailability.