Cadmium (Cd) and lead (Pb) are two typical heavy metals of the Jialing River, and their threat to the river has been considered by the government in recent years. In this study, the diffusive gradient in thin films (DGT) technique and sequential extraction were employed together to analyse the remobilization and fraction of Cd and Pb in the sediments. The total concentration of Cd and Pb in four sampling sites both followed the order S3>S4>S2>S1. The sequential extraction results indicated that large amounts of Cd and Pb (over 50% of the total concentration) were bound to the exchangeable and reducible fraction. The DGT results showed that both Cd and Pb presented a significant increasing trend at the bottom of the DGT probe (-10 cm to -12 cm) and that the two metals had a significant positive correlation (r = 0.831, p < 0.01). The apparent diffusive flux result indicated that Cd and Pb had a potential risk of release from surface sediments. A significant correlation was observed between the DGT-labile fraction and sequential extraction at the surface sediments. A further correlation analysis found that the concentration of labile Cd/Pb measured by DGT (CDGT-Cd and CDGT-Pb) had a strong negative correlation with CDGT-Fe, and this process was mainly mitigated by the iron oxides in the sediments. In addition, the correspondence of a "dark area" of AgI gel with corresponding "hotspots" of Chelex gel also proved that the release of Cd and Pb may regulate the dissolved sulfide in the sediments.
Keywords: Cadmium; DGT; Jialing river; Lead; Sediments.
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