Influence of sediment organic matter origin on the effectiveness of in-situ activated carbon amendment for heavy metal stabilization.

In-situ activated carbon (AC) amendment can be used to chemically stabilize both hydrophobic organic compounds and heavy metals (HMs) in co-contaminated sediment. Although previous findings have highlighted the influence of sediment organic matter (SeOM) on the adsorption of HMs by AC, the specific role of SeOM in HM stabilization remains unclear. In the present study, we investigated how the characteristics of SeOM extracted from field-collected sediment samples taken from two sites affected the adsorption behavior of Zn, Cd, and Pb in AC-amended systems. The two sediments contained SeOM with contrasting origins: one rich in allochthonous humic substances and the other dominated by autochthonous proteinaceous matter. It was found that the reduction in aqueous HM concentrations was up to 2.5 times higher in the AC-SeOM-HM systems than in the AC-HM systems. Independent experiments were then used to characterize both SeOM adsorption onto AC and the binding of HMs to SeOM, revealing that a considerable proportion of the HMs that adsorbed onto the AC in the AC-SeOM-HM systems were present in a SeOM-associated form. This trend was more noticeable in the presence of allochthonous SeOM due to its greater affinity for both AC and HMs. Slurry-phase experiments confirmed these results, finding that the HM stabilization efficiency was 1.4-2.1 times higher in raw sediment samples than in sediment samples from which the SeOM had been removed, with allochthonous SeOM contributing more strongly to HM stabilization. Overall, this study experimentally demonstrates that the presence and origin of SeOM can influence the effectiveness of in-situ AC amendment. These findings highlight the importance of considering the characteristics and source of SeOM when employing in-situ AC amendment for HM stabilization.