Assessing ecological risk of heavy metals in sediment cores using in-situ monitoring and species sensitivity distribution.

Conventional methods of ecological risk assessment for heavy metals in sediments are limited by static characteristics, neglecting bioavailability and relying on simplistic indices, which struggle to effectively predict ecological risks. Therefore, integrating the diffusive gradients in thin films (DGT) with species sensitivity distribution (SSD), a multi-level ecological risk assessment method (MERA) was developed. Then it was employed to accurately quantify short-term and long-term ecological risks of heavy metals (As, Cr, Cu, Ni, and Pb) during dynamic release in sediment cores from the Three Gorges Reservoir. Results showed lower total concentrations and non-residual fractions of five heavy metals in the downstream region compared to the upstream and midstream regions, whereas DGT-labile As and Ni displayed the opposite characteristics. The DGT-induced fluxes model further demonstrated that sediments had a significantly higher dynamic resupply capacity for As than that of other metals. The ecological risk assessment of heavy metals was conducted using conventional methods, including the geo-accumulation index, potential ecological risk index (PERI), risk assessment code, and modified PERI. These results indicated that Cu and Ni were priority contaminants, and the ecological risk in the upstream region was a priority concern. However, the DGT-SSD-MERA revealed that divergent consequences through the risk quotient, joint probability curves, and probabilistic risk assessment. The ecological risks in the short-term from individual metals were assessed as negligible, while metal mixtures exhibited a limited probability (0.31 %) of ecological risks. From a long-term perspective, only As posed a potential ecological risk in the downstream region, with the probability of ecological risks from metal mixtures increasing to 2.26 %. Consequently, the DGT-SSD-MERA highlighted the priority concern regarding the ecological risk of As in the downstream region. The DGT-SSD-MERA provides an effective tool for the refined assessment of the ecological risks under dynamic heavy metal release in sediments.