Evaluating ecological risks and metal bioavailability in post-dredging sediments of a wetland affected by artisanal gold mining.

The evaluation of metal contamination, ecological risk, bioavailability, and the environmental dredging depth in sediments of two Colombian riverine systems impacted by artisanal and small-scale gold mining (ASGM) and agricultural activities, was conducted following dredging processes. Results indicated significant contamination by Cd and Pb before dredging, based on the contamination factor (CF) and the geoaccumulation index (Igeo). Additionally, Cu and Hg were found to cause adverse biological effects according to sediment quality guidelines. Post-dredging, surface sediments exhibited a moderate ecological risk index (RI, 150-300), primarily due to increased contamination by Hg, Pb, and Cd. To mitigate this ecological risk (RI < 150), the environmental dredging depth needed to exceed 20 cm for all metals. On average, the bioavailable fraction increased 2.3 times within two months after dredging. However, the low environmental risk (%F1 = 1-10) calculated using risk assessment codes (RAC) indicates a potential risk due to metals entering the water column and bioaccumulating in organisms. These findings provide insights into the dynamics of metals and the impact of dredging activities on sediments in the Colombian Caribbean coast affected by various anthropogenic activities. The research underscores the importance of integrating sustainable practices in mining and agriculture to protect the ecological integrity of these riverine systems.