Assessing Mercury Distribution and Potential Ecological Risk in a Wetland of the Atrato River (Colombia) and Laboratory Screening of Biochar-Based Removal

This study evaluated the distribution and potential ecological risk of mercury in sediments from the Recuerdo Marsh, located in the Atrato River basin (Chocó, Colombia), and explored the potential of sawdust biochar for mercury removal from water. Surface sediments, a sediment core, and water samples were collected and analyzed for total mercury (THg) using thermal decomposition atomic absorption spectrometry. Potential ecological risk was assessed through contamination factor (CF), geoaccumulation index (Igeo), and potential ecological risk index (PERI). In parallel, sawdust biochar was characterized using BET surface area analysis, SEM-EDS, XRD, and FTIR spectroscopy; and its Hg adsorption capacity was assessed. THg concentrations in surface sediments ranged from 50.3 to 367 µg kg−1, with an average of 129.9 ± 97.1 µg kg−1, while ecological risk indices revealed moderate to considerable potential ecological risk. The biochar exhibited a high specific surface area (477 m2 g−1) and achieved up to 88.7% removal of Hg2+ from aqueous solutions within only 15 min. These results suggest that the wetlands of the Atrato basin act as sinks for mercury contamination and highlight the potential of a locally derived sawdust biochar as a low-cost and sustainable strategy for mercury removal and water treatment for local communities.