Abstract
Mercury (Hg) contamination in freshwater sediments represents a major environmental concern due to its persistence, bioaccumulation potential, and high toxicity. In agricultural regions, intensive land use and hydrological modifications may enhance mercury mobilization and accumulation in aquatic systems. This study quantified total mercury concentrations in surface sediments from the Marialabaja swamp, an agriculturally impacted freshwater ecosystem in northern Colombia, and evaluated their toxicological effects using Caenorhabditis elegans as an in vivo model. Total mercury was detected in all sediment samples, with concentrations ranging from 0.116 to 0.174 mg/kg. Measured values were compared with internationally recognized sediment quality guidelines, including the Threshold Effect Level (TEL = 0.13 mg/kg) and Probable Effect Level (PEL = 0.70 mg/kg) from CCME, as well as the Effects Range Low (ERL = 0.15 mg/kg) and Effects Range Median (ERM = 0.71 mg/kg) from NOAA. Sediment mercury concentrations at several sites exceeded TEL/ERL thresholds, indicating potential ecological risk. Exposure to aqueous sediment extracts induced concentration-dependent lethality and locomotor impairment in C. elegans. Transgenic reporter assays revealed activation of oxidative stress (sod-1, sod-3) and neurobehavioral pathways (nlg-1). These findings demonstrate that sediment-associated mercury poses ecotoxicological risk and confirm the value of C. elegans as a sensitive and integrative model for environmental monitoring, highlighting the importance of combining chemical and biological tools for environmental risk assessment in agricultural freshwater systems.
