Chemical profile of Thalassia testudinum under coastal pollution: Assessment of mercury, VOCs and secondary metabolites in the Colombian Caribbean.

Seagrass meadows of Thalassia testudinum are key components of blue carbon ecosystems and effective bioindicators of environmental contamination due to their ability to incorporate both inorganic and organic pollutants. This study evaluated total mercury (T-Hg) concentrations and the qualitative occurrence of volatile organic compounds (VOCs) and secondary metabolites in T. testudinum collected from two sites with contrasting environmental pressures in the Colombian Caribbean: Cartagena Bay (CTG Bay) and the reference area within the Corales del Rosario and San Bernardo National Natural Park (RSBC-NNP). Total mercury was quantified using a direct mercury analyzer, while VOCs were identified by GC-MS. T-Hg concentrations in T. testudinum, expressed on a dry-weight basis, ranged from 9.7 to 32.4 μg/kg in CTG Bay and from 8.0 to 10.0 μg/kg in the RSBC-NNP, although both ranges remained substantially lower than values previously reported for sediments and fish from the same area, yet consistent with a moderate bioaccumulation capacity of this seagrass species. Subsequently, a total of 89 VOCs were identified, mainly including aliphatic and aromatic hydrocarbons, terpenes, fatty acids, and sterols. CTG Bay exhibited a higher chemical diversity, whereas the 23 compounds detected in the reference area were also present in the bay, with no exclusive compounds observed in the protected site. Metabolites such as phytol, squalene, and (Z)-9-octadecenamide were detected in both areas, suggesting common physiological processes related to basal metabolism and general stress responses. Overall, these findings demonstrate that T. testudinum integrates signals of exposure to both metallic and organic contaminants, reinforcing its value as a sentinel species for environmental assessment in tropical coastal ecosystems.