Abstract
Total mercury was evaluated in the mangrove oyster Crassostrea rhizophorae, in sediments and seston from the Ciénaga Grande de Santa Marta (CGSM) and Cispatá Bay (BhC) in two climatic seasons (rainy and dry). Composite samples of sediments, seston and oysters in juvenile and adult sizes were collected at six stations (three in each ecosystem) and Hg was quantified by atomic absorption spectrophotometry (EPA method 7473 PLTX-017). BhC had the highest Hg concentrations in sediment, seston and oysters compared to CGSM, with values close to the tolerable threshold for the ecosystem and associated biota (TEL) of 0.13 µg/g Hg and with a low risk of Hg contamination in the mangrove oyster. Although at CGSM Hg was below the TEL in sediment and was considered safe in the oyster, significant bioaccumulation was evident with the metal content in the seston, indicating a potential risk to the ecosystem and humans. The variables organic matter and temperature influenced metal availability in the sediment and seston, respectively; in contrast, they had no significant relationship in the oyster. In CGSM, higher [Hg] was recorded in adult sizes, while in BhC the highest accumulation occurred in juveniles, especially during the dry season. These results emphasize the need for continuous monitoring of Hg contamination in both ecosystems. In addition, they highlight the importance of considering the size of oysters when assessing Hg contamination, as they may vary according to specific ecosystem and climatic conditions.