Changes in mercury content in oysters in relation to sediment and seston content in the Colombian Caribbean lagoons

Total mercury (Hg) was evaluated in the mangrove oyster <i>Crassostrea rhizophorae,</i> 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 ages were collected at six stations (three in each ecosystem) and Hg was quantified by atomic absorption spectrophotometry (Environmental Protection Agency (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. Although at CGSM Hg was below the TEL in sediment and was considered safe in the oyster, significant bioconcentration 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 concentration was recorded in adult ages, while in BhC the highest accumulation occurred in juveniles, especially during the dry season. These findings underscore the importance of continuous Hg monitoring in both ecosystems. When assessed using the adapted Nemerow Pollution Index based on the provisional tolerable weekly intake (PTWI) of one µg Hg/kg body weight, although both sites presented a very high risk in terms of consumption, they are well below the most contaminated global hotspots over the past five decades. This study also highlights the relevance of oyster age in contamination assessments, as Hg accumulation patterns vary depending on environmental and climatic conditions.