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Sedimentation rates in Guanabara Bay were determined by applying the 210pb CRS method to sediment cores collected at five different stations.The results showed a pronounced increase from 0.14).2 cm.year 1 to 1 2 cm.year 1, in sedimentation rate, over the last 40 50 years. Observed heavy metal profiles in sediment could also be explained on the basis 210pb dating and local industrial history.

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There is a need to assess the role of selenium in mercury accumulation in tropical ecosystems. Without further studies of the speciation of selenium in livers of fishes from this region, the precise role of this element, if any, cannot be verified in positively affecting mercury accumulation. Further studies of this element in the study of marine species should include liver samples containing relatively high concentrations of mercury. A basin-wide survey of selenium in fishes is also recommended.

Mercúrio total e metilmercúrio foram avaliados em três espécies de moluscos (Perna pernamexilhão, Crassostrea rhizophorae -ostra, Anomalocardia brasiliana -vôngole) provenientes de dois estuários no estado do Rio de Janeiro, impactados por matéria orgânica e metais pesados. O mexilhão foi a espécie que apresentou melhor capacidade para acumular o mercúrio dentre as espécies de molusco estudadas. Foi observada uma diferença significante nas concentrações de mercúrio entre os organismos de mexilhão, fêmeas e machos (81 ± 1 μg kg -1 e 70 ± 5 μg kg -1 em peso seco respectivamente), com comprimento de concha semelhante. Entretanto, não foi observada diferença significante na percentagem de metilmercúrio entre fêmeas (64%) e machos (63%) de mexilhão. Apesar de possuírem o hábito alimentar semelhante, o mexilhão apresentou concentrações de mercúrio total e metilmercúrio superiores (76 ± 7 μg kg -1 e 48 ± 5 μg kg -1 peso seco) às da ostra (19 ± 4 μg kg -1 e 6 ± 1 μg kg -1 peso seco). Este fato pode estar relacionado com diferenças na capacidade em selecionar o tamanho de partículas e os alimentos ingeridos; também, estar refletindo a maior habilidade do mexilhão em concentrar e excretar o metilmercúrio dos seus tecidos, bem como refletindo as condições ambientais.The paper assesses methyl and total mercury concentrations in three mollusc species (Perna perna -common mussel, Crassostrea rhizophorae -mangrove oyster, Anomalocardia brasiliana -clam) from two estuaries in Rio de Janeiro State, both impacted by organic matter and heavy metals. Mussels showed higher capacity to accumulate mercury compared to the other mollusc species (oyster, clam). A significant difference was observed between mercury concentration in the female mussel organisms and in males (81 ± 1 μg kg -1 dry wt. and 70 ± 5 μg kg -1 dry wt. respectively) with similar total shell length. No significant difference was observed among the % MeHg in the female (64%) and male (63%) mussel organisms. Even though the feeding habits of the molluscs are similar; mussels presented higher mercury and methylmercury concentrations in their soft tissues (76 ± 7 μg kg -1 dry wt. and 48 ± 5 μg kg -1 dry wt.) than oysters (19 ± 4 μg kg -1 dry wt. and 6 ± 1 μg kg -1 dry wt.). This is possible related to their capacity to select particle size and the composition of the ingested food they assimilate, and also reflects the greater ability of mussels to concentrate and excrete methylmercury and also to reflect their environmental conditions.

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