Total and methyl mercury in different species of molluscs from two estuaries in Rio de Janeiro state

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 mu g kg(-1) dry wt. and 70 +/- 5 mu g 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 mu g kg(-1) dry wt. and 48 +/- 5 mu g kg(-1) dry wt.) than oysters ( 19 +/- 4 mu g kg(-1) dry wt. and 6 +/- 1 mu g 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.