Element concentrations in sediments and marine bivalves (clam Tivela mactroides and oyster Crassostrea rhizophorae) from the central Venezuelan coasts: a comparative study.

Bivalves are recognized as bioindicator organisms of metal pollution in marine ecosystems. However, there is still an open debate on which species is the best candidate for biomonitoring studies. Therefore, this study determined the concentrations of twelve elements in sediments and soft tissues of two edible bivalves (clam Tivela mactroides and oyster Crassostrea rhizophorae) collected in two coastal locations of Central Venezuela during four sampling campaigns. Overall, none of the measured elements in sediments surpassed the severe effect level established by international guidelines, suggesting that element abundance in sediments is rarely associated with biological effects. The average concentrations of elements in soft tissues varied from 684 ± 97 for Zn to 0.6 ± 0.2 μg/g dry weight (d.w.) for Co in C. rhizophorae, whereas in T. mactroides the concentrations ranged from 792 ± 329 for Fe to 0.35 ± 0.18 μg/g d.w. for Cd. Zn, Cd, and Cu were mostly accumulated on both bivalves, although the bioaccumulation sediment factor (BASF) for Zn in T. mactroides (37 ± 23) and C. rhizophorae (75 ± 59) was much higher than those observed for Cd (4.1 ± 1.7 and 9.4 ± 4.2, respectively) and Cu (3.0 ± 0.7 and 2.8 ± 0.4, respectively). Although the oyster C. rhizophorae showed BASF values for Zn and Cd higher than those observed in the clam T. mactroides, the BASF values for the rest of the elements were the highest in T. mactroides. This was related to the fact that clams inhabit bottom sediments and feed by filtering element-rich porewater. Finally, this study showed that the sporadic consumption of both bivalves does not pose detrimental effects on humans.