The use of Cerastoderma glaucum as a sentinel and bioindicator species: Take-home message

Bivalves are frequently used to assess environmental contamination, and are often considered good sentinel and/or bioindicator species. For that reason the bioaccumulation and toxicity induced by metals and As in the cockle Cerastoderma glaucum, collected from areas with different contamination levels along the Óbidos lagoon (Portugal), were used to evaluate the use of this species as sentinel and/or bioindicator. The results showed that areas in the middle of the lagoon presented lower metals and As concentrations, lower total organic matter content and lower percentage of fine particles than areas in the Bom Sucesso arm. In all areas Cr, Pb and Cu were the most abundant elements, while Ni, As, Cd and Hg were less abundant. Results also showed a moderate correlation between total elements concentrations found in C. glaucum and in sediment, and thus caution should be taken when considering this species as a good sentinel species. The present study also revealed that, in general, C. glaucum from areas in the middle of the lagoon accumulated higher concentrations of metals and As (Biota-Sediment Accumulation Factor >1) than cockles from the most polluted areas located in the Bom Sucesso arm. However, in all areas, the majority of metals (Cu, Cr, Pb) were found in cockles insoluble fraction which may explain low cellular damage and reduced oxidative stress responses observed. Therefore, our results may further alert for caution when identifying C. glaucum as a good bioindicator species. Thus, our findings highlight the fact that studies should be cautious when selecting species for environmental monitoring, since good sentinels or bioindicators in highly polluted systems may not act in the same way in low or moderately contaminated areas. Furthermore, our study warns for the misclassification of cockles in different ecosystems.