Bioaccumulation of metals in mussels from four sites of the coastal region of Baja California

This study analyzes the concentrations and variations of Cu, Mn, Zn, Al, Cd, Ag, As and Se among different size classes of Modiolus capax, from Punta Estrella, Bahía de los Ángeles and Santa Rosalía in the Gulf of California, and of Modiolus modiolus and Mytilus californianus, from Bahía Tortugas in the Pacific. During November 1988, mussels of these species were collected and 45 organisms were selected (three replicates of 15 organisms each). Their biometric variables were measured: large size (88–98 mm), medium size (70–87 mm) and small size (56–66 mm). The reference standards and procedural blanks were analyzed for each group of 15 samples. The results indicate that the geographic distribution and accumulation of metals in the different sizes are mainly influenced by the sources of input, bioavailability in each place and the biological condition of the organisms. The mussels presented Cu levels independent of size in the region, except at Santa Rosalía. Zn, Cd and Se showed strong regional variability, but no clear trend with respect to the size of the organisms. Al showed high regional variability and a tendency to accumulate in small organisms. As and Se presented higher concentrations in the large to medium mussels, regardless of the sampling site. Mn tended to accumulate in large and medium mussels and was dependent on the sampling site. In Bahía Tortugas, M. californianus accumulates Cu, Mn and Cd at a rate three times lower than M. modiolus at the same level of exposure. Within the Gulf of California, the geographic distribution of Mn, Al and Zn was similar, with higher concentrations in the northern part. This is probably because the mussels are exposed to these metals through the sedimentary material resuspended in the Colorado River Delta. Cd presented levels of 70 and 27 µg g–1 at Bahía Tortugas and Bahía de los Angeles, respectively; both sites are exposed to coastal upwelling. Cu presented relatively low levels (<35 µg g–1), except at Santa Rosalía (89 µg g–1), where Cu is mined. As, Se and Ag presented low variability in the study area, with low levels that reflect natural levels at the sites studied.