Heavy Metal Concentrations and Dispersion in Wild Mussels along the Asturias Coastline (north of Spain)

Several international organisations have recommended the use of bioindicators to improve the evaluation of ecological risk in marine ecosystems. In this context, wild mussels, a recognised bioindicator, were collected from thirty sampling points along the Asturias coastline and studied in order to identify any relationship between metal(oid) concentrations in wild mussel tissues and the geological and environmental conditions of the coastal area via biochemical analyses. Two main concentration trends were observed: Concentrations of As, Cd, Cr, Ni, Pb and Zn slightly decrease from the western to the eastern areas of the region, while the opposite occurred for Fe, Hg and Se whose concentrations increased from the westernmost part of Asturias to the east. Correlations between the elements showed how essential metals for organisms such as Fe, Ni and Cr have good correspondences among them but not with other metal(oid)s. On the other hand, Cd, Hg, Se and Zn were found to be correlated with each other, suggesting the presence of the mussels’ natural bio-defence against Cd and Hg. In addition, samples were also grouped by a cluster analysis based on their element concentrations, showing two independent groups. Group 1 was associated with the sampling sites whose concentrations were related to anthropic sources, while mussel concentrations in Group 2 were attributed to natural sources. This last group was divided into two subgroups based on the lithology of the dominant geological materials of each area. Both geological and anthropic sources have caused an increase in the metal loads of mussels which at times surpassed international environmental criteria.