Basin-scale contributions of Cr, Ni and Co from Ortegal Complex to the surrounding coastal environment (SW Europe).

The enrichment of Cr and Ni in the coastal zones is usually associated with anthropogenic sources such as the tanning, galvanization, ceramic, and cement industries. However, geological complexes of specific lithologic composition located near shorelines may act as natural sources of metals to the continental shelf. Cape Ortegal (SW Europe) is an ultramafic complex that has Cr, Ni and Co enriched in rocks due to the minerals chromite, chromospinel, gersdorfite and pentlandite. Thus, the hypothesis that this geological complex contributes to metal enrichment in Ortigueira and Barqueiro Rias and the adjacent continental shelf was tested. Chromium, Ni, and Co were determined in water and in suspended particulate matter of ria tributaries, rainfall, surface sediments, mussels, and algae. High contents of Cr (max. 1670mg·kg(-1)) and Ni (max. 1360 mg · kg(-1)) were found in the sediments surrounding Cape Ortegal and the Ortigueira Ria as a result of erosion of exposed cliffs. Dissolved Cr and Ni concentrations in fluvial waters were significantly higher in the rivers that crosses the Ortegal Complex, i.e. Lourido (0.47 μg Cr · L(-1); 9.4 μg Ni · L(-1)) and Landoi (0.37 μg Cr · L(-1); 4.3 μg Ni · L(-1)), in comparison with the nearby basin out of the complex influence (Sor River: <0.01 μg Cr · L(-1); 0.57 μg Ni · L(-1)). The annual fluvial contributions of Cr and Ni to the Ortigueira Ria were higher than fluxes into the Barqueiro Ria. Moreover, the increase in Cr and Ni in the rainfall in summer demonstrated the importance of the atmosphere pathway for introducing these elements into the aquatic environment. As a consequence, the contents of these metals in soft tissues and shell of mussels and algae from the Ortigueira Ria were higher than the organisms from Barqueiro Ria. Thus, geological complexes, such as the Cape Ortegal, located in an uncontaminated area, can increase the land-sea exchange of trace metals.