Metal speciation in surface sediments of the Vigo Ria (NW Iberian Peninsula)

Abstract

Total concentrations and chemical forms of metals in surface sediments of the Vigo Ria (NW Iberian Peninsula) were determined following the sequential extraction method proposed by Tessier et al. (1979). Total values ranged from 7 to 14 µgCo g-1, 52 to 76 µgCr g-1, 18 to 82 µgCu g g-1, 136 to 209 µgMn g g-1, 18 to 30 µgNi g g-1, 24 to 112 µgPb g g-1, 62 to 185 µgZn g g-1 and 18 to 34 mg g g-1 for Fe. The distribution of metals is strongly influenced by the presence of urban and industrial centres. A decreasing concentration trend was observed towards (i) the outer-oceanic part of the ria and (ii) the northern shore in the middle part. Cobalt, Cr, Fe, Mn, and Ni were found to be strongly associated with the residual fraction of the sediment (65-78%), whereas Cu is significantly present in the oxidisable phase (34-72%) and Pb and Zn are found in both the reducible (14-49%) and the oxidisable (14-39%) phases. The speciation patterns reflect natural uncontaminated conditions in the outer part of the ria. However, a significant fraction of the Cu, Pb, and Zn in the sediments of the southern margin of the middle part of the ria, which supports most of the population and industrial activities, is present in labile forms, so a potential pollution risk may exist.

Keywords

• sediment
• metals
• speciation
• tessier sequential extraction
• vigo ria