Chemical forms of heavy metals in surface sediments of the San Simon inlet, Ria de Vigo, Galicia

The surface sediments of the San Simon inlet of the Ria de Vigo in Galicia, north-west Spain contain heavy metal concentrations largely within the range to be expected if these metals were derived from detrital inputs from soils and weathered granitic rocks. Thus, Cu ranged from 24-28 mu g g(-1), Cr from 37-69 mu g g(-1), Cd from 0.1-0.5 mu g g(-1), Ni from 12-29 mu g g(-1) and Zn from 71-151 mu g g(-1) of sediment. For Pb, however, the range was 84-394 mu g g(-1) of sediment which is well above the level which would be expected as background, indicating the likelihood of anthropogenic inputs. Sequential fractionation indicates that relatively high proportions (similar to 40%) of this Pb are associated with the oxide and carbonate fractions and may, therefore, be potentially mobile. In contrast, Cr and Ni are found largely in the residual fractions (similar to 72 and 65%), whereas Cu is mainly associated with the organic/sulphide fraction (similar to 58%). The distribution of Zn is somewhat similar to that of Pb. There is little evidence that diagenetic processes have significantly affected the various metal forms in the sediments with the possible exception of the sites closest to the sea.