Distribution of heavy metals in the river Ulla and its estuary (North-West Spain)
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The 131-km-long Ulla is one of the most important rivers in the region of Galicia, and flows into the R?a of Arosa, the largest r?a in Galicia. Water, surface sediments and suspended particulate matter were sampled along the Ulla and in its estuary. The grain size fractions below 500 mum, below 63 mum. and, for selected samples, below 2 mum were separated and their contents measured. The concentration of suspended matter, pH and water salinity were also determined. The solid samples were digested with HF+HNO3+HCl and the total concentration of heavy metals (Zn, Pb, Cd, Cu, Ni, Cr, Mn and Fe) analysed by AAS. The sediments and suspended matter in the upper reaches of the river Ulla were found to be enriched with heavy metals: Pb, Cu, Ni, Cr and Zn were present in the sediments in concentrations of up to 68, 300, 357, 1035 and 272 mg kg-1 respectively. The heavy metal concentration in the clay fraction of selected samples is higher than in the below 63 mum fraction. The surface sediments contain heavy metals in concentrations mostly well above what would be expected if these metals had been derived from detrital inputs from soils and weathered granitic rocks, especially in the upper reaches of the Ulla. Of the heavy metals investigated, Zn, Cu, Pb, Cr and Ni are derived from anthropogenic sources.
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M.J.Belzunce-Segarra, Instituto de Investigaciones Marinas (CSIC), Eduardo Cabello 6, 36208 Vigo, Spain