Evaluation of Heavy Metals Pollution Loadings in the Sediments of the Ave River Basin (Portugal)

Sediment samples from the Ave river basin were collected with the aim of determining metal total pollution contents. Cr, Cu, Fe, Mn, Pb, Zn and VM at 550 °C were determined. Some physico-chemical parameters were also quantified in water samples collected in the water column just above the sediments.

Metal contamination factors (CF) indicated that sediments were not contaminated with Cu and Pb, slightly with Zn and moderately with Cr.

For sediments with high metal pollution loadings, the original BCR (Community Bureau of Reference) metal speciation protocol was also applied. Speciation studies showed that chromium was mainly associated with the oxidisable plus residual fractions (>85%). These results suggest that changes in the physico-chemical properties of the river water (e.g. pH, Eh) should not be accompanied by a significative release of chromium from sediments.

The relationships between chromium speciation fractions, physic-chemical parameters of the sediments and water samples were studied by Principal Component Analysis, and allowed to reduce the dimensionality of the data matrix from 14 to 3 significant components accounting for 89% of the variance. It was found that hydrous Fe/Mn oxides and organic matter are the “carriers” of chromium associated to fractions exchangeable and oxidable.