ELEMENTAL COMPOSITION IN SEDIMENTS AND WATER IN THE TRANCAO RIVER BASIN - A PRELIMINARY-STUDY

The Trancao river basin, located in the Lisbon area shows preoccupying pollution levels, that constitute a threat to public health and the e cological system. This work reports on the results obtained in the ana lysis of surface sediments (EDXRF) and<INF></INF> water (PIXE) collect ed in the wet and dry season during 1996. In general, bulk sediments a nd water show high concentration levels for some heavy metals like Cr, Cu, Zn and Pb. The elemental contents variation of samples collected at the different sites of the river basin were large, owing apparently to pollution sources, seasonal variabilities and grain size distribut ion (sediments). In the dry season, effluents (industrial and domestic ) showed a stronger influence on the sediment composition. High levels of As and Br were found in the water that can be attributed to extend ed sources like sewage sludge and fertilizers. In some locations, the metals, Ca and organic matter enrichment could be associated with a pa per mill and metal processing industry (high levels of Cr). At the est uary, the decrease of metal content determined in the sampled water in dicates the flocculation of dissolved organic and inorganic materials. However, no effects were found for the surface sediment metal content ? probably due to a dilution with materials from the Tagus inner estua ry (the largest in Portugal). (C) 1998 Elsevier Science B.V.