Sources of Cd, Cu, Ni and Zn in Portuguese coastal waters

In order to identify the major sources of trace metals (TM) in the Portugue se coastal waters, 58 surface water samples were collected during September 1988. The area sampled extended from the Tagus Estuary (down to a salinity of 25) to cape Ste Marie on the southern coast of Portugal. Dissolved meta l concentrations in the fully marine waters ranged from 30 to 250 pM for Cd , 0.7-15 nM for Cu, 0.9-20 nM for Zn and 1.8-4.5 nM for Ni. Within the Tagu s Estuary (salinity 25), concentrations increased to 3400 pM for Cd, 26 nM for Cu, 14 nM for Ni and 230 nM for Zn. The large-scale distribution of these metals is dominated by two strong con tinental sources, both probably Linked to the exploitation of pyrite ores. In the Tagus Estuary, TM enrichments can be mostly attributed to a pyrite r oasting plant located on the shore in front of Lisbon. Concerning the south Portuguese shelf waters, several hypotheses are proposed to explain their elevated metal concentrations. We particularly discussed the likely influen ce of the Tinto/Odiel rivers located 100 km eastward, an influence well kno wn in the shelf waters of the Gulf of Cadiz. These rivers are extremely met al-rich because of acid mine tailings originating from their catchment. Bet ween these two regions, upwelling of relatively metal-poor water largely co ntributes to the dilution of the continental inputs. Indeed, water exchange s on the shelf linked to the upwelling involve water fluxes 500 times highe r than the Tagus River flow, and renew the coastal waters that are thus cle aned from terrestrial contamination. Contrary to many other upwelling syste ms in non-contaminated areas, the Portuguese upwelling does not act as a so urce of trace-metal enrichment of the continental margin waters. (C) 2000 E lsevier Science B.V. All rights reserved.