Retrospective study of metal contamination time trends in the French part of the Bay of Biscay.

Two cores were sampled in the Bay of Biscay: one a few miles off the Gironde estuary (pointe de la Coubre), the other near the Spanish border (Capbreton canyon) to study past variations in sediment contamination. Radiochronology (210Pb, 137Cs) and total metal determinations by ICP-MS allowed the study of time trends for metal concentrations in sediment. Off the Gironde, during the time interval recorded by the core (1958-1999), all metal concentrations remained less than OSPAR background values. Some variations occurred along the Cd and Zn profiles, which may correspond to a very attenuated signal from the Gironde outputs. This suggests that this area was not submitted to any significant anthropogenic input of metals between 1958 and 1999. In the canyon of Capbreton, the undisturbed part of the core recorded the influence of surface deposition between 1977 and 1999. From as early as 1977 high lead and mercury concentrations were noticed. Mercury concentrations increased until 1992, then decreased until 1999. This marks a drop of inputs in 1992, but the final concentration remained elevated. Lead had important concentrations (more than twice the OSPAR reference) all along the core and began to decrease only in the upper level of the unmixed layer. This shows a late (near 1998) drop of lead inputs. Other metals (Cd, Cu, Zn, Ni, Cr) stayed at a much lower level: less than the OSPAR reference for Cu, Cr and Ni or not far from the OSPAR reference for Cd and Zn.