Atmospheric input of dissolved and particulate metals to the northwestern Mediterranean

Concentrations of trace elements (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) were determined for aerosols, dry deposition, precipitation and total deposition samples collected from five stations on islands and in the coastal zone of the northwestern Mediterranean. Average concentrations of metals are very homogeneous over the sampled area, in particular at the three coastal sites. Cd and Pb are almost entirely of man-made origin, even in Saharan aerosols. For the other metals, the non-crustal fraction is lower in Saharan aerosols than in European aerosols, but there is an important man-made component in the Saharan aerosol, even for metals such as Fe and Cr. This confirms the results of Chester et al. (1992) who concluded that Mediterranean aerosols have a European background upon which are superimposed Saharan inputs. Dry deposition represents an important fraction of the total deposition. Partitioning of total atmospheric deposition between the dissolved and the particulate phases shows that Al, Fe and Cr originating from the atmosphere are mostly in a particulate form in the surface waters. For the other metals studied, the dissolved fraction represents more than 30% of the total input, and for Cd it is almost 100%. Extrapolation shows that more than 50% of the dissolved metals input to the northwestern Mediterranean originates from the atmosphere. Atmospheric input entirely dominates the total external input of pollution-derived elements, such as Pb and Cd. The dissolved input of atmospheric origin is also very important (> 80%) for elements of terrigeneous origin such as Al. (C) 1997 Elsevier Science Ltd