ATMOSPHERIC DEPOSITION - A POTENTIAL SOURCE OF TRACE-METAL ORGANIC COMPLEXING LIGANDS TO THE MARINE-ENVIRONMENT

The present study confirms the existence of rainwater and seawater sol uble metal (Cu, Pb, Cd, Ni and Co) complexing organic ligands associat ed with end-member aerosol populations. The end member aerosols being representative of a European urban aerosol population (LUAP - Liverpoo l Urban Aerosol Population), and an aerosol population representative of crustal dominated material (Mesh Saharan dust, collected off the we st African coast). The investigations carried out by ACSV (adsorptive cathodic stripping voltammetry) clearly indicated that these end-membe rs were a source of organic complexing ligands for all the considered metals. For LUAP Cu 26%, Pb 55%, Cd 36%, Ni 26% and Co 27% of the tota l seawater soluble fraction was ACSV(non-labile) (i.e. that fraction o f the dissolved metal which is released after UV irradiation) compared to the corresponding values for Saharan dust (Cu 59%, Pb 23%, Cd 56%, Ni 66%, Co 23%). From these studies it was apparent that the dissolut ion for all metals and their respective fractions in both seawater and artificial rainwater was a rapid process with no further release afte r ca. 30 minutes. The studies displayed for a number of the metals re- adsorption of ACSV(non-labile) metal to the aerosol particulate surfac e (Co and Pb - Saharan / seawater; Co and Cd - LUAP / seawater) implyi ng that different geochemical pathways are taken by different metal sp eciation fractions leading to potential differences in their marine re sidence times. Conditional formation stability constants and complexin g capacities for Ni were determined for seawater after being equilibra ted with both end member aerosols. Log K'(NiL) detected were 18.3 +/- 0.3 and 19.26 +/- 0.4 for LUAP and Saharan dust respectively. The equi valent complexing capacities were 1.0 +/- 0.1 nmol mg(-1) and 0.038 +/ - 0.005 nmol mg(-1) respectively.