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 soluble metal (Cu, Pb, Cd, Ni and Co) complexing organic ligands associated with end-member aerosol populations. The end member aerosols being representative of a European urban aerosol population (LUAP ¿ Liverpool Urban Aerosol Population), and an aerosol population representative of crustal dominated material (Mesh Saharan dust, collected off the west African coast). The investigations carried out by ACSV (adsorptive cathodic stripping voltammetry) clearly indicated that these end-members 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 total seawater soluble fraction was ACSVnon-labile (i.e. that fraction of 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 dissolution for all metals and their respective fractions in both seawater and artificial rainwater was a rapid process with no further release after ca. 30 minutes. The studies displayed for a number of the metals re-adsorption of ACSVnon-labile metal to the aerosol particulate surface (Co and Pb - Saharan / seawater; Co and Cd - LUAP / seawater) implying that different geochemical pathways are taken by different metal speciation fractions leading to potential differences in their marine residence times. Conditional formation stability constants and complexing capacities for Ni were determined for seawater after being equilibrated with both end member aerosols. Log K\u27NiL detected were 18.3 - 0.3 and 19.26 - 0.4 for LUAP and Saharan dust respectively. The equivalent complexing capacities were 1.0 - 0.1 nmol mg-1 and 0.038 - 0.005 nmol mg-1 respectively