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The overall objective of this work is to provide the first evaluation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) occurrence and deposition to Mediterranean open seawater. Σ2,3,7,8-PCDD/F air (gas+aerosol) concentrations over the Mediterranean Sea ranged from 60 to 1040 fg m-3. The highest value (1555 fg m-3) was measured in a reference sample taken in the SW Black Sea. No consistent trend regarding the diel cycle of PCDD/Fs was observed. PCDD/Fs transported to the open sea waters from continental areas and across the Atlantic as well as ship emissions may be significant sources to the open Mediterranean. Seawater concentrations in the Mediterranean ranged from 42 to 64 fg L-1. The Σ2,3,7,8-PCDD/F dry deposition fluxes in the Marmara and Black Seas (210 kg year-1) are from 2 to 55 times higher than dry fluxes in the Mediterranean Sea (4-156 kg year-1). Analysis of estimated diffusive air-water fluxes and air/water fugacity ratios show that a net volatilization of some PCDD congeners is feasible. However, evidence of a net absorption flux for the rest of PCDD/F is found. When both atmospheric deposition processes are considered together the open Mediterranean Sea is a net sink of PCDD/F, due to the importance of dry deposition fluxes of aerosol-bound PCDDFs. [ABSTRACT FROM AUTHOR]