Atmospheric occurrence, transport and deposition of polychlorinated biphenyls and hexachlorobenzene in the Mediterranean and Black seas

International audienceThe Mediterranean and Black seas are unique marineenvironments subject to important anthropogenic pressuresdue to direct and indirect loads of atmospheric inputsof organochlorine compounds (OCls) from primary andsecondary sources. Here we report the results obtained duringtwo east–west sampling cruises in June 2006 and May2007 from Barcelona to Istanbul and Alexandria, respectively,where gas-phase and aerosol-phase samples were collected.Both matrices were analyzed for 41 polychlorinatedbiphenyls (PCBs), including dioxin-like congeners, and hexachlorobenzene(HCB). The values reported in this study forgas-phase HCB andP41PCB limit of detection (LOD) to418.3 pgm−3 and from 81.99 to 931.6 pgm−3 respectively)are in the same range of those reported in former studies,possibly suggesting a limited decline in their atmosphericconcentrations during the last decade for the Mediterraneanregion due to land-based OCl sources. There is a clear influenceof the direction of the air mass on the atmosphericconcentrations of PCBs, with higher concentrations when theair mass was from southern Europe, and the lowest concentrationsfor air masses coming from the SW Mediterraneanand Atlantic Ocean. PCBs and HCB are close to air–waterequilibrium for most sampling periods, thus resulting in lowatmospheric deposition fluxes at open sea. This is consistentwith the oligotrophic character of the Mediterranean Seawith a small influence of the biological pump capturing atmosphericPCBs. Therefore, degradation of gas-phase PCBsby OH radicals is estimated to be the main loss process ofatmospheric PCBs during their transport over the MediterraneanSea. Conversely, atmospheric residence times of HCB are predicted to be very long due to a lack of atmosphericdegradation and low depositional fluxes due to concentrationsat air–water equilibrium