Atmospheric occurrence, transport and deposition of polychlorinated biphenyls and hexachlorobenzene in the Mediterranean and Black seas
Résumé
The Mediterranean and Black seas are unique marine
environments subject to important anthropogenic pressures
due to direct and indirect loads of atmospheric inputs
of organochlorine compounds (OCls) from primary and
secondary sources. Here we report the results obtained during
two east–west sampling cruises in June 2006 and May
2007 from Barcelona to Istanbul and Alexandria, respectively,
where gas-phase and aerosol-phase samples were collected.
Both matrices were analyzed for 41 polychlorinated
biphenyls (PCBs), including dioxin-like congeners, and hexachlorobenzene
(HCB). The values reported in this study for
gas-phase HCB and
P
41PCB limit of detection (LOD) to
418.3 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 atmospheric
concentrations during the last decade for the Mediterranean
region due to land-based OCl sources. There is a clear influence
of the direction of the air mass on the atmospheric
concentrations of PCBs, with higher concentrations when the
air mass was from southern Europe, and the lowest concentrations
for air masses coming from the SW Mediterranean
and Atlantic Ocean. PCBs and HCB are close to air–water
equilibrium for most sampling periods, thus resulting in low
atmospheric deposition fluxes at open sea. This is consistent
with the oligotrophic character of the Mediterranean Sea
with a small influence of the biological pump capturing atmospheric
PCBs. Therefore, degradation of gas-phase PCBs
by OH radicals is estimated to be the main loss process of
atmospheric PCBs during their transport over the Mediterranean
Sea. Conversely, atmospheric residence times of HCB are predicted to be very long due to a lack of atmospheric
degradation and low depositional fluxes due to concentrations
at air–water equilibrium.