Temporal trends in gaseous mercury evasion from the Mediterranean seawaters

Mercury evasion from seawaters is considered to be one of the main natural sources of mercury; released to the atmosphere. The temporal evolution of t his mechanism is related to biotic and abiotic processes that produce mercu ry in its elemental form and as DGM. The efficiency of these processes depe nds upon the intensity of the solar radiation, the ambient temperature of t he air parcel above the seawater, and the water temperature. In the Mediter ranean region, the magnitude of these mechanisms are particularly significa nt, due to favorable climate conditions and to the presence of large cinnab ar deposits that cross the whole region; all these synergic factors yield s ignificant evasional fluxes of mercury from the surface water during most o f the annual period. In this work, mercury fluxes were measured by using a floating flux chamber connected to an atomic absorption analyzer. Photosynt hetic active radiation (PAR) and UV components of the solar radiation were measured using the same system adopted in the EC 'ELDONet project'. The mea surements of the mercury evasional fluxes were carried out at three sites o f the northern Tyrrhenian Sea during 1998. Two sites were located at unpoll uted and polluted coastal areas, and the third was an offshore site. The ev asional flux showed a typical daily trend, highest at midday when the ambie nt temperature and solar radiation were at the maximum, and lowest, near to zero, during the night. Besides the day-night behavior, a seasonal trend w as also observed; with minimum values during the winter period (0.7-2.0 ng/ m(2) h) and maximum values during the summer (10-13 ng/m(2) h). (C) 2000 El sevier Science B.V. All rights reserved.