A portable device for continuous analysis of dissolved gaseous mercury in natural waters.

A fully automatic device for continuous analysis of DGM (Dissolved Gaseous Mercury) concentration in natural waters, controlled by a Notebook, with a resolution time of 10-15 min, equipped with an Atomic Absorption Spectrometer with a detection limit of 0.5 pg, is described. A particular feature of this instrument is the portability, making its use suitable in remote locations by means of a car battery. Comparison of the results obtained using the device in the continuous mode and in the discrete mode shows good agreement taking into consideration that water samples were collected with shifting sampling times. To compare samples collected at the same time, a second analytical device, running in the discrete mode, was used. In this case results show that measurements performed with the discrete mode are slightly higher than the continuous one. Avoiding the sample handling it was possible to reduce the contamination from external sources and to achieve low instrumental blank values (1-2 pg). The field performance of this portable instrument was tested on seawater and lagoon water, where the DGM daily behaviour was measured. In agreement with several authors, a time shifting between DGM and solar radiation intensity higher than the instrumental resolution time was noted.

Importance of the biogenic organic matter in photo-formation of dissolved gaseous mercury in a culture of the marine diatom Chaetoceros sp.

Laboratory experiments on DGM production under light/dark cycles in a culture of the marine diatom Chaetoceros sp. spiked with 200 ng l(-1) of mercury have been performed. DGM formation has been investigated also in the cell exudates, obtained by filtration of the cell culture. Results show that the cell culture and the filtrate give the same value of DGM production (2.24+/-0.88 pg min(-1) l(-1) and 2.23+/-0.02 pg min(-1) l(-1), respectively) in the light (40 W m(-2)), values much higher than to those obtained in the medium culture alone. A significant DGM production has been measured in dark conditions both in the cell culture (0.48+/-0.11 pg min(-1) l(-1)) and in the filtrate (0.85+/-0.10 pg min(-1) l(-1)). The results highlight that the organic compounds released by the cell in the culture medium play a fundamental role in the DGM photo-formation processes.

Mercury exposure and elimination rates in captive bottlenose dolphins.

Mercury concentrations in fish, faeces and exhaled air were investigated in order to evaluate total mercury exposure through the gut in captive bottlenose dolphin and excretion via intestine and pulmonary routes. Results showed that faeces account for elimination of 34-48% of dietary mercury; while only 0.9-1.2% of alimentary mercury is eliminated through exhaled air. The remaining 51.2-65.3% of ingested mercury, ranging approximately between 266 and 339 microg per day, is retained within the organism. The complexation of mercury with selenium, forming insoluble tiemannite granules, is discussed as an important mechanism, complementary to excretion, by which odontocetes are able to cope with elevated alimentary exposure to mercury.

Photo-induced formation of dissolved gaseous mercury in coastal and offshore seawater of the Mediterranean basin.

The first measurements on the daily trend of dissolved gaseous mercury (DGM) concentration determined in coastal and offshore waters of the Mediterranean basin are reported. Marked daily behaviour tracking solar radiation has been observed at the coastal sampling station with DGM values ranging from 11.0 to 38.9 pg/l. Contrary to these observations the DGM values in offshore water samples (11.9-20.0 pg/l) were independent of the sampling time, thus identifying the absence of higher levels during the hours of maximum insolation. The availability of Hg2+ substrate necessary for the photo-reaction processes of DGM formation has been evaluated by measuring the reactive mercury concentration. In offshore waters the lower DGM concentrations are attributable to the substrate as a limiting factor. The highest concentration of DOC measured in coastal seawater with respect to the offshore one could moreover enhance the reaction rates of DGM production through the formation of inorganic mercury complexes and weaker organic associations.

Daily trend of dissolved gaseous mercury concentration in coastal seawater of the Mediterranean basin.

A daily trend of DGM concentration in shallow coastal seawater has been measured in an area of the Mediterranean basin. Values up to 47 pg/l were determined for a photosynthetically active radiation (PAR) intensity of 350 W/m2. The lowest value (18 pg/l) has been observed before sunrise. A linear relationship between the PAR intensity and DGM production has been highlighted in an experiment on seawater samples exposed for 10 min to solar radiation. The processes involved in DGM production and losses are discussed.

Dissolved gaseous mercury concentration and mercury evasional flux from seawater in front of a chlor-alkali plant.

The dissolved gaseous mercury concentration and mercury degassing rate have been measured in a marine area polluted by a chlor-alkali plant (Rosignano Solvay, Italy), which uses mercury in chlorine production. During the summer the DGM concentration (130 pg l(-1)) and the evasional flux (14 ng m(-2) h(-1)) were 3-4 times higher than those measured at the control stations. A seasonal behaviour has been highlighted at all the sampling sites, with minimum levels in the winter.

Volcanoes as emission sources of atmospheric mercury in the Mediterranean basin

Emissions from volcanoes, fumaroles and solfataras as well as contributions from widespread geological anomalies could represent an important source of mercury released to the atmosphere in the Mediterranean basin. Volcanoes located in this area (Etna, Stromboli and Vulcano) are the most active in Europe; therefore, it is extremely important to know their mercury contributions to the regional atmospheric budget. Two main methods are used for the evaluation of volcanic mercury flux: a direct determination of the flux (by measuring in the plume) and an indirect one derived from the determination of the Hg/SO2 (or Hg/S) ratio value, as SO2 emissions are constantly monitored by volcanologists. An attempt to estimate mercury flux from the Vulcano volcano and to establish the Hg/S ratio value has been made along three field campaigns carried out in October 1998, in February and May 1999 sampling several fumaroles. Traditional sampling methods were used to collect both total Hg and S. The average Hg/S ratio value resulted to be 1.2 x 10(-7). From the Hg/S value we derived the Hg/SO2 value, and by assuming that all the volcanoes located in this area have the same Hg/SO2 ratio, mercury emissions from Vulcano and Stromboli were estimated to be in the range 1.3-5.5 kg/year and 7.3-76.6 kg/year respectively, while for Etna mercury flux ranged from 61.8 to 536.5 kg/year. Data reported in literature appear to be overestimated (Fitzgerald WF. Mercury emission from volcanos. In: 4th International conference on mercury as a global pollutant, August 4-8 1996, Hamburg, Germany), volcanic mercury emission does not constitute the main natural source of the metal.

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 this mechanism is related to biotic and abiotic processes that produce mercury in its elemental form and as DGM. The efficiency of these processes depends upon the intensity of the solar radiation, the ambient temperature of the air parcel above the seawater, and the water temperature. In the Mediterranean region, the magnitude of these mechanisms are particularly significant, due to favorable climate conditions and to the presence of large cinnabar deposits that cross the whole region; all these synergic factors yield significant evasional fluxes of mercury from the surface water during most of the annual period. In this work, mercury fluxes were measured by using a floating flux chamber connected to an atomic absorption analyzer. Photosynthetic active radiation (PAR) and UV components of the solar radiation were measured using the same system adopted in the EC 'ELDONet project'. The measurements of the mercury evasional fluxes were carried out at three sites of the northern Tyrrhenian Sea during 1998. Two sites were located at unpolluted and polluted coastal areas, and the third was an offshore site. The evasional flux showed a typical daily trend, highest at midday when the ambient temperature and solar radiation were at the maximum, and lowest, near to zero, during the night. Besides the day-night behavior, a seasonal trend was also observed, with minimum values during the winter period (0.7-2.0 ng/m2 h) and maximum values during the summer (10-13 ng/m2 h).