Formation of dissolved gaseous mercury in a tropical lake (Petit-Saut reservoir, French Guiana)

Formation of dissolved gaseous mercury (DGM) and its volatilization from aquatic systems can be considered as a natural attenuation process, which limits the methylation of mercury (Hg) and Hg accumulation in fish. Although gold-mining activity and erosion of tropical soils lead to increased Hg concentration in aquatic systems, little is known about DGM production and distribution in tropical aqueous systems. Our work explores the vertical distribution and principal sources of DGM in a meromictic Amazonian reservoir. Dissolved gaseous mercury measurements carried out in Petit-Saut reservoir (French Guiana, South America) revealed DGM increase in the surface waters and at the bottom layers of the reservoir during the dry season. As in arctic and temperate lakes, high DGM concentrations in surface waters were attributed to sunlight-mediated photochemical processes. Dissolved gaseous mercury concentrations in the anaerobic hypolimnion were larger than in temperate or arctic lakes. In order to elucidate Hg(II) reduction pathways in the bottom layer of tropical reservoir, laboratory Hg(II) reduction experiments were performed with anoxic aqueous suspensions of surface sediments either untreated or treated by gamma-ray and NaN3. Our results indicated that DGM production at the bottom layer of Petit-Saut reservoir was biologically mediated. Dissolved gaseous mercury formation rates in the surface sediment suspensions were of the same order of magnitude as formation rates in freshwater lakes reported in literature.     

Mercury in the air, water and biota at the Great Salt Lake (Utah, USA)

The Great Salt Lake, Utah (USA), is the fourth largest terminal lake on Earth and a stop-over location for 35 million birds on the Pacific Flyway. Recently, the Utah Department of Health and Utah Division of Wildlife Resources issued tissue mercury (Hg) consumption advisories for several species of birds that consume the lake's brine shrimp. We hypothesized that the chemistry of the atmosphere above the Great Salt Lake would facilitate atmospheric deposition of Hg to the water. Because little information was available on Hg at the Great Salt Lake, and to begin to test this hypothesis, we measured atmospheric elemental (Hg(0)) and reactive gaseous mercury (RGM) concentrations as well as Hg concentrations in water and brine shrimp five times over a ~year. Surrogate surfaces and a dry deposition model were applied to estimate the amount of Hg that could be input to the lake surface, and HYSPLIT model back trajectories were developed to investigate potential sources of RGM to the lake. Atmospheric Hg(0) concentrations were similar to global ambient background values and RGM concentrations were similar to those reported for rural areas. Both Hg(0) and RGM exhibited regular diel variability. Model estimated deposition velocities for RGM to the lake ranged from 0.9 to 3.0 cm s(-1) while that determined for surrogate surfaces ranged from 2.8 to 7.8 cm s(-1). Filtered total and methyl Hg concentrations in Great Salt Lake surface waters were consistent throughout the year (3.6+/-0.8 ng L(-1) and 0.93+/-0.59 ng L(-1), respectively), while brine shrimp concentrations had a statistically significant increase from summer to fall. Data collected and data analyses indicated no direct local or regional source of Hg to the lake and that factors within the Great Salt Lake basin are important in controlling Hg(0) and RGM concentrations.     

Probing Hg evasion from surface waters of two Chinese hyper/meso-eutrophic reservoirs

Measurements of water/air exchange flux of gaseous elemental mercury (GEM) were conducted in a hyper-eutrophic reservoir and a meso-eutrophic reservoir in southwest China in both warm and cold seasons by using a dynamic flux chamber (DFC) method coupled with an automatic gaseous Hg analyzer. Both strong diurnal and seasonal variations of GEM fluxes were observed. The diurnal cycle of the GEM flux was more pronounced during sunny days compared to cloudy and rainy days, which highlights the effect of solar intensity on the GEM flux. GEM fluxes in warm seasons were considerably higher (2.5 to 4.1 times higher) than in cold seasons, which was attributed to the combined factors including meteorological factors, water quality parameters and water Hg concentrations. Clear variation in GEM fluxes was observed between the two reservoirs. Mean GEM fluxes in the hyper-eutrophic reservoir (WJD) (3.2-20.1 ng m⁻² h⁻¹) were significantly higher than those in the meso-eutrophic reservoir (SFY) (0.6-4.4 ng m⁻² h⁻¹). Evasion of Hg played a distinct role in the mass balance of Hg in the two reservoirs. In WJD, evasion was the second most important mechanism for Hg losses from the reservoir (17.5% of the total losses); whereas in SFY, loss of Hg via volatilization constituted an extremely little portion to the total losses of Hg (0.8%).     

Urban environmental mercury in Changchun, a metropolitan city in Northeastern China: source, cycle, and fate

Mercury concentrations in each environmental compartment in Changchun City had obvious spatial and temporal trends. Particulate Hg (HgP) and total gaseous mercury (TGM) concentrations in air, total Hg (HgT) concentrations in precipitation and ratios of HgP to HgT (total Hg in air) in the atmosphere in heating season were higher than those in non-heating season, which resulted from civil heating. In contrast, reactive Hg (HgR) concentrations in precipitation were higher in non-heating season than those in heating season. TGM and SO2 in air had good agreement. HgP concentrations in the atmosphere were correlated with HgT concentrations in precipitation. Based on Hg concentrations in each environmental compartment, Hg exchange fluxes between environmental interfaces were estimated. Only 11.6% of Hg, emitted from coal combustion, deposited into land surface in urban district and the rest part participated in regional or global cycle, so urban district was the source of Hg global and regional cycle. Net fluxes of Hg into land surface and water were 34.26 kg year(-1) and 0.051 kg year(-1), respectively, which were clearly accumulated in the water and soil. Therefore considering urban local Hg cycle, each environmental compartment of urban ecosystem (water, air and soil) was the sink of Hg.     

Springtime depletion of mercury in the European Arctic as observed at Svalbard

This study was carried out to see whether the geographical extent of the mercury depletion events (MDEs), first seen at Alert in the Canadian High Arctic, is also covering Svalbard. Another goal was to determine the main reaction products from the MDE and their fate. Gaseous elemental mercury (GEM), total particulate mercury (TPM), reactive gaseous mercury (RGM) and total mercury in surface snow have been measured at the Zeppelin mountain during 2000. GEM has been measured with a high time resolution automatic monitor (Tekran 2537A) based on CV-AFS, TPM was sampled/measured using high volume samplers/CV-AFS and RGM was sampled with annular denuders and measured by CV-AFS (Gardis Hg-monitor). During spring of 2000, in the three-month period following polar sunrise, there were several episodic depletions in GEM concentration correlating well with the depletion of surface ozone. Measurements of RGM and TPM showed higher concentrations of these mercury species during the depletion period than during the rest of the year. Total mercury in surface snow showed a distinct increase from the polar night to the Arctic spring. MDEs are caused by the specific chemical and physical conditions observed in the Arctic during spring. GEM is oxidised and converted to more reactive forms (RGM and/or TPM), which have considerably higher deposition velocities than elemental mercury, leading to an overall enhanced deposition flux of mercury.     

Mercury distribution and speciation in Lake Balaton, Hungary

The distribution and speciation of mercury in air, rain, lake water, sediment, and zooplankton in Lake Balaton (Hungary) were investigated between 1999 and 2002. In air, total gaseous mercury (TGM) ranged from 0.4 to 5.9 ng m(-3) and particulate phase mercury (PPM) from 0.01 to 0.39 ng m(-3). Higher concentrations of both TGM and PPM occurred during daytime. Higher concentrations of PPM occurred in winter. In rain and snow, total mercury ranged from 10.8 to 36.7 ng L(-1) in summer but levels up to 191 ng L(-1) in winter. Monomethylmercury (MMHg) concentrations ranged from 0.09 to 1.26 ng L(-1) and showed no seasonal variations. Total Hg in the unfiltered lake water varied spatially, with concentrations ranging from 1.4 to 6.5 ng L(-1). Approximately 70% of the total Hg is dissolved. MMHg levels ranged from 0.08 to 0.44 ng L(-1) as total and from 0.05 to 0.37 ng L(-1) in the dissolved form. Lower Hg concentrations in the water column occurred in winter. In suspended particulate matter and in sediment, total mercury ranged from 9 to 160 ng g(-1) dw, and MMHg ranged from 0.07 to 0.84 ng g(-1) dw. In zooplankton, an average mercury level of 31.0+/-6.8 ng g(-1) dw occurred, with MMHg accounting for approximately 17%. In sediments, suspended-matter- and zooplankton-high Hg and MMHg levels occurred at the mouth of the River Zala, but, in the lake, higher concentrations occurred on the Northern side, and an increasing trend from north-west to north-east was observed. In general, regarding Hg, Lake Balaton can be considered as a relatively uncontaminated site. The high-pH and well-oxygenated water as well as the low organic matter content of the sediment does not favour the methylation of Hg. In addition, bioconcentration and bioaccumulation factors are relatively low compared to other aquatic systems.     

Dissolved gaseous mercury formation under UV irradiation of unamended tropical waters from French Guyana

Filtered and non-filtered natural waters from French Guyana were irradiated with lamps emitting within the wavelength range 300-450 nm for 4 days with and without oxygen. Dissolved gaseous mercury (DGM) evolution was observed and quantified in the course of the irradiation. Measurements of total mercury in waters prior to and after the irradiations were also performed. The mass balance in the various mercury species (Hg(total), Hg(reactive) and DGM) proves the capability of the light to extract the mercury linked to the organic matter. DGM evolvement was greater in N2- than in air-saturated solutions, and the formation of volatile oxidized species can account for the inhibiting effect of oxygen. Filtration did not affect the mercury photoreduction, but reduced the formation of DGM in the dark. Great care has to be taken with regard to the following artifact: it was found that DGM originated not only from the natural waters, but also from the experimental device itself when exposed to the light. These non-expected DGM entries were quantitatively evaluated. This stresses the difficulty in measuring mercury at environmental concentrations.     

Atmospheric mercury depletion event study in Ny-Alesund (Svalbard) in spring 2005. Deposition and transformation of Hg in surface snow during springtime

A field campaign was conducted in Ny-Alesund (78 degrees 54'N, 11 degrees 53'E), Svalbard (Norway) during April and May 2005. An Atmospheric Mercury (Hg) Depletion Event (AMDE) was observed from the morning of April 24 until the evening of April 27. Transport of already Hg and ozone (O3) depleted air masses could explain this observed depletion. Due to a snowfall event during the AMDE, surface snow Hg concentrations increased two fold. Hg deposition took place over a short period of time corresponding to 3-4 days. More than 80% of the deposited Hg was estimated to be reemitted back to the atmosphere in the days following the event. During the campaign, we observed night and day variations in surface snow Hg concentrations, which may be the result of gaseous elemental mercury (GEM) oxidation to divalent Hg at the snow/air interface by daylight surface snow chemistry. Finally, a decrease in the reactive Hg (HgR) fraction of total Hg (HgT) in the surface snow was observed during spring. We postulate that the transformation of HgR to a more stable form may occur in Arctic snow during spring.     

Intercomparison study of atmospheric mercury models: 1. Comparison of models with short-term measurements

Five regional scale models with a horizontal domain covering the European continent and its surrounding seas, one hemispheric and one global scale model participated in an atmospheric mercury modelling intercomparison study. Model-predicted concentrations in ambient air were compared against mercury species observed at four monitoring stations in Central and Northern Europe and a station on the Irish west coast. The modelled concentrations of total particulate mercury (TPM) were generally consistent with the measurements at all sites. The models exhibited significant ability to simulate concentrations of gaseous elemental mercury (GEM), but some of the short-duration peaks at the Central European stations could not be consistently reproduced. Possible reasons for these discrepancies include (1) errors in the anthropogenic emissions inventory utilized; (2) coarse spatial resolution of the models; and (3) uncertainty of natural and re-emitted mercury sources. The largest discrepancies between measurements and modelled concentrations were found for reactive gaseous mercury (RGM). For these models, the uncertainty in predicting short-term (two-week episode) variations of mercury species in air can be characterized by the following overall statistics: 90% of the results for TGM are within a factor of 1.35 of the measurements; for TPM, 90% are within a factor of 2.5; and for RGM, 90% are within a factor of 10.     

Mercury distribution, speciation and flux in the Sepetiba Bay tributaries, SE Brazil

Dissolved gaseous Hg, reactive Hg, total dissolved Hg and particulate Hg concentrations were measured in samples of majors tributaries of the Sepetiba Bay, SE Brazil (Itimirim, Itingu?u, Guarda, Guandu, S?o Francisco and Ita rivers), in dry and rainy seasons. The average Hg concentrations found varied from 0.02 to 0.18 ng L(-1) for dissolved gaseous Hg, from 0.1 to 18.1 ng L(-1) for reactive Hg, from 0.1 to 66.6 ng L(-1) for total dissolved Hg and from 0.3 to 250 ng L(-1) for particulate Hg. During the rainy season, a decrease in the dissolved Hg concentrations and an increase in the particulate Hg concentrations was observed. Positive correlations were found between the reactive Hg and the total dissolved Hg concentrations (r = 0.99), between the particulate Hg and TSS concentrations (r = 0.82) and between total Hg and particulate Hg concentrations (r = 0.95). The instantaneous Hg fluxes varied among rivers from 0.02 to 412 microgs(-1) for total dissolved Hg and from 0.03 to 12,572 microgs(-1) for particulate Hg. The log Kd varied from 3.76 to 6.43 and showed a significant increase in rainy season following an increase in particulate Hg and a decrease in dissolved Hg concentrations. These results suggest that erosion and runoff are the major pathways of Hg transport to rivers and eventually to Sepetiba Bay.     

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.     

Scavenging of gaseous mercury by acidic snow at Kuujjuarapik, Northern Québec

One fate of gaseous elemental mercury (GEM) in the Arctic has been identified as gas phase oxidation by halogen-containing radicals, leading to abrupt atmospheric mercury depletion concurrent with ozone depletion. Rapid deposition of oxidized mercury leads to snow enrichment in mercury. In this report, we describe experiments that demonstrate the ability of snow to directly scavenge atmospheric mercury. The study was conducted at Kuujjuarapik, Québec, Canada (latitude 55 degrees 17'N). A mercury depletion event (MDE) caused the mercury concentration in the surface snow of the coastal snowpack to double, from (9.4+/-2.0) to (19.2+/-1.7) ng/L. Independent of the MDE, mercury concentrations increased five-fold, from (10.0+/-0.1) to (51.4+/-6.0) ng/L, upon spiking the snow with 500 microM hydrogen peroxide under solar irradiation. Total organic carbon in the spiked irradiated snow samples also decreased, consistent with the formation of strongly oxidizing species. The role of the snowpack in releasing GEM to the atmosphere has been reported; these findings suggest that snow may also play a role in enhancing deposition of mercury.     

Changes in the non-protein thiol pool and production of dissolved gaseous mercury in the marine diatom Thalassiosira weissflogii under mercury exposure

Two detoxification mechanisms working in the marine diatom Thalassiosira weissflogii to cope with mercury toxicity were investigated. Initially, the effect of mercury on the intracellular pool of non-protein thiols was studied in exponentially growing cultures exposed to sub-toxic HgCl₂ concentrations. T. weissflogii cells responded by synthesizing metal-binding peptides, named phytochelatins (PCs), besides increasing the intracellular pool of glutathione and γ-glutamylcysteine (γ-EC). Intracellular Hg and PC concentrations increased with the Hg concentration in the culture medium, exhibiting a distinct dose-response relationship. However, considerations of the PCs-SH:Hg molar ratio suggest that glutathione could also be involved in the intracellular mercury sequestration. The time course of the non-protein thiol pool and Hg intracellular concentration shows that PCs, glutathione and γ-EC represent a rapid cellular response to mercury, although their role in Hg detoxification seems to lose importance at longer incubation times. The occurrence of a process of reduction of Hg(II) to Hg° and subsequent production of dissolved gaseous mercury (DGM) was also investigated at lower Hg concentrations, at which the PC synthesis doesn't seem to be involved. The significant (P < 0.01) correlation between the cellular density in solution and the production of DGM suggests that this diatom is capable of directly producing DGM, both in light and dark conditions. This finding has been confirmed by the absence of DGM production in the culture media containing formaldehyde-killed cells. Finally, the relationship between these two different pathways of Hg detoxification is discussed.     

Atmospheric mercury speciation in Yellowstone National Park

Atmospheric concentrations of elemental mercury (Hg(0)), reactive gaseous Hg (RGM), and particulate Hg (pHg) concentrations were measured in Yellowstone National Park (YNP), U.S.A. using high resolution, real time atmospheric mercury analyzers (Tekran 2537A, 1130, and 1135). A survey of Hg(0) concentrations at various locations within YNP showed that concentrations generally reflect global background concentrations of 1.5-2.0 ng m(-3), but a few specific locations associated with concentrated geothermal activity showed distinctly elevated Hg(0) concentrations (about 9.0 ng m(-3)). At the site of intensive study located centrally in YNP (Canyon Village), Hg(0) concentrations did not exceed 2.5 ng m(-3); concentrations of RGM were generally below detection limits of 0.88 pg m(-3) and never exceeded 5 pg m(-3). Concentrations of pHg ranged from below detection limits to close to 30 pg m(-3). RGM and pHg concentrations were not correlated with any criteria gases (SO(2), NO(x), O(3)); however pHg was weakly correlated with the concentration of atmospheric particles. We investigated three likely sources of Hg at the intensive monitoring site: numerous geothermal features scattered throughout YNP, re-suspended soils, and wildfires near or in YNP. We examined relationships between the chemical properties of aerosols (as measured using real time, single particle mass spectrometry; aerosol time-of-flight mass spectrometer; ATOFMS) and concentrations of atmospheric pHg. Based on the presence of particles with distinct chemical signatures of the wildfires, and the absence of signatures associated with the other sources, we concluded that wildfires in the park were the main source of aerosols and associated pHg to our sampling site.     

Apparent rates of production and loss of dissolved gaseous mercury (DGM) in a southern reservoir lake (Tennessee, USA)

Apparent rates of dissolved gaseous mercury (DGM) concentration changes in a southern reservoir lake (Cane Creek Lake, Cookeville, Tennessee) were investigated using the DGM data collected in a 12-month study from June 2003 to May 2004. The monthly mean apparent DGM production rates rose from January (3.2 pg L(-1)/h), peaked in the summer months (June-August: 8.9, 8.0, 8.6 pg L(-1)/h), and fell to the lowest in December (1.6 pg L(-1)/h); this trend followed the monthly insolation march for both global solar radiation and UVA radiation. The monthly apparent DGM loss rates failed to show the similar trend with no consistent pattern recognizable. The spring and summer had higher seasonal mean apparent DGM production rates than the fall and winter (6.8, 9.0, 3.9, 5.0 pg L(-1)/h, respectively), and the seasonal trend also appeared to closely follow the solar radiation variation. The seasonal apparent DGM loss featured similar rate values for the four seasons (5.5, 4.3, 3.3, and 3.9 pg L(-1)/h for spring, summer, fall, and winter, respectively). Correlation was found of the seasonal mean apparent DGM production rate with the seasonal mean morning solar radiation (r=0.9084, p<0.01) and with the seasonal mean morning UVA radiation (r=0.9582, p<0.01). No significant correlation was found between the seasonal apparent DGM loss rate and the corresponding afternoon solar radiation (r=0.5686 for global radiation and 0.6098 for UVA radiation). These results suggest that DGM production in the lake engaged certain photochemical processes, either primary or secondary, but the DGM loss was probably driven by some dark processes.     

Diurnal variation of dissolved gaseous mercury (DGM) levels in a southern reservoir lake (Tennessee, USA) in relation to solar radiation

Variations of dissolved gaseous mercury (DGM) concentrations in a southern reservoir lake (Cane Creek Lake, Cookeville, TN, USA) in relation to solar radiation were investigated consecutively from June 2003 to May 2004. The daytime DGM levels in the lake exhibited a two-phase diurnal trend; the DGM concentrations rose in the morning, peaked around noontime and then fell in the afternoon through the evening; these trends followed the general pattern of diurnal solar radiation variations. The morning and afternoon phases appeared to be asymmetrical with the former relatively steep and the latter gradual. A variety of daytime DGM level variations other than the typical two-phase diurnal patterns were also observed. For the time spans studied, the daytime mean DGM concentrations of the lake ranged from 12 to 68 pg L(-1) (60-340 fM). The daytime mean DGM levels in the summertime (June, July, August) showed values above 30 pg L(-1) (150 fM) in most cases and a large number of peak DGM concentrations above 50 pg L(-1) (250 fM). The summer DGM levels in the lake appear to be comparable to those observed in the large northern lakes for the summertime. The daytime DGM levels in the lake were found to correlate with solar radiation to various degrees (cases of r values above 0.8: approximately 12% and approximately 18% of the total sampling days for correlation with global solar radiation and UVA radiation, respectively). Correlating trends are recognizable between the daytime mean DGM concentration and the corresponding mean global solar radiation (r = 0.66, p < 0.0005) and between the daytime mean DGM concentration and the corresponding mean UVA radiation (r = 0.62, p < 0.0005).     

Amazonian former gold mined soils as a source of methylmercury: evidence from a small scale watershed in French Guiana

Total mercury (HgT) and monomethylmercury (MMHg) were investigated in a tropical head watershed (1 km²) of French Guiana. The watershed includes a pristine area on the hill slopes and a former gold mined flat in the bottomland. Concentrations of dissolved and particulate HgT and MMHg were measured in rain, throughfall, soil water and at three points along the stream. Samples were taken in-between and during 14 storm events at the beginning and middle of the 2005 and 2006 rainy seasons. Dissolved and particulate HgT concentrations in the stream slightly increased downstream, while dissolved and particulate MMHg concentrations were low at the pristine sub-watershed outlet (median = 0.006 ng L⁻¹ and 1.84 ng g⁻¹, respectively) and sharply increased at the gold mined flat outlet (median = 0.056 ng L⁻¹ and 6.80 ng g⁻¹, respectively). Oxisols, which are dominant in the pristine area act as a sink of HgT and MMHg from rain and throughfall inputs. Hydromorphic soils in the flat are strongly contaminated with Hg (including Hg⁰ droplets) and their structure has been disturbed by former gold-mining processes, leading to multiple stagnant water areas where biogeochemical conditions are favorable for methylation. In the former gold mined flat high dissolved MMHg concentrations (up to 0.8 ng L⁻¹) were measured in puddles or suboxic soil pore waters, whereas high dissolved HgT concentrations were found in lower Eh conditions. Iron-reducing bacteria were suggested as the main methylators since highest concentrations for dissolved MMHg were associated with high dissolved ferrous iron concentrations. The connection between saturated areas and stagnant waters with the hydrographic network during rain events leads to the export of dissolved MMHg and HgT in stream waters, especially at the beginning of the rainy season. As both legal and illegal gold-mining continues to expand in French Guiana, an increase in dissolved and particulate MMHg emissions in the hydrographic network is expected. This will enhance MMHg bio-amplification and present a threat to local populations, whose diet relies mainly on fish.     

Atmospheric mercury near a chlor-alkali plant in Sweden

Atmospheric mercury species/fractions were measured near a chlor-alkali plant in Sweden during August 28 to September 4, 2001. The concentration of total gaseous mercury in the plume from the plant was measured using TEKRAN and GARDIS instruments. Gaseous elemental mercury was measured using a light detection and ranging (LIDAR) technique. From vertical LIDAR sweeps through the plume from the chlor-alkali plant mercury emission rates could be calculated. The concentrations of reactive gaseous mercury (RGM) in the plume and also inside the cell house were measured using annular KCl coated denuders. The RGM emission constitutes 0.5-1.0% of the total mercury emitted from the plant. The mercury concentration adsorbed on particles was measured as well as the mercury flux from soil. The data presented also include an intercomparison showing an excellent agreement between TEKRAN/GARDIS and LIDAR gaseous mercury measurements.     

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.     

Determination of nitroarenes in precipitation collected in Kanazawa, Japan

Eight nitroarenes, 1,3-, 1,6- and 1,8-dinitropyrenes, 1-, 2- and 4-nitropyrenes, 6-nitrochrysene and 2-nitrofluoranthene, in precipitation collected in Kanazawa were determined. The nitroarenes in the precipitation were concentrated onto solid phase extraction cartridges, and identified with high-performance liquid chromatography with chemiluminescence detection. The nitroarene concentrations in the precipitation were in the range 0.016-15 pmol/L, and the nitroarene composition tended to be the same as that in airborne particulates. 1-Nitropyrene in river water and seawater were also determined. 1-nitropyrene concentrations on the days after rain (19-110 fmol/L) were higher than those on the days before rain (4,11 fmol/L). Moreover, 1-nitropyrene concentrations in the river water were much lower than those in the precipitation, but were higher than those in the seawater. These results suggested that the nitroarenes in the precipitation and the river water came from airborne particulates.