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1.
During one year, samples from eight drainage lakes, seven run-off stations and three deposition sites from various geographical areas in Sweden were collected and analyzed for methyl Hg (MeHg) and total Hg (Hg-tot). The MeHg concentrations ranged from 0.04 to 0.64 ng L?1, 0.04 to 0.8 ng L?1, and <0.05 to 0.6 ng L?1 in run-off, lake water and rain water, respectively. The corresponding Hg-tot concentrations were found in the range 2 to 12 ng L?1, 1.35 to 15 ng L?1, and 7 to 90 ng L?1, respectively. A Hg-tot level of about 60 ng Hg L?1 was found in throughfall water. The MeHg and Hg-tot concentrations are positively correlated in both run-off and lake water, but not in rain and throughfall water. A strong positive correlation between the MeHg, as well as the Hg-tot concentration, and the water color is observed in both run-off and lake waters, which suggests that the transport of MeHg and other Hg fractions from soil via run-off water to the lake is closely related to the transport of organic substances; and is a consequence of the biogeochemical processes and the water flow pathway. The ratio between the mean values of MeHg and Hg-tot seems to be an important parameter, with an indicated negative coupling to the mean value of pH for run-off water, but a strong positive correlation to Hg-content in fish, the ratio between the area of the catchment and the lake, as well as to the retention time of lake.  相似文献   

2.
Mercury (Hg) was measured in stream water and precipitation in the Loch Vale watershed in Rocky Mountain National Park, Colorado, during 2001–2002 to investigate processes controlling Hg transport in high-elevation ecosystems. Total Hg concentrations in precipitation ranged from 2.6 to 36.2 ng/L and showed a strong seasonal pattern with concentrations that were 3 to 4 times higher during summer months. Annual bulk deposition of Hg was 8.3 to 12.4 μ g/m2 and was similar to deposition rates in the Midwestern and Northeastern U.S. Total Hg concentrations in streams ranged from 0.8 to 13.5 ng/L and were highest in mid-May on the rising limb of the snowmelt hydrograph. Stream-water Hg was positively correlated with dissolved organic carbon suggesting organically complexed Hg was flushed into streams from near-surface soil horizons during the early stages of snowmelt. Methylmercury (MeHg) in stream water peaked at 0.048 ng/L just prior to peak snowmelt but was at or below detection (< 0.040 ng/L) for the remainder of the snowmelt season. Annual export of total Hg in Loch Vale streams ranged from 1.2 to 2.3 μ g/m2, which was less than 20% of wet deposition, indicating the terrestrial environment is a net sink of atmospheric Hg. Concentrations of MeHg in stream water and corresponding watershed fluxes were low, indicating low methylation rates or high demethylation rates or both.  相似文献   

3.
Surface waters of the Scheldt Estuary were sampled on various occasions between 1991 and 1994. Longitudinal particulate Hg (PM) concentrations ranged from 0.4 – 1.7 μgHg/g and are essentially controlled by physical mixing of polluted fluvial particulates with relatively unpolluted marine particulates. Total dissolved mercury (TDM)concentrations ranged from 0.5 to 5.2 ng/L and are strongly influenced by removal and mobilization processes in the upper estuary, while in the lower estuary mixing processes cause a progressive decrease in TDM towards the mouth. Speciation studies showed that dissolved Hg is predominantly bound to strong complexing ligands (organic substances) in the upper estuary, but this fraction decreases with increasing salinity. In June 1993, however, the reactive mercury fraction was also high in the upper estuary. Model calculations showed that a conditional stability constant for Hg- humic acid interactions of 1019 was a good estimate for the Scheldt estuary. Dissolved methylmercury was analyzed on three occasions. Significant seasonal variations were observed with concentrations ranging from 11 to 120 pg/L in the winter and 80 to 400 pg/L in summer. Supersaturation of Hg° is observed throughout the whole estuary resulting in an estimated evasion flux of 140–1400 ng/m2 day.  相似文献   

4.
The sources and concentrations of total mercury (total Hg) and methylmercury (MeHg) in the upper catchment of the Lake Gordon/Lake Pedder system in Tasmania, Australia were investigated. The catchment area, which contains over 50% wetlands, is located in a temperate region with no obvious point sources of mercury. Surface waters in the region had concentrations of total Hg ranging from 1.2 to 14.4 ng L-1 and MeHg from < 0.04 to 1.4 ng L-1. MeHg concentrations were seasonally dependent, with the highest concentrations occurring in summer. Sediments/soils in the catchment had concentrations of total Hg ranging from 4.0 to 194 ng g-1 and MeHg from <0.02 to 20.1 ng g-1. The low concentrations of total Hg confirmed that this region is pristine as regards mercury and has no geological enrichment of total Hg. The highest total Hg and MeHg concentrations in both sediment/soils and waters were found in bogs whereas the lowest concentrations typically occurred on the wetlandplains. MeHg concentrations, in bog and swamp sediments were correlatedwith the organic matter content (r = 0.942, P < 0.001). Acid volatile sulfide (AVS) measurements indicate that in most sediments AVS was greater than total Hg. Given the high reactivity of inorganic mercury and sulfide, this suggests that most of the particulate mercury in sediments is present as mercuric sulfide. The yield of MeHg from the catchment was estimated to be 3.2 mg ha-1 yr-1 and is higher than published rates measured in non-contaminated temperate catchments in the northern hemisphere. The higher yield was attributed to the generally warmer climatic conditions that favour net methylation and the relatively high rainfall (2–3 m yr-1) of the region, which supplies reactive inorganic mercury to the active zones ofmercury methylation and also flushes MeHg from the catchment.  相似文献   

5.
The upper Great Egg Harbor River watershed in New Jersey’s Coastal Plain is urbanized but extensive freshwater wetlands are present downstream. In 2006–2007, studies to assess levels of total mercury (THg) found concentrations in unfiltered streamwater to range as high as 187 ng/L in urbanized areas. THg concentrations were <20 ng/L in streamwater in forested/wetlands areas where both THg and dissolved organic carbon concentrations tended to increase while pH and concentrations of dissolved oxygen and nitrate decreased with flushing of soils after rain. Most of the river’s flow comes from groundwater seepage; unfiltered groundwater samples contained up to 177 ng/L of THg in urban areas where there is a history of well water with THg that exceeds the drinking water standard (2,000 ng/L). THg concentrations were lower (<25 ng/L) in unfiltered groundwater from downstream wetland areas. In addition to higher THg concentrations (mostly particulate), concentrations of chloride were higher in streamwater and groundwater from urban areas than in those from downstream wetland areas. Methylmercury (MeHg) concentrations in unfiltered streamwater ranged from 0.17 ng/L at a forest/wetlands site to 2.94 ng/L at an urban site. The percentage of THg present as MeHg increased as the percentage of forest + wetlands increased, but also was high in some urban areas. MeHg was detected only in groundwater <1 m below the water/sediment interface. Atmospheric deposition is presumed to be the main source of Hg to the wetlands and also may be a source to groundwater, where wastewater inputs in urban areas are hypothesized to mobilize Hg deposited to soils.  相似文献   

6.
The importance of participate mercury (Hg(p)) in the transport, chemistry and deposition of this toxic metal has long been underestimated and largely ignored. While it was once believed to constitute a small percentage of total atmospheric mercury, Hg(p) may contribute a significant portion of the deposition of this metal to adjacent natural waters. Recent measurements of Hg(p) in several urban/industrial areas have documented that Hg can be associated with large particles (>2.5 μm) and in concentrations similar to those of the vapor phase Hg (ng/m3). As part of ongoing effort to diagnose the sources, transport and deposition of Hg to the Great Lakes and other Great Waters, the University of Michigan Air Quality Laboratory (UMAQL) has investigated the physical and chemical properties of particulate-phase Hg in both urban and rural locations. It appears that particulate Hg may be the one of the most difficult of the Hg measurements to perform, and perhaps the one of the most important for deposition and source apportionment studies. Particulate Hg concentrations measured in rural areas of the Great Lakes Region and Vermont ranged from 1 to 86 pg/m3 whereas Hg(p) levels in urban/industrialized areas were in the range 15 pg/m3 to 1.2 ng/m3.  相似文献   

7.
Total and dissolved concentrations of Hg and methyl-Hg (MeHg) were determined in the surface waters of 19 northern Wisconsin lakes under ice-cover when differences due to temperature, hydrology, productivity, and atmospheric exchange were minimal. Measured concentrations ranged from 0.3 to 5.3 ng/L for HgT and from 0.01 to 2.8 ng/L for MeHgT. Dissolved species comprised 30% to 95% of the HgT and MeHgT. MeHg was strongly correlated with Hg for both total and dissolved fractions. Thirteen ancillary constituents were measured in conjunction with the Hg determinations (pH, DOC, DIC, DO2, conductivity, suspended particulate matter (SPM), Ca, Mg, Mn, Fe, Na, SO4, Cl). Simple linear regressions indicated that DOC explained 87% of the variability in HgT and 79% of the variability in MeHgT. Of the other measured variables, pH, DO2, Fe and Mn showed weak but significant simple correlations with Hg and MeHg (@ p < 0.05). Multiple regression models containing two independent variables, (DOC and pH), explained 92% of the variability in HgT and 83% of the variability in MeHgT. Models containing DOC alone fit the dissolved Hg data well. We conclude that organic carbon concentrations have a strong effect on the concentrations of Hg and MeHg in these lakewaters.  相似文献   

8.
Three months after neutralization concentrations of methylmercury (MeHg) were higher in the water of the limed than in the control basin of a small lake. After two years, the concentrations in the limed basin were somewhat lower than in the control (0.056–2.19 ng L?1 and 0.129–2.65 ng L?1, respectively). The highest concentrations were found in the anoxic hypolimnia. The total amount of MeHg in the water mass of the lake varied from 19 to 68 mg, showing a drop after spring and autumn overturns and a maximum during stratification periods. The total Hg concentrations of fish in L. Iso Valkjärvi varied from 0.06 to 0.14 μg g?1 (ww) in whitefish to 0.1 to 0.7 μg g?1 in perch and to 0.2 to 1.4 μg g?1 in pike. The total amount of MeHg bound in the fish of the lake was quite similar to that in the water column, 43 to 59 mg in 1990–1993, 33 to 47 mg of which was in the perch population.  相似文献   

9.
Ambient concentrations and dry deposition fluxes of Hg in the gas and particle phase to Lakes St. Clair, Erie and Huron were estimated with a hybrid receptor-deposition model (HRD). The ambient gas and particulate phase Hg concentrations were predicted to vary by a factor of 12 to 18 during the transport of air masses traversing the lakes. The ensemble average deposition fluxes of fine particle Hg ranged from 7 pg/m2-h to 15.3 pg/m2-h over Lake St. Clair, 0.5 to 4.2 pg/m2-h over Lake Huron and 5.1 to 20.6 pg/m2-h over Lake Erie. The deposition flux of coarse particle Hg was in the range of 50 to 84 pg/m2-h over Lake St. Clair, 4.7 to 24.2 pg/m2-h over Lake Huron and 5.1 to 20.6 pg/m2-h over Lake Erie. Gaseous Hg volatilized at a rate of 0.21 to 0.52 ng/m2-h from Lake Huron and 0.13 to 0.36 from Lake Erie. Gas phase Hg was deposited at a rate of 5.9 ng/m2-h and/or volatilized at a rate of 0.5 ng/m2-h from Lake St. Clair depending upon the location of the sampling site used in the HRD model. The effect of meteorological conditions, particle size distributions and type and location of the sampling sites played an important role in the transfer of atmospheric Hg to and/or from the lakes.  相似文献   

10.
The processes affecting the concentrations of total mercury (total Hg) and methylmercury (MeHg) in a freshwater system comprising two connected reservoirs in southwest Tasmania were investigated. Surface concentrations of total mercury (total Hg)were temporally and spatially uniform in both Lake Gordon (2.3±0.4 ng L-1, n = 27) and Lake Pedder (2.3±0.3 ng L-1, n = 11). The surface concentrations of MeHg in Lake Gordon (0.35±0.39 ng L-1, n = 25) were more variable than total Hg and MeHg typically comprised 10–20% of total Hg. The relatively high amount of total mercury present as MeHg in Lake Gordon was attributed to the high proportion of wetlandsin the upper catchment (50% of total area) and in-lake contributions (ca. 40% of total MeHg). Despite the close proximity of the two lakes, MeHg concentrations in Lake Pedder were consistently lower than in Lake Gordon. This phenomenon canbe explained in part by the greater contribution of direct rainfall to Lake Pedder leading to the dilution of MeHg. Water column MeHg concentrations were higher in warmer months in bothlakes, reflecting increased net methylation of inorganic mercury.Unlike previous studies of seasonally anoxic lakes, depth profiles of total mercury and MeHg in Lake Gordon were uniform and were not affected by water column stratification occurringin the summer months, and oxygen depletion with depth. This suggests that redox cycling and accumulation of MeHg in the hypolimnion following seasonally-induced anoxia is not a significant part of the mercury cycle in Lake Gordon. The primary location of MeHg production within the lake's water column is not conspicuous. Mercury speciation measurements made above and below the lake system over a period of 19 months indicates that after 20 yr of impoundment, the reservoirs are not significantly affecting MeHg concentrations in the downstreamriverine environment.  相似文献   

11.
The speciation of mercury (Hg) in Minamata Bay (Japan) was studied over a 2-year period (2006?C2008). Concentrations of dissolved total Hg, dissolved methylmercury (MeHg), particulate total Hg, and suspended solids were 0.43?±?0.14 ng/l (mean?±?standard deviation), 0.10?±?0.06 ng/l, 3.04?±?2.96 ng/l, and 5.94?±?2.10 mg/l, respectively. Correlations between concentrations of particulate total Hg and suspended solids at four depths (surface: 0 m; mid-depth: ?6 m, ?10 m; and bottom +1 m layer) were only significant in the bottom +1 m layer. The mean dissolved MeHg concentration and the ratio of dissolved MeHg to dissolved total Hg were considerably higher in summer compared to other seasons. The data suggest that bottom sediment was not the sole source of MeHg, and that MeHg may be produced in the water column by the conversion of divalent Hg eluted from resuspended bottom sediment. The correlation between seawater characteristics such as salinity, temperature, dissolved oxygen (DO), and dissolved MeHg concentration indicates that Hg methylation could be influenced by the heterotrophic activity of microorganisms in the seawater. In particular, inverse correlations were observed between DO, salinity, and MeHg concentration. However, dissolved MeHg concentrations did not correlate with seawater characteristics such as pH or chlorophyll-a.  相似文献   

12.
In the early 1980's the Amazon region in the North of Brazil was the scene of the most intense gold rush in the history of Brazil. Metallic mercury (Hg) in gold mining activities is used to amalgamate particulate gold. The other sources of Hg emissions in Amazonian are tailing deposits and biomass burning of tropical forests and savannas. Total Hg concentrations in the urban area of Alta Floresta ranged from 20 to 5800 ng/m3. Indoor total Hg concentration in gold shops ranged from 250 to 40600 ng/m3. Particulate Hg accounts for 5 to 20% of total Hg in Alta Floresta. Through Factor and cluster analysis it was obtained a pattern of relationships between total Hg, fine and coarse mode particulate Hg, Pt, Pb, Ag and several other trace elements associated with the amalgamation process. A clear correlation was also observed with the fine mode biomass burning aerosol and coarse mode soil dust.  相似文献   

13.
An intensive multi-site pilot study of atmospheric Hg was conducted in Broward County, Florida in August and September of 1993. Broward County, which contains the city of Fort Lauderdale, is located in southeastern Florida. The county borders the Florida Everglades on the west and the Atlantic Ocean on the east. A network of four sampling sites was set up for 20 days throughout Broward County to measure Hg in both the vapor phase and the particle phase as well as Hg in precipitation. The mean concentrations of total vapor phase Hg measured at two inland sites were found to be significantly higher (3.3 and 2.8 ng/m3) than that measured at a site located on the Atlantic shore (1.8 ng/m3). The mean concentrations of particle phase Hg collected at the two inland sites (51 and 49 pg/m3) were found to be 50% greater than that measured at the coastal site (34 pg/m3). In addition, event precipitation samples were collected at four sampling sites over the 20 day study period and were analyzed for both reactive and total Hg. The mean concentration of total Hg in the precipitation samples was found to be 44 ng/L, with a range of 14 to 130 ng/L. It was determined that further meteorological analysis and a more complete characterization of the aerosol and precipitation composition are needed to identify the probable source(s) contributing to the increased deposition of Hg.  相似文献   

14.
This study investigated the spatialand seasonal variations of MeHg concentrations andburdens of different sediments and soils of theTapajós river floodplain, one of the majorclear-water tributaries of the Amazon. The smallfloodplain of the Tapajós is typical of Amazonianfloodplain ecosystems. The studied lakes are borderedby inundated forest (igapó), while floatingmacrophyte mats (Paspalum sp.) develop at themargin of lakes during the flooded season. During theflood, we observed very low MeHg concentrations in theopen water lake sediments (<0.5 ng g-1 d.w or<0.5 μg m-2 cm-1 d.w.) as compared to thesemi-aquatic sediments of the macrophyte zone (0.2–1.4 ng g-1 d.w or 1–3 μg m-2cm-1 d.w.) and the igapó semi-terrestrial soils (0.2–3 ng g-1 d.w or2–12 μg m-2 cm-1 d.w.). The litter horizon fromthe igapó soils showed the highest value of MeHg(4–8 ng g-1 d.w.) representing 0.2–2 μg m-2cm-1 d.w. at the sediment/water interface during theaquatic phase. The inundation had no effect on theconcentrations and burdens of MeHg in the sediment ofthe central part of the lake. The inundation had aclear effect on the methylation of Hg at the surfaceof semi-aquatic shoreline sediments (macrophyte zone)and semi-terrestrial forest soils, where MeHgconcentrations and burdens appeared to be 3 timesgreater following inundation. In all cores, total Hgconcentrations follow those of Fe and Aloxy-hydroxides, whereas the MeHg concentrations arelinked to organic matter quality and quantity. It issuggested that organic matter and inundation controlMeHg production and accumulation at the benthicinterface. These results confirm previousobservations, in the same study area, of net203Hg methylation potentials. The fresh andlabile organic matter in the litter of the igapóforest appears as the most important factor leading tosignificant enrichment of MeHg in these particularterrestrial/aquatic sedimentary environments.  相似文献   

15.
Mercury content and speciation were determined in freshwater zooplankton from twelve northern Wisconsin (USA) lakes that spanned gradients of dissolved organic carbon (DOC, 1.6 to 20.9 mg/L) and pH (4.6 to 7.2). MeHg in crustacean taxa ranged from 1 to 479 ng/g dry weight, and from 2 to 45 ng/g in the invertebrate predators. Total Hg in the predators ranged from 20 to 153 ng/g. Although the highest MeHg values were found in the herbivores from high DOC lakes (and the experimentally acidified basin of Little Rock Lake), we observed considerable variation in the relationship between MeHg content of zooplankton and lakewater DOC. Bioconcentration factors (BCF) for both MeHg (3.5 to 7.1 log units) and Hg (3.7 to 5.4 log units) decreased with increasing lake DOC, while pH effects were not as apparent. Bioconcentration of MeHg was higher than Hg indicating that MeHg increases while non-methyl Hg declines in progressively higher trophic levels. Biomagnification factors (BMF) for Hg and MeHg were low relative to BCF. The BMF for crustaceans averaged 0.4 log units for MeHg and ?0.5 log units for Hg, indicating that MeHg increased 2.5-fold from seston to crustacean herbivores, while non-MeHg concentrations declined. Unlike BCF, BMF were not related to DOC or pH. In contrast to studies of vertebrate predators, both BCF and BMF in the invertebrate predatorChaoborus, were lower than those in presumed prey. These observations point toward several complexities in the transport of Hg species in the lower levels of aquatic foodwebs.  相似文献   

16.
Food as the Dominant Pathway of Methylmercury Uptake by Fish   总被引：1，自引：0，他引：1  
A field experiment was conducted to determine the degree to which fish accumulated methylmercury (MeHg) via their food or via passive uptake from water through the gills. Finescale dace (Phoxinus neogaeus) were held in 2000 L enclosed pens floating in an undisturbed, oligotrophic lake in northwestern Ontario. Fish were exposed to water containing either low (0.10–0.40 ng L-1), intermediate (0.45–1.30 ng L-1), or high (0.80–2.1 ng L-1) concentrations of MeHg. Zooplankton with either low (0.16–0.18 µg g-1 d.w.) or high (0.28–0.76 µg g-1 d.w.) concentrations of MeHg were added daily to each pen. Fish fed zooplankton with high concentrations of MeHg had significantly higher concentrations of mercury in muscle after 32 days than fish fed zooplankton with low concentrations of MeHg (ANCOVA, P<0.0001). Fish feeding on zooplankton with low concentrations of MeHg had the same amount of Hg in their tissues as fish at the start of the experiment. Uptake from water was at most 15%. This is the first experiment to confirm that food is the dominant pathway of MeHg bioaccumulation in fish at natural levels of MeHg.  相似文献   

17.
The effect of soil flooding on methylmercury (MeHg) production was studied by placing humus and peat with water in 40 liter vessels. Total mercury (Tot-Hg), MeHg, nutrients, total organic carbon (TOC) and color were measured in water. Potential mercury methylation and demethylation rates in water and in flooded soils (humus and peat) were measured using radiochemical methods under aerated and non-aerated conditions during a period of 117 days. In general, the potential methylation in humus and peat were one order of magnitude higher than in the water phase. During the experiment, methylation increased in humus and in peat but decreased in water. Demethylation decreased in all compartments. Anoxis increased methylation in soils but not in the water phase. On the other hand, demethylation was clearly higher in anoxic conditions. Tot-Hg increased more rapidly than MeHg in the water of the vessels, and a more rapid MeHg increase was observed in peat vessels than in humus vessels. Highest concentrations of MeHg (5.42 ng/L peat, 7.98 ng/L humus) were measured in non-aerated vessels. Water color correlated negatively with methylation in water but positively with MeHg concentrations, indicating that humic substances are the main MeHg carriers but are not active melhylating agents. Methylmercury fluxes to water (3.6–44 ng/m2*d) were of the same order of magnitude as those measured in field experiments in Canada and in a beaver lake in Finland but were notably higher than those fluxes from unflooded catchmets. The results indicate that increased net methylation in flooded humus and peat soils, especially in anoxic conditions, is the main reason for increased MeHg concentrations in reservoirs.  相似文献   

18.
Onondaga Lake, New York, is a hypereutrophic, urban lake that was subjected to industrial discharges of mercury (Hg) between 1947 and 1988. Water samples were collected from April through November 1992 and analyzed for filtered and unfiltered total Hg, methylmercury (CH3Hg), dimethylmercury, ionic Hg, and elemental Hg to characterize the biogeochemical cycling of Hg during water column stratification and hypolimnetic anoxia. In the spring and late fall when the water column was isothermal, total Hg and CH3Hg concentrations were relatively constant throughout the water column, at approximately 3–7 ng/L and 0.3–1 ng/L, respectively. Through the summer and early fall, CH3Hg concentrations systematically increased in the deeper waters, reaching peak concentration in August and September. In September 1992, CH3Hg concentrations increased from 0.3 ng/L in the epilimnion to 10.6 ng/L in the hypolimnion, an increase of nearly 2 orders of magnitude. At the same time, total Hg increased from 6.6 ng/L in surface water to 21.7 ng/L at depth, a 3-fold increase. The spatial and temporal patterns observed for CH3Hg agree well with manganese, suggesting that CH3Hg and manganese are controlled by processes of the same or parallel cycles.  相似文献   

19.
The “Great Waters” program, established in the 1990 Clean Air Act Amendments, mandated that atmospheric deposition of hazardous air pollutants to Lake Champlain (including Hg) be assessed. An assessment of the magnitude and seasonal variation of atmospheric Hg deposition in the Lake Champlain basin was initiated in December 1992 with one year of event precipitation collection, as well as collection of vapor and particle phase Hg in ambient air. Samples were collected at the Vermont Monitoring Cooperative air monitoring site at the Proctor Maple Research Center in Underhill Center, VT. The average volume-weighted concentration for Hg in precipitation was 8.3 ng/L for the sampling year and the average amount of Hg deposited with each precipitation event was 0.069 μg/m2. The total amount of Hg deposited through precipitation during 1993 was 9.26 μg/m2/yr. A seasonal pattern for Hg in precipitation was evident, with increased concentrations and deposition during spring and summer months. Meteorological analysis indicated the highest levels of Hg in precipitation were associated with regional transport from the south regardless of season, and with transport from the west, southwest and northwest during spring and summer months. Concentrations of ambient vapor phase Hg were typical of rural locations and consistent across seasons. Ambient particulate Hg concentrations averaged 11 pg/m3 with highest concentrations during the winter months.  相似文献   

20.
Dissolved and particulate Hg speciation was determined on four occasions in the Spring to Fall interval of 1989, at three depths of the water column of Onondaga Lake, New York; an urban system in which the sediments and fish flesh are contaminated with Hg. Species determined included total Hg (Hgt), reactive (‘ionic’) Hg (Hgi), monomethylmercury (CH3HgX), elemental Hg (Hg°) and dimethylmercury (CH3)2Hg). Onondaga Lake was found to contain very high levels of Hgt (2 to 25 ng L?1 Hg), Hgj (0.5 to 10 ng L?1 Hg), and CH3HgX (0.3 to 7 ng L?1 Hg), which generally increased with depth in the lake. These concentrations represent a significant level of contamination, based upon comparisons with other polluted and pristine sites. Elemental Hg levels were typically about 0.05 ng L?1 and (CH3)2Hg was near the limits of detection (?0.001 ng) L?1 in most samples. The greatest CH3HgX concentrations in the hypolimnion, as well as the largest gradients of both CH3HgX and (Hgt), were observed upon the first onset of stratification, in early summer. These concentrations did not become more pronounced, however, as stratification and H2S levels in the hypolimnion increased throughout the summer. The very low concentrations of (CH3)2Hg in these MeHg and sulfide-rich waters calls into question the belief that CH3HgX and H2S will react to yield volatile dimethyl-mercury, which can then escape to the atmosphere by diffusion. Mercury speciation was highly dynamic, indicating active cycling within the lake, and an apparent sensitivity to changes in attendant Iimnological conditions that track the stratification cycle.  相似文献   

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