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.     

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.     

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.     

Dissolved gaseous mercury production in the dark: Evidence for the fundamental role of bacteria in different types of Mediterranean water bodies

It is well established that the dissolved gaseous mercury (DGM) production in waters is mainly driven by photochemical processes. The present paper provides evidence for a significant bacteria-mediated DGM production, occurring also under dark conditions in environmentally different types of coastal water bodies of the Mediterranean basin. The DGM production was laboratory determined in sea, lagoon-brackish and lake water samples, comparing the efficiency of the DGM production processes in darkness and in the light. This latter condition was established by exposing samples at solar radiation intensity in the Photosyntetical Active Radiation region (PAR) of 200 W m^− 2. Mercury reduction rate in the dark was of the order of 2-4% of the DGM production in lightness, depending on the total mercury concentration in the water, rather than the bacterial abundance in it. Support for the active bacterial role in mercury reduction rate under dark conditions was provided by: 1) absence of significant DGM production in sterilized water samples (following filtration treatment or autoclaving), 2) restored DGM production efficiency, following re-inoculation into the same water samples of representatives of their bacterial community, previously isolated and separately cultured. Notwithstanding the low bacteria-mediated vs. the high photo-induced DGM production, whatever natural water body was considered, it is worth stressing the significant contribution of this organismal-mediated process to oceanic mercury evasion, since it occurs continuously along the entire water column throughout the 24 h of the day.     

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 speciation and exchanges at the air-water interface of a tropical artificial reservoir, French Guiana

The distribution and speciation of mercury (Hg) in air, rain, and surface waters from the artificial tropical lake of Petit-Saut in French Guiana were investigated during the 2003/04 period. In the air, total gaseous mercury (TGM) at the dam station averaged 12+/-2 pmol m(-3) of which >98% was gaseous elemental mercury (GEM). GEM distribution depicted a day-night cycling with high concentrations (up to 15 pmol m(-3)) at dawn and low concentrations (down to 5 pmol m(-3)) at nightfall. Reactive gaseous mercury (RGM) represented <1% of the GEM with a mean concentration of 4+/-3 fmol m(-3). Diel RGM variations were negatively related to GEM. In the rain, the sum of all Hg species in the unfiltered (HgT(UNF)) averaged 16+/-12 pmol L(-1). Temporal distribution of HgT(UNF) exhibited a pattern of high concentrations during the late dry seasons (up to 57.5 pmol L(-1)) and low concentrations (down to 2.7 pmol L(-1)) in the course of the wet seasons. Unfiltered reactive (HgR(UNF)), dissolved gaseous (DGM) and monomethyl (MMHg(UNF)) Hg constituted 20, 5 and 5% of HgT(UNF), respectively. All measured Hg species were positively related and displayed negative relationships with the pH of the rain. In the reservoir surface waters, dissolved total mercury (HgT(D)) averaged 3.4+/-1.2 pmol L(-1) of which 10% consisted of DGM. DGM showed a trend of high concentrations during the dry seasons (480+/-270 fmol L(-1)) and lower (230+/-130 fmol L(-1)) in the course of the wet seasons. Diel variations included diurnal photo-induced DGM production (of about 60 fmol L(-1) h(-1)) coupled to minute to hour oxidation/reduction cycles (of >100 fmol L(-1) amplitude). Finally, calculated atmospheric Hg inputs to the Petit-Saut reservoir represented 14 mol yr(-1) whereas DGM evasion reached 23 mol yr(-1). Apportionment among forms of Hg deposition indicated that up to 75% of the total Hg invasive flux follows the rainfall pathway.     

Sediment mercury dynamics and historical trends of mercury deposition in the St. Lawrence River area of concern near Cornwall, Ontario, Canada

The St. Lawrence River near Cornwall, Ontario was designated an Area of Concern by the International Joint Commission in 1985. Sediments from this area have historically been contaminated with mercury (Hg), and although concentrations have decreased since the 1970s, they still remain high. Nine sediment cores were collected from three sites within the Area of Concern in 2004/05 to determine the variability in historical profiles of Hg deposition to the river. Sediment and pore water phases were analyzed for total mercury (THg) and methyl mercury (MeHg) and cores were analyzed for ²¹⁰Pb to determine chronologies of sedimentation at these sites. Mercury diffusion rates in pore waters within the sediment column were determined to be very low (between 0 and 2.15 ng cm^− 2 year^− 1, n = 3) compared to the recent Hg sedimentation rates at these sites (183 ± 30 ng cm^− 2 year^− 1 SE, n = 9) determined by multiplying surface Hg concentrations with ²¹⁰Pb-derived sedimentation rates. These results indicate that Hg profiles in these cores accurately depict historical releases of Hg to the river bed. The influence of federal regulations in the early 1970s to restrict Hg emissions to the river was apparent in these dated sediment cores, as were the closures of several local industries in the mid 1990s. Mercury accumulation rates prior to 1970 were 60 times higher than those occurring after 1995. Methyl mercury showed surface enrichment in most of these sediment cores providing evidence that mercury methylation occurred most rapidly near the sediment surface.     

Wetland influences on mercury transport and bioaccumulation in South Carolina

There are three distinct geological provinces in South Carolina (SC), with the blue ridge/piedmont regions in the west/central portion of the state and the coastal plain region in the central/eastern region of the state. Samples were collected along this gradient to identify potential factors contributing to the concentrations of total Hg and total organic carbon (TOC) throughout the state. Overall, there is a gradient across the state, with water column concentrations of total Hg (9-53 pM) and TOC (80-2721 μM) increasing as one moves from the blue ridge/piedmont region to the coastal floodplain region. Total Hg at all sites in SC is significantly (R² = 0.78; P < 0.001) correlated with TOC in the water samples. This correlation explains 78% of the variance in the data and suggests that mercury is associated with organic matter in water bodies throughout the state. A study of mercury speciation within the coastal plain Waccamaw River indicates that concentrations of total Hg range from 10-68 pM and methyl Hg concentrations range from 1-7 pM. Watershed transport efficiencies for coastal floodplain rivers sampled in this study range from 32-72% for total Hg and 78-477% for methyl Hg. The coastal plain sites are located in watersheds that contain a significantly (P < 0.001) higher percentage of wetlands (16.3 ± 5%) than the blue ridge/piedmont region (1.14 ± 1.6%), suggesting that drainage through wetlands contributes to the increased concentrations of TOC and total Hg found in SC coastal plain rivers. There is a significant correlation between mean fish Hg concentrations in largemouth bass from each watershed and percent wetland area in each watershed (R² = 0.66; P = 0.003). This correlation explains 66% of the variance in the data and suggests that increasing percentages of wetland area contribute to fish Hg concentrations in SC coastal plain rivers.     

An evaluation of teeth of ringed seals (Phoca hispida) from Greenland as a matrix to monitor spatial and temporal trends of mercury and stable isotopes

Total mercury (Hg) concentrations were measured in teeth of ringed seals from Qeqertarsuaq, central West Greenland (1982 to 2006) and Ittoqqortoormiit, central East Greenland (1986 to 2006). Stable isotopic ratios of carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N) were determined as well to provide insights into diet variations between regions or through time. Mercury concentrations decreased the first years of life of the animals suggesting that Hg had been transferred from the mother to the foetus and newborn. The Hg concentrations in teeth were significantly lesser in ringed seals from central West Greenland compared to those from central East Greenland. Carbon and nitrogen stable isotopic values measured in the animals differed also significantly between the two regions. Increasing temporal trends of dental Hg concentrations between 1994 and 2006 were observed in ringed seals from both central West Greenland and central East Greenland. These increases were attributed to global changes in environmental Hg levels since no temporal trends in δ¹⁵N values were found to support the hypothesis of a diet shift over time. Furthermore, a decreasing temporal trend in δ¹³C values was observed in the teeth of seals from central East Greenland, and explained by a likely change over time towards more pelagic feeding habits; alternatively, the so-known Seuss effect was thought to be responsible for this decrease. Finally, it was concluded that the tooth of ringed seal was a good monitoring tissue to assess Hg trends.     

Human exposure to heavy metals in East Greenland I mercury

The concentration of mercury in 178 blood samples and 32 hair samples from the Angmagssalik district in East Greenland has been determined.For Greenlanders mercury concentrations are highly dependent on the amount of seal eaten. In the most heavily exposed group (eating more than six meals of seal per week), a significant positive correlation between blood mercury and age was demonstrated. No differences according to sex were demonstrated when the mean values were corrected for influence of age. In the most heavily exposed group, a mean value of 62.5 μg Hg/l was found, while in the group eating 1 meal of seal or less per week, the mean value was 22.2 μg Hg/l. In the control group consisting of Danes living temporarily in the district, the mean blood mercury concentration was 5.8 corresponding to the fact that they eat seal only occasionally.Hair mercury concentrations were found to correlate well with blood mercury concentrations (r = 0.9222). The hair/blood ratio was estimated to 289.It is concluded that the present relatively high mercury exposure in Greenland does not excert any immediate risk of intoxication to the adult population, but supplementary investigation on fetal exposure is needed.     

Perinatal lead and mercury exposure in Austria

Objective

The heavy metals lead (Pb) and mercury (Hg) are ubiquitous environmental pollutants with high neurotoxic potential. We aimed to compare perinatal Pb and Hg concentrations and to explore the potential association between Pb and Hg exposure and newborn anthropometry.

Study design

Pregnant women were recruited in 2005 at the General Hospital Vienna for participation in this longitudinal study. Pb and Hg concentrations were measured in maternal blood and hair, placenta, cord blood, meconium, and breast milk of 53 mother-child pairs by CV-AAS, GF-AAS, and HPLC-CV-ICPMS. We conducted bivariate analyses and categorical regression analysis (CATREG) to evaluate the determinants of Pb and Hg exposure, and of infant anthropometry.

Results

Median Pb and total Hg contents were low, i.e., 25 μg/L (maternal blood-Pb), 13 μg/L (cord blood-Pb), 0.7 μg/L (maternal blood-Hg), and 1.1 μg/L (cord blood-Hg). Hg levels in maternal and fetal tissues were frequently correlated (r > 0.3, P < 0.05, respectively). Regarding Pb, only maternal blood and cord blood concentrations correlated (P = 0.043). Cord blood levels indicated higher Hg exposure but lower Pb exposure relative to maternal blood contents. Adjusted CATREG models indicated the significant predictors of birth length (placenta-Pb, gestational length, meconium-Pb), birth weight (placenta-Pb, gestational length, maternal blood-Pb), and head circumference (maternal education, maternal height). Besides one significant correlation between maternal hair Hg and birth length, the mercury levels were not associated with newborn anthropometry.

Conclusions

Our data implicate that different modes of action may exist for placentar transfer of Pb and Hg as well as that low Pb exposure levels can result in lower birth weight. The findings related to newborn anthropometry need to be confirmed by the examination of larger study groups. Further research is needed to clarify the mechanisms of Pb and Hg transfer via the placenta, and to explore how prenatal Pb exposure is related to intrauterine growth.     

Continuous analysis of dissolved gaseous mercury in freshwater lakes

The concentration of dissolved gaseous mercury (DGM) in freshwaters changes more quickly than the 40-min processing time of current analytical methods. A new method for continuous field analysis of DGM was developed using a Tekran 2537A to achieve a DGM analysis time of 5 min. Samples were concurrently analyzed for temperature, oxygen, conductivity, pH, and oxidation-reduction potential using a Hydrolab. The detection limit for DGM ranged between 5 and 20 fmolL(-1) with 99% removal efficiency. Control experiments showed that there was no interference due to methyl mercury, which is present in similar concentrations to DGM. Controlled experiments comparing continuous DGM analysis with discrete DGM analysis showed that the results are not significantly affected by typical variations in water temperature (4-30 degrees C), oxidation-reduction potential (135-355 mV), dissolved organic carbon (4.5-10.5 mgL(-1)), or pH (3.5-7.8). The continuous analysis was within 4.5% of the discrete analysis when compared across 12 samples analyzed in triplicate. The field performance of this method was tested over two 48-h periods in two lakes in Kejimkujik Park, Nova Scotia where over 1000 data points were collected.     

Simulated rain events on an urban roadway to understand the dynamics of mercury mobilization in stormwater runoff

This research focuses on mercury (Hg) mobilization in stormwater runoff from an urban roadway. The objectives were to determine: how the transport of surface-derived Hg changes during an event hydrograph; the influence of antecedent dry days on the runoff Hg load; the relationship between total suspended sediments (TSS) and Hg transport, and; the fate of new Hg input in rain and its relative importance to the runoff Hg load. Simulated rain events were used to control variables to elucidate transport processes and a Hg stable isotope was used to trace the fate of Hg inputs in rain. The results showed that Hg concentrations were highest at the beginning of the hydrograph and were predominately particulate bound (HgP). On average, almost 50% of the total Hg load was transported during the first minutes of runoff, underscoring the importance of the initial runoff on load calculations. Hg accumulated on the road surface during dry periods resulting in the Hg runoff load increasing with antecedent dry days. The Hg concentrations in runoff were significantly correlated with TSS concentrations (mean r² = 0.94 ± 0.09). The results from the isotope experiments showed that the new Hg inputs quickly become associated with the surface particles and that the majority of Hg in runoff is derived from non-event surface-derived sources.     

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).     

Detoxification of selenite and mercury by reduction and mutual protection in the assimilation of both elements by Pseudomonas fluorescens

A study on the assimilation and detoxification of selenium and mercury and on the interaction between these two elements was conducted on Pseudomonas fluorescens. P. fluorescens was able to convert separately both elements to their elemental forms, which are less toxic and biologically less available. To study the converting mechanism of selenite to elemental Se, cells were grown in the presence of various selenite concentrations and several parameters such as extracellular protein concentrations, pH, carbohydrate concentrations, isocitrate dehydrogenase (ICDH) and malic enzyme were monitored. Transmission electron microscopy (TEM) and various analytical methods were applied to confirm the interaction between selenium and cell. The former appeared as a red precipitate localized predominantly in the consumed culture medium. P. fluorescens also resisted to the toxic effect of mercury by converting Hg2+ to the volatile and less toxic form Hg0. Mercury reductase was likely responsible for the conversion of Hg2+ to Hg0. More importantly, the interaction between mercury and selenium was also studied. The presence of selenite significantly reduced the accumulation of mercury in P. fluorescens. It was also interesting to note that mercury appeared to behave as a protecting agent against selenium intoxication as the bioaccumulation of Se was also inhibited by this metal. The formation of Se-Hg complexes could explain this mutual protective effect. No precipitate of elemental Se could be detected when Hg was present in the cultures.     

Biostrome communities and mercury and selenium bioaccumulation in the Great Salt Lake (Utah, USA)

The Great Salt Lake has a salinity near 150 g/L and is habitat for over 200 species of migratory birds. The diet of many of these birds is dependent on the food web of carbonaceous biostromes (stromatolites) that cover 260 km² of the lake's littoral zone. We investigated the biostrome community to understand their production processes and to assess whether they are a potential vector for bioconcentration of high mercury and selenium levels in the lake. The periphyton community of the biostromes was > 99% colonial cyanobacteria. Periphyton chlorophyll levels averaged 900 mg m⁻² or nine times that of the lake's phytoplankton. Lake-wide estimates of chlorophyll suggest that their production is about 30% of that of the phytoplankton. Brine fly (Ephydra gracilis) larval densities on the biostromes increased from 7000 m⁻² in June to 20000 m⁻² in December. Pupation and adult emergence halted in October and larvae of various instars overwintered at temperatures < 5 °C. Mean total dissolved and dissolved methyl mercury concentrations in water were 5.0 and 1.2 ηg L⁻¹. Total mercury concentrations in the periphyton, fly larvae, pupae, and adults were, respectively, 152, 189, 379 and 659 ηg g⁻¹ dry weight, suggesting that bioconcentration is only moderate in the short food web and through fly developmental stages. However, common goldeneye ducks (Bucephala clangula) that feed primarily on brine fly larvae at the Great Salt Lake had concentrations near 8000 ηg Hg g⁻¹ dry weight in muscle tissue. Data from a previous study indicated that selenium concentrations in periphyton, brine fly larvae and goldeneye liver tissue were high (1700, 1200 and 24,000 ηg g⁻¹, respectively) and Hg:Se molar ratios were < 1.0 in all tissues, suggesting that the high mercury concentration in the ducks may be partially detoxified by combining with selenium. The study demonstrated that the high mercury levels in the Great Salt Lake are routed through the biostrome community resulting in invertebrate prey that may provide health risks for birds and humans that consume them.     

Binding of mercury in soils and attic dust in the Idrija mercury mine area (Slovenia)

Total Hg concentrations and Hg speciation were determined in soils and attic dust in a 160 km2 area around Idrija mercury mine. Attic dust as well as a sample of soil was collected at 100 locations. Mercury phases were separated into cinnabar and non-cinnabar compounds via a thermo-desorption technique. The amount of the non-cinnabar fraction is important since it is potentially bioavailable and results are needed for further risk assessment studies. The concentrations of Hg in attic dust are many times higher than in surrounding soils and the attic dust/soil ratio changes with distance. The highest concentration ratios were identified at the greatest distance from the source of pollution and the lowest close to the source of pollution. This confirms the impact of air emissions on the wider area around Idrija. Furthermore the spatial mercury distribution in the attic dust shows that the influence of atmospheric emissions caused by the Idrija smelter resulted in impacts on the environment on a regional scale. The portions of non-cinnabar compounds increase with distance from the mercury source in both sampling media. Non-cinnabar fractions were found to be enriched in distant areas where fine grained material was deposited. There were two different transport mechanisms of dust particles and gaseous Hg(0) during the mercury production period. Obviously coarse grained particles, with mostly cinnabar-bound Hg settled in the immediate vicinity of the smokestack of the smelter, whereas the fine grained fraction could be dispersed further ahead. This is represented by the percentage of cinnabar-bound Hg in attic dust and soil decreasing with distance from the smelter. Gaseous Hg(0) is probably bound to fine and ultrafine aerosols with longer residence time against deposition. The consequence is that fine grained material with Hg2+ and Hg0 prevails in remote localities and is bound in soils and dust with matrix and organic matter as non-cinnabar mercury compounds. The distributions of mercury species in attic dust and soils along the Idrijca River show that in the region from Idrija to Spodnja Idrija the portions of cinnabar and non-cinnabar are about equal, while in the upper and in the lower Idrijca valley non-cinnabar bound mercury prevails. The applicability of attic dust for tracing the mercury halo in the Idrija area was successfully shown.     

Trophic structure and mercury distribution in a Gulf of St. Lawrence (Canada) food web using stable isotope analysis

Even at low concentrations in the environment, mercury has the potential to biomagnify in food chains and reaches levels of concern in apex predators. The aim of this study was to relate the transfer of total mercury (THg) and methylmercury (MeHg) in a Gulf of St. Lawrence food web to the trophic structure, from primary consumers to seabirds, using stable nitrogen (δ¹⁵N) and carbon (δ¹³C) isotope analysis and physical environmental parameters. The energy reaching upper trophic level species was principally derived from pelagic primary production, with particulate organic matter (POM) at the base of the food chain. We developed a biomagnification factor (BMF) taking into account the various prey items consumed by a given predator using stable isotope mixing models. This BMF provides a more realistic estimation than when using a single prey. Lipid content, body weight, trophic level and benthic connection explained 77.4 and 80.7% of the variation in THg and MeHg concentrations, respectively in this food web. When other values were held constant, relationships with lipid and benthic connection were negative whereas relationships with trophic level and body weight were positive. Total Hg and MeHg biomagnified in this food web with biomagnification power values (slope of the relationship with δ¹⁵N) of 0.170 and 0.235, respectively on wet weight and 0.134 and 0.201, respectively on dry weight. Values of biomagnification power were greater for pelagic and benthopelagic species compared to benthic species whereas the opposite trend was observed for levels at the base of the food chain. This suggests that Hg would be readily bioavailable to organisms at the base of the benthic food chain, but trophic transfer would be more efficient in each trophic level of pelagic and benthopelagic food chains.     

Dissolved mercury in the Lake Windermere catchment area

Typical dissolved mercury (Hg) concentrations in unpolluted waters are alleged to be < 50 ng 1⁻¹ and sometimes< 10 ng 1⁻¹. Mean concentrations found in the catchment area of Lake Windermere were found to range between 12 and 29 ng 1⁻¹ over a three month period. However in particular instances concentrations of 75 and 96 ng 1⁻¹ were found, thought to be due to runoff from mineral deposits and sewage outfalls respectively.     

Total mercury,methylmercury and selenium in mercury polluted areas in the province Guizhou,China

The province of Guizhou in Southwestern China is currently one of the world's most important mercury production areas. Emissions of mercury from the province to the global atmosphere have been estimated to be approximately 12% of the world total anthropogenic emissions. The main objective of this study was to assess the level of contamination with Hg in two geographical areas of Guizhou province. Mercury pollution in the areas concerned originates from mercury mining and ore processing in the area of Wanshan, while in the area of Quingzhen mercury pollution originates from the chemical industry discharging Hg through wastewaters and emissions to the atmosphere due to coal burning for electricity production. The results of this study confirmed high contamination with Hg in soil, sediments and rice in the Hg mining area in Wanshan. High levels of Hg in soil and rice were also found in the vicinity of the chemical plant in Quingzhen. The concentrations of Hg decreased with distance from the main sources of pollution considerably. The general conclusion is that Hg contamination in Wanshan is geographically more widespread, due to deposition and scavenging of Hg from contaminated air and deposition on land. In Quingzhen Hg contamination of soil is very high close to the chemical plant but the levels reach background concentrations at a distance of several km. Even though the major source of Hg in both areas is inorganic Hg, it was observed that active transformation of inorganic Hg to organic Hg species (MeHg) takes place in water, sediments and soils. The concentration of Hg in rice grains can reach up to 569 microg/kg of total Hg of which 145 microg/kg was in MeHg form. The percentage of Hg as MeHg varied from 5 to 83%. The concentrations of selenium can reach up to 16 mg/kg in soil and up to 1 mg/g in rice. A correlation exists between the concentration of Se in soil and rice, indicating that a portion of Se is bioavailable to plants. No correlation between Hg and Se in rice was found. Exposure of the local population to Hg may occur due to inhalation of Hg present in air (in particular in Hg mining area) and consumption of Hg contaminated food (in particular rice and fish) and water. Comparison of intake through these different routes showed that the values of Hg considerably exceed the USA EPA Reference Concentration (RfC) for chronic Hg exposure (RfC is 0.0004 mg/m(3)) close to the emission sources. Intake of Hg through food consumption, particularly rice and fish, is also an important route of Hg exposure in study area. In general, it can be concluded that the population mostly at risk is located in the vicinity of smelting facilities, mining activities and close to the waste disposal sites in the wider area of Wanshan. In order to assess the real level of contamination in the local population, it is recommended that biomonitoring should be performed, including Hg and MeHg measurements in hair, blood and urine samples.