Hg speciation and stable isotope signatures in human hair as a tracer for dietary and occupational exposure to mercury

Exposure of humans and wildlife to various inorganic and organometallic forms of mercury (Hg) may induce adverse health effects. While human populations in developed countries are mainly exposed to marine fish monomethylmercury (MMHg), this is not necessarily the case for developing countries and diverse indigenous people. Identification of Hg exposure sources from biomonitor media such as urine or hair would be useful in combating exposure. Here we report on the Hg stable isotope signatures and Hg speciation in human hair across different gold miner, indigenous and urban populations in Bolivia and France. We found evidence for both mass-dependent isotope fractionation (MDF) and mass-independent isotope fractionation (MIF) in all hair samples. Three limiting cases of dominant exposure to inorganic Hg (IHg), freshwater fish MMHg, and marine fish MMHg sources are used to define approximate Hg isotope source signatures. Knowing the source signatures, we then estimated Hg exposure sources for the Bolivian gold miner populations. Modeled IHg levels in hair correspond well to measured IHg concentrations (R = 0.9), demonstrating that IHg exposure sources to gold miners can be monitored in hair samples following either its chemical speciation or isotopic composition. Different MMHg and inorganic exposure levels among gold miners appear to correspond to living and working conditions, including proximity to small towns, and artisanal vs large scale mining activity.     

Methylated mercury species in Canadian high Arctic marine surface waters and snowpacks

We sampled seawater and snowpacks in the Canadian high Arctic for methylated species of mercury (Hg). We discovered that, although seawater sampled under the sea ice had very low concentrations of total Hg (THg, all forms of Hg in a sample; on average 0.14-0.24 ng L(-1)), 30-45% of the THg was in the monomethyl Hg (MMHg) form (on average 0.057-0.095 ng L(-1)), making seawater itself a direct source of MMHg for biomagnification through marine food webs. Seawater under the ice also contained high concentrations of gaseous elemental Hg (GEM; 129 +/- 36 pg L(-1)), suggesting that open water regions such as polynyas and ice leads were a net source of approximately 130 +/- 30 ng Hg m(-2) day(-1) to the atmosphere. We also found 11.1 +/- 4.1 pg L(-1) of dimethyl Hg (DMHg) in seawater and calculated that there could be a significant flux of DMHg to the atmosphere from open water regions. This flux could then resultin MMHg deposition into nearby snowpacks via oxidation of DMHg to MMHg in the atmosphere. In fact, we found high concentrations of MMHg in a few snowpacks near regions of open water. Interestingly, we discovered a significant log-log relationship between Cl- concentrations in snowpacks and concentrations of THg. We hypothesize that as Cl- concentrations in snowpacks increase, inorganic Hg(II) occurs principally as less reducible chloro complexes and, hence, remains in an oxidized state. As a result, snowpacks that receive both marine aerosol deposition of Cl- and deposition of Hg(II) via springtime atmospheric Hg depletion events, for example, may contain significant loads of Hg(II). Overall, though, the median wet/dry loads of Hg in the snowpacks we sampled in the high Arctic (5.2 mg THg ha(-1) and 0.03 mg MMHg ha(-1)) were far below wet-only annual THg loadings throughout southern Canada and most of the U.S. (22-200 mg ha(-1)). Therefore, most Arctic snowpacks contribute     

Absence of fractionation of mercury isotopes during trophic transfer of methylmercury to freshwater fish in captivity

We performed two controlled experiments to determine the amount of mass-dependent and mass-independent fractionation (MDF and MIF) of methylmercury (MeHg) during trophic transfer into fish. In experiment 1, juvenile yellow perch (Perca flavescens) were raised in captivity on commercial food pellets and then their diet was either maintained on unamended food pellets (0.1 μg/g MeHg) or was switched to food pellets with 1.0 μg/g or 4.0 μg/g of added MeHg, for a period of 2 months. The difference in δ(202)Hg (MDF) and Δ(199)Hg (MIF) between fish tissues and food pellets with added MeHg was within the analytical uncertainty (δ(202)Hg, 0.07 ‰; Δ(199)Hg, 0.06 ‰), indicating no isotope fractionation. In experiment 2, lake trout (Salvelinus namaycush) were raised in captivity on food pellets and then shifted to a diet of bloater (Coregonus hoyi) for 6 months. The δ(202)Hg and Δ(199)Hg of the lake trout equaled the isotopic composition of the bloater after 6 months, reflecting reequilibration of the Hg isotopic composition of the fish to new food sources and a lack of isotope fractionation during trophic transfer. We suggest that the stable Hg isotope ratios in fish can be used to trace environmental sources of Hg in aquatic ecosystems.     

Biogeochemical cycling of methylmercury in lakes and tundra watersheds of Arctic Alaska

The fate of atmospherically deposited and environmentally active Hg is uncertain in the Arctic, and of greatest toxicological concern is the transformation to monometh-ylmercury (MMHg). Lake/watershed mass balances were developed to examine MMHg cycling in four northern Alaska lakes near the ecological research station at Toolik Lake (68 degrees 38' N, 149 degrees 36' W). Primary features of the cycle are watershed runoff, sedimentary production and mobilization, burial, and photodecomposition in the water column. The principal source of MMHg is in situ benthic production with 80-91% of total inputs provided by diffusion from sediments. The production and contribution of MMHg from tundra watersheds is modest. Photodecomposition, though confined to a short ice-free season, provides the primary control for MMHg (66-88% of total inputs) and greatly attenuates bioaccumulation. Solid-phase MMHg and gross potential rates of Hg methylation, assayed with an isotopic tracer, vary positively with the level of inorganic Hg in filtered pore water, indicating that MMHg production is Hg-limited in these lakes. Moreover, sediment-waterfluxes of MMHg (i.e., net production at steady state) are related to sediment Hg loadings from the atmosphere. These results suggest that loadings of Hg derived from atmospheric deposition are a major factor affecting MMHg cycling in arctic ecosystems. However, environmental changes associated with warming of the Arctic (e.g., increased weathering, temperature, productivity, and organic loadings) may enhance MMHg bioaccumulation by stimulating Hg methylation and inhibiting photodecomposition.     

Some sources and sinks of monomethyl and inorganic mercury on Ellesmere Island in the Canadian High Arctic

We identified some of the sources and sinks of monomethyl mercury (MMHg) and inorganic mercury (HgII) on Ellesmere Island in the Canadian High Arctic. Atmospheric Hg depletion events resulted in the deposition of Hg(II) into the upper layers of snowpacks, where concentrations of total Hg (all forms of Hg) reached over 20 ng/L. However, our data suggest that much of this deposited Hg(II) was rapidly photoreduced to Hg(0) which then evaded back to the atmosphere. As a result, we estimate that net wet and dry deposition of Hg(II) during winter was lower at our sites (0.4-5.9 mg/ha) than wet deposition in more southerly locations in Canada and the United States. We also found quite high concentrations of monomethyl Hg (MMHg) in snowpacks (up to 0.28 ng/L), and at times, most of the Hg in snowpacks was present as MMHg. On the Prince of Wales Icefield nearthe North Water Polynya, we observed a significant correlation between concentrations of Cl and MMHg in snow deposited in the spring, suggesting a marine source of MMHg. We hypothesize that dimethyl Hg fluxes from the ocean to the atmosphere through polynyas and open leads in ice, and is rapidly photolyzed to MMHgCl. We also found that concentrations of MMHg in initial snowmelt on John Evans Glacier (up to 0.24 ng/L) were higher than concentrations of MMHg in the snowpack (up to 0.11 ng/L), likely due to either sublimation of snow or preferential leaching of MMHg from snow during the initial melt phase. This springtime pulse of MMHg to the High Arctic, in conjunction with climate warming and the thinning and melting of sea ice, may be partially responsible for the increase in concentrations of Hg observed in certain Arctic marine mammals in recent decades. Concentrations of MMHg in warm and shallow freshwater ponds on Ellesmere Island were also quite high (up to 3.0 ng/L), leading us to conclude that there are very active regions of microbial Hg(II) methylation in freshwater systems during the short summer season in the High Arctic.     

Mass balance of total mercury and monomethylmercury in coastal embayments of a volcanic island: significance of submarine groundwater discharge

To understand the contribution of submarine groundwater discharge (SGD) to the coastal mass budgets of Hg and monomethylmercury (MMHg), preliminary mass balance estimates were made for Hwasun and Bangdu Bays on Jeju Island, known to have large SGD due to the high permeability of the volcanic rocks. The mass balance results indicate that SGD is a main source of Hg in Hwasun Bay (23 ± 14 × 10(-2) mol yr(-1), 34%) and Bangdu Bay (23 ± 20 × 10(-2) mol yr(-1), 67%), although the contribution from atmospheric deposition was considerable (25% for Hwasun and 23% for Bangdu). MMHg was also discharged primarily from submarine groundwater at Hwasun (0.30 ± 0.17 × 10(-2) mol yr(-1), 55%) and Bangdu (0.65 ± 0.49 × 10(-2) mol yr(-1), 64%), which was higher than atmospheric deposition (6% for Hwasun and 2% for Bangdu) and sediment diffusion flux (5% for Hwasun and 3% for Bangdu). The overall mass balance results suggest that, although there are large spatial variations in SGD rates throughout the region, the coastal mass budgets of Hg and MMHg need to include SGD as well as atmospheric deposition and sediment diffusion as primary sources of Hg and MMHg.     

Tracing sources and bioaccumulation of mercury in fish of Lake Baikal--Angara River using Hg isotopic composition

This study presents the determination and comparison of isotopic compositions of Hg in sediments, plankton, roach, and perch of two freshwater systems in the Lake Baikal-Angara River aquatic ecosystem: the man-made Bratsk Water Reservoir contaminated by Hg from a chlor-alkali factory and the noncontaminated Lake Baikal. Isotopic ratios of biota exhibit both significant mass-independent fractionation (MIF) (Δ(199)Hg from 0.20 to 1.87‰) and mass-dependent fractionation (MDF) (δ(202)Hg from -0.97 to -0.16‰), whereas sediments exhibit high MDF (δ(202)Hg from -1.99 to -0.83‰) but no MIF. δ(15)N and δ(13)C are correlated with methylmercury in organisms from both sites, indicating bioaccumulation and biomagnification through food webs of both regions. Combining this with isotopic composition of samples shows that δ(202)Hg increases with the trophic level of organisms and also with methylmercury in fish from Lake Baikal. This study demonstrates that MIF in fish samples from Bratsk Water Reservoir allow to trace anthropogenic Hg, since fish with the highest levels of Hg in muscle have the same isotopic composition as the sediment in which anthropogenic Hg was deposited. Less contaminated fish do not exhibit this anthropogenic signature accumulating relatively lower Hg amount from the contaminated sediments. This work reveals that Hg isotopic composition can be used to track the contribution of anthropogenic sources in fish from a contaminated lake.     

Mercury in soils, lakes, and fish in Voyageurs National Park (Minnesota): importance of atmospheric deposition and ecosystem factors

Concentrations of methylmercury in game fish from many interior lakes in Voyageurs National Park (MN, U.S.A.) substantially exceed criteria for the protection of human health. We assessed the importance of atmospheric and geologic sources of mercuryto interior lakes and watersheds within the Park and identified ecosystem factors associated with variation in methylmercury contamination of lacustrine food webs. Geologic sources of mercury were small, based on analyses of underlying bedrock and C-horizon soils, and nearly all mercury in the 0- and A-horizon soils was derived from atmospheric deposition. Analyses of dated sediment cores from five lakes showed that most (63% +/- 13%) of the mercury accumulated in lake sediments during the 1900s was from anthropogenic sources. Contamination of food webs was assessed by analysis of whole, 1-year-old yellow perch (Perca flavescens), a regionally important prey fish. The concentrations of total mercury in yellow perch and of methylmercury in lake water varied substantially among lakes, reflecting the influence of ecosystem processes and variables that affect the microbial production and abundance of methylmercury. Models developed with the information-theoretic approach (Akaike Information Criteria) identified lake water pH, dissolved sulfate, and total organic carbon (an indicator of wetland influence) as factors influencing methylmercury concentrations in lake water and fish. We conclude that nearly all of the mercury in fish in this seemingly pristine     

Experimental evidence of a linear relationship between inorganic mercury loading and methylmercury accumulation by aquatic biota

Developing effective regulations on mercury (Hg) emissions requires a better understanding of how atmospheric Hg deposition affects methylmercury (MeHg) levels in aquatic biota. This study tested the hypothesis that MeHg accumulation in aquatic food webs is related to atmospheric Hg deposition. We simulated a range of inorganic Hg deposition rates by adding isotopically enriched Hg(II) (90.9% 202Hg) to 10-m diameter mesocosms in a boreal lake. Concentrations of experimentally added ("spike") Hg were monitored in zooplankton, benthic invertebrates, and fish. Some Hg(II) added to the mesocosms was methylated and incorporated into the food web within weeks, demonstrating that Hg(II) deposited directly to aquatic ecosystems can become quickly available to biota. Relationships between Hg(II) loading rates and spike MeHg concentrations in zooplankton, benthic invertebrates, and fish were linear and significant. Furthermore, spike MeHg concentrations in the food web were directly proportional to Hg(II) loading rates (i.e., a percent change in Hg(II) loading rate resulted in, statistically, the same percent change in MeHg concentration). This is the first experimental determination of the relationship between Hg(II) loading and MeHg bioaccumulation in aquatic biota. We conclude that changes in atmospheric Hg deposition caused by increases or decreases in Hg emissions will ultimately affect MeHg levels in aquatic food webs.     

Sunlight and iron(III)-induced photochemical production of dissolved gaseous mercury in freshwater

Mechanistic understanding of sunlight-induced natural processes for production of dissolved gaseous mercury (DGM) in freshwaters has remained limited, and few direct field tests of the mechanistic hypotheses are available. We exposed ferric iron salt-spiked fresh surface lake water (Whitefish Bay, Lake Superior, MI) in Teflon bottles and pond water (Oak Ridge, TN) in quartz bottles to sunlight in the field to infer if sunlight and Fe(III)-induced photochemical production of DGM could mechanistically contribute partly to natural photochemical production of DGM in freshwaters. We found that exposure of freshwater spiked with fresh Fe(III) (approximately 5 or 10 microM) to sunlight led to repeatable, significantly larger increases in DGM production (e.g., 380% in 1 h, 420% in 2 h, and 470% in 4 h for Whitefish Bay water) than exposure without the spike (e.g., 200% in 6 h). DGM increased with increasing exposure time and then often appeared to approach a steady state in the tests. Higher Fe(III) spike levels resulted in the same, or even less, DGM production. Storage of the water with or without Fe(III) spike in the dark after sunlight exposure led to significant, apparently first-order, decreases in DGM. These phenomena were hypothetically attributed to sunlight-induced photochemical production of highly reducing organic free radicals through photolysis of Fe(III)-organic acid coordination compounds and subsequent reduction of Hg(II) to Hg(0) by the organic free radicals; the reduction was also accompanied by dark oxidation of Hg(0) by photochemically originated oxidants (e.g., .OH). This study suggests that sunlight and Fe(III)-induced photochemical reduction of Hg(II) could be one of the mechanisms responsible for natural photochemical production of DGM in freshwaters and that Fe species may be influential in mediating Hg chemodynamics and its subsequent toxicity in aquatic ecosystems.     

Spatial and habitat-based variations in total and methyl mercury concentrations in surficial sediments in the San Francisco Bay-Delta

Recent studies indicate significant amounts of mercury (Hg) are annually transported into the San Francisco Bay-Delta (Bay-Delta) as a result of historic gold and Hg mining activities. We examined temporal and spatial variation in concentrations of total Hg (Hg(T)) and monomethylmercury (MMHg) in surficial sediments of various ecosystem types in the Bay-Delta. We sampled surficial sediments across the Bay-Delta system and found Hg(T) sediment concentrations in the central Delta were generally 100-200 ng g(-1) and increased westward through Suisun Bay to 250-350 ng g(-1). MMHg concentrations in the central Delta were between 1 and 3 ng g(-1), while those in sediments in the perimeter waterways and adjacent bays were less than 1 ng g(-1). Six sites were monitored monthly for over a year to identify seasonal changes in Hg sediment concentrations. Hgtau sediment concentrations ranged from 48 to 382 ng g(-1) and varied as a function of location not season. However, MMHg concentrations varied seasonally, increasing from 1 ng g(-1) during winter months to 6 ng g(-1) during spring and summer. Transects conducted at three marshes in the central Delta revealed MMHg sediment concentrations of 4-8 ng g(-1) at the interior and 2 ng g(-1) at the exterior of the marshes. Habitat type was a major factor controlling MMHg concentration and the MMHg to Hg(T) ratio in sediments of the Bay-Delta. MMHg was significantly correlated to Hgt (r2 = 0.49) in marsh sediments.     

Photodecomposition of methylmercury in an Arctic Alaskan lake

Sunlight-induced decomposition of monomethylmercury (MMHg) reduces its availability for accumulation in aquatic food webs. We examined MMHg degradation in epilimnetic waters of Toolik Lake (68 degrees 38' N, 149 degrees 36' W) in arctic Alaska, a region illuminated by sunlight almost continuously during the summer. MMHg decomposition in surface water of Toolik Lake is exclusively abiotic and mediated by sunlight; comparable rates of MMHg decomposition were observed in filter-sterilized and unfiltered surface waters incubated under in situ sunlight and temperature conditions, and no MMHg was degraded in unfiltered aliquots incubated in the dark. Rates of photodecomposition are first order with respect to both MMHg concentration and the intensity of photosynthetically active radiation (PAR), except at the lake surface where rates of photochemical degradation are enhanced relative to PAR intensity and may be attributed to an additional influence of ultraviolet light. The estimated annual loss of MMHg to photodecomposition in Toolik Lake, though limited to a 100-d ice-free season, accounts for about 80% of the MMHg mobilized annually from in situ sedimentary production, the primary source in Toolik Lake. These results suggest that greater light attenuation in lacustrine surface waters, a potential result of increased loadings of dissolved organic matter due to continued warming in the Arctic, may result in less photodecomposition and subsequently greater availability of MMHg for bioaccumulation.     

Laboratory investigation of the potential for re-emission of atmospherically derived Hg from soils

This paper presents data from controlled laboratory experiments focused on investigating the effect of moisture and visible and ultraviolet light on the emission and re-emission of mercury (Hg) from two soils, one with low or background Hg concentrations (14 ng g(-1)) and a soil naturally enriched in Hg (4800 ng g(-1)). Water addition was found to increase emissions from dry soils by an amount greater than that occurring during exposure to PAR or UV-A radiation, whereas UV-B and UV-C exposures facilitated the greatest release. Over all exposures, only a small percentage of Hg(ll) added in a wet spike simulating a precipitation input was released immediately after addition (< 3%). The majority of the Hg being released during all exposures was indigenous and either an original component of the soil or derived from past wet and dry deposition. Under dark and light conditions, elemental Hg was deposited to the dry low Hg-containing soil. On the basis of experimental results, it is hypothesized that dry deposition of gaseous elemental Hg is an important input to low Hg soils and that light, water, and UV-A exposure promote desorption and re-emission of elemental Hg. UV-B exposure is hypothesized to promote indirect photoreduction of Hg(II) existing in the soil. The available pool and the form of Hg in the soil, as well as the chemistry of the soil, will determine the overall flux response to environmental stimulation of emissions.     

Geochemical controls on the production and distribution of methylmercury in near-shore marine sediments

We examined temporal differences in sedimentary production of monomethylmercury (MMHg) at three sites in Long Island Sound (LIS). Sediment-phase concentrations of Hg species decreased from west to east in LIS surface sediments, following the trend of organic matter. However, Hg methylation potentials, measured by incubation with an isotopic tracer (200Hg), increased from west to east. 200Hg methylation potentials were enhanced in August relative to March and June, attributable to differences in activity of sulfate-reducing bacteria. Organic matter and acid-volatile sulfide influenced the distribution coefficient (KD) of inorganic Hg (Hg(II) = total Hg - MMHg) and inhibited 200Hg methylation in surface sediments. 200Hg methylation varied inversely with the KD of Hg(II) and positively with the concentration of Hg(II), mostly as HgS0, in LIS pore waters. Accordingly, we posit that a principal control on MMHg production in low-sulfide, coastal marine sediments is partitioning of Hg(II) between particle and dissolved phases, which regulates availability of Hg substrate to methylating bacteria. Most of the partitioning in LIS sediments is due to Hg-organic associations. This suggests that reductions in the organic content of coastal sediment, a potential result of nutrient abatement programs intended to inhibit eutrophication of near-shore waters, could enhance MMHg production by increasing the bioavailability of the large reservoir of "legacy Hg" buried within the sediment.     

Human exposure to methylmercury through rice intake in mercury mining areas, Guizhou province, China

The toxicity of methylmercury (Me-Hg) has caused widespread public human concern as a result of several widely publicized disasters. Me-Hg is highly toxic, and the nervous system is its principal target tissue for humans. Although the general population is primarily exposed to Me-Hg through contaminated fish and marine mammals, in Hg mining areas a long history of mining activities can produce serious Hg pollution to the local environment In a study of 98 persons from the Wanshan Hg mining area, hair Me-Hg levels indicated Me-Hg exposure. Rice, the staple food of the local inhabitants also showed high total Hg (T-Hg) and Me-Hg levels. The geometric mean concentration of T-Hg and mean concentration of Me-Hg in rice samples collected from 3 villages in Wanshan Hg mining area were 36.2 (ranging from 4.9 to 214.7), and 8.5 (ranging from 1.9 to 27.6) microg/kg, respectively, which were significantly elevated compared to the rice samples collected from a reference area, where the mean T-Hg and Me-Hg concentrations were 7.0 (3.2-15.1) and 2.5 (0.8-4.3) microg/kg, respectively. Pork meat, vegetable, and drinking water samples collected in Wanshan Hg mining area contained highly elevated T-Hg, but very low levels of Me-Hg. The relationships between the estimated rice Me-Hg intake and hair Me-Hg levels (r = 0.65, p < 0.001) confirmed rice with high Me-Hg levels indeed was the main route of Me-Hg exposure for the local residents in the Wanshan Hg mining area. From our study, we can conclude that the main human exposure to Me-Hg via food consumption is not restricted to fish, but in some cases in mining areas of China to frequent rice meals.     

Elimination of mercury by yellow perch in the wild

The rate of methylmercury (MeHg) elimination by fish is important in determining the extent of bioaccumulation and for predicting recovery times of MeHg-contaminated fisheries. Rates of MeHg elimination remain uncertain in existing bioaccumulation models due to a lack of field studies. We addressed this problem by monitoring fish that had naturally accumulated isotopically enriched MeHg (spike MeHg) during a whole-ecosystem experiment. We transported yellow perch (Perca flavescens) from the experimental lake to an untreated lake and monitored spike total mercury (THg, most of which was MeHg) losses over 440 d. Spike THg was distributed among fish tissues in a similar way as ambient THg (background non-spike THg). We observed rapid loss of spike THg from liver and other visceral tissues (approximately 90 d) followed by a plateau. Subsequently, there was prolonged redistribution of spike THg into muscle (180 d). Loss of spike THg from the whole fish occurred > 5 times slower (half-life of 489 d) than in past laboratory studies using this species. We determined that MeHg bioaccumulation models with laboratory-based elimination rates produced faster losses than those observed in wild fish. The present findings provide support for refining elimination rates in MeHg models and show the importance of examining biological processes under natural conditions.     

Mercury speciation and transport via submarine groundwater discharge at a southern California coastal lagoon system

We measured total mercury (Hg(T)) and monomethylmercury (MMHg) concentrations in coastal groundwater and seawater over a range of tidal conditions near Malibu Lagoon, California, and used (222)Rn-derived estimates of submarine groundwater discharge (SGD) to assess the flux of mercury species to nearshore seawater. We infer a groundwater-seawater mixing scenario based on salinity and temperature trends and suggest that increased groundwater discharge to the ocean during low tide transported mercury offshore. Unfiltered Hg(T) (U-Hg(T)) concentrations in groundwater (2.2-5.9 pM) and seawater (3.3-5.2 pM) decreased during a falling tide, with groundwater U-Hg(T) concentrations typically lower than seawater concentrations. Despite the low Hg(T) in groundwater, bioaccumulative MMHg was produced in onshore sediment as evidenced by elevated MMHg concentrations in groundwater (0.2-1 pM) relative to seawater (～0.1 pM) throughout most of the tidal cycle. During low tide, groundwater appeared to transport MMHg to the coast, resulting in a 5-fold increase in seawater MMHg (from 0.1 to 0.5 pM). Similarly, filtered Hg(T) (F-Hg(T)) concentrations in seawater increased approximately 7-fold during low tide (from 0.5 to 3.6 pM). These elevated seawater F-Hg(T) concentrations exceeded those in filtered and unfiltered groundwater during low tide, but were similar to seawater U-Hg(T) concentrations, suggesting that enhanced SGD altered mercury partitioning and/or solubilization dynamics in coastal waters. Finally, we estimate that the SGD Hg(T) and MMHg fluxes to seawater were 0.41 and 0.15 nmol m(-2) d(-1), respectively - comparable in magnitude to atmospheric and benthic fluxes in similar environments.     

The influence of product attributes, consumer attitudes and characteristics on the acceptance of: (1) Novel bread and milk, and dietary supplements and (2) fish and novel meats as dietary vehicles of long chain omega 3 fatty acids

Two conjoint studies were undertaken in the USA on relative preferences for sources and food vehicles for long chain omega-3 fatty acids (LCO3FA). Study 1 (n = 202) investigated consumer acceptance of the source of LCO3FA (fish oil, algal oil and novel oilseed) in the most popular, well established vehicle foods (bread, milk and supplements). Study 2 (n = 211) investigated consumer acceptance of the source of LCO3FA (fishmeal, novel oilseed and fish oil) used to enrich the diet of animals for meat production (beef, chicken, pork and fish). Product concepts were varied by base product (vehicle); source of LCO3FA; information source; health claim and additional cost.These samples of US consumers reported preferences for novel (genetically modified, GM) oilseed incorporated into enriched foods (i.e., bread, milk and supplements) and also for meats above fish and fish oil as sources of LCO3FA and vehicles for consumption. Overall conjoint analysis revealed a general positive relative utility (worth or value) for novel oilseeds which were related to neutral or positive attitudes towards GM.Generally, the acceptance of enriched foods was dependent on the type of the base food and the cost of fish, with bread preferred over milk and supplements. Similarly, for meat, base (vehicle) product was significantly the most important driver of preference, with about 80% of the sample expressing highest preferences for chicken, fed oilseed (as a source of LCO3FA). However, cost was not an important driver of acceptance of meat alternatives.Further, knowledge that the novel oilseed was derived from a GM source did not impact on the acceptance of food alternatives. Thus, incorporating GM oilseeds rich in LCO3FA into animal feed, particularly for chicken and beef, and for enriching bread was found to be acceptable amongst the majority. These two studies suggest the existence of a potential demand for novel ‘non-fish’ source of LCO3FA, providing potential health benefits not currently realised.     

Increasing mercury in yellow perch at a hotspot in Atlantic Canada, Kejimkujik National Park

In the mid-1990s, yellow perch (Perca flavescens) and common loons (Gavia immer) from Kejimkujik National Park and National Historic Site (KNPNHS), Nova Scotia, Canada, had among the highest mercury (Hg) concentrations across North America. In 2006 and 2007, we re-examined 16 lakes to determine whether there have been changes in Hg in the loon's preferred prey, yellow perch. Total Hg concentrations were measured in up to nine perch in each of three size classes (5-10 cm, 10-15 cm, and 15-20 cm) consumed by loons. Between 1996/97 and 2006/07, polynomial regressions indicated that Hg in yellow perch increased an average of 29% in ten lakes, decreased an average of 21% in three, and were unchanged in the remaining three lakes. In 2006/07, perch in 75% of the study lakes had Hg concentrations (standardized to 12-cm fish length) equal to or above the concentration (0.21 μg·g(-1) ww) associated with a 50% reduction in maximum productivity of loons, compared with only 56% of these lakes in 1996/97. Mercury contamination currently poses a greater threat to loon health than a decade ago, and further reductions in anthropogenic emissions should be considered to reduce its impacts on ecosystem health.     

Higher mass-independent isotope fractionation of methylmercury in the pelagic food web of Lake Baikal (Russia)

Mercury undergoes several transformations that influence its stable isotope composition during a number of environmental and biological processes. Measurements of Hg isotopic mass-dependent (MDF) and mass-independent fractionation (MIF) in food webs may therefore help to identify major sources and processes leading to significant bioaccumulation of methylmercury (MeHg). In this work, δ(13)C, δ(15)N, concentration of Hg species (MeHg, inorganic Hg), and stable isotopic composition of Hg were determined at different trophic levels of the remote and pristine Lake Baikal ecosystem. Muscle of seals and different fish as well as amphipods, zooplankton, and phytoplankton were specifically investigated. MDF during trophic transfer of MeHg leading to enrichment of heavier isotopes in the predators was clearly established by δ(202)Hg measurements in the pelagic prey-predator system (carnivorous sculpins and top-predator seals). Despite the low concentrations of Hg in the ecosystem, the pelagic food web reveals very high MIF Δ(199)Hg (3.15-6.65‰) in comparison to coastal fish (0.26-1.65‰) and most previous studies in aquatic organisms. Trophic transfer does not influence MIF signature since similar Δ(199)Hg was observed in sculpins (4.59 ± 0.55‰) and seal muscles (4.62 ± 0.60‰). The MIF is suggested to be mainly controlled by specific physical and biogeochemical characteristics of the water column. The higher level of MIF in pelagic fish of Lake Baikal is mainly due to the bioaccumulation of residual MeHg that is efficiently turned over and photodemethylated in deep oligotrophic and stationary (i.e., long residence time) freshwater columns.