Dimethylmercury in coastal upwelling waters, Monterey Bay, California

Exploring the spatial variation of mercury in the Gulf of St. Lawrence using northern gannets as fish samplers

Mercury (Hg) is a ubiquitous and pervasive environmental contaminant with detrimental effects on wildlife, which originates from both natural and anthropogenic sources. Its distribution within ecosystems is influenced by various biogeochemical processes, making it crucial to elucidate the factors driving this variability. To explore these factors, we employed an innovative method to use northern gannets (Morus bassanus) as biological samplers of regurgitated fish in the Gulf of St. Lawrence. We assessed fish total Hg (THg) concentrations in relation to their geographical catch location as well as to pertinent biotic and anthropogenic factors. In small fish species, trophic position, calculated from compound-specific stable nitrogen isotopes in amino acids, emerged as the most influential predictor of THg concentrations. For large fish species, THg concentrations were best explained by δ13C, indicating higher concentrations in inshore habitats. No anthropogenic factors, such as pollution, shipping traffic, or coastal development, were significantly related to THg concentrations in fish. Moreover, previously published THg data in mussels sampled nearby were positively linked with THg concentrations in gannet prey, suggesting consistent mercury distribution across trophic levels in the Gulf of St. Lawrence. Our findings point to habitat-dependent variability in THg concentrations across multiple trophic levels. Our study could have many potential uses in the future, including the identification of vulnerability hotspots for fish populations and their predators, or assessing risk factors for seabirds themselves by using biologically relevant prey.

Light-induced degradation of dimethylmercury in different natural waters

Photo-induced degradation of dimethylmercury (DMHg) is considered to be an important source for the generation of methylmercury (MMHg). However, studies on DMHg photodegradation are scarce, and it is even debatable about whether DMHg can be degraded in natural waters. Herein, we found that both DMHg and MMHg could be photodegraded in three natural waters collected from the Yellow River Delta, while in pure water only DMHg photodegradation occurred under visible light irradiation. The effects of different environmental factors on DMHg photodegradation were investigated, and the underlying mechanisms were elucidated by density functional theory calculations and a series of control experiments. Our findings revealed that the DMHg degradation rate was higher in the tidal creek water compared to Yellow River, Yan Lake, and purified water. NO3-, NO2-, and DOM could promote the photodegradation with DOM and NO3- showing particularly strong positive effects. Different light sources were employed, and UV light was found to be more effective in DMHg photodegradation. Moreover, MMHg was detected during the photodegradation of DMHg, confirming that the photochemical demethylation of DMHg is a source of MMHg in sunlit water. This work may provide a novel mechanistic insight into the DMHg photodegradation in natural waters and enrich the study of the global biogeochemical cycle of Hg.

An improved method for rapid and safe preparation and measurement of dimethylmercury using gas chromatography-atomic fluorescence spectrometry

Transformations between dimethylmercury (DMHg) and other mercury (Hg) species have been one of the critical knowledge gaps in the Hg global biogeochemical cycle due to the lack of detailed studies. The preparation and measurement of DMHg are challenging due to the high toxicity and volatility of DMHg. In this work, we invented a new DMHg generator for successfully preparing high-purity DMHg in a highly controllable and safe way. The DMHg could be spontaneously volatilized and diffused from the original preparation solution to the solution to be studied. The parameters for generating DMHg were optimized to be the pH value of 4.0 with a MeCo/Hg2+ molar ratio of 10 at 20 °C. The following measurement method of DMHg in the presence of various species of Hg was also investigated and optimized. Hg0 and DMHg could be separated effectively with the carrier gas flow rate of 15 mL min-1 and the gas chromatography column temperature of 30 °C. The interferences of Hg0, monomethylmercury and other species were excluded by systematic control experiments. A sensitive and reliable approach for quantifying trace DMHg in water was developed. Under the optimal conditions, the limits of detection for Hg0, MMHg and DMHg were 0.03, 0.002 and 0.024 ng L-1, respectively, with the relative standard deviation below 8.2%. The developed method was validated by the determination Hg species of different natural water samples. This work is expected to provide a new and safe strategy for DMHg preparation and a verified method for DMHg measurement.

Assessing comparability and uncertainty of analytical methods for methylated mercury species in seawater

BACKGROUND

The relative distribution and importance of monomethylmercury (MMHg) and dimethylmercury (DMHg) in seawater is still under debate. A lack of comparability between measurements at sub-picomolar levels hampered the further understanding of the biogeochemical Hg cycle. To overcome this, we assessed the relative standard measurement uncertainties (Uex,r) for direct measurements of MMHg and DMHg by species-specific isotope dilution ICP-MS and cryo-focusing GC-ICP-MS at femtomolar concentrations. Furthermore, Uex,r was determined for the indirect determination of DMHg (DMHgcalc = MeHg - MMHg) and MeHg (MeHgcalc = MMHg + DMHg) to compare the two methodologies.

RESULTS

Expanded Uex,r (confidence interval of 95%) for cryo-focusing GC-ICP-MS was 14.4 (<50 fM) and 14.2% (>50 fM) and for SS-ID GC-ICP-MS 5.6 (<50 fM) and 3.7% (>50 fM). For concentrations above 50 fM, Uex,r for DMHgcalc was always lower than for direct measurements (14.2%). For MeHgcalc, on the other hand, Uex,r was always higher for concentrations above 115 fM (range: 3.7-13.9%) than for direct measurements (3.7%). We evaluated the comparability of directly measured and calculated DMHg and MeHg concentrations based on Hg speciation measurements for two vertical profiles in the Mediterranean Sea. We show that directly measured and indirectly determined DMHg and MeHg concentrations yield comparable results.

SIGNIFICANCE

Our results validate the application of the indirect method for the determination of DMHg if a direct measurement method with a low Uex,r such as isotope dilution is used for MMHg and MeHg measurements. The validation of the indirect measurement approach opens new possibilities to generate more precise and accurate DMHg data in the global ocean.

Interaction of mercury species with proteins: towards possible mechanism of mercurial toxicology

The nature of the binding of mercurials (organic and inorganic) and their subsequent transformations in biological systems is a matter of great debate as several different hypotheses have been proposed and none of them has been conclusively proven to explain the characteristics of Hg binding with the proteins. Thus, the chemical nature of Hg-protein binding through the possible transportation mechanism in living tissues is critically reviewed herein. Emphasis is given to the process of transportation, and binding of Hg species with selenol-containing biomolecules that are appealing for toxicological studies as well as the advancement of environmental and biological research.

Description of a Dimethylmercury Automatic Analyzer for the High-Resolution Measurement of Dissolved Gaseous Mercury Species in Surface Ocean Waters

Our understanding of the significance of dimethylmercury (DMHg) to the mercury (Hg) global ocean biogeochemical cycle is unclear because of the lack of detailed DMHg measurements in the water column. To our knowledge, 30 years of published studies have generated no more than 200 DMHg data points in the ocean surface waters and marine boundary layer (MBL). To improve the precision and reduce the uncertainty in determining DMHg in surface seawater, we developed a simple and robust DMHg automatic analyzer (DAA). This DAA system couples the main sampling and analytic steps, including a continuous flow chamber, with dual Carbotrap preconcentration, a gas chromatographic column, a cold vapor atomic fluorescence spectrometry, and a data logger for signal integration. We compared the operation, performance, and reproducibility between our DAA and the traditional manual analytic method. Its advantages include the ease of operation, the high time resolution and precision (30 min sampling and <5% relative variation), and long-term stability (2 weeks). The DAA can determine DMHg in both the MBL and surface seawater. The estimated detection limits for DMHg with the DAA in the atmosphere and in surface seawater are 10 pg/m3 and 0.2 fM, respectively. The successful DAA field measurement in coastal waters indicates that it can help detect the low DMHg concentration in surface seawater, and the time series DMHg data helped our understanding of the DMHg behavior (sources and sinks) and its flux into the MBL. The comparison of DMHg concentration in various oceans also suggests that the coastal region had the lowest averaged DMHg, up to an order of magnitude lower than other ecosystems.

Mercury distribution in water masses of the South Atlantic Ocean (24°S to 20°S), Brazilian Exclusive Economic Zone

Mercury (Hg) is a toxic globally spread pollutant that has been found at increasing concentrations in the South Atlantic Ocean. The present work provides the first insight into the total mercury (HgT, unfiltered waters) content in the water of the Brazilian Exclusive Economic Zone (BEEZ), within a 24°S to 20°S. Water samples were collected from surface to 3400 m depth along transects, and analyzed with atomic fluorescence. The mean HgT concentration for the Tropical Water mass (TW) was 6.3 ± 1.4 pM (n = 16), for the South Atlantic Central Water (SACW), 5.9 ± 0.7 pM (n = 8), for the Antarctic Intermediate Water (AAIW), 5.0 ± 0.6 pM (n = 2), for the Upper Circumpolar Deep Water (UCDW), 6.5 pM (n = 1), and for the North Atlantic Deep Water (NADW), 5.7 ± 0.9 pM (n = 12). HgT concentrations were highest throughout the BEEZ in comparison with other parts of the Atlantic Ocean, farther from the coast.

An upwelling area as a hot spot for mercury biomonitoring in a climate change scenario: A case study with large demersal fishes from Southeast Atlantic (SE-Brazil)

Data concerning the monomethylmercury (MeHg) bioaccumulation in marine biota from Southeast Atlantic Ocean are scarce. This study purchased large specimens of demersal fishes from an upwelling region: Warsaw grouper (Epinephelus nigritus), Dusky grouper (Epinephelus marginatus) and Namorado sandperch (Pseudopercis numida). The authors addressed the bioaccumulation and toxicokinetic of mercury in fish organs, and the toxicological risk for human consumption of this metal in the muscle tissues accessed. Additionally, the present study discussed the possible implications of shifts in key variables of the environment related to a climate-changing predicted scenario, to the mercury biomagnification in a tropical upwelling system. The muscle was the main stock of MeHg, although the highest THg concentrations have been found in liver tissue. Regarding the acceptable maximum level (ML = 1 mg kg^-1), E. nigritus and E. marginatus showed 22% of the samples above this limit. Concerning P. numida, 77% were above 0.5 mg kg^-1, but below the ML. The %MeHg in liver and muscle showed no significative correlations, which suggest independent biochemical pathways to the toxicokinetic of MeHg, and constrains the indirect assessment of the mercury contamination in the edible tissue by the liver analyses. The present study highlights the food web features of a tropical upwelling ecosystem that promote mercury biomagnification. Additionally, recent studies endorse the enhancement of upwelling phenomenon due to the climate global changes which boost the pumping of mercury enriched water to the oceanic upper layer. Therefore, the upwelling areas might be hot spots for MeHg monitoring in marine biota.

Dimethylmercury Degradation by Dissolved Sulfide and Mackinawite

Potential degradation pathways of dimethylmercury (DMHg) remain as one of the critical knowledge gaps in the marine biogeochemical cycle of mercury (Hg). Although Hg is known to be highly reactive with reduced sulfur, demethylation of DMHg in the presence of sulfide has until now remained experimentally untested. Here, we provide the first experimental support for demethylation of DMHg to monomethylmercury (MMHg) in the presence of both dissolved sulfide and mackinawite (FeS(s)_m). The degradation of DMHg was shown to be pH dependent, with higher demethylation rates at pH 9 than pH 5. At room temperature and environmentally relevant DMHg to sulfide molar ratios, we observed demethylation rates up to 0.05 d^-1. When comparing the number of active sites available, FeS(s)_m was found to have a higher capacity to demethylate DMHg, in comparison with dissolved sulfide. Our study suggests that dissolved sulfide and FeS(s)_m mediated demethylation of DMHg may act as a sink for DMHg, and a potential source of MMHg, in aquatic systems.

Mercury exposure in relation to foraging ecology and its impact on the oxidative status of an endangered seabird

Mercury is a natural element extensively found in the Earth's crust, released to the atmosphere and waters by natural processes. Since the industrial revolution, atmospheric deposition of Hg showed a three-to-five-fold enrichment due to human activities. Marine top predators such as seabirds are recognized valuable bioindicators of ocean health and sensitive victims of Hg toxic effects. Hg negatively affects almost any aspect of avian physiology; thus, birds prove valuable to study the effect of Hg exposure in vertebrates. The Black-vented Shearwater is endemic to the North-Eastern Pacific Ocean, where it forages along the Baja California Peninsula during the breeding period. The area has no industrial settlement and is in the southern portion of the California Current System (CCS). After observing possible contamination effects in eggshells, we decided to quantify the exposure of breeding birds to Hg and test for possible effects on oxidative status of the species. The concentration of Hg in erythrocytes averaged 1.84 μg/g dw and varied from 1.41 to 2.40 μg/g dw. Males and females had similar Hg concentrations. The individual trophic level (reflected by δ¹⁵N) did not explain Hg exposure. In contrast, individuals foraging inshore had higher Hg concentrations than those foraging more offshore (reflected by δ¹³C). Shearwaters having higher concentrations of Hg had lower activity of the antioxidant enzyme glutathione peroxidase and showed lower non-enzymatic antioxidant capacity. Levels of plasma oxidative damage, superoxide dismutase and catalase were not associated with Hg. Our results indicate that (i) the foraging habitat is the factor explaining Hg exposure and (ii) there is some evidence for potential harmful effects of Hg exposure to this seabird species of conservation concern. CAPSULE: The foraging habitat is the factor explaining Hg exposure in seabirds and we observed potential harmful effects of Hg exposure in a seabird species of conservation concern.

Marine fog inputs appear to increase methylmercury bioaccumulation in a coastal terrestrial food web

Coastal marine atmospheric fog has recently been implicated as a potential source of ocean-derived monomethylmercury (MMHg) to coastal terrestrial ecosystems through the process of sea-to-land advection of foggy air masses followed by wet deposition. This study examined whether pumas (Puma concolor) in coastal central California, USA, and their associated food web, have elevated concentrations of MMHg, which could be indicative of their habitat being in a region that is regularly inundated with marine fog. We found that adult puma fur and fur-normalized whiskers in our marine fog-influenced study region had a mean (±SE) total Hg (THg) (a convenient surrogate for MMHg) concentration of 1544 ± 151 ng g-1 (N = 94), which was three times higher (P < 0.01) than mean THg in comparable samples from inland areas of California (492 ± 119 ng g-1, N = 18). Pumas in California eat primarily black-tailed and/or mule deer (Odocoileus hemionus), and THg in deer fur from the two regions was also significantly different (coastal 28.1 ± 2.9, N = 55, vs. inland 15.5 ± 1.5 ng g-1, N = 40). We suggest that atmospheric deposition of MMHg through fog may be contributing to this pattern, as we also observed significantly higher MMHg concentrations in lace lichen (Ramalina menziesii), a deer food and a bioindicator of atmospheric deposition, at sites with the highest fog frequencies. At these ocean-facing sites, deer samples had significantly higher THg concentrations compared to those from more inland bay-facing sites. Our results suggest that fog-borne MMHg, while likely a small fraction of Hg in all atmospheric deposition, may contribute, disproportionately, to the bioaccumulation of Hg to levels that approach toxicological thresholds in at least one apex predator. As global mercury levels increase, coastal food webs may be at risk to the toxicological effects of increased methylmercury burdens.

Dimethylmercury in Floodwaters of Mercury Contaminated Rice Paddies

Dimethyl mercury (CH₃HgCH₃, DMeHg) has been observed in upwelling marine environments and the deep ocean. However, little is known about the occurrence and mechanisms of DMeHg formation in freshwater environments. In this study, concentrations of dissolved gaseous DMeHg were investigated in floodwaters of rice paddies in China that have been contaminated by mercury from mining. Values of DMeHg in rice paddies were compared with measurements from nearshore surface seawater in the Bohai Gulf. High concentrations of dissolved gaseous DMeHg occurred in rice paddies. Average DMeHg concentration was 12 ± 22 pg L^-1 with range of 0.39 to 91 pg L^-1 in rice paddies at Shuijing, China, a site impacted by an abandoned mercury mine. These concentrations are comparable to those previously observed in the deep seawater and coastal upwelling environments (2.3-115pg L^-1). An alkaline environment was found to be necessary for DMeHg formation in rice paddies. Associated incubation experiments showed that production of DMeHg in paddy soil was limited by Hg availability. Although iron amendments accelerated the production of gaseous methylmercury (MeHg) species to floodwaters, available Hg²⁺ is crucial for this production in flooded rice paddies. These observations are the first to demonstrate the occurrence of DMeHg and reveal factors affecting DMeHg production in rice paddies. Given the high volatility of DMeHg, these measurements also suggest a source for observations of MeHg in atmospheric deposition and advance understanding of a potentially important aspect of the biogeochemical cycling of Hg.

PCB and PBDE contamination in Tursiops truncatus and Stenella frontalis, two data-deficient threatened dolphin species from the Brazilian coast

Polychlorinated biphenyls (PCB) and polybrominated diphenyl ethers (PBDE) levels were assessed in the liver and muscle of two data-deficient threatened dolphin species, the bottlenose dolphin (Tursiops truncatus, n = 4) and the Atlantic spotted dolphin (Stenella frontalis, n = 6), sampled off the Southeastern Brazilian coast. PCB concentrations were greater in liver compared to muscle, with males presenting higher concentrations than females. The three main detected PCB congeners were PCBs 138, 153 and 180. A predominance of hexachlorinated congeners was observed, followed by hepta- and penta-PCBs. For both species, Cl 3 and Cl 4 levels were higher in muscle compared to liver, while Cl 5 to Cl 8 and ∑PCBs were higher in liver. PBDE concentrations were significantly higher in Atlantic spotted dolphin muscle and liver compared to bottlenose dolphins. Similarly to PCBs, the highest PBDE concentrations were observed in males. The presence of PBDE congeners BDE-47, -100 and -99 in the muscle and liver of both species suggests the existence of a pollution source in Brazil by a penta-BDE mixture, as PBDEs have never been produced in Brazil. Interspecific PCB and PBDE profiles were very similar, which may be related to the similar characteristics of the analyzed species, mainly geographic distribution and life and feeding habits. This study furthers knowledge on environmental PCB and PBDE contamination, assisting in the establishment of dolphin population conservation strategies. In addition, this study calls into question the current threshold values established for PCBs and PBDEs, and demonstrates the lack of information and knowledge in this regard for cetaceans.

Mechanism of Accumulation of Methylmercury in Rice ( Oryza sativa L.) in a Mercury Mining Area

Rice consumption is the primary pathway for methylmercury (MeHg) exposure at inland mercury (Hg) mining areas of China. The sources and processes of formation and translocation for MeHg in rice plant are complex and remain largely unknown. In this study, rice ( Oryza sativa L.) was exposed to isotopically labeled dimethylmercury (DMe¹⁹⁹Hg) in field experiments using open top chambers to explore the response of MeHg accumulation in rice tissues to different levels of DMe¹⁹⁹Hg in air. Rice leaves assimilated DMeHg from air, which was subsequently largely stored in aboveground tissues, including the rice grain, with only a small amount reaching the root. Combining these experimental results with field investigations of DMeHg concentrations in air beneath the rice canopy in a Hg mining area, we estimate that 15.5%, 10.8%, and 8.50% MeHg in the brown rice, the leaf, and the upper stalk, respectively, could be derived from atmospheric sources of DMeHg, while 99.5% of MeHg in rice root originated from the rice soil-water system. These findings help refine the mechanism of MeHg accumulation in rice that, in addition to soil, a fraction of MeHg in rice plants can be derived from DMeHg emissions from flooded rice paddies in Hg mining areas.

Aircraft Measurements of Total Mercury and Monomethyl Mercury in Summertime Marine Stratus Cloudwater from Coastal California, USA

Water samples from marine stratus clouds were collected during 16 aircraft flights above the Pacific Ocean near the Central California coast during the summer of 2016. These samples were analyzed for total mercury (THg), monomethyl mercury (MMHg), and 32 other chemical species in addition to aerosol physical parameters. The mean concentrations of THg and MMHg in the cloudwater samples were 9.2 ± 6.0 ng L^-1 (2.3-33.8 ng L^-1) ( N = 97) and 0.87 ± 0.66 ng L^-1 (0.17-2.9 ng L^-1) ( N = 22), respectively. This corresponds to 9.5% (3-21%) MMHg as a fraction of THg. Low and high nonsea salt calcium ion (nss-Ca²⁺) concentrations in cloudwater were used to classify flights as "marine" and "continental", respectively. Mean [MMHg]_marine was significantly higher ( p < 0.05) than [MMHg]_continental consistent with an ocean source of dimethyl Hg (DMHg) to the atmosphere. Mean THg in cloudwater was not significantly different between the two categories, indicating multiple emissions sources. Mean [THg]_continental was correlated with pH, CO, NO₃^-, NH₄⁺, and other trace metals, whereas [THg]_marine was correlated with MMHg and Na⁺. THg concentrations were negatively correlated with altitude, consistent with ocean and land emissions, coupled with removal at the cloud-top due to drizzle formation.

Dimethylmercury Formation Mediated by Inorganic and Organic Reduced Sulfur Surfaces

Underlying formation pathways of dimethylmercury ((CH3)2Hg) in the ocean are unknown. Early work proposed reactions of inorganic Hg (Hg(II)) with methyl cobalamin or of dissolved monomethylmercury (CH3Hg) with hydrogen sulfide as possible bacterial mediated or abiotic pathways. A significant fraction (up to 90%) of CH3Hg in natural waters is however adsorbed to reduced sulfur groups on mineral or organic surfaces. We show that binding of CH3Hg to such reactive sites facilitates the formation of (CH3)2Hg by degradation of the adsorbed CH3Hg. We demonstrate that the reaction can be mediated by different sulfide minerals, as well as by dithiols suggesting that e.g. reduced sulfur groups on mineral particles or on protein surfaces could mediate the reaction. The observed fraction of CH3Hg methylated on sulfide mineral surfaces exceeded previously observed methylation rates of CH3Hg to (CH3)2Hg in seawaters and we suggest the pathway demonstrated here could account for much of the (CH3)2Hg found in the ocean.

Biogeochemical transformations of mercury in solid waste landfills and pathways for release

Mercury (Hg) is present in a variety of solid wastes including industrial wastes, household products, consumer electronics, and medical wastes, some of which can be disposed in conventional landfills. The presence of this neurotoxic metal in landfills is a concern due to the potential for it to leach or volatilize from the landfill and impact local ecosystems. The objective of this review is to describe general practices for the disposal of mercury-bearing solid wastes, summarize previous studies on the release of mercury from landfills, and delineate the expected transformations of Hg within landfill environments that would influence transport of Hg via landfill gas and leachate. A few studies have documented the emissions of Hg as landfill gas, primarily as gaseous elemental Hg(0) and smaller amounts as methylated Hg species. Much less is known regarding the release of Hg in leachate. Landfill conditions are unique from other subsurface environments in that they can contain water with very high conductivity and organic carbon concentration. Landfills also experience large changes in redox potential (and the associated microbial community) that greatly influence Hg speciation, transformations, and mobilization potential. Generally, Hg is not likely to persist in large quantities as dissolved species, since Hg(0) tends to evolve in the gas phase and divalent Hg(ii) sorbs strongly to particulate phases including organic carbon and sulfides. However, Hg(ii) has the potential to associate with or form colloidal particles that can be mobilized in porous media under high organic carbon conditions. Moreover, the anaerobic conditions within landfills can foster the growth of microorganisms that produced monomethyl- and dimethyl-Hg species, the forms of mercury with high potential for bioaccumulation. Much advancement has recently been made in the mercury biogeochemistry research field, and this study seeks to incorporate these findings for landfill settings.

Mercury Accumulation in Harbour Seals from the Northeastern Pacific Ocean: The Role of Transplacental Transfer, Lactation, Age and Location

Mercury (Hg) bioaccumulates in the aquatic food chain in the form of methylmercury, a compound well known for its neurotoxicity. We analyzed total mercury (THg) in hair collected from 209 harbour seals captured at 10 sites in British Columbia (Canada) and Washington State (USA) between 2003 and 2010. In addition, laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) allowed for a highly refined analysis of THg accumulation over time by examining nine whiskers taken from 4- to 6-week-old pups. We estimate that THg concentrations in pups increased sharply at a point corresponding to mid- to late gestation of their time in utero (4.7 ± 0.8 and 6.6 ± 1.3 µg/g dry weight (dw), respectively), and then again at the onset of nursing (8.1 ± 1.3 µg/g dw). These abrupt changes highlight the importance of both pre- and post-natal THg transfer from the mother to the growing fetus and the newborn pup. While THg levels varied among sites, hair analyses from seals collected at the same site demonstrated the influence of age in THg accumulation with pups (5.3 ± 0.3 µg/g) and juveniles (4.5 ± 0.5 µg/g) having lower levels than those in adults (8.3 ± 0.8 µg/g). Our results revealed that 33 % of the pups sampled (n = 167) had THg levels that surpassed a mammalian hair threshold for neurochemical alterations. This study suggests that Hg could represent a health concern to marine wildlife, especially as atmospheric emissions of this toxic element from human activities in the Pacific Rim and worldwide continue.

Importance of open marine waters to the enrichment of total mercury and monomethylmercury in lichens in the Canadian High Arctic

Caribou, which rely on lichens as forage, are a dietary source of monomethylmercury (MMHg) to many of Canada's Arctic Aboriginal people. However, little is understood about the sources of MMHg to lichens in the High Arctic. We quantified MMHg, total mercury (THg) and other chemical parameters (e.g., marine and crustal elements, δ(13)C, δ(15)N, organic carbon, calcium carbonate) in lichen and soil samples collected along transects extending from the coast on Bathurst and Devon islands, Nunavut, to determine factors driving lichen MMHg and THg concentrations in the High Arctic. Lichen MMHg and THg concentrations ranged from 1.41 to 17.1 ng g(-1) and from 36.0 to 361 ng g(-1), respectively. Both were highly enriched over concentrations in underlying soils, indicating a predominately atmospheric source of Hg in lichens. However, MMHg and THg enrichment at coastal sites on Bathurst Island was far greater than on Devon Island. We suggest that this variability can be explained by the proximity of the Bathurst Island transect to several polynyas, which promote enhanced Hg deposition to adjacent landscapes through various biogeochemical processes. This study is the first to clearly show a strong marine influence on MMHg inputs to coastal terrestrial food webs with implications for MMHg accumulation in caribou and the health of the people who depend on them as part of a traditional diet.

Mercury distribution, methylation and volatilization in microcosms with and without the sea anemone Bunodosoma caissarum

Mercury (Hg) has a complex biogeochemical cycle in aquatic environments. Its most toxic form, methylmercury (MeHg), is produced by microorganisms. This study investigated how the sea anemone Bunodosoma caissarum affects Hg distribution, methylation and volatilization in laboratory model systems. (203)Hg was added to microcosms and its distribution in seawater, specimens and air was periodically measured by gamma spectrometry. MeHg was measured by liquid scintillation. After the uptake period, specimens had a bioconcentration factor of 70 and in microcosms with and without B. caissarum, respectively 0.05% and 0.32% of the initial spike was found as MeHg. After depuration, MeHg in specimens ranged from 0.2% to 2.4% of total Hg. Microcosms with B. caissarum had higher Hg volatilization (58%) than controls (17%), possibly due to Hg(2+) reduction mediated by microorganisms associated with its tissues and mucus secretions. Marine organisms and their associated microbiota may play a role in Hg and MeHg cycling.

Determination of monomethylmercury and dimethylmercury in the Arctic marine boundary layer

Our understanding of the biogeochemical cycling of monomethylmercury (MMHg) in the Arctic is incomplete because atmospheric sources and sinks of MMHg are still unclear. We sampled air in the Canadian Arctic marine boundary layer to quantify, for the first time, atmospheric concentrations of methylated Hg species (both MMHg and dimethylmercury (DMHg)), and, estimate the importance of atmospheric deposition as a source of MMHg to Arctic land- and sea-scapes. Overall atmospheric MMHg and DMHg concentrations (mean ± SD) were 2.9 ± 3.6 and 3.8 ± 3.1 (n = 37) pg m(-3), respectively. Concentrations of methylated Hg species in the marine boundary layer varied significantly among our sites, with a predominance of MMHg over Hudson Bay (HB), and DMHg over Canadian Arctic Archipelago (CAA) waters. We concluded that DMHg is of marine origin and that primary production rate and sea-ice cover are major drivers of its concentration in the Canadian Arctic marine boundary layer. Summer wet deposition rates of atmospheric MMHg, likely to be the product of DMHg degradation in the atmosphere, were estimated at 188 ± 117.5 ng m(-2) and 37 ± 21.7 ng m(-2) for HB and CAA, respectively, sustaining MMHg concentrations available for biomagnification in the pelagic food web.

The dependence of the methylation of mercury on the landfill stabilization process and implications for the landfill management

Mercury species and other chemical characteristics of the leachate from anaerobic and semi-aerobic landfills were analyzed to investigate the factors that control mercury methylation during the landfill stabilization process. At the early landfill stage, the total mercury (THg) and the monomethyl mercury (MMHg) released rapidly and significantly, the THg concentration of the semi-aerobic landfill leachate was obviously higher than that of the anaerobic landfill leachate, while compared with the semi-aerobic landfill, the MMHg concentration in the anaerobic landfill was higher. As the landfill time increased, both of THg and MMHg concentration decreased quickly, the THg concentration in the anaerobic landfill was much higher than that in semi-aerobic landfill, while the MMHg concentration in the anaerobic landfill was lower than that in the semi-aerobic landfill. Generally, the concentrations of dimethyl mercury (DMHg) in the anaerobic landfill leachate were slightly higher than in the semi-aerobic landfill leachate during the stabilization process. A significant positive correlation was found between the DMHg concentrations and the pH value in anaerobic landfill leachate, but this correlation was opposite in the semi-aerobic landfill. The oxidative-reductive potential (ORP) condition was found to be the controlling factor of the methylation process during the early stage. However, the chemical characteristics, especially the TOC concentration, appeared to be the dominant factor affecting the methylation process as the landfill time increased.

Mercury speciation in plankton from the Cabo Frio Bay, SE--Brazil

Mercury (Hg) is considered a global pollutant, and the scientific community has shown great concern about its toxicity as it may affect the biota of entire systems, through bioaccumulation and bioamplification processes of its organic form, methylmercury (MeHg), along food web. However, few research studies deal with bioaccumulation of Hg from marine primary producers and the first-order consumers. So, this study aims to determine Hg distribution and concentration levels in phytoplankton and zooplankton in the Cabo Frio Bay, Brazil, a site influenced by coastal upwelling. The results from Hg speciation analyses show that inorganic mercury Hg(II) was the predominant specie in plankton from this bay. The annual Hg species distribution in plankton shown mean concentration of 2.00 ± 1.28 ng Hg(II) g(-1) and 0.15 ± 0.08 ng MeHg g(-1) wet weight (phytoplankton) and 2.5 ± 2.03 ng Hg(II) g(-1) and 0.25 ± 0.09 ng MeHg g(-1) wet weight (zooplankton). Therefore, upwelling zones should be considered in the Hg biogeochemical cycle models as a process that enhances Hg(II) bioaccumulation in plankton, raising its bioavailability and shelf deposition.

Mercury in cultured oysters (Crassostrea gigas Thunberg, 1793 and C. corteziensis Hertlein, 1951) from four coastal lagoons of the SE Gulf of California, Mexico

In order to determine the mercury concentrations in cultured oysters from coastal lagoons (SE Gulf of California), several individuals of Crassostrea gigas and C. corteziensis were collected and their mercury levels were measured with a cold vapor analyzer. The mean concentrations during the rainy and dry seasons, respectively, were 0.70 and 0.15 microg g(-1) in C. gigas and 0.56 and 0.18 microg g(-1) in C. corteziensis. During the rainy season, elevated mercury contents are apparently related to terrigen transport from the watershed, while during the dry season, the moderate levels are related to upwellings.

Stability of dimethyl mercury in seawater and its conversion to monomethyl mercury

Dimethyl mercury (DMHg) is commonly detected in the world's oceans, but little is known about the mechanisms responsible for DMHg degradation in natural waters or the products of this degradation. Similarly, the potential for the conversion of DMHg to monomethyl mercury (MMHg) under the acidic conditions commonly used to preserve samples for MMHg analysis has not been fully addressed. We provide evidence suggesting that DMHg in natural seawater is not readily photodegraded by sunlight as previously thought. Other experiments demonstrated that DMHg in seawater is, however, readily decomposed under acidic conditions, with MMHg as the predominant product. This facile conversion of DMHg to MMHg at low pH both necessitates an alternative preservation method to acidification for samples to be analyzed for MMHg when DMHg is present, and requires that data from previous studies of MMHg in seawater employing sample acidification be revisited in instances where appreciable DMHg concentrations were possible.