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There has been increasing concern about mercury (Hg) levels in marine and freshwater organisms in the Arctic, due to the importance of traditional country foods such as fish and marine mammals to the diet of Northern Peoples. Due to its toxicity and ability to bioaccumulate and biomagnify in food webs, methylmercury (MeHg) is the form of Hg that is of greatest concern. The main sources of MeHg to Arctic aquatic ecosystems, the processes responsible for MeHg formation and degradation in the environment, MeHg bioaccumulation in Arctic biota and the human health implications for Northern Peoples are reviewed here. In Arctic marine ecosystems, Hg(II) methylation in the water column, rather than bottom sediments, is the primary source of MeHg, although a more quantitative understanding of the role of dimethylmercury (DMHg) as a MeHg source is needed. Because MeHg production in marine waters is limited by the availability of Hg(II), predicted increases in Hg(II) concentrations in oceans are likely to result in higher MeHg concentrations and increased exposure to Hgin humans and wildlife. In Arctic freshwaters, MeHg concentrations are a function of two antagonistic processes, net Hg(II) methylation in bottom sediments of ponds and lakes and MeHg photodemethylation in the water column. Hg(II) methylation is controlled by microbial activity and Hg(II) bioavailability, which in turn depend on interacting environmental factors (temperature, redox conditions, organic carbon, and sulfate) that induce nonlinear responses in MeHg production. Methylmercury bioaccumulation-biomagnification in Arctic aquatic food webs is a function of the MeHg reservoir in abiotic compartments, as well as ecological considerations such as food-chain length, growth rates, life-history characteristics, feeding behavior, and trophic interactions. Methylmercury concentrations in Arctic biota have increased significantly since the onset of the industrial age, and in some populations of fish, seabirds, and marine mammals toxicological thresholds are being exceeded. Due to the complex connection between Hg exposure and human health in Northern Peoples--arising from the dual role of country foods as both a potential Hg source and a nutritious, affordable food source with many physical and social health benefits--reductions in anthropogenic Hg emissions are seen as the only viable long-term solution. Key words: mercury, methylation, Arctic, bioaccumulation, freshwater, marine. On observe une preoccupation accrue au sujet des teneurs en mercure (Hg) chez les organismes marins et d'eau douce dans l'Arctique, dues a l'importance de la nourriture traditionnelle du pays comme le poisson et les mammiferes marins. A cause de sa toxicite et de sa capacite d'accumulation et de bioamplification dans la chaine alimentaire, le methyle de mercure (MeHg) constitue la forme de Hg soulevant les plus grandes preoccupations. L'auteur passe en revue les principales sources de MeHg pour les systemes aquatiques de l'Arctique, les precedes responsables de la formation et de la degradation dans l'environnement, la bioaccumulation du Hg dans le biote arctique et les implications pour la sante humaine des peuplades nordiques. Dans les ecosystemes arctiques, la methylation du Hg(II) dans la colonne d'eau, plutot que dans sediments de fond constitue la premiere source de MeHg, bien qu'une comprehension plus quantitative du role du dimethyle mercure (DMHg) comme source de MeHg s'avere necessaire. Parce que la production du MeHg dans les eaux marines est limitee par la disponibilite du Hg(II), la prediction des augmentations des concentrations du Hg(II) dans les oceans conduira vraisemblablement a de plus fortes concentrations en MeHg et une exposition accrue des humains et de la faune. Dans les eaux douces de l'Arctique, les concentrations en MeHg dependent de deux processus antagonistes, methylation nette de Hg(II) dans les sediments de fond des marais et des lacs, et photodemethylation du MeHg dans la colonne d'eau. La methylation du Hg(II) est controlee par l'activite microbienne et la disponibilite du Hg(II), laquelle a son tour depend de l'interaction de facteurs environnementaux (temperature, conditions redox, carbone organique et sulfates) induisant des reactions non lineaires sur la production de MeHg. La bioaccumulation/bioamplification dans les chaines alimentaires aquatiques de l'Arctique est fonction du reservoir du MeHg dans les compartiments abiotiques, aussi bien que de considerations ecologiques telles que la longueur de la chaine alimentaire, des taux de croissance, des caracteristiques des cycles de vie, ainsi que des comportements nutritionnels et interactions trophiques. Les teneurs en MeHg dans le biote arctique ont augmente significativement depuis le debut de l'ere industrielle, et chez certaines populations de poissons, d'oiseaux de mer et de mammiferes marins, les seuils toxicologiques sont depasses. Du a la relation complexe entre l'exposition au Hg et la sante humaine des peuples nordiques--provenant du double role des aliments du pays a la fois comme source potentielle de Hg et a la fois comme source d'aliments nutritifs et abordables avec plusieurs avantages pour la sante physique et sociale--les reductions des emissions anthropogenes du Hg s'averent comme la seule solution viable a long terme. [Traduit par la Redaction] Mots-cles: mercure, methylation, Arctique, bioaccumulation, eau douce, marin., Introduction Mercury (Hg) is a global pollutant due to its ability to undergo long-range transport from source regions to remote parts of the world, and its ubiquitous presence in aquatic [...]

We present a detailed study of the biogeochemical factors controlling mercury (Hg) distribution, methylmercury (MeHg) production, and MeHg efflux in sediments of the mid-Atlantic continental shelf and slope. The mildly reduced surface sediments of the shelf and slope provide ideal conditions for MeHg production. They are sufficiently reduced to support microbial sulfate reduction, but contain very low dissolved sulfide concentrations. The redox zonation of sediments determined the depth distribution of MeHg production, whereas the bioavailability of inorganic Hg for methylation appeared to be the dominant driver of spatial patterns across the shelf and slope. Sediment total Hg concentrations were well predicted by sediment organic matter (SOM) content, with the highest concentrations of Hg and MeHg in the fine-grained organic clays of the slope. However, SOM-normalized Hg concentrations decreased with distance from shore. The changing character of organic matter with distance from shore appeared to affect Hg partitioning and bioavailability for methylation. The percentage of Hg in sediments as MeHg was well predicted by measured methylation rates, but not by demethylation rates. On the basis of measured concentrations in bottom waters and surficial pore waters, the average diffusive efflux of Hg(II) and MeHg from sediments to coastal waters was estimated to be 26 and 0.8 pmol [M.sup.-2] [d.sup.-1], respectively. Extrapolated globally, the diffusive input of MeHg from shelf and slope sediments is estimated to be 0.01 Mmol per year. As the actual fluxes can be substantially higher than diffusive fluxes, we suggest that shelf and upper slope sediments are a major source of MeHg to the coastal ocean. doi: 10.4319/lo.2010.55.6.2703

The watershed analysis risk management framework (WARMF) model was applied to Wetland $6 of the Marcell Experimental Forest, using the data from a field experiment, conducted to investigate the effect of sulfate additions on mercury methylation in the wetland. The wetland was modeled as interconnected land catchments. Actual meteorology data and mercury and sulfate concentrations of precipitation were input to the model. To simulate the sulfate sprinkling, the experimental section of the bog was irrigated with sulfate water on the actual dates of sulfate additions. The model simulated wetland outflows that matched the measured outflows with an R-square of 0.856. WARMF also simulated other phenomena observed in the experiment: higher sulfate and MeHg levels at the wetland outlet after every sulfate addition, and higher sulfate and MeHg levels in the pore water of the bog after only the May addition, not the July and September additions. According to WARMF, the low groundwater table in May allowed the sprinkled sulfate to percolate to the soil stratum 10-30 cm below the ground level of the bog, where the pore water was sampled. In July and September, the sulfate could not reach that zone because the percolation was blocked by high groundwater tables. The sampled soil stratum was not the site of methylation that contributed MeHg to the wetland outlet. The saturated zone of the top 10 cm of bog was the site that produced MeHg, which was flushed to the outlet after all sulfate additions. WARMF predicted that quadrupling the sulfate deposition would increase the MeHg output by 216%, which might become lower with more data and better model calibration. DOI: 10.1061/(ASCE)EE. 1943-7870.0000176 CE Database subject headings: Wetlands; Water pollution; Water quality; Mercury; Sulfates; Simulation models. Author keywords: Wetland; Atmospheric deposition; Mercury; Sulfate; Methylmercury output; Model simulation.

Total mercury and methylmercury concentrations ([THg], [MeHg]) were measured in littoral macroinvertebrates from Lake St. Pierre, Quebec, Canada. Functional groups (detritivore, grazer, edible predator, inedible predator) explained the greatest fraction of [MeHg] variation compared with time (year, month), and space (station and shore). Greatest [THg] and [MeHg] were found in inedible predators mostly from families of heteropterans and coleopterans. Detritivores and grazers exhibited the lowest Hg concentrations, while edible predators were intermediate. Inedible predators also had the highest percentage of MeHg ([MeHg]/[THg]), with some taxa close to 100%. Such high percentages are seldom observed in freshwater organisms other than piscivorous fish. MeHg burden (concentrations x biomass) in inedible predators accounted for 10% of the MeHg pool for the whole invertebrate community. These large quantities of MeHg are sequestrated in aquatic 'trophic dead ends' and could partly explain the low [MeHg] measured in fish, compared with [MeHg] of macroinvertebrates from Lake St. Pierre and other freshwater ecosystems with large littoral zones. We recommend taking into account the inedible organisms in Hg cycling models to avoid a possible overestimation of the MeHg pool available to fish. Nous avons mesure les concentrations en mercure total et methylmercure ([THg] et [MeHg]) chez les macroinverte bres littoraux du lac Saint Pierre, Quebec, Canada. Le groupe fonctionnel (detritivore, brouteur, predateur consommable, predateur non consommable) explique la plus forte proportion de la variation de [MeHg] compare au temps (annee, mois) et a l'espace (station, rive). Les plus fortes [THg] et [MeHg] se retrouvent chez les predateurs non consommables appartenant a des familles de coleopteres et d'heteropteres. Les detritivores et les brouteurs montrent les plus faibles concentrations, alors que les predateurs consommables sont intermediaires. Les predateurs non consommables presentent egalement les plus forts pourcentages de MeHg ([MeHg]/[THg]), avec certains taxons proches de 100 %. De tels pourcentages ne sont habituellement observes en eau douce que chez les poissons piscivores. La charge de MeHg (concentration x biomasse) chez les predateurs non consommables represente 10 % du reservoir de MeHg de la communaute des macroinvertebres. Cette quantite importante de MeHg est sequestree dans des impasses trophiques aquatiques et pourrait expliquer partiellement les faibles [MeHg] mesurees chez les poissons comparees aux [MeHg] des macroinvertebres du lac Saint Pierre et des autres ecosystemes d'eau douce avec des zones littorales etendues. Nous recommandons de tenir compte des organismes non consommables dans les modeles de cycle du Hg afin de ne pas surestimer les quantites de MeHg disponibles pour les poissons., Introduction Monomethylmercury (MeHg) is considered a global threat to human and ecosystem health because of its neurotoxicity and accumulation in food webs through biomagnification (Boening 2000). Since fish consumption is [...]

A study to identify unresolved issues about Methylmercury (MeHg) exposure, health effects and risk assessment was conducted. The results showed that the levels of exposure to MeHg have the potential to result in an elevated risk of cardiovascular disease to a significant fraction of the population.

Recent findings indicate that fishes from lakes in partially burned catchments contain greater mercury (Hg) concentrations than fishes from reference catchments. Increased methyl Hg (MeHg) concentrations in fishes can result in serious health problems for consumers. Here we show that a forest fire caused a 5-fold increase in whole-body Hg accumulation by rainbow trout (Oncorhynchus mykiss) and smaller Hg increases in muscle of several fish species in a mountain lake. The enhanced Hg accumulation was caused primarily by increased nutrient concentrations in the lake, which enhanced productivity and restructured the food web through increased piscivory and consumption of Mysis. This restructuring resulted in increases to the trophic positions and Hg concentrations of fishes. Forest fire also caused a large short-term release of total Hg (THg) and MeHg to streams and the lake. This release initiated a small pulse of MeHg in invertebrates that contributed to enhanced Hg accumulation by fishes. Climate change and prescribed burning to compensate for past fire suppression are predicted to increase future forest fire occurrence in North America, and increased Hg accumulation by fishes may be an unexpected consequence. productivity | stable isotopes | methyl mercury | food chain length | climate change

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2006.01.019 Byline: Nelia Cortes-Maramba (a), Jose Paciano Reyes (a), Ana Trinidad Francisco-Rivera (b), Hirokatsu Akagi (c), Rose Sunio (d), Lynn Crisanta Panganiban (a) Keywords: Mercury; Methylmercury; Small scale mining; Health effects Abbreviations: AAS, atomic absorption spectrophotometry; ALT, aspartate aminotransferase; ANOVA, analysis of variance; AST, alanine aminotransferase; BUN, blood urea nitrogen; DENR, Department of Environmental and Natural Resources; e.g., example; EHC, Environmental Health Criteria; EPA, Environmental Protection Agency; g, gram; Hg, mercury; IAEA, International Atomic Energy Agency; kg, kilograms; L, liter; m.sup.3, cubic meter; mg, milligrams; ng, nanogram; NIOSH, National Institute of Occupational Safety and Health; NV, normal value; PEFR, peak expiratory flow rate; ppb, parts per billion; ppm, parts per million; SSPS, statistical package for social sciences; [mu]g, micrograms; US-FDA, United States Food and Drug Administration; WHO, World Health Organization Abstract: The small-scale gold mining activities using mercury began in the late 1980s in Sibutad, Western Mindanao. It is located very near the Murcielagos Bay with tailing ponds directly discharging into bodies of water. This cross-sectional study aimed to determine the health and environmental effects of gold mining activities on the community. Residents were randomly selected and classified into two groups, namely, the directly exposed and indirectly exposed populations using a set inclusion criteria. Complete medical and laboratory examinations were performed. Environmental and biologic samples were collected for total mercury and methylmercury determinations. The results showed that the directly exposed group had significantly higher mean blood total mercury and methylmercury levels in comparison with the indirectly exposed population. Although there were no significant differences between hair total mercury and methylmercury levels, there was a trend for higher levels of these biomarkers among the directly exposed residents as compared with the unexposed group. The absence of statistically significant differences may be attributable to the small sample size. Ambient air quality monitoring for mercury exceeded the allowable levels. However, levels of mercury in drinking water and sediments were within allowable limits. Frequency of gastrointestinal complaints was significantly associated with elevated hair methylmercury levels (p=0.02). Also, there appears to be a trend towards higher blood total mercury levels and frequency of gastrointestinal complaints (p=0.09). An interesting finding in this study was the increasing incidence of elevated diastolic blood pressure with elevated hair total mercury levels (p=0.07). Mercury storage at home is a risk factor. Author Affiliation: (a) National Poison Control & Information Service, College of Medicine, University of the Philippines-Manila, Philippines (b) Environmental & Occupational Health Office, National Center for Disease Prevention & Control, Department of Health, Manila, Philippines (c) National Institute for Minamata Disease, Japan (d) Center for Health Development for Western Mindanao, Zamboanga City, Philippines Article History: Received 4 March 2004; Revised 26 January 2006; Accepted 31 January 2006

INTRODUCTION MERCURY (HG) IS A HEAVY METAL that exists in many different forms in the environment. One of these forms, monomethyl mercury (MMHg), is a strong vertebrate neurotoxin that bioaccumulates [...]

The cycle of waterborne methylmercury (meHg) in Little Rock Lake is characterized by a period of accumulation during summertime (when the lake is warm and open to the atmosphere) and a period of decline during winter (when the lake is sealed by ice). We followed this cycle for 16 yr, during which time the lake was acidified with [H.sub.2]S[O.sub.4] and then allowed to recover naturally as part of a long-term field experiment on acidic rain. Mass balance was used to quantify meHg sources and sinks during acidification and recovery. Although year-to-year variability in the summertime accumulation of meHg was high during both acidified and de-acidified years (C.V. = 0.7 and 0.5, respectively), on average 65% more meHg accumulated in the water column during acidification. Most of the meHg mass accumulated in the anoxic hypolimnion (>70%), even though the hypolimnion constituted

ABSTRACT This paper considers several broad issues in the context of probabilistic assessment of the benefits of curtailing mercury (Hg) emissions from U.S. coal-fired power plants, based on information developed [...]

The rates of methylmercury (MeHg) bioaccumulation in tree swallows breeding near man-made experimental reservoir nearly doubled after flooding. However, the mean MeHg burdens in the insectivorous, nestling songbird did not produce overt toxicological affects and did not affect reproductive success.

Methylmercury is an environmental toxicant that biomagnifies and causes severe neurological degeneration in animals. It is produced by bacteria in soils and sediments that have been contaminated with mercury. To explore the potential of plants to extract and detoxify this chemical, we engineered a model plant, Arabidopsis thaliana, to express a modified bacterial gene, merBpe, encoding organomercurial lyase (MerB) under control of a plant promoter. MerB catalyzes the protonolysis of the carbon - mercury bond, removing the organic ligand and releasing Hg(II), a less mobile mercury species. Transgenic plants expressing merBpe grew vigorously on a wide range of concentrations of monomethylmercuric chloride and phenylmercuric acetate. Plants lacking the merBpe gene were severely inhibited or died at the same organomercurial concentrations. Six independently isolated transgenic lines produced merBpe mRNA and MerB protein at levels that varied over a 10- to 15-fold range, and even the lowest levels of merBpe expression conferred resistance to organomercurials. Our work suggests that native macrophytes (e.g., trees, shrubs, grasses) engineered to express merBpe may be used to degrade methylmercury at polluted sites and sequester Hg(II) for later removal.

Emerging acid rain problems and problems related to various airborne toxins and effects in soils are discussed by David Schindler, the Volvo Environment Prize winner, a member of the Dept. of Biological Sciences, Univ. of Alberta, Canada. A chain of events involving depletion of basic cations in soils and global warming can result ultimately in a significant threat to indigenous peoples living at high latitudes.

Mercury contamination from gold mining is discussed as seen in environmental and human samples from two lakes in the state of Amapa of the Brazilian Amazon delta region where new gold mining activity exists. Mercury profiles in sediments of Duas Bocas Lake show evolving pollution with mercury significantly higher in fish and human hair than in the Pracuuba Lake area, a pristine area, but in both lakes bioavailability is high, a problem for humans, since daily fish intake is about 200 g.

Fall destratification appears to be a significant period for entry into the food chain of monomethylmercury (MMHg) in lakes with a hypolimnetic buildup of MMHg. Devil's Lake, WI, was the site of a study of mercury dynamics, with maximum concentrations of MMHg appearing close to the occurrence of complete mixis. Topics discussed include Hg concentration, Hg seasonal dynamics in biota fractions, Daphnia, planktivorous fish, and multiyear dynamics.

The major factor that determines the concentration of mercury in the biota is the methylmercury concentration in water. That concentrations is controlled by the relative efficiency of methylation/demethylation. Demethylation is both photochemical and biological. Methylmercury is better retained than the inorganic form by organisms. For that reason methylmercury is bioconcentrated instead of inorganic mercury. Anoxic waters/sediments are important sources of methylmercury, likely the result of the methylating activity of sulfate-reducing bacteria. In surface water methylcercury may come from anoxic layers. Understanding of factors that control the bioconcentration of mercury are not well understood.

The magnitude of four terrestrial boreal forest catchments as sources or sinks for methylmercury (MeHg) andd total mercury (THg) was studied at the Experimental Lakes Area in northwestern Ontario. Results showed that all catchments were sinks for THg but there was wide variation in the strength of the catchments as sinks for MeHg. This variation was apparently due to the differences in hydrology within the wetlands. The wetlands were greater sources of MeHg during years of high water yield than during low water yield years.

The widespread problem of mercury contamination in south Florida has prodded authorities and researchers to develop measures to stop the causes of mercury accumulation. Eutrophication has been suggested as one of the major causes of methylmercury accumulation in the peat soils of the Everglades due to their high phosphorus concentration. However, analysis of agricultural runoff show that eutrophication has no effect on methylmercury formation in peat soils.

The photodegradation of surface water decomposes methylmercury in lakes. The reaction rate is of the first order, and depends only on the methylmercury concentration and the intensity of solar radiation and is independent of biological influences. In situ incubation of lake water indicates that rates of photodegradation are nearly double the rates contributed by snow, rain water, land runoff, and streamflow. The levels of methylmercury in the bottom sediments are high. The decomposition rate decreases with depth and is associated with the exponential reduction in light intensity.

The total mercury and methylmercury content of Adirondack lake water as well as their concentrations in fish tissue were determined and the mechanisms regulating their concentrations were investigated. The results showed that mercury concentrations were elevated in Adirondack lake water and fish tissue. Both total and methylmercury concentrations were dependent on dissolved organic carbon concentrations as well as lake pH, aluminum concentration, anoxic hypolimnion, fish age and food sources.

An increased mobilization of mercury and methylmercury from forest soils to aquatic ecosystems is illustrated by two study examples. The results suggest that wind throw and logging of storm-felled trees with associated damage to soils leads to increase of MeHg leaching in relation to degree of damage.

I returned from Hawai'i in mid-December with 700 bottles of seawater. The bottles hold what I hope are solutions to an abiding mystery. In the middle of the ocean, waters [...]

The presence and cycling of mercury is a global issue and understanding of mercury cycling is limited in Africa. It is found that concentrations of this pollutant from Southeast and Central African lakes are indeed low in most fish species consumed and unlikely to pose a risk to consumers.