Mercury speciation in brain tissue of polar bears (Ursus maritimus) from the Canadian Arctic

An exploratory spatial contaminant assessment for polar bear (Ursus maritimus) liver, fat, and muscle from northern Canada

Since the industrial era, chemicals have been ubiquitous in worldwide ecosystems. Despite the discontinued release of highly toxic persistent organic pollutants (POPs) in the environment, the levels of some POPs are still being measured in the Canadian Arctic. These contaminants are of great concern due to their persistence, toxicity, and levels of bioaccumulation in food chains. Animals occupying top trophic positions in the Canadian Arctic, particularly polar bears, are exposed to these contaminants mainly through their diet. Our study investigated the levels of 30 metals (including total and methyl mercury) alkaline and alkaline earth metals, 15 polycyclic aromatic compounds and their alkyl congeners (PACs), 6 chlordanes (CHLs), and 20 polychlorinated biphenyls (PCBs), in 49 polar bears from the Canadian Arctic. Contaminant burden was measured in liver, muscle, and fat in bears of different sex, age, and locations. A principal component analysis did not distinguish differences between age and sex profiles for most contaminants. However, the concentrations measured and their distribution in the tissues confirm findings observed in past studies. This study highlights the importance of continual monitoring of polar bear health (e.g., newly detected PACs were measured within this study) and evaluating those impacts for the next generations of polar bears.

Lead and Other Trace Element Levels in Brains of Croatian Large Terrestrial Carnivores: Influence of Biological and Ecological Factors

Trace element pollution can adversely affect the brains of individuals and thus impact the entire population of apex predators, such as large European carnivores. We assessed exposure to prominent neurotoxicants As, Cd, Hg and Pb by measuring their brain stem levels in brown bears (n = 114), grey wolves (n = 8), Eurasian lynx (n = 3), and golden jackals (n = 2) sampled in 2015-2022 in Croatia. The highest of the non-essential elements was the Pb level in the bears' brains (median, Q1-Q3; 11.1, 7.13-24.1 μg/kg wet mass), with 4% of animals, all subadults, exceeding the established normal bovine levels (100 μg/kg wet mass). Species-specific differences were noted for Ca, Cd, Cu, Fe, Pb and Se brain levels. Female brown bears had higher As brain levels than males. Cubs and yearlings had lower brain Cd, but higher Zn, while subadults had higher Cu than adult bears. Hepatic As, Cd, Cu and Hg levels were shown to be a moderate proxy for estimating brain levels in bears (r_S = 0.30-0.69). Multiple associations of As, Cd, Hg and Pb with essential elements pointed to a possible interaction and disturbance of brain Ca, Cu, Fe, Se and Zn homeostasis. Non-essential element levels in the brains of four studied species were lower than reported earlier for terrestrial meso-carnivores and humans. The age and sex of animals were highlighted as essential factors in interpreting brain element levels in ecotoxicological studies of large carnivores.

Comparative review of the distribution and burden of contaminants in the body of polar bears

Historical (or legacy) contaminants, such as metals and persistent organic pollutants (POPs; e.g., polychlorinated biphenyls) have been measured in circumpolar subpopulations of polar bears, especially from Hudson Bay, East Greenland, and Svalbard, but substantially less is currently known about new and/or emerging contaminants such as polychlorinated naphthalenes, current-use pesticides, organotins, and polycyclic aromatic compounds (PACs). The polar bear (Ursus maritimus) is an apex Arctic predator that accumulates high levels of bioaccumulative POPs and mercury (Hg), but there is currently no comprehensive profiling of the present knowledge on contaminants in tissue and body compartments in polar bears. Based on current literature reports and data, and including archived museum samples (as far back as the 1300s) and up to 2018, the aim of this review is to utilize available data to examine the comparative distribution and burden of mainly lipophilic contaminants in kidney, liver, fat, and other body compartments, such as milk, blood, and brain. Highlight outcomes from this review include the following: (1) the kidneys are one of the most important tissue depots of contaminants in polar bears; (2) there is a critical lack of data concerning the presence of metals of concern (other than Hg); and (3) there currently are no data available on the concentrations of many newer and emerging contaminants, such as PACs, which is especially relevant given the increasing oil and gas development in regions, such as the Beaufort Sea (Canada). Additionally, given the vulnerability of polar bear populations worldwide, there is a need to develop non-invasive approaches to monitor contaminant exposure in polar bears.

A critical review about neurotoxic effects in marine mammals of mercury and other trace elements

Marine mammals are more exposed to mercury (Hg) than any others animals in the world. As many trace elements, Hg it is able to impair the brain function, which could be a cause of population decline. Nevertheless, these issues have been scarcely studied because of the technical and ethical difficulties. We conducted a systematic review about marine mammals' brain exposition to Hg and other trace elements, and their neurotoxic effects. Information was scarce and the lack of standardization of nomenclature of brain structures, sample collecting and results presentation made it difficult to obtain conclusions. Hg was the most studied metal and toothed whales the most studied group. Despite being its target organ, brain accumulates lesser concentrations of Hg than other tissues as liver. We found a significant positive correlation between both organs' burden (rho = 0.956 for cetaceans; rho = 0.756 for pinnipeds). Reported Hg values in brain of cetaceans (median 3.00 ppm ww) surpassed by one or two orders of magnitude those values found in other species as pinnipeds (median 0.33 ppm ww) or polar bears (median 0.07 ppm ww). Such values exceeded neurotoxicity thresholds. Although marine mammals ingest mostly the organic and more toxic form MeHg, different fractions of inorganic mercury can appear in brain, which could suggest some detoxification mechanisms. Other suggested mechanisms include Se-Hg interaction and liver sequestration. Although other elements are subjected to a rigid homeostatic control, appear in low concentrations or do not exert an important neurotoxic effect, they should be more studied to elucidate their neurotoxicity potential.

Selenium and stable mercury isotopes provide new insights into mercury toxicokinetics in pilot whales

High exposures of mammalian species to inorganic mercury (Hg^II) and methylmercury (MeHg) have been associated with adverse effects on behavior and reproduction. Different mammalian species exhibit varying responses to similar external exposure levels, reflecting potential differences in Hg toxicokinetics. Here, we use Hg stable isotopes, total Hg, MeHg and selenium (Se) concentrations measured in multiple tissues of North Atlantic pilot whales (Globicephala melas) to investigate processes affecting the distribution and accumulation of Hg^II and MeHg. We find that simple mixing of two distinct isotopic end-members: MeHg (1.4‰) and Hg^II (-1.6‰) can explain the observed variability of δ²⁰²Hg in brain tissue. A similar isotopic composition for the MeHg end-member in the brain, muscle, heart, and kidney suggests efficient exchange of MeHg in blood throughout the body. By contrast, the Hg isotopic composition of the liver of adult whales is different from younger whales and other tissues that follow the two-end member mixing model. Measured Se:Hg ratios are lowest in adult whales with the highest levels of MeHg exposure. In these individuals, Se availability is likely reduced by complexation with demethylated Hg^II. We speculate that this results in a higher fraction of labile Hg^II eliminated from the liver of adult whales compared to young whales and subsequent redistribution to other tissues, potentially affecting toxicity.

Mercury Accumulation and Effects in the Brain of the Atlantic Sharpnose Shark (Rhizoprionodon terraenovae)

Few published studies have examined whether the elevated concentrations of the nonessential toxic metal mercury (Hg) often observed in shark muscle also occur in the shark brain or whether Hg accumulation affects shark neurophysiology. Therefore, this study examined accumulation and distribution of Hg in the shark brain, as well as effects of Hg on oxidative stress in the shark central nervous system, with particular focus on the Atlantic sharpnose shark (Rhizoprionodon terraenovae). Sharks were collected along the southeastern U.S. coast throughout most of this species' U.S. geographical range. Total Hg (THg) concentrations were measured in and compared between shark muscle and brain, whereas known biomarkers of Hg-induced neurological effects, including glutathione depletion, lipid peroxidation, and concentrations of a protein marker of glial cell damage (S100b), were measured in shark cerebrospinal fluid. Brain THg concentrations were correlated with muscle THg levels but were significantly lower and did not exceed most published thresholds for neurological effects, suggesting limited potential for detrimental responses. Biomarker concentrations supported this premise, because these data were not correlated with brain THg levels. Hg speciation also was examined. Unlike muscle, methylmercury (MeHg) did not comprise a high percentage of THg in the brain, suggesting that differential uptake or loss of organic and inorganic Hg and/or demethylation of MeHg may occur in this organ. Although Hg accumulation in the shark brain generally fell below toxicity thresholds, higher THg levels were measured in the shark forebrain compared with the midbrain and hindbrain. Therefore, there is potential for selective effects on certain aspects of shark neurophysiology if brain Hg accumulation is increased.

The use of hair as a proxy for total and methylmercury burdens in polar bear muscle tissue

Polar bears (Ursus maritimus) are an ecologically important species in the Arctic, whose health, and that of the people whose livelihoods depend on them, are increasingly affected by climate change and the bioaccumulation of contaminants such as mercury (Hg). Although methylmercury (MeHg) is the toxic form of Hg that biomagnifies up food webs, risk assessment studies typically only report on total Hg (THg) concentrations because it is cheaper to quantify. Furthermore, hair is commonly analysed for THg in polar bear as well as human risk assessment studies because it is relatively non-invasive to collect, yet we know little of how THg and MeHg concentrations differ between hair and muscle tissues. In this study, we quantified THg and MeHg concentrations in hair and muscle from 44 polar bears (24 sub-adults: 9 females, 15 males; 18 adults: 5 females, 13 males, and 2 males of unknown age group), harvested in 2015 and 2016 from four subpopulations in Nunavut, Canada (Davis Strait, n = 3; Gulf of Boothia, n = 8; Baffin Bay, n = 15; Foxe Basin, n = 18). We found only moderately positive correlations (0.4 ≤ r ≤ 0.5) between THg concentrations in hair and THg and MeHg concentrations in muscle. Further, 75% and 88% of THg was MeHg in hair and muscle, respectively. High concentrations of THg in hair - 71% of the samples were above the suggested neurochemical no observed effect level for polar bears - suggest some of the bears may be adversely affected by Hg-related health effects. Despite this, all MeHg concentrations in muscle (0.1 to 0.4 mg/kg (wet weight, ww)) were below the consumption maximum Hg concentration of 0.5 mg/kg (ww) set by Canadian health authorities.

A veterinary perspective on One Health in the Arctic

Exposure to long-range transported industrial chemicals, climate change and diseases is posing a risk to the overall health and populations of Arctic wildlife. Since local communities are relying on the same marine food web as marine mammals in the Arctic, it requires a One Health approach to understand the holistic ecosystem health including that of humans. Here we collect and identify gaps in the current knowledge of health in the Arctic and present the veterinary perspective of One Health and ecosystem dynamics. The review shows that exposure to persistent organic pollutants (POPs) is having multiple organ-system effects across taxa, including impacts on neuroendocrine disruption, immune suppression and decreased bone density among others. Furthermore, the warming Arctic climate is suspected to influence abiotic and biotic long-range transport and exposure pathways of contaminants to the Arctic resulting in increases in POP exposure of both wildlife and human populations. Exposure to vector-borne diseases and zoonoses may increase as well through range expansion and introduction of invasive species. It will be important in the future to investigate the effects of these multiple stressors on wildlife and local people to better predict the individual-level health risks. It is within this framework that One Health approaches offer promising opportunities to survey and pinpoint environmental changes that have effects on wildlife and human health.

Assessment of mercury exposure and maternal-foetal transfer in Miniopterus schreibersii (Chiroptera: Miniopteridae) from southeastern Iberian Peninsula

Mercury (Hg) is a highly toxic and widely distributed metal that is bioaccumulated in insectivorous mammals and may cause adverse effects on the reproductive system. Bats are considered excellent Hg bioindicators due to their wide distribution, life span, trophic position, metabolic rate and food intake. However, few studies have analysed Hg residues in bats, and to the best of our knowledge, no studies have been made in the Iberian Peninsula. The main aim of this study was to undertake the first ever assessment of Hg exposure in Schreiber's bent-winged bats inhabiting a natural cave in the southeast of Spain. The findings suggest that Schreiber's bent-winged bats in the sampling area are chronically exposed to low levels of Hg. The Hg concentrations found in different tissues (fur, kidney, liver, muscle and brain) were below the threshold levels associated with toxic effects in mammals. Non-gestating females showed Hg concentrations in the brain and muscle that doubled those found in gestating females. This could be due to Hg mobilization from the mother to the foetus in gestating females, although other factors could contribute to explain this result such as variations in hunting areas and the insect-prey consumed and/or different energetic needs and average food consumption during the breeding season. Hg levels were 1.7 times higher, although not significant, in foetus' brains than in the maternal brains, and Hg concentration in foetus' brain was significantly correlated with levels in the corresponding mothers' kidney. These results suggest that there could be an active mother-to-foetus transfer of Hg in bats, which would be of special relevance in a scenario of higher Hg exposure than that found in this study. However, further research is needed to support this view due to the limited number of samples analysed. Given the scarce ecotoxicological data available for bats and their protected status, we encourage further opportunistic studies using carcasses found in the field, the validation of non-destructive samples such as fur and guano for Hg monitoring, and new modelling approaches that will increase the data needed for proper ecological risk assessment in bat populations.

Brains of Native and Alien Mesocarnivores in Biomonitoring of Toxic Metals in Europe

Mercury (Hg), lead (Pb) and cadmium (Cd) are involved in mammalian brain damage. However, little is known about Pb and Cd brain levels in wildlife that reflect the geochemical background. The aims of the study include the estimation of Hg, Pb and Cd concentrations, and the determination of relationships between these elements in the brains of 94 mesocarnivores. Road-killed or hunted animals were obtained from north-western Poland near the Polish-German border. The investigation covered the native Eurasian otter Lutra lutra, badger Meles meles, pine marten Martes martes, beech marten M. foina, European polecat Mustela putorius, red fox Vulpes vulpes, and alien species: feral and ranch American mink Neovison vison, raccoon Procyon lotor and raccoon dog Nyctereutes procyonoides. Depending on the diet and environmental pollution, the carnivore brains accumulated toxic metals in varying amounts. The highest median Hg levels (in mg/kg dry weight, dw) were found in the piscivorous Eurasian otter and feral mink (2.44 and 3.96), Pb in the omnivorous raccoon (0.47), while Cd in minks (~0.06). We indicated that Pb-based ammunition is a significant source of the element in scavengers from hunting area, and we also found a significant correlation between Pb and Cd levels in the fox brain. Finally, this study is the first to suggest background levels for brain Pb and Cd in mesocarnivores (<0.50 and <0.04 mg/kg dw, respectively).

Partitioning and kinetics of methylmercury among organs in captive mink (Neovison vison): A stable isotope tracer study

Despite the importance of methylmercury (MeHg) as a neurotoxin, we have relatively few good data on partitioning and kinetics of MeHg among organs, particularly across the blood-brain barrier, for mammals that consume large quantities of fish. The objective of this study was to determine the partition coefficients between blood and brain, liver and kidney and fur for MeHg under steady-state conditions and to measure the half-lives for MeHg in these organs. Captive mink (Neovison vison) were fed a diet enriched with two stable isotopes of Hg, Me(199)Hg and Me(201)Hg for a period of 60 days. After a period of 10 days the diet was changed to contain only Me(201)Hg so that, between days 10 and 60, we were able to measure both uptake and elimination rates from blood, brain, liver kidney and fur. Liver and kidney response was very rapid, closely following changes in blood concentrations but there was a small lag time between peak blood concentrations and peak brain concentrations. Half-lives for MeHg were 15.4, 10.2 and 13.4 days for brain, liver and kidney, respectively. There was no measurable conversion of the MeHg to inorganic Hg (IHg) in the brain over the 60 day period, unlike in liver and kidney.

Assessment of neurotoxic effects of mercury in beluga whales (Delphinapterus leucas), ringed seals (Pusa hispida), and polar bears (Ursus maritimus) from the Canadian Arctic

Marine mammals are indicator species of the Arctic ecosystem and an integral component of the traditional Inuit diet. The potential neurotoxic effects of increased mercury (Hg) in beluga whales (Delphinapterus leucas), ringed seals (Pusa hispida), and polar bears (Ursus maritimus) are not clear. We assessed the risk of Hg-associated neurotoxicity to these species by comparing their brain Hg concentrations with threshold concentrations for toxic endpoints detected in laboratory animals and field observations: clinical symptoms (>6.75 mg/kg wet weight (ww)), neuropathological signs (>4 mg/kg ww), neurochemical changes (>0.4 mg/kg ww), and neurobehavioral changes (>0.1mg/kg ww). The total Hg (THg) concentrations in the cerebellum and frontal lobe of ringed seals and polar bears were <0.5mg/kg ww, whereas the average concentration in beluga whale brain was >3mg/kg ww. Our results suggest that brain THg levels in polar bears are below levels that induce neurobehavioral effects as reported in the literature, while THg concentrations in ringed seals are within the range that elicit neurobehavioral effects and individual ringed seals exceed the threshold for neurochemical changes. The relatively high THg concentration in beluga whales exceeds all of the neurotoxicity thresholds assessed. High brain selenium (Se):Hg molar ratios were observed in all three species, suggesting that Se could protect the animals from Hg-associated neurotoxicity. This assessment was limited by several factors that influence neurotoxic effects in animals, including: animal species; form of Hg in the brain; and interactions with modifiers of Hg-associated toxicity, such as Se. Comparing brain Hg concentrations in wildlife with concentrations of appropriate laboratory studies can be used as a tool for risk characterization of the neurotoxic effects of Hg in Arctic marine mammals.

Recent progress on our understanding of the biological effects of mercury in fish and wildlife in the Canadian Arctic

This review summarizes our current state of knowledge regarding the potential biological effects of mercury (Hg) exposure on fish and wildlife in the Canadian Arctic. Although Hg in most freshwater fish from northern Canada was not sufficiently elevated to be of concern, a few lakes in the Northwest Territories and Nunavut contained fish of certain species (e.g. northern pike, Arctic char) whose muscle Hg concentrations exceeded an estimated threshold range (0.5-1.0 μg g(-1) wet weight) within which adverse biological effects begin to occur. Marine fish species generally had substantially lower Hg concentrations than freshwater fish; but the Greenland shark, a long-lived predatory species, had mean muscle Hg concentrations exceeding the threshold range for possible effects on health or reproduction. An examination of recent egg Hg concentrations for marine birds from the Canadian Arctic indicated that mean Hg concentration in ivory gulls from Seymour Island fell within the threshold range associated with adverse effects on reproduction in birds. Mercury concentrations in brain tissue of beluga whales and polar bears were generally lower than levels associated with neurotoxicity in mammals, but were sometimes high enough to cause subtle neurochemical changes that can precede overt neurotoxicity. Harbour seals from western Hudson Bay had elevated mean liver Hg concentrations along with comparatively high muscle Hg concentrations indicating potential health effects from methylmercury (MeHg) exposure on this subpopulation. Because current information is generally insufficient to determine with confidence whether Hg exposure is impacting the health of specific fish or wildlife populations in the Canadian Arctic, biological effects studies should comprise a major focus of future Hg research in the Canadian Arctic. Additionally, studies on cellular interactions between Hg and selenium (Se) are required to better account for potential protective effects of Se on Hg toxicity, especially in large predatory Arctic fish, birds, and mammals.

In vivo and in vitro changes in neurochemical parameters related to mercury concentrations from specific brain regions of polar bears (Ursus maritimus)

Mercury (Hg) has been detected in polar bear brain tissue, but its biological effects are not well known. Relationships between Hg concentrations and neurochemical enzyme activities and receptor binding were assessed in the cerebellum, frontal lobes, and occipital lobes of 24 polar bears collected from Nunavik (Northern Quebec), Canada. The concentration-response relationship was further studied with in vitro experiments using pooled brain homogenate of 12 randomly chosen bears. In environmentally exposed brain samples, there was no correlative relationship between Hg concentration and cholinesterase (ChE) activity or muscarinic acetylcholine receptor (mAChR) binding in any of the 3 brain regions. Monoamine oxidase (MAO) activity in the occipital lobe showed a negative correlative relationship with total Hg concentration. In vitro experiments, however, demonstrated that Hg (mercuric chloride and methylmercury chloride) can inhibit ChE and MAO activities and muscarinic mAChR binding. These results show that Hg can alter neurobiochemical parameters but the current environmental Hg exposure level does have an effect on the neurochemistry of polar bears from northern Canada.

Molecular and neurochemical biomarkers in Arctic beluga whales (Delphinapterus leucas) were correlated to brain mercury and selenium concentrations

Mercury (Hg) concentrations have increased in western Arctic beluga whales (Delphinapterus leucas) since the industrial revolution. Methylmercruy (MeHg) is a known neurotoxicant, yet little is known about the risk of exposure for beluga whales. Selenium (Se) has been linked to demethylation of MeHg in cetaceans, but its role in attenuating Hg toxicity in beluga whales is poorly understood. The objective of this study is to explore relationships between Hg and Se concentrations and neurochemical biomarkers in different brain regions of beluga whales in order to assess potential neurotoxicological risk of Hg exposure in this population. Brain tissue was sampled from hunter-harvested beluga whales from the western Canadian Arctic in 2008 and 2010. Neurochemical and molecular biomarkers were measured with radioligand binding assays and quantitative PCR, respectively. Total Hg (HgT) concentration ranged from 2.6-113 mg kg(-1) dw in temporal cortex. Gamma-amminobutyric acid type A receptor (GABAA-R) binding in the cerebellum was negatively associated with HgT, MeHg and total Se (SeT) concentrations (p ≤ 0.05). The expression of mRNA for GABAA-R subunit α2 was negatively associated with HgT and MeHg (p ≤ 0.05). Furthermore, GABAA-R binding was positively correlated to mRNA expression for GABAA-R α2 subunit, and negatively correlated to the expression of mRNA for GABAA-R α4 subunit (p ≤ 0.05). The expression of N-methyl-d-aspartate receptor (NMDA-R) subunit 2b mRNA expression was negatively associated with iHglabile concentration in the cerebellum (p ≤ 0.05). Variation of molecular and/or biochemical components of the GABAergic and glutamatergic signaling pathways were associated with MeHg exposure in beluga whales. Our results show that MeHg exposure is associated with neurochemical variation in the cerebellum of beluga whales and Se may partially protect from MeHg-associated neurotoxicity.

Selenium in brown bears (Ursus arctos) from Croatia: Relation to cadmium and mercury

Muscle (n = 111), liver (n = 111), and kidney cortex (n = 101) samples from brown bears (Ursus arctos) were collected in the 2009 and 2010 hunting seasons in Croatia and analysed for selenium (Se), cadmium (Cd), and total mercury (Hg). The aim was to assess the levels of these elements according to age, sex, and season of collection, and to investigate possible Se/Cd and Se/Hg interactions. Median Se concentrations were 0.139 μg/g in muscle, 0.409 μg/g in liver and 1.75 μg/g wet mass in kidney cortex. Median Cd and Hg were 0.0078 and 0.0018 μg/g in muscle, 1.09 and 0.031 μg/g in liver, and 16.5 and 0.206 μg/g wet mass in the renal cortex, respectively. Se/Cd molar ratios were less than 1 in the kidney cortex, and close to or above 1 in liver and muscle, respectively. Toxic Cd and Hg correlated with Se in all of the studied tissues. Sex differences were found for all three elements (except Se in liver), with females having higher tissue concentration than males. Only Cd showed age-dependence. Bear samples collected in fall had higher Se in muscles, and Hg in muscles and liver compared to samples collected in spring. Element concentrations in brown bear tissues were within the range of previously reported studies. Bear meat is considered a rich source of Se, safe for consumption with regard to its Cd and Hg content. According to the molar ratio and correlation results, we assume that Se binding is not the primary detoxification pathway for Cd and Hg in brown bears.

Mercury distribution and speciation in different brain regions of beluga whales (Delphinapterus leucas)

The toxicokinetics of mercury (Hg) in key species of Arctic ecosystem are poorly understood. We sampled five brain regions (frontal lobe, temporal lobe, cerebellum, brain stem and spinal cord) from beluga whales (Delphinapterus leucas) harvested in 2006, 2008, and 2010 from the eastern Beaufort Sea, Canada, and measured total Hg (HgT) and total selenium (SeT) by inductively coupled plasma mass spectrometry (ICP-MS), mercury analyzer or cold vapor atomic absorption spectrometry, and the chemical forms using a high performance liquid chromatography ICP-MS. At least 14% of the beluga whales had HgT concentrations higher than the levels of observable adverse effect (6.0 mg kg(-1) wet weight (ww)) in primates. The concentrations of HgT differed between brain regions; median concentrations (mgkg(-1) ww) were 2.34 (0.06 to 22.6, 81) (range, n) in temporal lobe, 1.84 (0.12 to 21.9, 77) in frontal lobe, 1.84 (0.05 to 16.9, 83) in cerebellum, 1.25 (0.02 to 11.1, 77) in spinal cord and 1.32 (0.13 to 15.2, 39) in brain stem. Total Hg concentrations in the cerebellum increased with age (p<0.05). Between 35 and 45% of HgT was water-soluble, of which, 32 to 41% was methyl mercury (MeHg) and 59 to 68% was labile inorganic Hg. The concentration of MeHg (range: 0.03 to 1.05 mg kg(-1) ww) was positively associated with HgT concentration, and the percent MeHg (4 to 109%) decreased exponentially with increasing HgT concentration in the spinal cord, cerebellum, frontal lobe and temporal lobe. There was a positive association between SeT and HgT in all brain regions (p<0.05) suggesting that Se may play a role in the detoxification of Hg in the brain. The concentration of HgT in the cerebellum was significantly associated with HgT in other organs. Therefore, HgT concentrations in organs that are frequently sampled in bio-monitoring studies could be used to estimate HgT concentrations in the cerebellum, which is the target organ of MeHg toxicity.

What are the toxicological effects of mercury in Arctic biota?

This review critically evaluates the available mercury (Hg) data in Arctic marine biota and the Inuit population against toxicity threshold values. In particular marine top predators exhibit concentrations of mercury in their tissues and organs that are believed to exceed thresholds for biological effects. Species whose concentrations exceed threshold values include the polar bears (Ursus maritimus), beluga whale (Delphinapterus leucas), pilot whale (Globicephala melas), hooded seal (Cystophora cristata), a few seabird species, and landlocked Arctic char (Salvelinus alpinus). Toothed whales appear to be one of the most vulnerable groups, with high concentrations of mercury recorded in brain tissue with associated signs of neurochemical effects. Evidence of increasing concentrations in mercury in some biota in Arctic Canada and Greenland is therefore a concern with respect to ecosystem health.