Elevated blood selenium levels in the Brazilian Amazon

Contaminated fish poses a difficult challenge throughout the world, on the one hand, fish is a very nutritious food source, while on the other hand it accumulates many toxic substances, including mercury (Hg). As part of our efforts in the Brazilian Amazon to maximize nutritional input from fish consumption, a dietary mainstay, and minimize toxic risk, we have been studying the role of selenium (Se), an essential element, that may influence the distribution of Hg in the body and influence Hg neurotoxicity. Se, which is naturally present in the soil, is ingested through consumption of various foods, notably fish, mammals and certain plants. The objectives of the present study were: (i) evaluate whole blood Se (B-Se) and Hg (B-Hg); (ii) characterize B-Se variations with respect to socio-demographic and dietary variables; and (iii) examine the relation between B-Se and B-Hg. A total of 236 persons from six riparian communities of the Tapajós River Basin, a tributary of the Amazon, participated in this study. Whole blood Se and Hg were measured and interview administered questionnaires were used to obtain data on socio-demographic variable, smoking and drinking habits, and fish and fruit consumption. The results show that B-Se are in the upper normal range (median=284.3 microg/L, range=142.1-2029.3 microg/L). No individuals presented B-Se deficiency, but 9 participants from the same extended family had relatively high B-Se levels, potentially a threat to their health. B-Se varied between communities, was significantly higher among alcohol drinkers and farmers, but not associated with age, sex or tobacco consumption. A significant positive relation between B-Se and B-Hg was noted, independently of the overall fish consumption. B-Se increased with consumption of Peacock bass (Cichla sp.), a piscivorous fish species, and coconut pulp (Cocos nucifera L.). The B-Se intercommunity variations may reflect geographic differences in local soil Se levels as well as traditional land use practices in the different ecosystems of the Tapajós River Basin. In this population with relatively high exposure to Hg, Se may play an important role. Further studies should examine, in this region, the sources of Se, its transmission through the terrestrial and aquatic ecosystem and its role with respect to human health.     

Teeth as biomonitors of selenium concentrations in tissues of beluga whales (Delphinapterus leucas)

Selenium (Se) is an essential element which has been shown to play an important role in protecting marine mammals against the toxic effects of mercury (Hg) and other metals. It has been suggested that metal concentration in marine mammal teeth can potentially be used as bioindicators for body burden. The objective of this study was to investigate the relationship between Se concentrations in beluga (Delphinapterus leucas) teeth and those previously measured in soft tissues (liver, kidney, muscle and muktuk). Tooth Hg concentrations are also measured, and the relationships between Se and Hg in teeth and soft tissues are examined. Se in the teeth of beluga was measured using hydride generation atomic fluorescence spectrometry (HG-AFS) and Hg in beluga teeth was measured by cold-vapour atomic absorption. Tooth Se concentrations ranged from 108 ng/g to 245 ng/g dry weight, and tooth Hg concentrations ranged from 10 to 189 ng/g dry weight. In the soft tissues, Se concentrations were highest in the liver, followed by kidney, muktuk, and muscle. There were significant correlations between tooth Se concentrations and animal age, tooth Se and liver and muscle Se, and between liver Se and animal age. The molar ratio of Hg:Se in the liver was found to be 0.70. This study is the first to measure Se in the teeth of a marine mammal species, and HG-AFS is found to be an effective technique for determining Se in beluga teeth. Tooth Se can be used as predictor for liver and muscle Se, although these relationships may be strongly influenced by the association of Se with Hg in marine mammal tissues. This study contributes to an increased understanding of the storage and metabolism of Se in marine mammals.     

Mercury and selenium levels in 19 species of saltwater fish from New Jersey as a function of species, size, and season

There are few data on risks to biota and humans from mercury levels in saltwater fish. This paper examines mercury and selenium levels in muscle of 19 species of fish caught by recreational fisherfolk off the New Jersey shore, as a function of species of fish, size, and season, and risk of mercury to consumers. Average mercury levels ranged from 0.01 ppm (wet weight) (Menhaden Brevoortia tyrannus) to 1.83 ppm (Mako Shark Isurus oxyrinchus). There were four categories of mercury levels: very high (only Mako), high (averaging 0.3-0.5 ppm, 3 species), medium (0.14-0.20 ppm, 10 species), and low (below 0.13 ppm, 5 species). Average selenium levels for the fish species ranged from 0.18 ppm to 0.58 ppm, and had lower variability than mercury (coefficient of variation = 38.3 vs 69.1%), consistent with homeostatic regulation of this essential element. The correlation between mercury and selenium was significantly positive for five and negative for two species. Mercury levels showed significant positive correlations with fish size for ten species. Size was the best predictor of mercury levels. Selenium showed no consistent relationship to fish length. Over half of the fish species had some individual fish with mercury levels over 0.3 ppm, and a third had fish with levels over 0.5 ppm, levels that pose a human health risk for high end consumers. Conversely several fish species had no individuals above 0.5 ppm, and few above 0.3 ppm, suggesting that people who eat fish frequently, can reduce their risk from mercury by selecting which species (and which size) to consume. Overall, with the exception of shark, Bluefin Tuna (Thunnus thynnus), Bluefish (Pomatomus saltatrix) and Striped Bass (Morone saxatilis), the species sampled are generally medium to low in mercury concentration. Selenium:mercury molar ratios were generally above 1:1, except for the Mako shark.     

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

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

Mercury and selenium concentrations in the internal organs of toothed whales and dolphins marketed for human consumption in Japan

Small cetaceans (toothed whales odontoceti and dolphins delphinidae) have been traditionally hunted along the coast of Japan and fresh red meat and blubber, as well as boiled internal organs such as liver, kidney, lung and small intestine, are still being sold for human consumption. We surveyed mercury contamination in boiled liver, kidney and lung products marketed in Japan between 1999-2001. The average +/- S.D. of total mercury (T-Hg) was 370 +/- 525 (range: 7.60 approximately 1980, n = 26) microg/g in liver, 40.5 +/- 48.5 (7.30-95.1, n = 15) microg/g in kidney and 42.8 +/- 43.8 (2.10-79.6, n = 23) microg/g in lung. A high correlation was observed between T-Hg and selenium (Se) concentrations in these organs, supporting the formation of a Hg-Se complex. The formation of a Hg-Se complex probably contribute to the detoxification of Hg for cetaceans and allows a very large accumulation of Hg in livers. The provisional permitted level of T-Hg in marine foods set by the Japanese Ministry of Health and Welfare is 0.4 microg/ g, and the provisional permitted weekly intake (PTWI) set by WHO is 5 microg/kg bw/week. The maximal T-Hg detected in boiled liver (1,980 microg/g) exceeds the permitted level by approximately 5,000 times and the consumption of only 0.15 g of liver exceeds the PTWI of 60 kg of body weight of the consumer, suggesting the possibility of an acute intoxication by T-Hg even after a single consumption of the product.     

Mercury distribution in waters and fishes of the upper Madeira rivers and mercury exposure in riparian Amazonian populations

In this paper, the results of mercury concentrations in two abiotic compartments (river water and suspended particles) and two biotic compartments (fish and human hair) from the upper Madeira rivers of the Bolivian Amazon basin are presented. Because of the local hydrological regimes and a high deposition rate in the plain, due to the presence of a subsidence zone at the bottom of the Andean piedmont, in the dry season, the highest mercury concentrations and fluxes were not found in rivers where mining activities took place (2.25–6.99 ng l⁻¹; and 1.07–8.67 mg Hg d⁻¹ km⁻²), but at the outlet of the Andean basins exploited for their alluvial gold (7.22–8.22 ng l⁻¹; and 9.47–9.52 mg Hg d⁻¹ km⁻²). The total mercury concentrations measured in surface waters of the upper Beni basin varied during the dry season, from 2.24 to 2.57 ng l⁻¹ in the glacial waters of the Zongo river, to 7.00 ng l⁻¹ in the Madeira River at Porto Velho and 9.49–10.86 ng l⁻¹ at its confluence with the Amazon. The results obtained from fish indicate, on one hand, that 86% of the piscivorous fishes collected in the Beni river were contaminated, and, on the other hand, their high mercury concentrations could exceed by almost four times the WHO (1976) safety limit. In the Beni River, the mercury concentrations found in omnivorous and mud-feeding fish ranged from 0.02 to 0.19 μg g⁻¹ (wet wt.), and in piscivorous fish, from 0.33 to 2.30 μg Hg g⁻¹ (wet wt.). The mercury accumulated by carnivorous fishes was mainly present in its organic form; methylmercury represented 73–98% of the total mercury analysed. Eighty persons were studied in the entire Bolivian Amazonian basin. Unlike the gold miners, who are more affected by tropical diseases, such as malaria and yellow fever, the indigenous people living on the banks of the Beni river, present elevated levels of mercury (9.81 μg g⁻¹ on average). We observed an increase in contamination in young children still being breast-fed, confirming that hair mercury concentration in babies was significantly affected by maternal mercury contamination during pregnancy. These results show that the major health impacts caused by mercury affect people who are not working directly in gold mining activities but who have a regular fish diet.     

The essential toxin: the changing perception of selenium in environmental sciences

During the last decades, the perception of selenium has undergone substantial changes. While its toxic effects were recognized causing hair and hoof loss in animals during the 1930s, its essential role in microbial, animal and human metabolism has been recognized later, i.e. with the discovery of selenium deficiency causing “white muscle disease” in feedstock in the 1950s. Nowadays, the positive effect of systematic selenium supplementation is discussed in manifold topics such as cancer or diabetes prevention and avian influenza susceptibility. Treatment of selenium containing waste streams poses a notable challenge to environmental engineers, and to date no ultimate solution has been found for e.g. the selenium contamination in agricultural areas of the western USA. For the future, selenium contamination carries an imminent danger, if the increasing energy demand is covered by fossil fuel combustion, which will lead to major selenium emission and toxicity. This review presents current knowledge of selenium’s role in environmental sciences and outlines potentially feasible treatment options targeting a variety of selenium contaminated waste streams.     

Inverse relationships between selenium and mercury in tissues of young walleye (Stizosedion vitreum) from Canadian boreal lakes

The concentrations of total mercury (Hg), methylmercury (MeHg) and total selenium (Se) were determined in muscle, liver and brain tissues of young-of-the-year walleye (Stizosedion vitreum) specimens collected from 8 boreal lakes that are located within 107 km around the Sudbury smelters in Ontario, Canada. Dry weight basis concentrations of Hg were highest in muscle and lowest in brain (p < 0.05), those of MeHg were higher in muscle than in liver and brain but there was no significant difference between liver and brain (p < 0.05). The highest Se concentrations were found in liver and the lowest in brain (p < 0.05). Considering the biomass of the studied tissues, muscle was the part of the body where most of Hg, MeHg and Se were accumulated. In fish muscle, the percentage of MeHg over Hg was the highest and this percentage was the lowest in liver. The concentrations of Hg, MeHg and Se in the studied tissues were closely related to the concentrations of total dissolved Se in lake waters which vary with the distance of the lakes from the smelters. Thresholds of Se concentrations in tissues were revealed (6.2, 12.0 and 3.5 mg kg^− 1 dry wt., for muscle, liver and brain, respectively), above which a significant reduction of MeHg concentrations was observed in all studied tissues compared to lower Se levels in the same tissues. Based on the collected information and data analysis, possible mechanisms for the biological processes behind the observed inverse relationships between Se and Hg in fish tissues are discussed.     

Accumulation of mercury and selenium in the brain of river otters (Lontra canadensis) and wild mink (Mustela vison) from Nova Scotia, Canada

Total Hg, methyl-Hg (MeHg) and Se levels were measured in the brain of river otters (Lontra canadensis) and wild mink (Mustela vison) carcasses collected from Nova Scotia, Canada. Total Hg concentrations in the otters' brain were highly variable, ranging from 0.3 to 18.0 μg/g dw and were significantly higher in animals caught from inland areas of the province versus coastal animals. Similarly, inland otters contained significantly more MeHg in the brain than did coastal otters. MeHg was highly correlated with total Hg in both inland and coastal otters and represented on average approximately 82% of the total Hg. Selenium concentrations in the otter brain ranged from 1.0 to 7.8 μg/g dw but unlike Hg, there was no significant difference in Se levels between inland and coastal otters. There was a significant positive relationship between Se and total Hg concentrations in the otters with the molar ratio of Se:Hg approximately 1:1 for animals having an Hg concentration > 18 nmol/g dw.The non-random sampling protocol for the mink precluded extensive statistical analysis of the data. However, unlike otters, virtually all (i.e. 98%) of the total Hg in mink brain was present as MeHg in both inland and coastal mink. Also unlike the otter results, Se concentrations showed no relationship with either total or MeHg in both inland and coastal mink.The data suggest that mink and otters may have different mechanisms for managing high levels of Hg in the brain.     

Plasma levels of copper, manganese and selenium in an adult population in southern Spain: Influence of age, obesity and lifestyle factors

Copper, manganese and selenium are elements involved in protecting the body against oxidative stress. Determining their plasma level may contribute to assessing the health and nutritional status of populations. The aim of this study was to assess factors influencing copper, manganese and selenium plasma levels in an adult Mediterranean population and to identify groups at risk of deficiency. A cross-sectional survey was carried out in Andalusia, a region in southern Spain. Blood samples were obtained in a random subsample of 340 subjects. Food consumption was assessed by 48-h recall. Height, weight, skinfolds, waist and hip circumferences were measured. Copper, manganese and selenium were measured in plasma. Information about physical exercise, educational level, alcohol and smoking habits was obtained with a structured questionnaire. Plasma copper was found to be higher in women than among men. Hypocupraemia was found in 4.4% of the population, while 9.7% presented hypomanganesemia. Moreover, 86.5% presented plasma selenium values below 125 µg/L (cutoff for optimal glutathione peroxidase activity). No association was found between plasma elements, anthropometric indices and lifestyle factors; there were tendencies, no more. Copper tended to decrease in obese and increase in sedentary, while selenium tended to decrease among smokers. Plasma Cu was positively correlated with the consumption of monounsaturated and polyunsaturated fats. Plasma Mn was directly correlated with the consumption of dairy products. Levels of Se were positively correlated with age, the consumption of fruit, vegetables, energy obtained from carbohydrates, and the consumption of fibre, and inversely correlated with the consumption of meat and sweets. Our results provide an estimate of the copper, manganese and selenium status in the adult population of southern Spain. The correlations found for Se suggest that there is a tendency for Se levels to be better maintained among the population that shows a stronger preference for the traditional diet.     

pp'DDE contamination of the blood and diet in central European populations

In this study, the actual risk of DDT pollution to two European human populations was assessed by analysing DDT residues in the diet, which is the main route of pollution for man, and in the blood and placenta, which are components affecting organs and new generations, respectively. The Gdańsk region was selected as representative of areas subjected to a recent DDT ban in Europe, while a rural area in Western Germany was considered representative of European regions where DDT use and production ceased many years ago. The results of three food series of food sampling carried out with market basket methods during 2003 showed that pp'DDE, which is by far the main constituent of DDT residues, was present in foods of animal origin and in cereals at rather high concentrations in both countries, and that a risk for human health cannot be excluded. The total daily intake was higher in Poland than in Germany, and agrees with the finding that body tissues, on the average, are more polluted in donors from Poland than those from Germany.     

Heavy coal combustion as the dominant source of particulate pollution in Taiyuan, China, corroborated by high concentrations of arsenic and selenium in PM10

Coal burning generates toxic elements, some of which are characteristic of coal combustion such as arsenic and selenium, besides conventional coal combustion products. Airborne particulate samples with aerodynamic diameter less than 10 microm (PM(10)) were collected in Taiyuan, China, and multi-element analyses were performed by inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). Concentrations of arsenic and selenium from ambient air in Taiyuan (average 43 and 58 ng m(-3), respectively) were relatively high compared to what is reported elsewhere. Arsenic and selenium were found to be highly correlated (r=0.997), indicating an overwhelmingly dominant source. Correlation between these two chalcophile elements and the lithophile element Al is high (r is 0.75 and 0.72 for As and Se, respectively). This prompted the hypothesis that the particles were from coal combustion. The enrichment of the trace elements could be explained by the volatilization-condensation mechanism during coal combustion process. Even higher correlations of arsenic and selenium with PM(10) (r=0.90 and 0.88) give further support that airborne particulate pollution in Taiyuan is mainly a direct result of heavy coal consumption. This conclusion agrees with the results from our previous study of individual airborne particles in Taiyuan.     

Ecological factors differentially affect mercury levels in two species of sympatric marine birds of the North Pacific

In 2003 and 2004, we measured mercury concentrations and δ¹⁵N and δ¹³C values in the whole blood of adults of two species of seabirds, Cassin's auklet (Ptychoramphus aleuticus) and rhinoceros auklet (Cerorhinca monocerata), during their prelaying, incubation, and provisioning periods. We also collected whole blood from the offspring of both seabirds. Among prey items, δ¹⁵N values were higher in fish than in crustaceans, while δ¹³C did not vary systematically between prey types. Mercury concentrations in prey showed little relationship with either stable isotope. In the zooplanktivorous Cassin's auklet, year, reproductive stage, and δ¹⁵N and δ¹³C stable isotope values explained only 14% of the variation in mercury concentrations in adult blood, and none of these variables had a statistically significant effect. In contrast, these same variables explained 41% of the variation in mercury levels in the more piscivorous rhinoceros auklet, and all but δ¹⁵N values had statistically significant effects. Mercury concentrations in adult rhinoceros auklets were higher in 2003 than in 2004; higher prior to laying than during the incubation or provisioning periods; and increased with δ¹³C values — but in just one of two years. In both species, mercury concentrations were substantially higher in adults than in nestlings. Our results accord with previous studies in showing that mercury concentrations can vary among years, species and age classes, while the marked variation with reproductive stage is noteworthy because it is so rarely considered. Our results may help to explain the disparate conclusions of previous studies: while many factors influence mercury concentrations in marine predators, they apparently do so in a manner that defies easy characterization. We believe that there is a need for more studies that consider a range of physiological, ecological and behavioral factors that might affect mercury burdens in marine predators.     

Elevated levels of arsenic in the sediments of an urban pond: sources, distribution and water quality impacts

The discovery of significantly elevated levels of arsenic (As) in the sediments of Spy Pond motivated us to identify the principal As source and to investigate the extent of contamination within the pond. Spy Pond is located in Arlington (MA, USA), a residential and commercial town with no known history of As use by industry or agriculture. Spy Pond is a kettle-hole pond composed of two basins (north and south) separated by a shallow sill. Sediment cores from the two basins were analyzed for As content by instrumental neutron activation analysis and dated by measuring 210Pb activity. The As concentration profiles for the north and south basins had maxima that dated to approximately 1962 and approximately 1956, respectively. These dates are consistent with records of arsenical herbicide use, which indicate that between 1960-1968 sodium arsenite (NaAsO2) and arsenic oxide (As2O3) were applied to the pond to control aquatic macrophytes. Estimates of As loadings to the two basins-- approximately 410 kg ( approximately 32 kg ha(-1)) to the north and approximately 5800 kg ( approximately 580 kg ha(-1)) to the south--are consistent with the range of application rates reported for other lakes treated with arsenical herbicides. To determine the extent of As contamination in the pond, 68 surface sediment samples were analyzed by energy dispersive X-ray fluorescence. Arsenic levels ranged from 1 to 2600 ppm in the north basin (n = 49) and from 120 to 1100 ppm in the south basin (n = 19). Background sediment-As levels for the area are 10-40 ppm. The highest concentrations of As in the sediments of Spy Pond are comparable to levels measured in lakes contaminated with chemical manufacturing and mining wastes. These results are discussed with respect to As remobilization and sediment treatment measures planned for the pond.     

The water quality of the River Thame in the Thames Basin of south/south-eastern England

The water quality of the River Thame, a tributary of the River Thames in the Thames basin, is described in relation to point and diffuse contaminant inputs and runoff from permeable and impermeable bedrock geology with their own characteristic water quality. The data is examined to see if the market town of Aylesbury in the upper part of the catchment influences water quality. Previous studies highlighted the influence of Aylesbury sewage treatment works (STW) on soluble reactive phosphorus (SRP) concentrations in the river before and after phosphorus (P) stripping at the STW. Variations in water quality along the river are described and the study indicates that, apart from SRP, water quality determinants seem to be relatively unaffected by Aylesbury. The Thame water quality is compared with other catchment typologies and it is very similar to that of the main stem of the Thames even though the Thames is mainly Chalk groundwater fed. Differences in water quality largely link to the amount of STW effluent within the rivers and to the endmember compositions of the groundwater and near surface water sources.     

Incorporating detoxified Argania spinosa press cake into the diet of Alpine goats affects the antioxidant activity and levels of polyphenol compounds in their milk

Goat’s milk is an excellent source of antioxidants that resist oxidative stress. This paper reports on a study of Alpine goats, showing that introducing detoxified Argane press cake (DAPC) into their diet affected the antioxidant activity and polyphenol compounds in their milk during lactation. The results showed that the bioactive compounds of goat milk vary significantly (p < 0.001) depending on both their feed and milk lactation stage. The milk samples obtained from goats fed DAPC ranked highest total phenolic content, flavonoids, and DPPH(1,1-diphenyl-2-picrylhydrazyl) assays (367.91 ± 102.17 mg GAE/g of milk dry matter [DM], 120.76 ± 24.21 mg QE/g of milk DM, and 71.19 ± 2.84%, respectively) compared to milk samples collected from goats fed a diet including non-detoxified Argane press cake (289.03 ± 104.42 mg GAE/g of milk DM, 105.72 ± 13.60 mg QE/g of milk DM, and 64.22 ± 2.45%, respectively) and milk samples from goats fed a local diet (179.26 ± 81.28 mg GAE/g of milk DM, 89.86 ± 17.83 mg QE/g of milk DM, and 61.57 ± 5.08%, respectively). Additionally, the data revealed that including DAPC in the goat diet offers a good method for raising the amounts of total phenolic compounds and total flavonoids, with antioxidant activity in goat’s milk.     

Long-term changes of mercury levels in ringed seal (Phoca hispida) from Amundsen Gulf, and beluga (Delphinapterus leucas) from the Beaufort Sea, western Canadian Arctic

Mercury (Hg) concentrations were determined in the canine teeth of ringed seals (Phoca hispida) harvested during the 13th–14th, late 19th and early 21st Centuries in Amundsen Gulf, Northwest Territories, Canada. Most historical and pre-industrial teeth contained undetectable Hg levels (i.e. < 1.0 ng/g DW), whereas samples from 2001–03 contained up to 12 ng/g DW in an age-dependent pattern. Assuming a median [Hg] value in 13th–14th Century teeth of half the detection limit (i.e. 0.5 ng/g DW), geometric means of Hg in modern teeth were 9–17 times those of seals in the 14th Century, equivalent to an anthropogenic input of 89–94% of total Hg in modern seals. These results corroborate a previous study of beluga (Delphinapterus leucas) in the nearby Beaufort Sea. While the seals' trophic position (inferred from δ¹⁵N values) did not change over time, modern δ¹³C values were lower by about 2‰ than in the 14th and 19th Centuries. This could be due to increased dissolution of anthropogenically derived CO₂ in the ocean from the atmosphere, but could also indicate more offshore pelagic feeding by modern seals, which might be a factor in their Hg exposure. New tooth [Hg] data are also presented for the Beaufort Sea beluga, using recently-discovered museum samples collected in 1960/61, which showed that most of the anthropogenic contribution to beluga Hg had already taken effect by 1960 (reaching  75% of total Hg). Taken together, the long-term seal and beluga data indicate that whereas Hg levels in the marine ecosystems of the western Canadian Arctic were probably unchanged from pre-industrial times up to the late 19th Century, there was a significant, many-fold increase in the early to mid-20th Century, but little or no change after about the early 1960s.