A risk assessment review of mercury exposure in Arctic marine and terrestrial mammals.

There has been a considerable number of reports on Hg concentrations in Arctic mammals since the last Arctic Monitoring and Assessment Programme (AMAP) effort to review biological effects of the exposure to mercury (Hg) in Arctic biota in 2010 and 2018. Here, we provide an update on the state of the knowledge of health risk associated with Hg concentrations in Arctic marine and terrestrial mammal species. Using available population-specific data post-2000, our ultimate goal is to provide an updated evidence-based estimate of the risk for adverse health effects from Hg exposure in Arctic mammal species at the individual and population level. Tissue residues of Hg in 13 species across the Arctic were classified into five risk categories (from No risk to Severe risk) based on critical tissue concentrations derived from experimental studies on harp seals and mink. Exposure to Hg lead to low or no risk for health effects in most populations of marine and terrestrial mammals, however, subpopulations of polar bears, pilot whales, narwhals, beluga and hooded seals are highly exposed in geographic hotspots raising concern for Hg-induced toxicological effects. About 6% of a total of 3500 individuals, across different marine mammal species, age groups and regions, are at high or severe risk of health effects from Hg exposure. The corresponding figure for the 12 terrestrial species, regions and age groups was as low as 0.3% of a total of 731 individuals analyzed for their Hg loads. Temporal analyses indicated that the proportion of polar bears at low or moderate risk has increased in East/West Greenland and Western Hudson Bay, respectively. However, there remain numerous knowledge gaps to improve risk assessments of Hg exposure in Arctic mammalian species, including the establishment of improved concentration thresholds and upscaling to the assessment of population-level effects.

Spatial variation in mercury concentrations in polar bear (Ursus maritimus) hair from the Norwegian and Russian Arctic.

We examined spatial variation in total mercury (THg) concentrations in 100 hair samples collected between 2008 and 2016 from 87 polar bears (Ursus maritimus) from the Norwegian (Svalbard Archipelago, western Barents Sea) and Russian Arctic (Kara Sea, Laptev Sea, and Chukchi Sea). We used latitude and longitude of home range centroid for the Norwegian bears and capture position for the Russian bears to account for the locality. We additionally examined hair stable isotope values of carbon (δ13C) and nitrogen (δ15N) to investigate feeding habits and their possible effect on THg concentrations. Median THg levels in polar bears from the Norwegian Arctic (1.99 µg g-1 dry weight) and the three Russian Arctic regions (1.33-1.75 µg g-1 dry weight) constituted about 25-50% of levels typically reported for the Greenlandic or North American populations. Total Hg concentrations in the Norwegian bears increased with intake of marine and higher trophic prey, while δ13C and δ15N did not explain variation in THg concentrations in the Russian bears. Total Hg levels were higher in northwest compared to southeast Svalbard. δ13C and δ15N values did not show any spatial pattern in the Norwegian Arctic. Total Hg concentrations adjusted for feeding ecology showed similar spatial trends as the measured concentrations. In contrast, within the Russian Arctic, THg levels were rather uniformly distributed, whereas δ13C values increased towards the east and south. The results indicate that Hg exposure in Norwegian and Russian polar bears is at the lower end of the pan-Arctic spectrum, and its spatial variation in the Norwegian and Russian Arctic is not driven by the feeding ecology of polar bears.

State of knowledge on current exposure, fate and potential health effects of contaminants in polar bears from the circumpolar Arctic.

The polar bear (Ursus maritimus) is among the Arctic species exposed to the highest concentrations of long-range transported bioaccumulative contaminants, such as halogenated organic compounds and mercury. Contaminant exposure is considered to be one of the largest threats to polar bears after the loss of their Arctic sea ice habitat due to climate change. The aim of this review is to provide a comprehensive summary of current exposure, fate, and potential health effects of contaminants in polar bears from the circumpolar Arctic required by the Circumpolar Action Plan for polar bear conservation. Overall results suggest that legacy persistent organic pollutants (POPs) including polychlorinated biphenyls, chlordanes and perfluorooctane sulfonic acid (PFOS), followed by other perfluoroalkyl compounds (e.g. carboxylic acids, PFCAs) and brominated flame retardants, are still the main compounds in polar bears. Concentrations of several legacy POPs that have been banned for decades in most parts of the world have generally declined in polar bears. Current spatial trends of contaminants vary widely between compounds and recent studies suggest increased concentrations of both POPs and PFCAs in certain subpopulations. Correlative field studies, supported by in vitro studies, suggest that contaminant exposure disrupts circulating levels of thyroid hormones and lipid metabolism, and alters neurochemistry in polar bears. Additionally, field and in vitro studies and risk assessments indicate the potential for adverse impacts to polar bear immune functions from exposure to certain contaminants.

Detection of serum antibodies to Brucella in Russian aquatic mammals.

A serologic survey of Brucella infection was performed in Caspian seals (Pusa caspica, n=71), Baikal seals (P. sibirica, n=7), ringed seals (P. hispida hispida, n=6), and beluga whales (Delphinapterus leucas, n=4) inhabiting Russian waters, by enzyme-linked immunosorbent assay (ELISA) using Brucella abortus and B. canis as antigens. The sera of 4 Caspian seals (4%) tested positive for B. abortus. The same sera samples demonstrated weaker yet detectable affinity for B. canis antigens. Several discrete bands against B. abortus and B. canis antigens were detected on Western blot analysis of the ELISA-positive seal sera; the bands against B. canis were weaker than those against B. abortus. The sera of 3 beluga whales (75%) were positive for B. abortus antigens but showed no binding to B. canis antigens in the ELISA. The positive whale sera showed a strong band appearance only against B. abortus antigens in the Western blot analysis. Many detected bands were discrete, while some of them had a smeared appearance. The present results indicate that Brucella infection occurred in Caspian seals and beluga whales inhabiting Russian waters, and that the Brucella strains infecting the seals and the whales were antigenetically distinct.

Implications of the circumpolar genetic structure of polar bears for their conservation in a rapidly warming Arctic.

We provide an expansive analysis of polar bear (Ursus maritimus) circumpolar genetic variation during the last two decades of decline in their sea-ice habitat. We sought to evaluate whether their genetic diversity and structure have changed over this period of habitat decline, how their current genetic patterns compare with past patterns, and how genetic demography changed with ancient fluctuations in climate. Characterizing their circumpolar genetic structure using microsatellite data, we defined four clusters that largely correspond to current ecological and oceanographic factors: Eastern Polar Basin, Western Polar Basin, Canadian Archipelago and Southern Canada. We document evidence for recent (ca. last 1-3 generations) directional gene flow from Southern Canada and the Eastern Polar Basin towards the Canadian Archipelago, an area hypothesized to be a future refugium for polar bears as climate-induced habitat decline continues. Our data provide empirical evidence in support of this hypothesis. The direction of current gene flow differs from earlier patterns of gene flow in the Holocene. From analyses of mitochondrial DNA, the Canadian Archipelago cluster and the Barents Sea subpopulation within the Eastern Polar Basin cluster did not show signals of population expansion, suggesting these areas may have served also as past interglacial refugia. Mismatch analyses of mitochondrial DNA data from polar and the paraphyletic brown bear (U. arctos) uncovered offset signals in timing of population expansion between the two species, that are attributed to differential demographic responses to past climate cycling. Mitogenomic structure of polar bears was shallow and developed recently, in contrast to the multiple clades of brown bears. We found no genetic signatures of recent hybridization between the species in our large, circumpolar sample, suggesting that recently observed hybrids represent localized events. Documenting changes in subpopulation connectivity will allow polar nations to proactively adjust conservation actions to continuing decline in sea-ice habitat.

Antibodies to human-related H3 influenza A virus in Baikal seals (Phoca sibirica) and ringed seals (Phoca hispida) in Russia.

Antibodies to influenza A virus were detected using enzyme-linked immunosorbent assay (ELISA) in the sera from two of seven Baikal seals (Phoca sibrica) and from five of six ringed seals (Phoca hispida) in Russia. In a hemagglutination-inhibition test using H1-H15 reference influenza A viruses, ELISA-positive sera from one Baikal seal and four ringed seals reacted to A/Aichi/2/68 (H3N2) and A/Bangkok/1/79 (H3N2) strains. One ringed seal serum sample reacted to A/seal/Massachusetts/1/80 (H7N7). The present results suggested that human-related H3 viruses were prevalent in Baikal seals and ringed seals inhabiting the central Russian Arctic.

Serological evidence of transmission of human influenza A and B viruses to Caspian seals (Phoca caspica).

Seroepidemiological surveillance of influenza in Caspian seals (Phoca caspica) was conducted. Antibodies to influenza A virus were detected in 54% (7/13), 57% (4/7), 40% (6/15) and 26% (11/42) of the serum samples collected in 1993, 1997, 1998 and 2000 by enzyme-linked immunosorbent assay (ELISA). In an hemagglutination-inhibition (HI) test using H1-H15 reference influenza A viruses as antigens, more than half of the examined ELISA-positive sera reacted with an H3N2 prototype strain A/Aichi/2/68. These sera were then examined by HI test with a series of naturally occurring antigenic variants of human H3N2 virus, and H3 viruses of swine, duck, and equine origin. The sera reacted strongly with the A/Bangkok/1/79 (H3N2) strain, which was prevalent in humans in 1979-1981. The present results indicate that human A/Bangkok/1/79-like virus was transmitted to Caspian seals probably in the early 1980s, and was circulated in the population. Antibodies to influenza B virus were detected by ELISA in 14% (1/7) and 10% (4/42) serum samples collected from Caspian seals in 1997 and 2000, respectively. Our findings indicate that seal might be a reservoir of both influenza A and B viruses originated from humans.