Temporal trends of mercury in Arctic biota: 10 more years of progress in Arctic monitoring.

Temporal trend analysis of (total) mercury (THg) concentrations in Arctic biota were assessed as part of the 2021 Arctic Monitoring and Assessment Programme (AMAP) Mercury Assessment. A mixed model including an evaluation of non-linear trends was applied to 110 time series of THg concentrations from Arctic and Subarctic biota. Temporal trends were calculated for full time series (6-46 years) and evaluated with a particular focus on recent trends over the last 20 years. Three policy-relevant questions were addressed: (1) What time series for THg concentrations in Arctic biota are currently available? (2) Are THg concentrations changing over time in biota from the Arctic? (3) Are there spatial patterns in THg trends in biota from the Arctic? Few geographical patterns of recent trends in THg concentrations were observed; however, those in marine mammals tended to be increasing at more easterly longitudes, and those of seabirds tended to be increasing in the Northeast Atlantic; these should be interpreted with caution as geographic coverage remains variable. Trends of THg in freshwater fish were equally increasing and decreasing or non-significant while those in marine fish and mussels were non-significant or increasing. The statistical power to detect trends was greatly improved compared to the 2011 AMAP Mercury Assessment; 70% of the time series could detect a 5% annual change at the 5% significance level with power ≥ 80%, while in 2011 only 19% met these criteria. Extending existing time series, and availability of new, powerful time series contributed to these improvements, highlighting the need for annual monitoring, particularly given the spatial and temporal information needed to support initiatives such as the Minamata Convention on Mercury. Collecting the same species/tissues across different locations is recommended. Extended time series from Alaska and new data from Russia are also needed to better establish circumarctic patterns of temporal trends.

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.

Factors affecting mercury concentrations in two oceanic cephalopods of commercial interest from the southern Caribbean.

Mercury (Hg) concentrations have significantly increased in oceans during the last century. This element accumulates in marine fauna and can reach toxic levels. Seafood consumption is the main pathway of methylmercury (MeHg) toxicity in humans. Here, we analyzed total Hg (T-Hg) concentrations in two oceanic squid species (Ommastrephes bartramii and Thysanoteuthis rhombus) of an increasing commercial interest off Martinique, French West Indies. Stable isotope ratios reveal a negative linear relationship between δ15N or δ13C in diamondback squid samples. No significant trend was observed between δ34S values and T-Hg concentrations, contrasting with the sulfate availability and sulfide abundance hypotheses. This adds to a growing body of evidence suggesting Hg methylation via sulfate-reducing bacteria is not the main mechanism driving Hg bioavailability in mesopelagic organisms. All squid samples present T-Hg levels below the maximum safe consumption limit (0.5 ppm), deeming the establishment of a commercial squid fishery in the region safe for human consumption.

First record of plastic debris in the stomach of a hooded seal pup from the Greenland Sea.

Plastic debris is globally found around the world and the remote Arctic is no exception. Arctic true seals are sentinel species of marine pollution and represent the link between marine food webs and Arctic apex predators like polar bears and humans. With regard to true seals, ingested macroplastics have never been reported in an Arctic species. We harvested 10 harp seals Pagophilus groenlandicus and 8 hooded seals Cystophora cristata from the breeding grounds in the pack ice of the Greenland Sea. The digestive tract was inspected exclusively for the presence of macroplastics (>5 mm). Two pieces of single-use plastic were found in the stomach of a weaned hooded seal pup. This study indicates that young Arctic marine predators may ingest macroplastics, and therefore may be at risk during their early stages of life due to human caused plastic pollution even in the remote Arctic pack ice.

Contamination levels and habitat use influence Hg accumulation and stable isotope ratios in the European seabass Dicentrarchus labrax.

Hg accumulation in marine organisms depends strongly on in situ water or sediment biogeochemistry and levels of Hg pollution. To predict the rates of Hg exposure in human communities, it is important to understand Hg assimilation and processing within commercially harvested marine fish, like the European seabass Dicentrarchus labrax. Previously, values of Δ199Hg and δ202Hg in muscle tissue successfully discriminated between seven populations of European seabass. In the present study, a multi-tissue approach was developed to assess the underlying processes behind such discrimination. We determined total Hg content (THg), the proportion of monomethyl-Hg (%MeHg), and Hg isotopic composition (e.g. Δ199Hg and δ202Hg) in seabass liver. We compared this to the previously published data on muscle tissue and local anthropogenic Hg inputs. The first important finding of this study showed an increase of both %MeHg and δ202Hg values in muscle compared to liver in all populations, suggesting the occurrence of internal MeHg demethylation in seabass. This is the first evidence of such a process occurring in this species. Values for mass-dependent (MDF, δ202Hg) and mass-independent (MIF, Δ199Hg) isotopic fractionation in liver and muscle accorded with data observed in estuarine fish (MDF, 0-1‰ and MIF, 0-0.7‰). Black Sea seabass stood out from other regions, presenting higher MIF values (≈1.5‰) in muscle and very low MDF (≈-1‰) in liver. This second finding suggests that under low Hg bioaccumulation, Hg isotopic composition may allow the detection of a shift in the habitat use of juvenile fish, such as for first-year Black Sea seabass. Our study supports the multi-tissue approach as a valid tool for refining the analysis of Hg sourcing and metabolism in a marine fish. The study's major outcome indicates that Hg levels of pollution and fish foraging location are the main factors influencing Hg species accumulation and isotopic fractionation in the organisms.

Humpback whales (Megaptera novaeangliae) breeding off Mozambique and Ecuador show geographic variation of persistent organic pollutants and isotopic niches.

Humpback whales (Megaptera novaeangliae) from the Southern Hemisphere carry information on persistent organic pollutants (POPs) from their feeding zones in Antarctica to their breeding grounds, making this species a sentinel of contaminants accumulation in the Southern Ocean. This study aimed to evaluate driving factors, namely feeding areas, trophic level, and sex, affecting POP concentrations in the blubber of humpback whales breeding off Mozambique and off Ecuador. Biopsies of free-ranging humpback whales including blubber and skin were collected in 2014 and 2015 from Ecuador (n = 59) and in 2017 from Mozambique (n = 89). In both populations, HCB was the major contaminant followed by DDTs > CHLs > PCBs > HCHs > PBDEs. POP concentrations were significantly higher in males compared to females. HCB, DDTs, HCHs and PBDEs were significantly different between whales from the Mozambique population and the Ecuador population. Sex and feeding habits were important driving factors accounting for POP concentrations in Ecuador whales. The whales from our study had some of the lowest POP concentrations measured for humpback whales in the world. These whales fed predominantly on krill as reflected from the low δ13C and δ15N values measured in the skin. However, the isotopic niches of whales from Mozambique and Ecuador did not overlap indicating that the two populations are feeding in different areas of the Southern Ocean.

Pelagic vs Coastal-Key Drivers of Pollutant Levels in Barents Sea Polar Bears with Contrasted Space-Use Strategies.

In the Barents Sea, pelagic and coastal polar bears are facing various ecological challenges that may explain the difference in their pollutant levels. We measured polychlorinated biphenyls, organochlorine pesticides, polybrominated diphenyl ethers in fat, and perfluoroalkyl substances in plasma in pelagic and coastal adult female polar bears with similar body condition. We studied polar bear feeding habits with bulk stable isotope ratios of carbon and nitrogen. Nitrogen isotopes of amino acids were used to investigate their trophic position. We studied energy expenditure by estimating field metabolic rate using telemetry data. Annual home range size was determined, and spatial gradients in pollutants were explored using latitude and longitude centroid positions of polar bears. Pollutant levels were measured in harp seals from the Greenland Sea and White Sea-Barents Sea as a proxy for a West-East gradient of pollutants in polar bear prey. We showed that pelagic bears had higher pollutant loads than coastal bears because (1) they feed on a higher proportion of marine and higher trophic level prey, (2) they have higher energy requirements and higher prey consumption, (3) they forage in the marginal ice zones, and (4) they feed on prey located closer to pollutant emission sources/transport pathways.

Stable isotope ratios of carbon, nitrogen and sulphur and mercury concentrations as descriptors of trophic ecology and contamination sources of Mediterranean whales.

The Mediterranean Sea remains a complex system for mercury (Hg) cycling and accumulation in marine vertebrates. The extremely high levels these animals present demand for an urgent understanding of such processes and the development of new analytical techniques that go beyond the simple contamination monitoring. It was often proposed that prey selection or habitat use may affect Hg contamination in animals; however, it was never possible to measure which factor influences more rates and pathways of contamination. In this paper, we directly integrate toxicological information (Hg levels) and ecological tracers (stable isotopes of C, N and S) into a common data analysis framework (isotopic niches), with the aim of quantifying the influence of species' trophic behaviour on Hg contamination. The analysis was conducted on skin biopsies of fin whales Balaenoptera physalus, long-finned pilot whales Globicephala melas and sperm whales Physeter microcephalus. Their different trophic modes and residency in the area make them model species for the analysis of Hg accumulation along NWMS food webs. We measured Total Hg (T-Hg) concentrations through absorbance spectrometry with the DMA80 Milestone. Carbon, nitrogen and sulphur isotope compositions were measured via mass spectrometry in an IRMS coupled to an Elemental Analyser (EA) Isoprime. Comparison of ecological and contamination niches allowed to explain Hg accumulation in Mediterranean marine predators. Factors such as food web complexity, trophic position, hunting distribution or habitat use (e.g., foraging depth) did not influence Hg exposure. It is rather the selection of prey type, which determines the range of potential Hg sources and as a consequence the rates of accumulation in whales' tissues. A generalist piscivorous species such as the pilot whales will bioaccumulate more Hg than specialised sperm whales feeding mostly on cephalopods.

Supporting evidence for PCB pollution threatening global killer whale population.

A recent Science report predicted the global killer whale population to collapse due to PCB pollution. Here we present empirical evidence, which supports and extends the reports' statement. In 2016, a neonate male killer whale stranded on the German island of Sylt. Neonatal attributes indicated an age of at least 3 days. The stomach contained ∼20 mL milk residue and no pathologies explaining the cause of death could be detected. Blubber samples presenting low lipid concentrations were analysed for persistent organic pollutants. Skin samples were collected for genotyping of the mitochondrial control region. The blubber PCB concentrations were very high [SPCBs, 225 mg/kg lipid weight (lw)], largely exceeding the PCB toxicity thresholds reported for the onset of immunosuppression [9 mg/kg lw ∑PCB] and for severe reproductive impairment [41 mg/kg lw ∑PCB] reported for marine mammals. Additionally, this individual showed equally high concentrations in p,p'-DDE [226 mg/kg lw], PBDEs [5 mg/kg lw] and liver mercury levels [1.1 µg/g dry weight dw]. These results suggest a high placental transfer of pollutants from mother to foetus. Consequently, blubber and plasma PCB concentrations and calf mortality rates are both high in primiparous females. With such high pollutant levels, this neonate had poor prerequisites for survival. The neonate belonged to Ecotype I (generalist feeder) and carried the mitochondrial haplotype 35 present in about 16% of the North Atlantic killer whale from or close to the North Sea. The relevance of this data becomes apparent in the UK West Coast Community, the UK's only residentorca population, which is currently composed of only eight individuals (each four males and females) and no calves have been reported over the last 19 years.Despite worldwide regulations, PCBs persist in the environment and remain a severe concern for killer whale populations, placing calves at high risk due to the mother-offspring PCB-transfer resulting in a high toxicological burden of the neonates.

Inter-individual differences in contamination profiles as tracer of social group association in stranded sperm whales.

Ecological and physiological factors lead to different contamination patterns in individual marine mammals. The objective of the present study was to assess whether variations in contamination profiles are indicative of social structures of young male sperm whales as they might reflect a variation in feeding preferences and/or in utilized feeding grounds. We used a total of 61 variables associated with organic compounds and trace element concentrations measured in muscle, liver, kidney and blubber gained from 24 sperm whales that stranded in the North Sea in January and February 2016. Combining contaminant and genetic data, there is evidence for at least two cohorts with different origin among these stranded sperm whales; one from the Canary Island region and one from the northern part of the Atlantic. While genetic data unravel relatedness and kinship, contamination data integrate over areas, where animals occured during their lifetime. Especially in long-lived animals with a large migratory potential, as sperm whales, contamination data may carry highly relevant information about aggregation through time and space.

Carbon, nitrogen and sulphur isotopic fractionation in captive juvenile hooded seal (Cystophora cristata): Application for diet analysis.

RATIONALE: Intrinsic biogeochemical markers, such as stable isotope ratios of carbon, nitrogen and sulphur, are increasingly used to trace the trophic ecology of marine top predators. However, insufficient knowledge of fractionation processes in tissues continues to hamper the use of these markers. METHODS: We performed a controlled feeding experiment with eight juvenile hooded seals (Cystophora cristata) that were held on a herring-based diet (Clupea harengus) for two years. Stable isotope ratios were measured via isotope ratio mass spectrometry in three of their tissues and related to values of these markers in their diet. RESULTS: Diet-tissue isotope enrichment (trophic enrichment factor, TEF) values between dietary herring and seal tissues for carbon (Δ13 C) were +0.7 ‰ for red blood cells, +1.9 ‰ for hair and +1.1 ‰ for muscle. The TEFs for nitrogen trophic (Δ15 N) were +3.3 ‰ for red blood cells, +3.6 ‰ for hair and +4.3 ‰ for muscle. For sulphur, the Δ34 S values were +1.1 ‰ for red blood cells, +1.0 ‰ for hair and +0.9 ‰ for muscle. CONCLUSIONS: These enrichment values were greater than those previously measured in adult seals. This increase may be related to the higher rate of protein synthesis and catabolism in growing animals. This study is the first report on sulphur isotope enrichment values for a marine mammal species.

POPs in free-ranging pilot whales, sperm whales and fin whales from the Mediterranean Sea: Influence of biological and ecological factors.

The pilot whale Globicephala melas, the sperm whale Physeter macrocephalus, and the fin whale Balaenoptera physalus are large cetaceans permanently inhabiting the Mediterranean Sea. These species are subjected to numerous anthropogenic threats such as exposure to high levels of contaminants. Therefore, selected persistent organic pollutants POPs (29 PCBs, 15 organochlorine compounds, 9 PBDEs and 17 PCDD/Fs) were analysed in blubber biopsies of 49 long-finned pilot whales, 61 sperm whales and 70 fin whales sampled in the North Western Mediterranean Sea (NWMS) from 2006 to 2013. Contamination profile and species feeding ecology were then combined through the use of stable isotopes. δ(13)C, δ(15)N values and POPs levels were assessed through IR-MS and GC-MS respectively. To assess the toxic potency of the dioxin-like compounds, the TEQ approach was applied. δ(15)N values were 12.2±1.3‰ for sperm whales, 10.5±0.7‰ for pilot whales and 7.7±0.8‰ in fin whales, positioning sperm whales at higher trophic levels. δ(13)C of the two odontocetes was similar and amounted to -17.3±0.4‰ for sperm whales and -17.8±0.3‰ for pilot whales; whilst fin whales were more depleted (-18.7±0.4‰). This indicates a partial overlap in toothed-whales feeding habitats, while confirms the differences in feeding behaviour of the mysticete. Pilot whales presented higher concentrations than sperm whales for ΣPCBs (38,666±25,731 ng g(-1)lw and 22,849±15,566 ng g(-1) lw respectively), ΣPBDEs (712±412 ng g(-1) lw and 347±173 ng g(-1) lw respectively) and ΣDDTs (46,081±37,506 ng g(-1) lw and 37,647±38,518 ng g(-1) lw respectively). Fin whales presented the lowest values, in accordance with its trophic position (ΣPCBs: 5721±5180 ng g(-1) lw, ΣPBDEs: 177±208 ng g(-1) lw and ΣDDTs: 6643±5549 ng g(-1) lw). Each species was characterized by large inter-individual variations that are more related to sex than trophic level, with males presenting higher contaminant burden than females. The discriminant analysis (DA) confirmed how DDTs and highly chlorinated PCBs were influential in differentiating the three species. Pollutant concentrations of our species were significantly higher than both their Southern Hemisphere and North Atlantic counterparts, possibly due to the particular Mediterranean geomorphology, which influences pollutants distribution and recycle. Dioxin-like PCBs accounted for over 80% of the total TEQ. This study demonstrated (1) an important exposure to pollutants of Mediterranean cetaceans, often surpassing the estimated threshold toxicity value of 17,000 ng g(-1) lw for blubber in marine mammals; and (2) how the final pollutant burden in these animals is strongly influenced not only by the trophic position but also by numerous other factors such as sex, age, body size and geographical distribution.