Changes in trace elements during lactation in a marine top predator, the grey seal

Regional variations and drivers of essential and non-essential elements in Steller sea lion pups from the Aleutian Islands, Alaska

Exposure and resulting tissue concentrations of various elements from natural and anthropogenic sources are influenced by multiple factors, such as geographic location, age, diet, and metabolic rate, that can influence wildlife health. Essential and non-essential elements were assessed in lanugo and whole blood collected in 2019 from 102 Steller sea lion (Eumetopias jubatus) pups from two rookeries from the western and central Aleutian Islands: Agattu (WAI, n = 54) and Ulak Islands (CAI, n = 48). Rookery, sex, dorsal standard length, and trophic ecology (ẟ15N, ẟ13C values) effects on element concentration were evaluated. Significant differences in element concentrations of lanugo were exhibited across rookeries (p < 0.05), except for zinc (Zn). For example, higher mercury (Hg) and selenium (Se) concentrations were observed in WAI than CAI, while other elements were lower in WAI. Whole blood showed higher sulfur (S) and Se concentrations in CAI compared to WAI, while WAI had elevated strontium (Sr) and Hg concentrations relative to CAI. Trophic ecology significantly influenced most element concentrations, possibly due to regional variations in adult female feeding and food web dynamics. Interactions between elements were found in lanugo across both rookeries, with varying strengths. Whole blood displayed less pronounced yet consistent associations, with variable intensities. Essential elements sodium (Na), potassium (K), and calcium (Ca) formed a distinct group whose interaction is crucial for nervous system function and muscle contraction. Another group comprised zinc (Zn), iron (Fe), manganese (Mn), magnesium (Mg), phosphorous (P), S, and Se, which are known for indirectly interacting with enzyme function and metabolic pathways. Hg and Se formed a distinct group probably due to their known chemical interactions and physiological protective interactions.

Biomonitoring of persistent pollutants in grey seal (Halichoerus seagrypus) pups from the Gulf of Riga, Baltic Sea

We analyzed for the first time the concentration of potentially toxic trace elements Hg, As, Pb, Cr and Se and POPs (PCBs and OCPs) in tissues of 41 grey seal pups (Halichoerus grypus) stranded on the shores of the Gulf of Riga. Lanugo was the sample with the highest concentrations of all trace elements except Hg. The concentrations found in this biological matrix appeared as follows: Hg (2.50 ± 1.43 μg/g); Se (1.22 ± 0.82 μg/g); Cr (0.96 ± 1.51 μg/g); As (0.95 ± 1.03 μg/g); Pb (0.50 ± 0.60 μg/g). POPs were∑PCB (0.566 ± 0.520 μg/g), ∑DDT (0.522 ± 0.454 μg/g), ∑HCH (0.043 ± 0.045 μg/g) and Chlordane (0.041 μg/g). We detected brain Hg levels above the threshold described for neurobehavioural changes and some individuals also exceeded the toxic threshold described for PCBs. Thus, the health of grey seal pups could be affected by both groups of pollutants.

Trophic and environmental influences on trace element concentrations in Australian fur seals

Trace elements (TE) in living organisms can have detrimental health impacts depending on their concentration. As many TEs are obtained through diet, trophic niche changes associated with the impacts of anthropogenic activities and climate-change may influence exposure to top predators. The Australian fur seal (Arctocephalus pusillus doriferus; AUFS) represents the greatest resident, marine predator biomass in south-eastern Australia. With adult female foraging ranges limited to the continental shelf, their source of TEs is geographically restricted. Plasma, red blood cell and milk samples collected between 1998 and 2022 at Kanowna Island, were analysed for TEs (As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Sn, V and Zn) using inductively-coupled plasma mass-spectrometry (ICP-MS). Plasma fatty-acid profiles and ocean climate variables were used to investigate trophic and environmental influences, respectively, on TE concentrations. Estimated whole blood concentrations in lactating females were comparable to levels reported in other marine mammals, except for Se and Mn. Correlations between adult tissues were negative for Mn and positive for As, Hg and Sn. Molar Se:Hg were high but within reported levels for pinnipeds. Element concentrations in pup plasma were greater than lactating females for Fe, Mn and Sn indicative of high transplacental transfer while doses of Se and As from milk exceeded tolerable effect levels for humans. Relationships with fatty-acid profiles suggest diet influenced concentrations of Cu, Hg, Mn, Sn, V and Zn in adult plasma. In addition, inter-annual variation in TE concentrations were influenced by broad-scale climate indices, including the Southern Annular Mode and the Southern Oscillation Index, and local conditions associated with the seasonally-active Bonney Upwelling. These findings indicate that TE concentrations in blood and milk of AUFS are and will continue to be affected by anticipated oceanographic changes, mediated by alterations in prey type availability, with potential impacts on the population's health.

Foraging behavior and age affect maternal transfer of mercury to northern elephant seal pups

Deep ocean foraging northern elephant seals (Mirounga angustirostris) consume fish and squid in remote depths of the North Pacific Ocean. Contaminants bioaccumulated from prey are subsequently transferred by adult females to pups during gestation and lactation, linking pups to mercury contamination in mesopelagic food webs (200-1000 m depths). Maternal transfer of mercury to developing seal pups was related to maternal mercury contamination and was strongly correlated with maternal foraging behavior (biotelemetry and isotopes). Mercury concentrations in lanugo (hair grown in utero) were among the highest observed worldwide for young pinnipeds (geometric mean 23.01 μg/g dw, range 8.03-63.09 μg/g dw; n = 373); thus, some pups may be at an elevated risk of sub-lethal adverse health effects. Fetal mercury exposure was affected by maternal foraging geographic location and depth; mercury concentrations were highest in pups of the deepest diving, pelagic females. Moreover, pup lanugo mercury concentrations were strongly repeatable among successive pups of individual females, demonstrating relative consistency in pup mercury exposure based on maternal foraging strategies. Northern elephant seals are biosentinels of a remote deep-sea ecosystem. Our results suggest that mercury within North Pacific mesopelagic food webs may also pose an elevated risk to other mesopelagic-foraging predators and their offspring.

Dietary methylmercury and fatty acids affect the lipid metabolism of adipose tissue and liver in rainbow trout

Methylmercury (MeHg) is a pervasive environmental contaminant in aquatic ecosystems that can reach elevated concentrations in fish of high trophic levels, such as salmonids. The present study aims at investigating the individual and combined impacts of dietary MeHg and fatty acids on lipid metabolism in juvenile rainbow trout (Oncorhynchus mykiss) with a focus on two key organs, adipose tissue and liver. MeHg and fatty acids are both known to act on energy homeostasis although little is known about their interplay on lipid metabolism in fish. Fish were fed diets enriched in linoleic acid (LA, 18:2 n-6), α-linolenic acid (ALA, 18:3 n-3), eicosapentaenoic acid (EPA, 20:5 n-3) or docosahexaenoic acid (DHA, 22:6 n-3) for ten weeks, with the addition of MeHg to the diets during the last six weeks (0, 2.4 or 5.5 mg MeHg/kg dry matter). LA and ALA are polyunsaturated fatty acids (PUFA) typical of plant-derived oils whereas EPA and DHA are n-3 long chain PUFA largely found in fish oil, all used in feed formulation in aquaculture. The results showed that the LA-enriched diet induced a higher whole-body lipid content compared to the three other diets. On the contrary, the addition of MeHg led to a significant reduction of the whole-body lipid content, regardless of the diet. Interestingly, the adipocytes were larger both in presence of LA, compared to EPA and DHA, or MeHg, indicating a lipogenic effect of these two compounds. No effect was, however, observed on lipid accumulation per gram of adipose tissue. The fatty acid composition of adipose tissue and liver was significantly modified by the dietary lipids, reflecting both the fatty acid composition of the diets and the high bioconversion capacity of the rainbow trout. Exposure to MeHg selectively led to a release of n-6 PUFA from the hepatic membranes of fish fed the LA-enriched diet, showing a disruption of the pathways using n-6 PUFA. This study highlights the significant impact of MeHg exposure and dietary fatty acids on lipid metabolism in fish. Further investigation is needed to elucidate the underlying mechanisms and to explore the potential involvement of other organs.

Whiskers provide time-series of toxic and essential trace elements, Se:Hg molar ratios, and stable isotope values of an apex Antarctic predator, the leopard seal

In an era of rapid environmental change and increasing human presence, researchers need efficient tools for tracking contaminants to monitor the health of Antarctic flora and fauna. Here, we examined the utility of leopard seal whiskers as a biomonitoring tool that reconstructs time-series of significant ecological and physiological biomarkers. Leopard seals (Hydrurga leptonyx) are a sentinel species in the Western Antarctic Peninsula due to their apex predator status and top-down effects on several Antarctic species. However, there are few data on their contaminant loads. We analyzed leopard seal whiskers (n = 18 individuals, n = 981 segments) collected during 2018-2019 field seasons to acquire longitudinal profiles of non-essential (Hg, Pb, and Cd) and essential (Se, Cu, and Zn) trace elements, stable isotope (ẟ15N and ẟ13C) values and to assess Hg risk with Se:Hg molar ratios. Whiskers provided between 46 and 286 cumulative days of growth with a mean ~ 125 days per whisker (n = 18). Adult whiskers showed variability in non-essential trace elements over time that could partly be explained by changes in diet. Whisker Hg levels were insufficient (<20 ppm) to consider most seals being at "high" risk for Hg toxicity. Nevertheless, maximum Hg concentrations observed in this study were greater than that of leopard seal hair measured two decades ago. However, variation in the Se:Hg molar ratios over time suggest that Se may detoxify Hg burden in leopard seals. Overall, we provide evidence that the analysis of leopard seal whiskers allows for the reconstruction of time-series ecological and physiological data and can be valuable for opportunistically monitoring the health of the leopard seal population and their Antarctic ecosystem during climate change.

Trace metal concentrations in California sea lions from rookeries exposed to different levels of coastal urbanization in Baja California, Mexico

Concentrations of total mercury, total selenium, and cadmium ([THg], [TSe], [Cd]) were determined in hair of California sea lion (Zalophus californianus) pups from four islands of the Gulf of California and the Baja California Pacific coast (NG, CG, NP, and CP) to identify geographical differences and the effect of Se against Hg toxicity (TSe:THg molar ratio). THg displayed a strong north-south trend for both ecoregions, while TSe presented a significantly high concentration only for CG. TSe:THg molar ratios decreased when [THg] increased, with the lowest ratios presenting in NG pups, in which [THg] exceeded toxicological thresholds of concern. [Cd] presented similar values at all study sites except CG, which presented the lowest level. The present study shows that proximity to urbanized coastal areas has a strong influence on [THg] in pups, while [TSe] and [Cd] are probably more related to the physiological requirements of the species, and environmental conditions.

Trace elements in blood of Baltic gray seal pups (Halichoerus grypus) from the Gulf of Riga and their relationship with biochemical and clinical parameters

Trace elements are pollutants of both natural and anthropogenic origin which can influence negatively on ecosystem and wildlife health. We evaluated trace element in blood samples of gray seal (Halichoerus grypus) stranded in the Gulf of Riga and their influence on their health status through hematological and biochemical profiles. Zn showed the highest levels followed by Cu > Se > Pb > THg > As. Cr and Cd were not detected. Most trace element levels were generally comparable to those reported in seal species; however, high Pb values were observed in those sample showing detectable concentrations (<0.046-257.6 μg/kg ww). Significant positive correlations were found between trace elements concentrations and various biochemical parameters, including Se-ASAT, Se:Hg-ASAT, Cu-TP, Cu-ALB, CuCa, Zn-ALAT, ZN-LDH, ZnP, Zn-Segment neutrophils, and Pb-CK. Nevertheless, most relationships were not strong enough (p > 0.04) to assume a toxicological implication. Despite its limitations, this information could serve as the baseline for future research.

A Multi-Matrix Metabolomic Approach in Ringed Seals and Beluga Whales to Evaluate Contaminant and Climate-Related Stressors

As a high trophic-level species, ringed seals (Pusa hispida) and beluga whales (Delphinapterus leucas) are particularly vulnerable to elevated concentrations of biomagnifying contaminants, such as polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and mercury (Hg). These species also face climate-change-related impacts which are leading to alterations in their diet and associated contaminant exposure. The metabolomic profile of marine mammal tissues and how it changes to environmental stressors is poorly understood. This study characterizes the profiles of 235 metabolites across plasma, liver, and inner and outer blubber in adult ringed seals and beluga whales and assesses how these profiles change as a consequence of contaminants and dietary changes. In both species, inner and outer blubber were characterized by a greater proportion of lipid classes, whereas the dominant metabolites in liver and plasma were amino acids, carbohydrates, biogenic amines and lysophosphatidylcholines. Several metabolite profiles in ringed seal plasma correlated with δ13C, while metabolite profiles in blubber were affected by hexabromobenzene in ringed seals and PBDEs and Hg in belugas. This study provides insight into inter-matrix similarities and differences across tissues and suggests that plasma and liver are more suitable for studying changes in diet, whereas liver and blubber are more suitable for studying the impacts of contaminants.

Iron mobilization during lactation reduces oxygen stores in a diving mammal

The profound impacts that maternal provisioning of finite energy resources has on offspring survival have been extensively studied across mammals. This study shows that in addition to calories, high hemoprotein concentrations in diving mammals necessitates exceptional female-to-pup iron transfer. Numerous indices of iron mobilization (ferritin, serum iron, total-iron-binding-capacity, transferrin saturation) were significantly elevated during lactation in adult female Weddell seals (Leptonychotes weddellii), but not in skip-breeders. Iron was mobilized from endogenous stores for incorporation into the Weddell seal’s milk at concentrations up to 100× higher than terrestrial mammals. Such high rates of iron offload to offspring drew from the female’s own heme stores and led to compromised physiologic dive capacities (hemoglobin, myoglobin, and total body oxygen stores) after weaning their pups, which was further reflected in shorter dive durations. We demonstrate that lactational iron transfer shapes physiologic dive thresholds, identifying a cost of reproduction to a marine mammal.

Here, the authors show that Weddell seal mothers mobilize endogenous iron stores during lactation to provide to pups, resulting in iron concentrations in milk 100x higher than terrestrial mammals. This was associated with reduced dive durations in the mother, a cost of reproduction.

EVALUATION OF TRACE ELEMENT CONCENTRATIONS IN THE SERUM AND VIBRISSAE OF PERUVIAN PINNIPEDS (ARCTOCEPHALUS AUSTRALIS AND OTARIA BYRONIA)

Concentrations of 15 trace elements (aluminum, arsenic, cadmium, chromium, cobalt, copper, iron, lead, manganese, mercury, nickel, selenium, tin, vanadium, and zinc) were determined in vibrissae (whiskers) and serum of two sympatric pinniped species, the Peruvian fur seal population (PFS; Arctocephalus australis Peruvian subpopulation) and South American sea lion (SASL; Otaria byronia) at Punta San Juan, Peru during 2011-19 sampling events. Element concentrations were 2-20 times higher in vibrissae than in serum. Vibrissae and serum concentrations of several elements, including aluminum, arsenic, and lead, suggest that environmental contaminants may affect the health of pinnipeds at Punta San Juan. Although toxicity thresholds are unknown in pinnipeds, high concentrations of some elements (especially aluminum, arsenic, and lead) may have adverse impacts on their health such as immunosuppression and impaired reproduction. Arsenic was the only element that increased in mean vibrissae concentration throughout the study period. Female SASL vibrissae contained a mean arsenic concentration three times higher than the male SASL vibrissae mean arsenic concentration, and twice as high as the arsenic mean for all PFS vibrissae. The mean male SASL vibrissae cadmium concentration was five times higher than the vibrissae cadmium mean for both PFS males and females and nearly three times higher than the vibrissae cadmium mean for SASL females. Serum concentrations of aluminum, arsenic, copper, and manganese were significantly higher during moderate to extreme El Niño years compared to La Niña years. With stronger and more frequent El Niño-Southern Oscillation events predicted in the future, it is vital to understand how these trace elements may affect pinniped population health.

Fetal mercury concentrations in central California Pacific harbor seals: Associated drivers and outcomes

Mercury (Hg) is a well-known toxicant in wildlife and humans. High total Hg concentrations ([THg]) have been reported in central California harbor seals Phoca vitulina richardii. We evaluated the effects of presence/absence of early natal coat (lanugo), year (2012 to 2017), sex, stranding location, and trophic ecology (ẟ¹³C and ẟ¹⁵N values) on hair [THg] along coastal central California. Also examined were [THg] effects on growth rates of pups in rehabilitation and probability of release (e.g., successful rehabilitation). The [THg] ranged from 0.46-81.98 mg kg^-1 dw, and ẟ¹⁵N and ẟ¹³C ranged from 13.6-21.5‰, and -17.2 to -13.0‰, respectively. Stranding location, year, and presence of lanugo coat were important factors explaining variation in [THg]. Seals from Sonoma and San Mateo County had higher [THg] than other locations. Seals with full or partial lanugo coat had lower [THg]. Seals from 2016 and 2017 had higher [THg] than those from 2015. Hair [THg] exceeded lower and upper toxicological thresholds (>20 mg kg^-1 by year (5.88% to 23.53%); >30 mg kg^-1 (0% to 12.31%)) with a pronounced increase from 2015 to 2016. Pups in 2017 had significantly higher odds ratio of [THg] above 20 mg kg^-1 than pups of 2015, and pups in 2016 had significantly higher odds ratio than those from 2013 and 2015 (similar when using 30 mg kg^-1). Pups in Sonoma County had the highest odds ratio for [THg] in lanugo above 20 mg kg^-1. ẟ¹⁵N values were higher in 2015-2017, particularly relative to 2014, probably associated with the El Niño event. The [THg] was not a good predictor for probability of release and mass-specific growth rates in captivity. Further investigation of temporal trends of [THg] in harbor seals is warranted given the relatively high percentage of samples exceeding threshold values, particularly in the most recent sampling years.

Case studies on longitudinal mercury content in humpback whale (Megaptera novaeangliae) baleen

Quantification of contaminant concentrations in baleen whales is important for individual and population level health assessments but is difficult due to large migrations and infrequent resighings. The use of baleen allows for a multiyear retrospective analysis of contaminant concentrations without having to collect repeated samples from the same individual. Here we provide case studies of mercury analysis using cold vapor atomic absorption spectroscopy in three individual humpback whales (Megaptera novaeangliae), a 44.5-year-old female and two males aged ≥35 and 66 years, over approximately three years of baleen growth. Mercury concentrations in the female's baleen were consistently 2-3 times higher than in either male. Age did not affect mercury concentrations in baleen; the younger male had comparable levels to the older male. In the female, mercury concentrations in the baleen did not change markedly during pregnancy but mercury did spike during the first half of lactation. Stable isotope profiles suggest that diet likely drove the female's high mercury concentrations. In conclusion, variations in baleen mercury content can be highly individualistic. Future studies should compare sexes as well as different populations and species to determine how the concentrations of mercury and other contaminants vary by life history parameters and geography.

Analysis of essential and non-essential trace elements in the organs of a mother-fetus pair of spotted seals (Phoca largha) from the Sea of Japan

Concentrations of 22 essential and non-essential trace elements (Be, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Ag, Cd, Sb, Ba, Tl, Pb, Th, U, and Hg) were measured in the organs of a mother-fetus pair (at the last trimester of pregnancy) of spotted seals from the Sea of ​Japan. The concentrations of eleven elements are reported for the first time. Eight organs of the pair were examined: lungs, heart, liver, kidneys, intestines, spleen, muscles, and bones. All trace elements detected in the organs of the mother were found also in the organs of the fetus at various concentrations. Placenta is not an effective barrier to prevent non-essential elements from getting into the fetus, but can control entry of some of them, e.g., aluminum, cadmium, and mercury. In most organs of the fetus, the concentrations of toxic trace elements (beryllium, antimony, thorium, and uranium) were noticeably higher than in the same organs of the mother, which indicates that during pregnancy female removes excess of non-essential trace elements by transferring them to the fetal body through the placental barrier.

Metals in the stomach contents and brain, gonad, kidney, and liver tissues of subsistence-harvested northern sea otters (Enhydra lutris kenyoni) from Icy Strait, Alaska

Southeast Alaska sea otters (Enhydra lutris) have had a rapid rise in their population. As they feed primarily on sessile prey, they are excellent sentinels for examining metals contamination. Objectives of this study on sea otters were to determine: (1) concentrations of metals in different tissues; (2) whether metals biomagnify from stomach contents (i.e., the prey) to other tissues; (3) whether selenium and mercury concentrations indicate an overall health benefit or risk; and (4) if metals concentrations in tissues vary with body size. Brain, kidney, gonad, liver, and stomach contents were collected from freshly harvested sea otters in Icy Strait, Alaska, and analyzed for arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), total mercury (THg), and selenium (Se). Metals concentrations varied significantly, and some were biomagnified, with livers and kidneys harboring the highest concentrations. Lead and arsenic appeared to be readily excreted. This study represents baseline metals concentrations to assist in monitoring the health of sea otters.

Alimentary exposure and elimination routes of rare earth elements (REE) in marine mammals from the Baltic Sea and Antarctic coast

Marine mammals found at the top of the trophic pyramid are excellent bioindicators of pollutants in the marine environment, the concentrations of which increase along with the trophic level of the organism. As these animals are usually protected species, their contamination has to be assessed non-invasively by analysing excrement and epidermal structures such as fur or claws. The present study involved testing the excrement and fur of the grey seal (Halichoerus grypus) from the Southern Baltic coast and the Southern elephant seal (Mirounga leonine) from Admiralty Bay, along with fish muscle (food) and the lithological background of both areas, for the presence of rare earth elements (REE). The soil on the Baltic coast is characterized by the predomination of light rare earth elements (LREE): yttrium, lanthanum and cerium (∑REE = 7.86 mg·kg^-1 dw). In the soil and bedrock of Admiralty Bay all REEs were found except for terbium, thulium and lutetium (∑REE = 96.1 mg·kg^-1 dw). The REE levels found in the muscles of Baltic herring (∑REE = 0.057 mg·kg^-1 ww) were lower than those in the muscles of marbled rockcod (∑REE = 0.540 mg·kg^-1 ww). The situation was analogous in the mammals, with the REE concentrations in grey seal fur (∑REE = 0.489 mg·kg^-1 dw) and excrement (∑REE = 0.676 mg·kg^-1 dw) being lower than those found in the fur (∑REE = 10.1 mg·kg^-1 dw) and excrement (∑REE = 83.6 mg·kg^-1 dw) of the elephant seal. The LREE/HREE partition coefficients in the grey seal excrement (3.37) and its fur (4.00), but also in the faeces of the elephant seal (2.63) and its fur (2.65), indicate that in each species the process of elimination from the body occurs in similar proportions.

Historic variation of trace elements in pinnipeds with spatially segregated trophic habits reveals differences in exposure to pollution

Marine mammals and the ecological functions they provide to coastal and pelagic ecosystems are increasingly threatened by the intensification of anthropogenic impacts. The Uruguayan coastline throughout the 20th century, like other coastal environments worldwide, has been the sink of a variety of trace metals derived from the rapid urbanization and industrialization of related land areas. This coastline is inhabited by two species of pinnipeds trophically and spatially segregated. Otaria byronia feeds in coastal environments while Arctocephalus australis preys mainly offshore. The present study aimed to analyze historic changes in concentrations of trace elements in teeth of both species from 1941 to the present day. We analyzed the dentin of 94 canine teeth using stable isotope analysis (δ¹³C) and ICP-MS to determine their feeding areas and the concentration of 10 trace elements (Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) respectively. The concentration of Cr was significantly higher during '70-'80s, in both species coinciding with tannery industry development. Both species of pinnipeds have been differentially exposed to trace elements depending on their feeding area. A pelagic diet, possibly based on squid, increased the concentration of Cd in A. australis, while O. byronia has been more exposed to anthropogenic Pb and Cu associated to a costal and more benthic diet. Our results highlight dentin as a reliable matrix for historic studies on the exposure to trace elements. In light of our results, the O. byronia's declining population could be the result of the synergistic effects of trace elements together with other ecological pressures faced in their environment.

Methylmercury displays pro-adipogenic properties in rainbow trout preadipocytes

Methylmercury (MeHg) is a ubiquitous contaminant largely found in aquatic environments, especially in species at high trophic level such as salmonids. The aim of this study was to evaluate the effects of MeHg on adipocyte differentiation and lipid metabolism in rainbow trout. Primary cultured preadipocytes were exposed to increasing concentrations of MeHg during six days with or without a hormonal cocktail. Main results showed a dose-dependent intracellular accumulation of neutral lipids with a preferential uptake of n-3 polyunsaturated fatty acids. Interestingly, this accumulation occurred after a fairly low uptake of MeHg by preadipocytes and was maintained after the cellular exposure to MeHg. In membrane phospholipids, arachidonic acid (20:4 n-6) was released in a dose-dependent manner. At the transcriptional level, the expression of several adipocyte-specific genes (perilipin 2 and apolipoprotein Eb) as well as lipid-related genes (fatty acid synthase and fatty acid binding protein 11a) was up-regulated in preadipocytes exposed to MeHg. These results highlight for the first time the disrupting effect of MeHg in trout adipocyte metabolism, providing new insights regarding the role of environmental pollutants in adipose tissue dysfunction and related pathologies.

Evaluating tooth strontium and barium as indicators of weaning age in Pacific walruses

Lactation length and weaning age provide important information about maternal investment, which can reflect the health and nutritional status of the mother, as well as broader reproductive strategies in mammals. Calcium-normalized strontium (Sr) and barium (Ba) concentrations in the growth layers of mammalian teeth differ for nursing animals and those consuming non-milk foods, thus can be used to estimate age-at-weaning. To date, this approach has been used only for terrestrial animals, and almost exclusively for primates.The goal of this study was to determine whether Sr and Ba concentrations in the cementum of Pacific walrus Odobenus rosmarus divergens teeth can be used to estimate weaning age. Teeth from 107 walruses were analysed using laser ablation inductively coupled plasma mass spectrometry, and calcium-normalized 88Sr and 137Ba concentrations were quantified.For most walruses, both Sr and Ba concentrations exhibited rapid changes in early life. Ba concentrations matched closely with expected patterns in the published literature, rapidly declining from high to low concentrations (typically from ~10 ppm to ~5 ppm). In contrast, Sr exhibited a pattern opposite to that presented in studies of terrestrial mammals, appearing nearly identical to Ba (typically declining from ~400 ppm to ~200 ppm). To explain these findings, we present conceptual models of the factors generating weaning signals in Sr and Ba for terrestrial mammals, as well as a new, hypothetical model for walruses. Both a visual and mathematical approach to weaning age estimation indicated a median weaning age of walruses at the end of the second year of life (in the second dark layer of the tooth cementum), with many walruses estimated to have weaned in their third year of life, and a smaller group weaning in their fourth or fifth year. This is later than expected, given a published estimate of walrus weaning at 18-24 months.These results do not conclusively support the use of tooth Sr and Ba for estimating weaning age in walruses, and further research is warranted to better understand the drivers of the observed patterns of Ba and Sr accumulation in walrus teeth.

Mercury exposure in mammalian mesopredators inhabiting a brackish marsh

Bioaccumulation of environmental contaminants in mammalian predators can serve as an indicator of ecosystem health. We examined mercury concentrations of raccoons (Procyon lotor; n = 37 individuals) and striped skunks (Mephitis mephitis; n = 87 individuals) in Suisun Marsh, California, a large brackish marsh that is characterized by contiguous tracts of tidal marsh and seasonally impounded wetlands. Mean (standard error; range) total mercury concentrations in adult hair grown from 2015 to 2018 were 28.50 μg/g dw (3.05 μg/g dw; range: 4.46-81.01 μg/g dw) in raccoons and 4.85 μg/g dw (0.54 μg/g dw; range: 1.53-27.02 μg/g dw) in striped skunks. We reviewed mammalian hair mercury concentrations in the literature and raccoon mercury concentrations in Suisun Marsh were among the highest observed for wild mammals. Although striped skunk hair mercury concentrations were 83% lower than raccoons, they were higher than proposed background levels for mercury in mesopredator hair (1-5 μg/g). Hair mercury concentrations in skunks and raccoons were not related to animal size, but mercury concentrations were higher in skunks in poorer body condition. Large inter-annual differences in hair mercury concentrations suggest that methylmercury exposure to mammalian predators varied among years. Mercury concentrations of raccoon hair grown in 2017 were 2.7 times greater than hair grown in 2015, 1.7 times greater than hair grown in 2016, and 1.6 times greater than hair grown in 2018. Annual mean raccoon and skunk hair mercury concentrations increased with wetland habitat area. Furthermore, during 2017, raccoon hair mercury concentrations increased with the proportion of raccoon home ranges that was wetted habitat, as quantified using global positioning system (GPS) collars. The elevated mercury concentrations we observed in raccoons and skunks suggest that other wildlife at similar or higher trophic positions may also be exposed to elevated methylmercury bioaccumulation in brackish marshes.

Fur and faeces - Routes of mercury elimination in the Baltic grey seal (Halichoerus grypus grypus)

This study focused on evaluating the elimination of Hg by Baltic grey seals (Halichoerus grypus grypus) via faeces and pelage. In addition, we investigated the potential for ecosystem contamination via these routes. Faeces and fur were collected in 2014-2017 from captive adult grey seals and their pups. The concentrations of total mercury (THg) and methylmercury (MeHg) were measured in the samples. The amount of mercury eliminated in a labile form (the sum of the bioavailable Hg(II) and methylmercury) was also determined. An adult seal removed about 46% of mercury supplied with food via the faeces, of which only 17% was MeHg. Considering that mercury is mainly supplied to the body as MeHg, it can be assumed that mercury excreted along with faeces has undergone transformation inside the animal body. Despite the much higher THg and MeHg concentrations measured in fur, the incorporation of mercury into newly formed fur is a less effective method of Hg elimination removing just 4% of mercury entering the body via the alimentary route. The presence of mercury in lanugo is evidence of maternal transfer. First droppings of the pups were characterised by the highest content of MeHg and a low THg concentration. Then, despite the limited supply of mercury with food, and the rapid growth of the pup, the concentration of THg increased, suggesting that mercury started to be transformed into less toxic forms. It was estimated that faeces and fur expelled by seals could deliver about 800 g of mercury to the Baltic Sea. For both faeces and fur, most of the mercury (>95% for excrements and >85% for fur) was expelled in a labile form that can be quickly recycled.

Trace Element Concentrations in Livers of Pacific Harbor Seals (Phoca vitulina richardii) from San Juan County, Washington, USA

Approximately 5,000 Pacific harbor seals (Phoca vitulina richardii) reside year-round in San Juan County (SJC), Washington (US) in the center of the binational Salish Sea. We retrospectively analyzed total cadmium (Cd), copper (Cu), iron (Fe), mercury (Hg), magnesium (Mg), manganese (Mn), lead (Pb), selenium (Se), and zinc (Zn) in livers of dead stranded harbor seals (n=57) collected in SJC between 2009 and 2012 to identify age-related and regional patterns of trace element exposure. Consistent with prior studies of contaminants in pinnipeds, Hg, Cd, and Se concentrations increased with age, and Se:Hg molar ratios approached 1:1 in adult seals. Concentrations of Cd and Hg were below putative marine mammal toxicity thresholds. Mercury concentrations were comparable among Salish Sea populations. Although SJC is less urbanized with fewer industrial inputs than South Puget Sound (SPS), SJC nonpups had greater concentrations of Cd, Cu, and Zn, and pups had greater concentrations of Zn compared to SPS seals. We hypothesize these regional differences could be due to prey preference and availability or to natural geochemical processes. Reported concentrations inform future sampling protocols and can assist in tracking long-term temporal and spatial trends of trace elements in marine organisms.

Changes in total mercury, methylmercury, and selenium blood levels during different life history stages of the Baltic grey seal (Halichoerus grypus grypus)

Using the blood of grey seal pups, the blood and milk of female grey seals inhabiting the Hel Marine Station of Gdansk University's Institute of Oceanography (HMS), we monitored the transfer of total mercury (THg), methylmercury (MeHg), and selenium (Se) with blood during foetal life and nursing. Changes in the concentration of mercury and selenium were characterised in the pups' blood during their first three months of life when they transition from suckling, to a post-weaning fast, to eating fish. In the blood of pregnant females, there was a significant decrease in THg and MeHg concentrations throughout the gestation, indicating the transfer of these toxins through the placenta into the foetus. At no other stage of the pup's development was there such a high level of THg and MeHg as on the day of birth, despite the incorporation of mercury into the lanugo during foetal growth. This suggests that the maternal transfer of mercury during gestation may be the time of greatest mercury exposure for a young seal pup. The consumption of milk caused a rapid increase in weight and a lowering of the mercury level in the blood in the subsequent days of the pups' life. The postweaning fast was the period of the lowest mercury concentration. The switch to a diet consisting of fish caused a systematic increase in the concentration of mercury in the blood of the pups. Milk was the significant source of selenium for pups and the selenium concentration in females' blood was reduced during lactation. The nursing period seemed to have the greatest impact on the mercury and selenium blood levels in examined seals. Natural development of the grey seal pup created an opportunity to decrease the levels of toxic substances obtained through the maternal transfer during foetal growth.

Foraging and fasting can influence contaminant concentrations in animals: an example with mercury contamination in a free-ranging marine mammal

Large fluctuations in animal body mass in relation to life-history events can influence contaminant concentrations and toxicological risk. We quantified mercury concentrations in adult northern elephant seals (Mirounga angustirostris) before and after lengthy at sea foraging trips (n = 89) or fasting periods on land (n = 27), and showed that mercury concentrations in blood and muscle changed in response to these events. The highest blood mercury concentrations were observed after the breeding fast, whereas the highest muscle mercury concentrations were observed when seals returned to land to moult. Mean female blood mercury concentrations decreased by 30% across each of the two annual foraging trips, demonstrating a foraging-associated dilution of mercury concentrations as seals gained mass. Blood mercury concentrations increased by 103% and 24% across the breeding and moulting fasts, respectively, demonstrating a fasting-associated concentration of mercury as seals lost mass. In contrast to blood, mercury concentrations in female's muscle increased by 19% during the post-breeding foraging trip and did not change during the post-moulting foraging trip. While fasting, female muscle mercury concentrations increased 26% during breeding, but decreased 14% during moulting. Consequently, regardless of exposure, an animal's contaminant concentration can be markedly influenced by their annual life-history events.

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.

Transcriptional effects of phospholipid fatty acid profile on rainbow trout liver cells exposed to methylmercury

Lipids, and their constitutive fatty acids, are key nutrients for fish health as they provide energy, maintain cell structure, are precursors of signalling molecules and act as nuclear receptor ligands. These specific roles may be of crucial importance in a context of exposure to pollutants. We recently showed that the fatty acid profile of rainbow trout liver cell phospholipids modulates sensitivity to an acute methylmercury challenge. In order to investigate mechanisms of effects, we herein tested whether specific polyunsaturated fatty acids (PUFAs) may protect cells from methylmercury through decreasing intracellular mercury accumulation and/or enhancing cellular defences (e.g. via modulation of gene expression patterns). We also investigated the inverse relationship and assessed the impact of methylmercury on cellular fatty acid metabolism. To do so, the fatty acid composition of rainbow trout liver cell phospholipids was first modified by incubating them in a medium enriched in a specific PUFA from either the n-3 family (alpha-linolenic acid, ALA; eicosapentaenoic acid, EPA) or the n-6 family (linoleic acid, LA; arachidonic acid, AA). Cells were then exposed to methylmercury (0.15 or 0.50 μM) for 24 h and sampled thereafter for assessing phospholipid fatty acid profile, intracellular total mercury burden, and expression pattern of genes involved in fatty acid metabolism, synthesis of PUFA-derived signalling molecules and stress response. We observed that cells incorporated the given PUFA and some biotransformation products in their phospholipids. Methylmercury had few impacts on this cellular phospholipid composition. None of the PUFA enrichments affected the cellular mercury burden, suggesting that the previously observed cytoprotection conferred by ALA and EPA was not linked to a global decrease in cellular accumulation of mercury. Fatty acid enrichments and methylmercury exposure both modulated gene expression patterns. Genes involved in the synthesis of PUFA-derived signalling molecules, in stress response and the orphan cytochrome P450 20A1 were identified as possible sites of interaction between fatty acids and methylmercury in rainbow trout liver cells.

Spatial variation in the accumulation of POPs and mercury in bottlenose dolphins of the Lower Florida Keys and the coastal Everglades (South Florida)

The bottlenose dolphin (Tursiops truncatus) is an upper trophic level predator and the most common cetacean species found in nearshore waters of southern Florida, including the Lower Florida Keys (LFK) and the Florida Coastal Everglades (FCE). The objective of this study was to assess contamination levels of total mercury (T-Hg) in skin and persistent organic pollutants (PCBs, PBDEs, DDXs, HCHs, HCB, Σ PCDD/Fs and Σ DL-PCBs) in blubber samples of bottlenose dolphins from LFK (n = 27) and FCE (n = 24). PCBs were the major class of compounds found in bottlenose dolphin blubber and were higher in individuals from LFK (Σ 6 PCBs LFK males: 13,421 ± 7730 ng g^-1 lipids, Σ 6 PCBs LFK females: 9683 ± 19,007 ng g^-1 lipids) than from FCE (Σ 6 PCBs FCE males: 5638 ng g^-1 ± 3627 lipids, Σ 6 PCBs FCE females: 1427 ± 908 ng g^-1 lipids). These levels were lower than previously published data from the southeastern USA. The Σ DL-PCBs were the most prevalent pollutants of dioxin and dioxin like compounds (Σ DL-PCBs LFK: 739 ng g^-1 lipids, Σ DL-PCBs FCE: 183 ng g^-1 lipids) since PCDD/F concentrations were low for both locations (mean 0.1 ng g^-1 lipids for LFK and FCE dolphins). The toxicity equivalences of PCDD/Fs and DL-PCBs expressed as TEQ in LFK and FCE dolphins is mainly expressed by DL-PCBs (81% LFK - 65% FCE). T-Hg concentrations in skin were significantly higher in FCE (FCE median 9314 ng g^-1 dw) compared to LFK dolphins (LFK median 2941 ng g^-1 dw). These concentrations are the highest recorded in bottlenose dolphins in the southeastern USA, and may be explained, at least partially, by the biogeochemistry of the Everglades and mangrove sedimentary habitats that create favourable conditions for the retention of mercury and make it available at high concentrations for aquatic predators.

Absence of selenium protection against methylmercury toxicity in harbour seal leucocytes in vitro

Previous studies described high concentrations of mercury (Hg) and selenium (Se) in the blood of harbour seals, Phoca vitulina from the North Sea. In the present study, we evaluated the in vitro potential protective effects of sodium selenite (Na2SeO3) and selenomethionine (SeMet) on cell proliferation of harbour seal lymphocytes exposed to MeHgCl 0.75μM. In vitro exposure of ConA-stimulated T lymphocytes resulted in severe inhibition of DNA synthesis, likely linked to severe loss of mitochondrial membrane potential at 0.75μM. Neither selenite nor SeMet showed a protective effect against MeHg toxicity expressed at the T lymphocyte proliferation level for harbour seals. Selenite and SeMet did not show negative effects regarding lymphocyte proliferation and mitochondrial membrane potential. To conclude, our results clearly demonstrated that MeHg affected in vitro immune cells exposure with no protective effects of selenium at a molar ratio Hg:Se of 1:10 in harbour seals from the North Sea.

Xenobiotic and Immune-Relevant Molecular Biomarkers in Harbor Seals as Proxies for Pollutant Burden and Effects

Harbor seals are exposed to increasing pressure caused by anthropogenic activities in their marine environment. Persistent organic pollutants (POPs) and trace elements are hazardous contaminants that accumulate in tissues of harbor seals. POPs and trace elements can negatively affect the immune-system and have been reported, e.g., to increase susceptibility to viral infections in seals. Biomarkers of the xenobiotic metabolism, cytokines, and heat-shock protein as cell mediators of the immune-system were established to evaluate the impact of environmental stressors on harbor seals. Harbor seals (n = 54) were captured on sandbanks in the North Sea during 2009-2012. Health assessments, including hematology, were performed, and RNAlater blood samples were taken and analyzed using quantitative polymerase chain reaction. Normalized transcript copy numbers were correlated to hematology and POP concentration in blood and trace metals in blood and fur. A significant correlation between xenobiotic markers and contaminant burden was found. Significant interrelationships between markers and POP compounds, as well as with season, weight, and hematology values, indicate that biomarkers reflect pollutant exposure and effects. A significant relationship between cortisol levels and heat-shock protein expression was observed indicating stress experienced during restraint of the seals. Interleukin-10 transcription showed significant correlations with trace elements in fur pointing toward immune regulatory effects of metal exposure. The molecular markers prove to be an important noninvasive tool that reflects contaminant exposure and the impact of anthropogenic stressors in seal species. The connection between interleukin-2, xenobiotic markers, and pollutants may indicate immune suppression in animals exposed to contaminants with subsequent susceptibility to inflammatory disease.

Mercury Accumulation in Harbour Seals from the Northeastern Pacific Ocean: The Role of Transplacental Transfer, Lactation, Age and Location

Mercury (Hg) bioaccumulates in the aquatic food chain in the form of methylmercury, a compound well known for its neurotoxicity. We analyzed total mercury (THg) in hair collected from 209 harbour seals captured at 10 sites in British Columbia (Canada) and Washington State (USA) between 2003 and 2010. In addition, laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) allowed for a highly refined analysis of THg accumulation over time by examining nine whiskers taken from 4- to 6-week-old pups. We estimate that THg concentrations in pups increased sharply at a point corresponding to mid- to late gestation of their time in utero (4.7 ± 0.8 and 6.6 ± 1.3 µg/g dry weight (dw), respectively), and then again at the onset of nursing (8.1 ± 1.3 µg/g dw). These abrupt changes highlight the importance of both pre- and post-natal THg transfer from the mother to the growing fetus and the newborn pup. While THg levels varied among sites, hair analyses from seals collected at the same site demonstrated the influence of age in THg accumulation with pups (5.3 ± 0.3 µg/g) and juveniles (4.5 ± 0.5 µg/g) having lower levels than those in adults (8.3 ± 0.8 µg/g). Our results revealed that 33 % of the pups sampled (n = 167) had THg levels that surpassed a mammalian hair threshold for neurochemical alterations. This study suggests that Hg could represent a health concern to marine wildlife, especially as atmospheric emissions of this toxic element from human activities in the Pacific Rim and worldwide continue.

Toxicology of Marine Mammals: New Developments and Opportunities

It is widely recognized that marine mammals are exposed to a wide variety of pollutants, with a weight of evidence indicating impacts on their health. Since hundreds of new chemicals enter the global market every year,the methods, approaches and technologies used to characterize pollution levels or impacts are also in a constant state of flux. However, legal and ethical constraints often limit the type and extent of toxicological research being carried out in marine mammals. Nevertheless, new and emerging in vivo, in vitro as well as in silico research opportunities abound in the field of marine mammal toxicology. In the application of findings to population-, species-, or habitat-related risk assessments, the identification of causal relationships which inform source apportionment is important. This, in turn, is informed by a comprehensive understanding of contaminant classes, profiles and fate overspace and time. Such considerations figure prominently in the design and interpretation of marine mammal (eco)-toxicology research. This mini-review attempts to follow the evolution behind marine mammal toxicology until now,highlight some of the research that has been done and suggest opportunities for future research. This Special Issue will showcase new developments in marine mammal toxicology, approaches for exposure-effect research in risk assessment as well as future opportunities.

Mercury and Selenium Balance in Endangered Saimaa Ringed Seal Depend on Age and Sex

The endangered Saimaa ringed seal (Pusa hispida saimensis) is exposed to relatively high concentrations of mercury (Hg) in freshwaters poor in selenium (Se), a known antagonist of Hg. The impact of age and sex on the bioaccumulation of Hg and Se was studied by analyzing liver, muscle, and hair samples from seals of different age groups. Adult females were found to accumulate significantly more Hg in the liver (with ca. 60% as HgSe), and less Hg in the muscles compared to adult males, which may be explained by accelerated metabolism during gestation and lactation. In adult seals, molar Se:Hg ratios in the muscles fall below one, which is considered a threshold for the emergence of adverse effects. As a result, Saimaa ringed seals may be at risk of developing health and reproductive problems. According to mass balance calculations, the pups are exposed to considerable amounts (μg/d) of mercury during gestation, although lactation is their main exposure route. In lanugo pups, Hg concentrates in the hair, and molting serves as a main detoxification route. For other age groups, demethylation followed by the formation of HgSe is the main detoxification route, and the demethylation capability develops in pups by the time of weaning.

Adiponectin and Insulin in Gray Seals during Suckling and Fasting: Relationship with Nutritional State and Body Mass during Nursing in Mothers and Pups

Animals that fast during breeding and/or development, such as phocids, must regulate energy balance carefully to maximize reproductive fitness and survival probability. Adiponectin, produced by adipose tissue, contributes to metabolic regulation by modulating sensitivity to insulin, increasing fatty acid oxidation by liver and muscle, and promoting adipogenesis and lipid storage in fat tissue. We tested the hypotheses that (1) circulating adiponectin, insulin, or relative adiponectin gene expression is related to nutritional state, body mass, and mass gain in wild gray seal pups; (2) plasma adiponectin or insulin is related to maternal lactation duration, body mass, percentage milk fat, or free fatty acid (FFA) concentration; and (3) plasma adiponectin and insulin are correlated with circulating FFA in females and pups. In pups, plasma adiponectin decreased during suckling (linear mixed-effects model [LME]: T = 4.49; P < 0.001) and the early postweaning fast (LME: T = 3.39; P = 0.004). In contrast, their blubber adiponectin gene expression was higher during the early postweaning fast than early in suckling (LME: T = 2.11; P = 0.046). Insulin levels were significantly higher in early (LME: T = 3.52; P = 0.004) and late (LME: T = 6.99; P < 0.001) suckling than in fasting and, given the effect of nutritional state, were also positively related to body mass (LME: T = 3.58; P = 0.004). Adiponectin and insulin levels did not change during lactation and were unrelated to milk FFA or percentage milk fat in adult females. Our data suggest that adiponectin, in conjunction with insulin, may facilitate fat storage in seals and is likely to be particularly important in the development of blubber reserves in pups.

Molecular biomarkers in grey seals (Halichoerus grypus) to evaluate pollutant exposure, health and immune status

Grey seals as top-predators bioaccumulate contaminants and can be considered as sentinels of eco-system health. Pups are weaned after a short nursing period, characterised by an enormous lipid transfer and exposure to contaminants. This study established molecular biomarkers of the xenobiotic metabolism and immune system to help assess health and immune status. mRNA transcription of AHR, ARNT, PPARα and cytokine IL-2 and heat-shock-protein HSP70 was measured in blood of grey seal pups and adults in rehabilitation and permanent care using RT-qPCR and compared to rehabilitating harbour seal pups and haematology values. In pups highest levels at admission in xenobiotic biomarker, HSP70 and cytokine transcription may show contaminant exposure via lactation, stress during abandonment and dehydration. The significant decrease may be linked to diet, health improvement and adaptation. Adults showed higher levels and more variation in biomarker transcription and clear species-specific differences between harbour and grey seal pups were found.

Relationships between in vitro lymphoproliferative responses and levels of contaminants in blood of free-ranging adult harbour seals (Phoca vitulina) from the North Sea

In vitro culture of peripheral blood leucocytes (PBLs) is currently used in toxicological studies of marine mammals. However, blood cells of wild individuals are exposed in vivo to environmental contaminants before being isolated and exposed to contaminants in vitro. The aim of this study was to highlight potential relationships between blood contaminant levels and in vitro peripheral blood lymphocyte proliferation in free-ranging adult harbour seals (Phoca vitulina) from the North Sea. Blood samples of 18 individuals were analyzed for trace elements (Fe, Zn, Se, Cu, Hg, Pb, Cd) and persistent organic contaminants and metabolites (ΣPCBs, ΣHO-PCBs, ΣPBDEs, 2-MeO-BDE68 and 6-MeO-BDE47, ΣDDXs, hexachlorobenzene, oxychlordane, trans-nonachlor, pentachlorophenol and tribromoanisole). The same samples were used to determine the haematology profiles, cell numbers and viability, as well as the in vitro ConA-induced lymphocyte proliferation expressed as a stimulation index (SI). Correlation tests (Bravais-Pearson) and Principal Component Analysis with multiple regression revealed no statistically significant relationship between the lymphocyte SI and the contaminants studied. However, the number of lymphocytes per millilitre of whole blood appeared to be negatively correlated to pentachlorophenol (r=-0.63, p=0.005). In adult harbour seals, the interindividual variations of in vitro lymphocyte proliferation did not appear to be directly linked to pollutant levels present in the blood, and it is likely that other factors such as age, life history, or physiological parameters have an influence. In a general manner, experiments with in vitro immune cell cultures of wild marine mammals should be designed so as to minimize confounding factors in which case they remain a valuable tool to study pollutant effects in vitro.

How are trace elements mobilized during the postweaning fast in Northern elephant seals?

Northern elephant seal (Mirounga angustirostris) pups undergo a substantial intertissue reorganization of protein, minerals, and other cellular components during their postweaning development, which might entail the mobilization of associated contaminants. The authors investigated the changes in concentrations of 11 elements (Ca, Cd, Cr, Cu, Fe, Hg, Ni, Pb, Se, V, and Zn) in a longitudinal study on 22 northern elephant seal pups during the postweaning fast. Slight changes in most element concentrations were observed in blood throughout the fast. Circulating levels of Hg, Se, and Cu appeared less altered during the postweaning fast than measured during suckling. Despite the considerable fat utilization, element concentrations, except Fe, in blubber remained stable throughout the fast, which suggests that elements are mobilized from blubber as efficiently as lipids. As indicators of the placental transfer, concentrations in lanugo hair revealed the existence of maternal transfer and accumulation of all assayed trace elements during fetal development. In addition, the new pelage, rapidly produced after weaning, appeared to be an important elimination route for toxic metals such as Hg, Cd, and Pb. The high mineral content detected in pup hair suggests that this species would be more exposed to trace elements than other phocids (except Cd and Pb). Nevertheless, this statement needs further monitoring and toxicological studies to determine better the exposition to trace elements and its potential impact on the health of the northern elephant seal.