Blood and Hair Mercury Concentrations in the Pacific Harbor Seal (Phoca vitulina richardii) Pup: Associations with Neurodevelopmental Outcomes

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.

Mercury and selenium concentrations in lanugo of free-ranging California sea lions in the southern Gulf of California, Mexico

Total mercury ([THg]) and selenium ([TSe]) concentrations were determined in California sea lion (Zalophus californianus) lanugo from the Gulf of California in 2021 and 2022. Relationships with sex, morphometrics, and year were evaluated. Following toxicological thresholds of concern for piscivorous mammals, most pups had a [THg] < 10 ppm, one pup (2021) had a [THg] > 20 ppm, no pups had a [THg] > 30 ppm. Females had significantly higher [TSe] than males; sex did not influence [THg]. [THg] and [TSe] in 2022 were significantly higher in the general population and male cohorts compared to 2021. Significant negative correlations were observed between [THg], [TSe], and morphometrics (2021). These results indicate that, compared to other pinniped species, regional California sea lions may have a decreased likelihood of experiencing Hg-related adverse health effects. Year-related changes in element concentrations suggest continued monitoring of this population to assess pinniped, environmental, and potentially, human health.

RETROSPECTIVE REVIEW OF NEUROLOGIC DISEASE IN STRANDED ATLANTIC HARBOR SEALS (PHOCA VITULINA CONCOLOR) ALONG THE NEW ENGLAND COAST

Harbor seals (Phoca vitulina) are a common species admitted to marine mammal rehabilitation facilities. As important indicators of marine ecosystem health, monitoring trends of disease in harbor seal populations is critical. However, few studies have evaluated neurologic disease in this species. The general objective of this study was to retrospectively review and delineate neurologic disease in free-ranging Atlantic harbor seals (P. vitulina concolor) that stranded along the New England (United States) coast and entered a rehabilitation facility between 2006 and 2019. Any Atlantic harbor seal that stranded live along the New England coast during the study period and was diagnosed with neurologic disease on either antemortem or postmortem evaluation was included; medical records and pathologic reports were reviewed. From 211 records, 24 animals met the inclusion criteria. Prevalence of neurologic disease was 11% in the study population and six major categories of neurologic disease were identified including: inflammatory (54%), idiopathic (33%), trauma (4%), congenital (4%), and degenerative (4%). Of the seals diagnosed with neurologic disease, 13 (54%) seals died during rehabilitation, 10 (42%) seals were euthanized, and 1 (4%) seal survived to release. Unique cases seen included a seal with Dandy-Walker-like malformation and another seal with histopathologic findings compatible with neuroaxonal dystrophy, a degenerative process that has not been previously reported in marine mammals. This study contributes to the overall knowledge of the health of free-ranging Atlantic harbor seals and may aid clinicians in characterizing neurologic conditions that may be present in seals undergoing rehabilitation.

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.

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.

Assessment of clinical outcomes associated with mercury concentrations in harbor seal pups (Phoca vitulina richardii) in central California

Monomethyl mercury (MeHg⁺) from the diet can cause mild to severe neurotoxicosis in fish-eating mammals. Chronic and low-level in utero exposure also can be neurotoxic, as documented in laboratory animal studies and epidemiologic investigations. In free-ranging animals, it is challenging to study low-level exposure related neurotoxicosis, and few studies have investigated the relationship between mercury (Hg) and adverse outcomes in wild populations. Relative to Hg concentrations on admission we evaluated different types of behaviors for 267 Pacific harbor seal (HS; Phoca vitulina richardii) pups at The Marine Mammal Center from 2015 to 2019 during rehabilitation after stranding and maternal separation. Admitted HS pups underwent a clinical exam; including sex and weight determination, and hair (partly lanugo grown in utero) and blood samples were collected for total Hg concentration ([THg]) determination. All pups were monitored weekly (behavior assessments included response to tactile stimulation, movement, swimming, interactions with other seals, hand feeding, and feeding independently), and days in rehabilitation and survival were recorded. There was a significant negative correlation between [THg] and responses to tactile stimulation and movements, measured in both hair and whole blood (p < 0.05). This relationship was found both during the intensive care unit (ICU) stage, and during the pool stage of rehabilitation. Additionally, there was a significant association between greater [THg] and number of days spent in rehabilitation, although there was no relationship between [THg] and survival. There was a significant sex difference, with greater [THg] in female pups, which contrasts with previously published findings in juvenile and adult harbor seals. Our findings support small, but significant associations between gestational THg exposure and clinical effects for tactile sensory response and movement, and longer rehabilitation durations for HS pups, although there was considerable variability among animals.

A comparison of individual-level vs. hypothetically pooled mercury biomonitoring data from the Maternal Organics Monitoring Study (MOMS), Alaska, 1999-2012

Biomonitoring for heavy metals is important to assess health risks, especially in Arctic communities where rural residents rely on locally harvested foods. However, laboratory testing for blood contaminants is expensive and might not be sustainable for long-term monitoring. We assessed whether pooled specimen biomonitoring could be a part of a plan for blood contaminant surveillance among pregnant women in rural Alaska using existing blood mercury level data from three cross sectional studies of pregnant women. We applied a hypothetical pooled specimen template stratified into 8 demographic groups based on age, coastal or inland residence, and pre-pregnancy weight. The hypothetical geometric mean blood mercury levels were similar to the individual-level geometric means. However, the 95% confidence intervals were much wider for the hypothetical geometric means compared to the true geometric means. Although the variability that resulted from pooling specimens using a small sample made it difficult to compare demographic groups to each other, pooled specimen results could be an accurate reflection of the population burden of mercury contamination in the Arctic in the context of large numbers of biomonitoring samples.

Regional variations and drivers of mercury and selenium concentrations in Steller sea lions

Mercury (Hg) can be neurotoxic to mammals and impact reproduction, whereas selenium (Se) is an important antioxidant known to ameliorate some adverse effects of Hg. Total Hg concentrations ([THg]) were measured in lanugo (pelage grown in utero) of 812 Steller sea lion (Eumetopias jubatus) pups across Alaska and Russia to assess fetal exposure during late gestation. The molar ratio of total Se to THg (TSe:THg) was determined in whole blood collected from 291 pups. Stable isotope ratios of carbon and nitrogen were measured in sections of vibrissae (whiskers, n = 498) and in lanugo (n = 480) of pups grown during late gestation to track diet variations among adult females that can drive Hg and Se exposure during this critical fetal development period. Lanugo [THg] ranged from 1.4 to 73.7 μg/g dry weight with the lowest median [THg] in Southeast Alaska. Pups from the Western Aleutian Islands had higher median lanugo [THg] than pups from other metapopulations in Alaska. Over 25% of pups in the Western Aleutian Islands had [THg] above published risk thresholds (20 μg/g) for other mammals. Whole blood molar TSe:THg was significantly lower in the Western Aleutian Islands and in some parts of the Central Aleutian Islands with higher molar ratios found in the Eastern Aleutian Islands and Central Gulf of Alaska. This suggests a limitation on potential protective functions of Se in the western regions with the highest relative [THg]. The Central Aleutian Island pups with [THg] over 20 μg/g had higher δ¹⁵N ratios than pups with lower [THg] suggesting dams consuming higher trophic level prey is a key driver for Hg exposure. However, regional differences likely reflect variability in diet of the dam during gestation and in Hg food web dynamics between oceanic regimes east and west of key passes in the Aleutian Islands.

Methyl mercury (MeHg) in vitro exposure alters mitogen-induced lymphocyte proliferation and cytokine expression in Steller sea lion (Eumetopias jubatus) pups

Steller sea lions (Eumetopias jubatus, SSLs) are managed as two distinct population segments within U.S. waters: the endangered western distinct population segment and the recently delisted eastern distinct population segment. Recent studies reported concentrations of mercury in several tissues collected from young SSLs in the Aleutian Islands that were at or above concentrations found to negatively impact health in other fish-eating mammals. However, there are limited studies which have investigated the range of mercury concentrations that may negatively influence the SSL immune system. This study assessed relationships between methyl mercury (MeHg⁺) concentrations and two immune functions, lymphocyte proliferation and cytokine expression. Peripheral blood mononuclear cells (PBMCs) were isolated and cryopreserved from pups on three rookeries within the western distinct population segment: Chiswell Island, Ulak, and Agattu Islands. Lymphocyte proliferation and cytokine expression were assessed in vitro using thawed PBMCs with exposure to MeHg⁺ (unexposed control, 0.001, 0.01, and 0.1 μg/ml). Lymphocyte proliferation was measured without and with stimulation with a T cell mitogen (ConA) and B cell mitogen (LPS) and the concentration of cytokines was measured in the cell culture supernatant (with and without ConA or LPS). Spontaneous lymphocyte proliferation was significantly increased at 0.01 and 0.1 μg/ml. T lymphocyte proliferation was significantly increased at 0.001 μg/ml and 0.1 μg/ml, while B lymphocyte proliferation was decreased at 0.1 μg/ml. Cytokine concentrations for INFγ, IL-10, IL-6, and TNFα were reduced at 0.1 μg/ml upon either T or B cell mitogen stimulation, with the exception for IL-10, where 0.1 μg/ml reduced IL-10 concentration compared to unstimulated cells. These data suggest immune functions were affected by MeHg⁺ exposure requiring in vivo follow up investigations. The observed modulation of immune functions is of concern as any toxicant-induced modulation may adversely affect the health of individuals, particularly younger animals undergoing periods of critical development.

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.

Hair mercury concentrations in the spotted seal (Phoca largha) pups from the Sea of Japan

This publication presents the results of a study of the total mercury (THg) concentration in the fetal hair (lanugo) of the young spotted seals inhabiting the Peter the Great Bay, Sea of Japan. We analyzed samples from pups that were collected in 2014-2017 at the seal breeding grounds. The concentration of total mercury was determined by atomic absorption spectrometry. The concentration of THg ranged from 1.52 to 6.68 μg/g dry weight. Mercury concentration in the lanugo exceeds that found in the environment (bottom sediments, sea water) and in other animals inhabiting the Bay. At the same time, the level was generally lower than that found in young seals of most other pinniped species (Steller sea lion Eumetopias jubatus, Northern fur seal Callorhinus ursinus, Harbor seal Phoca vitulina richardsi, Northern elephant seal Mirounga angustirostris, California sea lion Zalophus californianus) from the North Pacific.

Multiple metal exposures and their correlation with monoamine neurotransmitter metabolism in Chinese electroplating workers

Excessive metal exposure has been recognized as one of the detrimental factors for brain damage. However, the potential adverse effects induced by heavy metals on monoamine neurotransmitter pathways remains poorly understood. Our study aimed to investigate the possible association between metal exposure and neurotransmitter metabolism. By a cross-sectional investigation, 224 electroplating workers and 213 non-electroplating exposure workers were recruited in the exposure and control groups. Metal exposure levels were analyzed using inductively-coupled plasma mass spectrometry and monoamine neurotransmitter pathway metabolites were measured by ultra-performance liquid chromatography tandem mass spectrometry in human urine samples. Multivariate linear regression model was used to assess the dose-response relationships of urinary metals and neurotransmitter pathway metabolites. Significant dose-dependent trends of urinary vanadium quartiles with all metabolites were observed, and the trends demonstrated significance after multiple testing correction. It also showed that urinary chromium levels were significantly associated with decreased serotonin level and cadmium was positively associated with norepinephrine and epinephrine. In addition, arsenic was positively associated with tryptophan, serotonin, dopamine and norepinephrine. Iron was positively associated with increased homovanillic acid (HVA) and epinephrine while nickel was negatively associated with increased epinephrine levels. Zinc was positively related to tryptophan, kynurenin (KYN), 5-hydroxyindole acetic acid (5-HIAA), dopamine, HVA and norepinephrine. There was no significant association between urinary copper with any other metabolites after adjusting of multiple metal models. Metal exposure may be associated with neurotransmitter metabolism disturbances. The present work is expected to provide some support in the prevention and management of metal-associated neurological diseases.

Anti-parasite treatment, but not mercury burdens, influence nesting propensity dependent on arrival time or body condition in a marine bird

Arctic wildlife can be exposed to high mercury (Hg) levels, and are also naturally exposed to gastrointestinal parasites that can reduce condition and negatively affect reproductive output and/or survival in similar ways. Importantly, both Hg and parasites are increasing in wildlife in some Arctic regions. We studied the northern common eider duck (Somateria mollissima) to explore how Hg in association with both natural levels and experimentally reduced parasitic infections, affect reproduction and survival. Female eiders were measured, banded, and blood sampled to determine blood Hg burdens, prior to breeding. Propensity to nest, clutch size, nest survival, nest attendance, and return rates were assessed in relation to both Hg burden and parasite treatment. Neither reproduction nor return rates of females varied with Hg concentrations, but females arriving late to the colony, or in low body condition, showed increased nesting propensity when given the anti-parasite treatment as compared to placebo treatment. Our results suggest that parasites can play a critical role in decisions to invest in avian breeding annually, particularly among individuals with a late onset to breeding, and in poor condition.