To breed or not to breed: endocrine response to mercury contamination by an Arctic seabird

Sex- and age-specific mercury accumulation in a long-lived seabird

Mercury levels in the environment are increasing, such that they are also expected to accumulate in top-predators, but individual-based longitudinal studies required to investigate this are rare. Between 2017 and 2023, we therefore collected 1314 blood samples from 588 individual common terns (Sterna hirundo) to examine how total blood mercury concentration changed with age, and whether this differed between the sexes. Blood mercury concentrations were highly variable, but all exceeded toxicity thresholds above which adverse health effects were previously observed. A global model showed blood mercury to be higher in older birds of both sexes. Subsequent models partitioning the age effect into within- and among-individual components revealed a linear within-individual accumulation with age in females, and a decelerating within-individual accumulation with age in males. Time spent at the (particularly contaminated) breeding grounds prior to sampling, as well as egg laying in females, were also found to affect mercury concentrations. As such, our study provides evidence that male and female common terns differentially accumulate mercury in their blood as they grow older and calls for further studies of the underlying mechanisms as well as its consequences for fitness components, such as reproductive performance and survival.

The relationship between plastic ingestion and trace element concentrations in Arctic seabirds

Seabirds ingest contaminants linked to their prey's tissues, but also adsorbed to ingested plastic debris. To explore relationships between ingested plastics and trace elements concentrations, we analyzed 25 essential non-essential trace elements in liver tissue in relation to plastic content in the gastrointestinal tract in adults of four species of Arctic seabirds with different propensity to ingest plastic. Linear Discriminant Analysis (LDA) provided a clear separation between species based on element concentrations, but not among individuals with and without plastics. Molybdenum, copper, vanadium, and zinc were strong drivers of the LDA, separating northern fulmars (Fulmarus glacialis) from other species (60.4 % of explained between-group variance). Selenium, vanadium, zinc, and mercury were drivers separating black-legged kittiwakes (Rissa tridactyla) from the other species (19.3 % of explained between-group variance). This study suggests that ingestion of plastic particles has little influence on the burden of essential and non-essential trace elements in Arctic seabird species.

Mercury and rare earth elements (REEs) show different spatial trends in feathers of Kentish plover (Charadrius alexandrinus) breeding along the Adriatic Sea coast, Italy

Feather analysis is an ethical and effective method for assessing the exposure of wild birds to environmental contamination due to trace elements and organic pollutants. We used feather to monitor the exposure to three toxic and non-essential metals (Hg, Cd, and Pb) and rare earth elements (REEs) of Kentish plover (Charadrius alexandrinus) breeding in different coastal areas (Veneto, Emilia-Romagna, Marche, Abruzzo, and Apulia) along the Italian coast of the Adriatic Sea. Feathers (n = 113) were collected from April to June. Feather concentrations evidenced a significant exposure to Hg (13.05 ± 1.71 mg kg-1 dw) and REEs (447.3 ± 52.8 ng g-1 dw) in the Kentish plover breeding in Veneto (n = 21) compared to the other coastal areas, with several individuals showing Hg concentrations above the adverse effect (5 mg kg-1 dw) and high-risk (9.14 mg kg-1 dw) thresholds reported for birds. Higher REE concentrations compared to Marche (n = 29), Abruzzo (n = 11) and Apulia (n = 13) were also reported for birds breeding in Emilia-Romagna (474.9 ± 41.9 ng g-1 dw; n = 29). The exposure to Cd and Pb was low in all the coastal areas, and only a few samples (n = 6 and n = 4 for Cd and Pb, respectively) exceeded the adverse effect thresholds (0.1 and 4 mg kg-1 for Cd and Pb, respectively). A significant sex-related difference was observed for REE-concentrations, with females showing higher concentration than males. These data highlight the need to monitor the exposure of the Kentish plover to Hg and REEs, especially in the northern basin of the Adriatic Sea, since these elements might negatively affect species' reproductive success and threaten its conservation.

Global mercury concentrations in biota: their use as a basis for a global biomonitoring framework

An important provision of the Minamata Convention on Mercury is to monitor and evaluate the effectiveness of the adopted measures and its implementation. Here, we describe for the first time currently available biotic mercury (Hg) data on a global scale to improve the understanding of global efforts to reduce the impact of Hg pollution on people and the environment. Data from the peer-reviewed literature were compiled in the Global Biotic Mercury Synthesis (GBMS) database (>550,000 data points). These data provide a foundation for establishing a biomonitoring framework needed to track Hg concentrations in biota globally. We describe Hg exposure in the taxa identified by the Minamata Convention: fish, sea turtles, birds, and marine mammals. Based on the GBMS database, Hg concentrations are presented at relevant geographic scales for continents and oceanic basins. We identify some effective regional templates for monitoring methylmercury (MeHg) availability in the environment, but overall illustrate that there is a general lack of regional biomonitoring initiatives around the world, especially in Africa, Australia, Indo-Pacific, Middle East, and South Atlantic and Pacific Oceans. Temporal trend data for Hg in biota are generally limited. Ecologically sensitive sites (where biota have above average MeHg tissue concentrations) have been identified throughout the world. Efforts to model and quantify ecosystem sensitivity locally, regionally, and globally could help establish effective and efficient biomonitoring programs. We present a framework for a global Hg biomonitoring network that includes a three-step continental and oceanic approach to integrate existing biomonitoring efforts and prioritize filling regional data gaps linked with key Hg sources. We describe a standardized approach that builds on an evidence-based evaluation to assess the Minamata Convention's progress to reduce the impact of global Hg pollution on people and the environment.

Spatial distribution of selenium-mercury in Arctic seabirds

Mercury (Hg) is a metallic trace element toxic for humans and wildlife that can originate from natural and anthropic sources. Hg spatial gradients have been found in seabirds from the Arctic and other oceans, suggesting contrasting toxicity risks across regions. Selenium (Se) plays a protective role against Hg toxicity, but its spatial distribution has been much less investigated than that of Hg. From 2015 to 2017, we measured spatial co-exposure of Hg and Se in blood samples of two seabird species, the Brünnich's guillemot (Uria lomvia) and the black-legged kittiwake (Rissa tridactyla) from 17 colonies in the Arctic and subarctic regions, and we calculated their molar ratios (Se:Hg), as a measure of Hg sequestration by Se and, therefore, of Hg exposure risk. We also evaluated concentration differences between species and ocean basins (Pacific-Arctic and Atlantic-Arctic), and examined the influence of trophic ecology on Hg and Se concentrations using nitrogen and carbon stable isotopes. In the Atlantic-Arctic ocean, we found a negative west-to-east gradient of Hg and Se for guillemots, and a positive west-to-east gradient of Se for kittiwakes, suggesting that these species are better protected from Hg toxicity in the European Arctic. Differences in Se gradients between species suggest that they do not follow environmental Se spatial variations. This, together with the absence of a general pattern for isotopes influence on trace element concentrations, could be due to foraging ecology differences between species. In both oceans, the two species showed similar Hg concentrations, but guillemots showed lower Se concentrations and Se:Hg than kittiwakes, suggesting a higher Hg toxicity risk in guillemots. Within species, neither Hg, nor Se or Se:Hg differed between both oceans. Our study highlights the importance of considering Se together with Hg, along with different species and regions, when evaluating Hg toxic effects on marine predators in international monitoring programs.

Inter-colony variation in predation, mercury burden and adult survival in a declining seabird

Migratory species with disjunct and localized breeding distributions, including many colonial marine birds, pose challenges for management and conservation as their dynamics are shaped by both broad oceanographic changes and specific factors affecting individual breeding colonies. We compare six colonies of the declining Leach's storm-petrel, Hydrobates leucorhous, across their core range in Atlantic Canada using standard capture-mark-recapture methods to estimate annual survival of individually marked populations of breeding adults. Over the period analysed (5-20 years per colony; 2003-2022), mean annual survival varied among colonies (0.81-0.88) and annually (process error σ ranging from 0.01 to 0.09), though annual fluctuations were not synchronous across colonies. Two colonies with limited natural predation showed higher survival, and there was a decline in survival with increasing colony-specific total mercury burden. Our work shows that colony-specific pressures and regional contaminant burdens are potentially important contributors to current population declines, and highlights the importance of monitoring demographic rates at multiple sites for species that congregate at key life-history stages.

Deleterious effects of mercury contamination on immunocompetence, liver function and egg volume in an antarctic seabird

Mercury (Hg) is a globally important pollutant that can negatively impact metabolic, endocrine and immune systems of marine biota. Seabirds are long-lived marine top predators and hence are at risk of bioaccumulating high Hg concentrations from their prey. Here, we measured blood total mercury (THg) concentrations and relationships with physiology and breeding parameters of breeding brown skuas (Stercorarius antarcticus) (n = 49 individuals) at Esperanza/Hope Bay, Antarctic Peninsula. Mean blood THg concentrations were similar in males and females despite the differences in body size and breeding roles, but differed between study years. Immune markers (hematocrit, Immunoglobulin Y [IgY] and albumin) were negatively correlated with blood THg concentrations, which likely indicates a disruptive effect of Hg on immunity. Alanine aminotransferase (GPT) activity, reflecting liver dysfunction, was positively associated with blood THg. Additionally, triacylglycerol and albumin differed between our study years, but did not correlate with Hg levels, and so were more likely to reflect changes in diet and nutritional status rather than Hg contamination. Egg volume correlated negatively with blood THg concentrations. Our study provides new insights into the sublethal effects of Hg contamination on immunity, liver function and breeding parameters in seabirds. In this Antarctic species, exposure to sublethal Hg concentrations reflects the short-term risks which could make individuals more susceptible to environmental stressors, including ongoing climatic changes.

Broad-Scale Assessment of Methylmercury in Adult Amphibians

Mercury (Hg) is a toxic contaminant that has been mobilized and distributed worldwide and is a threat to many wildlife species. Amphibians are facing unprecedented global declines due to many threats including contaminants. While the biphasic life history of many amphibians creates a potential nexus for methylmercury (MeHg) exposure in aquatic habitats and subsequent health effects, the broad-scale distribution of MeHg exposure in amphibians remains unknown. We used nonlethal sampling to assess MeHg bioaccumulation in 3,241 juvenile and adult amphibians during 2017-2021. We sampled 26 populations (14 species) across 11 states in the United States, including several imperiled species that could not have been sampled by traditional lethal methods. We examined whether life history traits of species and whether the concentration of total mercury in sediment or dragonflies could be used as indicators of MeHg bioaccumulation in amphibians. Methylmercury contamination was widespread, with a 33-fold difference in concentrations across sites. Variation among years and clustered subsites was less than variation across sites. Life history characteristics such as size, sex, and whether the amphibian was a frog, toad, newt, or other salamander were the factors most strongly associated with bioaccumulation. Total Hg in dragonflies was a reliable indicator of bioaccumulation of MeHg in amphibians (R2 ≥ 0.67), whereas total Hg in sediment was not (R2 ≤ 0.04). Our study, the largest broad-scale assessment of MeHg bioaccumulation in amphibians, highlights methodological advances that allow for nonlethal sampling of rare species and reveals immense variation among species, life histories, and sites. Our findings can help identify sensitive populations and provide environmentally relevant concentrations for future studies to better quantify the potential threats of MeHg to amphibians.

Mercury contamination in the tropical seabird community from Clipperton Island, eastern Pacific Ocean

Mercury (Hg) pollution is a global problem affecting remote areas of the open ocean, but the bioaccumulation of this neurotoxic pollutant in tropical top predators remains poorly documented. The objective of this study was to determine Hg contamination of the seabird community nesting on Clipperton Island using blood and feathers to investigate short and longer-term contamination, respectively. We examined the significance of various factors (species, sex, feeding habitat [δ13C] and trophic position [δ15N]) on Hg concentrations in six seabird species. Among species, Great Frigatebirds had the highest Hg concentrations in blood and feathers, boobies had intermediate values, and Brown Noddies and Sooty Terns the lowest. At the interspecific level, although δ13C values segregated boobies from frigatebirds and noddies/terns, Hg concentrations were explained by neither δ13C nor δ15N values. At the intraspecific level, both Hg concentrations in blood and feathers show relatively small variations (16-32 and 26-74%, respectively), suggesting that feeding ecology had low seasonal variation among individuals. Despite most species being sexually dimorphic, differences in Hg contamination according to sex was detected only in Brown Boobies during the breeding period. Indeed, female Brown Boobies feed at a higher trophic level and in a different area than males during this period, resulting in higher blood Hg concentrations. The present study also shows that most of the seabirds sampled at Clipperton Island had little or no exposure to Hg toxicity, with 30% in the no risk category and 70% in the low risk category.

Combined threats of climate change and contaminant exposure through the lens of bioenergetics

Organisms face energetic challenges of climate change in combination with suites of natural and anthropogenic stressors. In particular, chemical contaminant exposure has neurotoxic, endocrine-disrupting, and behavioral effects which may additively or interactively combine with challenges associated with climate change. We used a literature review across animal taxa and contaminant classes, but focused on Arctic endotherms and contaminants important in Arctic ecosystems, to demonstrate potential for interactive effects across five bioenergetic domains: (1) energy supply, (2) energy demand, (3) energy storage, (4) energy allocation tradeoffs, and (5) energy management strategies; and involving four climate change-sensitive environmental stressors: changes in resource availability, temperature, predation risk, and parasitism. Identified examples included relatively equal numbers of synergistic and antagonistic interactions. Synergies are often suggested to be particularly problematic, since they magnify biological effects. However, we emphasize that antagonistic effects on bioenergetic traits can be equally problematic, since they can reflect dampening of beneficial responses and result in negative synergistic effects on fitness. Our review also highlights that empirical demonstrations remain limited, especially in endotherms. Elucidating the nature of climate change-by-contaminant interactive effects on bioenergetic traits will build toward determining overall outcomes for energy balance and fitness. Progressing to determine critical species, life stages, and target areas in which transformative effects arise will aid in forecasting broad-scale bioenergetic outcomes under global change scenarios.

Metals in the Réunion harrier: tissue concentrations and meaning for conservation

The Réunion harrier is an endemic raptor on Réunion Island. Several threats endanger its population, poisoning by rodenticides being considered as the main one currently. No information is available on its exposure to other chemicals notably trace metal elements such as lead (Pb), mercury (Hg), and cadmium (Cd). The Réunion harrier is still a victim of poaching nowadays. When shooting is not lethal, animals may carry embedded shot in their body and thus be exposed to toxic level of Pb as demonstrated for other raptors. Moreover, recent monitoring suggests a decrease of its breeding success over time. It is known that Hg and Cd could impair reproduction and disturb embryo development in birds. The aim is to measure metal concentrations in the tissues of 30 carcasses of harrier collected from 2016 to 2021. Lead was analyzed in the liver and humerus, while Hg and Cd were measured in livers. Concentrations were compared to toxicological reference values. Overall, the Réunion harrier was not exposed to toxic levels of Pb or Cd. For Hg, 53% of the individuals have residues higher than the threshold compatible with oxidative stress, and 13% have liver concentrations above those compatible with reproduction impairment. A positive correlation was found between the proportion of urban habitat in a 55 km2 area centered on the location where the harrier was found and the concentration of Hg in the liver. We conclude that Hg exposure could be a threat for the Réunion harrier population and recommend monitoring the exposure of the most sensitive stages, i.e., embryos and nestlings, to this metal with non-invasive methods.

Contaminant-by-environment interactive effects on animal behavior in the context of global change: Evidence from avian behavioral ecotoxicology

The potential for chemical contaminant exposure to interact with other stressors to affect animal behavioral responses to environmental variability is of mounting concern in the context of anthropogenic environmental change. We systematically reviewed the avian literature to evaluate evidence for contaminant-by-environment interactive effects on animal behavior, as birds are prominent models in behavioral ecotoxicology and global change research. We found that only 17 of 156 (10.9 %) avian behavioral ecotoxicological studies have explored contaminant-by-environment interactions. However, 13 (76.5 %) have found evidence for interactive effects, suggesting that contaminant-by-environment interactive effects on behavior are understudied but important. We draw on our review to develop a conceptual framework to understand such interactive effects from a behavioral reaction norm perspective. Our framework highlights four patterns in reaction norm shapes that can underlie contaminant-by-environment interactive effects on behavior, termed exacerbation, inhibition, mitigation and convergence. First, contamination can render individuals unable to maintain critical behaviors across gradients in additional stressors, exacerbating behavioral change (reaction norms steeper) and generating synergy. Second, contamination can inhibit behavioral adjustment to other stressors, antagonizing behavioral plasticity (reaction norms shallower). Third, a second stressor can mitigate (antagonize) toxicological effects of contamination, causing steeper reaction norms in highly contaminated individuals, with improvement of performance upon exposure to additional stress. Fourth, contamination can limit behavioral plasticity in response to permissive conditions, such that performance of more and less contaminated individuals converges under more stressful conditions. Diverse mechanisms might underlie such shape differences in reaction norms, including combined effects of contaminants and other stressors on endocrinology, energy balance, sensory systems, and physiological and cognitive limits. To encourage more research, we outline how the types of contaminant-by-environment interactive effects proposed in our framework might operate across multiple behavioral domains. We conclude by leveraging our review and framework to suggest priorities for future research.

A heavy burden: Metal exposure across the land-ocean continuum in an adaptable carnivore

Urbanisation and associated anthropogenic activities release large quantities of toxic metals and metalloids into the environment, where they may bioaccumulate and threaten both wildlife and human health. In highly transformed landscapes, terrestrial carnivores may be at increased risk of exposure through biomagnification. We quantified metallic element and metalloid exposure in blood of caracals (Caracal caracal), an adaptable felid inhabiting the rapidly urbanising, coastal metropole of Cape Town, South Africa. Using redundancy analysis and mixed-effect models, we explored the influence of demography, landscape use, and diet on the concentration of 11 metals and metalloids. Although species-specific toxic thresholds are lacking, arsenic (As) and chromium (Cr) were present at potentially sublethal levels in several individuals. Increased use of human-transformed landscapes, particularly urban areas, roads, and vineyards, was significantly associated with increased exposure to aluminium (Al), cobalt (Co) and lead (Pb). Foraging closer to the coast and within aquatic food webs was associated with increased levels of mercury (Hg), selenium (Se) and arsenic, where regular predation on seabirds and waterbirds likely facilitates transfer of metals from aquatic to terrestrial food webs. Further, several elements were linked to lower haemoglobin levels (chromium, mercury, manganese, and zinc) and elevated levels of infection-fighting cells (mercury and selenium). Our results highlight the importance of anthropogenic activities as major environmental sources of metal contamination in terrestrial wildlife, including exposure across the land-ocean continuum. These findings contribute towards the growing evidence suggesting cities are particularly toxic areas for wildlife. Co-exposure to a suite of metal pollutants may threaten the long-term health and persistence of Cape Town's caracal population in unexpected ways, particularly when interacting with additional known pollutant and pathogen exposure. The caracal is a valuable sentinel for assessing metal exposure and can be used in pollution monitoring programmes to mitigate exposure and promote biodiversity conservation in human-dominated landscapes.

Enhanced Mercury Accumulation in Riparian Spiders: An Evidence of Insects' Emergence Effect in Aquatic and Upland Terrestrial Crossed Habitat

Many studies have focused on mercury (Hg) accumulation in both aquatic and terrestrial organisms, but the effects of aquatic Hg on terrestrial organisms have rarely been documented. Here we report the accumulation of Hg in two species of spiders, Argiope bruennichi, inhabiting paddy fields, and Nephila clavata, inhabiting small forests in the riparian zones of two hydroelectric reservoirs in Guiyang, southwest China. The mean concentration of total mercury (THg) was higher in N. clavata (0.38 mg kg^-1) than in A. bruennichi (0.20 mg kg^-1). The monthly average THg in N. clavata, collected consecutively from May to October, and the highest values for THg in June (1.2 mg kg^-1) could be related to the emergence of aquatic insects during early summer, suggesting that emerging insects play a crucial role in the accumulation of Hg in riparian spiders. The high values could also be attributable to the different times of spider sampling or individual differences.

Do foraging ecology and contaminants interactively predict parenting hormone levels in common eider?

Global climate change is causing abiotic shifts such as higher air and ocean temperatures, and disappearing sea ice in Arctic ecosystems. These changes influence Arctic-breeding seabird foraging ecology by altering prey availability and selection, affecting individual body condition, reproductive success, and exposure to contaminants such as mercury (Hg). The cumulative effects of alterations to foraging ecology and Hg exposure may interactively alter the secretion of key reproductive hormones such as prolactin (PRL), important for parental attachment to eggs and offspring and overall reproductive success. However, more research is needed to investigate the relationships between these potential links. Using data collected from 106 incubating female common eiders (Somateria mollissima) at six Arctic and sub-Arctic colonies, we examined whether the relationship between individual foraging ecology (assessed using δ¹³C, δ¹⁵N) and total Hg (THg) exposure predicted PRL levels. We found a significant, complex interaction between δ¹³C, δ¹⁵N and THg on PRL, suggesting that individuals cumulatively foraging at lower trophic levels, in phytoplankton-dominant environments, and with the highest THg levels had the most constant significant relationship PRL levels. Cumulatively, these three interactive variables resulted in lowered PRL. Overall, results demonstrate the potential downstream and cumulative implications of environmentally induced changes in foraging ecology, in combination with THg exposure, on hormones known to influence reproductive success in seabirds. These findings are notable in the context of continuing environmental and food web changes in Arctic systems, which may make seabird populations more susceptible to ongoing stressors.

Comparison of Plasma Trace Elements Between 2 Captive Humboldt Penguin (Spheniscus humboldti) Populations

Environmental pollutants and their effect on wildlife health play an important role in the conservation of endangered species and can be clinically relevant in captive animals too. Data on relevant concentrations of trace elements in captive birds with no known exposures are rare. For this study, silver, arsenic, gold, barium, cadmium, cobalt, chromium, copper, iron, mercury, magnesium, manganese, molybdenum, thallium, selenium, and zinc were measured by inductively coupled plasma mass spectrometry in lithium heparinized plasma samples from 18 Humboldt penguins at 2 zoological collections in Germany. The results showed that the plasma concentrations of silver, arsenic, gold, cadmium, cobalt, chromium, mercury, and selenium differed significantly (P ≤ 0.05) between the 2 penguin collections. The results indicate that the location of the birds has a strong influence on the plasma trace element concentrations. Well water used in the enclosures was suspected to be associated with these significant differences. Trace elemental concentrations in feed (eg, marine fish) and contamination from enclosure construction materials may also play a role. This study could provide a basis for further comparative, biomonitoring, toxicity, and reference interval studies.

Factors influencing mercury levels in Leach's storm-petrels at northwest Atlantic colonies

Mercury (Hg) is a globally distributed heavy metal, with negative effects on wildlife. Its most toxic form, methylmercury (MeHg), predominates in aquatic systems. Levels of MeHg in marine predators can vary widely among individuals and populations. Leach's storm-petrels (Hydrobates leucorhous) have elevated levels of Hg but the role of Hg in storm-petrel population declines is unknown. In this study, we used egg and blood samples to study variation in Hg exposure among several northwest Atlantic colonies during breeding seasons, thereby evaluating relative toxicity risk within and among colonies. Total mercury (THg) concentrations were higher with increasing colony latitude, and were more pronounced in blood than in eggs. THg concentrations in blood were mostly associated with low toxicity risk in birds from the southern colonies and moderate risks in birds from the northern colonies; however, those values did not affect hatching or fledging success. THg concentrations in both eggs and blood were positively correlated with δ³⁴S, emphasizing the role of sulfate-reducing bacteria in methylation of THg acquired through marine food webs, which is consistent with enriched δ³⁴S profiles. By associating tracking data from foraging trips with THg from blood, we determined that blood THg levels were higher when storm-petrel's intensive search locations were over deeper waters. We conclude that spatial variation in THg concentrations in Leach's storm-petrels is attributable to differences in ocean depth at foraging locations, both at individual and colony levels. Differences in diet among colonies observed previously are the most likely cause for observed blood THg differences. As one of the few pelagic seabird species breeding in Atlantic Canada, with limited overlap in core foraging areas among colonies, Leach's storm-petrels can be used as biomonitors for less sampled offshore pelagic regions. The global trend in Hg emissions combined with legacy levels warrant continued monitoring for toxicity effects in seabirds.

Seabirds as Biomonitors of Mercury Bioavailability in the Venice Lagoon

Seabirds accumulate mercury (Hg) due to their long-life span together with their high trophic position. A Hg monitoring in Venice's Lagoon using three seabird species occupying different trophic habitat (Thalasseus sandvicensis, Ichthyaetus melanocephalus, and Chroicocephalus ridibundus) confirmed that fledgelings might effectively be used as sentinels of Hg bioavailability. The significant differences in Hg residues in feathers observed among the species highlighted a possible differential exposure due to different diets, with C. ridibundus accumulating more Hg than the other species. Average residues in feathers were not above the threshold associated with adverse effects on birds (5 mg kg^- 1). Nevertheless, a large part of the C. ridibundus individuals (58%) exceeded the adverse effect level, underlining the need for strengthening Hg monitoring. Seabirds indeed may provide relevant insight on Hg transfer in food webs and a better picture of the hazards to men when bird species forage on species exploited for human consumption.

Total and methylmercury concentrations in nocturnal migratory birds passing through Mount Ailao, Southwest China

Despite growing concerns over mercury (Hg) accumulation in birds in recent decades, little is known about Hg exposure in nocturnal migratory birds. Here, total mercury (THg) and methylmercury (MeHg) were detected in the feathers of nocturnal migratory birds (n = 286, belonging to 46 species) passing through Mount Ailao in Southwest China. The stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) were also determined to clarify the effects of trophic position, foraging guild, and foraging behavior on Hg bioaccumulation. Our results show that the THg and MeHg concentrations varied by two orders of magnitude among all nocturnal migratory birds investigated, with the lowest values (THg: 0.056 mg kg^-1; MeHg: 0.038 mg kg^-1) in the Asian koel (Eudynamys scolopaceus) and the highest (THg: 12 mg kg^-1; MeHg: 7.8 mg kg^-1) in the hair-crested drongo (Dicrurus hottentottus). Waterbirds showed higher δ¹⁵N values and higher THg and MeHg concentrations than songbirds, and the Hg concentrations in piscivorous species were significantly higher than those in herbivores, omnivores, and insectivores. Significant effects of foraging guilds (Kruskal-Wallis one-way ANOVA, p < 0.001) and foraging behaviors (Kruskal-Wallis one-way ANOVA, p < 0.001) on the Hg concentrations in migratory bird feathers were detected. A risk assessment indicated that approximately 7.0% of individuals were at moderate (2.4-5.0 mg kg^-1) to high (>5.0 mg kg^-1) risk of Hg exposure, and were therefore vulnerable to adverse physiological and behavioral effects. A long-term monitoring campaign during the migratory period is highly recommended to better understand the bioaccumulation of Hg in these nocturnal migratory bird populations over time.

Mercury contamination and potential health risks to Arctic seabirds and shorebirds

Since the last Arctic Monitoring and Assessment Programme (AMAP) effort to review biological effects of mercury (Hg) on Arctic biota in 2011 and 2018, there has been a considerable number of new Arctic bird studies. This review article provides contemporary Hg exposure and potential health risk for 36 Arctic seabird and shorebird species, representing a larger portion of the Arctic than during previous AMAP assessments now also including parts of the Russian Arctic. To assess risk to birds, we used Hg toxicity benchmarks established for blood and converted to egg, liver, and feather tissues. Several Arctic seabird populations showed Hg concentrations that exceeded toxicity benchmarks, with 50 % of individual birds exceeding the "no adverse health effect" level. In particular, 5 % of all studied birds were considered to be at moderate or higher risk to Hg toxicity. However, most seabirds (95 %) were generally at lower risk to Hg toxicity. The highest Hg contamination was observed in seabirds breeding in the western Atlantic and Pacific Oceans. Most Arctic shorebirds exhibited low Hg concentrations, with approximately 45 % of individuals categorized at no risk, 2.5 % at high risk category, and no individual at severe risk. Although the majority Arctic-breeding seabirds and shorebirds appeared at lower risk to Hg toxicity, recent studies have reported deleterious effects of Hg on some pituitary hormones, genotoxicity, and reproductive performance. Adult survival appeared unaffected by Hg exposure, although long-term banding studies incorporating Hg are still limited. Although Hg contamination across the Arctic is considered low for most bird species, Hg in combination with other stressors, including other contaminants, diseases, parasites, and climate change, may still cause adverse effects. Future investigations on the global impact of Hg on Arctic birds should be conducted within a multi-stressor framework. This information helps to address Article 22 (Effectiveness Evaluation) of the Minamata Convention on Mercury as a global pollutant.

Integument carotenoid-based colouration reflects contamination to perfluoroalkyl substances, but not mercury, in arctic black-legged kittiwakes

Anthropogenic activities are introducing multiple chemical contaminants into ecosystems that act as stressors for wildlife. Perfluoroalkyl substances (PFAS) and mercury (Hg) are two relevant contaminants that may cause detrimental effects on the fitness of many aquatic organisms. However, there is a lack of information on their impact on the expression of secondary sexual signals that animals use for mate choice. We have explored the correlations between integument carotenoid-based colourations, blood levels of carotenoids, and blood levels of seven PFAS and of total Hg (THg) in 50 adult male black-legged kittiwakes (Rissa tridactyla) from the Norwegian Arctic during the pre-laying period, while controlling for other colouration influencing variables such as testosterone and body condition. Kittiwakes with elevated blood concentrations of PFAS (PFOSlin, PFNA, PFDcA, PFUnA, or PFDoA) had less chromatic but brighter bills, and brighter gape and tongue; PFOSlin was the pollutant with the strongest association with bill colourations. Conversely, plasma testosterone was the only significant correlate of hue and chroma of both gape and tongue, and of hue of the bill. Kittiwakes with higher concentrations of any PFAS, but not of THg, tended to have significantly higher plasma concentrations of the carotenoids astaxanthin, zeaxanthin, lutein, and cryptoxanthin. Our work provides the first correlative evidence that PFAS exposure might interfere with the carotenoid metabolism and the expression of integument carotenoid-based colourations in a free-living bird species. This outcome may be a direct effect of PFAS exposure or be indirectly caused by components of diet that also correlate with elevated PFAS concentrations (e.g., proteins). It also suggests that there might be no additive effect of THg co-exposure with PFAS on the expression of colourations. These results call for further work on the possible interference of PFAS with the expression of colourations used in mate choice.

Higher mercury contamination is associated with shorter telomeres in a long-lived seabird - A direct effect or a consequence of among-individual variation in phenotypic quality?

Mercury is a heavy metal, which is pervasive and persistent in the marine environment. It bioaccumulates within organisms and biomagnifies in the marine food chain. Due to its high toxicity, mercury contamination is a major concern for wildlife and human health. Telomere length is a biomarker of aging and health, because it predicts survival, making it a potential tool to investigate sublethal effects of mercury contamination. However, the relationship between telomeres and mercury contamination is unclear. We measured feather mercury concentration in Cory's Shearwaters Calonectris borealis, long-lived seabirds and top predators, between 9 and 35 years of age and related it to telomere length in erythrocytes. Cory's Shearwaters with higher mercury concentrations had shorter telomeres and the effect was sex-dependent, reaching significance in males only. This may be explained by the fact that males have longer telomeres and higher and more variable mercury concentrations than females in this population. The mercury effect on telomere length was stronger on longer telomeres in the genome within individuals. We discuss the hypotheses that the negative correlation could either be a direct effect of mercury on telomere shortening and/or a consequence of variation in phenotypic quality among individuals that results in a covariation between mercury contamination and telomere length.

Mercury, legacy and emerging POPs, and endocrine-behavioural linkages: Implications of Arctic change in a diving seabird

Arctic species encounter multiple stressors including climate change and environmental contaminants. Some contaminants may disrupt hormones that govern the behavioural responses of wildlife to climatic variation, and thus the capacity of species to respond to climate change. We investigated correlative interactions between legacy and emerging persistent organic pollutants (POPs), mercury (Hg), hormones and behaviours, in thick-billed murres (Uria lomvia) (N = 163) breeding in northern Hudson Bay (2016-2018). The blood profile of the murres was dominated by methylmercury (MeHg), followed by much lower levels of sum (∑) 35 polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB) and p,p'-dichlorodiphenyltrichloroethylene (DDE), polybrominated diphenyl ethers (PBDEs) BDE-47, -99 and BDE-100; all other measured organochlorine pesticides and replacement brominated flame retardants had low concentrations if detected. Inter-annual variations occurred in MeHg, circulating triiodothyronine (T3), thyroxine (T4), and the foraging behaviours of the murres, identified using GPS-accelerometers. Compared to the 50-year mean date (1971-2021) for 50% of sea-ice coverage in Hudson Bay, sea-ice breakup was 1-2 weeks earlier (2016, 2017) or comparable (2018). Indeed, 2017 was the earliest year on record. Consistent with relationships identified individually between MeHg and total T3, and T3 and foraging behaviour, a direct interaction between these three parameters was evident when all possible interactions among measured chemical pollutants, hormones, and behaviours of the murres were considered collectively (path analysis). When murres were likely already stressed due to early sea-ice breakup (2016, 2017), blood MeHg influenced circulating T3 that in turn reduced foraging time underwater. We conclude that when sea-ice breaks up early in the breeding season, Hg may interfere with the ability of murres to adjust their foraging behaviour via T3 in relation to variation in sea-ice.

Blood mercury concentrations in four sympatric gull species from South Western France: Insights from stable isotopes and biologging

Mercury (Hg) is a toxic trace element widely distributed in the environment, which particularly accumulates in top predators, including seabirds. Among seabirds, large gulls (Larus sp) are generalist feeders, foraging in both terrestrial and marine habitats, making them relevant bioindicators of local coastal Hg contamination. In the present study, we reported blood Hg concentrations in adults and chicks of four different gull species breeding on the French Atlantic coast: the European herring gull (Larus argentatus), the Lesser black-backed gull (L. fuscus), the Great black-backed gull (L. marinus) and the Yellow-legged gull (L. michahellis). We also investigated the potential role of foraging ecology in shaping Hg contamination across species, using the unique combination of three dietary tracers (carbon, nitrogen and sulfur stable isotopes) and biologging (GPS tracking). A high concentration of Hg was associated with high trophic position and a marine diet in gulls, which was corroborated by birds' space use strategy during foraging trips. Adults of all four species reached Hg concentrations above reported toxicity thresholds. Specifically, adults of Great black-backed gulls had a high trophic marine specialized diet and significantly higher Hg concentrations than the three other species. Blood Hg was 4-7 times higher in adults than in chicks, although chicks of all species received mainly marine and high trophic position prey, which is expected to be the cause of blood Hg concentrations of toxic concern. By using both stable isotopes and GPS tracking, the present study provides compelling insights on the main feeding habits driving Hg contamination in a seabird assemblage feeding in complex coastal environments.

Mercury biomagnification in an Antarctic food web of the Antarctic Peninsula

Under the climate change context, warming Southern Ocean waters may allow mercury (Hg) to become more bioavailable to the Antarctic marine food web (i.e., ice-stored Hg release and higher methylation rates by microorganisms), whose biomagnification processes are poorly documented. Biomagnification of Hg in the food web of the Antarctic Peninsula, one of the world's fastest-warming regions, was examined using carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios for estimating feeding habitat and trophic levels, respectively. The stable isotope signatures and total Hg (T-Hg) concentrations were measured in Antarctic krill Euphausia superba and several Antarctic predator species, including seabirds (gentoo penguins Pygoscelis papua, chinstrap penguins Pygoscelis antarcticus, brown skuas Stercorarius antarcticus, kelp gulls Larus dominicanus, southern giant petrels Macronectes giganteus) and marine mammals (southern elephant seals Mirounga leonina). Significant differences in δ¹³C values among species were noted with a great overlap between seabird species and M. leonina. As expected, significant differences in δ¹⁵N values among species were found due to interspecific variations in diet-related to their trophic position within the marine food web. The lowest Hg concentrations were registered in E. superba (0.007 ± 0.008 μg g^-1) and the highest values in M. giganteus (12.090 ± 14.177 μg g^-1). Additionally, a significant positive relationship was found between Hg concentrations and trophic levels (reflected by δ¹⁵N values), biomagnifying nearly 2 times its concentrations at each level. Our results support that trophic interaction is the major pathway for Hg biomagnification in Southern Ocean ecosystems and warn about an increase in the effects of Hg on long-lived (and high trophic level) Antarctic predators under climate change in the future.

Spatial and sex differences in mercury contamination of skuas in the Southern Ocean

Antarctic marine ecosystems are often considered to be pristine environments, yet wildlife in the polar regions may still be exposed to high levels of environmental contaminants. Here, we measured total mercury (THg) concentrations in blood samples from adult brown skuas Stercorarius antarcticus lonnbergi (n = 82) from three breeding colonies south of the Antarctic Polar Front in the Southern Ocean (southwest Atlantic region): (i) Bahía Esperanza/Hope Bay, Antarctic Peninsula; (ii) Signy Island, South Orkney Islands; and, (iii) Bird Island, South Georgia. Blood THg concentrations increased from the Antarctic Peninsula towards the Antarctic Polar Front, such that Hg contamination was lowest at Bahía Esperanza/Hope Bay (mean ± SD, 0.95 ± 0.45 μg g^-1 dw), intermediate at Signy Island (3.42 ± 2.29 μg g^-1 dw) and highest at Bird Island (4.47 ± 1.10 μg g^-1 dw). Blood THg concentrations also showed a weak positive correlation with δ¹⁵N values, likely reflecting the biomagnification process. Males had higher Hg burdens than females, which may reflect deposition of Hg into eggs by females or potentially differences in their trophic ecology. These data provide important insights into intraspecific variation in contamination and the geographic transfer of Hg to seabirds in the Southern Ocean.

Drivers of biomagnification of Hg, As and Se in aquatic food webs: A review

Biomagnification of trace elements is increasingly evident in aquatic ecosystems. In this review we investigate the drivers of biomagnification of mercury (Hg), arsenic (As) and selenium (Se) in aquatic food webs. Despite Hg, As and Se biomagnify in food webs, the biomagnification potential of Hg is much higher than that of As and Se. The slope of trophic increase of Hg is consistent between temperate (0.20), tropical (0.22) and Arctic (0.22) ecosystems. Se exerts a mitigating role against Hg toxicity but desired maximum and minimum concentrations are unknown. Environmental (e.g. latitude, temperature and physicochemical characteristics) and ecological factors (e.g. trophic structure composition and food zone) can substantially influence the biomagnification process these metal (oids). Besides the level of bioaccumulated concentration, biomagnification depends on the biology, ecology and physiology of the organisms that play a key role in this process. However, it may be necessary to determine strictly biological, physiological and environmental factors that could modulate the concentrations of As and Se in particular. The information presented here should provide clues for research that include under-researched variables. Finally, we suggest that biomagnification be incorporated into environmental management policies, mainly in risk assessment, monitoring and environmental protection methods.

Quantitative meta-analysis reveals no association between mercury contamination and body condition in birds

Mercury contamination is a major threat to the global environment, and is still increasing in some regions despite international regulations. The methylated form of mercury is hazardous to biota, yet its sublethal effects are difficult to detect in wildlife. Body condition can vary in response to stressors, but previous studies have shown mixed effects of mercury on body condition in wildlife. Using birds as study organisms, we provide the first quantitative synthesis of the effect of mercury on body condition in animals. In addition, we explored the influence of intrinsic, extrinsic and methodological factors potentially explaining cross-study heterogeneity in results. We considered experimental and correlative studies carried out in adult birds and chicks, and mercury exposure inferred from blood and feathers. Most experimental investigations (90%) showed a significant relationship between mercury concentrations and body condition. Experimental exposure to mercury disrupted nutrient (fat) metabolism, metabolic rates, and food intake, resulting in either positive or negative associations with body condition. Correlative studies also showed either positive or negative associations, of which only 14% were statistically significant. Therefore, the overall effect of mercury concentrations on body condition was null in both experimental (estimate ± SE = 0.262 ± 0.309, 20 effect sizes, five species) and correlative studies (-0.011 ± 0.020, 315 effect sizes, 145 species). The single and interactive effects of age class and tissue type were accounted for in meta-analytic models of the correlative data set, since chicks and adults, as well as blood and feathers, are known to behave differently in terms of mercury accumulation and health effects. Of the 15 moderators tested, only wintering status explained cross-study heterogeneity in the correlative data set: free-ranging wintering birds were more likely to show a negative association between mercury and body condition. However, wintering effect sizes were limited to passerines, further studies should thus confirm this trend in other taxa. Collectively, our results suggest that (i) effects of mercury on body condition are weak and mostly detectable under controlled conditions, and (ii) body condition indices are unreliable indicators of mercury sublethal effects in the wild. Food availability, feeding rates and other sources of variation that are challenging to quantify likely confound the association between mercury and body condition in natura. Future studies could explore the metabolic effects of mercury further using designs that allow for the estimation and/or manipulation of food intake in both wild and captive birds, especially in under-represented life-history stages such as migration and overwintering.

A U-Turn for Mercury Concentrations over 20 Years: How Do Environmental Conditions Affect Exposure in Arctic Seabirds?

Mercury (Hg) is highly toxic in its methylated form (MeHg), and global change is likely to modify its bioavailability in the environment. However, it is unclear how top predators will be impacted. We studied blood Hg concentrations of chick-rearing black-legged kittiwakes Rissa tridactyla (2000-2019) in Svalbard (Norway). From 2000 to 2019, Hg concentrations followed a U-shaped trend. The trophic level, inferred from nitrogen stable isotopes, and chlorophyll a (Chl a) concentrations better predicted Hg concentrations, with positive and U-shaped associations, respectively. As strong indicators of primary productivity, Chl a concentrations can influence production of upper trophic levels and, thus, fish community assemblage. In the early 2000s, the high Hg concentrations were likely related to a higher proportion of Arctic prey in kittiwake's diet. The gradual input of Atlantic prey in kittiwake diet could have resulted in a decrease in Hg concentrations until 2013. Then, a new shift in the prey community, added to the shrinking sea ice-associated release of MeHg in the ocean, could explain the increasing trend of Hg observed since 2014. The present monitoring provides critical insights about the exposure of a toxic contaminant in Arctic wildlife, and the reported increase since 2014 raises concern for Arctic seabirds.

Microbiota composition and diversity of multiple body sites vary according to reproductive performance in a seabird

The microbiota is suggested to be a fundamental contributor to host reproduction and survival, but associations between microbiota and fitness are rare, especially for wild animals. Here, we tested the association between microbiota and two proxies of breeding performance in multiple body sites of the black-legged kittiwake, a seabird species. First we found that, in females, nonbreeders (i.e., birds that did not lay eggs) hosted different microbiota composition to that of breeders in neck and flank feathers, in the choanae, in the outer-bill and in the cloacae, but not in preen feathers and tracheae. These differences in microbiota might reflect variations in age or individual quality between breeders and nonbreeders. Second, we found that better female breeders (i.e., with higher body condition, earlier laying date, heavier eggs, larger clutch, and higher hatching success) had lower abundance of several Corynebacteriaceae in cloaca than poorer female breeders, suggesting that these bacteria might be pathogenic. Third, in females, better breeders had different microbiota composition and lower microbiota diversity in feathers, especially in preen feathers. They had also reduced dispersion in microbiota composition across body sites. These results might suggest that good breeding females are able to control their feather microbiota-potentially through preen secretions-more tightly than poor breeding females. We did not find strong evidence for an association between reproductive outcome and microbiota in males. Our results are consistent with the hypothesis that natural variation in the microbiota is associated with differences in host fitness in wild animals, but the causal relationships remain to be investigated.

Exposure to cumulative stressors affects the laying phenology and incubation behaviour of an Arctic-breeding marine bird

Wildlife are exposed to multiple stressors across life-history stages, the effects of which can be amplified as human activity surges globally. In Arctic regions, increasing air and ocean temperatures, more severe weather systems, and exposure to environmental contaminants all represent stressors occurring simultaneously. While Arctic vertebrates, including marine birds, are expected to be at risk of adverse effects from these individual stressors, few studies have researched their combined impacts on breeding behaviour and reproductive success. The interactive effects of environmental conditions and mercury (Hg) contamination on laying phenology and incubation behaviour were examined in female common eiders (Somateria mollissima, mitiq, ᒥᑎᖅ ᐊᒪᐅᓕᒡᔪᐊᖅ) nesting at Canada's largest Arctic breeding colony. Conditions with higher pre-breeding air temperatures were linked to females with higher egg Hg concentrations laying earlier than those with lower Hg values. Furthermore, examination of a total of 190 days of incubation behaviour from 61 eiders across two years revealed a negative relationship between wind speed and the frequency of incubation interruptions. Importantly, exposure to higher air temperatures combined with lower Hg concentrations was significantly correlated with increased incubation interruptions. Although previous research has shown that warmer spring temperatures could afford lower quality females more time to improve body condition to successfully lay, results suggest these females may face stronger cumulative fitness costs during incubation in warmer years, potentially in combination with the effects of Hg on physiological stress and hormone secretion. This study highlights how multiple stressors exposure, driven by human-induced environmental changes, can have a complex influence on reproduction.

Environmental and life-history factors influence inter-colony multidimensional niche metrics of a breeding Arctic marine bird

Human industrialization has resulted in rapid climate change, leading to wide-scale environmental shifts. These shifts can modify food web dynamics by altering the abundance and distribution of primary producers (ice algae and phytoplankton), as well as animals at higher trophic levels. Methylmercury (MeHg) is a neuro-endocrine disrupting compound which biomagnifies in animals as a function of prey choice, and as such bioavailability is affected by altered food web dynamics and adds an important risk-based dimension in studies of foraging ecology. Multidimensional niche dynamics (MDND; δ¹³C, δ¹⁵N, THg; total mercury) were determined among breeding common eider (Somateria mollissima) ducks sampled from 10 breeding colonies distributed across the circumpolar Arctic and subarctic. Results showed high variation in MDND among colonies as indicated by niche size and ranges in δ¹³C, δ¹⁵N and THg values in relation to spatial differences in primary production inferred from sea-ice presence and colony migratory status. Colonies with higher sea-ice cover during the pre-incubation period had higher median colony THg, δ¹⁵N, and δ¹³C. Individuals at migratory colonies had relatively higher THg and δ¹⁵N, and lower δ¹³C, suggesting a higher trophic position and a greater reliance on phytoplankton-based prey. It was concluded that variation in MDND exists among eider colonies which influenced individual blood THg concentrations. Further exploration of spatial ecotoxicology and MDND at each individual site is important to examine the relationships between anthropogenic activities, foraging behaviour, and the related risks of contaminant exposure at even low, sub-lethal concentrations that may contribute to deleterious effects on population stability over time. Overall, multidimensional niche analysis that incorporates multiple isotopic and contaminant metrics could help identify those populations at risk to rapidly altered food web dynamics.

Accounting for food availability reveals contaminant-induced breeding impairment, food-modulated contaminant effects, and endpoint-specificity of exposure indicators in free ranging avian populations

It remains unclear how sub-lethal effects of contaminants play out in relation to other stressors encountered by free-ranging populations. Effects may be masked or influenced by interactions with field stressors such as food availability. We predicted that (1) including food availability, and particularly its interaction with Hg, would reveal or enhance associations between Hg and breeding endpoints. We further predicted that (2) breeding impairment associated with Hg would be higher under food stress conditions. We monitored Hg and nest success of great egrets (Ardea alba) in eight breeding colonies in the Florida Everglades over 11 years. We characterized variation in local food availability among colonies and years using fish biomass and recession range -a proxy to fish vulnerability. We used two Hg exposure indicators (egg albumen Hg and nestling feather Hg) and six breeding endpoints (clutch-size, brood-size, fledged-size, hatching success, post-hatching success and fledglings per egg) to assess whether variation in food availability influenced associations between Hg and these endpoints. Accounting for interactions between Hg and food availability, we identified statistically significant associations in all 12 indicator-endpoint combinations, while only three were detectable without food. Further, 10 combinations showed interactions between Hg and components of food availability. Our results also indicated an endpoint-specific affinity, with albumen [Hg] explaining more variation in hatching success while nestling feather [Hg] explained more variation in post-hatching survival. Both Hg indicators accounted for relevant (6-10%) amounts of variation in fledglings produced per egg laid, an integrative endpoint. Increased Hg exposure resulted in overall reduced reproductive success when food availability was low, but our models predicted low or no effects of increasing Hg exposure when food availability was high. Our results indicate that Hg induced impairment is strongly driven by food availability, providing a framework that accommodates previously contradictory results in the literature.

Lead, mercury, and selenium alter physiological functions in wild caimans (Caiman crocodilus)

Environmental contaminants affect ecosystems worldwide and have deleterious effects on biota. Non-essential mercury (Hg) and lead (Pb) concentrations are well documented in some taxa and are described to cause multiple detrimental effects on human and wildlife. Additionally, essential selenium (Se) is known to be toxic at high concentrations but, at lower concentrations, Se can protect organisms against Hg toxicity. Crocodilians are known to bioaccumulate contaminants. However, the effects of these contaminants on physiological processes remain poorly studied. In the present study, we quantified Hg, Pb and Se concentrations in spectacled caimans (Caiman crocodilus) and investigated the effects of these contaminants on several physiological processes linked to osmoregulatory, hepatic, endocrine and renal functions measured through blood parameters in 23 individuals. Mercury was related to disruption of osmoregulation (sodium levels), hepatic function (alkaline phosphatase levels) and endocrine processes (corticosterone levels). Lead was related to disruption of hepatic functions (glucose and alanine aminotransferase levels). Selenium was not related to any parameters, but the Se:Hg molar ratio was positively related to the Na⁺ and corticosterone concentrations, suggesting a potential protective effect against Hg toxicity. Overall, our results suggest that Hg and Pb alter physiological mechanisms in wild caimans and highlight the need to thoroughly investigate the consequences of trace element contamination in crocodilians.

Bioaccumulation of mercury is equal between sexes but different by age in seabird (Sula leucogaster) population from southeast coast of Brazil

Since several seabird species have sexual size dimorphism, in which one sex is larger than the other, and may consume bigger prey, this size difference may affect the contamination concentration in the seabird's tissues depending on their sex and age. In this study, mercury contamination was investigated in brown booby (Sula leucogaster) adults and juveniles during their breeding season at the Santana Archipelago, on the southeast coast of Brazil. Two hypotheses were evaluated: 1. As females consume larger prey than males due to the reverse sexual dimorphism, higher total mercury (THg) and methylmercury (MeHg) concentrations are expected in females tissues than in males; 2. Adult seabirds have more time to accumulate mercury than juveniles, so it is expected that adults will show higher THg and MeHg concentrations than juveniles in their feathers, but none in blood since the last indicates the exposure of short time (30-60 days), as it is a constantly synthesized tissue. Feathers and blood were sampled from 20 individuals of each group (males, females and juveniles). Also, 10 eggs of the brown booby and muscle tissue samples of their main prey were collected, from February to October 2018. Females and males had similar THg concentrations in the tissues with no statistical differences between sexes. Thus, the sexual size dimorphism did not influence mercury concentrations among the tissues and both genders can be used as a biomonitor. Brown booby juveniles had low THg and MeHg concentrations compared to adults due to a shorter time of exposure for mercury to bioaccumulate in their tissues. This is the first study, to the best of our knowledge, analyzing methylmercury in feathers, blood and eggs of a tropical seabird, which can be a useful baseline for future studies on the effects of contaminants on this species in tropical regions.

Foraging in marine habitats increases mercury concentrations in a generalist seabird

Methylmercury concentrations vary widely across geographic space and among habitat types, with marine and aquatic-feeding organisms typically exhibiting higher mercury concentrations than terrestrial-feeding organisms. However, there are few model organisms to directly compare mercury concentrations as a result of foraging in marine, estuarine, or terrestrial food webs. The ecological impacts of differential foraging may be especially important for generalist species that exhibit high plasticity in foraging habitats, locations, or diet. Here, we investigate whether foraging habitat, sex, or fidelity to a foraging area impact blood mercury concentrations in western gulls (Larus occidentalis) from three colonies on the US west coast. Cluster analyses showed that nearly 70% of western gulls foraged primarily in ocean or coastal habitats, whereas the remaining gulls foraged in terrestrial and freshwater habitats. Gulls that foraged in ocean or coastal habitats for half or more of their foraging locations had 55% higher mercury concentrations than gulls that forage in freshwater and terrestrial habitats. Ocean-foraging gulls also had lower fidelity to a specific foraging area than freshwater and terrestrial-foraging gulls, but fidelity and sex were unrelated to gull blood mercury concentrations in all models. These findings support existing research that has described elevated mercury levels in species using aquatic habitats. Our analyses also demonstrate that gulls can be used to detect differences in contaminant exposure over broad geographic scales and across coarse habitat types, a factor that may influence gull health and persistence of other populations that forage across the land-sea gradient.

Chronological Trends and Mercury Bioaccumulation in an Aquatic Semiarid Ecosystem under a Global Climate Change Scenario in the Northeastern Coast of Brazil

Simple Summary

Managing aquatic systems is becoming increasingly complex due to human impacts, multiple and competing water needs and climate variability. Considering the Hg concentration present in the top layers of sediment (~20 cm around 30 to 40 years) with the outer layers in the tree cores tree rings cores and in the sediment’s cores from Pacoti estuary and the Ceará estuary, overall data indicate an increase in mercury in recent years. A positive and significant correlation (p < 0.05) was revealed between Hg trends in sediments and Hg trends in annular tree rings. This shared Hg pattern reflects local environmental conditions. The results of this work reinforce the indicators previously described in the semiarid NE region of Brazil, showing that global climate change and some anthropogenic factors are key drivers to Hg exposure and biomagnification for wildlife and humans. Possible climate-induced shifts in these aquatic systems highlight the need for accurate and regionally specific metrics of change in the past in response to climate and for improved understanding of response to climate factors. These processes are inducing a greater mobilization of bioavailable Hg, which could allow an acceleration of the biogeochemical transformation of Hg.

Abstract

Due to global warming, in the northeastern semiarid coastal regions of Brazil, regional and global drivers are responsible for decreasing continental runoff and increasing estuarine water residence time, which promotes a greater mobilization of bioavailable mercury (Hg) and allows increasing fluxes and/or bioavailability of this toxic trace element and an acceleration of biogeochemical transformation of Hg. In this work, an application of dendrochemistry analysis (annular tree rings analysis) was developed for the reconstruction of the historical pattern of mercury contamination in a contaminated area, quantifying chronological Hg contamination trends in a tropical semiarid ecosystem (Ceará River Estuary, northeastern coast of Brazil) through registration of mercury concentration on growth rings in specimens of Rhizophora mangle L. and using the assessment in sediments as a support for the comparison of profiles of contamination. The comparison with sediments from the same place lends credibility to this type of analysis, as well as the relationship to the historical profile of contamination in the region, when compared with local data about industries and ecological situation of sampling sites. In order to evaluate the consequences of the described increase in Hg bioavailability and bioaccumulation in aquatic biota, and to assess the biological significance of Hg concentrations in sediments to fish and wildlife, muscle and liver from a bioindicator fish species, S. testudineus, were also analyzed. The results of this work reinforce the indicators previously described in the semiarid NE region of Brazil, which showed that global climate change and some anthropogenic factors are key drivers of Hg exposure and biomagnification for wildlife and humans. Considering the Hg concentration present in the top layers of sediment (~20 cm around 15 to 20 years) with the outer layers in the tree ring cores and in the sediment’s cores from Pacoti estuary and the Ceará estuary, overall the data indicate an increase in mercury in recent years in the Hg surface sediments, especially associated with the fine sediment fraction, mainly due to the increased capacity of small particles to adsorb Hg. There was revealed a positive and significant correlation (p < 0.05) between Hg trends in sediments and Hg trends in annular tree rings. This shared Hg pattern reflects local environmental conditions. The Hg concentration values in S. testudineus from both study areas are not restrictive to human consumption, being below the legislated European limit for Hg in foodstuffs. The results from S. testudineus muscles analysis suggest a significant and linear increase in Hg burden with increasing fish length, indicating that the specimens are accumulating Hg as they grow. The results from both rivers show an increase in BSAF with fish growth. The [Hg] liver/[Hg] muscles ratio >1, which indicates that the S. testudineus from both study areas are experiencing an increase in Hg bioavailability. Possible climate-induced shifts in these aquatic systems processes are inducing a greater mobilization of bioavailable Hg, which could allow an acceleration of the biogeochemical transformation of Hg.

Detecting silent stressors: Trace element effects on nutritional status of declining scoter ducks of Puget Sound, USA

White-winged scoters (Melanitta fusca; WWSC) and surf scoters (M. perspicillata; SUSC) have declined by over 60% in recent decades. Identifying contributing factors from within a mosaic of sublethal, multiple stressors is challenging. In urbanized Puget Sound, Washington, USA where scoters winter, changes in prey availability explained only a portion of local declines, suggesting that other "silent stressors" such as sublethal contaminants might play a role. Past studies of pollutant effects on scoters used Fisherian statistics that often revealed few correlates; however, novel statistical approaches could detect and provide more insights about sublethal impacts. Our objectives were to (1) relate pollutant accumulation to health of the birds, and (2) compare permutational multivariate statistics with traditional approaches in identifying sublethal health effects. We collected scoters from three locations in Puget Sound in December 2005 and March 2006, and measured cadmium (Cd), mercury (Hg), and selenium (Se) levels in livers and kidneys. To assess impacts of low contaminants levels in tissues on nutritional status (whole-body mass, lipid, and protein; and triglycerides, β-hydroxybutyrate, and uric acid in blood), we compared statistical methods. Permutational multivariate methods use Monte Carlo techniques to assess how an integrated matrix of physiological responses in each animal respond to contaminants. Univariate regressions revealed very few and inconsistent relationships. In contrast, multivariate models showed that liver Hg and Se explained 25% of the variance in nutritional status of white-winged scoters; and in surf scoters, Cd, Hg, and Se in tissues explained 14 to 27% of nutritional status depending on site. The influence of these factors equals other aspects of habitat such as foraging conditions. Our study indicates that permutational multivariate statistics can be a powerful tool for identifying sublethal contaminant associations that, with non-contaminant stressors, can influence nutritional status and thus, contribute to population dynamics.

I got it from my mother: Inter-nest variation of mercury concentration in neonate Smooth-fronted Caiman (Paleosuchus trigonatus) suggests maternal transfer and possible phenotypical effects

The deleterious effects of mercury (Hg) contamination are well documented in humans and wildlife. Chronic exposure via diet and maternal transfer are two pathways which increase the toxicological risk for wild populations. However, few studies examined the physiological impact of Hg in crocodilians. We investigated the Hg contamination in neonate Smooth-fronted Caimans, Paleosuchus trigonatus, and the use of keratinized tissues and blood to evaluate maternal transfer. Between November 2017 and February 2020, we sampled 38 neonates from 4 distinct nests. Mercury concentration was measured in claws, scutes and total blood. Highest Hg concentrations were found in claws. Strong inter-nest variations (Hg ranging from 0.17 ± 0.02 to 0.66 ± 0.07 μg.g^-1 dw) presumably reflect maternal transfer. Reduced body size in neonates characterized by elevated Hg concentrations suggests an influence of Hg during embryonic development. We emphasize the use of claws as an alternative to egg collection to investigate maternal transfer in crocodilians. Our results demonstrated the need of further investigation of the impact of Hg contamination in the first life stages of crocodilians.

Foraging ecology drives mercury contamination in chick gulls from the English Channel

Although mercury (Hg) occurs naturally, human activity is currently the greatest source of release and the ocean receives Hg inputs by rivers and atmospheric deposition. Seabirds including chicks serve as valuable bioindicators of Hg contamination, reflecting local contamination around the colony. This study investigates the ecological drivers (trophic position and foraging habitat) influencing Hg concentrations in blood and feathers of chicks of three sympatric marine gull species. Chicks were sampled between 2015 and 2017 in the Seine Estuary, one of the most Hg contaminated rivers in Europe, and in the Normand-Breton Gulf (the Chausey Islands), 200 km west, as a reference site with limited contaminant inputs. The trophic status of the chicks was evaluated based on the relative abundance of stable isotopes (δ¹³C, δ¹⁵N and δ³⁴S). There was a tight correlation between Hg concentrations, as well as the abundance of stable isotopes, in blood and feathers. Great black-backed gull had the highest blood Hg concentrations of the species (1.80 ± 0.92 μg⋅g^-1 dry weight (dw)); the Lesser black-backed gull had intermediate concentrations (0.61 ± 0.18 μg⋅g^-1 dw); and the European herring gull had the lowest (0.37 ± 0.26 μg⋅g^-1 dw). Individuals with the highest trophic position showed consistently the highest Hg concentrations. The positive relationship between Hg concentrations and the feeding habitat (marine vs terrestrial) indicated that the main source of Hg for gulls in the English Channel is marine prey. This exposure led to relatively high Hg concentrations in Great black-backed gull, which may produce toxic effects to individuals with potential consequences for their populations.

Influence of Species-Specific Feeding Ecology on Mercury Concentrations in Seabirds Breeding on the Chatham Islands, New Zealand

Mercury (Hg) is a toxic metal that accumulates in organisms and biomagnifies along food webs; hence, long-lived predators such as seabirds are at risk as a result of high Hg bioaccumulation. Seabirds have been widely used to monitor the contamination of marine ecosystems. In the present study, we investigated Hg concentrations in blood, muscle, and feathers of 7 procellariform seabirds breeding on the Chatham Islands, New Zealand. Using bulk and compound-specific stable isotope ratios of carbon and nitrogen as a proxy of trophic position and distribution, we also tested whether Hg contamination is related to the species-specific feeding ecology. Mercury exposure varied widely within the seabird community. The highest contaminated species, the Magenta petrel, had approximately 29 times more Hg in its blood than the broad-billed prion, and approximately 35 times more Hg in its feathers than the grey-backed storm petrel. Variations of Hg concentrations in blood and feathers were significantly and positively linked to feeding habitats and trophic position, highlighting the occurrence of efficient Hg biomagnification processes along the food web. Species and feeding habitats were the 2 main drivers of Hg exposure within the seabird community. The Pterodroma species had high blood and feather Hg concentrations, which can be caused by their specific physiology and/or because of their foraging behavior during the interbreeding period (i.e., from the Tasman Sea to the Humboldt Current system). These 2 threatened species are at risk of suffering detrimental effects from Hg contamination and further studies are required to investigate potential negative impacts, especially on their reproduction capability. Environ Toxicol Chem 2021;40:454-472. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Trophic and fitness correlates of mercury and organochlorine compound residues in egg-laying Antarctic petrels

Understanding the drivers and effects of exposure to contaminants such as mercury (Hg) and organochlorine compounds (OCs) in Antarctic wildlife is still limited. Yet, Hg and OCs have known physiological and fitness effects in animals, with consequences on their populations. Here we measured total Hg (a proxy of methyl-Hg) in blood cells and feathers, and 12 OCs (seven polychlorinated biphenyls, PCBs, and five organochlorine pesticides, OCPs) in plasma of 30 breeding female Antarctic petrels Thalassoica antarctica from one of the largest colonies in Antarctica (Svarthamaren, Dronning Maud Land). This colony is declining and there is poor documentation on the potential role played by contaminants on individual physiology and fitness. Carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope values measured in the females' blood cells and feathers served as proxies of their feeding ecology during the pre-laying (austral spring) and moulting (winter) periods, respectively. We document feather Hg concentrations (mean ± SD, 2.41 ± 0.83 μg g^-1 dry weight, dw) for the first time in this species. Blood cell Hg concentrations (1.38 ± 0.43 μg g^-1 dw) were almost twice as high as those reported in a recent study, and increased with pre-laying trophic position (blood cell δ¹⁵N). Moulting trophic ecology did not predict blood Hg concentrations. PCB concentrations were very low (Σ₇PCBs, 0.35 ± 0.31 ng g^-1 wet weight, ww). Among OCPs, HCB (1.02 ± 0.36 ng g^-1 ww) and p, p'-DDE (1.02 ± 1.49 ng g^-1 ww) residues were comparable to those of ecologically-similar polar seabirds, while Mirex residues (0.72 ± 0.35 ng g^-1 ww) were higher. PCB and OCP concentrations showed no clear relationship with pre-laying or moulting feeding ecology, indicating that other factors overcome dietary drivers. OC residues were inversely related to body condition, suggesting stronger release of OCs into the circulation of egg-laying females upon depletion of their lipid reserves. Egg volume, hatching success, chick body condition and survival were not related to maternal Hg or OC concentrations. Legacy contaminant exposure does not seem to represent a threat for the breeding fraction of this population over the short term. Yet, exposure to contaminants, especially Mirex, and other concurring environmental stressors should be monitored over the long-term in this declining population.

Marine pollution in fledged Leach's storm-petrels (Hydrobates leucorhous) from Baccalieu Island, Newfoundland and Labrador, Canada

The Leach's storm-petrel (Hydrobates leucorhous) is one of the most abundant and widely distributed marine birds in the North Atlantic but is under global population decline, possibly linked to marine pollution. We determined levels of ingested plastic and hepatic total mercury (THg) in recently fledged juveniles that stranded in Newfoundland and Labrador, Canada, and assessed the relationship to body condition, size and diet. Plastic prevalence was high (87.5%) but hepatic THg was relatively low (mean 486.7 ng/g dry weight) compared to other studies. Levels of neither pollutant were significantly related to body metrics of health. Our data confirm that plastic and mercury are pervasive in the western North Atlantic Ocean, prominent even in young birds.

Mercury exposure in an endangered seabird: long-term changes and relationships with trophic ecology and breeding success

Mercury (Hg) is an environmental contaminant which, at high concentrations, can negatively influence avian physiology and demography. Albatrosses (Diomedeidae) have higher Hg burdens than all other avian families. Here, we measure total Hg (THg) concentrations of body feathers from adult grey-headed albatrosses (Thalassarche chrysostoma) at South Georgia. Specifically, we (i) analyse temporal trends at South Georgia (1989-2013) and make comparisons with other breeding populations; (ii) identify factors driving variation in THg concentrations and (iii) examine relationships with breeding success. Mean ± s.d. feather THg concentrations were 13.0 ± 8.0 µg g^-1 dw, which represents a threefold increase over the past 25 years at South Georgia and is the highest recorded in the Thalassarche genus. Foraging habitat, inferred from stable isotope ratios of carbon (δ¹³C), significantly influenced THg concentrations-feathers moulted in Antarctic waters had far lower THg concentrations than those moulted in subantarctic or subtropical waters. THg concentrations also increased with trophic level (δ¹⁵N), reflecting the biomagnification process. There was limited support for the influence of sex, age and previous breeding outcome on feather THg concentrations. However, in males, Hg exposure was correlated with breeding outcome-failed birds had significantly higher feather THg concentrations than successful birds. These results provide key insights into the drivers and consequences of Hg exposure in this globally important albatross population.

A "seabird-eye" on mercury stable isotopes and cycling in the Southern Ocean

Since mercury (Hg) biogeochemistry in the Southern Ocean is minimally documented, we investigated Hg stable isotopes in the blood of seabirds breeding at different latitudes in the Antarctic, Subantarctic and Subtropical zones. Hg isotopic composition was determined in adult penguins (5 species) and skua chicks (2 species) from Adélie Land (66°39'S, Antarctic) to Crozet (46°25'S, Subantarctic) and Amsterdam Island (37°47'S, Subtropical). Mass-dependent (MDF, δ²⁰²Hg) and mass-independent (MIF, Δ¹⁹⁹Hg) Hg isotopic values separated populations geographically. Antarctic seabirds exhibited lower δ²⁰²Hg values (-0.02 to 0.79 ‰, min-max) than Subantarctic (0.88 to 2.12 ‰) and Subtropical (1.44 to 2.37 ‰) seabirds. In contrast, Δ¹⁹⁹Hg values varied slightly from Antarctic (1.31 to 1.73 ‰) to Subtropical (1.69 to 2.04 ‰) waters. The extent of methylmercury (MeHg) photodemethylation extrapolated from Δ¹⁹⁹Hg values was not significantly different between locations, implying that most of the bioaccumulated MeHg was of mesopelagic origin. The larger increase of MDF between the three latitudes co-varies with MeHg concentrations. This supports an increasing effect of specific biogenic Hg pathways from Antarctic to Subtropical waters, such as Hg biological transformations and accumulations. This "biogenic effect" among different productive southern oceanic regions can also be related to different mixed layer depth dynamics and biological productivity turnover that specifically influence the vertical transport between the mesopelagic and the photic zones. This study shows the first Hg isotopic data of the Southern Ocean at large scale and reveals how regional Southern Ocean dynamics and productivity control marine MeHg biogeochemistry and the exposure of seabirds to Hg contamination.

Early Breeding Failure in Birds Due to Environmental Toxins: A Potentially Powerful but Hidden Effect of Contamination

Toxin emissions and legacies are major global issues affecting many species through, among other effects, endocrine disruption and reproductive impairment. Assessment of toxin risk to wildlife focuses mostly on offspring-related metrics, while the lack of breeding initiation or early breeding failure has received less attention. We tested whether exposure to methyl mercury (MeHg) results in early breeding failure and reduced number of breeding birds using observational and experimental data. We used 21 years of numbers of breeding pairs of colonially breeding wild Great Egrets (Ardea alba) in response to annual and geographical variation upon exposure to environmental MeHg. After controlling for food availability, we found a strong negative association between MeHg exposure and the number of breeding Great Egrets. We report reductions of >50% in breeding numbers under exposure levels otherwise associated with <20% reduction in post-egg-laying breeding success. Experimental exposure of White Ibises (Eudocimus albus) to MeHg also caused early breeding failure and a ∼20% reduction in breeding numbers at environmentally relevant exposures. The demographic consequences of reductions in breeding pairs are additive to known and typically studied impairments in postlaying reproductive success. Net demographic effects of exposure to endocrine disruptors may often be strongly underestimated if early breeding failure is not measured.

Yellow-legged gull eggs (Larus michahellis) as persistent organic pollutants and trace metal bioindicator for two nearby areas with different human impact

The concentration of different persistent organic pollutants (POPs including chlorinated and brominated compounds) and trace metals and metalloids (As, Cd, Cu, Cr, Pb, Hg, Ni, and Zn) was examined in eggs from two colonies of yellow-legged gulls. The two colonies are established in Ría de Vigo, Northwest Spain, with a distance between them of only 10 km, one in Vigo town (industrial and harbour activities) and the other in the Cíes Islands in a Natural Park and Marine Protected Area -MPA- (with no known anthropogenic inputs). Statistically significant differences for the two colonies were observed for Hg, the sum of 7 CBs, the sum of DDTs y and the sum of 9 PBDEs, with values that could be causing some toxic effects in the area of the most anthropogenically influenced colony. The estimated isotopic niche was also calculated, based on δ¹⁵N and δ¹³C, for the two colonies, pointing to a wider diet in the Cíes colony when compared to the diet in the Vigo colony. The study supports the use of the yellow-legged seagull eggs as a bioindicator of pollution capable of differentiating pollution level even in geographically close areas.

Mercury exposure in migrating songbirds: correlations with physical condition

Many migratory songbirds are at high risk of methylmercury (MeHg) exposure due to their trophic position and foraging in and around wetland habitats. Methylmercury has the potential to alter migratory behaviors and physiology via neurological impairment or reduced flight performance and can be remobilized from songbird muscle tissue during migration, increasing the risk of acute MeHg exposure. To document MeHg exposure and its relationship with physical condition in migratory songbirds, we sampled passerine blood and feathers at a migration stopover site on Key Biscayne, FL during fall and spring from 2009 to 2012. We found evidence that spring blood total mercury (THg) concentrations decreased throughout the day and that fall feather THg concentrations changed over the migratory season. Total mercury exposure was marginally correlated with migratory fat stores and related to changes in pectoral muscle thickness by time of day. These patterns suggest that environmentally relevant levels of THg are related to, and may be influencing, the physical condition of free-living migrating songbirds. Further research and monitoring during the migratory period will be important to elucidate exposure risk across multiple species and assess the potential for effects during this complex period of the annual cycle.