A century of mercury: Ecosystem-wide changes drive increasing contamination of a tropical seabird species in the South Atlantic Ocean

Exceptionally high levels of total mercury in deep-sea sharks of the Southeastern Mediterranean sea over the last ∼ 40 years

Deep-sea habitats are currently recognized as a hot spot for mercury (Hg) accumulation from anthropogenic sources, resulting in elevated concentrations of total mercury (THg) in deep-sea megafauna. Among them, deep-sea sharks (Class Chondrichthyes) are characterized by high trophic position and extended longevity and are, therefore, at high risk for mercury contamination. Despite this, sharks are overexploited by fishing activity in increasingly deeper water, worldwide, imposing health risks to human consumption. While it is imperative to better understand long-term mercury contamination in deep-sea megafauna, few historical data sets exist to capture this process. Here we explore four decades (1985-2022) of THg accumulation in five species of deep-sea sharks (G. melastomus, E. spinax, S. rostratus, C. granulosus, and D. licha) of the ultra-oligotrophic Southeastern Mediterranean Sea (SEMS) sampled during 19 research cruises. We exhibited exceptionally high THg levels (per length/weight), the highest as 16.6 μg g-1 (wet wt.), almost entirely (98.9 %; n = 298 specimens) exceeding the limit for safe consumption (0.3-0.5 μg THg g-1 wet wt.). The maximal THg levels of the long-lived species D. licha and C. granulosus in the SEMS were enriched by a factor of ∼ 7 and >10 compared to counterpart species from other oceanic areas, respectively. We attribute this to the ultra-oligotrophic conditions of the SEMS, which cause slower growth rates and dwarfism in deep-sea sharks, resulting in an extended exposure time to mercury contamination. In the long-lived species, C. granulosus and D. licha, a temporal increase of average THg levels of ∼ 80 % was recorded between 1987-1999 and 2021-2022. This likely reflects the long-term accumulation of historical anthropogenic Hg in deep-sea environments, which is further amplified in marginal seas such as the Mediterranean, impacted by global air pollution crossroads and surrounded by land-based pollution sources. Future consumption of products from deep-sea sharks is potentially high risk to human health.

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.

Characteristic features of toxic metal content in hair samples of foreign students at RUDN University from different geographic regions

BACKGROUND

This study explores the regional variations in toxic metal accumulation among RUDN University students from various global regions.

METHODS

This comparative analysis examined hair samples from students hailing from different regions, including Russia, Asia, the Middle East, Africa, and Latin America. The concentrations of Aluminium (Al), Arsenic (As), Cadmium (Cd), Mercury (Hg), Lead (Pb), and Tin (Sn) were measured in the hair samples. The data was then evaluated using regression models to assess the link between the region of residence and toxic metal content in the hair.

RESULTS

The analysis indicated significant regional variations in the levels of toxic metals in the students' hair. The highest content of Al, Cd, and Pb was observed in students from Africa (13.542, 0.028, 0.794 µg/g) and Latin America (9.947, 0.025, 0.435 µg/g). Arsenic levels in students from all regions exceeded that of Russian students by over two-fold. No substantial group differences were found in the Sn content. The regression models suggested that residing in Asia, Africa, and Latin America was a predictor of high Hg levels in hair (0.130, 0.096, 0.227 µg/g). Living in Africa was significantly associated with higher Pb levels (0.794 µg/g), and living in Latin America was close to significantly associated with the Cd level in the hair (0.025 µg/g).

CONCLUSION

This study confirmed an increased accumulation of toxic metals, especially Hg, Cd, and Pb, in students primarily from Latin America and Africa. The findings highlighted the importance of understanding the regional variations in toxic metal accumulation to address associated health risks and the potential impact on students' well-being and academic performance. These insights may guide the development of targeted interventions to reduce exposure to toxic metals in students from various regions around the world.

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.

Are tunas relevant bioindicators of mercury concentrations in the global ocean?

Humans are exposed to toxic methylmercury mainly by consuming marine fish. The Minamata Convention aims at reducing anthropogenic mercury releases to protect human and ecosystem health, employing monitoring programs to meet its objectives. Tunas are suspected to be sentinels of mercury exposure in the ocean, though not evidenced yet. Here, we conducted a literature review of mercury concentrations in tropical tunas (bigeye, yellowfin, and skipjack) and albacore, the four most exploited tunas worldwide. Strong spatial patterns of tuna mercury concentrations were shown, mainly explained by fish size, and methylmercury bioavailability in marine food web, suggesting that tunas reflect spatial trends of mercury exposure in their ecosystem. The few mercury long-term trends in tunas were contrasted and sometimes disconnected to estimated regional changes in atmospheric emissions and deposition, highlighting potential confounding effects of legacy mercury, and complex reactions governing the fate of mercury in the ocean. Inter-species differences of tuna mercury concentrations associated with their distinct ecology suggest that tropical tunas and albacore could be used complementarily to assess the vertical and horizontal variability of methylmercury in the ocean. Overall, this review elevates tunas as relevant bioindicators for the Minamata Convention, and calls for large-scale and continuous mercury measurements within the international community. We provide guidelines for tuna sample collection, preparation, analyses and data standardization with recommended transdisciplinary approaches to explore tuna mercury content in parallel with observation abiotic data, and biogeochemical model outputs. Such global and transdisciplinary biomonitoring is essential to explore the complex mechanisms of the marine methylmercury cycle.