Mercury concentrations in Antarctic zooplankton with a focus on the krill species, Euphausia superba

Mercury, methylmercury, and its fractions at the base of the trophic pyramid of the maritime Antarctic ecosystem of Admiralty Bay

Mercury (Hg) pollution in polar regions is a critical environmental concern, exacerbated by glacier melting due to climate change. This study investigated the impact of glacial meltwater on total mercury (THg), methylmercury (MeHg), and various Hg fractions levels in seawater, suspended particulate matter, and microplankton in Admiralty Bay, Antarctica. Stable isotope analyses of carbon and nitrogen complement Hg measurements, providing insights into food web dynamics and pollutant transfer. The average THg concentration in water samples from creeks, which may represent runoff from melting glaciers and snow, was 2.5 times higher than in sea water from Admiralty Bay. The proportion of methylmercury in total mercury varied depending on the environmental component: in water, it was 1.1 %; in SPM, 0.7 %; and in microplankton, 2.4 %. Increased microplankton biomass, which provides a larger surface area, enhanced the proportion of adsorbed HgF1, in microplankton, indicating that mercury adsorbs onto available planktonic surfaces. This research enhances our understanding of Hg cycling in Antarctic ecosystems and underscores the implications of climate change for Hg contamination, with potential effects on marine food webs and human health.

Total mercury accumulation in Antarctic krill (Euphausia superba) in the northern Antarctic Peninsula during late autumn to early winter

Antarctic krill (Euphausia superba) is a key species in the Antarctic marine ecosystem and also the largest fishery in terms of catch in the Southern Ocean. Bransfield Strait on the northern Antarctic Peninsula is a key fishing ground. Mercury is a globally recognized toxic element that can affect pelagic organisms through bioaccumulation and biomagnification. Understanding mercury dynamics in krill is crucial for understanding its impacts on Antarctic food webs and potential impacts on the uses of krill in the human food chain. However, the factors influencing Hg accumulation in krill remain unclear, especially in the autumn when there is a transition from an environment of abundant food to a period of lower abundance in winter. We therefore investigated the total mercury (THg) accumulation in krill using randomly collected samples (n = 60) from the krill fishery in the Bransfield Strait from 14 May to June 15, 2023. We further explored the potential drivers influencing THg accumulation in krill. The results indicated that THg levels in male krill (46.7 ± 10.8 ng g-1) are comparable to those in females (40.0 ± 7.8 ng g-1), and that krill THg levels in May (47.1 ± 11.5 ng g-1) are significantly higher than in June (41.3 ± 8.2 ng g-1), indicating seasonal variation in krill THg levels. Moreover, the THg concentration of krill showed a significant positive correlation with krill size, regardless of sex or month. Krill size and sex, slope, water mass at 100 m, and sea ice dynamics all affected THg accumulation. Briefly, the THg level decreased with the increases in seafloor slope, and krill accumulated higher level of THg in the open water compared to ice-covered regions, highlighting the importance of seafloor slope and sea ice dynamics in THg dynamics in krill.

Impact of sediment resuspension on near-bottom mercury dynamics: Insights from a Baltic Sea experiment

Marine sediments are major sources of legacy pollution, capable of releasing toxic mercury (Hg) into the water column when disturbed. This study evaluated Hg remobilization from surface sediments during resuspension events by examining sediment properties, Hg concentrations, and speciation. Research was conducted in the southern Baltic Sea, representing diverse environmental conditions and human impacts. The findings showed that sediment resuspension was the primary driver of Hg remobilization, with diffusion flux playing a minimal role. Both dissolved and particulate Hg were released almost immediately after resuspension, with elevated concentrations persisting long enough to be transported beyond the disturbed area. The diffusion of dissolved Hg was enhanced by labile Hg fractions in the sediment, with reducing conditions and high organic matter content further promoting this process. Particulate Hg remobilization was influenced by sediment characteristics, particularly bulk density, which affected resuspension susceptibility and dispersion of suspended matter. The total Hg concentration and labile organic-bound Hg fractions also significantly influenced particulate Hg release. These results highlight the importance of sediment properties in managing Hg-contaminated sites and have implications for environmental protection and marine operations planning.

Evaluation of the Adriatic Sea pollution using mesozooplankton as an environmental indicator

The Adriatic Sea is an enclosed basin threatened by marine pollution due to its hydrographic features and anthropogenic pressure. Although zooplankton has been worldwide regarded as an immediate warning signal of contamination, limited information is available on the contamination of these organisms at the Adriatic level. Hence, this study provides comprehensive data on the presence and levels of multiple pollutants in zooplankton collected from 46 locations. With regards to legacy contaminants, both PCB and DDT levels have declined since the 1980s. Specifically, most samples were characterized by low DDT contamination (average of 3 ± 2.7 ng g- 1 dry weight) and only few of these accumulated levels of concern for what concerns PCB, pointing out possible hotspots of contamination in the central-eastern Adriatic Sea. As regards metal(loid)s, the Metal Pollution Index identified areas of concern in the north Adriatic Sea (Gulf of Venice) with high levels of Co, Cu, Hg, Cr and Pb; in the Central Adriatic Sea (Tremiti islands) with high levels of Co, Ni, Hg, Cr and Pb; in the Southern Adriatic Sea (Taranto and offshore Corfu), with high levels of most metal(loid)s, especially Cr, Ni and Zn. Certain metal(loid)s (e.g. Cd, Pb and Hg) have declined over time and most of them are lower than well-known contaminated worldwide marine ecosystems. Only Cu appears to be particularly high in the Mediterranean zooplankton. Overall, this work suggests a general improvement of the status of contamination of the Adriatic Sea.

Mercury dynamics at the base of the pelagic food web of the Gulf of Gdańsk, southern Baltic Sea

Planktonic organisms, which have direct contact with water, serve as the entry point for mercury (Hg), into the marine food web, impacting its levels in higher organisms, including fish, mammals, and humans who consume seafood. This study provides insights into the distribution and behavior of Hg within the Baltic Sea, specifically the Gulf of Gdańsk, focusing on pelagic primary producers and consumers. Phytoplankton Hg levels were primarily influenced by its concentrations in water, while Hg concentrations in zooplankton resulted from dietary exposure through suspended particulate matter and phytoplankton consumption. Hg uptake by planktonic organisms, particularly phytoplankton, was highly efficient, with Hg concentrations four orders of magnitude higher than those in the surrounding water. However, unlike biomagnification of Hg between SPM and zooplankton, biomagnification between zooplankton and phytoplankton was not apparent, likely due to the low trophic position and small size of primary consumers, high Hg elimination rates, and limited absorption.

Interspecific Variations in the Internal Mercury Isotope Dynamics of Antarctic Penguins: Implications for Biomonitoring

Mercury (Hg) biomonitoring requires a precise understanding of the internal processes contributing to disparities between the Hg sources in the environment and the Hg measured in the biota. In this study, we investigated the use of Hg stable isotopes to trace Hg accumulation in Adélie and emperor penguin chicks from four breeding colonies in Antarctica. Interspecific variation of Δ199Hg in penguin chicks reflects the distinct foraging habitats and Hg exposures in adults. Chicks at breeding sites where adult penguins predominantly consumed mesopelagic prey showed relatively lower Δ199Hg values than chicks that were primarily fed epipelagic krill. Substantial δ202Hg variations in chick tissues were observed in both species (Adélie: -0.11 to 1.13‰, emperor: -0.27 to 1.15‰), whereas only emperor penguins exhibited the lowest δ202Hg in the liver and the highest in the feathers. Our results indicate that tissue-specific δ202Hg variations and their positive correlations with % MeHg resulted from MeHg demethylation in the liver and kidneys of emperor penguin chicks, whereas Adélie penguin chicks showed different internal responses depending on their exposure to dietary MeHg. This study highlights the importance of considering intra- and interspecific variations in adult foraging ecology and MeHg demethylation when selecting penguin chicks for Hg biomonitoring.

The non-selective Antarctic filter feeder Salpa thompsoni as a bioindicator of mercury origin

Hg is considered as the most toxic metal in the environment. Sources of Hg in the environment include burning fossil fuels, burning waste, and forest fires. The long residence time of the gaseous form in the atmosphere allows mercury to be transported over long distances. The pelagic tunicate Salpa thompsoni is an important component of the Antarctic environment. Over the past few decades an expansion of this species to the higher latitudes has been noted, mainly due to the ongoing climate change. The study material consisted of samples of S. thompsoni individuals, collected in the waters surrounding Elephant Island (Western Antarctic). Total mercury and five of its fractions were determined. Whole organisms were analyzed as well as internal organs: stomachs, muscle strips, and tunics. Obtained results showed that the highest concentrations of mercury in salps were observed in stomachs. With the Hg fraction results, it can be concluded that the main route of exposure of S. thompsoni to Hg is presumably absorption from the food-filtered organic and non-organic particles. Moreover, the process of transformation of simple soluble forms into organic forms of Hg in stomachs and intestines and its distribution to other tissues was observed.