Bioaccumulation of inorganic and organic mercury in the cuttlefish Sepia officinalis: Influence of ocean acidification and food type

Seasonal variations in feeding ecology and mercury contamination of golden cuttlefish (Sepia esculenta) in the coastal waters of China

The golden cuttlefish (Sepia esculenta), a key ecological and economic cephalopod in China's coastal waters, exhibits seasonal adaptations in feeding ecology and mercury (Hg) bioaccumulation. This study investigated muscle fatty acid profiles, stable isotopes (δ13C, δ15N), and total Hg concentrations in S. esculenta from the East China Sea across autumn (September-November 2021) and winter (December 2022-February 2023). Results revealed distinct seasonal shifts: polyunsaturated fatty acids (PUFAs) dominated winter muscles (55.3 ± 7.87 %), notably docosahexaenoic acid (DHA: 37.38 ± 4.17 %) and arachidonic acid (ARA: 7.05 ± 1.06 %), while monounsaturated fatty acids (MUFAs) peaked in autumn (9.44 ± 2.27 %). Stable isotopes indicated no significant niche differentiation (SEAc overlap: 76 %), but δ15N ranges narrowed in winter (10.16-13.17 ‰ vs. autumn: 9.74-14.39 ‰). Total Hg concentrations were 41.4 % higher in winter (0.280 ± 0.151 μg g-1) than autumn (0.198 ± 0.099 μg g-1), driven by increased consumption of Hg-rich benthic organisms and reduced metabolic detoxification in colder temperatures. These findings highlight how dietary plasticity and environmental stressors jointly regulate Hg dynamics in cephalopods, providing actionable insights for mitigating contamination risks and managing S. esculenta fisheries under climate change.

Synchronous changes in mercury stable isotopes and compound-specific amino acid nitrogen isotopes in organisms through food chains

The relationship between stable isotope of mercury (Hg, Δ199Hg and δ202Hg) and compound-specific nitrogen isotope of amino acids (CSIA-AA, δ15NGlu and δ15NPhe) remains poorly understood. In this study, we investigated bird species and their prey in an abandoned Hg mining area, southern China to elucidate these correlations for a better understanding of Hg sources, biological transfer, accumulation and amplification through food chains. Our findings revealed distinct isotopic patterns: Δ199Hg showed a positive correlation with δ15NGlu, indicating trophic transfer processes, while a negative correlation with δ15NPhe suggested differences in Hg sources among birds. The wide ranges of δ15NPhe and Δ199Hg observed in birds appear to reflect mixtures of multiple nitrogen and Hg sources, likely due to their diverse food sources and the large variation in the proportion of MeHg in total Hg (MeHg%). The consistent slope between Δ199Hg/δ15Nphe and MeHg%/δ15Nphe, reflecting both energy and Hg sources, provides new insights into the biotransfer and accumulation of Hg in organisms. Notably, the trophic magnification factor (TMF) of MeHg observed in water birds, such as egrets, reached an exceptionally high value of 97.7 estimated from CSIA of multiple amino acids (i.e., TMFM), underscoring the significance of investigating Hg sources in birds. Our results demonstrate that the synchronous changes between CSIA-AA and odd Hg isotopes effectively identify Hg sources and transfer across multiple ecological systems.

Ecotoxicology of cephalopod early life phases: review and perspectives

The present review provides the first analysis and synthesis of the available scientific information on the effects of anthropogenic contaminants on cephalopod embryos, paralarvae, and juveniles. We evaluated 46 articles published between 1970 and 2023 that focused on trace elements (69%), pharmaceutical compounds (11%), persistent organic compounds (11%), and plastics (9%). To date, the greatest scientific effort has originated from Europe and Asia (France [57%], China [9%], Italy [7%], and Spain [4%]), with few reports available from the rest of the world. Most studies focused on species of economic importance (cuttlefish [69%], octopuses [18%], and squid [13%]), with few reports on species of low commercial value or that reside in remote habitats such as nautiluses. Although 28 contaminants have been evaluated, cadmium, copper, zinc, fluoxetine (FLX), polycyclic aromatic hydrocarbons (PAHs), organophosphorus compounds, and tributyltin (TBT) were the only contaminants associated with adverse effects on various biological, physiological, and ethological processes during early life phases. Despite these advances, the present review demonstrates the crucial need for ecotoxicology studies that focus on (i) embryotoxicology and the interactions among toxic agents during the early stages of cephalopod development, (ii) survival and recruitment, and (iii) species that inhabit coastal and oceanic environments that have not yet been the focus of previous studies, especially those in countries with few published records. With this information, critical areas can be identified, marine biodiversity monitoring programs can be developed, and effective conservation strategies can be created that include measures to mitigate marine pollution.

Toxicity of methylmercury in aquatic organisms and interaction with environmental factors and coexisting pollutants: A review

Mercury is a hazardous heavy metal that is distributed worldwide in aquatic ecosystems. Methylmercury (MeHg) poses significant toxicity risks to aquatic organisms, primarily through bioaccumulation and biomagnification, due to its strong affinity for protein thiol groups, which results in negative effects even at low concentrations. MeHg exposure can cause various physiological changes, oxidative stress, neurotoxicity, metabolic disorders, genetic damage, and immunotoxicity. To assess the risks of MeHg contamination in actual aquatic ecosystems, it is important to understand how MeHg interacts with environmental factors such as temperature, pH, dissolved organic matter, salinity, and other pollutants such as microplastics and organic compounds. Complex environmental conditions can cause potential toxicity, such as synergistic, antagonistic, and unchanged effects, of MeHg in aquatic organisms. This review focuses on demonstrating the toxic effects of single MeHg exposure and the interactive relationships between MeHg and surrounding environmental factors or pollutants on aquatic organisms. Our review also recommends further research on biological and molecular responses in aquatic organisms to better understand the potential toxicity of combinational exposure.

Baseline study for the total mercury determination in Yemeni fish

The high levels of mercury toxicity in humans make it necessary to monitor mercury levels in food, pharmaceuticals, and the environment to minimize human exposure. Between June 2020 and October 2021, researchers collected 240 fish samples from different locations along the Yemeni coast to evaluate mercury contamination. The Direct Mercury Analyzer was used to determine the concentration of mercury in each sample. To ensure method accuracy, a series of triplicate mercury concentration analyses were conducted. The samples ranged from 2 to 100 ng to determine linearity and repeatability i.e., within-day variation. The results showed a high level of precision, with a correlation coefficient of 0.9990 and a repeatability of 1.34 %-5.62 % RSD range. The method was also highly accurate, as the mercury recovery results from the contaminated fish samples ranged from 96.77 % to 105.14 %. The limits of detection and quantitation of mercury were 0.0015 ppm and 0.0049 ppm, respectively. This allowed the method to detect trace amounts of mercury in fish meat. Mercury concentration in the 240 fish samples did not exceed the FDA, but below the 0.5 ppm specified limit of YSMO.

The acute neurotoxicity of inorganic mercury in Mactra chinensis philippi

Inorganic mercury (IHg) is hazardous to marine organisms especially resulting in neurotoxicity, bivalves are sensitive to pollutants as "ocean sentinel", but data on the neurotoxicity of IHg in bivalves are sparse. So we chosed M. chinensis philippi with typical neural structures in bivalves to investigate the neurotoxicity of IHg, which could be helpful to understand the specificity of neural regulation and the response characteristics of bivalves. After acute exposed to IHg (HgCl2) for 24 h, the metabolites of ganglion tissues in M. chinensis philippi were evaluated using 1H-nuclear magnetic resonance based metabolomics; Ca2+, neurotransmitters (nitric oxide, glutamate, acetylcholine) and related enzymes (calcineurin, nitric oxide synthase and acetylcholinesterase) were measured using biochemical detection. Compared to the control group, the levels of the nitric oxide (81.04 ± 12.84 μmol/g prot) and acetylcholine (30.93 ± 12.57 μg/mg prot) in M. chinensis philippi of IHg-treated were decreased, while glutamate (2.11 ± 0.61 mmol/L) increased significantly; the activity of nitric oxide synthase (679.34 ± 135.33 U/mg prot) was increased, while acetylcholinesterase (1.39 ± 0.44 U/mg prot) decreased significantly, and the activity of calcineurin (0.52 ± 0.02 U/mg prot) had a statistically insignificant increasing tendency. The concentration of Ca2+ (0.92 ± 0.46 mmol/g prot) in the IHg-treated group was significantly higher than that in the control group. OPLS-DA was performed to reveal the difference in metabolites between the control and IHg-challenged groups, the metabolites of glucose, glutamine, inosine, succinate, glutamate, homarine, and alanine were sensitive to IHg, subsequently metabolic pathways that were affected including glucose metabolism, glutamine metabolism, nucleotide metabolism, Krebs cycle, amino acid metabolism and osmotic regulation. In our study, IHg interfered with metabolites in M. chinensis philippi, thus the corresponding metabolic pathways were changed, which influenced the neurotransmitters subsequently. Furthermore, Ca2+overload affected the synthesis or degradation of the neurotransmitters, and then the altered neurotransmitters involved in changes in metabolic pathways again. Overall, we hypothesized that the neurotoxic effects of IHg on bivalve were in close contact with metabolism, neurotransmitters, related enzymes and Ca2+, which could be effective neurotoxic biomarkers for marine environmental quality assessment, and also provide effective data for the study of the regulatory mechanism of the nervous system in response to IHg in bivalves.

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.

In Vivo Mercury (De)Methylation Metabolism in Cephalopods under Different pCO2 Scenarios

This work quantified the accumulation efficiencies of Hg in cuttlefish, depending on both organic (MeHg) and inorganic (Hg(II)) forms, under increased pCO₂ (1600 μatm). Cuttlefish were fed with live shrimps injected with two Hg stable isotopic tracers (Me²⁰²Hg and ¹⁹⁹Hg(II)), which allowed for the simultaneous quantification of internal Hg accumulation, Hg(II) methylation, and MeHg demethylation rates in different organs. Results showed that pCO₂ had no impact on Hg bioaccumulation and organotropism, and both Hg and pCO₂ did not influence the microbiota diversity of gut and digestive gland. However, the results also demonstrated that the digestive gland is a key organ for in vivo MeHg demethylation. Consequently, cuttlefish exposed to environmental levels of MeHg could exhibit in vivo MeHg demethylation. We hypothesize that in vivo MeHg demethylation could be due to biologically induced reactions or to abiotic reactions. This has important implications as to how some marine organisms may respond to future ocean change and global mercury contamination.