Relations between total mercury, methylmercury and selenium in five tissues of Sepia officinalis captured in the south Portuguese coast

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

The bioaccumulation of mercury (Hg) in marine organisms through various pathways has not yet been fully explored, particularly in cephalopods. This study utilises radiotracer techniques using the isotope ²⁰³Hg to investigate the toxicokinetics and the organotropism of waterborne inorganic Hg (iHg) and dietary inorganic and organic Hg (methylHg, MeHg) in juvenile common cuttlefish Sepia officinalis. The effect of two contrasting CO₂ partial pressures in seawater (400 and 1600 μatm, equivalent to pH 8.08 and 7.54, respectively) and two types of prey (fish and shrimp) were tested as potential driving factors of Hg bioaccumulation. After 14 days of waterborne exposure, juvenile cuttlefish showed a stable concentration factor of 709 ± 54 and 893 ± 117 at pH 8.08 and 7.54, respectively. The accumulated dissolved i²⁰³Hg was depurated relatively rapidly with a radiotracer biological half-life (Tb_1/2) of 44 ± 12 and 55 ± 16 days at pH 8.08 and 7.54, respectively. During the whole exposure period, approximately half of the i²⁰³Hg was found in the gills, but i²⁰³Hg also increased in the digestive gland. When fed with ²⁰³Hg-radiolabelled prey, cuttlefish assimilated almost all the Hg provided (>95%) independently of the prey type. Nevertheless, the prey type played a major role on the depuration kinetics with Hg Tb_1/2 approaching infinity in fish fed cuttlefish vs. 25 days in shrimp fed cuttlefish. Such a difference is explained by the different proportion of Hg species in the prey, with fish prey containing more than 80% of MeHg vs. only 30% in shrimp. Four days after ingestion of radiolabelled food, iHg was primarily found in the digestive organs while MeHg was transferred towards the muscular tissues. No significant effect of pH/pCO₂ variation was observed during both the waterborne and dietary exposures on the bioaccumulation kinetics and tissue distribution of i²⁰³Hg and Me²⁰³Hg. Dietary exposure is the predominant pathway of Hg bioaccumulation in juvenile cuttlefish.

Elemental composition of whole body soft tissues in bivalves from the Bijagós Archipelago, Guinea-Bissau

Marine bivalves are bioindicators of coastal environmental pollution, integrating monitoring programs worldwide. Nonetheless, the choice of particular species as an indicator requires validation, achieved by understanding the differences in element concentrations among and within species. The present study compares the chemical composition of whole body soft tissues of four common bivalve species from the Bijagós Archipelago, a pristine region of West Africa. Significant differences were recorded in the concentrations of various elements among studied species, which likely arise from species-specific uptake and bioaccumulation processes. Overall, there was a segregation between a group including the bloody cockle Senilia senilis and oyster Crassostrea tulipa (with high Cd and Zn concentrations) versus the two other species, Austromacoma nymphalis (with low Cu and high Mn, Se, Hg, Pb concentrations) and Diplodonta spp. (with high values of Cu, Al, Fe, V, Cr, Hg, Pb). C. tulipa was sampled in two different substrates (rock beds and mangrove roots), and the two groups revealed different chemical profiles, with significantly higher concentrations of P, Si, Zn and Cr and lower Cu in specimens fixed in mangrove roots. These results strongly suggest the influence of small-scale environmental variability on the accumulation of particular elements. We found extremely high Cd concentrations in S. senilis (27.1 ± 7.53 μg g^-1 DW) and identified C. tulipa as another high Cd-accumulating species (ca. 10 μg g^-1 DW). Our results suggest a detoxifying mechanism linked with the presence of Se to reduce the potential toxic effects of Cd in these two species. Cadmium concentrations reported for some bivalve species in this area largely exceed the maximum values proposed by the European Union, emphasizing the need for a regular contamination assessment.

Factors affecting mercury concentrations in two oceanic cephalopods of commercial interest from the southern Caribbean

Mercury (Hg) concentrations have significantly increased in oceans during the last century. This element accumulates in marine fauna and can reach toxic levels. Seafood consumption is the main pathway of methylmercury (MeHg) toxicity in humans. Here, we analyzed total Hg (T-Hg) concentrations in two oceanic squid species (Ommastrephes bartramii and Thysanoteuthis rhombus) of an increasing commercial interest off Martinique, French West Indies. Stable isotope ratios reveal a negative linear relationship between δ¹⁵N or δ¹³C in diamondback squid samples. No significant trend was observed between δ³⁴S values and T-Hg concentrations, contrasting with the sulfate availability and sulfide abundance hypotheses. This adds to a growing body of evidence suggesting Hg methylation via sulfate-reducing bacteria is not the main mechanism driving Hg bioavailability in mesopelagic organisms. All squid samples present T-Hg levels below the maximum safe consumption limit (0.5 ppm), deeming the establishment of a commercial squid fishery in the region safe for human consumption.

The role of intestinal microbiota of the marine fish (Acanthopagrus latus) in mercury biotransformation

Both inorganic (IHg) and organic (MeHg) forms of Hg can be converted into each other by methylation or demethylation, leading to changes of Hg speciation and distribution in fish. However, Hg biotransformation in fish is not thoroughly understood and the key factors in this process are unclear. The present study investigated the in vivo Hg transformation in a marine fish (Acanthopagrus latus) and explored the roles of intestinal microbiota in Hg biotransformation. We first demonstrated that Hg methylation or demethylation occurred in the fish gut under dietary IHg or MeHg exposure, respectively. The demethylation was observed to be faster than methylation, suggesting that demethylation could significantly influence the Hg speciation in fish. This study also strongly suggested that intestinal microbiota played a predominant role in Hg biotransformation and thus significantly affected the overall Hg accumulation and distribution in fish body. The richness of Hg methylators or demethylators was elevated under IHg or MeHg treatment, respectively. Furthermore, the intestinal microbiota composition was also altered by Hg exposure. This study highlights the importance of intestinal microbiota in Hg biotransformation in fish body, and suggests that modulating the gut microbiome could be a possible solution to minimize Hg contamination in fish.

Mercury concentrations in the tissues of blue shark (Prionace glauca) from Sagami Bay and cephalopods from East China Sea

The toxicity of mercury (Hg), is generally known, and around 90% of Hg exist as methylmercury (CH₃Hg⁺) in marine organism. Mercury concentrates in sharks and whales, which are at the top of the food chain as predators to cephalopods. The concentrations of Hg in liver and muscle of blue shark, caught in Sagami Bay, and in digestive gland and mantles of Todarodes pacificus, Sepia madokai, and Uroteuthis edulis caught in East China Sea were measured and analyzed. The Hg concentrations in the sharks, squids, and cuttlefishes determined in this study were almost same as those in the other sea regions. In addition, the Hg concentration in the blue shark was higher in the muscle than in the liver. In S. madokai and U. edulis, Hg accumulated in the digestive gland but not in the mantle. Although the Hg concentration in the digestive gland of T. pacificus is lower than those of S. madkai and U edulis, Hg concentration in the mantle is critically higher. More than 90% of Hg is present as CH₃Hg⁺ in muscle of blue shark and mantle of T. pacificus. This feature is explained due to amino acids with the thiol groups and chain genes in the muscle of blue shark as well as in the mantle of T. pacificus. Myosin in the mantle of T. pacificus and blue shark enhances the stability of CH₃Hg⁺. The amount of Hg in the digestive gland of T. pacificus could be too large to store; thus, Hg is released to the mantle, whereas the nutrients in the digestive gland of T. pacificus are supplied to other tissues. It is considered that the muscle fiber of T. pacificus is strong; therefore, large amounts of myosin levels may be present in T. pacificus than in S. madokai and U. edulis.

Critical review of mercury contamination in Sri Lankan fish and aquatic products

Mercury (Hg) in fish and aquatic products is a potential threat to human health and international trade, and guidelines of international advisory bodies are established for assessing Hg in these foods. As fish are the most consumed animal protein in Sri Lanka, this assessment summarises for the first-time total mercury concentrations in Sri Lankan marine and freshwater fish, invertebrates, aquatic plants, and fisheries products. It reveals that Hg levels in fish and other edible aquatic species are mostly below the published safety limits, except for certain top trophic level fish (swordfish, tuna, marlin). The review also highlights gaps in Sri Lankan Hg assessments such as a total lack of data for methyl‑mercury in these aquatic species and food products. This data compilation and assessment will serve as an initial baseline for comparison with results from future monitoring and research studies in Sri Lanka while adding to the world-wide Hg database.

Methylmercury, cadmium and arsenic(III)-induced toxicity, oxidative stress and apoptosis in Pacific red snapper leukocytes

Methylmercury (MeHg), cadmium (Cd) and arsenic (As(III)) are among the most toxic metals in aquatic systems that have been associated with multiple animal and human health problems. This study investigated cytotoxic, oxidative stress, and apoptosis effects on fish leukocytes following their exposure to metals. A preliminary study indicated that leukocytes exposed to MeHg at a concentration of 0.01 mM, Cd at 0.05 mM, and As(III) at 2 mM showed a time-dependent cell viability reduction (around 40%), so they were selected for further experiments. To evaluate the effect of MeHg, Cd and As(III) on Pacific red snapper Lutjanus peru, we measured cytotoxicity, reactive oxygen species, antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT)), nitric oxide production, apoptosis-related and immune-related genes on head-kidney and spleen leukocytes following exposure to MeHg (0.01 mM), Cd (0.05 mM) and As(III) (2 mM) for 30 min and 2 h. Reactive oxygen species (ROS) generation highly increased in time-dependent doses in head-kidney leukocytes compared with the control group. Regarding antioxidant activity, SOD increased significantly in leukocytes exposed to any heavy metals after two h. Expressly, CAT activity decreased in those leukocytes exposed to Cd and As(III). Apoptotic function genes (Casp-2, Casp-3, and Casp-7) strongly up-regulated after heavy metal exposure, but Cd was more toxic. Finally, granzyme A and perforin 1 strongly up-regulated in leukocytes exposed to MeHg and As(III) compared with the control group. Our data showed that MeHg, Cd, and As(III) might have been cytotoxic and induced oxidative stress and apoptosis with possible biological consequences in fish.

Response of the freshwater diatom Halamphora veneta (Kützing) Levkov to copper and mercury and its potential for bioassessment of heavy metal toxicity in aquatic habitats

This study investigates the effects of copper and mercury on growth rate, chlorophyll a content, superoxide dismutase (SOD) activity, SOD mRNA gene expression, and frustule morphology of the benthic freshwater diatom Halamphora veneta (Kützing) Levkov and the potential utility of each for toxicity assessment in aquatic habitats. Results showed the following: (1) Compared to mercury, exposure to copper resulted in greater growth inhibition of H. veneta even at low concentrations and after short durations of exposure; (2) high accumulation of chlorophyll a in H. veneta is a stress response to the presence of heavy metals; (3) SOD activity and SOD gene expression varied in H. veneta according to the concentration, exposure time, and type of heavy metal; and (4) exposure to mercury resulted in deformity in the shape and an increase in size of the frustule of H. veneta. Growth rate, chlorophyll a content, SOD activity and gene expression, and frustule morphology of H. veneta are all potential candidates for the toxicological assessment of copper and mercury in aquatic habitats.

In Vivo Mercury Demethylation in a Marine Fish (Acanthopagrus schlegeli)

Mercury (Hg) in fish has attracted public attention for decades, and methylmercury (MeHg) is the predominant form in fish. However, the in vivo MeHg demethylation and its influence on Hg level in fish have not been well-addressed. The present study investigated the in vivo demethylation process in a marine fish (black seabream, Acanthopagrus schlegeli) under dietary MeHg exposure and depuration and quantified the biotransformation and interorgan transportation of MeHg by developing a physiologically based pharmacokinetic (PBPK) model. After exposure, we observed a 2-fold increase of the whole-body inorganic Hg (IHg), indicating the existence of an in vivo demethylation process. The results strongly suggested that the intestine played a predominant role in MeHg demethylation with a significant rate (6.6 ± 1.7 day^-1) during exposure, whereas the hepatic demethylation appeared to be an extremely slow (0.011 ± 0.001 day^-1) process and could hardly affect the whole-fish Hg level. Moreover, demethylation in the intestine served as an important pathway for MeHg detoxification. Our study also pointed out that in vivo MeHg demethylation could influence Hg level and speciation in fish although food is the major pathway for Hg accumulation. Enhancing in vivo MeHg biotransformation (especially in the intestine) could be a potential key solution in minimizing Hg contamination in fish. The related factors involved in intestinal demethylation deserve more attention in the future.

Metal bioaccumulation and detoxification processes in cephalopods: A review

In recent decades, cephalopods have been shown to have very high capacities to accumulate most trace elements, regardless of whether they are essential (e.g., Cu and Zn) or non-essential (e.g., Ag and Cd). Among the different pathways of exposure to trace elements, the trophic pathway appears to be the major route of assimilation for numerous metals, including Cd, Co, Hg and Zn. Once assimilated, trace elements are distributed in the organism, accumulating in storage organs. The digestive gland is the main organ in which many trace elements accumulate, whichever of the exposure pathway. For example, this organ can present Cd concentrations reaching hundreds to thousands of ppm for some species, even though the digestive gland represents only a small proportion of the total mass of the animal. Such a specific organotropism towards the digestive gland of both essential and non-essential elements, regardless of the exposure pathway, poses the question of the detoxification processes evolved by cephalopods in order to sustain these high concentrations. This paper reviews the current knowledge on the bioaccumulation of trace elements in cephalopods, the differences in pharmaco-dynamics between organs and tissues, and the detoxification processes they use to counteract trace element toxicity. A peculiar focus has been done on the bioaccumulation within the digestive gland by investigating the subcellular locations of trace elements and their protein ligands.

Hg and Se exposure in brain tissues of striped dolphin (Stenella coeruleoalba) and bottlenose dolphin (Tursiops truncatus) from the Tyrrhenian and Adriatic Seas

In this study we analyzed Hg and Se concentrations in dolphin brain tissues of fifteen specimens of striped dolphin (Stenella coeruleoalba) and eight specimens of bottlenose dolphin (Tursiops truncatus) stranded in the Tyrrhenian and Adriatic Seas, in order to assess the toxicological risks associated with Hg exposure. High Hg concentrations were found in brain tissues of both analyzed specie (1.86-243 mg/kg dw for striped dolphin and 2.1-98.7 mg/kg dw for bottlenose dolphin), exceeding levels associated with marine mammals neurotoxicity. Althougth the results clearly suggest that the protective effects of Se against Hg toxicity occur in cetaceans' brain tissues, a molar excess of mercury with respect to selenium was found, particularly in adult specimens of Stenella coeruleoalba. On contrary, negligible neurotoxicological risks were found for Tursiops truncatus specimens, due to detoxification processes. Data obtained allowed to prove a more marked neurotoxicological risk for adult specimens of Stenella coeruleoalba in both Tyrrhenian and Adriatic Seas.

Environmental remediation of heavy metal ions from aqueous solution through hydrogel adsorption: a critical review

Heavy metal ions such as Cd(2+), Pb(2+), Cu(2+), Mg(2+), and Hg(2+) from industrial waste water constitute a major cause of pollution for ground water sources. These ions are toxic to man and aquatic life as well, and should be removed from wastewater before disposal. Various treatment technologies have been reported to remediate the potential toxic elements from aqueous media, such as adsorption, precipitation and coagulation. Most of these technologies are associated with some shortcomings, and challenges in terms of applicability, effectiveness and cost. However, adsorption techniques have the capability of effectively removing heavy metals at very low concentration (1-100 mg/L). Various adsorbents have been reported in the literature for this purpose, including, to a lesser extent, the use of hydrogel adsorbents for heavy metal removal in aqueous phase. Here, we provide an in-depth perspective on the design, application and efficiency of hydrogel systems as adsorbents.