Warmer temperature increases mercury toxicity in a marine copepod

Elevated temperature as a dominant driver to aggravate cadmium toxicity: Investigations through toxicokinetics and omics

Despite the great interest in the consequences of global change stressors on marine organisms, their interactive effects on cadmium (Cd) bioaccumulation/biotoxicity are very poorly explored, particularly in combination with the toxicokinetic model and molecular mechanism. According to the projections for 2100, this study investigated the impact of elevated pCO2 and increased temperature (isolated or joint) on Cd uptake dynamics and transcriptomic response in the marine copepod Tigriopus japonicus. Toxicokinetic results showed significantly higher Cd uptake in copepods under increased temperature and its combination with elevated pCO2 relative to the ambient condition, linking to enhanced Cd bioaccumulation. Transcriptome analysis revealed that, under increased temperature and its combination with elevated pCO2, up-regulated expression of Cd uptake-related genes but down-regulation of Cd exclusion-related genes might cause increased cellular Cd level, which not only activated detoxification and stress response but also induced oxidative stress and concomitant apoptosis, demonstrating aggravated Cd biotoxicity. However, these were less pronouncedly affected by elevated pCO2 exposure. Therefore, temperature seems to be a primary factor in increasing Cd accumulation and its toxicity in the future ocean. Our findings suggest that we should refocus the interactive effects between climate change stressors and Cd pollution, especially considering temperature as a dominant driver.

Genotoxic effects of marine pollutants on coastal meso-zooplankton populations - A mini-review

Meso-zooplankton plays a vital role in maintaining healthy marine ecosystems, and some of the taxa provide biological indications for the monitoring of environmental and climate change. Recently, several newly emerging stressors were shown to impact marine and coastal meso-zooplankton in some ways. Marine organisms' genomic core, tightly packed with high-level integrity, can be damaged by anthropogenic activities in coastal zones worldwide and impact their integrity. Genomic integrity loss leads to a cascade of effects on the destruction of the food chain sequences, from primary producers to higher invertebrates. Therefore, monitoring genomic integrity loss using ecotoxicological approaches that focus on genetic changes appears to be a suitable approach. A literature review shows that different stressors severely impact genomic integrity through DNA damage at different concentrations and exposure times. Contaminated sediments also strongly impact the genomic integrity of estuaries and adjacent coastal meso-zooplankton communities.

MAPK/ERK-PK(Ser11) pathway regulates divergent thermal metabolism of two congeneric oyster species

Pyruvate kinase (PK), as a key rate-limiting enzyme in glycolysis, has been widely used to assess the stress tolerance and sensitivity of organisms. However, its phosphorylation regulatory mechanisms mainly focused on human cancer research, with no reports in marine organisms. In this study, we firstly reported a conserved PK Ser11 phosphorylation site in mollusks, which enhanced enzyme activity by promoting substrate binding, thereby regulating divergent thermal metabolism of two allopatric congeneric oyster species with differential habitat temperature. It was phosphorylated by ERK kinase, and regulated by the classical MAPK pathway. The MAPK/ERK-PK signaling cascade responded to increased environmental temperature and exhibited stronger activation pattern in the relatively thermotolerant species (Crassostrea angulata), indicating its involvement in shaping temperature adaptation. These findings highlight the presence of complex and unique phosphorylation-mediated signaling transduction mechanisms in marine organisms, and provide new insights into the evolution and function of the crosstalk between classical pathways.

Global survey of hgcA-carrying genomes in marine and freshwater sediments: Insights into mercury methylation processes

Mercury (Hg) methylation is a microbially mediated process that produces methylmercury (MeHg), a bioaccumulative neurotoxin. A highly conserved gene pair, hgcAB, is required for Hg methylation, which provides a basis for identifying Hg methylators and evaluating their genomic composition. In this study, we conducted a large-scale omics analysis in which 281 metagenomic freshwater and marine sediment samples from 46 geographic locations across the globe were queried. Specific objectives were to examine the prevalence of Hg methylators, to identify horizontal gene transfer (HGT) events involving hgcAB within Hg methylator communities, and to identify associations between hgcAB and microbial biochemical functions/genes. Hg methylators from the phyla Desulfobacterota and Bacteroidota were dominant in both freshwater and marine sediments while Firmicutes and methanogens belonging to Euryarchaeota were identified only in freshwater sediments. Novel Hg methylators were found in the Phycisphaerae and Planctomycetia classes within the phylum Planctomycetota, including potential hgcA-carrying anammox metagenome-assembled genomes (MAGs) from Candidatus Brocadiia. HGT of hgcA and hgcB were identified in both freshwater and marine methylator communities. Spearman's correlation analysis of methylator genomes suggested that in addition to sulfide, thiosulfate, sulfite, and ammonia may be important parameters for Hg methylation processes in sediments. Overall, our results indicated that the biochemical drivers of Hg methylation vary between marine and freshwater sites, lending insight into the influence of environmental perturbances, such as a changing climate, on Hg methylation processes.

The role of warming in modulating neodymium effects on adults and sperm of Mytilus galloprovincialis

The use of rare earth elements (REEs) has been increasing and one of the most used is neodymium (Nd). Being an emergent contaminant, its negative impacts are poorly understood. Aquatic organisms are also threatened by climate change-related factors, as is the case of warming, which can change the effects of REEs. Thus, the impacts of Nd, warming, and the combination of both stressors were studied in adult mussels and sperm of the species Mytilus galloprovincialis, after an exposure period of 28 days (adults) and 30 min (sperm). The effects were evaluated through the analysis of biochemical and histopathological alterations in adults and biochemical and physiological responses given by sperm. The results showed that mussels only activated their biotransformation capacity when exposed to the stressors acting alone, which was insufficient to avoid lipid peroxidation. Furthermore, warming (alone and combined with Nd) also produces damage to proteins. The digestive gland was the most sensitive organ to Nd, presenting several histopathological alterations. In the case of sperm, all stressors induced lipid peroxidation, a higher oxygen demand, and a decrease in velocity, even if the sperm viability was maintained. It seems that warming influenced the effects of Nd to some extent. The present findings contribute significantly to the field of REEs environmental toxicology by offering valuable insights into the impacts of Nd on various biological levels of mussels. Additionally, within the context of climate change, this study sheds light on how temperature influences the effects of Nd. The obtained results indicate that both stressors can potentially compromise the overall health of mussel populations, thereby affecting other species reliant on them for food and habitat. Moreover, this study highlights impaired sperm health, which could adversely affect their reproductive capacity and ultimately lead to population decline.

A Meta-analysis Reveals Global Change Stressors Potentially Aggravate Mercury Toxicity in Marine Biota

Growing evidence demonstrates that global change can modulate mercury (Hg) toxicity in marine organisms; however, the consensus on such effect is lacking. Here, we conducted a meta-analysis to evaluate the effects of global change stressors on Hg biotoxicity according to the IPCC projections (RCP 8.5) for 2100, including ocean acidification (-0.4 units), warming (+4 °C), and their combination (acidification-warming). The results indicated an overall aggravating effect (ln RRΔ = -0.219) of global change on Hg toxicity in marine organisms, while the effect varied with different stressors; namely, acidification potentially alleviates Hg biotoxicity (ln RRΔ = 0.117) while warming and acidification-warming have an aggravating effect (ln RRΔ = -0.328 and -0.097, respectively). Moreover, warming increases Hg toxicity in different trophic levels, i.e., primary producers (ln RRΔ = -0.198) < herbivores (ln RRΔ = -0.320) < carnivores (ln RRΔ = -0.379), implying increasing trends of Hg biomagnification through the food web. Notably, ocean hypoxia appears to boost Hg biotoxicity, although it was not considered in our meta-analysis because of the small sample size. Given the persistent global change and combined effects of these stressors in marine environments, multigeneration and multistressor research is urgently needed to fully disclose the impacts of global change on Hg pollution and its risk.

Can temperature rise change the impacts induced by e-waste on adults and sperm of Mytilus galloprovincialis?

Nowadays, it is of utmost importance to consider climate change factors, such as ocean warming, since the risk of negative impacts derived from increased surface water temperature is predicted to be high to the biodiversity. The need for renewable energy technologies, to reduce greenhouse gas emissions, has led to the increasing use of rare earth elements (REEs). Dysprosium (Dy) is widely used in magnets, motors, electrical vehicles, and nuclear reactors, being considered a critical REE to technology due to its economic importance and high supply risk. However, the increasing use of this element contributes to the enrichment of anthropogenic REEs in aquatic systems. Nevertheless, the information on the potential toxicity of Dy is limited. Moreover, the effects of pollutants can be amplified when combined with climate change factors. Thus, this study aimed to assess the effects of Dy (10 μg/L) in the species Mytilus galloprovincialis under actual (17 °C) and predicted warming conditions (21 °C). The Dy concentration in contaminated mussels was similar between temperatures, probably due to the detoxification capacity in individuals under these treatments. The combined stressors affected the redox balance, but higher impacts were caused by Dy and warming acting alone. In terms of cellular damage, although Dy acting alone was prejudicial to mussels, warming and both stressors acting together induced higher levels of LPO and PC. The histopathological effects of Dy in the digestive tubules were independent of the temperature tested. Regarding effects on sperm, only warming induced cellular damage, while both stressors, alone and together, impaired sperm movement. Overall, this study highlights that warming might influence the effects induced by Dy, but greater impacts were caused by the element. Eventually, the tested stressors may have consequences on mussels' reproduction capacity as well as their growth, abundance, and survival.

Seawater warming intensifies nickel toxicity to a marine copepod: a multigenerational perspective

Due to human activities, marine organisms are frequently co-stressed with nickel (Ni) pollution and seawater warming; nevertheless, very scarce information is known about their interaction in marine biota under a multigenerational scenario. Here, after verifying the interaction of Ni and warming via a 48-h acute test, we conducted a multigenerational experiment (F0-F2), in which the marine copepod Tigriopus japonicus was exposed to Ni at environmentally realistic concentrations (0, 2, and 20 µg/L) under ambient (22℃) and predicted seawater warming (26℃) conditions. Ni accumulation and the important life history traits were analyzed for each generation. Results showed that Ni exposure caused Ni bioaccumulation and thus compromised the survivorship and egg production of T. japonicus. In particular, seawater warming significantly increased Ni accumulation, thus intensifying the negative effects of Ni on its survivorship and development. Overall, this study suggests that Ni multigenerational exposure even at environmentally realistic concentrations could produce a significant impact on marine copepod's health, and this impact would be intensified under the projected seawater warming, providing a mechanistic understanding of the interaction between warming and Ni pollution in marine organisms from a multigenerational perspective.

Metal-specific biomagnification and trophic dilution in the coastal foodweb of the California sea lion (Zalophus californianus) off Bahía Magdalena, Mexico: The role of the benthic-pelagic foodweb in the trophic transfer of trace and toxic metals

Trace metals concentrations along with stable isotopes ratios were measured in marine algae, sea grass, sponges, echinoderms, mollusks, crustaceans, fishes, and the California sea lion, to assess the bioaccumulation potential and detect potential risks for top predators off Bahia Magdalena, Mexico. We assessed the trophic magnification factor (TMF) to determine the potential for biomagnification of 11 trace metals. The concentrations of Fe and Zn were one order of magnitude higher than all other metals. Concentrations of As, Cu, Cd, Co, Cr, Fe, Mn and Ni correlated negatively with trophic level, supporting trophic dilution (TMF < 1, p > 0.05), while Zn and Hg had significant trophic magnification (TMF > 1, p < 0.05) when assessing only the benthic-pelagic foodweb. This research provides a baseline concentration of metals in multiple species, metal-specific foodweb bioaccumulation and biomagnification of mercury, underscoring the key role of the macrobenthic community as biovectors for trophic transfer of Hg through the foodweb to the California sea lion.

Concentration of mercury and other metals in an Arctic planktonic food web under a climate warming scenario

Arctic marine ecosystems act as a global sink of mercury (Hg) and other metals, and high concentrations of these have been measured in higher trophic-level organisms. Nevertheless, the concentrations of metals at the basis of the marine food web in the Arctic is less known despite the likelihood of biomagnification from dietary sources. We investigated the concentrations of mercury (Hg) and other metals in different size fractions of plankton in West Greenland. All size fractions contained detectable levels of Hg (ranging from 4.8 to 241.3 ng g dw-1) at all stations, although with high geographic variability, likely reflecting the sources of mercury (e.g., meltwater). In many cases, the concentrations in the larger-size fractions were lower than in the smaller-size fractions, suggesting depuration through the metabolic activity of mesozooplankton. Concentrations of Cd, Pb, V, Ni, and Cr were higher than previously reported elsewhere in the Arctic.

Mercury contamination in seafood from an aquatic environment impacted by anthropic activity: seasonality and human health risk

Petroleum activity and the dumping of domestic and industrial sewage are important sources of mercury (Hg) contamination in the aquatic environment. Thus, this article aimed to biomonitor the Hg concentration in fish, mussels, and swimming crabs of commercial importance in southeastern Brazil. The quantifications were carried out over a year to verify the influence of seasonality. Finally, a risk assessment was applied to identify whether the concentrations found could lead to long-term damage to the population. Our results indicate that the contaminations were higher in spring, summer, and winter than in autumn, mainly among fish and swimming crabs. The results of quantification in the animal and estimated monthly intake, despite being below the limit established nationally and internationally, were indicative of risk for these two animals after calculating the Hazard quotient. The highest risk values were attributed to the infant population. Based on the data generated by this work, the consumption of mussels is encouraged throughout the year, to the detriment of the other types of seafood studied, especially during summer, spring, and winter. Our work reinforces the importance of risk assessment for a more reliable understanding of the impact of contaminants in seafood on the population's health.

Nanoplastics pose a greater effect than microplastics in enhancing mercury toxicity to marine copepods

Due to human activities, high abundances of nano/microplastics (N/MPs) concurrent with metal pollution have become a serious problem in the global marine environment. Because of displaying a high surface-area-to-volume ratio, N/MPs can serve as the carriers of metals and thus increase their accumulation/toxicity in marine biota. As one of the most toxic metals, mercury (Hg) causes adverse effects on marine organisms but whether environmentally relevant N/MPs can play a vector role of this metal in marine biota, as well as their interaction, is poorly known. To evaluate the vector role of N/MPs in Hg toxicity, we first performed the adsorption kinetics and isotherms of N/MPs and Hg in seawater, as well as ingestion/egestion of N/MPs by marine copepod Tigriopus japonicus, and second, the copepod T. japonicus was exposed to polystyrene (PS) N/MPs (500-nm, 6-μm) and Hg in isolation, combined, and incubated forms at environmentally relevant concentrations for 48 h. Also, the physiological and defense performance including antioxidant response, detoxification/stress, energy metabolism, and development-related genes were assessed after exposure. The results indicated N/MPs significantly increased Hg accumulation and thus its toxicity effects in T. japonicus as exemplified by decreased transcription of genes related to development and energy metabolism and increased transcriptional levels of genes functioning in antioxidant and detoxification/stress defense. More importantly, NPs were superimposed onto MPs and produced the most vector effect in Hg toxicity to T. japonicus, especially in the incubated forms. Overall, this study highlighted the role of N/MPs as a potential risk factor for increasing the adverse effects of Hg pollution, and emphasized the adsorption forms of contaminants by N/MPs should doubly be considered in the continuing researches.

Will warmer summers increase the impact of UV filters on marine bivalves?

Marine organisms are constantly exposed to multiple stressors including pollutants released into the environment, such as personal care products (PCPs), and climate change-derived factors, namely warming, which are aggravated by anthropogenic drivers and pose increasing pressure on coastal ecosystems. Avobenzone (AVO) is one of the most used ultraviolet (UV) filters in PCPs which have been increasingly used and, thereby, identified in aquatic environments. However, data regarding the influence of warming on the impacts caused by AVO in bivalves is lacking. Mussels are considered good bioindicators thus being often employed in ecotoxicology studies. Hence, the present study aimed to evaluate the toxic effects of an environmentally relevant concentration of AVO (0.5 μg/L) and warming (21 °C), acting alone or in combination, on sperm and adults of the Mediterranean mussel species Mytilus galloprovincialis, through in vitro and in vivo tests, respectively. AVO and warming effects were evaluated by assessing oxidative status, viability, genotoxicity, motility, and kinetics in sperm, together with the quantification of energy content, metabolic capacity, biological defence mechanisms, cellular damage, and neurotoxicity in adults. AVO induced genotoxicity and increased respiration rate in sperm while enhancing the biotransformation enzymes' activity in adults. Exposure to warming led to an increase in respiration rate, ROS overproduction, cellular damage, and viability decrease in sperm whereas metabolic capacity increased in adults. AVO combined with warming caused oxidative stress, cellular damage, genotoxicity, and decreased motility in sperm, while only antioxidant enzymes' activity was enhanced in adults. Overall, the present study demonstrated that when acting in combination the effects of both stressors were more prominent. Furthermore, considering the multiple-stressor scenario tested, major toxic effects occurred in male gametes in comparison to adults.

Effects of N-acetyl-l-cysteine on chronic heat stress-induced oxidative stress and inflammation in the ovaries of growing pullets

The aims of this study were to investigate the effects of supplemental N-acetyl-l-cysteine (NAC) on chronic heat stress-induced oxidative stress and inflammation in the ovaries of growing pullets. A total of 120, 12-wk-old, Hy-Line Brown hens were randomly separated into 4 groups with 6 replicates of 5 birds in each group for 21 d. The 4 treatments were as follows: the CON group and CN group were supplemented with basal diet or basal diet with 1 g/kg NAC, respectively; and the HS group and HSN group were heat-stressed groups supplemented with basal diet or basal diet with 1 g/kg NAC, respectively. The results indicated that the ovaries suffered pathological damage due to chronic heat stress and that NAC effectively ameliorated these changes. Compared with the HS group, antioxidant enzyme activities (including SOD, GSH-Px, CAT, and T-AOC) were enhanced, while the MDA contents and the expression levels of HSP70 were decreased in the HSN group. In addition, NAC upregulated the expression levels of HO-1, SOD2, and GST by upregulating the activity of Nrf2 at different time points to mitigate oxidative stress caused by heat exposure. Simultaneously, NAC attenuated chronic heat stress-induced NF-κB pathway activation and decreased the expression levels of the proinflammatory cytokines IL-8, IL-18, TNF-α, IKK-α, and IFN-γ. Cumulatively, our results indicated that NAC could ameliorate chronic heat stress-induced ovarian damage by upregulating the antioxidative capacity and reducing the secretion of proinflammatory cytokines.

Toxicological risk of mercury for fish and invertebrate prey in the Arctic

We assessed the risks of mercury (Hg) to Arctic marine and freshwater fish by compiling published muscle Hg concentrations and information on tissue concentrations associated with adverse effects. The assessment included 333 groups of fish representing 35 genera and 14,002 individuals sampled from sites across the circumpolar Arctic. Mean or median Hg concentrations in fish muscle varied widely from 0.005 μg/g ww to a maximum of 2.2 μg/g ww. Results indicate that most (n = 139 of 333 or ~ 42%) Arctic fish are not at risk for Hg toxicity, based on the large number of fish mean or median muscle Hg concentrations below 0.1 μg/g ww. A smaller number of the identified groups (n = 76 of 333 or ~ 23%) of Arctic fish had mean or median Hg concentrations consistent with moderate (0.3-0.5 μg/g ww), high (0.5-2 μg/g ww), and severe risk (≥2 μg/g ww). Most of the fish with Hg concentrations in these risk categories were long-lived predators (e.g., non-anadromous Arctic char, northern pike, lake trout, Greenland halibut, Greenland shark). We also, for the first time, conducted a risk assessment of Arctic marine and freshwater invertebrates to evaluate the potential for Hg effects at lower trophic levels and to support risk assessment for Arctic fish. The vast majority (90%) of site-specific Hg or methylmercury (MeHg) concentrations in taxa of marine and freshwater invertebrates (n = 321) were < 0.5 μg/g dw, which is well below critical body residues of Hg in aquatic invertebrates associated with acute and sublethal effects determined in laboratory dosing studies. As the screening-level approach we carried out in the present study is not indicative of actual effects, more studies which directly evaluate the effects of Hg exposure in Arctic fish species are needed. The information here will be of use to Article 22 (Effectiveness Evaluation) of the Minamata Convention.

Multiple anthropogenic stressors in the Galápagos Islands' complex social-ecological system: Interactions of marine pollution, fishing pressure, and climate change with management recommendations

For decades, multiple anthropogenic stressors have threatened the Galápagos Islands. Widespread marine pollution such as oil spills, persistent organic pollutants, metals, and ocean plastic pollution has been linked to concerning changes in the ecophysiology and health of Galápagos species. Simultaneously, illegal, unreported, and unregulated fishing are reshaping the composition and structure of endemic and native Galápagos pelagic communities. In this novel review, we discuss the impact of anthropogenic pollutants and their associated ecotoxicological implications for Galápagos species in the face of climate change stressors. We emphasize the importance of considering fishing pressure and marine pollution, in combination with climate-change impacts, when assessing the evolutionary fitness of species inhabiting the Galápagos. For example, the survival of endemic marine iguanas has been negatively affected by organic hydrocarbons introduced via oil spills, and endangered Galápagos sea lions exhibit detectable concentrations of DDT, triggering potential feminization effects and compromising the species' survival. During periods of ocean warming (El Niño events) when endemic species undergo nutritional stress, climate change may increase the vulnerability of these species to the impacts of pollutants, resulting in the species reaching its population tipping point. Marine plastics are emerging as a deleterious and widespread threat to endemic species. The Galápagos is treasured for its historical significance and its unparalleled living laboratory and display of evolutionary processes; however, this unique and iconic paradise will remain in jeopardy until multidisciplinary and comprehensive preventative management plans are put in place to mitigate and eliminate the effects of anthropogenic stressors facing the islands today. We present a critical analysis and synthesis of anthropogenic stressors with some progress from local and international institutional efforts and call to action more precautionary measures along with new management philosophies focused on understanding the processes of change through research to champion the conservation of the Galápagos. Integr Environ Assess Manag 2022;00:1-26. © 2022 SETAC.

Mercury can be transported into marine copepod by polystyrene nanoplastics but is not bioaccumulated: An increased risk?

Plastic pollution is a serious problem in the global marine environment because it can produce negative effects at the biological and ecological levels. Due to large surface-area-to-volume ratio and inherent hydrophobicity, nanoplastics can serve as carriers of contaminants, and may affect their fate and toxicity in marine environments. However, the combined effects of nanoplastics and mercury (Hg) in marine organisms have not been well characterized. In this study, after verifying the ingestion of polystyrene nano-size plastics (PS NPs, 50 nm) by the copepod Tigriopus japonicus and adsorption of Hg to PS NPs, we investigated the effects of PS NPs and Hg exposure (alone or in combination) for 48 h on the copepods. Specifically, a 72-h depuration was performed after 48 h exposure. The results showed that after 48 h exposure, the copepod's Hg concentration was significantly increased in the combined exposure group compared to that in the Hg treatment group, but these differences did not persist following 24 h of depuration. Therefore, PS NPs transported Hg into the copepods but did not promote Hg bioaccumulation. Treatment with PS NPs alone did not induce toxicity in T. japonicus, but co-exposure to PS NPs and Hg resulted in elevated transcription of genes related to energy production, antioxidant response, and detoxification/stress defense when compared with Hg treatment alone, demonstrating the synergistic interaction between PS NPs and Hg. Our findings contribute to a comprehensive understanding about the combined toxicity of nanoplastics and metals and the potential ecological risks of associated with these effects in marine environments.

Predicted Near-Future Oceanic Warming Enhances Mercury Toxicity in Marine Copepods

The effects of acute mercury exposure (118 µg/L) on the marine copepod Tigriopus japonicus were examined at 22 and 25 °C for 24 h and compared with controls. Mercury accumulation and seven genes related to antioxidant/stress responses were analyzed after exposure. The 24-h LC₅₀ value decreased in the warmer environment and mercury accumulation was elevated. Under both temperatures, mercury significantly affected the expression of all analyzed genes and probably caused oxidative stress. Intriguingly, at the same mercury concentration, most genes were upregulated at the higher relative to the lower temperature, and the copepods likely initiated more compensatory reactions to counteract increased mercury toxicity associated with the warmer temperature. Overall, this study suggests a molecular mechanism by which marine copepods could respond to future oceanic warming and mercury pollution.

Multigenerational study of life history traits, bioaccumulation, and molecular responses of Pseudodiaptomus annandalei to cadmium

Metal pollution provide a substantial challenge for environmental health. This study investigated the multigeneration effects of cadmium on populations of the copepod species Pseudodiaptomus annandalei, exposed to a sublethal concentration, 40 µg/L of cadmium (Cd), over 10 generations. At the end of each generation, copepod individuals were collected to estimate fecundity, bioaccumulation, and real time qPCR quantification of selected differentially expressed genes to evaluate Cd effects and sex-specific responses of copepods across multiple generations. Our results revealed a sex-specific accumulation of Cd integrating 10 successive generations. The concentration of Cd was significantly higher (p < 0.05) in males than in females. We also observed a generational increase in Cd accumulation. Fecundity increased, with the exception of the first generation, possibly as a compensation for a decrease of copepod population size under Cd exposure. Protein expression of copepods exposed to Cd occurred in a sex-specific manner. Hemerythrin was mostly up-regulated in both copepod sexes exposed to Cd with males having the highest expression levels, while heat shock protein 70 was mostly up-regulated in males and down-regulated in female copepods, both exposed to Cd. Although copepods are known to develop adaptive mechanisms to tolerate toxic chemicals, continuous exposure to metals could lead to the bioaccumulation of metals in their offspring through maternal transfer and direct uptake from the medium over several generations. As a consequence, increased metal concentrations in copepods could result in physiological damage, reducing their fitness, and possibly compromise copepod population structures. This study showed that mortality, life history traits and molecular responses of a copepod species provided important toxicological endpoints and bio-markers for environmental risk assessments. Environmental pressure resulting from continuous exposure to persistent pollutants like Cd, could have evolutionary significance. The tendency for copepods to selectively adapt to a toxic environment through modifications, could increase their chance of survival over a long term.

Projected near-future ocean acidification decreases mercury toxicity in marine copepods

Here, we examined the combinational effect of ocean acidification (OA) and mercury (Hg) in the planktonic copepod Pseudodiaptomus annandalei in cross-factored response to different pCO₂ (400, 800 μatm) and Hg (control, 1.0 and 2.5 μg/L) exposures for three generations (F0-F2), followed by single-generation recovery (F3) under clean condition. Several phenotypic traits and Hg accumulation were analyzed for F0-F3. Furthermore, shotgun-based quantitative proteomics was performed for F0 and F2. Our results showed that OA insignificantly influenced the traits. During F0-F2, combined exposure reduced Hg accumulation as compared with the counterpart Hg treatment, supporting the mitigating effect of OA on Hg toxicity in copepods. Proteomics analysis indicated that the copepods probably increased energy production/storage and stress response to ensure physiological resilience against OA. However, Hg induced many toxic events (e.g., energy depletion and degenerated organomorphogenesis/embryogenesis for F0; cell cycle arrest and detrimental stress-defense for F2), which were translated to the population-level adverse outcome, i.e., compromised growth/reproduction. Particularly, compensatory proteome response was identified (e.g., increased immune defense for F0; energetic compensation and enhanced embryogenesis for F2), accounting for a negative interaction between OA and Hg. Together, this study provides the molecular mechanisms behind the effects of OA and Hg pollution in marine copepods.

Interactions between mercury and environmental factors: A chemometric assessment in seafood from an eutrophic estuary in southeastern Brazil

Guanabara Bay (GB) is an estuary in Brazil, constantly the target of pollutants, such as mercury (Hg). Thus, our study aimed to evaluate (i) total mercury (THg) content in shrimp and squid species from GB; (ii) associate THg content to contamination in swimming crabs; (iii) explore potential differences between species, and size; (iv) correlate abiotic water data to the determined THg contents; (v) verify if Hg concentrations are below acceptable limits. Swimming crabs showed greater Hg contamination compared to other species. For shrimp only biometric variables are related to Hg, while for squid, only abiotic. Only squids did not show a correlation between Hg and animal size. Finally, the detected Hg values are below the tolerable limits established by legislations. Our results indicate that the dynamics of Hg contamination differs between groups and that further studies are needed to elucidate the mechanisms that affect bioaccumulation in different species.

Inorganic mercury effects on biomarker gene expressions of a freshwater amphipod at two temperatures

Mercury (Hg) is a global contaminant resulting of both natural processes and human activities. In aquatic environments, studies conducted on vertebrates highlighted changes of gene expression or activity of antitoxic and oxidative enzymes. However, although Hg is a highly toxic compound in aquatic environments, only a few studies have evaluated the lethal and sublethal effects of inorganic Hg on Gammarus sp. Therefore, this study aimed at evaluating the effects of inorganic Hg (HgCl₂) on the expression of 17 genes involved in crucial biological functions or mechanisms for organisms, namely respiration, osmoregulation, apoptosis, immune and endocrine system, and antioxidative and antitoxic defence systems. The study was performed in males of the freshwater amphipod Gammarus pulex exposed to two environmentally relevant concentrations (50 and 500 ng/L) at two temperature regime fluctuations (16 °C and 20 °C +/-2 °C) for 7 and 21 days. Results showed that G. pulex mortality was dependent on Hg concentration and temperature; the higher the concentration and temperature, the higher the mortality rate. In addition, the Integrated Biomarker Response emphasized that HgCl₂ toxicity was dependent on the concentration, time and temperature of exposure. Overall, antioxidant and antitoxic defences, as well as the endocrine and immune systems, were the biological functions most impacted by Hg exposure (based on the concentration, duration, and temperature tested). Conversely, osmoregulation was the least affected biological function. The results also demonstrated a possible adaptation of G. pulex after 21 days at 500 ng/L, regardless of the exposure temperature. This study allowed us to show that Hg deregulates many crucial biological functions after a short exposure, but that during a long exposure, an adaptation phenomenon could occur, regardless of temperature.