Physiological impacts of acute Cu exposure on deep-sea vent mussel Bathymodiolus azoricus under a deep-sea mining activity scenario

Potential biomarkers of metal toxicity in deep-sea invertebrates - A critical review of the omics data

Deep-sea mining (DSM) activities are expected to release potentially toxic metal mixtures through the generation of sediment plumes to the marine environment. This may disrupt the normal functioning of biological mechanisms, adversely affecting deep-sea invertebrate organisms. It is thus essential to understand the ecotoxicological effects from these toxic elements in deep-sea organisms and the omics approaches applied to ecotoxicology are seen as promising tools. Here, we provide an overview of the principal biological modifications identified in deep-sea invertebrates when exposed to metals and critically evaluate the current knowledge and discuss which potential biomarkers may be useful after metal exposure. Most of the 50 omics studies on deep-sea invertebrates revised are comparative transcriptomes (n = 41). Forty-three potential biomarker candidates are highlighted from immune system, 46 from cellular metabolism and 29 from oxidative stress. The processes mostly affected by metal toxicity in deep-sea invertebrates are related to innate immune defense; sulfur, chitin, and catabolic metabolism; antioxidation; and detoxification. We acknowledge the current limitations and future perspectives for their uses and emphasize the need to invest in further ecotoxicological studies using the omics approaches.

Integrated transcriptomic and metabolomic approaches reveal molecular response and potential biomarkers of the deep-sea mussel Gigantidas platifrons to copper exposure

Metal pollution caused by deep-sea mining activities has potential detrimental effects on deep-sea ecosystems. However, our knowledge of how deep-sea organisms respond to this pollution is limited, given the challenges of remoteness and technology. To address this, we conducted a toxicity experiment by using deep-sea mussel Gigantidas platifrons as model animals and exposing them to different copper (Cu) concentrations (50 and 500 μg/L) for 7 days. Transcriptomics and LC-MS-based metabolomics methods were employed to characterize the profiles of transcription and metabolism in deep-sea mussels exposed to Cu. Transcriptomic results suggested that Cu toxicity significantly affected the immune response, apoptosis, and signaling processes in G. platifrons. Metabolomic results demonstrated that Cu exposure disrupted its carbohydrate metabolism, anaerobic metabolism and amino acid metabolism. By integrating both sets of results, transcriptomic and metabolomic, we find that Cu exposure significantly disrupts the metabolic pathway of protein digestion and absorption in G. platifrons. Furthermore, several key genes (e.g., heat shock protein 70 and baculoviral IAP repeat-containing protein 2/3) and metabolites (e.g., alanine and succinate) were identified as potential molecular biomarkers for deep-sea mussel's responses to Cu toxicity. This study contributes novel insight for assessing the potential effects of deep-sea mining activities on deep-sea organisms.

Toxicology assessment of deep-sea mining impacts on Gigantidas platifrons: A comparative in situ and laboratory metal exposure study

Deep-sea toxicology is essential for deep-sea environmental impact assessment. Yet most toxicology experiments are conducted solely in laboratory settings, overlooking the complexities of the deep-sea environment. Here we carried out metal exposure experiments in both the laboratory and in situ, to compare and evaluate the response patterns of Gigantidas platifrons to metal exposure (copper [Cu] or cadmium [Cd] at 100 μg/L for 48 h). Metal concentrations, traditional biochemical parameters, and fatty acid composition were assessed in deep-sea mussel gills. The results revealed significant metal accumulation in deep-sea mussel gills in both laboratory and in situ experiments. Metal exposure could induce oxidative stress, neurotoxicity, an immune response, altered energy metabolism, and changes to fatty acid composition in mussel gills. Interestingly, the metal accumulating capability, biochemical response patterns, and fatty acid composition each varied under differing experimental systems. In the laboratory setting, Cd-exposed mussels exhibited a higher value for integrated biomarker response (IBR) while in situ the Cu-exposed mussels instead displayed a higher IBR value. This study emphasizes the importance of performing deep-sea toxicology experiments in situ and contributes valuable data to a standardized workflow for deep-sea toxicology assessment.

Ocean acidification impact on the uptake of trace elements by mussels and their biochemical effects

This study delves into the intricate interplay between ocean acidification (OA), metal bioaccumulation, and cellular responses using mussels (Mytilus galloprovincialis) as bioindicators. For this purpose, environmentally realistic concentrations of isotopically labelled metals (Cd, Cu, Ag, Ce) were added to investigate whether the OA increase would modify metal bioaccumulation and induce adverse effects at the cellular level. The study reveals that while certain elements like Cd and Ag might remain unaffected by OA, the bioavailability of Cu and Ce could potentially escalate, leading to amplified accumulation in marine organisms. The present findings highlight a significant rise in Ce concentrations within different mussel organs under elevated pCO2 conditions, accompanied by an increased isotopic fractionation of Ce (140/142Ce), suggesting a heightened potential for metal accumulation under OA. The results suggested that OA influenced metal accumulation in the gills of mussels. Conversely, metal accumulation in the digestive gland was unaffected by OA. The exposure to both trace metals and OA affects the biochemical responses of M. galloprovincialis, leading to increased metabolic capacity, changes in energy reserves, and alterations in oxidative stress markers, but the specific effects on other biomarkers (e.g., lipid peroxidation, some enzymatic responses or acetylcholinesterase activity) were not uniform, suggesting complex interactions between the stressors and the biochemical pathways in the mussels.

To live or die: "Fine-tuning" adaptation revealed by systemic analyses in symbiotic bathymodiolin mussels from diverse deep-sea extreme ecosystems

Hydrothermal vents (HVs) and cold seeps (CSs) are typical deep-sea extreme ecosystems with their own geochemical characteristics to supply the unique living conditions for local communities. Once HVs or CSs stop emission, the dramatic environmental change would pose survival risks to deep-sea organisms. Up to now, limited knowledge has been available to understand the biological responses and adaptive strategy to the extreme environments and their transition from active to extinct stage, mainly due to the technical difficulties and lack of representative organisms. In this study, bathymodiolin mussels, the dominant and successful species surviving in diverse deep-sea extreme ecosystems, were collected from active and extinct HVs (Southwest Indian Ocean) or CSs (South China Sea) via two individual cruises. The transcriptomic analysis and determination of multiple biological indexes in stress defense and metabolic systems were conducted in both gills and digestive glands of mussels, together with the metagenomic analysis of symbionts in mussels. The results revealed the ecosystem- and tissue-specific transcriptional regulation in mussels, addressing the autologous adaptations in antioxidant defense, energy utilization and key compounds (i.e. sulfur) metabolism. In detail, the successful antioxidant defense contributed to conquering the oxidative stress induced during the unavoidable metabolism of xenobiotics commonly existing in the extreme ecosystems; changes in metabolic rate functioned to handle toxic matters in different surroundings; upregulated gene expression of sulfide:quinone oxidoreductase indicated an active sulfide detoxification in mussels from HVs and active stage of HVs & CSs. Coordinately, a heterologous adaptation, characterized by the functional compensation between symbionts and mussels in energy utilization, sulfur and carbon metabolism, was also evidenced by the bacterial metagenomic analysis. Taken together, a new insight was proposed that symbiotic bathymodiolin mussels would develop a "finetuning" strategy combining the autologous and heterologous regulations to fulfill the efficient and effective adaptations for successful survival.

Stressors of emerging concern in deep-sea environments: microplastics, pharmaceuticals, personal care products and deep-sea mining

Although most deep-sea areas are remote in comparison to coastal zones, a growing body of literature indicates that many sensitive ecosystems could be under increased stress from anthropogenic sources. Among the multiple potential stressors, microplastics (MPs), pharmaceuticals and personal care products (PPCPs/PCPs) and the imminent start of commercial deep-sea mining have received increased attention. Here we review recent literature on these emerging stressors in deep-sea environments and discuss cumulative effects with climate change associated variables. Importantly, MPs and PPCPs have been detected in deep-sea waters, organisms and sediments, in some locations in comparable levels to coastal areas. The Atlantic Ocean and the Mediterranean Sea are the most studied areas and where higher levels of MPs and PPCPs have been detected. The paucity of data for most other deep-sea ecosystems indicates that many more locations are likely to be contaminated by these emerging stressors, but the absence of studies hampers a better assessment of the potential risk. The main knowledge gaps in the field are identified and discussed, and future research priorities are highlighted to improve hazard and risk assessment.

A modelling framework to assess multiple metals impacts on marine food webs: Relevance for assessing the ecological implications of deep-sea mining based on a systematic review

Industrial deep-sea mining will release plumes containing metals that may disperse over long distances; however, there is no general understanding of metal effects on marine ecosystems. Thus, we conducted a systematic review in search of models of metal effects on aquatic biota with the future perspective to support Environmental Risk Assessment (ERA) of deep-sea mining. According to results, the use of models to study metal effects is strongly biased towards freshwater species (83% freshwater versus 14% marine); Cu, Hg, Al, Ni, Pb, Cd and Zn are the best-studied metals, and most studies target few species rather than entire food webs. We argue that these limitations restrain ERA on marine ecosystems. To overcome this gap of knowledge, we suggest future research directions and propose a modelling framework to predict the effects of metals on marine food webs, which in our view is relevant for ERA of deep-sea mining.

Bacillus coagulans XY2 ameliorates copper-induced toxicity by bioadsorption, gut microbiota and lipid metabolism regulation

Excessive copper pollutes the environment and endangers human health, attracting plenty of global attention. In this study, a novel strain named Bacillus coagulans XY2 was discovered to have a great copper tolerance and adsorption capacity. B. coagulans XY2 might maintain copper homeostasis through multisystem synergies of copper resistance, sulfur metabolism, Fe-S cluster assembly, and siderophore transport. In mice, by promoting the expression of SREBF-1 and SREBF-2 and their downstream genes, B. coagulans XY2 significantly inhibited the copper-induced decrease in weight growth rate, ameliorated dyslipidemia, restored total cholesterol and triglyceride contents both in serum and liver. Furthermore, B. coagulans XY2 recovered the diversity of gut microbiota and suppressed the copper-induced reduction in the ratio of Firmicutes to Bacteroidota. Serum metabolomics analysis showed that the alleviating effect of B. coagulans XY2 on copper toxicity was mainly related to lipid metabolism. For the first time, we demonstrated mechanisms of copper toxicity mitigation by B. coagulans XY2, which was related to self-adsorption, host copper excretion promotion, and lipid metabolism regulation. Moreover, working model of B. coagulans XY2 on copper homeostasis was predicted by whole-genome analysis. Our study provides a new solution for harmfulness caused by copper both in human health and the environment.

A multi-criteria decision analysis model for ship biofouling management in the Baltic Sea

Biofouling of ship hulls form a vector for the introduction of non-indigenous organisms worldwide. Through increasing friction, the organisms attached to ships' hulls increase the fuel consumption, leading to both higher fuel costs and air emissions. At the same time, ship biofouling management causes both ecological risks and monetary costs. All these aspects should be considered case-specifically in the search of sustainable management strategies. Applying Bayesian networks, we developed a multi-criteria decision analysis model to compare biofouling management strategies in the Baltic Sea, given the characteristics of a ship, its operating profile and operational environment, considering the comprehensive environmental impact and the monetary costs. The model is demonstrated for three scenarios (SC1-3) and sub-scenarios (A-C), comparing the alternative biofouling management strategies in relation to NIS (non-indigenous species) introduction risk, eco-toxicological risk due to biocidal coating, carbon dioxide emissions and costs related to fuel consumption, in-water cleaning and hull coating. The scenarios demonstrate that by the careful consideration of the hull fouling management strategy, both money and environment can be saved. We suggest biocidal-free coating with a regular in-water cleaning using a capture system is generally the lowest-risk option. The best biocidal-free coating type and the optimal in-water cleaning interval should be evaluated case-specifically, though. In some cases, however, biocidal coating remains a justifiable option.

Beyond deep-sea mining sublethal effects: Delayed mortality from acute Cu exposure of the cold-water octocoral Viminella flagellum

The potential release of metals, especially copper (Cu) during mining of seafloor massive sulphides (SMS), represents a potential toxicological threat to cold-water coral (CWC) habitats. Herein, we evaluated for the first time the response of the whip coral Viminella flagellum to short-term acute Cu exposure. Nubbins of V. flagellum were exposed to Cu concentrations of 0 (control); 60; 150; 250; 450 and 600 μg/L for 96 h. After exposure, V. flagellum nubbins were transferred to a continuous flow-through aquarium and feed once a day for 3 weeks. No immediate mortality was detected during the short-term Cu exposure. However, a delayed mortality, which was concentration dependent was observed. The first signs of tissue loss occurred after 1 week of recovery in non-contaminated conditions in V. flagellum nubbins previously exposed to Cu concentrations of 60 and 150 μg/L followed by nubbins exposed to Cu concentrations of 250, 450 μg/L after 2 weeks and 600 μg/L after 3 weeks. A delayed mortality impact should be considered in future Cu tolerance experiments and scenarios of deep-sea mining exploitation.

Global qualitative and quantitative distribution of micropollutants in the deep sea

Micropollutants (MPs) include a wide range of biological disruptors that can be toxic to wildlife and humans at very low concentrations (<1 μg/L). These mainly anthropogenic pollutants have been widely detected in different areas of the planet, including the deep sea, and have impacts on marine life. Because of this potential toxicity, the global distribution, quantity, incidence, and potential impacts of deep-sea MPs were investigated in a systematic review of the literature. The results showed that MPs have reached different zones of the ocean and are more frequently reported in the Northern Hemisphere, where higher concentrations are found. MPs are also concentrated in depths up to 3000 m, where they are also more frequently studied, but also extend deeper than 10,000 m. Potentially toxic metals (PTMs), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDTs), organotins, and polycyclic aromatic hydrocarbons (PAHs) were identified as the most prevalent and widely distributed MPs at ≥200 m depth. PTMs are widely distributed in the deep sea in high concentrations; aluminum is the most prevalent up to 3000 m depth, followed by zinc and copper. PCBs, organotins, hexachlorocyclohexanes (HCHs), PAHs, and phenols were detected accumulated in both organisms and environmental samples above legislated thresholds or known toxicity levels. Our assessment indicated that the deep sea can be considered a sink for MPs.

Biochemical and metabolic responses of the deep-sea mussel Bathymodiolus platifrons to cadmium and copper exposure

Greater interest in commercial deep-sea mining has been accompanied by mounting environmental concerns, including metal contamination resulting from mining activities. However, little is known about the toxic effects of metal exposure on deep-sea life. Given its ability to accumulate metals from the surrounding environment, its wide distribution at both vents and seeps, and its high abundance, the deep-sea mussel Bathymodiolus platifrons could serve as an ideal model to investigate the toxicological responses of deep-sea organisms to metal exposure. Here, we evaluated metal accumulation, traditional metal-related biomarkers, namely acid phosphatase (ACP), alkaline phosphatase (AKP), superoxide dismutase, catalase, reduced glutathione, metallothioneins, and malondialdehyde, as well as metabolic profiles in the gills of B. platifrons after a 7-day exposure to copper (100 μg/L), cadmium (500 μg/L), or copper-plus-cadmium treatments (100 μg/L Cu and 500 μg/L Cd). Metal exposure concentrations selected in this study can be found in deep-sea hydrothermal environments. Metal exposure resulted in significant metal accumulation in the gills of the mussel, indicating that B. platifrons has promise for use as an indicator of deep-sea metal pollution levels. Traditional biomarkers (AKP, ACP, and measured antioxidants) revealed cellular injury and oxidative stress in mussels following metal exposure. Metabolic responses in the three treatment groups indicated that metal exposure perturbed osmoregulation, energy metabolism, and nucleotide metabolism in mussels, in a response marked by differentially altered levels of amino acids, hypotaurine, betaine, succinate, glucose 6-phosphate, fructose 6-phosphate, guanosine, guanosine 5'-monophosphate, and inosine. Nevertheless, several uniquely altered metabolites were found in each treatment exposure group, suggesting dissimilar modes of toxicity between the two metal types. In the Cd-exposed group, the monosaccharide D-allose, which is involved in suppressing mitochondrial ROS production, was downregulated, a response consistent with oxidative stress in Cd-exposed B. platifrons. In the Cu-exposed group, the detected alterations in dopamine, dopamine-related, and serotonin-related metabolites together suggest disturbed neurotransmission in Cu-exposed B. platifrons. In the Cu-plus-Cd group, we detected a decline in fatty acid levels, implying that exposure to both metals jointly exerted a negative influence on the physiological functioning of the mussel. To the best of our knowledge, this is the first study to investigate changes in metabolite profiles in Bathymodiolus mussels exposed to metal. The findings reported here advance our understanding of the adverse impact of metal exposure on deep-sea life and can inform deep-sea mining assessments through the use of multiple biomarkers.

Ocean acidification effects on the stress response in a calcifying antarctic coastal organism: The case of Nacella concinna ecotypes

Ocean acidification (OA) could become a serious threat for the Antarctic marine ecosystem over coming years, as the solubility of atmospheric CO₂ and CaCO₃ minerals increases at lower temperatures. We evaluated the effect of OA on the stress response of the limpet Nacella concinna by measuring gene expression levels. The experiment was performed with the two ecotypes (Littoral and Sublittoral) of the species during 54 days (IPCC, 2019 scenario RCP8.5; control, ~375 ppm; low-pH treatment, ~923 ppm). Exposure to low-pH treatment during 15 days triggered the down-regulation of two heat-shock protein genes (HSP70A, HSP70B) only in sublittoral individuals. Little variation in the relative expression values of all genes in both ecotypes was observed probably, due to a historical exposure to the substantial daily natural pH fluctuations recorded in the study area during the experiment. This study provides relevant baseline data for future OA experiments on coastal species in Antarctica.

Functional, biochemical and molecular impact of sediment plumes from deep-sea mining on Mytilus galloprovincialis under hyperbaric conditions

The deep-sea is the biggest ecosystem in the world and despite the extreme conditions that characterize it, is highly biodiverse and complex. Deep-sea mining has been foreseen as a potential and concerning new stressor, and among the deep-sea mining associated stressors, sediment plumes, likely to be released into the water column as a side effect of mining, can reach habitats within a radius of more than a hundred kilometers. The present study examined the effects of suspended sediments of different grain sizes (63-125 μm, 125-250 μm and 250-500 μm) in the model species Mytilus galloprovincialis, at 4 bar, as a proxy to address the potential effects of sediment plumes, in the water column, with different grain sizes under high pressure conditions. Functional (filtration rate - FR), biochemical (catalase - CAT, glutathione s-transferase - GST, lipid peroxidation - LPO) and molecular (gene expression of [actin (ACTN), glutathione S-transferase alpha (GSTA), superoxide dismutase 2 (SOD2), catalase (CAT), heat shock protein 60 (HSP60), cytochrome c oxidase (COI) and DNA mismatch repair protein (MSH6)]) endpoints were studied in juvenile organisms. The FR decreased significantly for all tested grain size ranges, with a more severe effect for the particles with a diameter between 63 and 125 μm. In addition to the FR, significant changes were also observed for all tested biomarkers. Gene expression was significantly downregulated for CAT and ACTN. Overall, this study demonstrated that the smaller sized particles are the ones leading to more severe effects. Given their high dispersion potential and longer suspension periods under mining operation scenarios, particular attention should be given to the release of sediment plumes that may affect deep-sea environments and the water column. It is, therefore, vital to create standards and guidelines for sustainable mining practices.

Metal adaptation strategies of deep-sea Bathymodiolus mussels from a cold seep and three hydrothermal vents in the West Pacific

Deep-sea Bathymodiolus mussels are ubiquitous in most cold seeps and hydrothermal fields, where they have adapted to various toxic environments including high metal exposure. However, there is scarce knowledge of metal accumulation and metal-related biomarkers in B. mussels. Here, we present data for metal concentrations (Ag, Cd, Cr, Cu, Fe, Mn, Pb, and Zn) and metal related biomarkers (superoxide dismutase-SOD, catalase-CAT, glutathione peroxidase-GPX, glutathione-GSH, metallothioneins-MTs, and lipid peroxidation-LPO) in different tissues of B. mussels from four different deep-sea geochemical settings: one cold seep and three vent fields in the West Pacific Ocean. Results showed that mussel gills generally exhibited higher metal enrichment than the mantle. Mussels from hydrothermal vents usually had higher metal concentrations (Fe, Cr, Cd, and Pb) than those from cold seep, which could be related to their higher contents in fluids or sediments. However, despite quite different metals loads among the geochemical environment settings, Mn, Zn, and Cu concentrations varied over a smaller range across the sampling sites, implying biological regulation by deep-sea mussels for these elements. Several statistically significant correlations were observed between SOD, CAT, GSH, MTs, and metal levels in analyzed tissues. Although the vent ecosystem is harsher than the cold seep ecosystem, according to our results their mussels' biomarker levels were not so different. This finding suggests that some adaptive or compensatory mechanisms may occur in chronically polluted deep-sea mussels. Principal component analysis allowed for distinguishing different deep-sea settings, indicating that B. mussels are robust indicators of their living environments. We also compared our results with those reported for coastal mussels. To our best knowledge, this is the first integrated study to report metal accumulation and metal-related biomarkers in the deep-sea B. mussels from the West Pacific.

Gametogenesis-Related Fluctuations in Ovothiol Levels in the Mantle of Mussels from Different Estuaries: Fighting Oxidative Stress for Spawning in Polluted Waters

Reactive oxygen species present a challenge for marine organisms releasing gametes into the water. Thiol-containing molecules protect cells against oxidative stress, and ovothiol (OSH), an antioxidant-reducing mercaptohistidine, has been described as especially relevant in the oocytes of marine invertebrates. Ovothiol synthase (ovoA), in charge of the first step in OSH synthesis, was sequenced in mussels, Mytilus galloprovincialis. Transcription levels of ovoA in mantle did not significantly change along the reproductive cycle. No alterations of ovoA transcription were observed after a laboratory copper (10 µg/L) exposure or in mussels captured in a highly polluted site. Conversely, the metabolomic analysis of the hydrophilic metabolite content in mantle clearly classified mussels according to their site of origin, especially at the most advanced stages of oogenesis. Quantification of OSH-A and -B and glutathione (GSH), revealed stable levels in mantle at early gametogenesis in the unpolluted sampling site, but a strong increase in female mantle previous to spawning in the polluted site. These increased concentrations under pollution suggest that OSH-A accumulates along oogenesis, independent of gene transcription regulation. The concerted accumulation of OSH-A and GSH suggests the building of a balanced cellular redox-system to scavenge ROS produced in the oocyte before and during fertilization.

Toxicity, gut microbiota and metabolome effects after copper exposure during early life in SD rats

Copper, an essential microelement, can still be harmful to health and has a significant impact on the gut microbiota, which is closely related to health when copper is ingested excessively. However, the effects of low dose exposure to copper early in life on health and the gut microbiota are not well understood. Here, the effects of early-life exposure of copper on the toxicity, gut microbiota and the metabolome were investigated in Sprague-Dawley (SD) rats. The results showed that 0.20 and 1.00 mg/kg BW copper early-life exposure in SD rats significantly increased ALT, AST, and ALP levels in the blood and caused liver damage. Copper exposure had a dose-dependent effect on the alpha and beta diversity and reduced the abundance of probiotics, the ratio of Firmicutes to Bacteroidetes (F/B), and changed the abundance of fat metabolism and intestinal inflammation-related bacteria. The results of the fecal metabolome also demonstrated the effects of early-life copper exposure on liver damage and intestinal inflammation-related metabolic pathways. Together, our findings demonstrated that copper exposure during early life induced liver damage and gut microbiota dysbiosis and affected the relevant metabolic pathways.

Copper Changes Intestinal Microbiota of the Cecum and Rectum in Female Mice by 16S rRNA Gene Sequencing

The aim of the present study was to investigate the effects of high concentrations of copper (Cu) on the cecum and rectum of intestinal microbiota in female mice. Twenty-four Kunming mice were weighed and randomly divided into two groups (n = 12 per group) including the control group and Cu group. Cu group was given drinking water with 5 mg/kg-bw copper chloride (CuCl₂), while the control group was treated with drinking water without CuCl₂. At the 90th day, results showed that compared with the control group, mice in the treatment group had a lower body weight, and the feces turned yellow and had a lower pH value. Histopathological lesions showed that the intestinal tissue from the treatment group had increased thickness of outer muscularis and smoothed muscle fiber, widened submucosa, decreased goblet cells, and showed blunting of intestinal villi and severe atrophy of central lacteal. In addition, at the genus level, 16S rRNA gene sequencing from the Cu group showed that Corynebacterium were significantly increased whereas Staphylococcaceae, Odoribacter, Rikenella, and Jeotgalicoccus were significantly decreased in the cecum. Dehalobacterium, Coprococcus, and Spirochaetales increased significantly whereas Salinicoccus, Bacillales, Staphylococcus, and Lactobacillales decreased sharply in the rectum. This study demonstrated that high concentrations of Cu could induce tissue injury and interrupt the homeostasis of microbiota.

Comparative Proteomics on Deep-Sea Amphipods after in Situ Copper Exposure

The interest in deep-sea mining increased along with the environmental concerns of these activities to the deep-sea fauna. The discovery of optimal biomarkers of deep-sea mining activities in deep-sea species is a crucial step toward the supply of important ecological information for environmental impact assessment. In this study, an in situ copper exposure experiment was performed on deep-sea scavenging amphipods. Abyssorchomene distinctus individuals were selected among all the exposed amphipods for molecular characterization. Copper concentration within the gut was assessed, followed by a tandem mass tag-based coupled with two-dimensional liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) applied to identify and quantify the protein expression changes after 48 h of exposure. 2937 proteins were identified and annotated, and 1918 proteins among all identified proteins were assigned by at least two nonambiguous peptides. The screening process was performed based on the differences in protein abundance and the specific correlation between the proteins and copper in previous studies. These differentially produced proteins include Na⁺/K⁺ ATPase, cuticle, chitinase, and proteins with unknown function. Their abundances showed correlation with copper and had high sensitivity to indicate the copper level, being here proposed as biomarker candidates for deep-sea mining activities in the future. This is a key step in the development of environmental impact assessment of deep-sea mining activities integrating ecotoxicological data.

Are shallow-water shrimps proxies for hydrothermal-vent shrimps to assess the impact of deep-sea mining?

Polymetallic seafloor massive sulphide deposits are potential targets for deep-sea mining, but high concentrations of metals (including copper - Cu) may be released during exploitation activities, potentially inducing harmful impact. To determine whether shallow-water shrimp are suitable ecotoxicological proxies for deep-sea hydrothermal vent shrimp the effects of waterborne Cu exposure (3 and 10 days at 0.4 and 4 μM concentrations) in Palaemon elegans, Palaemon serratus, and Palaemon varians were compared with Mirocaris fortunata. Accumulation of Cu and a set of biomarkers were analysed. Results show different responses among congeneric species indicating that it is not appropriate to use shallow-water shrimps as ecotoxicological proxies for deep-water shrimps. During the evolutionary history of these species they were likely subject to different chemical environments which may have induced different molecular/biochemical adaptations/tolerances. Results highlight the importance of analysing effects of deep-sea mining in situ and in local species to adequately assess ecotoxicological effects under natural environmental conditions.

Gene expression study in Bathymodiolus azoricus populations from three North Atlantic hydrothermal vent sites

The deep-sea hydrothermal vents are known as harsh environments, abundant in animal diversity surrounded by fluids with specific physiological and chemical composition. Bathymodiolus azoricus mussels are endemic species dwelling at hydrothermal vent sites and at distinct depth ranges. Mussels from Menez Gwen (MG), Lucky Strike (LS), Rainbow (Rb) were collected at 800 m, 1730 m and 2310 m depths respectively, along the Mid-Atlantic Ridge. Five different tissues including gill, digestive gland, mantle, adductor muscle and foot from MG, LS and Rb mussels were selected for gene expression analyses by qPCR. 30 genes were tested to investigate the level of immune and apoptotic gene expression among B. azoricus populations. Statistical analyses confirmed tissue-specific gene expression differences among the five tissues. The digestive gland tissue showed a higher transcriptional activity characterized by an up-regulation of gene activities, contrary to what was assessed in the adductor muscle tissue. Five categories included recognition, signaling, transcription, effector and apoptotic genes were analyzed in this study. The majority of genes differed in levels of expression between MG/LS and LS/Rb in the digestive gland. Our findings suggest that gene expression profiles are inherent to the tissue analyzed, thus implying an immune tissue-specificity controlling defense responses across B. azoricus mussel body as a whole.

Effects of single and mixture exposure of cadmium and copper in apoptosis and immune related genes at transcriptional level on the midge Chironomus riparius Meigen (Diptera, Chironomidae)

Metals and heavy metals are natural contaminants with an increasing presence in aquatic ecosystems as a result of human activities. Although they are mixed in the water, research is usually focused on analyzing them in isolation, so there is a lack of knowledge about their combined effects. The aim of this work was to assess the damage produced by mixtures of cadmium and copper, two frequent metals used in industry, in the harlequin midge Chironomus riparius (Diptera). The effects of acute doses of cadmium and copper were evaluated in fourth instar larvae by analyzing the mRNA levels of six genes related to apoptosis (DRONC, IAP1), immune system (PO1, Defensin), stress (Gp93), and copper homeostasis (Ctr1). DRONC, Ctr1, and IAP1 transcripts are described here for first time in this species. Individual fourth instar larvae were submitted to 10 μM, 1 μM and 0.1 μM of CdCl₂ or CuCl_2, and mixture. The employed individuals came from different egg masses. Real-time PCR analysis showed a complex pattern of alterations in transcriptional activity for two genes, DRONC and Gp93, while the rest of them did not show any statistically significant differences. The effector caspase DRONC showed upregulation with the highest concentration tested of the mixture. In case of gp93, chaperone involved in regulation of immune response, differences in expression levels were found with 1 and 10 μM Cu and 0.1 and 10 μM of mixtures, compared to control samples. These results suggest that mixtures affect the transcriptional activity differently and produce changes in apoptosis and stress processes, although it is also possible that Gp93 alteration could be related to the immune system since it is homologous to human protein Gp96, which has been related with Toll-like receptors. In conclusion, cadmium and copper mixtures can affect the population by affecting the ability of larvae to respond to the infection and the apoptosis, an important process in the metamorphosis of insects.

Ecotoxicology of deep-sea environments: Functional and biochemical effects of suspended sediments in the model species Mytilus galloprovincialis under hyperbaric conditions

The deep-sea is the biggest ecosystem in the world and is characterized by extreme conditions such as high pressure, low temperatures and absence or limited light. Despite the scarce studies due to inaccessibility, these ecosystems are considered highly biodiverse. The deep-sea is subjected to anthropogenic stressors with deep-sea mining being a likely new form of disruption. Understanding how it affects the surrounding environments is paramount to develop guidelines to protect sensitive habitats and allow for responsible exploitation of resources. One of the potential stressors associated with deep-sea mining are the sediment laden plumes that can be generated during the mining process. The present study examined, for the first time, the effects of suspended sediments (0, 1, 2 and 4 g/L) in the model mussel species, Mytilus galloprovincialis, under hyperbaric conditions (1, 4 and 50 Bar). Functional endpoints, i.e. feeding assays, together with biochemical biomarkers of oxidative stress [catalase (CAT), lipid peroxidation (LPO), glutathione-s-transferase (GST) and superoxide dismutase (SOD)] were studied in juvenile mussels. The filtration rate (FR) of M. galloprovincialis decreased with the increment in the sediment concentrations, for all tested pressure conditions (1, 4 and 50 Bar). Significant alterations were also observed for all tested biomarkers, being sediment and pressure-dependent. Interestingly, pressure had an effect in GST activity, that increased in the 4 and 50 Bar experiments in comparison with the results at 1 Bar. Remarkably, filtration rates were significantly affected by pressure. These findings will support the filling of the knowledge gaps related with the hazard assessment of deep-sea mining associated stressors.

High Doses of Copper and Mercury Changed Cecal Microbiota in Female Mice

The aim of the present study was to investigate the effects of high doses of copper (Cu) and mercury (Hg) on the cecal microbiota in female mice. Forty-eight Kunming mice were randomly divided into the control group (CCk group), the Cu group (CCu group), the Hg group (CHg group), and the Cu + Hg group (CCH group). At the 90th day, cecal tissues were prepared for histopathological analysis and cecal contents for analysis by 16S rRNA sequencing method. Cecal tissues from treatment groups had histopathological lesions including increased thickness of inner muscularis and outer muscularis, widened submucosa, decreased goblet cells, mild to moderate necrosis of enterocytes, blunting of intestinal villi, and severe atrophy of central lacteal. Furthermore, compared to the CCk group, the abundance of bacteria genera Rikenella, Jeotgailcoccus, and Staphylococcus were significantly decreased, whereas the bacteria genus Corynebacterium was significantly increased in the CCu group. The abundance of bacteria genera of Sporosarcina, Jeotgailcoccus, and Staphylococcus were significantly decreased in the CHg group and CCH group. The bacteria genus Anaeroplasma was significantly increased in the CCH group. The results indicated that high doses of Cu and Hg caused histopathological lesions and changed the diversity of microbiota in the cecum of female mice, which provide a theoretical basis for more accurate assessment of the risk in intestinal diseases caused by Cu and Hg.

Geological, Mineralogical and Textural Impacts on the Distribution of Environmentally Toxic Trace Elements in Seafloor Massive Sulfide Occurrences

With mining of seafloor massive sulfides (SMS) coming closer to reality, it is vital that we have a good understanding of the geochemistry of these occurrences and the potential toxicity impact associated with mining them. In this study, SMS samples from seven hydrothermal fields from various tectonic settings were investigated by in-situ microanalysis (electron microprobe (EMPA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)) to highlight the distribution of potentially-toxic trace elements (Cu, Zn, Pb, Mn, Cd, As, Sb, Co, Ni, Bi, Ag and Hg) within the deposits, their minerals and textures. We demonstrate that a combination of mineralogy, trace element composition and texture characterisation of SMS from various geotectonic settings, when considered along with our current knowledge of oxidation rates and galvanic coupling, can be used to predict potential toxicity of deposit types and individual samples and highlight which may be of environmental concern. Although we cannot quantify toxicity, we observe that arc-related sulfide deposits have a high potential toxicity when compared with deposits from other tectonic settings based on their genetic association of a wide range of potentially toxic metals (As, Sb, Pb, Hg, Ag and Bi) that are incorporated into more reactive sulfosalts, galena and Fe-rich sphalerite. Thus, deposits such as these require special care when considered as mining targets. In contrast, the exclusive concern of ultra-mafic deposits is Cu, present in abundant, albeit less reactive chalcopyrite, but largely barren of other metals such as As, Pb, Sb, Cd and Hg. Whilst geological setting does dictate metal endowment, ultimately mineralogy is the largest control of trace element distribution and subsequent potential toxicity. Deposits containing abundant pyrrhotite (high-temperature deposits) and Fe-rich sphalerite (ubiquitous to all SMS deposits) as well as deposits with abundant colloform textures also pose a higher risk. This type of study can be combined with “bulk lethal toxicity” assessments and used throughout the stages of a mining project to help guide prospecting and legislation, focus exploitation and minimise environmental impact.