How does the metallothionein induction in bivalves meet the criteria for biomarkers of metal exposure?

A metallothionein from disk abalone (Haliotis discus discus): Insights into its functional roles in immune response, metal tolerance, and oxidative stress

Metallothioneins (MTs) are cysteine-rich metal-binding proteins whose expression is induced by exposure to essential and non-essential metals, making them potential biological markers for assessing metal pollution in various biomonitoring programs. However, the functional properties of these proteins are yet to be comprehensively characterized in most marine invertebrates. In this study, we identified and characterized an MT homolog from the disk abalone (Haliotis discus discus), referred to as disk abalone MT (AbMT). AbMT exhibited the same primary structural features as MTs from other mollusks containing two β-domains (β2β1-form). AbMT protein demonstrated metal-binding and detoxification abilities against Zn, Cu, and Cd, as evidenced by Escherichia coli growth kinetics, metal tolerance analysis, and UV absorption spectrum. Transcriptional analysis revealed that AbMT was ubiquitously expressed in all analyzed tissues and upregulated in gill tissue following challenge with Vibrio parahaemolyticus, Listeria monocytogenes, and viral hemorrhagic septicemia virus (VHSV). Additionally, overexpression of AbMT suppressed LPS-induced NO production in RAW264.7 macrophages, protected cells against H2O2-induced oxidative stress, and promoted macrophage polarization toward the M1 phase. Conclusively, these findings suggest an important role for AbMT in environmental stress protection and immune regulation in disk abalone.

Differential effects of oxytetracycline on detoxification and antioxidant defense in the hepatopancreas and intestine of Chinese mitten crab under cadmium stress

This study aims to evaluate the effects of oxytetracycline (OTC) on detoxification and oxidative defense in the hepatopancreas and intestine of Chinese mitten crab (Eriocheir sinensis) under cadmium (Cd) stress. The crab was exposed to 0.6 μM Cd, 0.6 μM OTC, and 0.6 μM Cd plus 0.6 μM OTC for 42 days. Our results showed that in the intestine, OTC alone enhanced protein carboxylation (PC) and malondialdehyde (MDA) contents, which was associated with the increased OTC accumulation. Compared to Cd alone, Cd plus OTC increased Cd and OTC contents, and reduced detoxification (i.e., glutathione (GSH) content, gene expressions of cytochrome P450 (CYP) isoforms, 7-ethoxyresorufin O-deethylase (EROD) activity, mRNA levels and activities of glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione-S-transferase (GST)), and antioxidant defense (i.e., gene expressions and activities of catalase (CAT) and superoxide dismutase (SOD)) in the intestine, leading to the increased in PC and MDA contents, suggesting that OTC had a synergistic effect on Cd-induced oxidative damage. In the hepatopancreas, although OTC alone increased OTC accumulation, it did not affect PC and MDA contents. Compared to Cd alone, Cd plus OTC reduced MDA content, which was closely related to the improvement of detoxification (i.e., GSH content, mRNA levels of CYP isoforms, EROD activity, gene expressions and activities of GPx, GR and GST), and antioxidant defense (gene expressions and activities of CAT and SOD, metallothionein content). Aryl hydrocarbon receptor (AhR) and nuclear factor E2-related factor 2 (Nrf2) transcriptional expressions were positively correlated with most detoxification- and antioxidant-related gene expressions, respectively, indicating that AhR and Nrf2 were involved in the regulation of these gene expressions. Our results unambiguously demonstrated that OTC had tissue-specific effects on Cd-induced toxicological effect in E. sinensis, which contributed to accurately evaluating Cd toxicity modulated by TCs in crab.

Effect of acute cadmium exposure on oxidative stress and antioxidant system of the scallop Aequipecten tehuelchus

This study aimed to assess the impact of acute exposure (96 h) to Cd in gills, digestive gland and muscle of the Tehuelche scallop Aequipecten tehuelchus from San José gulf in Patagonia, Argentina. Scallops were exposed to Cd concentrations of 0, 25, 50, 100, 150, 204, 275, 371, and 500 μg/L, and mortality rates were recorded after 96 h of exposure. Surviving organisms were analyzed for the biochemical response through reactive oxygen and nitrogen species (RONS), activities of catalase (CAT) and glutathione-S-transferase (GST), metallothioneins (MT), lipid peroxidation (LPO) and liposoluble antioxidants α-tocopherol (α-T) and β-carotene (β-C). The mean lethal concentration (LC50) was 155.8 μg Cd/L, a lower value than other scallops' species, showing that A. tehuelchus has a particular sensitivity to Cd. In the three tissues, at all exposure concentrations, there was no significant response in RONS levels, GST activity or LPO. Nevertheless, CAT activity and α-T levels decreased in the gills but increased in the digestive gland, with no significant response in the muscle. Two-way ANOVA revealed a significant interaction between Cd concentration and tissue on MT, which increased significantly in gills, decreased in digestive gland with 100 compared to 50 μg Cd/L; whereas in muscle a significant increase was observed with 25 μg Cd/L compared to control. The results show a significant effect of Cd in scallop's gills on CAT activity and α-T levels, highlighting this tissue as the primary target against relevant concentrations of metal in seawater. The effect on digestive gland and muscle was minimal. The overall results suggest that Cd toxicity is tissue-specific. This study will help reduce the existence knowledge gap regarding potential impacts of acute exposure to Cd in a bivalve species with high ecological and commercial importance, as well as identifying the most responsive biomarkers associated with Cd stress for monitoring assessment.

Identification and organ-specific patterns of expression of two metallothioneins in the sentinel species Gammarus fossarum

Metal pollution is a major concern for aquatic environments. Widespread contamination by various trace metal ions has been described in freshwater streams as well as their subsequent bioaccumulation, potentially leading to toxicity and trophic transfer. Metallothioneins constitute an evolutionary conserved family of low molecular weight, cysteine-rich, metal-chelating proteins, whose known physiological functions are the maintenance of the homeostasis of essential metals, the detoxification of non-essential metals, and the protection against oxidative stress and free radicals. In this study, we identified two metallothionein-coding transcripts, mt1 and mt2, in the transcriptome of the amphipod Gammarus fossarum, a sentinel species widely used to assess the quality of watersheds. For the first time, we investigated the organ-specific patterns of expression of these two mt transcripts at the individual level in the gills and the caeca of this small crustacean. In silico analysis and experimental exposures to environmentally relevant concentrations of cadmium, zinc and silver showed that G. fossarum mt1 induction is stronger after Cd exposure compared to the other tested metals. G. fossarum mt1 was more significantly induced in the caeca than in the gills of exposed organisms for any metal exposure, while G. fossarum mt2 was, at least at the individual level, more inducible in the gills than in the caeca of G. fossarum exposed to Cd and Zn. Our results provide new genetic resources that will help to improve the understanding of metal homeostasis in this sentinel species.

Evidences of metabolic alterations and cellular damage in different tissues of scallops Aequipecten tehuelchus exposed to cadmium

Scallops Aequipecten tehuelchus (Patagonia, Argentina) were exposed to 0, 2, 5 and 12 μg Cd/L for 7 and 14 days, causing in digestive gland a significant production of reactive oxygen and nitrogen species (RONS), induction of catalase (CAT) and glutathione S-transferase (GST) activities and metallothioneins (MT) synthesis. In gills, there was inhibition of GST and induction of CAT, MT and α-tocopherol (α-Toc). In muscle, a significant increment of MT was also registered and inhibition of CAT. Lipid peroxidation, measured as TBARS, was not promoted in any tissue. More significant effects were observed in digestive gland than in gills and muscle, evidencing the critical role of digestive gland in Cd accumulation and metabolisation. This research would evidence dose-dependent effects of Cd on MT, GST, CAT and α-Toc in the three organs assayed, as well as a time-dependent effect of Cd on the response of CAT, GST and TBARS in digestive gland.

A comparative study of the accumulation and detoxification of copper and zinc in Chlamydomonas reinhardtii: The role of extracellular polymeric substances

Extracellular polymeric substances (EPS) form an interface between microalgae and the surrounding water environment. Copper (Cu) and zinc (Zn) are essential micronutrients but may negatively affect microbial growth when their concentrations reach toxic thresholds. However, how EPS affect the accumulation and resistance of Cu and Zn in microalgae remains largely unknown. Here, we investigated EPS production upon Cu/Zn exposure and compared the tolerance strategies to the two metals by Chlamydomonas reinhardtii with and without EPS. Microalgal EPS synthesis was induced by Cu/Zn treatments, and the functional groups of polysaccharides and proteins were involved in complexation with metal ions. The extraction of EPS aggravated the toxicity and reduced the removal of metals from solution, but the effect was more pronounced for Cu than for Zn. Copper bound on the cell surface accounted for 54.6 ± 2.0 % of the Cu accumulated by C. reinhardtii, whose EPS components strongly correlated with Cu adsorption. In contrast, 74.3 ± 3.0 % of accumulated Zn was absorbed in cells, and glutathione synthesis was significantly induced. Redundancy and linear correlation analyses showed that the polysaccharide, protein and DNA contents in EPS were significantly correlated with Cu accumulation, absorption and adsorption but not with Zn. Data fitted to a Michaelis-Menten model further showed that the EPS-intact cells had higher binding capacity for Cu²⁺ but not for Zn²⁺. These differential impacts of EPS on Cu/Zn sorption and detoxification contribute to a more comprehensive understanding of the roles of microalgal EPS in the biogeochemical cycle of metals.

Pollutant load and ecotoxicological effects of sediment from stormwater retention basins to receiving surface water on Lumbriculus variegatus

The overflow of stormwater retention basins during intense and prolonged precipitation events may result in the direct input of particulate pollutants and remobilization of already sedimented particle-bound pollutants to receiving freshwater bodies. Particle-bound pollutants may cause adverse effects on aquatic biota, particularly sediment dwellers. Therefore, we investigated the sediment pollution load of a stream connected to the outfalls of two stormwater basins to determine the impact of the basins' discharges on the metal and organic pollutant content of the sediment. Also, the possible adverse effects of the pollutant load on benthic dwellers were evaluated in sediment toxicity tests with Lumbriculus variegatus and the effects on its growth, reproduction and the biomarkers catalase, acetylcholinesterase and metallothionein were analyzed. The results showed that the retention basins contained the highest load of pollutants. The pollutant load in the stream did not show a clear pollution pattern from the inlets. However, metal enrichment ratios revealed contamination with Cu, Pb and Zn with Pb and Zn above threshold effect concentrations in all sites. Ecotoxicity results showed that the retention basin samples were the most toxic compared to sediment from the stream. Exposure experiments with the stream sediment did not show considerable effects on reproduction, catalase activity and metallothionein concentration. However, modest inhibitions of growth and activity of acetylcholinesterase were detected. Based on the observed results, it cannot be concluded that overflows of the retention basin are responsible for the pollutant contents downstream of their inlet. Other sources that were not considered in this study, such as diffuse input, historic pollution and point sources further upstream as well as along the stream, are likely the major contributors of pollutant load in the sediment of the studied transects of the stream. Additionally, the observed results in the stormwater basin sediment further highlight their importance in retaining particle-bound pollutants and preventing ecotoxicological effects from receiving surface water bodies.

Meta-analysis reveals the species-, dose- and duration-dependent effects of cadmium toxicities in marine bivalves

Cadmium (Cd) is a typical pollutant in marine environment. Increasing studies have focused on the toxicological effects of Cd in marine bivalves. However, there were many conflicting findings of toxicological effects of Cd in marine bivalves. An integrated analysis performed on the published data of Cd toxicity in marine bivalves is still absent. In this study, a meta-analysis was performed on the toxic endpoints in bivalves exposed to aqueous-phase Cd from 87 studies screened from 1519 papers. Subgroup analyses were conducted according to the categories of species, tissue, exposure dose and duration. The results showed significant species-, duration- and dose-dependent responses in bivalves to aqueous-phase Cd exposure. In details, clams were more sensitive to Cd than oysters, mussels and scallops, indicated by the largest effect size in clams. Gill, hepatopancreas and hemolymph were top three tissues used to indicate Cd-induced toxicity and did not present a significant tissue-specific manner among them. With regard to toxicological effect subgroups, oxidative stress and detoxification were top two subgroups indicating Cd toxicities. Detoxification and genotoxicity subgroups presented higher response magnitudes. What is more, toxicological effect subgroups presented multiple dose- and duration-dependent curves. Oxidative stress and genotoxicity related endpoints presented significant increase trends with Cd exposure dose and were preferable biomarkers to marine Cd pollution. Detoxification and energy metabolism related endpoints showed inverted U-shaped and U-shaped dose-response curves, both of which could be explained by hormesis. The linear decrease in oxidative stress and energy metabolism related endpoints over time suggested their involvement into the adaptive mechanism in bivalves. Overall, this study provided not only a better understanding the responsive mechanisms of marine bivalves to Cd stress, but also a selection reference for biomarkers to aqueous-phase Cd pollution in marine environment.

Energy dispersive X-Ray microanalysis in conjunction with scanning electron micrography to establish nematodes as bioindicators in marine fish environment

Energy Dispersive X-Ray Microanalysis has been used as the non-invasive technique on Indian helminthes to explore the role of nematode parasites as bioindicators in the marine ecosystem of Central West coast of India for the first time. The accumulation of sulphur and iron were analysed from a raphidascaridoid roundworm, Rostellascaris spinicaudatum (Malhotra and Anas) parasitizing marine catfish, Arius maculatus from the Central West coast of India at Goa. Quantitatively, the cuticle on oral armature comprised as much as ten times more sulphur than iron content in the roundworm under study. However, only carbon and oxygen were detected over caudal papillae, where no metals or other elements were recorded. The utility of a raphidascaridoid nematode to act as a bioindicator, that had the potential of a bioaccumulator effector, is highlighted.

Mechanism of Cadmium Exposure Induced Hepatotoxicity in the Mud Crab (Scylla paramamosain): Activation of Oxidative Stress and Nrf2 Signaling Pathway

Cadmium, one of the most toxic heavy metals, can cause severe oxidative damage to aquatic animals. However, the mechanism whereby the mud crabs respond to cadmium exposure remains unclear. This study investigated the effects of cadmium exposure on oxidative stress and histopathology changes and evaluated the role of the Nrf2 signaling pathway in regulating responses to cadmium-induced hepatotoxicity were investigated in mud crabs. Mud crabs were exposed to 0, 0.01, 0.05, and 0.125 mg/L cadmium for 21 d. The present results indicated that cadmium exposure increased hydrogen peroxide (H₂O₂) production, lipid peroxidation and tissue damage, but decreased the activity of superoxide dismutase (SOD) and catalase (CAT), and caused lipid peroxidation and tissue damage. The results of an integrated biomarker index analysis suggested that the toxicity of cadmium was positively related to cadmium concentration. The expression levels of the Nrf2 signaling pathway (Nrf2, metallothionein, and cytochrome P450 enzymes) were up-regulated after cadmium exposure. Silencing of Nrf2 in vivo decreased antioxidant gene (SOD, CAT, and glutathione S-transferase) expression, suggesting that Nrf2 can regulate antioxidant genes. Knocking down Nrf2 in vivo also significantly decreased the activity of SOD and CAT after cadmium exposure. Moreover, silencing of Nrf2 in vivo enhanced H₂O₂ production and the mortality rates of mud crabs after cadmium exposure. The present study indicated that cadmium exposure induced hepatotoxicity in the mud crab by increasing H₂O₂ content, which decreased the antioxidant capacity, leading to cell injury. In addition, the Nrf2 is activated to bound with antioxidant response element, initiating the expression of antioxidant enzyme genes during cadmium induced hepatotoxicity in the mud crabs.

Assessment of the heavy metal levels and biomarker responses in the smooth scallop Flexopecten glaber from a heavily urbanized Mediterranean lagoon (Bizerte lagoon)

Marine heavy metal pollution is a worldwide serious issue. Like almost all Mediterranean lagoons, the Bizerte lagoon is highly urbanized and suffers from intensive anthropogenic pressure. In the present study, we screened the metal contamination and biomarker responses in the smooth scallop Flexopecten glaber inhabiting this vulnerable ecosystem. To this end, the concentrations of six heavy metals (HM) (i.e., Cu, Pb, Zn, Cd, Hg, and Fe) and a panel of biochemical endpoints including malondialdehyde (MDA), metallothioneins (MT), reduced glutathione (GSH), glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT) were determined in the gills and digestive gland across seasons (warm and cold) and sites (S1 and S2). The distribution of almost all analyzed metals in F. glaber tissues varied significantly between sites, seasons, and organs. The highest levels were recorded at S2 during the warm period. Moreover, the digestive gland was found to accumulate greater concentrations of HM than the gills. Marked spatio-temporal variations were also observed for oxidative stress biomarkers, mainly in the gills, while the digestive gland seems to be rather sensitive to seasonal variability. Particularly, we noticed that among the used biomarkers, MT did not show significant variations in the two tested organs across seasons and sites. From the obtained results, F. glaber appears as a sensitive organism to anthropogenic metal contamination and can be proposed as a promising bioindicator species for marine pollution.

Differences in chemical contaminants bioaccumulation and ecotoxicology biomarkers in Mytilus edulis and Mytilus galloprovincialis and their hybrids

The Mytilus mussels are spread all over the world and many related species coexist in several areas and can produce hybrid offspring. Mussels have been used for decades in national and international programs to monitor chemical contamination in the environment. Differences in bioaccumulation and biotransformation abilities between species and their hybrids should be evaluated to assess the comparability of the results obtained within the international biomonitoring programs. The objective of this study was to characterize bioaccumulation abilities and biomarker responses in Mytilus edulis, Mytilus galloprovincialis and their hybrids via an in situ transplantation experimentation on their progenies. Four mussel groups (M. edulis, M. galloprovincialis and two hybrids batches) issued from genetically characterized parents were transplanted for one year in Charente Maritime (France) to ensure their exposure to identical sources of contamination. The bioaccumulation of several families of contaminants (trace metals, polycyclic aromatic hydrocarbons, polybrominated diphenyl ethers, polychlorinated biphenyls), the response of several biomarkers (DNA strand breaks level, lysosomal membrane stability, metallothionein content, acetylcholine esterase activity) and some physiological parameters (growth, mortality, gonadal development), were analyzed. Differences were observed between species, however they were contaminant-specific. Variations in contaminants levels were observed between progenies, with higher levels of Cu, PBDE, PCB in M. edulis, and higher levels of Cd, Hg, Zn in M galloprovincialis. This study demonstrated that variations in contaminant bioaccumulation and different biomarker responses exist between Mytilus species in the field. Data on species or the presence of hybrid individuals (or introgression) is an important additional parameter to add to biomonitoring programs databases.

Biomarkers of Exposure and Effect in Nile Tilapia (Oreochromis niloticus) Environmentally Exposed to Multiple Stressors in Egypt

Chemical pollution poses adverse effects on aquatic organisms, including altered gene expression. This study, therefore, investigated the hepatic expression of biomarkers of exposure and effect in Oreochromis niloticus inhabiting the drainage canal of a sugarbeet factory (an industrially polluted habitat) and the Nile River (a reference habitat). Compared to the Nile River, the drainage canal contained significantly elevated levels of heavy metals (Cd, Fe, Mn, Co, and Pb), nitrate, ammonia, nitrite, chemical oxygen demand, and biological oxygen demand. The liver of O. niloticus from the drainage canal accumulated significantly higher concentrations of the heavy metals. O. niloticus from the drainage canal had significantly higher hepatic expressions of genes related to oxidative stress (GSTa, GPx, and NRF2), metal toxicity (MT), endocrine disruption (Vtg), and hypoxia (HIF1a) and a significantly lower hepatic expression of the apoptosis-associated CAS gene. CYP1A (a detoxification biomarker) expression did not exhibit significant differences. These results provide insights into complex adaptive responses of O. niloticus to multiple chemicals and support the utilization of molecular biomarkers as warning signals for water pollution.

Assessment spermatogenic cell apoptosis and the transcript levels of metallothionein and p53 in Meretrix meretrix induced by cadmium

Cadmium (Cd) has been widely used in industry and can accumulate in the water, soil, and food. Meretrix meretrix is one of the marine shellfishes cultivated for economic purpose in China. The increasing Cd levels in coastal marine water could adversely affect the economic benefits of shellfish cultivation. In the present study, M. meretrix were exposed to different Cd²⁺ concentrations (0, 1.5, 3, 6, and 12 mg L^-1) for 5 d to evaluate the effects of Cd on spermatogenic cell. The Cd accumulation, survival rate and the indices of oxidative stress and apoptosis were determined in the spermatogenic cells of M. meretrix. The expression levels of p53 and metallothionein (MT) mRNA were also measured in the spermatogenic cells. Cd accumulation and the mortality rate of spermatogenic cells were found to increase in a dose-response manner with Cd²⁺ concentrations. Histopathology changes, especially the damage of membranous structure, were more severe as the Cd²⁺ levels in the testis became higher. The indexes of oxidative stress, including reactive oxygen species, malondialdehyde, protein carbonyl derivates and DNA-protein crosslinks all increased after exposure to Cd²⁺. However, the total antioxidant capacity gradually decreased with the increasing Cd²⁺ concentration. In addition, exposure to Cd²⁺ increased the apoptotic rate and caspase-3 and 9 activities but decreased the level of mitochondrial membrane potential and cytochrome C oxidase in the spermatogenic cells. MT mRNA expression increased in lower Cd²⁺ concentration treated groups whereas decreased in higher groups, while the p53 mRNA expression increased in a dose-response manner with Cd²⁺ and was positively correlated with the oxidative damage indices. These results indicated that Cd²⁺ caused oxidative stress and p53 induced apoptosis in the spermatogenic cells, and thus decreased the survival rate of sperm cells. This finding highlights that Cd can reduce the reproductive capacity of M. meretrix, thus threatening to wild shellfish populations and reducing the efficiency of shellfish farming.

Contrasting detoxification mechanisms of Chlamydomonas reinhardtii under Cd and Pb stress

Chlamydomonas reinhardtii has been frequently investigated for its resistance to metals; however, few studies have systematically compared the intracellular and extracellular processes involved in the detoxification of Cd and Pb by this microalga. We found that C. reinhardtii was more tolerant to Pb (concentration for 50% of the maximal effect; EC50: 29.48 ± 8.83 mg L^-1) than to Cd (EC50: 12.48 ± 1.30 mg L^-1) after 96 h of exposure. Extracellular polymeric substances (EPS), intracellular starch granules, lipid droplets, and glutathione were significantly increased under Cd and Pb treatments. Lead-containing particles were formed outside of the cells exposed to 30 mg L^-1 of Pb, whereas no minerals were present when Cd was added. Various EPS functional groups, including -COOH, C-O-C (polysaccharides), and amide I and II (proteins), were involved in the interactions with Cd and Pb. The Pb removal rate (60.46-78.27%) by C. reinhardtii was higher than that of Cd (50.61-59.38%), and the microalgal cells with intact EPS bound more metals than those without EPS. Adsorption accounted for 79.62% of the total Cd accumulation in the low-Cd treatment, whereas absorption dominated the Pb accumulation at low Pb concentrations. The distributions of Cd and Pb in and out of the microalgal cells were reversed when the concentrations of the two metals increased. The detoxification strategies of C. reinhardtii for Cd and Pb were completely different, and these findings may assist in the phycoremediation of metal pollution in aquatic environments.

Molecular response of a sub-antarctic population of the blue mussel (Mytilus edulis platensis) to a moderate thermal stress

The Kerguelen Islands (49°26'S, 69°50'E) represent a unique environment due to their geographical isolation, which protects them from anthropogenic pollution. The ability of the endemic mussel, part of the Mytilus complex, to cope with moderate heat stress was explored using omic tools. Transcripts involved in six major metabolic functions were selected and the qRT-PCR data indicated mainly changes in aerobic and anaerobic energy metabolism and stress response. Proteomic comparisons revealed a typical stress response pattern with cytoskeleton modifications and elements suggesting increased energy metabolism. Results also suggest conservation of protein homeostasis by the long-lasting presence of HSP while a general decrease in transcription is observed. The overall findings are consistent with an adaptive response to moderate stresses in mussels in good physiological condition, i.e. living in a low-impact site, and with the literature concerning this model species. Therefore, local blue mussels could be advantageously integrated into biomonitoring strategies, especially in the context of Global Change.

Trace metal bioaccumulation in oysters (Crassostrea gigas) from Liaodong Bay (Bohai Sea, China)

Cd, Cr, Cu, Pb, and Zn concentrations were measured in oysters (C. gigas), plankton, and seawater during spring, summer, and autumn in Liaodong Bay (Bohai Sea, China) to elucidate the effects of season, region, and oyster size on metal bioaccumulation in oysters. Metal concentrations were quantified via atomic absorption spectrophotometry. Our study determined that metal concentrations in oysters, plankton, and seawater were the highest in summer, whereas the lowest levels occurred in autumn. Regarding oyster sizes, the highest Pb levels occurred in C3-sized oysters (> 5-cm length), whereas the highest Cd, Cr, Cu, and Zn levels occurred in C2 (3-5-cm length) oysters. In contrast, the lowest Cu and Pb levels occurred in C1 (< 3-cm length) oysters, whereas the lowest mean Cd, Cr, and Zn concentrations were observed in C3 oysters. Significant differences in trace metal concentrations in the three sample types were observed in all sampling sites.

Bioaccumulation of trace metals and speciation of copper and zinc in Pacific oysters (Crassostrea gigas) using XANES/EXAFS spectroscopies

Copper (Cu) and zinc (Zn) concentrations in oyster soft tissues can be particularly high due to contamination, leading to extremely green/blue colors. This raises key questions regarding the behavior and speciation of trace metals in oyster soft tissues. This study investigated trace metal concentration profiles of contaminated Pacific oyster (Crassostrea gigas) soft tissues collected from trace metal-contaminated coastal area of Xiangshan District using inductively coupled plasma optical emission spectrometry (ICP-OES), energy dispersive X-ray (EDX), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Moreover, Cu and Zn speciation in contaminated and non-contaminated oyster soft tissues were investigated by X-ray absorption near edge structure spectroscopy/extended X-ray absorption fine structure (XANES/EXAFS) spectroscopic methods. The contents of Cu (1,100-1,400 mg/kg) and Zn (500-700 mg/kg) dry weight were high in oyster soft tissue samples. The XANES/EXAFS results revealed that Cu and Zn existed primarily as copper (II) oxide (CuO) and zinc oxide (ZnO) in contaminated oysters. Furthermore, Cu and Zn formed clusters with Cu-O and Zn-O interatomic distances of 1.97 and 2.21 Å, (coordination numbers 1.0 and 5.6), respectively. In non-contaminated oysters, the less abundant Cu and Zn existed mainly as copper(I) sulfide (Cu₂S) and zinc sulfide (ZnS) forming clusters with Cu-S and Zn-S (thiolates) bond distances of 2.09 and 1.23 Å (coordination numbers of 4.6 and 2.4). These results provide further understanding on the chemical speciation of Cu and Zn in contaminated and non-contaminated oyster soft tissues as well as the bioaccumulation of trace metals in the oyster soft tissues.

Ecotoxicological effects of traffic-related metal sediment pollution in Lumbriculus variegatus and Gammarus sp

To reduce direct discharges of surface runoff to receiving waters, separate sewer systems have been implemented, with runoff retention basins (RRB) for pollutant pretreatment by sedimentation and infiltration. However, due to frequent and intense precipitation events, most RRBs are overwhelmed by runoff resulting in overflow into the receiving freshwater bodies. Hence, the present study evaluates the impact of traffic-related runoff overflow on metal concentrations in sediment and Gammarus sp. Downstream of the RRB outfall in the receiving stream. Samples were collected from the RRB, upstream (reference site) and at different distances downstream from the RRB outfall in the stream. The samples were analyzed for the presence and distribution of metals using ICP-MS. Furthermore, ecotoxicological effects of the overflow on benthic species were assessed using Lumbriculus variegatus exposed to the field sediments. Our findings reveal that overflow of the RRB results in elevated traffic-related metal concentrations in sediment and biota of the stream. Within the first 50 m downstream increased sediment metal concentrations were found. The gammarids downstream of the RRB outfall showed an increased accumulation of several metals. Similarly, the metals were found to be taken up by the endobenthic L. variegatus under laboratory conditions and the bioaccumulation pattern was related to the sediment concentrations. Bioaccumulation by both organisms is an indication that overflow of the RRB also leads to uptake of increased element amounts in organisms downstream. Laboratory-based studies addressing standard toxicity endpoints showed no clear toxic effects on growth and reproduction. However, elevated levels of metallothioneins were measured in the annelids during the test period. This indicates a physiological response induced by increased metal concentrations due to RRB overflow. Hence, the results of this study show that discharges by the RRB increase the metal concentration in the receiving stream with the possibility of adverse effects on organisms.

Season specific influence of projected ocean changes on the response to cadmium of stress-related genes in Mytilus galloprovincialis

Anthropogenic inputs of carbon dioxide in the atmosphere are driving ocean warming and acidification. The potential threat represented by these changes for marine species could be amplified in coastal areas, characterized by higher levels of pollutants. In addition, temperate organisms may exhibit a different seasonal tolerance to stressors influenced by fluctuations of environmental and physiological factors. In this study, Mediterranean mussels Mytilus galloprovincialis collected both in summer and winter were exposed to combinations of two temperatures (SST, seasonal surface temperature and SST+5 °C) and two levels of pH (8.20 and 7.40) in clean or cadmium contaminated seawater (20 μg/L Cd). mRNA levels of genes related to metal-induced stress response were investigated, including metallothionein mt-20, heat-shock protein hsp70, superoxide dismutase Cu/Zn-sod, catalase cat, glutathione peroxidase gpx1 and glutathione S-transferase gst-pi. To further elucidate if tissues with different physiological roles could exhibit different responsiveness, such analyses were carried out in digestive gland and in gills of exposed mussels. mt-20 mRNA increase after Cd-exposure was higher in the digestive gland than in the gills, with few modulations by temperature or pH only in the latter. Acidification, alone or in combination with other stressors, increased hsp70 mRNA, with seasonal- and tissue-specificities (higher in summer and in digestive gland). Among antioxidants, gpx1 mRNA was affected by Cd in both tissues and seasons, with further modulations due to pH and temperature variation tissue- and season-specific; in winter the combination of Cd, warming and acidification affected Cu/Zn-sod both in digestive gland and gills and cat only in gills, while weak seasonal variations were observed for gst-pi transcripts only in digestive gland. The overall results highlighted the importance of considering seasonality and responsiveness of different tissues to predict the effects of sudden changes in environmental parameters on responsiveness to and toxicity of chemicals in marine coastal organisms.

Quantitative immunodetection of metalloprotein II in Perinereis aibuhitensis after heavy metal exposure

The metal detoxification mechanism is essential for the accumulation activity of some polychaetes. In order to investigate the detoxification function of metalloprotein II in polychaete Perinereis aibuhitensis, a recombinant fusion protein of MP II was successfully expressed in vitro and an anti-MP II polyclonal antibody was got. The tissue distribution of MP II in P. aibuhitensis and the protein expression under Cd, Pb and Zn exposure were detected by ELISA with this antibody. The results showed that MP II was higher in the intestine of P. aibuhitensis, followed by the body wall and parapodium. Cd, Zn and Pb exposure can induced MP II expression, but the change trend of MP II under various heavy metal exposure was different. The amount of MP II induced in P. aibuhitensis increased with the rises of Cd concentration, but there is no significant relationship between Zn and Pb concentration and MP II level.

Integrated assessment of the acclimation capacity of the marine bivalve Crenomytilus grayanus under naturally highly contaminated conditions: Subcellular distribution of trace metals and structural alterations of nephrocytes

The aim of our work was to assess whether the cellular processes in the nephrocytes of the long-lived mussel Crenomytilus grayanus tend to acclimation or destruction under trace metal contamination. Mussels were collected from three sites in the north-western Pacific Ocean: reference site, upwelling site, and a site highly contaminated with trace metals. Concentration, subcellular distribution of trace metals (Cd, Cu, Zn, and Pb) in the mussel kidneys, and ultrastructural alterations of the nephrocytes were studied. To assess the total load of accumulated trace metals, the total concentration coefficient (∑СС) was determined. In the kidneys of the reference C. grayanus, trace metals were eliminated from cell metabolism mainly by lysosomal granules or residue bodies. Under high levels of contamination, the defense mechanisms of C. grayanus are practically suppressed (no metallothionein-like protein peak, decreased content of granules) by the total effect of accumulated pollutants that leads to the destruction of cellular structures. Under natural conditions (upwelling site), increased accumulation of trace metals in the mussel kidneys did not lead to an increase in the number or size of lysosomal granules. However, abnormal high Cd accumulation in the kidneys caused the synthesis of high levels of metallothionein-like proteins that sequester most of the studied trace metals. To quickly lower the metal levels in nephrocytes under these conditions, a unique long-term acclimatory response - apocrine-like secretion in nephrocytes, which provides rapid elimination of me-MTLP complexes from the cell arose. Thus, our integrated study of the subcellular distribution of trace metals and ultrastructural alterations in nephrocytes allowed us to characterize the features of the structural and functional alterations in mussel cells under the field conditions tested.

Heavy metal contamination in a highly consumed Brazilian fish: immunohistochemical and histopathological assessments

Due to industrial, rural, and domestic waste disposal, heavy metals such as cadmium (Cd), chromium (Cr), lead (Pb), zinc (Zn), copper (Cu), and iron (Fe) continually infiltrate aquatic environments. These pollutants do not degrade naturally and, thus, have a high capacity for bioaccumulation in tissues and organs. The present study uses histological and immunohistochemical analyses to evaluate the contamination status of Salminus franciscanus, a large and economically important fish. Levels of Cd, Cr, Pb, Zn, Cu, and Fe were evaluated by atomic absorption spectrometry in the liver and muscle of fish sampled from two tributaries of the upper São Francisco River Basin, Brazil: the Abaeté and Paraopeba Rivers. In addition, histopathological alterations and expressions of three environmental biomarkers were assessed: metallothionein (MT), heat shock protein-70 (HSP70), and cytochrome P450-1A (CYP1A). The results show that fish from the Paraopeba River are unsuitable for human consumption, with several metals being detected above the safe limits established by the World Health Organization. Histopathological alterations in the liver and spleen were also significantly more frequent in fish from the Paraopeba River than in those from the Abaeté River (P < 0.05). Significant differences in the expressions of environmental biomarkers were observed between the rivers. Fish from the Abaeté River presented significantly higher values of the gonadosomatic index (GSI) and lower levels of metal contamination in the liver and muscle.

Modulation of copper-induced antioxidant defense, Cu transport, and mitophagy by hypoxia in the large yellow croaker (Larimichthys crocea)

This study aimed to investigate the effects of hypoxia on Cu-induced antioxidant defense, Cu transport, and mitophagy in the liver of the large yellow croaker. Fish were exposed to hypoxia (3.0 mg L^-1), Cu (120 μg L^-1), and hypoxia (3.0 mg L^-1) plus Cu (120 μg L^-1) for 48 h. Hypoxia exposure increased antioxidant abilities to maintain cellular redox balance. Although Cu exposure alone improved antioxidant defense, Cu transport, and mitophagy, these stress responses could not completely neutralize Cu toxicity, as reflected by the elevated reactive oxygen species (ROS) and lipid peroxidation (LPO) and hepatic vacuoles. When compared with Cu stress alone, hypoxia increased Cu toxicity by inhibiting antioxidant defense, Cu transport, and mitophagy, leading to the increment of mortality, ROS, and LPO, and the deterioration of histological structure. The adverse effects of hypoxia on Cu-induced metal transport and mitophagy might be involved in metal-responsive element-binding transcription factor-1 (MTF-1) and Forkhead box O-3 (FoxO3) signaling pathways, respectively. Overall, hypoxia reduced antioxidant response, Cu transport, and mitophagy in fish exposed to Cu, which contributes to understanding the molecular mechanisms underlying negative effects of hypoxia on Cu toxicity in fish.

Changes in oxidative stress biomarkers in Sinonovacula constricta in response to toxic metal accumulation during growth in an aquaculture farm

Clam farming comprises an important part of China's economy. However, increasing pollution in the ocean caused by toxic metals has led to the bioaccumulation of toxic metals in marine animals, especially the bivalves such as clams, and the consequence of heavy metal-associated toxicity in these animals. Such toxicity can enhance the production of reactive oxygen species (ROS) within the tissues of the animals. In aquatic species, oxidative stress mechanisms have been studied by measuring the antioxidant and oxidative damage index in the tissues. The objectives of this study were to investigate the levels of different toxic metals and the extent of oxidative stress responses in the clam Sinonovacula constricta at different growth periods (from May to October) in an aquaculture farm in Wengyang, an important economic shellfish culture zone in Zhejiang Province, China. Water and sediment samples taken from the farm were subjected to Pb, Hg, Cd, Cr assays. Overall, the levels of these metals in the water and sediment could be considered as light pollution, though the levels of Hg in the water (0.266) and Cd in the sediment (0.813) could be considered as reaching moderate pollution. In addition, the levels of these metals, H₂O₂, MDA and GSH content, antioxidant enzyme (CAT, SOD, GPx) activities as well as the level of metallothioneins (MT) mRNA in the tissues of S. constricta were also analyzed. The levels of Pb, Hg, Cd, Cr increased with increasing culturing time, and a higher level of these metals was accumulated in the visceral mass than in the foot. The levels of MDA and GSH, as well as the level of SOD activity in the viscera and foot of S. constricta increased with increasing metal accumulation. However, CAT and GPX activities, H₂O₂ level and the expression of MT initially increased and then decreased. This suggested that S. constricta might have the ability to control oxidative damage by triggering antioxidant defense in coordination with the metal sequestering response. The results also implied that toxic metal pollution should be taken into account when selecting the site to be used as an aquaculture farm. In addition, the visceral mass should be considered to be a good tissue for measuring the level of metal pollutants.

Effects of waterborne exposure to cadmium on biochemical responses in the freshwater gastropod, Bellamya aeruginosa

The biochemical responses of Bellamya aeruginosa as a dominant and widespread freshwater gastropod throughout China to waterborne cadmium (Cd) were investigated to explore the impacts of exposure concentration and duration in this potential sentinel species. After the 7 days' test of dosage-mortality relationship, gastropods were exposed for either 7 days at the LC₅₀ (1.7 mg/L), the LC₁₀ (0.7 mg/L) and 0.02 mg/L Cd, or 28 days at 0.02 mg/L Cd. A suite of biochemical indicators including metallothionein-like protein (MTLP), reduced glutathione (GSH), catalase (CAT), contents of tissue metal (Cd, Fe, Mn, Cu, Zn), and the compartments of these metals bound to MTLP were examined. The treatment of 0.02 mg/L Cd led to the increase of Cd bound to MTLP (Cd-MTLP) levels, the decrease of GSH content, and the upregulation of CAT activity, but no induction of MTLP, indicating that the intrinsic MTLP and GSH worked together for the detoxification of Cd at the low exposure. When the exposure concentration increased, GSH was depleted severely and synthesis of MTLP was triggered, leading to a strong and significant relationship between MTLP level and Cd accumulation. At the lethal concentrations (1.7 mg/L), both MTLP induction and CAT activity were inhibited while the proportion of Cd-MTLP to total Cd were increased, suggesting more intrinsic MTLP were utilized to sequester free Cd ions. Therefore, the content of Cd-MTLP in digestive glands of B. aeruginosa was recommended as a reliable biomarker for Cd contamination.

Pre-hypoxia exposure inhibited copper toxicity by improving energy metabolism, antioxidant defence and mitophagy in the liver of the large yellow croaker Larimichthys crocea

This study investigated the effects of moderate hypoxia pre-exposure on energy metabolism, antioxidant defence and mitophagy in the liver of the large yellow croaker Larimichthys crocea exposed to Cu. Fish were pre-exposed to either normoxia or hypoxia (~3.0 mg L^-1, 42% O₂ saturation) for 48 h, and subsequently were subjected to either control (without Cu addition) or Cu (168 μg L^-1) under normoxic conditions for another 48 h. Copper exposure under normoxia induced Cu toxicity that increased mortality, the production of reactive oxygen species (ROS) and malondialdehyde, and aberrant hepatic mitochondrial ultrastructure. Interestingly, hypoxia pre-exposure improved energy metabolism, antioxidant ability and mitophagy response, and reduced the Cu content to inhibit Cu toxicity, reflecting the enhanced survival rate and reduced oxidative damage. In these processes, hypoxia-inducible factor-1α (HIF-1α), transcription factors NFE2-related nuclear factor 2 (Nrf2), and forkhead box O-3 (FoxO3) mRNA levels were correlated with expression of genes related to energy metabolism, antioxidant defence and mitophagy, respectively, indicating HIF-1α, Nrf2, and FoxO3 are required for the induction of their respective target genes. Overall, moderate hypoxia pre-exposure was able to generate adaptive responses to mitigate Cu-induced toxicological effects, underlining a central role of hormesis.

Mechanistic simulation of bioconcentration kinetics of waterborne Cd, Ag, Pd, and Pt in the zebra mussel Dreissena polymorpha

Mechanistic models based on chemical properties of metals and body size have received substantial attention for their potential application to various metals and to different conditions without required calibration. This advantage has been demonstrated for a number of metals, such as Cd and Ag. However, the capacity of metal-specific chemical properties to explain variations in the accumulation for platinum-group elements (PGEs) has not been investigated yet, although emission of these metals is of increasing concern. Once being released, PGEs exist in the environment in mixtures with other metals. The present study attempted to model the accumulation of Pd and Pt in mixtures with Ag and Cd in the zebra mussel (Dreissena polymorpha) from the aqueous phase; and to investigate the potential application of mechanistic models to Pd and Pt. The present study showed statistically insignificant differences in metal accumulation among size groups in a narrow range of shell length (16-22 mm). Kinetic models could simulate well the accumulation of Cd, Ag, and Pt when metal-specific responses of zebra mussels are taken into consideration. These responses include enhanced immobilisation as a detoxifying mechanism and exchange between soft tissues and shells via the extrapallial fluid. Environmental conditions, e.g. the presence of abiotic ligands such as chloride, might also play an important role in metal accumulation. Significant relationships between the absorption efficiency and the covalent index indicate the potential application of mechanistic models based on this chemical property to Pt.

Assessment of metal concentrations in oysters and shrimp from Atlantic Coast of the Democratic Republic of the Congo

Oysters and shrimp are abundant and commonly consumed seafood by the indigenous population of the Kongo central region of the Democratic Republic of the Congo (DRC). Literature reviews suggest that no data were available for the metal concentrations in these species. Consequently, the purpose of this study is to determine the metal concentrations in tissues of oysters (Egeria congica) and shrimp (Macrobrachium spp., Parapenaeus spp., Penaeus spp.) collected in November 2017 from the Atlantic Ocean Coast of DRC in the territory of Muanda. Metal levels in the seafood species studied here were put into context using international regulation for human consumption set by the Food and Agriculture Organization (FAO), Canadian Food Inspection Agency (CFIA), European Union (EU), and World Health Organization (WHO). Our results demonstrated that the concentration of heavy metals varied considerably between sampling sites and analyzed species (P < 0.05), with the values (in mg kg1) ranged between 0.05-0.41, 0.03-2.25, Collapse

Key Words

• Atlantic Ocean
• Bioaccumulation
• Congo DR
• Environmental pollution
• Environmental risk assessment
• Environmental science
• Heavy metal
• Oysters
• Shrimp
• Water pollution
• Water quality

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Affiliation(s)

Robert B. Suami University of Kinshasa (UNIKIN), Faculty of Science, Department of Chemistry, B.P. 190, Kinshasa XI, Democratic Republic of the Congo University of Kinshasa (UNIKIN), Faculty of Pharmaceutical Sciences, B.P. 212, Kinshasa XI, Democratic Republic of the Congo
Dhafer Mohammed M. Al Salah Department F.-A. Forel for Environmental and Aquatic Sciences and Institute of Environmental Sciences, School of Earth and Environmental Sciences, Faculty of Science, University of Geneva, Uni Carl Vogt, 66 Boulevard Carl-Vogt, Geneva 4, CH-1211, Switzerland King Abdulaziz City for Science and Technology, Joint Centers of Excellence Program, Prince Turki the 1st Street, Riyadh, 11442, Saudi Arabia
César D. Kabala University of Kinshasa (UNIKIN), Faculty of Pharmaceutical Sciences, B.P. 212, Kinshasa XI, Democratic Republic of the Congo
J.-P. Otamonga Université Pédagogique Nationale (UPN). Croisement Route de Matadi et Avenue de la Libération. Quartier Binza/UPN, B.P. 8815, Kinshasa, République Démocratique du Congo
Crispin K. Mulaji University of Kinshasa (UNIKIN), Faculty of Science, Department of Chemistry, B.P. 190, Kinshasa XI, Democratic Republic of the Congo
Pius T. Mpiana University of Kinshasa (UNIKIN), Faculty of Science, Department of Chemistry, B.P. 190, Kinshasa XI, Democratic Republic of the Congo
John W. Poté University of Kinshasa (UNIKIN), Faculty of Science, Department of Chemistry, B.P. 190, Kinshasa XI, Democratic Republic of the Congo Department F.-A. Forel for Environmental and Aquatic Sciences and Institute of Environmental Sciences, School of Earth and Environmental Sciences, Faculty of Science, University of Geneva, Uni Carl Vogt, 66 Boulevard Carl-Vogt, Geneva 4, CH-1211, Switzerland Université Pédagogique Nationale (UPN). Croisement Route de Matadi et Avenue de la Libération. Quartier Binza/UPN, B.P. 8815, Kinshasa, République Démocratique du Congo

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Cu pre-exposure alters antioxidant defense and energy metabolism in large yellow croaker Larimichthys crocea in response to severe hypoxia

The aim of the present study was to evaluate the effects of Cu pre-exposure on antioxidant defense and energy metabolism in the liver of the large yellow croaker exposed to severe hypoxia. Fish were pre-acclimated to 0 and 30 μg Cu L^-1 for 96 h, and subsequently exposed to 7.0 and 1.5 mg DO L^-1 for another 24 h. Hypoxic stress alone increased reactive oxygen species and hepatic vacuoles. When compared to hypoxic stress alone, hypoxic stress plus Cu pre-exposure increased mortality and ROS production, and worsened histological structure by inhibiting antioxidant defense and aerobic metabolism, and enhancing anaerobic metabolism, suggesting Cu pre-acclimation aggravated hypoxia-induced oxidative damage. NFE2-related nuclear factor 2 and hypoxia-inducible factor-1α might participate in the transcriptional regulation of genes related to antioxidant response and energy metabolism, respectively. In conclusion, Cu pre-acclimation had a synergistic effect on antioxidant response and energy metabolism in fish under severe hypoxia, which contributes to understanding the molecular mechanisms underlying negative effects of Cu pre-acclimation against hypoxic damage in fish.

Biomarker responses in oysters Crassostrea hongkongensis in relation to metal contamination patterns in the Pearl River Estuary, southern China

The Pearl River Estuary (PRE) is the third largest estuary in China, where estuarine organisms are under metal stress at various biological levels. Based on the metal concentrations measured in oyster Crassostrea hongkongensis, we documented a change in dominance of metal contamination from Cd, Cr, Cu, Ni and Zn to Ag, Cd, Cu and Zn. In general, metal concentrations were higher in upstream stations and displayed a clear up-downstream gradient. Compared to the historical values, we noted the reductions in Cd, Cr and Ni concentrations, and the changing inputs due to evolving industrial activities were responsible for shaping the metal contamination profile in the PRE region. Along with metal concentrations, a suite of biomarkers was analyzed. Among the metals measured in the oyster tissues, Ag, Cd, Cu, Ni and Zn showed the strongest associations with pro-oxidant and oxidative stress responses (superoxide dismutase, lipid peroxidation and lysosomal membrane destabilization) and detoxification responses (glutathione and metallothionein), suggesting that the present metal contamination still exerts significant amount of stress in biota in the PRE. Metal contamination in estuaries in China is still severe compared to other countries, therefore continuous efforts should be taken to monitor the changing metal profiles with necessary control and remediation measures.

Heavy metals accumulation and endocrine disruption in Prochilodus argenteus from a polluted neotropical river

Heavy metals are considered major pollutants of aquatic environments due to the difficulty of metabolization and the bioaccumulative potential in tissues of aquatic organisms, especially fish muscle that is often used as food worldwide. In addition to causing cell damage, some metals such as aluminium (Al), cadmium (Cd), copper (Cu), and lead (Pb) can act as endocrine disrupting chemicals in fish. The Paraopeba and Abaete Rivers are important tributaries of the upper São Francisco River basin, but the Paraopeba River receives, along its course, the discharge of many types of effluents that affect fish species, including widely consumed species such as Prochilodus argenteus. This study evaluated histological and molecular changes caused by chronic exposure to heavy metals in P. argenteus from the Paraopeba River and compared this to fish from the non-impacted Abaete River. Sampled fish from both rivers were used in histological analyses and immunohistochemical assays. The results showed increased incidence of histopathologies and changes in number and morphology of germline cells in both sexes. In addition, up-regulated expression of oestrogens-induced proteins in the liver of males were detected in polluted environment. All the alterations were related to the concentration of metals in water and fish. The high concentration of various metals observed in water and fish from Paraopeba River serves as an alert to the environmental and public health regulatory authorities.

Assessment of trace elements pollution in the sea ports of New South Wales (NSW), Australia using oysters as bioindicators

In this study Sydney rock oysters (S. glomerata) from six major sea ports of NSW, Australia were used as bioindicators to assess the distribution and levels of trace element accumulation in the ports. Substantial enrichment of Cu, Pb and Zn in the oysters of the sea ports were detected when compared to their background samples and the US Environmental Protection Agency (USEPA) provisional tolerable intake standard. Enrichment of As, Al, Fe, Mn, Br, Sr were also found in the oysters at the port areas. The bioconcentration ratios of the trace elements illustrated significant Fe, Cu, Zn, As, Mn, Al, Pb and Cr accumulation in S. glomerate. The biota sediment accumulation factor suggested Cu, Mn and Zn accumulation at two of the ports (Port Yamba and Botany), indicating availability of these metals in the oysters as strong metal accumulators. In addition, integrated metal contamination illustrated notable Fe, Zn, Cu and Al contamination at port environment, whereas cluster analysis portrayed interconnection between the contaminants and the study sites.

Mercury(II) Binding to Metallothionein in Mytilus edulis revealed by High Energy-Resolution XANES Spectroscopy

Of all divalent metals, mercury (HgII ) has the highest affinity for metallothioneins. HgII is considered to be enclosed in the α and β domains as tetrahedral α-type Hg4 Cys11-12 and β-type Hg3 Cys9 clusters similar to CdII and ZnII . However, neither the four-fold coordination of Hg nor the existence of Hg-Hg atomic pairs have ever been demonstrated, and the HgII partitioning among the two protein domains is unknown. Using high energy-resolution XANES spectroscopy, MP2 geometry optimization, and biochemical analysis, evidence for the coexistence of two-coordinate Hg-thiolate complex and four-coordinate Hg-thiolate cluster with a metacinnabar-type (β-HgS) structure in the α domain of separate metallothionein molecules from blue mussel under in vivo exposure is provided. The findings suggest that the CXXC claw setting of thiolate donors, which only exists in the α domain, acts as a nucleation center for the polynuclear complex and that the five CXC motifs from this domain serve as the cluster-forming motifs. Oligomerization is driven by metallophilic Hg⋅⋅⋅Hg interactions. Our results provide clues as to why Hg has higher affinity for the α than the β domain. More generally, this work provides a foundation for understanding how metallothioneins mediate mercury detoxification in the cell under in vivo conditions.

Molecular cloning and characterization of two genes encoding peroxiredoxins from freshwater bivalve Anodonta woodiana: Antioxidative effect and immune defense

Members of Prx family function as an important players in host defense against oxidative stress, and modulate immune responses. In the current study, two complete Prx sequences were isolated from bivalve Anodonta woodiana and respectively named AwPrx4a and AwPrx4b. Regulative characterizations of AwPrx4a and AwPrx4b derived from perfluorooctanesulfonate (PFOS), perfluoroocanoic acid (PFOA), lipopolysaccharide (LPS) and polyinosinic:polycytidylic (Poly I:C) challenge in hepatopancreas, gill and hemocytes were measured by quantitative real-time PCR, respectively. The full-length cDNA of AwPrx4a had an open reading frame ORF of 588 bp encoding 196 amino acids. Two highly conserved Prxs signature motifs were observed in deduced amino acid sequence, one was FYPLDFTFACPTEI, and the other was GEVCPA. Complete cDNA sequence of AwPrx4b was comprised of a 5' untranslated region (UTR) of 120 nucleotides, a 426 bp ORF which was encoded 142 amino acids, and a long 3'-UTR of 412 nucleotides. Expressions of AwPrx4a and AwPrx4b showed a significant up-regulation pattern in groups at lower concentration treatment of PFOS and PFOA, a biphasic profile in groups with a higher concentration treatment. Compared with that of control group, expressions of AwPrx4a and AwPrx4b were significantly induced by LPS and Poly I:C treatment in the hepatopancreas, gill and hemocytes. These results indicate up-regulations of AwPrx4a and AwPrx4b expression are associated with eliminating oxidative stress derived from PFOS and PFOA administration as well as enhancing immune defense against LPS and Poly I:C challenge.

Single and combined effects of Zn, Mn and Fe on the Neotropical freshwater bivalve Anodontites trapesialis: Bioaccumulation and biochemical biomarkers

Important concentrations of Zn, Mn and Fe were detected in a stream near a coal mining area and promoted, in field, biomarkers alterations in the bivalve Anodontites trapesialis. In order to understand the isolated and mixed effects of these metals on these Neotropical bivalves, we run short-term experiments under laboratory controlled conditions. After 96 h-exposure, tissues (gills, mantle, digestive gland, muscle, hemolymph) were removed for metal bioaccumulation analysis, oxidative stress biomarkers (reactive oxygen species (ROS), total antioxidant capacity, lipoperoxidation (LPO), proteins carbonylation (PC), metallothionein (MT), activity of superoxide dismutase and glutathione S-transferase and hemocytes DNA damage) and cholinesterase (ChE versus ASCh activity) activity evaluation. We run three independent tests. In Zn test, clams were exposed to three concentrations of Zn (0.18 mg L^-1, 1.0 mg L^-1, 5.0 mg L^-1); in Mn test, clams were exposed to three concentrations of Mn (0.1 mg L^-1, 0.5 mg L^-1, 5.0 mg L^-1) and in Mix test, clams were exposed to the mixture Zn (1 mg L^-1) + Mn (0.5 mg L^-1), with and without Fe (5.0 mg L^-1). After single exposure to 5.0 mg L^-1, Zn bioaccumulated in all tissues, but only in mantle and hemolymph after exposure to 1.0 mg L^-1. The increased MT in gills of A. trapesialis exposed to Zn appears to be sufficient to avoid damage, since LPO occurred only in digestive glands from animals exposed to 5.0 mg L^-1. We suggested that A. trapesialis had a metabolic suppression in consequence of Mn presence, based on the following results: the decrease of ROS in gills, the decrease of the Zn and Mn concentrations in tissues and the decrease of ChE versus ASCh activity in muscle. Despite this, animals exposed to Mn suffer oxidative damages (LPO and PC) in the mantle and digestive gland and MT increased in the mantle. These results showed A. trapesialis responded differently to each metal and Mn caused more damage. When exposed to Fe, gills level of ROS was increased, despite no changes in metal accumulation occurred. On the other hand, after exposure to the mixtures, tissues bioaccumulated Zn and previously observed damages caused by Mn and Fe disappeared. Consequently, biomarkers were less affected under mixture treatments, demonstrating mixtures effects or responses were not simply a combination of single exposures to Zn, Mn and Fe, but depend on metals toxicokinetics.

Characterization of calmodulin in the clam Anodonta woodiana: differential expressions in response to environmental Ca2+ and Cd2+

Aims

To explore effect of Ca2+ and Cd2+ on the calmodulin (CaM), one complete cDNA sequence (AwCaM1) was cloned and characterized from the freshwater mussel Anodonta woodiana and its expressions were analyzed.

Materials and methods

The AwCaM1 was cloned from the A. woodiana using the rapid amplification of cDNA ends methods and its expression was determined by real-time PCR.

Results

In the hepatopancreas, AwCaM1 expression was up-regulated with a time and dose dependent pattern in the Ca2+ treated groups (0.01, 0.02, 0.04 and 0.08 mg/L) during experiment observed, and increased more than 56.15% (p<0.05) compared with that of control group. AwCaM1 mRNA level increased more 65.04% (p<0.05) in the Cd2+ treated groups (8 and 16 mg/L). In the gill, AwCaM1 expression increased more than 79.41% (p<0.05) compared with that of control group in all the Ca2+ treated groups, and more than 88.23% (p<0.05) in all the Cd2+ treated groups.

Conclusion

These results indicated that up-regulations of AwCaM1 expression in bivalve A. woodiana are associated with Ca2+ absorb and environmental adaption derived from Ca2+ and Cd2+ treatment.

Heavy Metal Contamination in the Cultivated Oyster Crassostrea rivularis and Associated Health Risks from a Typical Mariculture Zone in the South China Sea

With the rapid development of mariculture in potentially contaminated regions in China and the world, food safety, is a growing concern. To evaluate heavy metals and their associated health risks in the cultivated oyster Crassostrea rivularis, the concentrations of heavy metals (Cd, Cr, Pb, Zn) in oysters and water/sediment were examined in a typical mariculture environment (Kaozhou Bay, South China Sea). Trends in the seasonal dynamics of heavy metals in oysters revealed a potential synergistic effects among the concentrations of Cd, Cr, and Zn; trends associated with Pb were less clear, although the ability of oysters to bioaccumulate and depurate Pb was excellent. Bioconcentration factors (BCF) indicated that C. rivularis has a strong ability to accumulate heavy metals, and the BCF was the highest for Zn (2.32 × 10⁵), followed by Cd (6.84 × 10⁴), Pb (2.77 × 10⁴) and Cr (1.23 × 10³) through the four seasons. Results showed that Cd concentrations in oysters could pose a risk to human health (HQ > 1). This study, therefore, suggests that there are potential human health risks due to heavy metal exposure through the consumption of C. rivularis from mariculture zones in South China Sea.

Effect of cadmium exposure on essential omega-3 fatty acids in the edible bivalve Donax trunculus

Donax trunculus is the most consumed bivalve by the local population of the Northeast Algeria for its nutritional value. Therefore, the aim of the current study was to determine the effects of cadmium (Cd), a known toxic metal, on the alterations in main essential omega-3 fatty acids, i.e., eicosapentaenoic acid (EPA; C20:5n-3) and docosahexaenoic acid (DHA; C22:6n-3), in male and female gonads of D. trunculus during the reproduction period at spring (before spawning). Additionally, this work seeks to describe the relation between EPA and DHA with non-methylene-interrupted dienoic (NMID) fatty acids, and explores their possible contribution of to protect against Cd stress. The samples were collected at El Battah, a relatively clean sea shore, and reared in the laboratory. Physico-chemical parameters such as temperature, pH, salinity, and dissolved oxygen were measured. Cd was added to the rearing water at two sublethal concentrations (LC₁₀ and LC₂₅-96h, as determined previously). A two-way ANOVA analysis indicated significant effects of concentrations and genders for both fatty acids. Our results showed a significant reduction in EPA and DHA concentrations in the both genders, with a strong effect in females. There was also a negative correlation between NMID fatty acids and the two essential omega-3 fatty acids for each gender.

Trace metals and macroelements in mussels from Chinese coastal waters: National spatial patterns and normalization

Metal contamination is one of the most ubiquitous and complex problems in the Chinese coastal environment. To explore the large-scale spatial patterns of bioavailable metals, we sampled three major mussels, including 784 blue mussels (Mytilus edulis Linnaeus, 1758) of 14 sites, 224 hard-shelled mussels (Mytilus unguiculatus Valenciennes, 1858) of 4 sites, and 392 green mussels (Perna viridis (Linnaeus, 1758)) of 7 sites, ranging from temperate to tropical coastlines of China, during August and September 2015. The concentrations of macroelements (Na, K, Ca, Mg, and P) and toxic trace metals (Ag, Cd, Cr, Cu, Ni, Pb, Ti, and Zn) in the mussel's whole soft tissues were determined. Among the four Chinese coastal basins, Cd, Ti and Cr in the mussel tissues were the highest at Bohai Sea (BS) and Yellow Sea (YS), and Cu, Ni, Pb and Ag in the mussel tissues were the highest at East China Sea (ECS) and South China Sea (SCS). Zinc concentrations in mussels from YS were significantly higher than those from the other regions. Given the variability of environmental conditions such as salinity and nutrients, we further normalized the measured tissue metal concentrations with tissue Na and P levels. After Na normalization as the salinity proxy, the variability of Cd, Cu, Zn, Ag, and Ni was reduced. Trace elements accumulation in the mussel tissues was significantly related to both macroelements (Na or P) and body dry weight. The present study demonstrated that nonlinear optimization of different elements was necessary in assessing metal bioaccumulation patterns in marine mussels at a large spatial scale.

Interrelationships among trace metals and metallothionein in digestive glands and gills for field samples of Merceneria merceneria

More widespread use of metallothionein (MT) as a biomarker for trace metal pollution continues to be partly dependent on obtaining reliable baseline concentrations and identifying increased induction of the enzyme with only modest increases in metal concentrations. In this study, new data on metals and MT levels in whole clams tissue, gills, and digestive glands from field samples and in sediments are presented. Concentrations of Cd, Cu, Fe, and Zn in depurated (24 h) clam samples of digestive glands, gills, and the whole clam Merceneria merceneria from the Indian River Lagoon, Florida, varied with location and showed moderate to strong correlations among Zn, Cu, and Fe. Concentrations of metallothionein (dry wt.) ranged from 34─270 μg/g in gills and 150-440 μg/g in digestive glands and showed moderate to strong correlations between organs and with metal concentrations in those organs. Observed trends support increased synthesis of metallothionein with only moderate increases in metal values and in response to statistically higher sediment metal concentrations.

Bioaccumulation of trace metals in farmed pacific oysters Crassostrea gigas from SW Gulf of California coast, Mexico

The aim of the study was to evaluate the bioavailability of trace metals (Chromium, Copper, Nickel, Lead, Zinc, Cadmium, Arsenic, and Mercury) in the commercially consumed Crassostrea gigas oysters collected over a 12-month growth period (2011-12) from an experimental cultivation farm in La Pitahaya, Sinaloa State, Mexico. Sediment and water samples were also collected from four different zones adjacent to the cultivation area to identify the concentration patterns of metals. The results revealed that sewage disposals, fertilizers used for agricultural practices and shrimp culture are the major sources for the enrichment of certain toxic metals. The metal concentrations in oysters presented a decreasing order of abundance (all values in mg Kg^-1): Zn (278.91 ± 93.03) > Cu (63.13 ± 31.72) > Cr (22.29 ± 30.23) > Cd (14.54 ± 4.28) > Ni (9.41 ± 11.33) > Pb (2.22 ± 1.33) > As (0.58 ± 0.91) > Hg (0.04 ± 0.06). Bioconcentration Factor (BCF) and Biota Sediment Accumulation Factor (BSAF) exhibited that C. gigas in the region are strong accumulators for Zn and Cd respectively. Thus, the present study proves to fulfill the gap in understanding the rate of bioaccumulation of metals in C. gigas which is regarded as the most sought after oyster species globally.

Blue mussels (Mytilus edulis spp.) as sentinel organisms in coastal pollution monitoring: A review

The blue mussel (Mytilus spp.) is widely used as a bioindicator for monitoring of coastal water pollution (mussel watch programs). Herein we provide a review of this study field with emphasis on: the suitability of Mytilus spp. as environmental sentinels; uptake and bioaccumulation patterns of key pollutant classes; the use of Mytilus spp. in mussel watch programs; recent trends in Norwegian mussel monitoring; environmental quality standards and background concentrations of key contaminants; pollutant effect biomarkers; confounding factors; particulate contaminants (microplastics, engineered nanomaterials); climate change; harmonization of monitoring procedures; and the use of deployed mussels (transplant caging) in pollution monitoring. Lastly, the overall state of the art of blue mussel pollution monitoring is discussed and some important issues for future research and development are highlighted.

Oyster-based national mapping of trace metals pollution in the Chinese coastal waters

To investigate the distribution and variability of trace metal pollution in the Chinese coastal waters, over 1000 adult oyster individuals were collected from 31 sites along the entire coastline, spanning from temperate to tropical regions (Bohai Sea, Yellow Sea, East China Sea and South China Sea), between August and September 2015. Concentrations of macroelements [sodium (Na), potassium (K), calcium (Ca), magnesium (Mg) and phosphorus (P)] and trace elements [cadmium (Cd), copper (Cu), zinc (Zn), nickel (Ni), lead (Pb), chromium (Cr), silver (Ag), and titanium (Ti)] in these oysters were concurrently measured and analyzed. The results showed high Ti, Zn and Cu bioaccumulation in oysters from Guangdong (South China Sea) and Zhejiang (East China Sea). Oysters at Nanji Island (Wenzhou) and Daya Bay (Huizhou) accumulated significantly high concentrations of Ni and Cr. The elements in these oysters were several times higher than the national food safety limits of China. On the other hand, the present study found that normalization of metals by salinity (Na) and nutrient (P) could reflect more details of metal pollution in the oysters. Biomonitoring of metal pollution could benefit from incorporating the macroelement calibration instead of focusing only on the total metal concentrations. Overall, simultaneous measurement of macroelements and trace metals coupled with non-linear analysis provide a new perspective for revealing the underlying mechanism of trace metal bioavailability and bioaccumulation in marine organisms.

Variations of biomarkers response in mussels Mytilus galloprovincialis to low, moderate and high concentrations of organic chemicals and metals

The changes of acetylcholinesterase activity (AChE), metallothioneins content (MTs), catalase activity (CAT) and lipid peroxidation (LPO) were assessed after 4 days exposure of mussels Mytilus galloprovincialis to a wide range of sublethal concentrations of chlorpyrifos (CHP, 0.03-100 μg/L), benzo(a)pyrene (B(a)P, 0.01-100 μg/L), cadmium (Cd, 0.2-200 μg/L) and copper (Cu, 0.2-100 μg/L). The activity of AChE in the gills decreased after exposure to CHP and Cu, whereas no change of activity was detected after exposure to B(a)P and Cd. Both induction and decrease of MTs content in digestive gland occurred after exposure to CHP and B(a)P, while a marked increase was evident at highest exposure concentrations of Cd. The content of MTs progressively decreased of MTs with increasing concentration of Cu. CAT activity and LPO in the gills did not change after exposure to any of the chemicals. The results demonstrate different response profile in relation to the type of chemical compound, and highlight the potential implications for evaluation of biological effect of contaminants in marine environment. Furthermore, the AChE activity in the gills and MTs content in the digestive gland could be modulated by CHP and Cu at environmentally relevant concentrations indicating the potential risks of short-term transient mussels exposure that may occur due to run-off from land or accidental releases.

Nanoparticulate versus ionic silver: Behavior in the tank water, bioaccumulation, elimination and subcellular distribution in the freshwater mussel Dreissena polymorpha

Zebra mussels (Dreissena polymorpha) were exposed to polyvinylpyrrolidone (PVP)-coated silver nanoparticles (AgNP; hydrodynamic diameter 80 nm; solid diameter 50 nm) to investigate the behavior of Ag in the tank water with respect to its uptake, bioaccumulation, elimination and subcellular distribution in the mussel soft tissue. Parallel experiments were performed with ionic Ag (AgNO₃) to unravel possible differences between the metal forms. The recovery of the applied Ag concentration (500 μg/L) in the tank water was clearly affected by the metal source (AgNP < AgNO₃) and water type (reconstituted water < tap water). Filtration (<0.45 μm) of water samples showed different effects on the quantified metal concentration depending on the water type and Ag form. Ag accumulation in the mussel soft tissue was neither influenced by the metal source nor by the water type. Ag concentrations in the mussel soft tissue did not decrease during 14 days of depuration. For both metal forms the Ag distribution within different subcellular fractions, i.e. metal-rich granules (MRG), cellular debris, organelles, heat-sensitive proteins (HSP) and metallothionein-like proteins (MTLP), revealed time-dependent changes which can be referred to intracellular Ag translocation processes. The results provide clear evidence for the uptake of Ag by the mussel soft tissue in nanoparticulate as well as in ionic form. Thus, zebra mussels could be used as effective accumulation indicators for environmental monitoring of both Ag forms.