Concentrations of cadmium and zinc in seawater of Bohai Bay and their effects on biomarker responses in the bivalve Chlamys farreri

Dissolved and particulate heavy metal pollution status in seawater and sedimentary heavy metals of the Bohai Bay

Heavy metal contamination has been the focus of many studies owing to its potential risk on the health of coastal ecosystems. The Bohai Bay (BHB) is the second largest bay of Bohai Sea and subjected to serious anthropogenic perturbations. The aim of this study was to evaluate the distribution and pollution status of toxic heavy metals in seawater with two fractions (dissolved and suspended particulate phases) and surface sediments of this coastal system. Therefore, several hydrochemical parameters and concentration of seawater metals and sediment metals were measured at two cruises of 2020 summer and autumn. The spatial distribution and potential ecological risks were examined and their inter-element relationships were analyzed to identify potential geochemical processes. By comparing historical data since 1978, we find declining trends in contents of most trace metals in seawater and sediments, suggesting that recent pollution control in BHB have an effect on diminishing metal pollution. Dissolved metals showed no significant dependence on their particulate phase. The seawater posed a moderate to high level of ecological risk. The hydrochemical factors mainly had a greater impact on dissolved metals during summer, whereas they influenced suspended metals more significantly during autumn. These results provide fundamental information to support environmental quality management and ecological protection in coastal systems.

Stress response to trace elements mixture of different embryo-larval stages of Paracentrotus lividus

This study investigated for the first time the oxidative biomarkers responses in all larval stages of sea urchin. The contamination effects were reproduced by using contaminated seawater to concentrations measured in the area adjacent to an old asbestos mine at factors of 5 and 10. The results suggested that the concentrations were not sufficiently high to induce a major oxidative stress. The biometric differences make this method a more sensitive approach for assessing the effects on sea urchin larvae. Measurements of specific activities of antioxidant enzymes at each stage suggested a high capacity of the larvae to respond to oxidative stress. This normal activity of the organism must be considered in future research. This work also highlighted the importance of spawners provenance in ecotoxicological studies. These data are essential to better understand the stress responses of sea urchin larvae and provide baseline information for later environmental assessment research.

Dose-dependent responses of metabolism and tissue injuries in clam Ruditapes philippinarum after subchronic exposure to cadmium

Marine cadmium (Cd) pollution has been globally occurring, which creates a pressing need to characterize toxicological effects and develop biomarkers for Cd. However, the dose-response relationships challenge toxicity characterization and biomarkers selection. Metabolic processes have been frequently targeted by Cd. In this work, we investigated the dose-dependent effects of Cd on metabolic endpoints in whole soft tissues as well as gill and hepatopancreas injuries in clam Ruditapes philippinarum, aiming to better understand the metabolic responses and develop biomarkers. Nuclear magnetic resonance (NMR)-based metabolomic analysis was conducted on clam whole soft tissues to identify metabolites. The enzymes and metabolites associated with tricarboxylic acid (TCA) cycle, glycolysis, and oxidative phosphorylation showed both monotonic and non-monotonic curves with the increase of Cd dose. In details, glutamine, glucose-1-phosphate, hexokinase (HK), and citrate synthase (CS) presented monotonic decreases with the increase of Cd dose, among which glutamine and CS were preferable biomarkers to Cd exposure based on lower benchmark dose (BMD) values. The monotonic decreases of HK and CS activities suggested Cd exposure potentially disrupted glycolysis and TCA cycle via inhibiting rate-limiting enzymes. In contrast, the non-monotonic responses of succinate dehydrogenase (SDH), alanine aminotransferase (ALT), and their substrates (succinate and alanine) were approximate to U- or J-shaped curves, suggesting the adaptive strategy of metabolic responses to different degrees of Cd stress, like induction of anaerobiosis as energy compensation. Especially, the alterations of succinate and SDH presented typical hormetic dose-response curves. What is more, clam hepatopancreas was more sensitive to Cd than gill in terms of injury occurrence. Overall, characterization of dose-dependent effect of Cd on metabolism and tissue injuries provides a new insight into understanding the metabolic adaptation in marine clams and risk assessment of Cd pollution.

Modulation of endogenous antioxidants by zinc and copper in signal crayfish (Pacifastacus leniusculus)

Metal pollution is a long-standing concern and bioindicators are commonly used in ecotoxicological studies to monitor impacted wildlife populations for evidence of sublethal effects. Significant variation in the response of common biomarkers to metals is reported across taxa, thus necessitating careful characterization in model organisms. In this study, we describe the regulation of glutathione S-transferase (GST), glutathione (GSH), and metallothionein (MT) by zinc chloride (0.6, 0.9, 1.2, 2.4, 4.8, 9.6 μg g^-1) and copper chloride (0.6, 0.9, 1.2 μg g^-1) in signal crayfish (Pacifastacus leniusculus). Zinc chloride did not alter GST activity relative to controls in the hepatopancreas. Crayfish exposed to copper chloride exhibited decreased GST activity at the lowest dose tested (0.6 μg g^-1) with no change observed at the higher doses. GSH did not change in response to either metal when sexes were grouped together. MT concentrations increased in response to zinc (2.4, 4.6, and 9.6 μg g^-1 doses) and copper (0.6, 0.9, and 1.2 μg g^-1 doses) in gill tissue. In tail tissue, MT increased at the 2.4 and 4.8 μg g^-1 zinc chloride doses and all the concentrations of copper tested. Sex-specific differences in endogenous antioxidant expression were also analyzed with no clear patterns emerging. We concluded that these endpoints are sensitive to zinc and copper in signal crayfish, although careful interpretation is needed when applying them in field studies given the variation in responses, non-monotonic dose responses, and differences in biotic and abiotic factors that inevitably exist in different aquatic ecosystems.

Global characterization of dose-dependent effects of cadmium in clam Ruditapes philippinarum

Cadmium (Cd) is being frequently detected in marine organisms. However, dose-dependent effects of Cd challenged unraveling the toxicological mechanisms of Cd to marine organisms and developing biomarkers. Here, the dose-dependent effects of Cd on clams Ruditapes philippinarum following exposure to 5 doses of Cd (3, 9, 27, 81, 243 μg/L) were investigated using benchmark dose (BMD) method. By model fitting, calculation of BMD values was performed on transcriptomic profiles, metals concentrations, and antioxidant indices. Cd exposure induced not only significant Cd accumulation in clams, but also marked alterations of essential metals such as Ca, Cu, Zn, Mn, and Fe. Gene regulation posed little influence on essential metal homeostasis, indicated by poor enrichment of differentially expressed genes (DEGs) associated with metal binding and metal transport in lower concentrations of Cd-treated groups. BMD analysis on biological processes and pathways showed that peptide cross-linking was the most sensitive biological process to Cd exposure, followed by focal adhesion, ubiquitin mediated proteolysis, and apoptosis. Occurrence of apoptosis was also confirmed by TUENL-positive staining in gills and hepatopancreas of clams treated with Cd. Furthermore, many DEGs, such as transglutaminases (TGs), metallothionein (MT), STEAP2-like and laccase, which presented linear or monotonic curves and relatively low BMD values, were potentially preferable biomarkers in clams to Cd. Overall, BMD analysis on transcriptomic profiles, metals concentrations and biochemical endpoints unraveled the sensitiveness of key events in response to Cd treatments, which provided new insights in exploring the toxicological mechanisms of Cd in clams as well as biomarker selection.

Sediment quality of the Bohai Sea and the northern Yellow Sea indicated by the results of acid-volatile sulfide and simultaneously extracted metals determinations

The surface sediments from the Bohai Sea (BS) and the northern Yellow Sea (NYS) were analyzed for acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) to assess the sediment quality. The results indicated that >60% of the samples were found to have possible adverse effects on aquatic life in the BS based on the difference between the concentrations of AVS ([AVS]) and SEM ([SEM]), and the corresponding percentage in the NYS was <25%. Nevertheless, there was no indication of adverse effects for all the BS and the NYS samples when the total organic carbon (TOC) concentration was introduced in the sediment quality evaluation with [AVS] and [SEM]. The grain size composition, TOC, water content and pH all had significant influence on the distribution of [SEM] and the [SEM]/[AVS] ratios; while, in contrast, the distribution of [AVS] could be mainly determined by the redox condition of sediment.

Simultaneous Speciation Analysis of Trace Heavy Metals (Cu, Pb, Cd and Zn) in Seawater from Sishili Bay, North Yellow Sea, China

Different species of trace heavy metals (HMs) in seawater samples were simultaneously analyzed by anodic stripping voltammetric method, an analytical technique that does not require sample pre-concentration or the addition of reagents. The effects of the crucial parameters, deposition potential and time, on the determination of HMs were investigated. Concentrations of the total dissolved, dissolved active, and dissolved inert HMs were obtained through different analysis processes. The three species of Cu, Pb, Cd and Zn in seawater samples collected in different locations across Sishili Bay, North Yellow Sea, China were studied. The relative concentration of the dissolved active Cu, Pb, Cd and Zn in the total dissolved concentrations is 59.0%, 69.6%, 87.3% and 84.1%, respectively. The concentrations of different HMs species in Sishili Bay could be affected by the discharged effluent, sea current, and uptake of marine organism.

Chronic waterborne zinc and cadmium exposures induced different responses towards oxidative stress in the liver of zebrafish

Based on the same toxic level of 0.6% LC50 for 96-h and the severe situation of water pollution, we compared effects of chronic Zn (180μgL(-1)) and Cd exposures (30μgL(-1)) on growth, survival, histology, ultrastructure, and oxidative stress in the liver of zebrafish for 5 weeks. Growth performance and survival rate remained relatively constant under Zn stress, but was reduced under Cd exposure. Cd exposure also induced severe pyknotic nuclei, evident ultrastructure damage, and considerable lipid inclusions in the hepatocytes. However, these phenomena were not pronounced under Zn exposure. The negative effects caused by Cd may be explained by an increase in hepatic oxidative damage, as reflected by the enhanced levels of lipid peroxidation (LPO) and protein carbonylation (PC). The reduced activity of Cu/Zn-superoxide dismutase (Cu/Zn-SOD) and catalase (CAT) may result in the enhanced hepatic oxidative damage, though the mRNA and protein levels of both genes increased and remained unchanged respectively. On the contrary, Zn up-regulated the levels of mRNA, protein and activity of Cu/Zn-SOD, which may contribute to the decreased LPO levels. Nonetheless, the sharply up-regulated mRNA levels of CAT did not induce an increase in the protein and activity levels of CAT under Zn stress. Furthermore, transcription factor NF-E2-related factor 2 (Nrf2) expression parelleled with its target genes, suggesting that Nrf2 is required for the protracted induction of antioxidant genes. In conclusion, our data demonstrated that essential and non-essential metals induced some differences in oxidative damage in fish. The differences were not caused by the transcriptional level of related genes but depended on post-transcriptional modifications.

Trace elements in major marketed marine bivalves from six northern coastal cities of China: concentrations and risk assessment for human health

One hundred and fifty nine samples of nine edible bivalve species (Argopecten irradians, Chlamys farreri, Crassostrea virginica, Lasaea nipponica, Meretrix meretrix, Mytilus edulis, Ruditapes philippinarum, Scapharca subcrenata and Sinonovacula constricta) were randomly collected from eight local seafood markets in six big cities (Dalian, Qingdao, Rizhao, Weifang, Weihai and Yantai) in the northern coastal areas of China for the investigation of trace element contamination. As, Cd, Cr, Cu, Hg, Pb and Zn were quantified. The risk of these trace elements to humans through bivalve consumption was then assessed. Results indicated that the concentrations of most of the studied trace element varied significantly with species: the average concentration of Cu in C. virginica was an order of magnitude higher than that in the remaining species; the average concentration of Zn was also highest in C. virginica; the average concentration of As, Cd and Pb was highest in R. philippinarum, C. farreri and A. irradians, respectively. Spatial differences in the concentrations of elements were generally less than those of interspecies, yet some elements such as Cr and Hg in the samples from different cities showed a significant difference in concentrations for some bivalve species. Trace element concentrations in edible tissues followed the order of Zn>Cu>As>Cd>Cr>Pb>Hg generally. Statistical analysis (one-way ANOVA) indicated that different species examined showed different bioaccumulation of trace elements. There were significant correlations between the concentrations of some elements. The calculated hazard quotients indicated in general that there was no obvious health risk from the intake of trace elements through bivalve consumption. But care must be taken considering the increasing amount of seafood consumption.

Heavy metals induce oxidative stress and trigger oxidative stress-mediated heat shock protein (hsp) modulation in the intertidal copepod Tigriopus japonicus

Heat shock proteins (hsps) are induced by a wide range of environmental stressors including heavy metals in aquatic organisms. However, the effect of heavy metals on zooplankton at the molecular level remains still unclear. In this study, we measured the intracellular reactive oxygen species (ROS) level and the antioxidant enzyme activities for 96 h after exposure to five heavy metals: arsenic (As), cadmium (Cd), copper (Cu), silver (Ag), and zinc (Zn) in the intertidal copepod Tigriopus japonicus. Activities of the antioxidant enzymes were highly elevated in metal-exposed copepods, indicating that heavy metals can induce oxidative stress by generating ROS, and stimulate the involvement of antioxidant enzymes as cellular defense mechanisms. Subsequently, transcriptional changes in hsp gene families were further investigated in the metal-exposed groups for 96 h. The ROS level and glutathione (GSH) content were significantly increased in Ag-, As-, and Cu-exposed copepods, while they were only slightly elevated in Cd- and Zn-exposed groups. Based on the numbers of significantly modulated hsp genes and their expression levels for 96 h, we measured the effect of heavy metals to stress genes of T. japonicus in the following order: Cu > Zn > Ag > As > Cd, implying that Cu acts as a stronger oxidative stress inducer than other heavy metals. Of them, the expression of hsp20 and hsp70 genes was substantially modulated by exposure to heavy metals, indicating that these genes would provide a sensitive molecular biomarker for aquatic monitoring of heavy metal pollution.

Pollution status of the Bohai Sea: an overview of the environmental quality assessment related trace metals

It is well recognized that the ecosystem of the Bohai Sea is being rapidly degraded and the Sea has basically lost its function as a fishing ground. Billions of funds have been spent in slowing down, halting and finally reversing the environmental deterioration of the Bohai Sea. Although trace metals are routinely monitored, the data with high temporal resolution for a clear understanding of biogeochemical processes in the ecosystem of the Bohai Sea are insufficient, especially in the western literature. In this review, status of trace metal contamination in the Bohai Sea is assessed based on a comprehensive review of their concentrations recorded in the waters, sediments and organisms over the past decades. Studies show that metal contamination in the Bohai Sea is closely associated with the fast economic growth in the past decades. Concentrations of trace metals are high in coastal areas especially in the estuaries. Alarmingly high metal concentrations are observed in the waters, sediments and organisms from the western Bohai Bay and the northern Liaodong Bay, especially the coasts near Huludao in the northernmost area of the Bohai Sea, which is being polluted by industrial sewage from the surrounding areas. The knowledge of the speciation and fractionation of trace metals and the influence of submarine groundwater discharge on the biogeochemistry of trace metals in the Bohai Sea is far from enough and related work needs to be done urgently to get a better understanding of the influence of trace metals on the ecosystem of the Bohai Sea. A clear understanding of the trace metal pollution status of the Bohai Sea could not be achieved presently for lack of systematic cooperation in different research fields. It is quite necessary to apply the environmental and ecological modeling to the investigation of trace metals in the Bohai Sea and then provide foundations for the protection of the environment and ecosystem of the Bohai Sea.

Influence of cadmium on the morphology and functionality of haemocytes in the compound ascidian Botryllus schlosseri

In order to get insights into the effects of cadmium (Cd) on cell morphology and functions, we exposed haemocytes of the colonial ascidian Botryllus schlosseri to sub-lethal concentrations of CdCl(2). Results indicate that Cd hampers haemocyte spreading and phagocytosis in a dose-dependent way, through the alteration of the actin cytoskeleton. In addition, the metal decreases the stability of the internal membranes, as revealed by the Neutral Red assay. The fraction of cells showing positivity for the lysosomal enzyme acid phosphatase is also reduced in the presence of Cd, whereas the number of cells responsive to the Annexin-V assay and showing chromatin condensation increases, suggesting a metal-dependent induction of apoptosis in exposed cells. As Cd is a known cause of oxidative stress, the decrease in the percentage of cells positive to the assay for superoxide anion, observed at low Cd concentrations, is indicative of the synthesis of metal-chelating molecules, such as metallothioneins, whereas, the increase at high Cd concentrations suggests a depletion of the cell reducing redox potential.

Cu/Zn- and Mn-superoxide dismutase (SOD) from the copepod Tigriopus japonicus: molecular cloning and expression in response to environmental pollutants

Superoxide dismutase (SOD) is an important antioxidant enzyme which catalyzes conversion of superoxide to oxygen and hydrogen peroxide in aerobic organisms. Here, we cloned and sequenced the full-length cDNA and genomic DNA of two SODs from the copepod, Tigriopus japonicus: copper/zinc SOD (TJ-Cu/Zn-SOD) and manganese SOD (TJ-Mn-SOD). To define whether TJ-Mn-SOD is a cytosolic or a mitochondrial protein, a phylogenetic analysis was performed. The genomic structure of both TJ-SOD genes was determined with the promoter region sequences. In order to investigate their potential role in response to environmental pollutants, T. japonicus were treated with heavy metal (copper, zinc, and silver; 0, 10, 25, 50, and 100 μg L(-1)) and industrial chemicals (benzo[α]pyrene, 4-nonylphenol, and tributyltin; 0, 1, 5, 10, and 20 μg L(-1)) for 96 h. Subsequently, the TJ-Cu/Zn-SOD and TJ-Mn-SOD mRNA level was measured with quantitative real-time RT-PCR along with total SOD activity. The deduced amino acid residues of TJ-Cu/Zn-SOD and TJ-Mn-SOD possessed evolutionary conserved domains that are required for metal binding and Cu/ZnSOD-conserved signature sequences. The phylogenetic analysis revealed that TJ-Mn-SOD was closely clustered to mitochondrial Mn-SOD of another copepod, Lepeophtheirus salmonis. TJ-Cu/Zn-SOD gene had four exons and three introns, while the TJ-Mn-SOD gene consisted of two exons interrupted by one intron. In the 5'-flanking region of TJ-Cu/Zn-SOD and TJ-Mn-SOD, we observed several transcription regulatory elements such as p53, XRE, MRE, and ERE-half sites. In the response to heavy metals, Cu, Zn, and Ag, both TJ-Cu/Zn-SOD and TJ-Mn-SOD transcript levels along with enzyme levels were significantly increased at high concentrations (50 μg L(-1) and 100 μg L(-1)). Particularly, in the Cu- and Ag-exposed group, the expression of TJ-Mn-SOD mRNA was regulated more sensitively than the TJ-Cu/Zn-SOD mRNA level, indicating that the chemical susceptibility would be not correlated with the form of chemicals. B[a]P treatment showed a significant increase in the expression of both TJ-SODs mRNA level and enzyme level from 5 μg L(-1) concentration, while TBT decreased its expression at high concentrations (10 μg L(-1) and 20 μg L(-1)). 4-NP increased both TJ-SODs mRNA level at 1 μg L(-1) concentration, and then inhibited its expression from 5 μg L(-1) concentration to a lower level than the control. This finding suggests that TJ-Cu/Zn-SOD and TJ-Mn-SOD would be an inducible gene upon exposure to heavy metals and B[α]P, and could be used as a potential biomarker for the risk assessment of these environmental pollutants. This is the first report to elucidate response of SOD to environmental pollutants in copepods. Therefore, this study would give a clue to better understand the mode of action of antioxidant genes and enzymes under oxidative stress in marine invertebrates.