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

Copper redox state in cells and aquatic organisms: Implication for toxicity

Copper (Cu) redox state has been an important issue in biology and toxicology research, but many research gaps remain to be explored due to the limitations in the detecting techniques. Herein, the regulation of Cu homeostasis, including absorption, translocation, utilization, storage, and elimination behavior is discussed. Cuproptosis, a newly identified type of cell death caused by excessive Cu accumulation, which results in the aggregation of DLAT protein or the loss of Fe-S cluster and finally proteotoxic stress, is reviewed. Several longstanding mysteries of diseases such as Wilson disease and toxic effects, may be attributed to cuproptosis. Furthermore, we review the advanced detection methods and application of Cu(I) and Cu(II), especially the in-situ imaging techniques such as XANES, and chemosensors. Most of the existing studies using these detection techniques focus on the bioaccumulation and toxicity of Cu(I) and Cu(II) in cells and aquatic organisms. Finally, it will be important to identify the roles of Cu(I) and Cu(II) in the growth, development, and diseases of organisms, as well as the relationship between bioaccumulation and toxicity of Cu(I) and Cu(II) in cellular and aquatic toxicology.

Toxicokinetics and Mussel Watch: Addressing Interspecies Differences for Coastal Cadmium Contamination Assessment

Bivalves are often employed for biomonitoring contaminants in marine environments; however, in these large-scale programs, unavoidably, using multiple species presents a significant challenge. Interspecies differences in contaminant bioaccumulation can complicate data interpretation, and direct comparisons among species may result in misleading conclusions. Here, we propose a robust framework based on toxicokinetic measurements that accounts for interspecies differences in bioaccumulation. Specifically, via a recently developed double stable isotope tracer technique, we determined the toxicokinetics of cadmium (Cd)─a metal known for its high concentrations in bivalves and significant interspecies bioaccumulation variability─in six widespread bivalve species including mussels (Perna viridis, Mytilus unguiculatus, Mytilus galloprovincialis) and oysters (Magallana gigas, Magallana hongkongensis, Magallana angulata). Results show that oysters generally have higher Cd uptake rate constants (ku: 1.18-3.09 L g-1 d-1) and lower elimination rate constants (ke: 0.008-0.017 d-1) than mussels (ku: 0.21-0.64 L g-1 d-1; ke: 0.018-0.037 d-1). The interspecies differences in tissue Cd concentrations are predominantly due to Cd uptake rather than elimination. Utilizing toxicokinetic parameters to back-calculate Cd concentrations in seawater, we found that the ranking of Cd contamination levels at the six sites markedly differs from those based on tissue Cd concentrations. We propose that this approach will be useful for interpreting data from past and future biomonitoring programs.

Ecological risk assessment of heavy metal(loid)s in riverine sediments along the East China Sea: A large-scale integrated analysis

This study comprehensively assesses spatial distribution, pollution levels, and potential sources of heavy metal(loid)s in surface sediments across multiple river systems along the coastal area of the East China Sea. Copper in Qiantang River and Xiangshan Bay showed higher concentations and exceeded the threshold effect value, while the higher content of Lead was mainly found in the Saijiang River, Oujiang River, and Minjiang River. Heavy metal(loid)s in the alluvium of Qiantang River, Jiaojiang River, and Yangtze River showed low to moderate pollution levels, with Cd posing the highest ecological risk, followed by Hg. Meanwhile, Qiantang River, Jiaojiang River, Yangtze River, and Oujiang River exhibited considerable to moderate ecological risks and low toxic risk. PMF model analysis results reveal that concentrations of Cr, Ni, and As were closely related with natural geogenic input (36.56 %), while industrial and traffic activities (48.77 %) were primary source of Cu, Pb, Zn, and Hg, and main source of Cd was agricultural emissions (14.67 %).

Comprehensive effects of salinity, dissolved organic carbon and copper on mortality, osmotic regulation and bioaccumulation of copper in Oryzias melastigma

Cu, as an essential and toxic element, has gained widespread attention. Both salinity and dissolved organic carbon (DOC) are known to influence Cu toxicity in marine organisms. However, the intricate interplay between these factors and their specific influence on Cu toxicity remains ambiguous. So, this study conducted toxicity tests of Cu on Oryzias melastigma. The experiments involved three salinity levels (10, 20, and 30 ppt) and three DOC levels (0, 1, and 5 mg/L) to comprehensively investigate the underlying mechanisms of toxicity. The complex toxic effects were analyzed by mortality, NKA activity, net Na+ flux and Cu bioaccumulation in O. melastigma. The results indicate that Cu toxicity is notably influenced by both DOC and salinity. Interestingly, the discernible variation in Cu toxicity across different DOC levels diminishes as salinity levels increase. The presence of DOC enhances the impact of salinity on Cu toxicity, especially at higher Cu concentrations. Additionally, Visual MINTEQ was utilized to elucidate the chemical composition of Cu, revealing that DOC had a significant impact on Cu forms. Furthermore, we observed that fluctuations in salinity lead to the inhibition of Na+/K+-ATPase (NKA) activity, subsequently hindering the inflow of Na+. The effects of salinity and DOC on the bioaccumulation of copper were not significant. The influence of salinity on Cu toxicity is mainly through its effect on the osmotic regulation and biophysiology of O. melastigma. Additionally, DOC plays a crucial role in the different forms of Cu. Moreover, DOC-Cu complexes can be utilized by organisms. This study contributes to understanding the mechanism of copper's biological toxicity in intricate marine environments and serves as a valuable reference for developing marine water quality criteria for Cu.

Introducing bio-indicator fish of the Persian Gulf based on health risk assessment of 27 commercial species

BACKGROUND

The increasing consumption of seafood may bring health risks. It will be especially important for the people living along the coasts who are highly dependent on seafood for food and income.

METHODS

In this research, a comprehensive health risk assessment was performed on 27 species of high-consumption commercial fish sampled from stations located in Hormozgan province within the Northeast Persian Gulf. Concentrations of trace metals and their health risk were investigated.

RESULTS

Spatial distribution of trace metals in commercial fish showed central stations including Kong and Greater Tonb have higher concentrations of all trace metals except Pb. Some metals showed a significant correlation between concentrations. Our finding indicated the average concentration of all trace metals except Ni in all species was below the concentrations proposed by WHO/FAO/USEPA. EDI for all metals in all species in both adult and child age groups was lower than its RfD (oral reference dose of trace metal) showing the daily consumption of these fish does not pose any health risk and implicates seafood consumption guidelines or policies. Values of THQ for each metal and HI for all metals were lower than 1 in all commercial fish indicating the lack of non-cancerous health risk through the long-term consumption of these fish. The research found potential health risks associated with the consumption of these fish, specifically related to the metals Cr, Ni, and Cd.

CONCLUSION

In total, health risk indices proposed eight fish as bio-indicator species of the Persian Gulf. The findings emphasize the risk management of commercial fish consumption, especially bio-indicator species, in Hormozgan province, the Northeast Persian Gulf.

Explainable machine learning for predicting the geographical origin of Chinese Oysters via mineral elements analysis

The traceability of geographic origin is essential for guaranteeing the quality, safety, and protection of oyster brands. However, the current outcomes of traceability lack credibility as they do not adequately explain the model's predictions. Consequently, we conducted a study to evaluate the efficacy of utilizing explainable machine learning combined with mineral elements analysis. The study findings revealed that 18 elements have the ability to determine regional orientation. Simultaneously, individuals should pay closer attention to the potential risks associated with oyster consumption due to the regional differences in essential and toxic elements they contain. Light gradient boosting machine (LightGBM) model exhibited indistinguishable performance, achieving flawless accuracy, precision, recall, F1 score and AUC, with values of 96.77%, 96.43%, 98.53%, 97.32% and 0.998, respectively. The SHapley Additive exPlanations (SHAP) method was used to evaluate the output of the LightGBM model, revealing differences in feature interactions among oysters from different provinces. Specifically, the features Na, Zn, V, Mg, and K were found to have a significant impact on the predictive process of the model. Consistent with existing research, the use of explainable machine learning techniques can provide insights into the complex connections between important product attributes and relevant geographical information.

Copper and zinc isotope systematics in different bivalve mollusk species from the French coastline: Implications for biomonitoring

Zinc (Zn) and copper (Cu) stable isotopic compositions have been analyzed in various species of bivalve mollusks worldwide, but no comprehensive systematic interspecies comparison exists. Thus, we assessed isotope differences between species harvested in emblematic French coastal ecosystems to unveil biologically driven Cu and Zn isotope fractionation patterns. Inter-species isotopic variability of Cu is larger than Zn, with organisms that regulate internal concentrations displaying preferential bioaccumulation of heavy isotopes. The degree of internal isotope fractionation decreases from mussels > clams > oysters, affecting Cu more than Zn. The less pronounced Zn inter-specie variability helps preserve source information more reliably. Spatial analysis of a single oyster species denotes thus an important isotope variability of environmental Zn sources, including natural, anthropogenic and dietary components. Overall, results highlight the importance of considering systematic offset in Cu and Zn isotope values when comparing data from different bivalve species.

Microplastics as carriers of toxic pollutants: Source, transport, and toxicological effects

Microplastic pollution has emerged as a new environmental concern due to our reliance on plastic. Recent years have seen an upward trend in scholarly interest in the topic of microplastics carrying contaminants; however, the available review studies have largely focused on specific aspects of this issue, such as sorption, transport, and toxicological effects. Consequently, this review synthesizes the state-of-the-art knowledge on these topics by presenting key findings to guide better policy action toward microplastic management. Microplastics have been reported to absorb pollutants such as persistent organic pollutants, heavy metals, and antibiotics, leading to their bioaccumulation in marine and terrestrial ecosystems. Hydrophobic interactions are found to be the predominant sorption mechanism, especially for organic pollutants, although electrostatic forces, van der Waals forces, hydrogen bonding, and pi-pi interactions are also noteworthy. This review reveals that physicochemical properties of microplastics, such as size, structure, and functional groups, and environmental compartment properties, such as pH, temperature, and salinity, influence the sorption of pollutants by microplastic. It has been found that microplastics influence the growth and metabolism of organisms. Inadequate methods for collection and analysis of environmental samples, lack of replication of real-world settings in laboratories, and a lack of understanding of the sorption mechanism and toxicity of microplastics impede current microplastic research. Therefore, future research should focus on filling in these knowledge gaps.

The French Mussel Watch Program reveals the attenuation of coastal lead contamination over four decades

The mid-20th century industrial peak caused severe global lead (Pb) marine contamination. Although Europe initiated Pb emission reduction regulations in the 1980s, the short- and long-term impacts remain unclear. This study investigates the evolution of Pb contamination on the French coast through elemental and isotope analysis in oysters and mussels from the French "Mussel Watch" Program. Observations at 114 monitoring stations over four decades have shown decreasing Pb levels in these bivalve mollusks. In 1988, 95 % exceeded the background reference values; this level had dropped to 39 % by 2021. The Pb isotope ratios in bivalves from eight target sites revealed a reduction in bioaccumulated anthropogenic Pb, albeit without complete elimination. The long residence time of legacy Pb combined with inputs from diffuse urban sources likely explains the persistent presence of anthropogenic Pb on the French coast. This study endorses the importance of continuous biomonitoring to evaluate environmental regulations and policies.

Differentiation and decreased genetic diversity in field contaminated oysters Crassostrea hongkongensis: Identification of selection signatures

The extent to which chemical contamination affects the population structure and genetic diversity of natural populations remains elusive. Here, we used the whole-genome resequencing and transcriptome to diagnose the effects of long-term exposure to multiple elevated chemical pollutants on the population differentiation and genetic diversity in oysters Crassostrea hongkongensis in a typically polluted Pearl River Estuary (PRE) of Southern China. Population structure revealed an obvious differentiation between the PRE oysters and those collected from a nearby clean Beihai (BH) individuals, while no significant differentiation was observed among individuals collected from the three pollution sites within PRE due to the high gene flow. The decreased genetic diversity in the PRE oysters reflected the long-term effects of chemical pollutants. Selective sweeps between BH and PRE oysters revealed that chemical defensome genes, including glutathione S-transferase, zinc transporter, were responsible for their differentiation, sharing common metabolic process of other pollutants. Combined with the genome-wide association analysis, 25 regions containing 77 genes were identified to be responsible for the direct selection regions of metals. Linkage disequilibrium blocks and haplotypes within these regions provided the biomarkers of permanent effects. Our results provide important insights to the genetic mechanisms underlying the rapid evolution under chemical contamination in marine bivalves.

Field study of metal concentrations and biomarker responses in resident oysters of an estuarine system in southern Brazil

Pollutant exposure is considered an important factor responsible for the decline in marine biodiversity of Latin American coastal ecosystems. This threat has been detected in an estuarine system in southern Brazil, which prompted an investigation into the long-term biological effects of a chronic metal contamination on resident oysters from the Laguna Estuarine System (LES). Here, we present the species- and size-specific variations of biomarker responses (catalase, glucose-6-phosphate dehydrogenase, glutathione S-transferase, and protein carbonylation) in the gills and digestive gland of Crassostrea gigas and Crassostrea gasar. In parallel, concentrations of eight metals (Al, Cd, Cr, Cu, Fe, Mn, Pb, Zn) in soft tissues were measured. Our analyses revealed that the metal levels exhibited decreasing order in both species: Zn > Fe > Al > Cu > Mn > Cd. Except for Cu and Al, metal concentrations did not differ between oyster species. Biomarker results highlighted that C. gasar presented higher antioxidant responses, whereas C. gigas showed increased biotransformation upon exposure to LES pollutants, which varied according to the tissue. However, C. gasar showed a significant higher content of protein carbonylation but was not related to metals. In our research approach, the observation of metals presence and biomarkers-related responses are considered biologically relevant from an ecotoxicological perspective and serve as a baseline for future pollution studies in estuaries of Latin America. Finally, we recommend adopting a suite of biomarkers in both C. gasar and C. gigas, regardless their size and weight, as sentinel organisms in future regional biomonitoring studies in southern Brazil.

Geochemical controls on the distribution and bioavailability of heavy metals in sediments from Yangtze River to the East China Sea: Assessed by sequential extraction versus diffusive gradients in thin-films (DGT) technique

This study conducted a comprehensive investigation on the distribution and bioavailability of heavy metals (Cr, Co, Ni, Cu, Zn, Cd and Pb) in sediments along two typical transects from Yangtze River to the East China Sea continental shelf that spanning large physicochemical gradients. Heavy metals were mainly associated with the fine-grained sediments (enriched with organic matter), exhibiting decreasing trends from nearshore to offshore sites. The turbidity maximum zone showed the highest metal concentrations, which evaluated as polluted for some tested metals (especially Cd) using the geo-accumulation index. Based on the modified BCR procedure, the non-residual fractions of Cu, Zn and Pb were higher within the turbidity maximum zone, and significantly negatively correlated with bottom water salinity. The DGT-labile metals all positively correlated with the acid-soluble metal fraction (especially for Cd, Zn and Cr), and negatively correlated with salinity (except Co). Therefore, our results suggest salinity as the key factor controlling metal bioavailability, which could further modulate metal diffusive fluxes at the sediment-water interface. Considering that DGT probes could readily capture the bioavailable metal fractions, and reflect the impacts of salinity, we suggest DGT technique can be used as a robust predictor for metal bioavailability and mobility in estuary sediments.

Interspecies calibration for biomonitoring metal contamination in coastal waters using oysters and mussels

Differences in metal bioaccumulation among species make it difficult to compare biomonitoring results obtained using different marine bivalve species. To address this challenge and improve the interpretation of biomonitoring data, we studied the toxicokinetic mechanisms underlying these differences and developed a method to estimate seawater metal concentrations based on metal concentrations in the organisms. We transplanted six common species of oysters and mussels found in Chinese coastal waters into the Jiulong River estuary and monitored metal concentrations in the organisms, water, and suspended particles every three days over a six-week period. A one-compartment first-order toxicokinetic model was used to describe the relationship between metal bioaccumulation and metal concentrations in the environment. The model parameters, including aqueous uptake (k_u) and dietary assimilation (k_p) rate constants, and elimination rate constant (k_e), were estimated using a Markov Chain Monte Carlo fitting method with a priori information from a systematic review we conducted. The toxicokinetic model successfully fitted the temporal changes in metal bioaccumulation in all six bivalve species and explained the interspecies differences. Using the calibrated models, we were able to calculate metal concentrations in the seawater at the bivalve collection sites and enable comparisons of biomonitoring data across multiple species. In conclusion, we have established a toxicokinetic framework to explain interspecies differences in metal bioaccumulation in six commonly found bivalves and provided a useful tool for interpreting biomonitoring data in coastal environments.

Tissue-based trace element pollution of clam Ruditapes philippinarum in China: Hotspot identification and multiple nonlinear analysis

Considering the complexity of coastal and estuarine systems, a great challenge of environmental health assessment is to distinguish between natural and anthropogenically induced stress. Quantification of trace element accumulation in the tissues of sedentary bivalves with subsequent hotspot identification is important to assess the pollution status. The present study conducted a nationwide mapping of bioavailable macro- and trace elements in a widely distributed biomonitoring clam Ruditapes philippinarum from China. Ag, As, Cd, Cr, Cu, and Zn concentrations in the clams showed similar levels as those documented previously in mussels, but were lower than those in oysters at similar sites from China. Notably, the total As concentrations in clams at Xinkai Estuary and Beibu Bay were relatively higher than those at other sites in China. After normalization by tissue biomass, salinity (Na) and nutrient (P), some hotspots were identified with high pollution of trace elements at Liaodong Bay of Bohai Sea, Gold Beach of Qingdao, Dongling Port of Yellow Sea, Hangzhou Bay and adjacent coasts of East China Sea, and Pearl River Estuary and Beibu Bay of South China Sea. This study demonstrated that most trace elements had a path-dependent effect of biomass, except for Cd which showed an indirect pathway of AgNi related accumulation. Results showed significant correlations between Cd, Zn, Ag and Ni, and between Pb/Cr and Ti in clams. After mass normalization, all trace elements displayed significantly positive correlations with Na or P. Simultaneously, the clam biomass played an intermediary role in trace element accumulation in non-linear patterns related to salinity and nutrient. These results are important in evaluating the composite ambiguous information of the historical data of trace element biomonitoring.

Integrated biomarker responses and metal contamination survey in the wedge clam Donax trunculus from the Atlantic coast of Morocco

In Morocco, the marine environment has always been a major occupation for socioeconomic activities (industry, tourism, urbanization, etc.). Thus, this work displays a case study of Taghazout coast in the central Atlantic part of the country, which becomes the center of several development projects, such as the touristic resort Taghazout Bay. In the aim to assess the health status of this coastal ecosystem, a multi-indicator approach based on the response of biomarkers in the wedge clam Donax trunculus was adopted during two years (2016/2017). The undertaken investigations on the response of biomarkers (AChE, GST, MDA, and CAT) in the sentinel species D. trunculus showed an activation of defense mechanisms in this bivalve, which would imply exposure to chemical stress in this ecosystem. The monitoring of seasonal bioaccumulation of cadmium (Cd), lead (Pb), and copper (Cu) by D. trunculus indicates that the bivalves collected have been exposed to these metal sources in the study area. In addition, the correlation study has reported a significant effect of environmental parameters on biomarker response. Overall, the multi-indicator approach has clearly revealed the health status of Taghazout coast registered in a coastal urbanization.

Bioaccumulation and human health implications of trace metals in oysters from coastal areas of China

This study recompiled a national dataset to characterize the pollution level and health risk of cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) in oysters along the coastal areas of China. Results showed that the median concentrations of Cd, Cu, Pb and Zn in nationwide oysters were 5.5, 335, 1.3 and 1280 mg/kg dry weight, respectively. Generally, oysters from the north coasts presented lower metal pollution and higher quality than those from the south. The regional characteristics of trace metals in oysters might be contributed by the interspecific differences. Nationally, the noncarcinogenic risk posed by these four metals in oysters was relatively low, with the risk only occurring in a few hotspots such as the Pearl River Estuary and the Jiulong River Estuary. However, more attention should be paid to the carcinogenic risk of Cd, and priority should be given to formulating control measures to mitigate Cd pollution.

Metal bioaccumulation and transfer in benthic species based on isotopic signatures of individual amino acids in South China Sea cold seep environments

Cold seeps are deep-sea 'oases' with dense and dominant coexisting populations of large mussels and tubeworms under extreme environments. Under such natural source of high metal concentrations, the present study investigated the metal bioaccumulation and transfer with trophic positions in six benthic species by the isotopic δ¹⁵N and δ¹³C signatures in the active Haima cold seep, South China Sea. Comparing the isotopic signatures of bulk-tissue and amino acids by compound-specific isotopic analysis (CSIA-AA), we found that the bulk trophic (TP_B) values in the benthos except mussels were significantly higher than those of CSIA-based TP_Glu-Phe values. The estimated CSIA-based TP_Glu-Phe values showed a relatively compressed food chain with much changeable and unique amino acid isotopic heterogeneity, followed slim tubeworms (1.20)<mussels (1.38)<clams (1.52)<brittle stars (1.82)<giant tubeworms (2.16)<shrimps (2.31). All species accumulated relatively high concentrations of Fe, Zn, Cu, and Cr, especially for Zn in clams. Pearson correlation analysis showed that most metals had no significant relationship between their bioaccumulation and trophic positions, whereas Hg showed a significantly positive bioaccumulation through trophic transfer in such a compressed food chain. Water exposure was a major metal source rather than bacterial assimilation for most metals in the cold seep higher consumers. Hyperaccumulation of specific metals in some tissues of different benthos indicated different metal overflows in the Haima cold seep (As and Ni for tubeworms, Zn and Cd for clam gills, Ag and Cu for mussel gills). This study demonstrated high metal adaptations in different species and stable isotopic characteristics of amino acid metabolism in a natural high metal source of an active deep-sea cold seep, which is important for deep-sea development and environmental protection.

Transport of trace metals and their bioaccumulation in zooplankton from Changjiang (Yangtze River) to the East China Sea

The present study conducted a comprehensive field investigation on the transport and bioaccumulation of six trace metals (Cr, Cd, Pb, Mn, Ni, Cu) along a transect from Changjiang (Yangtze River) to the East China Sea continental shelf, which exhibited large variations in physiochemical properties (salinity, turbidity, pH, chlorophyll a, total nitrogen, dissolved oxygen, dissolved and particulate organic matter). From riverine sites to marine sites, dissolved Cr and Cd significantly increased, dissolved Pb and Mn showed less variations, while dissolved Cu and Ni showed complex spatial distribution patterns. Particulate trace metals (for Cr, Mn, Ni and Cu) were significantly negatively correlated with salinity. As a result, partition coefficients of trace metals (except Pb) were all significantly negatively correlated with salinity, indicating high salinity facilitated desorption/dissolution of metals from particulate phase. Additionally, the Changjiang derived particulate Pb, Mn, Ni and Cu sharply decreased (particularly for Mn) at the downstream of turbidity maximum zone, suggesting the efficient trapping of metals within this region. We further investigated the site-specific bioaccumulation of trace metals in size-fractionated zooplankton. Metal contents in macro-zooplankton were lower than micro- and meso-zooplankton owing to size-dependent zooplankton communities, while site-specific metal bioaccumulation mainly driven by site-specific zooplankton communities and salinity. The bioaccumulation factors of metals (Cr, Cd, Ni and Cu) were significantly negatively correlated with salinity, indicating high salinity hampered metal uptake which might attribute to competition of cations and formation of less bioavailable inorganic complexes with anions. Overall, high salinity generated two-sided effects (elevated dissolved metal concentrations Vs. reduced metal bioaccumulation) on metal contents in zooplankton (especially for Cr, Cd, Ni, and Cu), resulting in metal- and site-specific metal contents. We noticed relatively higher metal contents in zooplankton at hypoxia sites which could further transfer to predators in the East China Sea, and the underlying mechanisms still require future investigation.

Bioaccumulation of 35 metal(loid)s in organs of a freshwater mussel (Hyriopsis cumingii) and environmental implications in Poyang Lake, China

Benthic bioaccumulation of hazardous materials has been a great challenge to the health of lake ecosystems. As representative benthic macroinvertebrates, freshwater mussels and their accumulation characteristics have been regarded as effective indicators for assessing potential risks induced by sedimentary metal(loid)s in lakes. Here we profile organ-specific accumulation of 35 metal(loid)s in a freshwater mussel (Hyriopsis cumingii) and their correlations to metal speciation in sediments of Poyang Lake, the largest lake of China. Significant organ-specific characteristics of metal accumulation were found in gills, though higher thallium (Tl) and selenium (Se) were found in the hepatopancreas, and greater arsenic (As) mostly accumulated in gonads. Pearson correlation analysis revealed that the bioaccumulation of silver (Ag), cobalt (Co), and rare earth elements (ΣREE) in gills and As in gonads were closely associated with those in bioavailable fraction of sediments. Based on the biochemical analysis in the major organs, gills exhibited the highest enzymatic activity compared with hepatopancreas and gonads. Sedimentary metals, particularly for available Ag, Co, and ΣREE, play key roles in causing lipid peroxidation in gills and significantly promote the activities of superoxide dismutase (SOD)/glutathione reductase (GR), while many metals (e.g., cadmium, manganese, Se) inhibit the glutathione (GSH) content in gonads and hepatopancreas. Our study indicates a high physiological sensitivity of mussels to these target metals, which highlights the significance of organ-specific accumulation of metal(loid)s in understanding the potential ecological risks of sedimentary metal(loid)s in lake ecosystems.

Evaluation of the Use of Diluted Formic Acid in Sample Preparation for Elemental Determination in Crustacean Samples by MIP OES

A simple procedure for determination of Al, Cr, K, Mg, Mn, and Zn using diluted organic acid in the preparation of shrimp (Macrobrachium amazonicum) and crab samples (Ucides cordatus) was proposed in this study. Determinations were performed using microwave-induced plasma optical emission spectrometer (MIP OES). The contents of elements were evaluated after solubilization of samples in 50% formic acid (v v^-1) and subsequent heating in bath with stirring and heating at 90 °C. The accuracy of the proposed procedure was assessed using certified fish protein reference material (DORM-4) and the recovery percentages ranged from 91 to 117%. Microwave-assisted acid decomposition was used for a comparison of results with the procedure proposed using diluted formic acid, and the values obtained for all analytes were statistically equal at 95% confidence level. Cr levels were below the limit of detection. Potassium (7917-19,644 mg kg^-1), Mg (1319-5376 mg kg^-1), and Zn (43-307 mg kg^-1) were the most abundant elements in the crustacean species studied can be considered good sources of these constituents for human diet. The proposed procedure using diluted formic acid was considered simple and suitable to determine Al, Cr, K, Mg, Mn, and Zn concentrations in crustaceans using MIP OES.

Spatiotemporal patterns and influencing factors of dissolved heavy metals off the Yangtze River Estuary, East China Sea

Dissolved heavy metal pollution in the ocean is becoming an environmental concern. Their distribution patterns are complex and influenced by multiple factors in the coastal ocean. Therefore, more investigations are needed to understand their behavior in the seawater. This study systematically investigated the distribution of Cu, Pb, Cd, As, Zn and seawater properties in the surface and bottom water off the Yangtze River Estuary, East China Sea in spring, summer and autumn, 2019. The results showed significant spatiotemporal distribution that three-zone-pattern of estuary, nearshore, and offshore can be divided. While sources, hydrodynamics, biological uptake and sediment resuspension affected the overall distribution, dissolved oxygen and pH dominantly influenced the estuary and offshore respectively, with more complex factors in the nearshore. Low ecological risks were assessed during the study, but global warming, ocean acidification and hypoxia are essential concerns to understand the biogeochemistry of dissolved heavy metals in the ocean.

Long-term investigation of heavy metal variations in mollusks along the Chinese Bohai Sea

Biomonitoring is an effective way to assess the effects of pollutants on marine ecosystems. As an important fishing region in China, the Chinese Bohai Sea has been contaminated with heavy metals, posing great risks to seafood safety and human health. Herein, the spatiotemporal variations in the concentrations of seven heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) in 11 species of mollusks (658 samples) collected from the Chinese Bohai Sea were studied during 2006-2016. The concentrations of Cr, As, Cd, and Pb in approximately 41%, 100%, 71%, and 18% of the sampled mollusks exceeded the maximum permissible levels in aquatic products set by China, indicating that the mollusks were contaminated with varied concentrations of heavy metals. Except for slight fluctuations, no significant temporal variations were observed during the sampling period, suggesting a relatively stable status of these metals. Cluster analysis showed that oyster had higher bioaccumulation potential for Zn and Cu, whereas Mactra veneriformis, Rapana venosa, Meretrix meretrix, Chlamys farreri, and Mya arenaria had higher bioaccumulation potentials for Cr, As, Ni, Cd, and Pb, respectively. These findings are useful for biomonitoring and developing guidelines for seafood consumption in coastal regions. Significant relationships were observed between heavy metal concentrations in mollusks and socioeconomic indices (gross domestic product, per capita gross domestic product, and population amount), suggesting the effects of anthropogenic activities on heavy metal contamination. Our study established a good model to evaluate the risks of heavy metals and provided a sound scientific basis for controlling seafood safety in coastal regions.

Highly Sensitive and Specific Responses of Oyster Hemocytes to Copper Exposure: Single-Cell Transcriptomic Analysis of Different Cell Populations

Oyster hemocytes are the primary vehicles transporting and detoxifying metals and are regarded as important cells for the occurrence of colored oysters due to copper (Cu) contamination. However, its heterogeneous responses under Cu exposure have not been studied. Single-cell transcriptome profiling (scRNA-seq) provides high-resolution visual insights into tissue dynamics and environmental responses. Here, we used scRNA-seq to study the responses of different cell populations of hemocytes under Cu exposure in an estuarine oyster Crassostrea hongkongensis. The 1900 population-specific Cu-responsive genes were identified in 12 clusters of hemocytes, which provided a more sensitive technique for examining Cu exposure. The granulocyte, semigranulocyte, and hyalinocyte had specific responses, while the granulocyte was the most important responsive cell type and displayed heterogeneity responses of its two subtypes. In one subtype, Cu was transported with metal transporters and chelated with Cu chaperons in the cytoplasm. Excess Cu disturbed oxidative phosphorylation and induced reactive oxygen species production. However, in the other subtype, endocytosis was mainly responsible for Cu internalization, which was sequestered in membrane-bound granules. Collectively, our results provided the first mRNA expression profile of hemocytes in oysters and revealed the heterogeneity responses under Cu exposure.

Oyster arsenic, cadmium, copper, mercury, lead and zinc levels in the northern South China Sea: long-term spatiotemporal distributions, combined effects, and risk assessment to human health

Estuarine and coastal ecosystems are often considered vulnerable due to the complex biogeochemical processes and the human disturbances through a variety of pollution. Among environmental contaminants, heavy metals in estuarine and coastal ecosystems have been of increasing concern in environmental conservation. Long-term exposure to heavy metal contamination, mainly through food and water, could be harmful to human health. It is therefore critical to understand the quantitative comparisons and combined effects of different heavy metals in common seafood species, such as oysters. This work studied the long-term spatiotemporal trends and health risk assessment of oyster arsenic (As), cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb), and zinc (Zn) levels in the coastal waters of northern South China Sea. Cultured oysters (Crassostrea rivularis) from 23 estuaries and harbors in the coastal areas of northern South China Sea in 1989-2015 were analyzed for the spatiotemporal trends of the six heavy metal levels. Metal pollution index (MPI), target hazard quotient (THQ), and hazard index (HI) were used for quantifying the exposure of the six heavy metals to human health through oyster consumption. Principal component analysis (PCA) was used for assessing the relative importance of the six metals in oyster heavy metal distribution patterns in the northern South China Sea. Overall, the As, Cd, Cu, Hg, Pb, and Zn levels in oysters from the northern South China Sea generally declined from 1989 to 2015, stayed relatively high (MPI = 2.42-3.68) during 1989-2000, gradually decreased since 2000, and slightly increased after 2010. Oyster heavy metal levels were highest in the Pearl River Estuary (MPI = 1.20-5.52), followed by west Guangdong and east Guangdong, Guangxi, and Hainan coastal waters. This pattern is probably because economics and industry around the Pearl River Estuary have been growing faster than the other areas of this work in the recent two decades, and it should be taken as a hotspot for the monitoring of seafood safety in southern China. Principal component analysis indicated that Cu, Zn, and Cd were the most important metals in the long-term distributions of oyster heavy metal levels in the northern South China Sea. Health risk assessment suggested that the risk of the six heavy metals exposure through oyster consumption were relatively high during 1989-2005 (THQ = 1.01-5.82), significantly decreased since 2005 (THQ < 1), and slightly increased after 2010.

Metal stable isotopes in transplanted oysters as a new tool for monitoring anthropogenic metal bioaccumulation in marine environments: The case for copper

Metal release into the environment from anthropogenic activities may endanger ecosystems and human health. However, identifying and quantifying anthropogenic metal bioaccumulation in organisms remain a challenging task. In this work, we assess Cu isotopes in Pacific oysters (C. gigas) as a new tool for monitoring anthropogenic Cu bioaccumulation into marine environments. Arcachon Bay was taken as a natural laboratory due to its increasing contamination by Cu, and its relevance as a prominent shellfish production area. Here, we transplanted 18-month old oysters reared in an oceanic neighbor area into two Arcachon Bay mariculture sites under different exposure levels to continental Cu inputs. At the end of their 12-month long transplantation period, the oysters' Cu body burdens had increased, and was shifted toward more positive δ⁶⁵Cu values. The gradient of Cu isotope compositions observed for oysters sampling stations was consistent with relative geographic distance and exposure intensities to unknown continental Cu sources. A binary isotope mixing model based on experimental data allowed to estimate the Cu continental fraction bioaccumulated in the transplanted oysters. The positive δ⁶⁵Cu values and high bioaccumulated levels of Cu in transplanted oysters support that continental emissions are dominantly anthropogenic. However, identifying specific pollutant coastal source remained unelucidated mostly due to their broader and overlapping isotope signatures and potential post-depositional Cu isotope fractionation processes. Further investigations on isotope fractionation of Cu-based compounds in an aqueous medium may improve Cu source discrimination. Thus, using Cu as an example, this work combines for the first time a well-known caged bivalve approach with metal stable isotope techniques for monitoring and quantifying the bioaccumulation of anthropogenic metal into marine environments. Also, it states the main challenges to pinpoint specific coastal anthropogenic sources utilizing this approach and provides the perspectives for further studies to overcome them.

Distinguishing multiple Zn sources in oysters in a complex estuarine system using Zn isotope ratio signatures

The Pearl River Estuary (PRE), the largest estuary in Southern China, historically has suffered from metal contamination as a result of inputs from different riverine discharges. Determining the sources of metals accumulation in local aquatic flora and fauna remains a great challenge for this estuarine system with complex water circulation. In this study, Zn isotope ratios were measured in local oysters (Crassostrea hongkongensis) collected at 8 locations in the estuary on four occasions from 2014 to 2018, to better understand and assess the contamination sources. The results showed no significant differences (p < 0.05) in δ⁶⁶Zn values in oysters among the four sampling dates within individual sites. However, approximately a 0.67‰ (range from -0.66‰ to 0.01‰) difference in average δ⁶⁶Zn values was consistently found in oysters collected from the east side of the estuary compared to the west side, despite their comparable Zn concentrations. A mixing model was subsequently used to estimate the relative contributions from various sources to the δ⁶⁶Zn values in these oysters. The mixing model predicts that zinc derived from the dissolved fraction (approximately 80 %) was the dominant uptake pathway for oysters collected at the east shore whereas approximately 50 % of the Zn in oysters collected at the west shore was derived from the particulate fraction. The mixing model also was used to estimate the relative impacts of fresh versus saline water on the measured δ⁶⁶Zn values. Contributions from these two sources also varied between the east and west shores. This study presents the first data for Zn isotope ratios in oysters from the PRE, providing new insight for using Zn isotope ratios in oysters as a powerful tracer of sources in a complex estuarine system.

Copper promoting oyster larval growth and settlement: Molecular insights from RNA-seq

As a cofactor of key enzymes, Cu is required in living organisms, although Cu levels in the natural environment are typically low. In this study, the promotion of growth and settlement on the larvae of oyster Crassostrea angulata was observed at an environmentally relevant concentration (10 μg/L Cu). Interestingly, Cu accumulation in the soft tissue of oyster larvae increased during the larval development and exhibited a sharp increase at the late pelagic stage. With the help of RNA-seq, we constructed a high-quality transcriptional database of the oyster C. angulata larvae (24,257 genes with an average length of 1594 bp) via de novo assembly, which provided the basic molecular changes during the larval development. Network analysis of five early developmental stages and differential expression under Cu exposure were integrated to examine the roles of Cu in oyster larvae. Our molecular analysis demonstrated that both ion channels and organic transporters contributed to Cu internalization from the external environment, including zinc transporters and amino acid transporters. The followed distribution of Cu across cells was achieved by ATP7A, the circulatory system, and the Cu transporters (CTRs). Cu exposure enhanced the ribosome and the calcium binding proteins with a higher rate of translation and shell formation, giving rise to faster growth of oyster larvae. Furthermore, Cu facilitated the settling process by upregulating the chitin binding genes and then promoting the formation of the proteinaceous matrix between larvae and substrate. Our study presents the molecular basis for Cu promotion (i.e., hormesis) effects on oyster larval growth and settlement.

Tracing the heavy metals zinc, lead and nickel in banana shrimp (Penaeus merguiensis) from the Persian Gulf and human health risk assessment

Seafood has long been considered a unique source of nutrition. However, increasing trends in consumption of marine products must be considered, especially in potentially polluted environments such as the Persian Gulf. This study was undertaken to analyse the level of heavy metal contamination of nickel (Ni), zinc (Zn), and lead (Pb) in shrimp (Penaeus merguiensis) captured from the northern Persian Gulf. The concentration of heavy metals in the muscle of shrimp followed the order Zn > Ni > Pb. The content of Zn and Ni was higher than recommended standard limits by the FAO/WHO. The combined impact of all metals was lower than the acceptable limit of 1 in shrimp. The carcinogenic risk for Ni was higher than the unacceptable value. In total, our finding indicated no potential health risk from the daily consumption of this species. However, long-term consumption of shrimp can pose a risk of carcinogenic effects of nickel. Continuous monitoring of these trace metals in seafood is necessary to ensure the quality of seafood and food safety.

Assessment of the transfer of heavy metals in seawater, sediment, biota samples and determination the baseline tissue concentrations of metals in marine organisms

The majority of tissue-specific environmental quality standards (EQSs) considering metal tolerance are prior to the chemical-specific EQSs in aquatic organisms. However, metal baseline levels in marine organisms were very scarce. We explored the correlation between Hg, Cd, Pb, Cu, and Zn concentrations in water or sediments and those metal concentrations in marine organisms (crustacean, mollusc, and fish) by generalized additive models (GAMs) and executed a meta-analysis of Hg, Cd, Pb, Cu, and Zn contents in those three organisms by implementing cumulative frequency distribution analysis of individual metal distribution in a heavy metal-contaminated semi-enclosed Bay, China. Results showed that the average contents of Hg, Cd, Pb, Cu, and Zn were 0.042±0.01, 0.38±0.22, 1.72±0.65, 3.61±1.01, and 16.08±6.33 μg/L in water; 0.064±0.02, 0.42±0.04, 20.54±7.76, 28.97±3.90, and 96.74±35.11 μg/g dw in sediment; and 0.0049±0.0028, 0.52±0.28, 0.24±0.15, 11.05±6.95, and 21.12±4.47 μg/g dw in crustacean, 0.015±0.0087, 0.24±0.17, 0.08±0.02, 0.37±0.35, and 10.62±6.79 μg/g dw in mollusc; and 0.0038±0.0028, 0.065±0.05, 0.32±0.19, 2.01±0.59, and 16.04±4.97 μg/g dw in fish. The mercury content in mollusc presented a negative correlation with mercury content in sediment, while the content of other metals (Cd, Pb, Cu, and Zn) in organisms showed positive correlations with the content of those metals in water or sediment. We further obtained tissue-baseline-C5% in crustacean, mollusc, and fish which were 1.191, 3.341, and 0.014 μg/g dw for Cu; 0.013, 0.072, and 0.033 μg/g dw for Cd, 0.015, 0.027, and 0.052 μg/g dw for Pb; 9.515, 14.422, and 0.056 μg/g dw for Zn; and 0.0009, 0.004, and 0.0035 μg/g dw for Hg, respectively. However, there were no obvious relationships of the 4d-NOEC in laboratory toxicity tests with C5%, as well as C50% and 4d-LC50 or tolerance index a for Cu, Cd, Pb, Zn, and Hg in organisms. Our results pointed out the controversy of laboratory sensitive species toxicity results for deriving chemical-specific EQSs with field studies. We advocated to set up the metal concentration baselines in aquatic organisms and further served the tissue-specific EQSs, which are essential basis for geochemical recordings, bio-monitoring, and semi-enclosed bay management in the world.

Accumulation of different metals in oyster Crassostrea gigas: Significance and specificity of SLC39A (ZIP) and SLC30A (ZnT) gene families and polymorphism variation

The Zrt/Irt-like proteins (ZIP, SLC39A) and zinc transporters (ZnT, SLC30A) are the two major gene families responsible for the import/export of Zn and other metals. In this study, the mRNA expression levels and genetic variations of eight ZnTs and 14 ZIPs were identified in Crassostrea gigas after exposure to Zn, Cd, Cu, Hg, and Pb. Metal exposure induced reactive oxygen species (ROS) and malondialdehyde (MDA) accumulation and antioxidant enzyme expression. The expanded gene numbers of superoxide dismutase (SOD) in the oysters exhibited diverse expression under exposure to the five metals, and the contrasting expressions of both ZnTs and ZIPs under different metal exposures were observed, revealing their ion-specific responses. Zn and Cu have similar transporters and induce high expression levels of ZnT1, 2, 7, and 9 and ZIP1, 3, 6, 9, 10, 11, and 14. Pb induced high expression levels of ZIP7, and 13 and ZnT5, 6, and 7, which are mainly expressed in the endoplasmic reticulum (ER). Cd induced high expression levels of ZnT1, 2, and 7 and ZIP1, 6, 9, 10, 11, and 13. Hg exposure was found to have little effect on the ZIP and ZnT expression levels. Based on 3784 single nucleotide polymorphisms (SNPs) within the ZnTs and ZIPs, genetic association analysis for Zn accumulation was conducted on 427 oyster samples. The 38 SNPs, which were located within 12 genes, were identified to be associated with Zn content (p < 0.01), explaining the phenotypic variation from 1.61% to 3.37%. One nonsynonymous mutation and related haplotypes were identified within ZIP1, explaining 1.69% of the variation in Zn. Its high expression under Zn exposure revealed its important role in Zn transportation. To the best of our knowledge, this study is the first comprehensive investigation of the transportation mechanisms of ZIPs and ZnTs under different metal exposures and the genetic effect of Zn accumulation in oysters, and provides valuable biomarkers and genetic resources to evaluate environmental metal pollution.

Trophic transfer of emerging metallic contaminants in a neotropical mangrove ecosystem food web

Emerging metallic contaminants (EMCs) are of concern due their presence in aquatic ecosystems and the lack of environmental regulations in several countries. This study verifies the presence of EMCs in two neotropical mangrove estuarine ecosystems (Espírito Santo Brazil) by evaluating abiotic and biotic matrices across six trophic levels (plankton, oyster, shrimp, mangrove trees, crabs and fish) and hence interrogates the trophic transfer of these elements and their possible input sources. Using the oyster Crassostrea rhizophorae as a biomonitor, ten EMCs (Bi, Ce, La, Nb, Sn, Ta, Ti, W, Y and Zr) were determined. Bi input was from iron export and pelletizing industries; Ce, La and Y inputs were mainly associated with solid waste from steel production, while Zr, Nb and Ti were related to atmospheric particulate matter emissions. EMCs were detected at various trophic levels, showing biomagnification for most of them in the Santa Cruz estuary but biodilution in Vitória Bay. These contrasting results between the estuaries could be attributed to different pollution degrees, needing further research to be fully understood. This is the first report demonstrating EMCs trophic pathways in situ, constituting an essential baseline for future research and safety regulations involving EMCs in the environment.

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.

Protein molecular responses of field-collected oysters Crassostrea hongkongensis with greatly varying Cu and Zn body burdens

The oyster Crassostrea hongkongensis is an ideal biomonitor due to its widespread distribution along the coast of Southern China and the ability to hyperaccumulate metals including Cu and Zn. In this study, we conducted the first investigation of the molecular responses to metal hyperaccumulation based on quantitative shotgun proteomics technique and genome information. Gill tissue of oysters collected from the uncontaminated environment (Site 1, 59.6 μg/g and 670 μg/g dry weight for Cu and Zn) displayed significant protein profile differentiation compared to those from a moderately contaminated (Site 2, 1,465 μg/g and 10,170 μg/g for Cu and Zn) and a severely contaminated environment (Site 3, 3,899 μg/g and 39,170 μg/g for Cu and Zn). There were 626 proteins identified to be differentially expressed at Site 3 but only 247 proteins at Site 2. Oysters from a moderately contaminated estuary (Site 2) displayed fewer effects as compared to oysters under severe contamination, with fluctuated small molecule metabolism and enhanced translation process. At Site 3, the induction of reactive oxygen species (ROS) was the main toxicity under the extremely high level of metal stress, which resulted in protein damage. Additionally, the impaired structure of cytoskeleton and modified membrane tracking process at Site 3 oysters led to the blockage or less efficient protein or macromolecule distribution within cells. Nonetheless, proteomic analysis in this study revealed that oysters could partly alleviate the adverse metal effects by boosting the translation process, enhancing the ability to recycle the misfolded proteins, and enhancing the potential to eliminate the excess ROS. Our study demonstrated an adaptive potential of oysters at the protein level to survive under conditions of metal hyper-accumulation.

Intra- and Intercellular Silver Nanoparticle Translocation and Transformation in Oyster Gill Filaments: Coupling Nanoscale Secondary Ion Mass Spectrometry and Dual Stable Isotope Tracing Study

The extensive application of silver nanoparticles (AgNPs) requires a full examination of their biological impacts, especially in aquatic systems where AgNPs are likely to end up. Despite numerous toxicity studies from molecular to individual levels, it is still a daunting challenge to achieve in situ subcellular imaging of Ag and to determine the sites of AgNP interaction with organelles or macromolecules simultaneously. Here, by coupling high-resolution nanoscale secondary ion mass spectrometry elemental mapping with scanning electron microscopy ultrastructural characterization, we successfully visualized the subcellular localization and the potential toxicity effects of AgNPs in the oyster gill filaments. The stable isotope tracing method was also adopted to investigate the respective uptake and transport mechanisms of differently labeled ¹⁰⁹AgNPs and ¹⁰⁷Ag⁺ ions. ¹⁰⁹Ag hotspots were colocalized with endosomes or lysosomes, proving an endocytosis-based entry of AgNPs which passed through the barrier of oyster gill epithelium. These ¹⁰⁹Ag hotspots showed a strong colocalization with ³²S^-. For the first time, we provided visualized evidence of AgNP-induced autophagy in the oyster gill cells. We further identified two categories of hemocytes (blood cells) and illustrated their roles in AgNP transport and sequestration. The integration of morphological and functional aspects of Ag subcellular distribution in different target cells suggested that oysters were equipped with a specialized endolysosomal (epithelial cells) or phagolysosomal system (hemocytes) in regulating the cellular process of AgNPs, during which the lysosome was the most involved organelle and sulfur was the most relevant macronutrient element. This study highlighted not only the intracellular but also the intercellular AgNP translocation and transformation, providing important subcellular imaging of silver and reliable methodology regarding bio-nano interactions in natural environments.

Differences in Copper Isotope Fractionation Between Mussels (Regulators) and Oysters (Hyperaccumulators): Insights from a Ten-Year Biomonitoring Study

Copper (Cu) isotope compositions in bivalve mollusks used in marine-monitoring networks is a promising tool to monitor anthropogenic Cu contamination in coastal and marine ecosystems. To test this new biomonitoring tool, we investigated Cu isotope variations of two bivalves-the oyster Crassostrea gigas and the mussel Mytilus edulis-over 10 years (2009-2018) in a French coastal site contaminated by diffuse Cu anthropogenic sources. Each species displayed temporal concentration profiles consistent with their bioaccumulation mechanisms, that is, the Cu-regulating mussels with almost constant Cu concentrations and the Cu-hyperaccumulating oysters with variable concentrations that track Cu bioavailability trends at the sampling site. The temporal isotope profiles were analogous for both bivalve species, and an overall shift toward positive δ⁶⁵Cu values with the increase of Cu bioavailabilities was associated with anthropogenic Cu inputs. Interestingly, mussels showed wider amplitudes in the isotope variations than oysters, suggesting that each species incorporates Cu isotopes in their tissues at different rates, depending on their bioaccumulation mechanisms and physiological features. This study is the first to demonstrate the potential of Cu isotopes in bivalves to infer Cu bioavailability changes related to anthropogenic inputs of this metal into the marine environment.

Heavy metal pollution in the East China Sea: A review

Due to rapid urbanization and industrialization, heavy metal (HM) pollution in coastal areas of the East China Sea (ECS) has attracted extensive attention. This article attempts to review recent studies on the temporal and spatial distributions, ecological risks, and possible sources of HMs in typical bays and estuaries of ECS. The levels of HMs are closely related to local economic development and local characteristics. The anthropogenic activities and the particle size of sediments are important factors affecting the distribution of HMs. During the late 1970s to the 1990s, HMs levels in the Yangtze Estuary (YRE) sediments showed an upward tendency due to the increased emissions. However, HMs levels in the early 2000s were lower than that in the late 1970s to the mid-1990s. Cd caused serious pollution and brought potential ecological risks in the Yangtze Estuary, Hangzhou Bay (HZB), Sanmen Bay (SMB), and Quanzhou Bay (QZB). In Fujian province of China, the Quanzhou Bay was heavily polluted by HMs and high contents of HMs were found in biota. Among different species, molluscs in the coastal areas of ECS have the highest levels of HMs exceeding safety limits.

Accumulation of trace elements in selected fish and shellfish species from the largest natural carp fish breeding basin in Asia: a probabilistic human health risk implication

Intake of fish contaminated with non-essential hazardous trace elements poses a significant risk to human health. In this study, trace elements (As, Pb, Cd, Cu, Ni, and Zn) were measured in edible tissues of seven commercially important fish and shellfish species (Otolithoides pama, Pseudapocryptes elongatus, Macrobrachium rosenbergii, Liza parse, Notropis atherinoides, Apocryptes bato, and Rhinomugil corsula) from a natural carp breeding basin, Halda river, Bangladesh. The elements were detected by inductively coupled plasma-mass spectrometry (ICP-MS), and the hierarchy of elemental levels (mg/kg) was Zn (61.56) > Pb (30.45) > Ni (26.81) > Cu (21.09) > As (1.49) > Cd (0.24). Among the analyzed elements, Pb, Ni, and Zn for some fish species exceeded the permissible dietary limit, suggested by national and international agencies. In addition, results of bioaccumulation factor (BAF) indicated that most of the studied species were bioaccumulative in nature (BAFs > 1000), and the mean BAF of elements were found in the following order: Zn (3156.74) > Ni (1629.30) > Cu (1566.77) > As (997.14) > Pb (259.98) > Cd (216.52). However, the species, L. parse being omnivorous represented the highest BAF (stored higher concentrations of metals) as compared to other species. The growth pattern of all the species was negatively allometric, and the health condition of the species varied from poor to good state revealed from the estimated Fulton's condition factor (FC). For the evaluation of health hazards, estimated weekly (EWI), target hazard quotient (THQ), and carcinogenic risk (CR) were calculated for both adults and children. Results of EWI showed As, Pb, and Ni surpassed provisional tolerable weekly intake (PTWI)-recommended guidelines. The non-carcinogenic health effect (TTHQ) might not appear for both types of consumers (as TTHQ < 1), and CRs of all consumers were also in acceptable range (10^-6 to 10^-4). However, the probabilistic distribution through Monte Carlo simulation revealed that children were more vulnerable to non-carcinogenic (67.3%) and carcinogenic risk effect (47.3%) for Pb. Meanwhile, adults obtained the probability of 0.7% and 36% for THQ and CR effect, respectively, interpreting less vulnerable.

Spatial-temporal variations and trends predication of trace metals in oysters from the Pearl River Estuary of China during 2011-2018

Estuaries are often considered to be the filters of pollutants from the land-derived outflows of freshwater to open seawater. Oysters are efficient bioaccumulators of metals in the estuarine environment, however, little information is available on the long-term tissue variability of metals in a large dynamic estuary under complex urbanized and anthropogenic impacts. Thus, an eight-year biomonitoring study of metals (Ag, Cd, Cr, Cu, Ni, Pb, and Zn) in the oysters from 10 sites were carried out to reveal the highly spatial-temporal variations in the Pearl River Estuary (PRE) of China during 2011-2018. Cd, Cu, and Zn in oysters were significantly correlated with the dissolved metals in seawater. Geographically, Ag, Cd, and Cr were higher in the western sites, and Cu, Ni, and Zn were higher in the eastern sites. High seasonal variations of Ag, Cu, and Zn were found in the wet season. The calculated annual change rates (v_c) of Cd, Cu, Zn, Ag, Pb, Ni, and Cr in the oysters were -1.1, -45, -48, 0.338, -0.216, -2.2, and -2.8 μg/g/y, respectively. If such decreasing rates of v_c (or natural logarithm rates v) were maintained, Cd, Cu, Zn, Pb, and Ni in oysters from PRE would be expected to recover to the national 50% concentrations in years 2022 (2024), 2045 (2079), 2073 (2110), 2021 (2023), and 2019 (2020), respectively. Long-term series observations of metals in organisms reflected the real bioavailability of metals, pollution status, and trends for environmental management and control in a large dynamic and contaminated estuary.

Polymer-modified mesoporous silica microcubes (P@MSMCs) for the synergistic oxidative entrapment of Ag(i), Ti(iv), and Zn(ii) from natural river water

Herein, we demonstrate a hydrothermal route to the one-pot synthesis of polymeric mesoporous silica microcubes (P@MSMCs) for the adsorption of heavy metal ions. During the synthesis of P@MSMCs from column silica gel, the roles and combination of the polymer and an etchant were characterized. Moreover, the porosity of P@MSMCs was tailored by adjusting the reaction temperature between 75 °C and 200 °C. The characterization through UV, FTIR, FESEM, XRD, BET, and EDX techniques exhibited that P@MSMCs have a well-ordered mesoporous structure with cubic morphology. The P@MSMCs had a diameter of 2 μm, with an average pore volume and pore size of 0.69 cm3 g-1 and 10.08 nm, respectively. The results indicated that the P@MSMCs have excellent adsorption capacity for Ag(i), Ti(iv), and Zn(ii) due to the formation of an aggregated complex. These aggregations led to affordable density difference-based separation of these metal ions through centrifugation, filtration or simple decantation. The removal efficiencies for Ag(i), Ti(iv), and Zn(ii) were observed to be 520, 720, and 850 mg g-1, respectively. The kinetic studies demonstrated that the adsorption performance fitted well to the pseudo-second-order kinetic model. The as-synthesized P@MSMCs were stable in the wide pH range of 4-8. Significantly, the recycling or reuse results displayed effective adsorption performance of these P@MSMCs for up to 5 cycles. The adsorption results obtained herein will promote the development of similar strategies for the removal of heavy metal ions from natural water.

Innovative health risk assessments of heavy metals based on bioaccessibility due to the consumption of traditional animal medicines

Few studies reported the extent of heavy metal accumulation in traditional Chinese medicines (TCMs). Currently, oral bioaccessibility of lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg), and copper (Cu) present in traditional animal medicines was investigated with physiologically based extraction test-extracted in vitro model. We are the first to develop a health risk assessment strategy by combinational analysis of bioaccessible heavy metal levels to calculate target hazard quotient (THQ), target hazard index (THI) and cancer risk (CR), which has capacity to evaluate the heavy metal associated heath risk of traditional animal medicines. To precisely acquire a realistic risk assessment, questionnaire data was adopted to measure the frequency and duration of the exposure to traditional animal medicines, and the safety factor was highlighted as well. Our data revealed that the bioaccessibility of Hg was the lowest among the five heavy metals. After the adjustment with the bioaccessibility of each heavy metal to target hazard index (THI) values, excitingly, the results manifested that the consumption of traditional animal medicines might not exert an unacceptable health risk in a broad community. In addition, the CR values of As and Pb indicated that the risk of developing cancers was quite lower than their acceptable levels in the clinic.

Bioaccumulation of microplastics and its in vivo interactions with trace metals in edible oysters

Microplastics have been an emerging threat to marine environments and marine life. Oysters as seafood are popular worldwide, yet also a high-risk group to accumulate pollutants due to their filter-feeding nature. In this study, edible oysters were collected from Yantai, a coastal city in China, to study the uptake, accumulation and translocation of microplastics in marine life, as well as their in vivo interactions with other persistent pollutants. Microplastics were found in all of the studied oyster tissue samples with an average concentration around 4.53 items/g wet weight (24.49 items/g dry weight). Microplastics were mainly translocated and distributed in the gills and mantle of the studied oysters in the form of fibers. The detected microplastics in the oysters were mostly cellophane and polyester as identified by the micro-Fourier transform infrared spectroscope. Cellophane tends to accumulate in gills, mantle and muscle while polyester tends to accumulate in digestive glands of the studied oysters. Excessive concentrations of trace metals (30.484, 4.415, 0.395 and 181.044 μg/g dry weight of Cr, Cd, Pb and Cu, respectively) were detected in the studied oysters using inductively coupled plasma mass spectrometry. Trace metals of Cr, Mn, Ni, Cu, Zn, Cd and Pb were found to be adsorbed on the surface of microplastics isolated from the oysters. There was a correlation between the in vivo concentration of microplastics and the in vivo concentration of four trace metals: Cd, Cr, Cu and Pb, which suggests potential in vivo interactions between microplastics and trace metals. This study can help to understand the impacts of microplastics and their joint toxicity with other pollutants on marine life, especially on aquaculture seafood. This study will be an important reference for the assessment of health risks associated with consumption of edible coastal oysters in China.

Distribution and source of heavy metals in the sediments of the coastal East China sea: Geochemical controls and typhoon impact

The present study conducted a comprehensive study on the distribution and source of heavy metals (Cu, Zn, Ni, Pb, Cd) in the sediments of the coastal East China Sea (ECS), one of the most developed regions in China with very active land-sea interactions, using 119 surface sediment samples and a 2-m sediment core collected after super Typhoon Chan-hom in 2015. Heavy metals in the surface sediments exhibited metal-dependent and regional distribution patterns, showing higher levels in the southern inner shelf (SIS) than the Yangtze River estuary (YRE), and generally being evaluated as unpolluted to moderately polluted in the coastal ECS (except few sites adjacent to Xiangshan Harbor were strongly polluted by Cd). Based on the organic carbon isotope compositions (δ¹³C) data as well as the strong correlations between heavy metals and natural major elemental contents (Al₂O₃, Fe₂O₃, and SiO₂), we suggest natural weathering detritus as the major source of heavy metals in the YRE region and the spatial distributions were highly controlled by sediment grain size and organic matter. In contrast, the spatial distributions of heavy metals in the SIS region were less correlated with sediment properties, due to more complex sources and stronger hydrodynamic impacts. The vertical distribution of heavy metals in the sediment core indicated significant enrichments since 1950s, but showed unusual gradually decreasing trends in top layer (30 cm-0.5 cm), attributing to the strong disturbance of super Typhoon Chan-hom on sediment transportation and metal partitioning. Besides, we also observed that heavy metal levels in shallow water regions of Zhejiang coast were reduced due to the passage of typhoon. Such strong impacts of super Typhoon Chan-hom on heavy metal distributions in the ECS indicates that the impacts of extreme hydrodynamic events should raise more concern when assessing the distribution and potential risks of contaminants in coastal regions.

Using Zn Isotopic Signatures for Source Identification in a Contaminated Estuary of Southern China

Zinc isotope ratios in water and suspended particles (SP) were measured in the Pearl River Estuary (PRE), China. Site-to-site δ⁶⁶Zn values in water varied by approximately 1.3‰ (i.e., -0.66‰ to 0.65‰ relative to IRMM-3702 in August 2017). There were larger variations in δ⁶⁶Zn values in water collected from the east shore (i.e., -0.66‰ to 0.37‰) of the PRE close to industrialized areas, in comparison to those from the western shore (i.e., -0.23‰ to 0.13‰), indicating that the PRE was influenced by different Zn sources. The variations in δ⁶⁶Zn values in water from estuarine locations were much larger than those collected from river mouths. Similarly, larger variations in δ⁶⁶Zn values were observed in suspended particles (i.e., -1.45‰ to 0.63‰) relative to the water. Zinc isotopic differences (i.e., Δ⁶⁶Zn‰) between particles and water were significantly (p < 0.05) and linearly correlated with Zn concentrations in particles between 0.8 and 10 μm in size at most of the estuary stations, suggesting that Zn partitioning between dissolved and particulate phases influences the observed differences in Zn isotope ratios. A significant (p < 0.0001) linear correlation between the predicted δ⁶⁶Zn values (using variations in water salinities) vs observed δ⁶⁶Zn values indicates that Zn isotope ratios in water in the PRE can be useful for predicting the mixing processes in the water.

Heavy metal concentrations in tissues of marine fish and crab collected from the middle coast of Zhejiang Province, China

Concentrations of the heavy metals As, Cd, Cu, Hg, Pb, and Zn in various tissues of five marine fish species and one crab species collected from the middle coast of Zhejiang Province of China were investigated in this study. The results indicated considerable variation in heavy metal concentrations in different tissues and species. Elevated concentrations of most heavy metals were identified in fish gills and crab gills and hepatopancreas, with some differences by heavy metal type. In addition, carnivorous and benthivorous fish species generally contained relatively high concentrations of heavy metals due to feeding habits and habitats. Geographical variations of heavy metal concentrations in muscle may be attributable to species-dependent differences and terrigenous contamination. The potential health risk assessment suggested that exposure doses of most heavy metals were safe for human consumption, with the exception of As.

Transparent Exopolymer Particle (TEPs) Dynamics and Contribution to Particulate Organic Carbon (POC) in Jaran Bay, Korea

Transparent exopolymer particles (TEPs) are defined as acidic polysaccharide particles and they are influenced by various biotic and abiotic processes that play significant roles in marine biogeochemical cycles. However, little information on their monthly variation, relationship and contribution to particulate organic carbon (POC) is currently available particularly in coastal regions. In this study, the water samples were collected monthly to determine TEP concentrations and POC concentrations in a southern coastal region of Korea, Jaran Bay from April 2016 to March 2017. The TEP concentrations varied from 26.5 to 1695.4 μg Xeq L−1 (mean ± standard deviation (S.D.) = 215.9 ± 172.2 μg Xeq L−1) and POC concentrations ranged from 109.9 to 1201.9 μg L−1 (mean ± S.D. = 399.1 ± 186.5 μg L−1) during our observation period. Based on the 13C stable isotope tracer technique, monthly carbon uptake rates of phytoplankton ranged from 3.0 to 274.1 mg C m−2 h−1 (mean ± S.D. = 34.5 ± 45.2 mg C m−2 h−1). The cross-correlation analysis showed a lag-time of 2 months between chlorophyll a and TEP concentrations (r = 0.86, p < 0.01; Pearson’s correlation coefficient). In addition, we observed a 2 month lag-phased correlation between TEP concentrations and primary production (r = 0.73, p < 0.05; Pearson’s correlation coefficient). In Jaran Bay, the TEP contribution was as high as 78.0% of the POC when the TEP-C content was high and declined to 2.4% of the POC when it was low. These results showed that TEP-C could be a significant contributor to the POC pool in Jaran Bay.

A comprehensive assessment of environmental pollution by means of heavy metal analysis for oysters' reefs at Hab River Delta, Balochistan, Pakistan

The heavy metal pollution status of oyster reefs has been assessed with respect to ten metals pollutants in seawater, sediments, and tissues of above two oysters (soft tissues and shells) for assessing the pollution status in a short food chain in Hab River Delta. The results showed that heavy metals accumulated in M. bilineata were higher than those in M. cuttackensis. Simultaneously, the population of M. bilineata species has been ironically decreasing as a results of high pollution. The determined concentrations revealed a significant differences in their profiles among sediments, seawater and bioaccumulation in tissues and shells of two native oysters. The present study also compared these metal concentrations with national and international database by applying different pollution indices. Heavy metals in all samples were above the national environmental quality standards (NEQS-Pakistan). High level of pollution with an alarming condition of Hab River Delta need more attention for coastal management.

Molecular responses of an estuarine oyster to multiple metal contamination in Southern China revealed by RNA-seq

The estuarine oysters Crassostrea hongkongensis hyper-accumulate many metals and survive under high levels of metal exposure. In the present study, three natural populations of oysters with various levels of accumulated metals (mainly Cu and Zn) were collected from Southern China. The morphological characteristics and metal concentrations revealed their phenotypic differentiation. Further transcripts sequences acquired from their gill tissues were analyzed and 44,801 genes (with effective reads) were obtained via de novo assembly. The principal component analysis (PCA) revealed that the gene expression patterns also displayed differentiation among the three populations. A total of 3,199 differentially expressed genes (DEGs) was identified in the contaminated oysters as compared to the 'clean' oysters, which were used to explain the molecular mechanisms of metal accumulation and toxicity. GO and KEGG enrichment analysis revealed that energy production and cytoskeleton metabolism-related genes were particularly enriched in the contaminated sites during chronic metal exposure. Besides, increasing expressions of Zn/Cu transporters and metallothionein may explain their high accumulation in contaminated populations. We showed that oysters with less metal accumulation tended to cope with metal stress actively, but severe contamination destroyed part of the normal function. Our study analyzed the gene expression patterns of C. hongkongensis in Southern China and demonstrated the phenotypic differentiation of oysters under chronical metal exposure in the field.

Biokinetics and subcellular distribution of metals in Daphnia magna following Zn exposure: Implication for metal regulation

Although many studies have addressed the effects of various physicochemical and biological factors on metal bioaccumulation in aquatic organisms, the influences of metal exposure history have drawn much less attention. In the present study, we investigated the effects of different Zn exposure regimes (concentration: 1-200 μg/L, duration: 1-7 d) on the subsequent biokinetics, metallothionien-like protein (MTLP) induction and subcellular distribution of Cd and Zn in Daphnia magna. Zn body burden increased significantly with elevated exposure concentrations, but was kept within a narrow range regardless of the 200-fold variation of Zn concentrations. Significant induction (7-14 folds) of MTLP by Zn exposure was evident, but was decoupled from the Zn body accumulation. Under different regimes of Zn exposure, Zn was evenly distributed in insoluble (cellular debris, intracellular organelles and metal-rich granules) and soluble fractions (heat sensitive protein and MTLP). However, >60% of Cd was bound with MTLP regardless of the exposure concentration and duration. The biokinetic processes including uptake from the dissolved phase, food assimilation and excretion of Cd and Zn were quantified with radioactive tracers. The uptake rate constants of Cd and Zn from the dissolved phase either remained comparable or increased following Zn pre-exposure, and the efflux of Zn increased by nearly two-fold to counteract the increased uptake from water. The dietary assimilation of Zn also decreased significantly in response to Zn exposure. However, Cd assimilation efficiency was kept relatively constant in each Zn pre-exposure regime. Our results showed that Zn exposure had significant influences on the biokinetics and physiology of daphnids. Daphnids attempted to maintain the Zn body burden within a narrow range by modification of biokinetic processes instead of subcellular distribution.

Inter-species difference of copper accumulation in three species of marine mussels: Implication for biomonitoring

Marine mussels have been used widely as biomonitors of coastal contamination in many countries. Due to the restrain of their geographical distributions, it is often necessary to employ more than one species of mussels within a large-scale biomonitoring program. In the present study, we compared the differences of copper (Cu) bioaccumulation in three species of marine mussels (green mussel Perna viridis, blue mussel Mytilus edulis, and hard-shelled mussel Mytilus coruscus) widely distributing along the Chinese coastal waters, under identical Cu exposure conditions. Over the 21-days exposure to dissolved Cu, the green mussels and blue mussels exhibited comparable newly accumulated Cu concentrations, possibly due to their comparable Cu uptake rate constant k_u (blue mussel, 0.573 L g^-1 d^-1; green mussel, 0.530 L g^-1 d^-1) and efflux rate constant k_e (blue mussel, 0.053 d^-1; green mussel, 0.065 d^-1). In contrast, there was no net Cu accumulation in the hard-shell mussels, which may be accounted by the lower k_u (0.394 L g^-1 d^-1) but higher k_e (0.081 d^-1) than the other two mussel species. Further subcellular distribution analyses showed that the cellular debris and metallothionein-like protein (MTLP) fraction were the key binding sites for Cu, and the MTLP fraction may act as a main contributor in Cu regulation and elimination in the blue mussels and hard-shell mussels. There was no strong evidence that the subcellular partitioning and dynamics of Cu in the mussels were responsible for the difference underlying the Cu accumulation in the three species of mussels. Our comparative study thereby suggested that it may be feasible to directly compare the Cu bioavailability in the green mussels and blue mussels based on their Cu biomonitoring data. Cu biomonitoring data from the hard-shell mussels may underestimate the actual Cu bioavailability of the sampling area given its much stronger regulation of Cu bioaccumulation as compared to the other two mussel species.