Linking trace element variations with macronutrients and major cations in marine mussels Mytilus edulis and Perna viridis

Low salinity influences the dose-dependent transcriptomic responses of oysters to cadmium

Species in estuaries tend to undergo both cadmium (Cd) and low salinity stress. However, how low salinity affects the Cd toxicity has not been fully understood. Investigating the impacts of low salinity on the dose-response relationships between Cd and biological endpoints has potential to enhance our understanding of the combined effects of low salinity and Cd. In this work, changes in the transcriptomes of Pacific oysters were analyzed following exposure to Cd (5, 20, 80 μg/L Cd2+) under normal (31.4 psu) and low (15.7 psu) salinity conditions, and then the dose-response relationship between Cd and transcriptome was characterized in a high-throughput manner. The benchmark dose (BMD) of gene expression, as a point of departure (POD), was also calculated based on the fitted dose-response model. We found that low salinity treatment significantly influenced the dose-response relationships between Cd and transcripts in oysters indicated by altered dose-response curves. In details, a total of 219 DEGs were commonly fitted to best models under both normal and low salinity conditions. Nearly three quarters of dose-response curves varied with salinity condition. Some monotonic dose-response curves in normal salinity condition even were replaced by nonmonotonic curves in low salinity condition. Low salinity treatment decreased the PODs of differentially expressed genes induced by Cd, suggesting that gene differential expression was more prone to being triggered by Cd in low salinity condition. The changed sensitivity to Cd in low salinity condition should be taken into consideration when using oyster as an indicator to assess the ecological risk of Cd pollution in estuaries.

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.

Accumulation of chemical elements and occurrence of microplastics in small pelagic fish from a neritic environment

The assessment of contaminant exposure in marine organisms often focuses on the most toxic chemical elements from upper trophic level species. Information on mid-trophic level species and particularly on potentially less harmful elements is lacking. Additionally, microplastics have been considered emergent contaminants in aquatic environments which have not been extensively studied in species from mid-trophic levels in food chains. This study aims to contribute to an overall assessment of environmental impacts of such chemicals in a community of small pelagic fish in the North Atlantic. The concentrations of 16 chemical elements, rarely simultaneously quantified (including minerals, trace elements and heavy metals), and the presence of microplastics were analysed in sardines (Sardina pilchardus) and mackerels (Scomber spp. and Trachurus trachurus) sampled along the Portuguese coast. Biochemical stress assessments and stable isotope analyses were also performed. The chemical element concentrations in S. pilchardus, T. trachurus, and Scomber spp. were relatively low and lower than the levels reported for the same species in the North Atlantic and adjacent areas. No clear relationships were found between chemical elements and oxidative damage in fish. However, the concentration of several chemical elements showed differences among species, being related with the species' habitat use, trophic niches, and specific feeding strategies. The presence of plastic pieces in the stomachs of 29% of the sampled fishes is particularly concerning, as these small pelagic fish from mid-trophic levels compose a significant part of the diet of humans and other top predators. This study highlights the importance of multidisciplinary approaches focusing on the individual, including position data, stable isotopes, and oxidative stress biomarkers as complementary tools in contamination assessment of the marine mid-trophic levels in food chains.

Human health risk assessment associated with the consumption of mussels (Perna perna) and oysters (Crassostrea rhizophorae) contaminated with metals and arsenic in the estuarine channel of Vitória Bay (ES), Southeast Brazil

The estuarine channel of Vitória Bay was evaluated regarding bioaccumulation of metals (Al, Ba, Mn, Fe, Zn, Cu, Cr, Pb, Ni, Cd, Hg) and As in mollusks. Mussels from an aquaculture farm and transplanted into the estuary, whereas oysters were collected in situ in the same area. Concentrations of Al, Mn, Fe, Cr and As were higher in P. perna, whereas C. rhizophorae bioaccumulated more Ba, Zn and Cu. Arsenic concentrations in P. perna exceeded the limit of the Brazilian legislation in the outer estuary. Salinity seemed to influence metal uptake differently for each bivalve, with P. perna absorbing more metal at higher salinities and C. rhizophorae in areas of lower salinity. Hazard index (HI) >1 revealed risk for both bivalves for high level consumers. Target Cancer Risk (TCR) for As revealed threat for human health associated with the consumption of mussels and oysters from the study area.

Evaluation of bioavailability of trace metals through bioindicators in a urbanized estuarine system in southeast Brazil

The mussel Perna perna is one of the most used bioindicators of coastal areas and the most economically exploited species in Brazil through mariculture. In the present study, P. perna was used to investigate metal pollution in the estuarine area of Vitória Bay. Four sampling sites were located along an estuarine branch of Vitória Bay and stations were sampled during three campaigns. Trace metals in the tissues of P. perna were evaluated as well as dissolved trace metals and other ancillary variables in the water column. Dissolved Cd, Pb, Cu, Ni, and Fe concentrations surpassed the tolerance limits stablished by legislation in all the sampling campaigns. P. perna exhibited concentrations in disagreement with the Brazilian legislation for Cr and As. A general trend of higher concentrations in outer stations was observed for most metals, what suggested the occurrence of flocculation process in the lower estuary, reducing the concentrations of dissolved elements and increasing their bioavailability for the biota through the particulate form. Cd was highlighted with elevated concentrations in dissolved fraction but not detected in P. perna, probably due to chlor-complex formation under influence of more saline waters. Al, Ba, Mn, Fe, Cu, Zn, Ni, Cr, Pb, and As were considered bioavailable, once they were accumulated in the mussels' tissues. Hazard index (HI) and target cancer risk (TCR) showed that the consumption of mussels from the study area offers health risk issues, being iron and arsenic the main contributors for the high indexes.

Arsenic in shellfish: A systematic review of its dynamics and potential health risks

Arsenic is the most toxic element for humans. Presenting naturally in aquatic ecosystems and due to anthropogenic action, this semi-metal transfers to shellfish through the food chain. This systematic review aims to explain the dynamic of arsenic in the marine aquatic system, investigating factors that affect its bioaccumulation. A total of 64 articles were considered from three databases. The key abiotic factor influencing the presence of arsenic in shellfish is anthropogenic contamination, followed by geographic location. The crucial biotic factor is the genetics of each species of shellfish, including their diet habits, habitat close to the sediment, metabolic abilities, physiological activities of organisms, and metal levels in their habitats and food. Finally, arsenic presents an affinity for specific tissues in shellfish. Despite containing mostly less toxic organic arsenic, shellfish are a relevant source of arsenic in the human diet.

Identification of SNPs involved in Zn and Cu accumulation in the Pacific oyster (Crassostrea gigas) by genome-wide association analysis

Oysters accumulate high concentrations of zinc (Zn) and copper (Cu), which can be transferred to human due to sea food consumption. Breeding new oyster varieties with low Zn and Cu accumulations is one important way to improve food safety. However, the genetic basis for metal accumulation in mollusks is not well understood. To address this issue, oysters collected in the field were used for genome-wide association study (GWAS) and then the identified genes were used for mRNA expressions analysis in laboratory. First, GWAS were conducted for Zn and Cu accumulation in 288 wild Pacific oysters (Crassostrea gigas) farmed in the same ocean environment. The oysters did not show obvious population structure or kinship but exhibited 8.43- and 10.0- fold changes of Zn and Cu contents respectively. GWAS have identified 11 and 12 single nucleotide polymorphisms (SNPs) associated with Zn and Cu, respectively, as well as 16 genes, which were Zn-containing proteins or participated in caveolae-dependent endocytosis. Second, the mRNA expressions of these 16 genes were observed under Zn and Cu exposure. After 9 days of Zn exposure, Zn contents increased 3.1-fold, while the mRNA expression of cell number regulator 3 increased 1.65-fold. Under 9 days of Cu exposure, Cu contents increased 1.97-fold, while the mRNA expression of caveolin-1 decreased 0.61-fold. These provide the evidence for their roles in regulating physiological levels of these two metals. The findings advance our understanding of the genetic basis of Zn and Cu accumulation in mollusks, which can be useful for breeding new, less toxic varieties of oysters.

Bioaccumulation and health risk assessment of heavy metals to bivalve species in Daya Bay (South China Sea): Consumption advisory

Bivalves are one of the key components of the biogeochemical cycle in the marine system, and respond to heavy metal (HM) sensitively as filter feeders. To determine relationship of HMs in edible bivalve and seawater and HM effects on human health when digesting bivalves, HMs were analyzed in bivalves and seawater. The results showed that the mean HM concentrations in bivalves decreased in the order of Zn > Cu > Cr > Pb > As > Cd > Hg. Generally, all the bioconcentration factor values of bivalves were higher than 100, suggesting that bivalves have a high bioaccumulation ability. Nonmetric multidimensional scaling analysis indicated that all bivalves have a high bioaccumulation capacity for Cu and Zn. It was found that there are health risks associated with consuming bivalves, and children are more vulnerable than adults. Finally, the maximum allowable consumption rates of non-carcinogenic and carcinogenic risk were determined. These results provide the underlying insights needed to guide the consumption of seafood.

Seasonal fluctuations of metal bioaccumulation and reproductive health of local oyster populations in a large contaminated estuary

Despite of much evidence of trace metal pollution in the Pearl River Estuary (PRE), the seasonal dynamics of metal bioavailability as well as the potential impacts of metal pollution on the local marine organisms in this estuary is poorly understood. In the present study, the accumulation of trace metals and reproductive states of three populations of oyster Crassostrea hongkongensis, a keystone bivalve species in the PRE, were for the first time investigated throughout a one-year field study. Significant temporal fluctuations of metal accumulation were observed in the somatic tissues of oysters, suggesting seasonal variations of metal bioavailability in the PRE. A major feature of the seasonal variations was the increased levels of metal bioaccumulation in the summer season for the contaminated sites nearby the major river inlets. High riverine inputs accompanied by relatively lower salinity in summer may greatly contribute to such variations. Furthermore, oyster populations from two contaminated sites had a poor reproductive condition in comparison with the reference oyster population, as reflected by a significant decrease of gonad-somatic index (GSI) and gonad cover area (GCA), as well as an obvious change of sex ratios. Gonadal metal accumulation of Cu, Zn, Ni, Co and Pb in the contaminated oysters was much higher than that in the relatively uncontaminated oysters. Especially, the concentrations of these metals in the gonad during the breeding season had significantly negative correlations with the gonad condition indexes (GSI and GCA). Our results suggested strong seasonal fluctuations of bioavailability of trace metals in this highly contaminated estuary as well as an adverse effect of metal pollution on the reproduction of local oyster populations.

Determination of the geographical origin of marine mussels (Mytilus spp.) using 143Nd/144Nd ratios

Geographical traceability of marine bivalves is critical to guarantee their quality and safeguard the interest of both consumers and producers. The neodymium isotopic ratio (¹⁴³Nd/¹⁴⁴Nd) of the coastal water mainly reflects the geology of its neighboring watershed, displaying the distinct and systematic variability at high level of geographical detail and thereby shedding light on its potential as a geochemical tracer. For the first time, the present study investigated the utility and robustness of ¹⁴³Nd/¹⁴⁴Nd archived in mytilid mussel shells for geographical traceability purposes. The reproducibility of ¹⁴³Nd/¹⁴⁴Nd ratios maintained in mussels shells from the same cohort demonstrates that the Nd isotopic ratio meets the major requirement for an ideal geochemical tracer, i.e., the biologically induced variation should be rather minimal. The distribution and variability of mussel shell ¹⁴³Nd/¹⁴⁴Nd patterns were subsequently mapped along the Japanese and Chinese coastal waters. Neodymium isotopes of mussel shells record ¹⁴³Nd/¹⁴⁴Nd variations among local regions and between the two countries, which are rather compatible with the ages and lithology of the continental bedrocks. These findings highlight the great potential of ¹⁴³Nd/¹⁴⁴Nd for tracing the geographical origin of marine bivalves.

Multiple trace element accumulation in the mussel Septifer virgatus: Counteracting effects of salinity on uptake and elimination

Salinity effects on the bioaccumulation and biokinetic processes of eight trace elements (Cu, Cr, Pb, Ni, Zn, Cd, Se, and As) in the black mussel Septifer virgatus were explored in the present study. A 6-week laboratory waterborne exposure first showed that salinity (15, 20, 25, and 30) had relatively weak or even no significant influence on trace element accumulation in the black mussels. Biokinetics including uptake and efflux was then quantified in the mussels at different salinities. Uptake rates of Ni and Zn were negatively correlated with the salinity, while the uptake of Cd was not significantly influenced by salinity. The efflux rates of Ni and Zn also exhibited an inverse relationship with salinity, whereas the case of Cd was on the contrary. Biokinetic modeling showed that the salinity effects on uptake and elimination of Ni and Zn counteracted with each other, thus weakening the combined effects on accumulation. Overall, the response of uptake to salinity could weakened, removed, or even overturned by elimination, depending on the relative magnitude of the change of the two processes. The combined effects of uptake and elimination further led to negative, no, or positive relationship between trace element accumulation and salinity.

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

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

Beyond the mean: A comparison of trace- and macroelement correlation profiles of two lacustrine populations of the crayfish Procambarus clarkii

In invertebrate biomonitors of chemical pollution, emphasis has been generally given to mean accumulation patterns and how they reflect varying environmental levels of contamination. Intra-population variability, and how it relates with individual phenotypic traits, has received less attention. Here, a set of analytes including trace elements (B, Ba, Cd, Cr, Cu, Fe, Li, Mn, Ni, Pb, Sr, V, and Zn), macroelements (C, Ca, K, Mg, N, Na), and carbon and nitrogen stable isotopes (δ¹³C and δ¹⁵N) was measured in two populations of the crayfish Procambarus clarkii from Lake Trasimeno and Lake Bolsena (Central Italy). The influence of location, sex, body size, and condition factor was assessed; in addition, the analyte correlation profiles of the two populations were compared to verify their congruence. In general, significant inter-lake differences were observed in the concentration of both trace- and macroelements in crayfish tissues, generally mirroring the local chemistry of water and of benthic non-living matrices (sediment and plant detritus). Crayfish CN isotopic signatures excluded the occurrence of inter-lake variations in their omnivorous trophic habits. Correlation profiles varied considerably between the two populations in the nature and strength of bivariate relationships. However, Mantel tests and procrustean analyses indicated a general, significant congruence; C, N, and, to a lesser extent K, Li, Ni, Pb, and δ¹³C showed the highest procrustean residuals, suggesting that their associations with other analytes may be partially influenced by inter-population differences in growing phases. Our study indicates that the local geochemistry of the lacustrine environment influences the elemental fingerprint of Procambarus clarkii; the considerable inter-individual variability in the concentration of analytes, however, does not significantly reflect on their association, thus corroborating its effectiveness as an indicator species.

Dynamics of maternally transferred trace elements in oyster larvae and latent growth effects

Understanding the maternal transfer of contaminants and their potential effects has great implications for a valid ecological assessment of environmental pollution. However, relevant studies on marine bivalves are very limited. Here, we examined the maternal transfer of trace metals in populations of oyster Crassostrea hongkongensis with contrasting metal exposure histories. Elevated accumulation of trace metals was observed in eggs and larvae from contaminated sites, suggesting maternal transfer of multi-metals in natural oyster populations. The dynamics of maternally transferred metals was for the first time documented in this study. We demonstrated that excessively transferred metals in contaminated larvae were rapidly eliminated during the early developmental stage, and the efflux rate of metals in larvae was greatly dependent on environmental contamination level. These results provided the first field evidence of modified metal biokinetics in offsprings due to exposure history of adults in marine bivalves. Moreover, egg production was negatively correlated with the contamination level of metals in eggs. There was a further lagged growth in the contaminated larvae, indicating the potential adverse and latent effects of maternally transferred metals on the viability of oyster offspring. Our findings highlighted the importance of transgenerational studies on long-term metal exposure in marine bivalves.

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

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

Relating metals with major cations in oyster Crassostrea hongkongensis: A novel approach to calibrate metals against salinity

Despite salinity has been well documented for its significant effects on the bioaccumulation of many trace elements in biomonitors, no calibration method has been proposed to reduce such influences. For the first time, the present study established a novel method to calibrate biomonitoring data against salinity. Relationships between trace element concentration in oyster Crassostrea hongkongensis and the biological proxy for salinity were quantified based on laboratory exposure experiments. The method was then verified by the biomonitoring data of Pearl River Estuary (PRE). Tissue concentrations of trace elements (Cu, Zn, Ag, Cd, Pb, Cr, As, Se, and Ni) and major cations (Na, Mg, K, and Ca) in oysters exposed at 4 salinities (5, 12, 20, and 28psu) and low concentrations for 6weeks were measured to establish such quantitative relationships. Tissue Na, Mg, and K could be the proxy for salinity, while Na was the best one. Negative correlations between tissue concentrations of trace elements and Na after exposure were observed for metal cations such as Cu, Zn, Ag, Cd, and Pb, while tissue As, Se, and Ni were positively correlated with Na. In PRE, salinity significantly influenced the bioaccumulation of trace elements even under the multifactor-affected field conditions. The calibration method applied to the biomonitoring of PRE was verified to be feasible, and effectively reduced the influences of salinity. Therefore, calibration against salinity could facilitate the interpretation, comparability, and analysis of biomonitoring data.

"Manganese-induced neurotoxicity: a review of its behavioral consequences and neuroprotective strategies"

Manganese (Mn) is an essential heavy metal. However, Mn’s nutritional aspects are paralleled by its role as a neurotoxicant upon excessive exposure. In this review, we covered recent advances in identifying mechanisms of Mn uptake and its molecular actions in the brain as well as promising neuroprotective strategies. The authors focused on reporting findings regarding Mn transport mechanisms, Mn effects on cholinergic system, behavioral alterations induced by Mn exposure and studies of neuroprotective strategies against Mn intoxication. We report that exposure to Mn may arise from environmental sources, occupational settings, food, total parenteral nutrition (TPN), methcathinone drug abuse or even genetic factors, such as mutation in the transporter SLC30A10. Accumulation of Mn occurs mainly in the basal ganglia and leads to a syndrome called manganism, whose symptoms of cognitive dysfunction and motor impairment resemble Parkinson’s disease (PD). Various neurotransmitter systems may be impaired due to Mn, especially dopaminergic, but also cholinergic and GABAergic. Several proteins have been identified to transport Mn, including divalent metal tranporter-1 (DMT-1), SLC30A10, transferrin and ferroportin and allow its accumulation in the central nervous system. Parallel to identification of Mn neurotoxic properties, neuroprotective strategies have been reported, and these include endogenous antioxidants (for instance, vitamin E), plant extracts (complex mixtures containing polyphenols and non-characterized components), iron chelating agents, precursors of glutathione (GSH), and synthetic compounds that can experimentally afford protection against Mn-induced neurotoxicity.