Exposure to environmental levels of 2,4-di-tert-butylphenol affects digestive glands and induces inflammation in Asian Clam (Corbicula fluminea)

2,4-Di-tert-butylphenol (2,4-DTBP) is used as an antioxidant added to plastics. Due to its potential toxicity and relatively high concentrations in environments and presence in human tissue, concern has been raised for 2,4-DTBP as a contaminant associated with adverse health outcomes. However, studies on the toxicity of 2,4-DTBP are relatively limited, especially for benthic aquatic organisms. In this study, Asian clams (Corbicula fluminea) were exposed to environmentally relevant concentrations of 2,4-DTBP (0.01-1 μM, corresponding to 2.06-206.32 μg/L) for 21 days. Accumulation of 2,4-DTBP was noted in both gills and digestive glands, with the latter presenting as the primary target tissue. Increased damage rate of digestive tube and cellular DNA damage were observed in the digestive glands of 2,4-DTBP exposed clams. The injury was attributed to the imbalance of the antioxidant system, characterized by elevated oxidative stress and inflammation (upregulation of ROS, MDA, NO, and pro-inflammatory factors). In contrast, upon 2,4-DTBP exposure, antioxidant system in gills was activated, while ROS and NO were not promoted. Moreover, NF-κB and IL-1 were significantly decreased. These results suggested that biochemical mechanisms were activated in gills to maintain homeostasis. Internal exposure in the digestive gland was significantly correlated with the biochemical biomarkers tested, underscoring the potential risk associated with the bioaccumulation of 2,4-DTBP from contaminated environments. These findings provide novel insights into toxicity of 2,4-DTBP in bivalves, contributing valuable knowledge to risk assessment and chemical management.

Fate, subcellular distribution and biological effects of rare earth elements in a freshwater bivalve under complex exposure

Rare earth elements (REE) are emerging contaminants due to their increased use in diverse applications including cutting-edge and green-technologies. Their environmental concerns and contradicting results concerning their biological effects require an extensive understanding of REE ecotoxicology. Thus, we have studied the fate, bioaccumulation and biological effects of three representative REE, neodymium (Nd), gadolinium (Gd) and ytterbium (Yb), individually and in mixture, using the freshwater bivalve Corbicula fluminea. The organisms were exposed for 96 h at 1 mg L-1 REE in the absence and presence of dissolved organic matter (DOM) reproducing an environmental contamination. Combined analysis of the fate, distribution and effects of REE at tissue and subcellular levels allowed a comprehensive understanding of their behaviour, which would help improving their environmental risk assessment. The bivalves accumulated significant concentrations of Nd, Gd and Yb, which were decreased in the presence of DOM likely due to the formation of REE-DOM complexes that reduced REE bioavailability. The accumulation of Nd, Gd and Yb differed between tissues, with gills > digestive gland ≥ rest of soft tissues > hemolymph. In the gills and in the digestive gland, Nd, Gd and Yb were mostly (>90 %) distributed among metal sensitive organelles, cellular debris and detoxified metal-rich granules. Gadolinium, Yb and especially Nd decreased lysosome size in the digestive gland and disturbed osmo- and iono-regulation of C. fluminea by decreasing Na concentrations in the hemolymph and Ca2+ ATPase activity in the gills. Individual and mixed Nd, Gd and Yb exhibited numerous similarities and some differences in terms of fate, accumulation and biological effects, possibly because they have common abiotic and biotic ligands but different affinities for the latter. In most cases, individual and mixed effects of Nd, Gd, Yb were similar suggesting that additivity approach is suitable for the environmental risk assessment of REE mixtures.

The Synergistic Effects of Corbicula fluminea and Sarcodia montagneana on Alleviating Systemic Inflammation and Osteoarthritis Progression

Osteoarthritis (OA) is a progressive disease that causes pain, stiffness, and inflammation in the affected joints. Currently, there are no effective treatments for preventing the worst outcomes, such as synovitis or cartilage degradation. Sarcodia montagneana and Corbicula fluminea are common species found in the ocean or in freshwater areas. Their extracts are demonstrated to possess both antioxidative and anti-inflammatory functions. This study aimed to investigate the synergistic effects of the extracts of Sarcodia montagneana (SME) and Corbicula fluminea (FCE) on reducing local and systemic inflammation, as well as their efficacy in OA symptom relief. An in vitro monocytic LPS-treated THP-1 cell model and in vivo MIA-induced mouse OA model were applied, and the results showed that the combinatory usage of SME and FCE effectively suppressed IFN-γ and TNF-α production when THP-1 cells were treated with LPS. SME and FCE also significantly decreased the systemic TNF-α level and joint swelling and prevented the loss of proteoglycan in the cartilage within the joints of OA mice. The data shown here provide a potential solution for the treatment of osteoarthritis.

Exposure to Oxidized Multi-Walled CNTs Can Lead to Oxidative Stress in the Asian Freshwater Clam Corbicula fluminea (Müller, 1774)

The increasing attention that carbon-based nanomaterials have attracted due to their distinctive properties makes them one of the most widely used nanomaterials for industrial purposes. However, their toxicity and environmental effects must be carefully studied, particularly regarding aquatic biota. The implications of these carbon-based nanomaterials on aquatic ecosystems, due to their potential entry or accidental release during manufacturing and treatment processes, need to be studied because their impacts upon living organisms are not fully understood. In this research work, the toxicity of oxidized multi-walled carbon nanotubes (Ox-MWCNTs) was measured using the freshwater bivalve (Corbicula fluminea) after exposure to different concentrations (0, 0.1, 0.2, and 0.5 mg·L-1 Ox-MWCNTs) for 14 days. The oxidized multi-walled carbon nanotubes were analyzed (pH, Raman microscopy, high-resolution electron microscopy, and dynamic light scattering), showing their properties and behavior (size, aggregation state, and structure) in water media. The antioxidant defenses in the organism's digestive gland and gills were evaluated through measuring oxidative stress enzymes (glutathione-S-transferase, catalase, and superoxide dismutase), lipid peroxidation, and total ubiquitin. The results showed a concentration-dependent response of antioxidant enzymes (CAT and GST) in both tissues (gills and digestive glands) for all exposure periods in bivalves exposed to the different concentrations of oxidized multi-walled carbon nanotubes. Lipid peroxidation (MDA content) showed a variable response with the increase in oxidized multi-walled carbon nanotubes in the gills after 7 and 14 exposure days. Overall, after 14 days, there was an increase in total Ub compared to controls. Overall, the oxidative stress observed after the exposure of Corbicula fluminea to oxidized multi-walled carbon nanotubes indicates that the discharge of these nanomaterials into aquatic ecosystems can affect the biota as well as potentially accumulate in the trophic chain, and may even put human health at risk if they ingest contaminated animals.

Toxicity assessment of environmental MPs and NPs and polystyrene NPs on the bivalve Corbicula fluminea using a multi-marker approach

Small plastic particles, microplastics (MPs) and nanoplastics (NPs) represent a major threat in aquatic environments. Freshwater organisms are exposed to MPs and NPs, particularly in industrial and urban areas. The present study aimed to compare the toxicity between polystyrene NPs (PS NPs) and environmental microplastics (ENV MPs) and nanoplastics (ENV NPs) generated from macro-sized debris collected in the Garonne River on the freshwater bivalve C. fluminea. The organisms were exposed to the different plastic particles at three environmentally relevant concentrations: 0.008, 10, and 100 μg L-1 for 21 days. The biological responses of organisms were assessed using a multi-biomarker approach from the sub-individual to the individual level. The results demonstrated that: i) ENV NPs triggered more effects on detoxification processes and immune response, confirming that using manufactured NPs for laboratory exposure can lead to misleading conclusions on the risks posed by plastic particles; ii) effects of ENV MPs were less marked than ENV NPs, emphasizing the importance of testing a size continuum of plastic particles from NPs to MPs; iii) some effects were only observed for the low and/or intermediate concentrations tested, underlining the importance of using environmentally relevant concentrations. In light of these results, laboratory studies should be continued by exposing aquatic species to environmental MPs and NPs. The properties of these particles have to be characterized for a better risk assessment of environmental plastic particles.

Characterizing the Gut Microbial Communities of Native and Invasive Freshwater Bivalves after Long-Term Sample Preservation

Freshwater mussels are important indicators of the overall health of their environment but have suffered declines that have been attributed to factors such as habitat degradation, a loss of fish hosts, climate change, and excessive nutrient inputs. The loss of mussel biodiversity can negatively impact freshwater ecosystems such that understanding the mussel's gut microbiome has been identified as a priority topic for developing conservation strategies. In this study, we determine whether ethanol-stored specimens of freshwater mussels can yield representative information about their gut microbiomes such that changes in the microbiome through time could potentially be determined from museum mussel collections. A short-term preservation experiment using the invasive clam Corbicula fluminea was used to validate the use of ethanol as a method for storing the bivalve microbiome, and the gut microbiomes of nine native mussel species that had been preserved in ethanol for between 2 and 9 years were assessed. We show that ethanol preservation is a valid storage method for bivalve specimens in terms of maintaining an effective sequencing depth and the richness of their gut bacterial assemblages and provide further insight into the gut microbiomes of the invasive clam C. fluminea and nine species of native mussels. From this, we identify a "core" genus of bacteria (Romboutsia) that is potentially common to all freshwater bivalve species studied. These findings support the potential use of ethanol-preserved museum specimens to examine patterns in the gut microbiomes of freshwater mussels over long periods.

Molecular Diet Analysis of Asian Clams for Supplementary Biodiversity Monitoring: A Case Study of Nakdong River Estuary

Environmental DNA (eDNA) extracted from the gut contents of filter feeders can be used to identify biodiversity in aquatic ecosystems. In this study, we used eDNA from the gut contents of the Asian clam Corbicula fluminea to examine biodiversity within estuarine ecosystem. Field sampling was conducted at three points in the Nakdong River Estuary, which is characterised by closed estuarine features resulting from the presence of an estuarine barrage. The collected C. fluminea samples were dissected to separate the gut contents, and the extracted eDNA was amplified using 18S V9 primer targeting all eukaryote-derived DNA. The amplified DNA was sequenced using a next-generation sequencing (NGS) technique, and a BLASTn search was performed based on the National Centre for Biotechnology Information (NCBI) database for taxa identification. We obtained 23 unique operational taxonomic units (OTUs), including fish (approximately 8.70%), copepods (approximately 17.39%), and green algae (approximately 21.74%), representing a wide range of habitats. Furthermore, 8 out of the 20 families were identified through comparisons with reference data from conventional field surveys, and the OTUs of elusive migratory fish were detected. The results support the application of C. fluminea as an eDNA sampler for supplementary biodiversity monitoring.

Comparative toxicogenomics of benzotriazole ultraviolet stabilizers at environmental concentrations in Asian clam (Corbicula fluminea): Insight into molecular networks and behavior

Benzotriazole ultraviolet stabilizers (BUVSs) are widespread emerging pollutants, which can pose exposure risks to benthic organisms. However, the toxicity and mechanisms of BUVSs congeners in benthic clams are far from elucidated. In this study, Asian clams (Corbicula fluminea) were exposed to one of UV-234, UV-326, UV-329, or UV-P at environmentally relevant levels (0.1, 1, and 10 μg/L) for 21 days. Filtration rate (FR) was increased in clams exposed to all BUVSs and there were notable histopathologic changes, including irregular digestive lumen, lipid droplet vacuolation, and degraded epithelial cells. To determine the molecular underpinnings following BUVSs exposure, the transcriptome responses in digestive glands were compared. Differentially expressed genes shared among BUVSs treatments were associated with focal adhesion, TNF-α/NF-κB proinflammatory pathways, and apoptosis. Following this, biochemical analysis of biomarkers related to apoptosis were conducted to further validate response. Exposure to BUVSs inhibited anti-oxidant enzyme activity and induced oxidative stress. Heat shock proteins were also triggered with exposure, and there was an induction of caspase-3 and caspase-9 activity. Molecular responses were not identical in the digestive gland of C. fluminea when comparing responses to BUVSs; nevertheless conserved mechanism (impairment of the oxidative defense system, immune system disruption, and induction of apoptosis) among BUVSs congeners was noted. This study provides novel insight into the toxicity and hazards of BUVSs in benthic organisms.

Transcriptome analysis of growth and shell color between two genetic variants of Corbicula fluminea with different shell colors

To clarify the molecular mechanism of the black and yellow shell coloration, we performed a transcriptome analysis of whole tissue of Corbicula fluminea in Hongze Lake (Jiangsu Province, China). After assembly, 335,247 unigenes were obtained, and 136,804 unigenes were functionally identified using public databases (NR, GO, KEGG, eggnog, and Swissprot). 1567 differentially expressed genes (DEGs) were detected through pairwise comparisons, of which 941 DEGs were up-regulated and 626 were down-regulated in the black-shelled clam. We compared the DEGs between two clams and identified some coloration-related genes. Notably, the black-shelled clam was larger than the yellow-shelled. We speculated that higher digestion and anabolic ability of black-shelled clam might lead to this phenomenon. In contrast, the yellow-shelled clam appeared to be more sensitive to environmental stress. The metabolic energy of the yellow-shelled clam was depleted to maintain or recover from stress, and provide less energy for growth. In summary, our finding provides a theoretical basis for the molecular mechanism of pigmentation and the difference of somatotype in bivalve, as well as promotes the future breeding of more elite varieties.

Benzotriazole UV stabilizer-induced genotoxicity in freshwater benthic clams: A survey on apoptosis, oxidative stress, histopathology and transcriptomics

Benzotriazole UV stabilizer-329 (UV-329) is frequently detected in various environmental and biological matrices. However, the toxicity effect on freshwater benthos induced by UV-329 has rarely been described. In this study, genotoxicity, apoptosis, oxidative stress, histopathological alterations, siphoning behavior, and bioaccumulation in the gill and digestive gland of Corbicula fluminea exposed to UV-329 at 10, 100, and 1000 μg/L for 21 days were investigated. Toxicity screening using transcriptomics confirmed that UV-329 preferentially stimulated cellular process-related pathways including gap junctions, apoptosis, phagosomes and necroptosis. The transcript levels of a large number of apoptosis genes were significantly upregulated. This apoptosis mechanism was further confirmed by the fact that UV-329 exposure significantly increased the percentage of apoptotic cells, activated caspase-3, -8, and -9, and affected the antioxidant enzyme activities. Following exposure to 1000 μg/L UV-329, significant histological alterations were reflected in the corrosion of cilia, cellular swelling of epithelial cells in the gills, degeneration of digestive tubules, and necrosis of epithelial cells in the digestive glands. These results may aid in elucidating the toxicity mechanism of UV329 in bivalves and evaluating the hazards of UV-329 in benthic ecosystems.

New insights into the mechanism of ammonia toxicity: Focus on Cactus

The NF-κB signaling pathway is the most critical pathway in innate immunity. IκB (Cactus) is the primary cytoplasmic inhibitor of NF-κB (Dorsal). In this study, we found that ammonia exposure could significantly induce the expression of Cactus, in a dose-dependent manner in different tissues, with the highest expression in the gill of Corbicula fluminea. The expression pattern-related elements (Tube and Dorsal) in the NF-κB signaling pathway were also analyzed, showing significant up-regulation in 48 h. There was an inhibitory effect between up-regulated Cactus and Dorsal in 72 h, which may regulate Dorsal as a negative feedback pathway function to control the expression of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α). Besides, through molecular docking simulation, we found that the Cactus could be directly activated by NH₃, complementing the regulatory mechanism of the Cactus. To further test our hypothesis, the levels of pro-inflammatory cytokines decreased after adding PDTC (the antioxidant of Cactus/IκB), suggesting that PDTC can prevent the degradation of Cactus, inhibit Dorsal translocating into the nucleus, and activate the pro-inflammatory cytokines. This revealed the inhibitory effect of Cactus on activating Dorsal/NF-κB factors in the NF-κB signaling pathway. Thus, we suggested that the Cactus is an essential regulator of ammonia-activated inflammation in C. fluminea, which was reported to be activated only by bacteria and immune stimulators. Our study provides a new perspective on the mechanism of ammonia toxicity in invertebrates.

Feeding behavior, microcystin accumulation, biochemical response, and ultramicrostructure changes in edible freshwater bivalve Corbicula fluminea exposed to Microcystis aeruginosa

As filter-feeders, bivalves naturally come into direct contact with microcystins (MCs) in eutrophic water bodies suffering from cyanobacteria blooms. To date, however, no studies have quantified the dynamics of microcystin accumulation and depuration in the edible freshwater bivalve Corbicula fluminea when exposed to dense bloom concentrations of Microcystis aeruginosa, while considering dynamic changes of biochemical indexes and feeding structure. In the present study, the bioaccumulation and detoxification of microcystin-LR (MC-LR) in C. fluminea were investigated. Our results showed that C. fluminea would graze equally efficiently on green algae and M. aeruginosa, irrespective of whether the M. aeruginosa strains were toxic or non-toxic. MCs could be accumulated and depurated by C. fluminea efficiently. In addition, linear and exposure time-dependent MC-LR accumulation patterns were observed in C. fluminea. Activities of biotransformation (glutathione S-transferase, GST) and antioxidant enzymes (superoxide dismutase, SOD, and catalase, CAT) and malondialdehyde (MDA) contents in various tissues of treated clams were stimulated by MCs in a tissue-specific manner. Our findings indicated that C. fluminea hepatopancreas was the primary target organ for MC-LR detoxification processes, as evidenced by a significant increase in GST activity. Besides, gills and mantle were more sensitive than the other tissues to oxidative stress in the initial microcystin exposure period with a significant increase in SOD activity. The scanning electron microscopy (SEM) observations revealed that the lateral cilia in the gill aperture were well developed during the MCs exposure period, which could perform the filter-feeding function instead of the damaged frontal cilium. This study provides insight into the possible tolerance of C. fluminea exposed to dense bloom concentrations of M. aeruginosa.

Freshwater Clam Extract Attenuates Indomethacin-Induced Gastric Damage In Vitro and In Vivo

Contemporary pharmacological studies have reported that freshwater clam (Corbicula fluminea) can provide a broad spectrum of bioactivities, including antioxidant, anticancer, antihypertensive, hepatoprotective, and hypocholesterolemic effects. The aim of this study was to evaluate the gastroprotective effects of water extract of freshwater clam (WEC) on indomethacin (IND)-induced gastric mucosal cell damage in vitro and gastric ulcer in vivo. The cell viability of rat gastric mucosa RGM-1 cells was markedly decreased by 0.8 mM of IND treatment, and pre-treated with various concentration of WEC significantly restored IND-induced cell damage in a dose-dependent manner. WEC also significantly attenuated the elevated reactive oxygen species (ROS) levels, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression, and nuclear factor-κB (NF-κB) p65 nuclear translocation induced by IND. In the in vivo study, IND caused severe gastric ulcer in Wistar rats, while WEC pretreatment effectively reduced the ulcer area and edema in the submucosa. We found that WEC significantly restored glutathione (GSH) content in gastric mucosa in a dose-dependent manner (p < 0.05). The reduction of prostaglandin E2 (PGE2) caused by IND was also improved with higher doses of WEC administration. Moreover, the overexpression of COX-2, iNOS, and tumor necrosis factor-α (TNF-α) proteins in gastric mucosa was downregulated by administration of WEC. Consequently, WEC can be used as a potential nutritional supplement to improve NSAIDs-caused gastric mucosal lesions.

When worlds collide: Invader-driven benthic habitat complexity alters predatory impacts of invasive and native predatory fishes

Interactions between multiple invasive alien species (IAS) might increase their ecological impacts, yet relatively few studies have attempted to quantify the effects of facilitative interactions on the success and impact of aquatic IAS. Further, the effect of abiotic factors, such as habitat structure, have lacked consideration in ecological impact prediction for many high-profile IAS, with most data acquired through simplified assessments that do not account for real environmental complexities. In the present study, we assessed a potential facilitative interaction between a predatory invasive fish, the Ponto-Caspian round goby (Neogobius melanostomus), and an invasive bivalve, the Asian clam (Corbicula fluminea). We compared N. melanostomus functional responses (feeding-rates under different prey densities) to a co-occurring endangered European native analogue fish, the bullhead (Cottus gobio), in the presence of increased levels of habitat complexity driven by the accumulation of dead C. fluminea biomass that persists within the environment (i.e. 0, 10, 20 empty bivalve shells). Habitat complexity significantly influenced predation, with consumption in the absence of shells being greater than where 10 or 20 shells were present. However, at the highest shell density, invasive N. melanostomus maximum feeding-rates and functional response ratios were substantially higher than those of native C. gobio. Further, the Relative Impact Potential metric, by combining per capita effects and population abundances, indicated that higher shell densities exacerbate the relative impact of the invader. It therefore appears that N. melanostomus can better tolerate higher IAS shell abundances when foraging at high prey densities, suggesting the occurrence of an important facilitative interaction. Our data are thus fully congruent with field data that link establishment success of N. melanostomus with the presence of C. fluminea. Overall, we show that invader-driven benthic habitat complexity can alter the feeding-rates and thus impacts of predatory fishes, and highlight the importance of inclusion of abiotic factors in impact prediction assessments for IAS.

Seasonal trends of mercury bioaccumulation and assessment of toxic effects in Asian clams and microbial community from field study of estuarine sediment

This study investigated seasonal trends in bioaccumulation potential and toxic effects of mercury (Hg) in Asian clams (Corbicula fluminea) and microbial community. For this, a clam-exposure experiment was performed during summer, fall, and winter seasons in four different sites (HS1: control/clean site; HS2, HS3, and HS4: contaminated sites) of Hyeongsan River estuary, South Korea. Total mercury (THg) and methylmercury (MeHg) in whole sediments were highest at HS4 site during fall, sustained similar levels during winter, but decreased during summer. Unlike whole sediment, pore water reported higher levels in summer, and gradually declined during fall and winter. Asian clams from HS4 site collected during summer presented highest bioaccumulations of THg (521.52 μg/kg, dry weight) and MeHg (161.04 μg/kg, dry weight), which also correlated with the higher levels of Hg present in pore water in the same season. Moreover, biota-sediment-pore water accumulation factor (BSpAF) were comparatively greater in clams collected from HS2∼HS4 compared to HS1 sites, suggesting that porewater was a better indicator of accumulation of Hg. Upregulation of biomarker genes responsible for detoxifying process (gsts1), scavenging oxidative stress (cat), and protein reparation (hsp70 and hsp90) were observed in clams collected from HS2∼HS4. The overexpression of these biomarkers implied that Asian clams can be considered as promising warning tools for Hg-contamination. Both bacterial and metabolic diversities were negatively affected by higher levels of THg and MeHg. Phylum Proteobacteria was enriched in HS2∼HS4 compared to HS1. In contrast, phylum Bacteroidetes showed a reverse trend. The metabolic profile was highest in HS1 and lowest in HS4, revealing higher stress of Hg in HS4 site. Overall, the outcomes of this field study broaden the information on seasonal trends of bioaccumulation of Hg and its toxic effects. These findings may be helpful in Hg monitoring and management programs in other river systems.

Graphene oxide chronic exposure enhanced perfluorooctane sulfonate mediated toxicity through oxidative stress generation in freshwater clam Corbicula fluminea

Graphene oxide (GO), a frequently utilized graphene family nanomaterial, is inevitably released into the aquatic environment and interacts with organic pollutants, including perfluorooctane sulfonate (PFOS), a well-known persistent organic pollutant. To determine the adverse effects of GO chronic exposure on PFOS bioaccumulation and toxicity, adult freshwater bivalves, namely Asian clams (Corbicula fluminea) were treated for 28 days with PFOS (500 ng/L) and different concentrations of GO (0.2, 1, 5 mg/L) as PFOS single and GO single exposure groups, as well as PFOS-GO mixture exposure groups. Our results demonstrated that the bioaccumulation of PFOS was significantly enhanced by co-exposure in gills and visceral masses, which was 1.64-2.91 times higher in gills than in visceral masses. Both single, as well as co-exposure, caused a significant reduction in clams' siphoning behavior, compared to the controls. Further, the co-exposure significantly increased the production of reactive oxygen species (ROS), exacerbating malondialdehyde (MDA) content, enhancing superoxide dismutase (SOD) and catalase (CAT), while decreasing glutathione reductase (GR) and glutathione S-transferase (GST) enzymatic activities in clam tissues. And co-exposure significantly altered the expressions of se-gpx, sod, cyp30, hsp40, and hsp22 genes (associated with oxidative stress and xenobiotic metabolism) both in gills and visceral masses. Moreover, co-exposure caused significant histopathological changes such as cilia degradation in the gills, expansion of tubule lumens in digestive glands, and oocyte shrinkage in gonads. Finally, the enhanced integrated biomarker response (EIBR) index revealed that co-exposure to 500 ng/L PFOS + 1 mg/L/5 mg/L GO was the most stressful circumstance. Overall, our findings suggested that the presence of GO increased PFOS bioaccumulation in tissues, inducing multifaceted negative implications at molecular and behavioral levels through oxidative stress generation in Asian clams.

Intrahabitat Differences in Bacterial Communities Associated with Corbicula fluminea in the Large Shallow Eutrophic Lake Taihu

The Asian clam Corbicula fluminea is a keystone zoobenthos in freshwater ecosystems. However, its associated microbiome is not well understood. We investigated the bacterial communities of this clam and its surrounding environment, including sediment and water simultaneously, in a large lake by means of 16S rRNA gene sequencing. Approximately two-thirds of the bacterial operational taxonomic units (OTUs) associated with clams were observed in the surrounding environment and mostly from particle-associated samples. The associated bacterial communities were site specific and more similar to environmental bacteria from the same site than those at other sites, suggesting a local environmental influence on host bacteria. However, the significant differences in bacterial diversities and compositions between the clam and the environment also indicated strong host selection pressure on bacteria from the surrounding environment. Bacteria affiliated with Firmicutes, Spirochaetes, Tenericutes, Bacteroidetes, Epsilonbacteraeota, Patescibacteria, and Fusobacteria were found to be significantly enriched in the clams in comparison to their local environment. Oligotyping analyses of the core-associated bacterial OTUs also demonstrated that most of the core OTUs had lower relative abundances and occurrence frequencies in environmental samples. The core bacterial OTUs were found to play an important role in maintaining the stability of the bacterial community network. These core bacteria included the two most abundant taxa Romboutsia and Paraclostridium with the potential function of fermenting polysaccharides for assisting host clams in food digestion. Overall, we demonstrate that clam-associated bacteria were spatially dynamic and site specific, which were mainly structured both by local environments and host selection. IMPORTANCE The Asian clam Corbicula fluminea is an important benthic clam in freshwater ecosystems due to its high population densities and high filtering efficiency for particulate organic matter. While the associated microbiota is believed to be vital for host living, our knowledge about the compositions, sources, and potential functions is still lacking. We found that C. fluminea offers a unique ecological niche for specific lake bacteria. We also observed high intrahabitat variation in the associated bacterial communities. Such variations were driven mainly by local environments, followed by host selection pressure. While the local microbes served as a source of the clam-associated bacteria, host selection resulted in enrichments of bacterial taxa with the potential for assisting the host in organic matter digestion. These results significantly advance our current understanding of the origins and ecological roles of the microbiota associated with a keynote clam in freshwater ecosystems.

Hypoglycemic peptide-enriched hydrolysates of Corbicula fluminea and Chlorella sorokiniana possess synergistic hypoglycemic activity through inhibiting α-glucosidase and dipeptidyl peptidase-4 activity

BACKGROUND

The prevalence of diabetes mellitus worldwide has increased in recent decades. Maintaining the level of blood glucose is the most basic and important issue for diabetics. This study aimed to investigate the hypoglycemic activity of a combination of hypoglycemic peptide-enriched hydrolysates of Corbicula fluminea (ACH) and Chlorella sorokiniana (PCH).

RESULTS

Combined supplementation of ACH and PCH synergistically inhibited α-glucosidase and DPP4 activities in vitro. After 4 weeks of treatment with ACH and/or PCH, the plasma glucose concentration and insulin, homeostasis model assessment-estimated insulin resistance (HOMA-IR), total cholesterol (TC) and triglyceride (TG) levels significantly decreased. The hypoglycemic peptides in ACH and PCH were purified and assayed for α-glucosidase and DPP4 activity. The hypoglycemic peptides in ACH and PCH effectively decreased α-glucosidase and DPP4 activities. In silico assays showed that these two peptide types have different docking poses, which determined their inhibitory effect against α-glucosidase and DPP4 activity.

CONCLUSION

Combined treatment with hypoglycemic peptide-enriched ACH and PCH could modulate blood glucose by synergistically inhibiting α-glucosidase and DPP4 activities. © 2021 Society of Chemical Industry.

Toxic effects of ammonia on the intestine of the Asian clam (Corbicula fluminea)

Intestines contain a large number of microorganisms that collectively play a vital role in regulating physiological and biochemical processes, including digestion, water balance, and immune function. In this study, we explored the effects of ammonia stress on intestinal inflammation, the antioxidant system, and the microbiome of the Asian clam (Corbicula fluminea). Exposure to varying ammonia concentrations (10 and 25 mg N/L) and exposure times (7 and 14 days) resulted in damage to C. fluminea intestinal tissue, according to histological analysis. Furthermore, intestinal inflammatory responses and damage to the antioxidant system were revealed through qPCR, ELISA, and biochemical analysis experiments. Inflammatory responses were more severe in the treatment group exposed to a lower concentration of ammonia. High-throughput 16S rDNA sequencing showed that ammonia stress under different conditions altered intestinal bacterial diversity and microbial community composition, particularly impacting the dominant phylum Proteobacteria and genus Aeromonas. These results indicate that ammonia stress can activate intestinal inflammatory reactions, damage the intestinal antioxidant system, and alter intestinal microbial composition, thereby impeding intestinal physiological function and seriously threatening the health of C. fluminea.

Application of a Multi-Metal Stable-Isotope-Enriched Bioassay to Assess Changes to Metal Bioavailability in Suspended Sediments

The direct measurement of particulate contaminant bioavailability is a challenging aspect for the environmental risk assessment of contaminated sites. Here, we demonstrated a multi-metal stable-isotope-enriched bioassay to simultaneously measure the bioavailability of Cd, Cu, and Zn in naturally contaminated sediments following differing periods of resuspension treatment. Freshwater filter-feeding clams were pre-labeled with the isotopes ¹¹⁴Cd, ⁶⁵Cu, and ⁶⁸Zn to elevate isotope abundances in their tissues and then exposed to metal-contaminated suspended sediments. The assimilation of sediment-associated metals by clams would decrease the isotope ratios (Cd^114/111, Cu^65/63, and Zn^68/64) in tissues, providing a direct measurement of metal bioavailability. For the sediments tested here, the method revealed bioavailable cadmium and non-bioavailable copper in sediments but was inconclusive for zinc. With a longer resuspension time, the bioavailability of particulate cadmium increased, but that of copper was unaffected. Metal bioavailability predicted using traditional wet-chemical extraction methods was inconsistent with these findings. The study indicated that multi-metal stable-isotope-enriched bioassay provides a new tool for directly assessing metal bioavailability in sediments, and this method is amenable for use in in situ assessments.

Combined toxicity of micro/nano scale polystyrene plastics and ciprofloxacin to Corbicula fluminea in freshwater sediments

Plastic pollution has become a global environmental threat, and its potential to affect the bioavailability and toxicity of pharmaceuticals to aquatic organism are of growing concern. However, little is known regarding the combined toxicity of micro/nano-plastics and pharmaceuticals to benthic organisms in sediments. Thus, we employed a freshwater benthic bivalve, Corbicula fluminea (C. fluminea), to investigate the individual and co-toxicity of model plastics, microscopic fluorescent polystyrene (PS) (PS nano-plastic (PS-NP) and PS micro-plastic (PS-MP), 80 nm and 6 μm, respectively) and the common antibiotic ciprofloxacin (CIP) in formulated sediments. Our results suggest that oxidative damage and neurotoxicity were confirmed to occur in C. fluminea in all the treatments. The oxidative damage in the digestive glands reduced the clam ability to scavenge free radicals, causing severe tissue damage to the digestive glands of C. fluminea. Filtration rates of C. fluminea were significantly decreased in a concentration-dependent manner across all the treatments, which might be due to the inhibition of acetylcholinesterase activities. Interactions between CIP and micro/nano-plastic were observed, whereby the presence of PS decreased the toxicity of CIP in the digestive glands but aggravated the C. fluminea siphoning inhibition rate in the nano-plastic co-treatments group; in addition, the CIP toxicity to C. fluminea decreased because that the concentration of free dissolved CIP was lowered by micro/nano-PS. Taken together, the current study could contribute greatly to evaluating the ecological risk of CIP and PS in aquatic environments and sheds light on potential issues of food safety caused by both emerging pollutants.

Lipidomics phenotyping of clam (Corbicula fluminea) through graphene/fibrous silica nanohybrids based solid-phase extraction and HILIC-MS analysis

Polyunsaturated phospholipids are abundant in clam (Corbicula fluminea) but difficult to be fully extracted. Herein, graphene/fibrous silica (G/KCC-1) nanohybrids were synthesized, characterized, and applied for solid-phase extraction (SPE) of phospholipids in clam. The effectiveness of G/KCC-1 SPE was verified by hydrophilic interaction chromatography mass spectrometry (HILIC-MS) based lipidomics and statistical analysis. The ions of PE 16:0/18:1 (m/z 716.4), PC 16:0/20:5 (m/z 824.6) and etc. were regarded as the main difference among the crude lipids, acetone washed extract, and eluate of G/KCC-1 SPE. Finally, this method was validated in terms of linearity (R² 0.9965 to 0.9981), sensitivity (LOD 0.19-0.51 μg·mL^-1 and LOQ 0.48 - 1.47 μg·mL^-1), and precision (RSD_intra-day ≤ 7.16% and RSD_inter-day ≤ 7.30%). In conclusion, the G/KCC-1 SPE and HILIC-MS method was shown to be accurate and efficient in selective extracting and phenotyping phospholipids in C. fluminea.

Characterization of the GABAergic system in Asian clam Corbicula fluminea: Phylogenetic analysis, tissue distribution, and response to the aquatic contaminant carbamazepine

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter involved in the neuro-endocrine-immune (NEI) system. In this study, we sequenced the partial length of cDNA fragments of three genes involved in GABA neurotransmitter system of the Asian clam (Corbicula fluminea) (GABA_A receptor-associated protein (GABARAP), GABARAPL2 and GABA transporter (GAT-1)). These genes exhibited high amino acid sequence identity compared with other invertebrate orthologs. Expression patterns of the three genes were determined in mantle, gill, gonad, digestive gland and muscle, and the steady state levels of mRNA for each were determined to be highest in gonad and lowest in muscle. To determine their regulation by pharmaceuticals that are present as contaminants in waterways, clams were exposed to carbamazepine (CBZ) for 30 days. CBZ is an agonist for GABA receptors and is an anticonvulsant pharmaceutical that is often detected in aquatic ecosystems. GABARAP and GABARAPL2 mRNA levels were significantly downregulated by 5 and 50 μg/L CBZ in mantle and gill (p < 0.05), while in the gonad and digestive gland, steady state levels (p < 0.05) were decreased with exposure to all three doses. GAT-1 mRNA was upregulated by CBZ (p < 0.05) in the mantle and gill at all three doses tested and in the gonad and digestive system with 5 and 50 μg/L. These data suggest that CBZ disrupt the expression of the GABAergic neurotransmitter system in C. fluminea. Moreover, GABARAP, GABARAPL2 and GAT-1 may be useful biomarkers for the screening of substances that are hazardous to the NEI system of mollusks.

Suspended sediment exacerbates perfluorooctane sulfonate mediated toxicity through reactive oxygen species generation in freshwater clam Corbicula fluminea

Perfluorooctane sulfonate (PFOS) potentially adsorbs on the surface of suspended sediment (SPS), which can develop a toxic "pool" bioavailable to benthic organisms. In this study, the freshwater clam Corbicula fluminea was employed as a zoobenthos model to study the effects of SPS (collected from the Yellow River) on the bioaccumulation and toxicity (from the molecular level to cellular and physiological levels) caused by PFOS exposure. Besides, the enhanced integrated biomarker response (EIBR) system was applied as an index to evaluate the in-depth toxic effects of PFOS and SPS single and co-exposure at various treatment levels. Our results demonstrated that PFOS-SPS co-exposure (at sub-lethal doses of PFOS) significantly increased the bioaccumulation of PFOS, and induced the elevated levels of reactive oxygen species (ROS), the significantly increased activities of superoxide dismutase (SOD) and catalase (CAT) enzymes, the significantly increased content of malondialdehyde (MDA), and the significantly upregulated expression levels of sod, selenium-dependent glutathione peroxidase (se-gpx), heat shock protein 22 (hsp22), heat shock protein 40 (hsp40) and cytochrome P450 30 (cyp30) genes. Further, the co-exposure induced the significantly higher histopathological alterations in the gonads and digestive glands, and even elevated the inhibition of siphoning behavior in clams. In addition, the EIBR index also revealed the highest values for PFOS and SPS co-exposure, compared to the individual SPS or PFOS exposure. The results indicated that at high levels of PFOS exposure (especially at 1000 μg/L), the presence of SPS might increase the generation of ROS by influencing the bioaccumulation of PFOS, which enhanced the toxicity of PFOS to C. fluminea. These results potentially provide basic information for the comprehensive evaluation of the toxic effects of PFOS on benthos in a multi-sediment river ecosystem.

A multibiomarker approach to assess toxic effects of wastewater treatment plant effluents and activated defence mechanisms in marine (Ruditapes philippinarum) and fresh water (Corbicula fluminea) bivalve species

Since it has been demonstrated that urban effluents can have adverse effects on aquatic organisms, a multibiomarker study was used to evaluate the effects of wastewater treatment plant (WWTP) effluents discharged into the marine and freshwater environments on clams in Cádiz, Spain. One bioassay was performed in the Bay of Cádiz, exposing Ruditapes philippinarum (marine) to a reference site as well as two sites close to WWTP discharges for 14 days. A second bioassay was performed in the Guadalete River, exposing Corbicula fluminea (fresh water) to three sites for 21 days. The biomarkers analysed included defence mechanisms and various toxic effects. Results indicated that WWTP effluents activated defence mechanisms and induced toxic effects in clams exposed to both environments, thus indicating bioavailability of contaminants present in water. Elevated enzymatic activity was found in clams deployed in La Puntilla and El Trocadero compared to control clams and those exposed to the reference site, and 96% of clams deployed at G2 in the Guadalete River died before day 7. Clams exposed to G1 and G3 indicated significant differences in all biomarkers analysed with respect to control clams (p < 0.05). Both species were sensitive to contaminants present in studied sites. This is the first time that these species were used in cages to assess the environmental risk of wastewater effluent discharges in freshwater and marine column environments. The multibiomarker approach provided important ecotoxicological information and is useful for the assessment of the bioavailability and effect of contaminants from WWTP effluents on marine and fresh water invertebrates.

The effects of wet wipe pollution on the Asian clam, Corbicula fluminea (Mollusca: Bivalvia) in the River Thames, London

The aim of the present study was to evaluate "flushable" and "non-flushable" wet wipes as a source of plastic pollution in the River Thames at Hammersmith, London and the impacts they have on the invasive Asian clam, Corbicula fluminea, in this watercourse. Surveys were conducted to assess whether the density of wet wipes along the foreshore upstream of Hammersmith Bridge affected the distribution of C. fluminea. High densities of wet wipes were associated with low numbers of clams and vice versa. The maximum wet wipe density recorded was 143 wipes m^-2 and maximum clam density 151 individuals m^-2. Clams adjacent to the wet wipe reefs were found to contain synthetic polymers including polypropylene (57%), polyethylene (9%), polyallomer (8%), nylon (8%) and polyester (3%). Some of these polymers may have originated from the wet wipe reefs.

fluminea) tissue in Kelantan, Malaysia

Corbicula fluminea (C. fluminea) is one of the mollusc species commonly eaten as a popular snack in Kelantan, Malaysia. This species contributes to the local economic activity. However, the handling process of C. fluminea at different processing stages (raw, smoke and selling stages) is believed to have affected the nutritional value in their soft tissue. Hence, this study aims to provide information about the chemical content (moisture, crude fat, ash, crude protein and carbohydrate) of C. fluminea and fatty acid of smoked C. fluminea at different processing stages. Samples were collected from Pasir Mas and Tumpat, Kelantan, Malaysia. The chemical content analysis was carried out based on the Association of Official Analytical Chemists (AOAC) standard procedures. The results have indicated that moisture (80.93 ± 0.37%) and crude fat (10.82 ± 0.21%) in C. fluminea were significantly higher (p < 0.05) at the raw stage. On the other hand, the ash (2.09 ± 0.03%) and crude protein (9.45 ± 0.42%) were significantly higher (p < 0.05) at smoked stage. Meanwhile, carbohydrate (3.39 ± 0.49%) was significantly higher (p < 0.05) at the selling stage. The fatty acid percentage of smoked C. fluminea indicates that the total saturated fatty acid (SFA) content was higher than the total of both monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA). The obtained data indicates that the composition percentage of omega-6 (n-6) in PUFA is significantly greater than omega-3 (n-3). The n-6/n-3 ratio of smoked C. fluminea is 2.95-3.11 and therefore can be considered as a healthy diet. The findings of this study can improve consumers' health through sufficient nutrient consumption and also provide economic benefits by increasing sellers' income in Kelantan.

Effects of acute ammonia toxicity on oxidative stress, DNA damage and apoptosis in digestive gland and gill of Asian clam (Corbicula fluminea)

Ammonia is one of the major pollutants associated with the main river basins due to ammonification of uneaten food and animal excretion, which usually brings detrimental health effects to aquatic invertebrate. However, the mechanisms of ammonia toxicity in aquatic invertebrate have rarely been reported. In this study, C. fluminea was exposed to different levels of ammonia (control group, 10 mg/L, and 25 mg/L) for 24 h and 48 h, and digestive gland and gill were collected to explore toxic effects on oxidative stress, DNA damage and apoptosis under ammonia stress. The results showed that ammonia poisoning could increase the activity of oxidative stress enzyme (SOD and CAT), inducing differentially expressed genes (DRAM2, GADD45, P53, BAX, BCL2, CASP8, CASP9, CASP3, HSP70 and HSP90) and different cytokines (IL-1 beta, IL-8, IL-17 and TNF-alpha) of DNA damage and apoptosis. The difference of toxic effects induced by ammonia among digestive gland and gill were also observed by real-time PCR and TUNEL staining. Our results will be helpful to understand the mechanism of aquatic toxicology induced by ammonia in C. fluminea.

Bioaccumulation dynamics and gene regulation in a freshwater bivalve after aqueous and dietary exposures to gold nanoparticles and ionic gold

Gold nanoparticles (AuNPs) are being developed and produced for a wide variety of industrial and biomedical applications, which raises the concern about their release and potential effects in the environment. In this study, we aim to assess the effects of PEGylated AuNPs and ionic gold on the freshwater bivalve Corbicula fluminea. As NP bioavailability is conditioned by many factors of variability, we focused on the determination of biodynamic parameters which control AuNP uptake and elimination in bivalves. Three experiments were conducted: (1) a waterborne exposure (0-24 mg/L for AuNPs and 0-12 mg/L for ionic gold), (2) a dietborne exposure (0-48 mg/L for AuNPs and 0-24 mg/L for ionic gold), and (3) an elimination phase (after waterborne exposure to 12 mg/L for AuNPs and 24 mg/L for ionic gold), to calculate rate constants for uptake from water(kuw), from food (kuf), and for the physiological elimination (ke) for AuNPs and AuCl(OH)₃^-. Jointly, the relative expression of several genes was investigated in the hemolymph cells to relate AuNPs and gold ion exposures to detoxification, oxidative stress, immune, and apoptosis responses in C. fluminea. Results show that kuw and kuf were around 10 and 30 times higher for AuNPs compared to AuCl(OH)₃^-, respectively. The ke was also faster in clams exposed to AuNPs meaning that they also had greater excretion capacities in comparison to gold ions. Water seems to be the main exposure pathway for C. fluminea according to kuw and kuf values for AuNPs and AuCl(OH)₃^- (kuw = 0.28 and 0.03, kuf = 0.009 and 0.001, respectively). The gene analyses pointed out important responses against oxidative stress, strong activations of genes of the immunity, and apoptosis after the waterborne exposure to AuNPs and to a lesser extent after exposure to gold ions. Very few responses were observed after the dietary exposure to both forms of gold, probably due to valve closure in response to contamination. While some studies suggest that the toxicity of nanoparticles may come from the release of metal ions, our results showed that the AuNPs we used were very stable (less than 1% of ion release) and generated more effects at the gene level than ionic gold. Therefore these results highlight the strong potential of toxicity of AuNPs compared to ionic gold and raise new concerns about the toxicity inherent to NPs in the environment.

Radical scavenging activities of peptide from Asian clam (Corbicula fluminea) and its protective effects on oxidative damage induced by hydrogen peroxide in HepG2 cells

The soft part of Asian clam (Corbicula fluminea) was hydrolyzed using trypsin and the hydrolysates were separated by ultrafiltration using the membrane with molecular weight cutoff of 10 and 5 kDa. Three fractions (F10000, F10000-5000, and F5000) were obtained. The F5000 showed the strongest scavenging abilities to DPPH (2,2-diphenyl-1-picrylhydrazyl), superoxide anion, and hydroxyl radicals, and was further fractionated into four fractions (component I, II, III, and IV) by gel chromatography. The protective effects of these components on oxidative damage induced by hydrogen peroxide (H₂ O₂ ) in HepG2 cells were evaluated. Meanwhile, component I separated from F5000 had more positive effects on increasing the activity of catalase, decreasing lipid peroxidation, inhibiting H₂ O₂ -induced apoptosis, and higher yield. The component I was further separated using anion exchange chromatography and reversed phase high-performance liquid chromatography, and the peptide sequence of Lys-Gly-Pro-Ala- Pro-Phe-Tyr-Pro-Leu was identified by mass with molecular weight of 988.3 Da. PRACTICAL APPLICATIONS: Asian clam (C. fluminea) is used for liver protection in traditional Chinese medicine. The present study investigated the radical scavenging activity of the hydrolysates from C. fluminea and the protective effects of the hydrolysate fractions on oxidative damage induced by H₂ O₂ in HepG2 cells. In addition, a peptide was purified from the hydrolysate and the amino acid sequence of it was identified. Although chemical antioxidant has some side effects on health, the peptide with antioxidant activity obtained from C. fluminea would have more extensive application in food and nutraceutical.

Tracking sources and transfer of contamination according to pollutants variety at the sediment-biota interface using a clam as bioindicator in peri-alpine lakes

Point pollution sources may differently impact lakes littoral, possibly leading to local ecological risks. The concomitant chemical analysis of littoral-benthic organisms and sediment can provide insights into the bioavailability and thus the ecological risk of contaminants. In this study, the autochthonous Corbicula fluminea was used to assess the sources and transfer of six trace metals (TMs) and fourteen Polycyclic Aromatic Hydrocarbons (PAHs) to the littoral-benthic biota of a large lake. The contaminant concentrations spatially varied with a value scale from 1 to 280 000 times along the lake littoral in both the sediment and clams. Multiple linear regressions were performed to explain the spatial variability of Corbicula fluminea contamination by considering both watershed and in-lake sources. The concentration of the sum of PAHs in clams was significantly correlated with sediment contamination, suggesting that PAHs contamination of the benthic biota mainly occur from the sediment. Most of the internal TM concentrations of clams were significantly correlated with stormwater drainage areas in the lake watershed, highlighting the importance of stormwater runoffs in the littoral biota contamination. The transfer of TMs and PAHs was assessed through the bioconcentration factor defined as the ratio of internal and sediment concentrations. As, Cd, Cu, Zn and light molecular weight PAHs were more bioconcentrated in C. fluminea than Pb, Sn and heavy molecular weight PAHs, suggesting differences in their bioavailability. This study underlines the relevance of using autochthonous organisms as bioindicators of lake littoral biota contamination concomitantly with sediment matrices, and illustrates the challenge of tracking pollution sources in lakes.

Effect of imidacloprid on the behavior, antioxidant system, multixenobiotic resistance, and histopathology of Asian freshwater clams (Corbicula fluminea)

In the current study, to investigate the effect of imidacloprid on benthic bivalves, adult Asian clams (Corbicula fluminea) were exposed to 0, 20, 200, and 2000 μg/L imidacloprid for 30 d. Imidacloprid significantly inhibited the siphoning and burrowing behaviour (p < 0.05) of the clams. Significant histopathological changes were associated with degeneration of the cilium, the contraction and adhesion of the lymphocyte, and the swelling of epithelium cells in gills, and there was notable degeneration in the digestive tubules, haemolytic infiltration in the connective tissue and epithelial cell necrosis in the digestive glands in the 2000 μg/L treatment group. The activity of AChE in the digestive glands was significantly inhibited at all treatment levels, whereas this inhibition was observed in gills only in the 2000 μg/L treatment (p < 0.05). Additionally, indicators of the antioxidant system (e.g., SOD, CAT, and GST activity) and MDA content were significantly increased in the gills and digestive glands with all treatments (p < 0.05). Moreover, the mRNA expression levels of Hsp genes (hsp 22, hsp 40, hsp 60, hsp 70, hsp 90) and multixenobiotic resistance (MXR) system-related genes (abcb1, abcc1) were significantly downregulated (p < 0.05). Therefore, our results suggest that imidacloprid changes the oxidative stress, cellular detoxification, and MXR system of C. fluminea. Our findings provide new insights into the effects of neonicotinoids on benthic bivalves such as C. fluminea.

New lake in a changing world: the construction and filling of a small hydropower reservoir in the tropics (Rio de Janeiro, Brazil)

Climate change has affected rainfall patterns in tropical regions, where simultaneous demands for water and energy, habitat loss, declining biodiversity, and spread of invasive species have reflected a rapidly changing world underway. In Brazil, hydropower generation accounts for 64% of the electricity matrix, which presently includes 1007 small hydropower plants (SHPs) having many others under construction or planned. This paper aimed to evaluate changes in water quality, plankton communities, and benthic macroinvertebrates during dam construction, filling, and the first year of operation of a SHP. Suspended solids, turbidity, and silica were variables that highlighted the impact of this construction on the river. Fast changes in water quality (increases in calcium, chlorides, and nitrate) and on aquatic communities (i.e. euglenophyceans and testate amoebae increased in numbers) were detected during the filling phase. Following SHP construction, the concentrations of metals and total phosphorus tended to decrease. Two striking findings observed in the aquatic communities from the riverine conditions to the new lake were the increase in picocyanobacteria abundance, expanding population stocks throughout the river basin, and the constant presence of the invasive mollusc Corbicula fluminea in the macroinvertebrate assemblage, revealing once again its resistance to environmental variability. The lake soon became a natural trap for ions from the drainage basin, as revealed by the increase in electrical conductivity, ammonium, potassium, and magnesium concentrations and the abundance of cyanobacteria, highlighting the need for watershed management to improve ecological conditions in the lake.

Transcriptome-wide identification and characterization of the Sox gene family and microsatellites for Corbicula fluminea

The Asian clam, Corbicula fluminea, is a commonly consumed small freshwater bivalve in East Asia. However, available genetic information of this clam is still limited. In this study, the transcriptome of female C. fluminea was sequenced using the Illumina HiSeq 2500 platform. A total of 89,563 unigenes were assembled with an average length of 859 bp, and 36.7% of them were successfully annotated. Six members of Sox gene family namely SoxB1, SoxB2, SoxC, SoxD, SoxE and SoxF were identified. Based on these genes, the divergence time of C. fluminea was estimated to be around  476 million years ago. Furthermore, a total of 3,117 microsatellites were detected with a distribution density of 1:12,960 bp. Fifty of these microsatellites were randomly selected for validation, and 45 of them were successfully amplified with 31 polymorphic ones. The data obtained in this study will provide useful information for future genetic and genomic studies in C. fluminea.

Transcriptome analysis of response mechanism to ammonia stress in Asian clam (Corbicula fluminea)

Corbicula fluminea is highly sensitive to ammonia, and its response mechanism to ammonia stress is unclear. In this study, C. fluminea was exposed to different levels of ammonia (control group, 10 mg/L, and 25 mg/L) for 24 h and 48 h. A comparative analysis of transcriptome sequencing (RNA-seq) of C. fluminea digestive gland showed that the expression of 6742 genes (11.54%) was significantly affected by ammonia stress. The TLR, NF-κB, FOXO, and apoptotic signaling pathways were involved in the regulation. The differential expression of 14 genes was confirmed by real-time PCR. In summary, the response mechanism of C. fluminea digestive gland under ammonia stress may be different from that of oxidative stress in marine vertebrates. Also, the NMDAR-mediated pathway may not be the main mechanism in the response to ammonia stress in C. fluminea. The present study is a preliminary study for further investigation into ammonia toxicity in shellfish.

Bioturbation effects on metal release from contaminated sediments are metal-dependent

Metal flux measurements inform the mobility, potential bioavailability and risk of toxicity for metals in contaminated sediments and therefore is an important approach for sediment quality assessment. The binding and release of metals that contribute to the net flux is strongly influenced by the presence and behaviors of benthic organisms. Here we studied the effects of bioturbation on the mobility and efflux of metals from multi-metal contaminated sediments that inhabited by oligochaete worms or both worms and bivalves. Presence of bivalves enhanced the release of Mn, Co, Ni and Zn but not for copper and chromium, which is likely due to the high affinities of copper and chromium for the solid phase. Metals in the overlying water were primarily associated with fractions smaller than 10 kDa, and the fractionation of all metals were not affected by the presence of the bivalve. Metal fluxes attributed to different processes were also distinguished, and the bioturbation induced effluxes were substantially higher than the diffusive effluxes. Temporal variabilities in the total net effluxes of Mn, Co, Ni and Zn were also observed and were attributed to the biological activities of the bivalves. Overall, the present study demonstrated that the response of different metals to the same bioturbation behavior was different, resulting in distinct mobility and fate of the metal contaminants.

Corbicula fluminea gene expression modulated by CeO2 nanomaterials and salinity

Cerium dioxide nanomaterials (CeO₂ NMs) are used in different fields and incorporated in daily products. Several studies highlighted their effects on organism physiology, although molecular studies remain scarce. NM behavior is strongly dependent on the environment but few data are available using complex exposure media, raising the question of its environmental impacts. The aim of the present work was to assess the toxic potential of three CeO₂ NMs in Corbicula fluminea at a molecular level by RT-qPCR under a more realistic scenario of exposure, in a multistress context at two different salinities (1.5 and 15 psu). C. fluminea was exposed for 28 days to pulses of the three selected NMs (reference, manufactured, and aged manufactured). In bivalves, the gills and digestive gland are two key organs used for ecotoxicological studies. The expression change of 12 genes was measured in control organisms after 28 days in both organs, allowing us to clearly separate the responses for both organs and salinities. As gills come in contact with the environment first, we monitored gene the expression at intermediate time points (7, 14, and 21 days) for this organ in order to highlight clams responses to NM and salinity. Two genes (Se-GPx, MnSOD) had a salinity-dependent level of expression. HSP70, Se-GPx, and Trxr mRNAs presented significant changes in their expressions in the presence of NM. This study was completed using an integrated statistical approach. The exposed organisms differed more from control at field salinity than those exposed to hyper-saline conditions. At 15 psu, salinity pressure seems to cause the first molecular impact. At 1.5 psu, gene expression patterns allowed the effect of each NM to separate clearly. These results confirmed the usefulness of gene expression studies. Moreover, we highlighted the necessity to assess the environmental toxicity of the different forms of manufactured NM.

Sediment quality assessment in the Guadalquivir River (SW, Spain) using caged Asian clams: A biomarker field approach

This study assesses the sediment quality of the Guadalquivir River watercourse between the Alcalá del Río dam and the city of Seville. The main objective of this work is to address sediment quality in the area using an integrative approach that links sediment contamination and toxicity using the Asiatic clam (Corbicula fluminea) under field conditions. This is the first study conducted in the area that use of a battery of biomarkers from exposure (GST, GPx) to adverse biological effect (DNA and histopathological damage) to identify the contamination adverse effects in a river area affected by a cocktail of different anthropogenic activities (urban, industrial, agricultural, etc.). The sediment quality characterized in the area shows a significant biological stress related to metal(loid)s at station located in Alcalá del Río in the river upper part of the studied area, being this stress toxic when approaching the city of Seville. The sediments located nearby this city showed toxicity by means of positive values in the biomarkers of effects measured in the caged clams and related to contaminants with an industrial and urban discharge origins. These results have shown the useful and strength of the biomarker approach used in this study that combines biomarker responses from exposure to effects and allows identifying the contamination adverse effects by means of using caging individuals of the Asian clam. It has been proved in the different experiments how once the exposure biomarkers reach a maximum value of their system the detoxification ability of the organisms is collapsed and then the biomarkers of effect are measured significantly in the different tissues. The use of field surveys using tolerant specie such as the Asian clam is recommendable to determine sediment quality under an integrative point of view as here reported.

Whole-transcriptome response to wastewater treatment plant and stormwater effluents in the Asian clam, Corbicula fluminea

The increase in human population and urbanization are resulting in an increase in the volume of wastewater and urban runoff effluents entering natural ecosystems. These effluents may contain multiple pollutants to which the biological response of aquatic organisms is still poorly understood mainly due to mixture toxicity and interactions with other environmental factors. In this context, RNA sequencing was used to assess the impact of a chronic exposure to wastewater treatment plant and stormwater effluents at the whole-transcriptome level and evaluate the potential physiological outcomes in the Asian clam Corbicula fluminea. We de-novo assembled a transcriptome from C. fluminea digestive gland and identified a set of 3,181 transcripts with altered abundance in response to water quality. The largest differences in transcriptomic profiles were observed between C. fluminea from the reference site and those exposed to wastewater treatment plant effluents. On both anthropogenically impacted sites, most differentially expressed transcripts were involved in signaling pathways in relation to energy metabolism such as mTOR and FoxO, suggesting an energy/nutrient deficit and hypoxic conditions. These conditions were likely responsible for damages to proteins and transcripts in response to wastewater treatment effluents whereas exposure to urban runoff might result in immune and endocrine disruptions. In absence of comprehensive chemical characterization, the RNAseq approach could provide information regarding the mode of action of pollutants and then be useful for the identification of which parameters must be studied at higher integration level in order to diagnose sites where the presence of complex and variable mixtures of chemicals is suspected.

Effects of microplastics and mercury in the freshwater bivalve Corbicula fluminea (Müller, 1774): Filtration rate, biochemical biomarkers and mercury bioconcentration

The main objectives of this study were to investigate the effects of a mixture of microplastics and mercury on Corbicula fluminea, the post-exposure recovery, and the potential of microplastics to influence the bioconcentration of mercury by this species. Bivalves were collected in the field and acclimated to laboratory conditions for 14 days. Then, a 14-day bioassay was carried out. Bivalves were exposed for 8 days to clean medium (control), microplastics (0.13 mg/L), mercury (30 µg/L) and to a mixture (same concentrations) of both substances. The post-exposure recovery was investigated through 6 additional days in clean medium. After 8 and 14 days, the following endpoints were analysed: the post-exposure filtration rate (FR); the activity of cholinesterase enzymes (ChE), NADP-dependent isocitrate dehydrogenase (IDH), octopine dehydrogenase, catalase, glutathione reductase, glutathione peroxidase and glutathione S-transferases (GST), and the levels of lipid peroxidation (LPO). After 8 days of exposure to mercury, the bioconcentration factors (BCF) were 55 in bivalves exposed to the metal alone and 25 in bivalves exposed to the mixture. Thus, microplastics reduced the bioconcentration of mercury by C. fluminea. Bivalves exposed to microplastics, mercury or to the mixture had significantly (p ≤ 0.05) decreased FR and increased LPO levels, indicating fitness reduction and lipid oxidative damage. In addition, bivalves exposed to microplastics alone had significant (p ≤ 0.05) reduction of adductor muscle ChE activity, indicating neurotoxicity. Moreover, bivalves exposed to mercury alone had significantly (p ≤ 0.05) inhibited IDH activity, suggesting alterations in cellular energy production. Antagonism between microplastics and mercury in FR, ChE activity, GST activity and LPO levels was found. Six days of post-exposure recovery in clean medium was not enough to totally reverse the toxic effects induced by the substances nor to eliminate completely the mercury from the bivalve's body. These findings have implications to animal, ecosystem and human health.

Biofiltration using C. fluminea for E.coli removal from water: Comparison with ozonation and photocatalytic oxidation

Corbicula fluminea, an Asian clam, is one of the worst invasive species in Europe that can survive in very adverse environmental conditions. Despite its negative impacts, the species also has the capacity to bioaccumulate heavy metals, contaminants and can be exploited for wastewater treatment purposes. The capacity of the Asian clam to remove Escherichia coli, used as fecal contamination indicator, was analyzed. Conventional wastewater treatment plants are not suitable to remove bacteria, thus resulting in treated municipal wastewater with high bacterial loads. E. coli clearance rate was analyzed as function of the number of clams. The bivalves can remove bacteria until concentrations below the detection limit in about 6 h. The adsorption on the clam shells' and bioaccumulation on the soft tissues were also analyzed. The depuration of clams along 48 h were analyzed revealing that no bacteria was detected in the water. Thus, these results suggest that Asian clam can bioprocess E. coli. On the other hand, results obtained by this methodology were compared with ozonation and photocatalytic oxidation using TiO₂, Ag, Au, Pd-TiO₂. In all treatments it was possible to achieve concentrations of E. coli below the detection limit. However, photocatalytic oxidation demands about 4700 folds more energy than ozonation, besides the costs associated with catalysts. Comparing complexity of ozonation with biofiltration, this study suggests that application of biofiltration using C. fluminea can be a suitable solution to minimize the presence of bacteria in wastewater, reducing environmental and economic impacts.

Integrative assessment of sediment quality in lower basin affected by former mining in Brazil

The Ribeira de Iguape River (Southeast Brazil) is metal contaminated by mining activities. Despite it has been cataloged as "in via of restoration" by the literature, this basin is still a sink of pollution in some segments of the fluvial system. This study aimed to assess the sediment quality in the lower part of the RIR basin. The employed approach was based on biological responses of the freshwater clam Corbicula fluminea after 7-day exposure bioassays using as the reference site the Perequê Ecological Park. Toxic responses (burial activity and lethality) and biochemical biomarkers (GST, GR, GPx, LPO, MTs, AChE and DNA damage) were evaluated and then integrated with metal bioavailability and chemical concentrations to address the sediment quality in the area through the weight-of-evidence approach. A multivariate analysis identified linkages between biological responses and contamination. Results pointed that, despite being below the benchmarks of the US Environmental Protection Agency, there is slight metal contamination in the lower part of the basin which induces oxidative stress in C. fluminea; other toxic responses were sometimes attributed to As and Cr bioaccumulation. The sediment quality values (TEL-PEL values in mg/kg) were calculated for the current study for As (0.63-1.31), Cr (3.5-11.05), Cs (1.0-1.17), Cu (6.32-7.32), Ni (6.78-7.46), Ti (42.0-215), V (1.77-8.00). By comparison with other international guidelines, the sediment quality of the lower basin of the Vale de Ribeira does not identify a significant environmental risk.

Biological toxicity response of Asian Clam (Corbicula fluminea) to pollutants in surface water and sediment

As a typical test species, Asian Clam (Corbicula fluminea) is widely used in the identification and evaluation of freshwater toxicity. This study provides a summary of the research published from 1979 to 2018. The focus was on the bioaccumulation, morphological and behavioral changes, and biochemical index alterations of Corbicula fluminea to target pollutants (i.e., ammonia, metal(loid)s, and organic chemicals) in surface water and sediment. The applications on the evaluation of actual aquatic pollution, determination of toxicological mechanisms, prediction of toxicity, and bioremediation are also specifically discussed. The primary purpose is to facilitate the comprehensive understanding and accurate application of Corbicula fluminea in freshwater ecotoxicological studies.

Uptake and effects of the antimicrobial florfenicol, microplastics and their mixtures on freshwater exotic invasive bivalve Corbicula fluminea

Microplastics and antimicrobials are widely spread environmental contaminants and more research on their toxicity is needed. The uptake and effects of the antimicrobial florfenicol, microplastics, and their mixtures on Corbicula fluminea were investigated. Bivalves were exposed for 96h to florfenicol (1.8 and 7.1mg/l), microplastics (0.2 and 0.7mg/l), or mixtures of the two substances. After 96h, all bivalves exposed to antimicrobial treatments had florfenicol in their body (e.g. 2±1μg/g). Microplastics were found in the gut, lumen of the digestive gland, connective tissue, hemolymphatic sinuses, and gills surface of animals. Florfenicol caused a significant inhibition of cholinesterase (ChE) activity (~32%). Animals exposed to 0.2mg/l of microplastics showed ChE activity inhibition (31%), and no other significant alterations. Mixtures caused feeding inhibition (57-83%), significant ChE inhibition (44-57%) and of isocitrate dehydrogenase activity, and increased anti-oxidant enzymes activity and lipid peroxidation levels. Overall, the results indicate that C. fluminea take up florfenicol and microplastics from the water and accumulated or at least retained it in their body for some time; both florfenicol (low ppm range) and microplastics (ppb range) were toxic to C. fluminea, with mixtures containing florfenicol and microplastics being more toxic. Thus, the risk of exposure and toxic effects of florfenicol to C. fluminea and other bivalves, and its predators increase in ecosystems contaminated with the antimicrobial and microplastics, as well as to humans consuming contaminated species from these ecosystems.

TiO2 nanoparticles in sediments: Effect on the bioavailability of heavy metals in the freshwater bivalve Corbicula fluminea

Most studies investigating the influence of TiO₂ NPs on heavy metal bioavailability have focused on the aqueous phase; however, few have examined the sediments containing more nanoparticles. Here, we investigated the effects of TiO₂ NPs on heavy metal bioavailability in C. fluminea in sediments. The interactions between the TiO₂ NPs and metals in sediments, the influence of TiO₂ NPs on metals levels in aqueous phase and geochemical speciation were also explored. The results indicated the large adsorption capacity of TiO₂ NPs and the strong adsorption affinity to metals caused the metals adsorbed on nanoparticles, which decreased the metals concentrations in water phase. Changes in metal speciation caused by metals in EXC, CAR, and IMO partly transported from sediments to TiO₂ NPs during the aging of sediments. Heavy metals contents in C. fluminea tissues were in the order of gill>visceral mass>mantle>foot and increased with the increasing TiO₂ NPs contents in sediments. TiO₂ NPs enhanced the bioavailability of metals in the speciation of EXC, CAR, and IMO in sediments by the Trojan horse effects. The results can facilitate a more realistic evaluation of the environmental risks of TiO₂ NPs to benthic organisms in heavy metal-contaminated sediments.

Ultrasound synergized with three-phase partitioning for extraction and separation of Corbicula fluminea polysaccharides and possible relevant mechanisms

Ultrasound and three-phase partitioning (USTPP) were combined to extract and separate polysaccharides (PS) efficiently from Corbicula fluminea crude extracts. The following optimum experimental conditions were established: 20% (w/v) ammonium sulfate concentration, 1:1 (v/v) t-butanol to crude extract ratio, 180W ultrasonic power, 40kHz frequency, 100% duty cycle, 10min irradiation time, and 35°C. The maximum extraction yield of PS obtained from USTPP was approximately 11.22%, which was higher than the maximum yields from conventional three-phase partitioning (TPP; 9.32%) and ultrasound extraction (USE; 6.05%). The extraction time for USTPP was significantly reduced to 10min from 30 and 60min for TPP and USE methods, respectively. The primary chemical structures of PS collected through the three extraction protocols were basically conserved. The synergistic effects of ultrasound and TPP on PS extraction were also determined. Results revealed that USTPP is an effective technique to extract and separate PS from C. fluminea potentially applied in food, cosmetics, and medicines.

Lead accumulation (adsorption and absorption) by the freshwater bivalve Corbicula fluminea in sediments contaminated by TiO2 nanoparticles

With the increasing production and applications of TiO₂ nanoparticles (NPs), their presence in aquatic environments, especially in sediments, will inevitably increase over time. Most studies investigating the influence of TiO₂ NPs on the bioaccumulation of co-existing contaminants have focused on the aqueous phase; however, few have examined the sediment phase, which contains more TiO₂ NPs and contaminants. We investigated the effects of TiO₂ NPs on Pb accumulation by Corbicula fluminea in sediments, and explored extracellular and intracellular Pb concentrations in the various soft tissues of the bivalve. Pb was spiked with 50 mg/kg in sediment and TiO₂ NPs/sediments ratios were within the range 0.2-3.0%. The results showed that TiO₂ NPs presented larger adsorption capacity and affinity to Pb ions than the sediments. In addition, the large adsorption capacity of TiO₂ NPs and the strong adsorption affinity to Pb ions caused part of the Pb ions released from sediments to aqueous phase were re-adsorbed by TiO₂ NPs in sediments. The concentration of TiO₂ NPs in C. fluminea tissues significantly increased with increasing TiO₂ NP content in sediments, following the order: gill > mantle > foot > visceral mass, which differed from the results found in the aqueous phase. In addition, the proportions of extracellular and intracellular Pb concentrations changed significantly in all the tissues as a result of TiO₂ NP contamination of sediments. TiO₂ NPs promote increased extracellular Pb in foot, mantle, and gill tissues, and increased intracellular Pb in the visceral mass. These results may be beneficial to more scientifically evaluate and predict the environmental risks of TiO₂ NPs to benthic organisms in sediments contaminated by heavy metals.

Modulation of hepatic glutathione transferases isoenzymes in three bivalve species exposed to purified microcystin-LR and Microcystis extracts

This study compares the role of hepatic cytosolic glutathione transferases (cGST) isoforms of three different bivalve species to a Microcystis aeruginosa extract and purified MC-LR exposure (both at 150 μg MC-LR L^-1) for 24 h. Characterization and alterations of the cytosolic GST activities in Mytilus galloprovincialis, Ruditapes philippinarum and Corbicula fluminea were measured using four class-specific substrates and changes in individual GST isoforms expression were achieved by a subsequent two-dimensional electrophoresis analysis. Evaluation of cGST activity basal levels using the four class-specific substrates denoted quantitative differences between the three bivalves. Purified MC-LR did not induce any significant response from bivalves. On the other hand, cell extracts caused significant alterations according to bivalves and substrates. Among the three bivalves, only R. philippinarum showed a significant induction of cGST activity using generic 1-chloro-2,4-dinitrobenzene (CDNB) substrate. However, no significant alterations were detected in these clams by cell extracts using the other specific substrates. In contrast, C. fluminea revealed significant induction of cGST activity when using 3,4-dichloronitrobenzene (DCNB) and ethacrynic acid (EA). In M. galloprovincialis, cell extracts promoted a significant decrease of cGST activity when using EA substrate. Altered protein expression was quantitatively detected upon exposure to cell extracts for one spot in R. philippinarum and another for C. fluminea, both upregulated (2.0 and 8.5-fold, respectively) and identified as a sigma1-class GST in the case of the first. The results showed that the three bivalves presented specific adaptive biotransformation responses to MCs and other cyanobacteria compounds supported by the modulation of distinct cGST classes.

Genetic diversity analysis of Asian clam Corbicula fluminea in the Hongze Lake based on mitochondrial cytochrome b gene

The Asian clam Corbicula fluminea is a small bivalve with high nutritional and medical values. However, natural resources of C. fluminea have declined in many areas of China including the Hongze Lake. In this study, 119 individuals from 10 sites of this lake and 2 outgroups were analyzed using a 456 bp mitochondrial cytochrome b (cytb) gene segment. Totally, 19 polymorphic sites were detected, which defined 16 haplotypes. Polymorphism varied among the 10 populations with those at the water inlet being more polymorphic. Most F_ST values among these populations were below 0.15 with the overall value of 0.060 (p < .05), meanwhile, the overall gene flow was 7.67, both of which indicated the low level of population differentiation in this lake. Neutrality test and mismatch analyses indicated that population explosion may have occurred in this lake. The results obtained in this study will provide useful information for artificial breeding and resource protection of this species in the Hongze Lake.

Freshwater clam extract supplementation improves wound healing by decreasing the tumor necrosis factor α level in blood

BACKGROUND

The freshwater clam (Corbicula fluminea) is a widely consumed functional food in Asia and is traditionally used to improve health and either prevent or treat inflammation-related diseases. Numerous studies have proposed that freshwater clams act to prevent and attenuate inflammatory responses, and also serve as a possible inhibitor to systemic inflammation. However, there is limited information available about the effects of freshwater clams on wound healing.

RESULTS

The present study investigated the influence of freshwater clam extract (FCE) on wound healing and inflammatory responses in a cutaneous incision model. Sixteen rats were used and divided into two groups: the FCE group and the normal saline (NS) group. The rats underwent dorsal full-thickness skin excisional wounds (diameter 20 × 10 mm). FCE or NS was administered for oral feeding twice daily for 14 days after wounding. Blood samples were taken and analyzed, and wound areas were measured at several time points during the 2 weeks after excision. On day 14 after wounding, skin biopsies from the wound sites were sent for histological examination. Treatment with FCE (71.63 ± 9.51 pg mL^-1 ) decreased tumor necrosis factor-α levels compared to the NS group (109.86 ± 12.55 pg mL^-1 ) after wounding at 3 h (P < 0.05). There were no significant differences in the levels of white blood cells, interleukin (IL)-6, or IL-10. The wound areas of the NS group (23.9%) were larger than those in the FCE group (8.26%) on day 14 (P < 0.05). Numerous fibroblasts and collagen fiber organization were observed in the FCE group.

CONCLUSION

FCE supplementation improves the wound healing process. © 2016 Society of Chemical Industry.