Concentrations of heavy metals (Cu, Cd, Zn and Ni) and PAHs in Perna viridis collected from seaport and non-seaport waters in the Straits of Johore

A broad-taxa approach as an important concept in ecotoxicological studies and pollution monitoring

Aquatic invertebrates play a pivotal role in (eco)toxicological assessments because they offer ethical, cost-effective and repeatable testing options. Additionally, their significance in the food chain and their ability to represent diverse aquatic ecosystems make them valuable subjects for (eco)toxicological studies. To ensure consistency and comparability across studies, international (eco)toxicology guidelines have been used to establish standardised methods and protocols for data collection, analysis and interpretation. However, the current standardised protocols primarily focus on a limited number of aquatic invertebrate species, mainly from Arthropoda, Mollusca and Annelida. These protocols are suitable for basic toxicity screening, effectively assessing the immediate and severe effects of toxic substances on organisms. For more comprehensive and ecologically relevant assessments, particularly those addressing long-term effects and ecosystem-wide impacts, we recommended the use of a broader diversity of species, since the present choice of taxa exacerbates the limited scope of basic ecotoxicological studies. This review provides a comprehensive overview of (eco)toxicological studies, focusing on major aquatic invertebrate taxa and how they are used to assess the impact of chemicals in diverse aquatic environments. The present work supports the use of a broad-taxa approach in basic environmental assessments, as it better represents the natural populations inhabiting various ecosystems. Advances in omics and other biochemical and computational techniques make the broad-taxa approach more feasible, enabling mechanistic studies on non-model organisms. By combining these approaches with in vitro techniques together with the broad-taxa approach, researchers can gain insights into less-explored impacts of pollution, such as changes in population diversity, the development of tolerance and transgenerational inheritance of pollution responses, the impact on organism phenotypic plasticity, biological invasion outcomes, social behaviour changes, metabolome changes, regeneration phenomena, disease susceptibility and tissue pathologies. This review also emphasises the need for harmonised data-reporting standards and minimum annotation checklists to ensure that research results are findable, accessible, interoperable and reusable (FAIR), maximising the use and reusability of data. The ultimate goal is to encourage integrated and holistic problem-focused collaboration between diverse scientific disciplines, international standardisation organisations and decision-making bodies, with a focus on transdisciplinary knowledge co-production for the One-Health approach.

Biomonitoring of heavy metals accumulation in molluscs and echinoderms collected from southern coastal India

Distribution of five heavy metals (Cd, Cr, Cu, Pb, and Zn) in molluscan and echinoderm species collected from Kerala and Gulf of Mannar in Southern India is presented. Atomic absorption spectrometry was used to determine metal concentrations. Concentrations of metals showed a descending order of Zn > Cu > Pb > Cd > Cr. Zn and Cu might have originated from both natural and man-made sources. However, Cd, Cr, and Pb could have strong anthropogenic influences such as harbour activities and untreated industrial and agricultural runoff. Bioaccumulation factor (BAF) value of Cd in two edible bivalves from Munambam is slightly greater than one. Regular consumption of Cd-loaded shellfish can cause serious health hazards and concerns to humans. BAF results showed that Zn, Cu, Pb, and Cd were more bioaccumulated and beyond the threshold limits in certain species. It is evident that consumption of shellfish from the Kerala coastal waters may have adverse health impacts to the consumers.

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

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

Molecular cloning and expression analysis of mytilin-like antimicrobial peptides from Asian green mussel Perna viridis

Mytilin is one of the most important CS-αβ peptides involved in innate immune response in Mytilidae. In this study, we successfully identified four mytilin-like antimicrobial peptides (pernalins) from Asian green mussel Perna viridis by aligning the P. viridis transcriptome with 186 mytilins and myticins related sequences collected from the transcriptome data of six Mytilus species. Analysis on gene structure showed that pernalin genes had high conservation with mytilin B of Mediterranean mussel Mytilus galloprovincialis. Interestingly, all pernalin genes have a similar tissue expression feature, evidenced by the highest transcription level observed in the hemocytes and followed by the mantle. The lowest transcription level was observed in the foot and gills. qRT-PCR analysis showed that all pernalin genes were significantly down-regulated at each time points from 3 h to 48 h after Vibrio parahaemolyticus infection, suggesting their timely immune responses after bacterial infection.

Occurrence of heavy metals and their removal in Perna viridis mussels using chemical methods: a review

Despite the nutritional benefits, bivalves like mussels are also an excellent aquatic heavy metal biomonitoring agent due to their high tolerance to varying levels of temperature, salinity and oxygen, as well as pollutants. Although the accumulated toxic heavy metals may not exert direct negative impacts on the mussels, such toxicants in mussel tissues can give harmful effects on human body when consumed in toxic quantities and/or over prolonged period. The booming of urban and industrial activities, and consequently the increment of runoffs, as well as wastewater effluents and leaching, further exacerbated the magnitude of this issue. Hence, continuous monitoring of heavy metal contents in mussels is vital to ensure its compliance with food safety regulations, protecting consumers at large. This review paper discusses the occurrence of heavy metals in mussels especially that of Perna viridis in Malaysia and other parts of the world since year 2000 until 2021. Heavy metal concentration data and patterns from various coastal and/or estuaries were compared. Where applicable, statistical data that indicate variations between sampling sites, sampling months or years and chemical treatments for heavy metal removal were critically reviewed. Health risk assessment findings were also discussed. More importantly, related chemical-based interventions to minimize and/or eliminate toxic heavy metals from mussels are also reviewed.

Ecological-Health Risk Assessments of Heavy Metals (Cu, Pb, and Zn) in Aquatic Sediments from the ASEAN-5 Emerging Developing Countries: A Review and Synthesis

The ASEAN-5 countries (Malaysia, Indonesia, Thailand, Philippines, and Vietnam) of the Association of Southeast Asian Nations as a group is an ever-increasing major economy developmental hub in Asia besides having wealthy natural resources. However, heavy metal (HM) pollution in the region is of increasing environmental and public concern. This study aimed to review and compile the concentrations of Cu, Pb, and Zn in the aquatic sediments of the ASEAN-5 countries published in the literature from 1981 to February 2021. The mean values of Cu, Pb, and Zn in aquatic sediments were elevated and localized in high human activity sites and compared to the earth's upper continental crust and reference values. Based on 176 reports from 113 publications, the ranges of concentrations (mg/kg dry weight) were 0.09-3080 for Cu, 0.37-4950 for Zn, and 0.07-2666 for Pb. The ecological risk (ER) values ranged from 0.02-1077 for Cu, 0.01-95.2 for Zn, and 0.02-784 for Pb. All reports (100%) showed the Zn ER values were categorized as being between 'low potential ecological risk' and 'considerable potential ecological risk'. Almost all Cu ER values (97.7%) also showed similar ranges of the above two risk categories except for a few reports. The highest Cu level (3080 mg/kg dry weight) was reported from a mine-tailing spill in Marinduque Island of the Philippines with 'very high ecological risk'. In addition, drainage sediments in the western part of Peninsular Malaysia were categorized as Cu 'high potential ecological risk'. Almost all reports (96%) showed Pb ER values categorized as between 'low potential ecological risk' and 'moderate potential ecological risk' except for a few reports. Six reports showed Pb ER values of 'considerable potential ecological risk', while one report from Semarang (Indonesia) showed Pb ER of 'very high ecological risk' (Pb level of 2666 mg/kg dry weight). For the ingestion and dermal contact pathways for sediments from the ASEAN-5 countries, all non-carcinogenic risk (NCR) values (HI values 1.0) for Cu, Pb, and Zn reflected no NCR. The ER and human health risk assessment of Cu, Pb, and Zn were compared in an integrative and accurate manner after we reassessed the HM data mentioned in the literature. The synthesis carried out in this review provided the basis for us to consider Cu, Pb, and Zn as being of localized elevated levels. This provided evidence for the ASEAN-5 group of countries to be considered as being a new socio-economic corridor. Beyond any reasonable doubt, an ever-increasing anthropogenic input of HMs is to be expected to a certain degree. We believe that this paper provides the most fundamental useful baseline data for the future management and sustainable development of the aquatic ecosystems in the region. Lastly, we claim that this review is currently the most up-to-date review on this topic in the literature.

Small RNA analysis of Perna viridis after exposure to Prorocentrum lima, a DSP toxins-producing dinoflagellate

Diarrheic shellfish poisoning toxins (DSP toxins) are a set of the most important phycotoxins produced by some dinoflagellates. Studies have shown that DSP toxins have various toxicities such as genotoxicity, cytotoxicity, and immunotoxicity to bivalve mollusks. However, these toxicities appear decreasing with exposure time and concentration of DSP toxins. The underlying mechanism involved remains unclear. In this study, small RNA sequencing was performed in the digestive gland of the mussel Perna viridis after exposure to DSP toxins-producing dinoflagellate Prorocentrum lima for different time periods. The potential roles of miRNAs in response and detoxification to DSP toxins in the mussel were analyzed. Small RNA sequencing of 12 samples from 72 individuals was conducted by BGISEQ-500. A total of 123 mature miRNAs were identified, including 90 conserved miRNAs and 33 potential novel miRNAs. After exposure to P. lima, multiple important miRNAs displayed some alterations. Further miRNA target prediction revealed some important genes involved in cytoskeleton, apoptosis, complement system and immune stress. qPCR demonstrated that miR-71_5, miR-750_1 and novel_mir4 were significantly up-regulated at 6 h after exposure to P. lima, while miR-100_2 was significantly down-regulated after 96 h of exposure. Accordingly, putative target genes of these differentially expressed miRNAs experienced some changes. After 6 h of DSP toxins exposure, NHLRC2 and C1q-like were significantly down-regulated. After 96 h of DSP toxins exposure, NHLRC2 was significantly up-regulated. It is reasonable to speculate that the mussel P. viridis might respond to DSP toxins through miR-750_1, novel_mir4 and miR-71_5 regulating the expression of relevant target genes involved in apoptosis, cytoskeleton, and immune response, etc. This study might provide new clues to uncover the toxic response of bivalve to DSP toxins and lay a foundation for revealing the roles of miRNAs in the environmental adaptation in shellfish.

Cinnamaldehyde Could Reduce the Accumulation of Diarrhetic Shellfish Toxins in the Digestive Gland of the Mussel Perna viridis under Laboratory Conditions

Diarrhetic shellfish toxins (DSTs), some of the most important phycotoxins, are distributed almost all over the world, posing a great threat to human health through the food chain. Therefore, it is of great significance to find effective methods to reduce toxin accumulation in shellfish. In this paper, we observed the effects of four phytochemicals including cinnamaldehyde (CA), quercetin, oridonin and allicin on the accumulation of DSTs in the digestive gland of Perna viridis after exposure to the DSTs-producing Prorocentrum lima. We found that, among the four phytochemicals, CA could effectively decrease the accumulation of DSTs (okadaic acid-eq) in the digestive gland of P. viridis. Further evidence demonstrated that CA could reduce the histological alterations of the digestive gland of a mussel caused by DSTs. RT-qPCR showed that CA could suppress the CYP3A4 induction by DSTs, suggesting that the DSTs’ decrease induced by CA might be related to the inhibition of CYP3A4 transcription induction. However, further studies on the underlying mechanism, optimal treatment time, ecological safety and cost should be addressed before cinnamaldehyde is used to decrease the accumulation of DSTs in field.

De novo transcriptome analysis of the mussel Perna viridis after exposure to the toxic dinoflagellate Prorocentrum lima

Diarrheic shellfish poisoning (DSP) toxins are produced by harmful microalgae and accumulate in bivalve mollusks, causing various toxicity. These toxic effects appear to abate with increasing DSP concentration and longer exposure time, however, the underlying mechanisms remain unclear. To explore the underlying molecular mechanisms, de novo transcriptome analysis of the digestive gland of Perna viridis was performed after Prorocentrum lima exposure. RNA-seq analysis showed that 1886 and 237 genes were up- and down-regulated, respectively after 6 h exposure to P. lima, while 265 genes were up-regulated and 217 genes were down-regulated after 96 h compared to the control. These differentially expressed genes mainly involved in Nrf2 signing pathways, immune stress, apoptosis and cytoskeleton, etc. Combined with qPCR results, we speculated that the mussel P. viridis might mainly rely on glutathione S-transferase (GST) and ABC transporters to counteract DSP toxins during short-term exposure. However, longer exposure of P. lima could activate the Nrf2 signaling pathway and inhibitors of apoptosis protein (IAP), which in turn reduced the damage of DSP toxins to the mussel. DSP toxins could induce cytoskeleton destabilization and had some negative impact on the immune system of bivalves. Collectively, our findings uncovered the crucial molecular mechanisms and the regulatory metabolic nodes that underpin the defense mechanism of bivalves against DSP toxins and also advanced our current understanding of bivalve defense mechanisms.

Integrated assessment of heavy metal pollution using transplanted mussels in eastern Guangdong, China

Heavy metal contamination has been widely studied in coastal areas around the world. However, integrative studies of heavy metals pollution by monitoring and characterizing sediments, organisms, and biomarkers as well as their holistic interactions are rare. Here, we selected a developed coastal area in eastern Guangdong, China as the study field. Heavy metal analysis (both in sediment and mussel) and biomarker tests, including neutral red retention time test (NRRT) and micronuclei (MN) test, were employed in the current research. Anthropogenic activities influenced the heavy metal levels in sediments. Significant relationships (p < 0.05) were observed in the concentrations of Cd, Cu, and Zn between sediments and transplanted mussel, and significant relationships (p < 0.05) were also observed in between the concentrations of Cd, Cu, and Zn in sediments and the NRRT of mussel. The potential ecological risk index (RI) of sediments significantly correlated with NRRT (R = -0.991, p < 0.05). In Hao River, where the highest RI of sediments was found, the highest MN frequency and the lowest NRRT in mussels were detected simultaneously. The results indicated that the heavy metal pollution might cause subcellular toxic and genotoxic effects on mussels, especially for those from polluted areas (i.e., Hao River). The present study suggests that the transplanted green-lipped mussels are suitable for assessing heavy metal pollution, especially for Cd, Cu, and Zn.

The potential accumulation of polycyclic aromatic hydrocarbons in phytoplankton and bivalves in Can Gio coastal wetland, Vietnam

Polycyclic aromatic hydrocarbons (PAHs) are one of the most important classes of anthropogenic persistent organic contaminants in the marine environment. This review discusses a whole range of findings that address various aspects of the bioaccumulation of PAHs in two common marine biota (phytoplankton and bivalves) globally and especially for Can Gio coastal wetland, Vietnam. The published information and collected data on the bioconcentration and accumulation mechanisms of PAHs as well as implications for Can Gio coastal wetland are compiled for phytoplankton and bivalves. PAHs are still released to Can Gio coastal environments from various sources and then transported to coastal environments through various physical processes; they may enter marine food chains and be highly accumulated in phytoplankton and bivalves. Thus, PAHs' bioaccumulation should be considered as one important criterion to assess the water's quality, directly linked to human health due to seafood consumption. Ecologically, Can Gio coastal wetland plays an important role to the South Vietnam key economic zone. However, it is also an area of potential PAHs inputs. With the abundant phytoplankton and bivalves in Can Gio coastal wetland, the PAHs bioaccumulation in these biota is inevitably detected. Thus, further study on the bioavailability of these contaminants is urgently needed in order to mitigate their negative effects and protect the ecosystems.

Polycyclic aromatic hydrocarbons and heavy metals in the Cispata Bay, Colombia: A marine tropical ecosystem

The concentrations of polycyclic aromatic hydrocarbons and heavy metals were evaluated in shallow sediments, water, fish and seabird samples from the Cispata Bay, Colombia. The heavy metals concentrations in the sediment was in the following order: Cu>Pb>Hg>Cd. The heavy metal concentration was different (p<0.05) in juvenile and adult birds. High concentrations of mercury were registered in the seabird (10.19±4.99mgkg^-1) and fish (0.67μgg^-1) samples. The total concentration of polycyclic aromatic hydrocarbons ranged from 7.0-41ngg^-1 in sediment, 0.03-0.34ngmL^-1 in water samples, 53.24ngg^-1 in fish, and 66ngg^-1 in seabirds. The high concentrations of heavy metals in seabirds may be explained by their feeding habits. The presence of polycyclic aromatic hydrocarbons in the Cispata Bay may be due to hydrocarbon spills during oil transport at the nearby oil port.

De novo transcriptome analysis of Perna viridis highlights tissue-specific patterns for environmental studies

BACKGROUND

The tropical green-lipped mussel Perna viridis is a common biomonitor throughout the Indo-Pacific region that is used for environmental monitoring and ecotoxicological investigations. However, there is limited molecular data available regarding this species. We sought to establish a global transcriptome database from the tissues of adductor muscle, gills and the hepatopancreas of P. viridis in an effort to advance our understanding of the molecular aspects involved during specific toxicity responses in this sentinel species.

RESULTS

Illumina sequencing results yielded 544,272,542 high-quality filtered reads. After de novo assembly using Trinity, 233,257 contigs were generated with an average length of 1,264 bp and an N50 length of 2,868 bp; 192,879 assembled transcripts and 150,111 assembled unigenes were obtained after clustering. A total of 93,668 assembled transcripts (66,692 assembled genes) with putative functions for protein domains were predicted based on InterProScan analysis. Based on similarity searches, 44,713 assembled transcripts and 25,319 assembled unigenes were annotated with at least one BLAST hit. A total of 21,262 assembled transcripts (11,947 assembled genes) were annotated with at least one well-defined Gene Ontology (GO) and 5,131 assembled transcripts (3,181 assembled unigenes) were assigned to 329 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The quantity of assembled unigenes and transcripts obtained from male and female mussels were similar but varied among the three studied tissues, with the highest numbers recorded in the gills, followed by the hepatopancreas, and then the adductor muscle. Multivariate analyses revealed strong tissue-specific patterns among the three different tissues, but not between sexes in terms of expression profiles for annotated genes in various GO terms, and genes associated with stress responses and degradation of xenobiotics. The expression profiles of certain selected genes in each tissue type were further validated using real-time quantitative polymerase chain reaction assays and a similar tissue-specific trend was seen.

CONCLUSIONS

The extensive sequence data generated from this study will provide a valuable molecular resource for facilitating environmental studies with P. viridis, and highlight the importance of tissue-specific approaches in the future.

Heavy metals in bivalve mollusks collected from Da-Peng Bay Lagoon in south-southwestern Taiwan

In this study, concentrations of several heavy metals (Cu, Pb, Zn, Ni, Cr, and Cd) were measured in Katelysia hiantina, Anomalocardia squamosa, Perna viridis, Anadara antiquata, Paphia undulata, and Sanguinolaria diphos bivalve mollusks from Da-Peng Bay Lagoon near the south-southwestern coast of Taiwan. The metal pollution index (MPI) values were highest and lowest in winter and autumn, respectively. The MPI value in the viscera of P. viridis was higher than in muscles. In all four seasons, Zn concentrations in viscera and muscles of P. viridis were higher than for other metals. The capacities of A. squamosa to accumulate the concentrations of Cu, Ni, and Cr and of A. antiquata to accumulate concentrations of Pb, Zn, and Cd were significant. Analytical results suggested that A. squamosa and A. antiquata may be used as bioindicators for monitoring Cu, Ni, Cr, Pb, Zn, and Cd heavy-metal pollution in Da-Peng Bay Lagoon throughout the year.