First detection of tetrodotoxin and high levels of paralytic shellfish poisoning toxins in shellfish from Sicily (Italy) by three different analytical methods

Sudden peak in tetrodotoxin in French oysters during the summer of 2021: Source investigation using microscopy, metabarcoding and droplet digital PCR

Tetrodotoxin (TTX) is a potent neurotoxin causing human intoxications from contaminated seafood worldwide and is of emerging concern in Europe. Shellfish have been shown to contain varying TTX concentrations globally, with concentrations typically higher in Pacific oysters Crassostrea gigas in Europe. Despite many decades of research, the source of TTX remains unknown, with bacterial or algal origins having been suggested. The aim of this study was to identify potential source organisms causing TTX contamination in Pacific oysters in French coastal waters, using three different techniques. Oysters were deployed in cages from April to September 2021 in an estuary where TTX was previously detected. Microscopic analyses of water samples were used to investigate potential microalgal blooms present prior or during the peak in TTX. Differences in the bacterial communities from oyster digestive glands (DG) and remaining flesh were explored using metabarcoding, and lastly, droplet digital PCR assays were developed to investigate the presence of Cephalothrix sp., one European TTX-bearing species in the DG of toxic C. gigas. Oysters analysed by liquid chromatography-tandem mass spectrometry contained quantifiable levels of TTX over a three-week period (24 June-15 July 2021), with concentrations decreasing in the DG from 424 μg/kg for the first detection to 101 μg/kg (equivalent to 74 to 17 μg/kg of total flesh), and trace levels being detected until August 13, 2021. These concentrations are the first report of the European TTX guidance levels being exceeded in French shellfish. Microscopy revealed that some microalgae bloomed during the TTX peak, (e.g., Chaetoceros spp., reaching 40,000 cells/L). Prokaryotic metabarcoding showed increases in abundance of Rubritaleaceae (genus Persicirhabdus) and Neolyngbya, before and during the TTX peak. Both phyla have previously been described as possible TTX-producers and should be investigated further. Droplet digital PCR analyses were negative for the targeted TTX-bearing genus Cephalothrix.

Analysis of the original notifications in the Tuscany region "Rapid Alert System for Food and Feed" in the seven-year period 2015-2021

The original notifications (n=1355) managed by the Rapid Alert System for Food and Feed of the Tuscany region in the seven-year period 2015-2021 were analyzed. 68.9% of them were classified as alert notifications, and they mostly originated (56.3%) from official controls on the market, followed by the company's own checks (29.1%). Italy was the most represented notifying country (73.3%) and the most represented country of origin of the notified products (64.5%). Out of the 28 considered food categories, "fish and products thereof" (F), "cereals and bakery products" (C), "bivalve mollusks and products thereof" (B), and "meat and meat products (other than poultry)" (M) were the most notified. F were especially notified for the presence of heavy metals (45.7%), C for undeclared allergens (32.1%), B for microbial contaminants (Escherichia coli, 49.6%), and M for pathogenic microorganisms (55.9%), mostly Salmonella spp. and Listeria monocytogenes. This study provides an updated framework for the main food safety issues at the regional level. The Rapid Alert System for Food and Feed should be periodically analyzed to evaluate historical trends and emerging or poorly known hazards. This is especially important for the planning of official control activities and the prevention of risks through the food supply chain.

Advances in Biosensors for the Rapid Detection of Marine Biotoxins: Current Status and Future Perspectives

Marine biotoxins (MBs), harmful metabolites of marine organisms, pose a significant threat to marine ecosystems and human health due to their diverse composition and widespread occurrence. Consequently, rapid and efficient detection technology is crucial for maintaining marine ecosystem and human health. In recent years, rapid detection technology has garnered considerable attention for its pivotal role in identifying MBs, with advancements in sensitivity, specificity, and accuracy. These technologies offer attributes such as speed, high throughput, and automation, thereby meeting detection requirements across various scenarios. This review provides an overview of the classification and risks associated with MBs. It briefly outlines the current research status of marine biotoxin biosensors and introduces the fundamental principles, advantages, and limitations of optical, electrochemical, and piezoelectric biosensors. Additionally, the review explores the current applications in the detection of MBs and presents forward-looking perspectives on their development, which aims to be a comprehensive resource for the design and implementation of tailored biosensors for effective MB detection.

Marine phycotoxin levels in shellfish-14 years of data gathered along the Italian coast

Along the Italian coasts, toxins of algal origin in wild and cultivated shellfish have been reported since the 1970s. In this study, we used data gathered by the Veterinary Public Health Institutes (IZS) and the Italian Environmental Health Protection Agencies (ARPA) from 2006 to 2019 to investigate toxicity events along the Italian coasts and relate them to the distribution of potentially toxic species. Among the detected toxins (OA and analogs, YTXs, PTXs, STXs, DAs, AZAs), OA and YTX were those most frequently reported. Levels exceeding regulatory limits in the case of OA (≤2,448 μg equivalent kg-1) were associated with high abundances of Dinophysis spp., and in the case of YTXs (≤22 mg equivalent kg-1) with blooms of Gonyaulax spinifera, Lingulodinium polyedra, and Protoceratium reticulatum. Seasonal blooms of Pseudo-nitzschia spp. occur all along the Italian coast, but DA has only occasionally been detected in shellfish at concentrations always below the regulatory limit (≤18 mg kg-1). Alexandrium spp. were recorded in several areas, although STXs (≤13,782 µg equivalent kg-1) rarely and only in few sites exceeded the regulatory limit in shellfish. Azadinium spp. have been sporadically recorded, and AZAs have been sometimes detected but always in low concentrations (≤7 µg equivalent kg-1). Among the emerging toxins, PLTX-like toxins (≤971 μg kg-1 OVTX-a) have often been detected mainly in wild mussels and sea urchins from rocky shores due to the presence of Ostreopsis cf. ovata. Overall, Italian coastal waters harbour a high number of potentially toxic species, with a few HAB hotspots mainly related to DSP toxins. Nevertheless, rare cases of intoxications have occurred so far, reflecting the whole Mediterranean Sea conditions.

NIR-responsive photoelectrochemical sensing platform for the simultaneous determination of tetrodotoxin and okadaic acid in Nassariidae

Simultaneous detection of tetrodotoxin (TTX) and okadaic acid (OA) is important for seafood safety. In this work, a novel paper electrode-based near-infrared (NIR) light-responsive photoelectrochemical (PEC) immunosensor was constructed using Ag2S quantum dots (QDs) and NaYF4: Yb, Er upconversion nanoparticles (UCNPs) matched with BiOI for the simultaneous detection of TTX and OA in aquatic products. A low-cost, easily prepared gold nanoparticle-functionalized paper-based screen-printed electrode with six channels was designed to immobilize OA and Ab1 of TTX. Correspondingly, PEC signal immunoprobes (BiOI@UCNPs-Ab and Ab2-Ag2S QDs) with NIR-light response were introduced to construct competitive-type and sandwich-type PEC immunosensors for OA and TTX, respectively. Under optimal conditions, the linear ranges for TTX and OA were 0.001-100 and 0.001-80 ng mL-1, respectively, and the detection limits were 5 and 7 pg mL-1, respectively. The proposed sensor was successfully used for the simultaneous analysis of TTX and OA in Nassariidae samples.

Tetrodotoxin in bivalve mollusks: An integrated study towards the comprehension of the influencing factors of a newly native phenomenon

Tetrodotoxins (TTXs) are potent neurotoxins named after the Tetraodontidae fish family. The ingestion of TTX-contaminated flesh can cause neurotoxic symptoms and can lead to death. In 2017 symptoms the European Food Safety Authority (EFSA) recognized the threat to food safety resulting from TTX exposure via food consumption and, thus, proposed a safety limit of 44 μg/kg of TTX in marine gastropods and bivalves. To date, however, TTXs have not yet been included in the list of biotoxins to be monitored within the European Union, even though, in a few cases, levels of TTX found were higher than the EFSA limit. The origin of TTX production is debated and the roles of both biotic and abiotic factors on TTX-mediated toxic events remain unclear. In order to meet these knowledge requests the present study was aimed to investigate the role of seawater temperature, pH, water conductivity, and oxygen saturation, along with the marine phytoplankton community and the bacterial community of mussels and oysters on the accumulation of TTX and analogues in the bivalves. Abiotic parameters were measured by means of a multi-parametric probe, phytoplankton community was analyzed by optic microscopy while microbial community was described by amplicon metataxonomic sequencing, TTXs concentration in the collected matrices were measured by HILIC-MS/MS. A possible role of seawater pH and temperature, among the investigated abiotic factors, in regulating the occurrence of TTXs was found. Regarding biotic variables, a possible influence of Vibrio, Shewanella and Flavobacteriaceae in the occurrence of TTXs was found. Concurrently, Prorocentrum cordatum cell numbers were correlated to the incidence of TTX in mussels. The results herein collected suggest that environmental variables play a consistent part in the occurrence of TTX in the edible bivalve habitats, and there are also indications of a potential role played by specific bacteria taxa in association with phytoplankton.

Assessing the Toxicity of Lagocephalus sceleratus Pufferfish from the Southeastern Aegean Sea and the Relationship of Tetrodotoxin with Gonadal Hormones

Given the dramatic increase in the L. sceleratus population in the southeastern Aegean Sea, there is growing interest in assessing the toxicity of this pufferfish and the factors controlling its tetrodotoxin (TTX) content. In the present study, liver, gonads, muscle and skin of 37 L. sceleratus specimens collected during May and June 2021 from the island of Rhodes, Greece, were subjected to multi-analyte profiling using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in order to quantitate TTX and evaluate whether this biotoxin interrelates with hormones. TTX and its analogues 4-epiTTX, 11-deoxyTTX, 11-norTTX-6-ol, 4,9-anhydroTTX and 5,11/6,11-dideoxyTTX were detected in all tissue types. Liver and gonads were the most toxic tissues, with the highest TTX concentrations being observed in the ovaries of female specimens. Only 22% of the analyzed muscle samples were non-toxic according to the Japanese toxicity threshold (2.2 μg TTX eq g-1), confirming the high poisoning risk from the inadvertent consumption of this species. Four steroid hormones (i.e., cortisol, testosterone, androstenedione and β-estradiol) and the gonadotropin-releasing hormone (GnRH) were detected in the gonads. Androstenedione dominated in female specimens, while GnRH was more abundant in males. A positive correlation of TTX and its analogues with β-estradiol was observed. However, a model incorporating sex rather than β-estradiol as the independent variable proven to be more efficient in predicting TTX concentration, implying that other sex-related characteristics are more important than specific hormone-regulated processes.

Evaluation of Toxicity Equivalency Factors of Tetrodotoxin Analogues with a Neuro-2a Cell-Based Assay and Application to Puffer Fish from Greece

Tetrodotoxin (TTX) is a potent marine neurotoxin involved in poisoning cases, especially through the consumption of puffer fish. Knowledge of the toxicity equivalency factors (TEFs) of TTX analogues is crucial in monitoring programs to estimate the toxicity of samples analyzed with instrumental analysis methods. In this work, TTX analogues were isolated from the liver of a Lagocephalus sceleratus individual caught on South Crete coasts. A cell-based assay (CBA) for TTXs was optimized and applied to the establishment of the TEFs of 5,11-dideoxyTTX, 11-norTTX-6(S)-ol, 11-deoxyTTX and 5,6,11-trideoxyTTX. Results showed that all TTX analogues were less toxic than the parent TTX, their TEFs being in the range of 0.75-0.011. Then, different tissues of three Lagocephalus sceleratus individuals were analyzed with CBA and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The obtained TEFs were applied to the TTX analogues' concentrations obtained by LC-MS/MS analysis, providing an indication of the overall toxicity of the sample. Information about the TEFs of TTX analogues is valuable for food safety control, allowing the estimation of the risk of fish products to consumers.

First Toxicological Analysis of the Pufferfish Sphoeroides pachygaster Collected in Italian Waters (Strait of Sicily): Role of Citizens Science in Monitoring Toxic Marine Species

Pufferfish (Tetraodontidae) inhabiting the Mediterranean Sea may represent an emerging public health risk due to the possible accumulation of marine neurotoxins such as tetrodotoxin (TTXs) and saxitoxin (STXs) in their tissues. In this study, the presence of pufferfish species in the Strait of Sicily (Lampedusa Island, Italy) was investigated using a citizen science (CS) approach, involving local fishermen. Samples (liver, intestine, gonads, muscle, skin) from 20 specimens were sent to the National Reference Laboratory on Marine Biotoxins for TTXs detection using a validated HILIC-MS/MS method on fish tissue. The presence of STXs was also screened in part of the specimens. Overall, 56 specimens identified as Sphoeroides pachygaster (Müller &Troschel, 1848) were collected. Data on their total length, body weight, fishing method and catch area (with relative depth temperature and salinity) were analyzed and compared with the S. pachygaster records reported in literature which were updated to 2022. All the analysed tissues were found to be negative for both TTXs and STXs. CS played an essential role in monitoring potentially toxic marine species in this investigation. Outcomes from this study, which is the first investigating S. pachygaster toxicity in Italian waters, may provide useful data for the proper assessment of this emerging risk.

Shellfish sanitation monitoring in La Spezia gulf: Chemometric evaluation of data from 2015 to 2021

Shellfish sanitary controls are very important to guarantee consumer health because bivalve molluscs (BVM) are filter-feeders so they can accumulate pathogens, environmental contaminants and biotoxins produced by some algae, causing infections and food poisoning in humans after ingestion. The purpose of this work was to analyse with chemometric methods the historical data relating to routine analyses carried out by the competent authority (Liguria Local Health Unit, National Health Service) on the BVM reared in a shellfish farm located in the Gulf of La Spezia (Italy). Chemometric analysis was aimed at identifying any correlations between the variables, as well as any seasonal trends and similarities between the stations, in order to be able to provide further material for a more accurate risk assessment and to improve the monitoring organization for example by reducing sampling stations and/or sampling frequency. The dataset used included 31 variables classified as biotoxicological, microbiological and chemical variables, measured twice a week, monthly or half yearly respectively, for a total of 6 years (from 2015 to 2021), on samples of Mytilus galloprovincialis coming from 7 monitoring stations. The results obtained by the application of principal component analysis have shown positive alga-biotoxin correlations, as well as seasonal trends linked to algae growth, with a greater algal biomass and their toxins during the spring months. In addition, periods characterised by low rainfall were found to affect algal development, promoting especially species such as Dinophysis spp. Considering the microbiological and biotoxicological variables, significant differences between the monitoring stations were not found. However, stations could be distinguished on the basis of the nature of the predominant chemical pollutants.

Detection of Ciguatoxins and Tetrodotoxins in Seafood with Biosensors and Other Smart Bioanalytical Systems

The emergence of marine toxins such as ciguatoxins (CTXs) and tetrodotoxins (TTXs) in non-endemic regions may pose a serious food safety threat and public health concern if proper control measures are not applied. This article provides an overview of the main biorecognition molecules used for the detection of CTXs and TTXs and the different assay configurations and transduction strategies explored in the development of biosensors and other biotechnological tools for these marine toxins. The advantages and limitations of the systems based on cells, receptors, antibodies, and aptamers are described, and new challenges in marine toxin detection are identified. The validation of these smart bioanalytical systems through analysis of samples and comparison with other techniques is also rationally discussed. These tools have already been demonstrated to be useful in the detection and quantification of CTXs and TTXs, and are, therefore, highly promising for their implementation in research activities and monitoring programs.

Detection, occurrence, influencing factors and environmental risks of paralytic shellfish toxins in seawater in a typical mariculture bay

Paralytic shellfish toxins (PSTs) producing algae are widely distributed in the global coastal aquatic environment, posing a threat to coastal ecosystem health and mariculture safety. However, the levels and potential environmental risks of PSTs frequently detected in shellfish remain largely unexplored in seawater of mariculture zones. In this study, a new method for trace detection of 13 common PSTs (<1.0 ng/L) in seawater was established based on off-line solid phase extraction (SPE) and on-line SPE-liquid chromatography-tandem mass spectrometry (on-line SPE-LC-MS/MS), and a systematic investigation of PSTs in seawater of the Laizhou Bay, a typical aquaculture bay in China, was conducted to understand their pollution status, environmental impact factors and ecological risks for the first time. Eleven PSTs were detected in the seawater of Laizhou Bay with total concentrations ranging from 0.75 to 349.47 ng/L (mean, 176.27 ng/L), which indicates the rich diversity of PSTs in the mariculture bay and demonstrates the reliability of the proposed analytical method. C1, C2, GTX2, GTX3, dcGTX2, and dcGTX3 were found to be the predominant PSTs, which refreshed the knowledge of PST contamination in the coastal aquatic environment. PST levels in seawater exhibited the highest levels in the southeastern mouth of Laizhou Bay and decreased toward the inner bay. Correlation analyses showed that climatic factors, nutrient status and hydrological conditions had significant effects on the distribution of PST in mariculture bay. Preliminary environmental risk assessments revealed that aquatic organisms throughout the waters of Laizhou Bay are at risk of chronic PST toxicity. These findings imply that the risk of PST in seawater of mariculture bay has previously been grossly underestimated, and that the coastal aquatic environment in North China and even the world may be at more serious risk of PST pollution, which should be taken seriously.

Solvent-driven biotoxin into nano-units as a versatile and sensitive SERS strategy

In recent years, marine biotoxins have posed a great threat to fishermen, human security and military prevention and control due to their diverse, complex, toxic and widespread nature, and the development of rapid and sensitive methods is essential. Surface-enhanced Raman spectroscopy (SERS) is a promising technique for the rapid and sensitive in situ detection of marine biotoxins due to its advantages of rapid, high sensitivity, and fingerprinting information. However, the complex structure of toxin molecules, small Raman scattering cross-section and low affinity to conventional substrates make it difficult to achieve direct and sensitive SERS detection. Here, we generate a large number of active hotspot structures by constructing monolayer nanoparticle films with high density hotspots, which have good target molecules that can actively access the hotspot structures using nanocapillaries. In addition, the efficient and stable signal can be achieved during dynamic detection, increasing the practicality and operability of the method. This versatile SERS method achieves highly sensitive detection of marine biotoxins GTX and NOD, providing good prospects for convenient, rapid and sensitive SERS detection of marine biotoxins.

A Hotspot of TTX Contamination in the Adriatic Sea: Study on the Origin and Causative Factors

Tetrodotoxins (TTXs), the pufferfish venom traditionally associated with Indo-Pacific area, has been reported during last decades in ever wider range of marine organisms and ever more geographical areas, including shellfish in Europe. Wild mussels (Mytilus galloprovincialis) grown in the Marche Region (N Adriatic Sea, Italy) were shown to be prone to TTX contamination during the warm season, with a suspected role of Vibrio alginolyticus characterized by non-ribosomal peptide synthetase (NRPS) and polyketide synthase (PKS)-encoding genes. This work aimed to deepen the knowledge about the toxin's origin and the way through which it accumulates in mussels. A two-year study (spring-summer 2020-2021) confirmed the recurrent presence of TTX (11-68 µg kg^-1) in the official monitored natural mussel beds of the Conero Riviera. During 2021, a supplementary nonroutine monitoring of a natural mussel bed in the same area was carried out weekly from June until August for TTXs and/or the presence of V. alginolyticus. Biotic (mussels, mesozooplankton, worms and phytoplankton); abiotic (water and sediment) matrices and phytoplankton assemblage characterizations were studied. Mussels showed relevant TTX contamination levels (9-296 µg kg^-1) with extremely rapid TTX accumulation/depletion rates. The toxin presence in phytoplankton and its distribution in the different mussel tissues supports its possible exogenous origin. The V. alginolyticus count trend overlaps that of TTX contamination in mussels, and similar trends were reported also for some phytoplankton species. The role of V. alginolyticus carrying NRPS or PKS genes as a possible TTX source and of phytoplankton as a "potential vector" should therefore be further investigated.

Trace determination of multiple hydrophilic cyanotoxins in freshwater by off- and on-line solid phase extraction coupled to liquid chromatography-tandem mass spectrometry

Hydrophilic cyanotoxins (HCTs), such as paralytic shellfish toxins (PSTs), anatoxin-a (ATX-a), and cylindrospermopsin (CYN) are highly toxic and toxin-producing algae are widely distributed worldwide. However, HCTs, especially PSTs, are rarely reported in freshwater due to analytical limitations. This may result in an underestimation of the ecological risks and health risks. This study developed a new method to detect ATX-a, CYN, and thirteen common PSTs in freshwater simultaneously by using off-line solid phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The limits of detection (LODs) of all targets were lower than 0.05 μg/L, which could meet the regulatory requirements for monitoring of HCTs in drinking water in different countries and regions. To improve the detection sensitivities for trace PSTs, a method based on off-line SPE and on-line SPE-LC-MS/MS was established with LOD around 0.001 μg/L. GTX1&4, GTX2&3, and GTX5 were detected in freshwater in China for the first time, highlighting that overall communities are facing potential risks of exposure to various PSTs in China. High concentrations of ATX-a and CYN were also detected in freshwater from Northern China. The proposed method helps to understand the pollution status of HCT in water bodies, especially during the non-algal bloom period.

New insights into the dynamics of causative dinoflagellates and the related contamination of molluscs by paralytic toxins in the southwestern Mediterranean coastal waters of Morocco

The distribution of the two potentially toxic dinoflagellates Gymnodinium catenatum and Alexandrium spp. was investigated in the Mediterranean Moroccan Sea from March 2018 to March 2019. The cockle Acanthocardia tuberculata and the smooth clam Callista chione were collected at four stations, and their toxin levels were assessed using the mouse bioassay. The toxin profile was analysed by LC-MS/MS in G. catenatum and in the bivalves harvested in M'diq and Djawn. The species G. catenatum was present throughout the year, whereas Alexandrium spp. was less abundant. The paralytic shellfish toxin (PST) level in cockles was, on average, six times above the sanitary threshold; GTX5 was the major contributor to the total PST level, followed by dc-STX and STX. The toxin level of the smooth clam was considerably lower than that of the cockle; GTX5 and C-toxins were the dominating analogues. Our results suggest the responsibility of G. catenatum for the recurrent PST contamination in the Moroccan Mediterranean Sea, with a west-east gradient.

Tetrodotoxin and Its Analogues in Food: Recent Updates on Sample Preparation and Analytical Methods Since 2012

Tetrodotoxin (TTX), found in various organisms including pufferfish, is an extremely potent marine toxin responsible for numerous food poisoning accidents. Due to its serious toxicity and public health threat, detecting TTX and its analogues in diverse food matrices with a simple, fast, efficient method has become a worldwide concern. This review summarizes the advances in sample preparation and analytical methods for the determination of TTX and its analogues, focusing on the latest development over the past five years. Current state-of-the-art technologies, such as solid-phase microextraction, online technology, novel injection technology, two-dimensional liquid chromatography, high-resolution mass spectrometry, newly developed lateral flow immunochromatographic strips, immunosensors, dual-mode aptasensors, and nanomaterials-based approaches, are thoroughly discussed. The advantages and limitations of different techniques, critical comments, and future perspectives are also proposed. This review is expected to provide rewarding insights to the future development and broad application of pretreatment and detection methods for TTX and its analogues.

Isolation and Biological Activity of 9-epiTetrodotoxin and Isolation of Tb-242B, Possible Biosynthetic Shunt Products of Tetrodotoxin from Pufferfish

Tetrodotoxin (TTX, 1) is a potent voltage-gated sodium channel blocker detected in certain marine and terrestrial organisms. We report here a new TTX analogue, 9-epiTTX (2), and a TTX-related compound, Tb-242B (4), isolated from the pufferfish Takifugu flavipterus and Dichotomyctere ocellatus, respectively. NMR analysis suggested that 2 exists as a mixture of hemilactal and 10,8-lactone forms, whereas other reported TTX analogues are commonly present as an equilibrium mixture of hemilactal and 10,7-lactone forms. Compound 2 and TTX were confirmed not to convert to each other by incubation under neutral and acidic conditions at 37 °C for 24 h. Compound 4 was identified as the 9-epimer of Tb-242A (3), previously reported as a possible biosynthetic precursor of TTX. Compound 4 was partially converted to 3 by incubation in a neutral buffer at 37 °C for 7 days, whereas 3 was not converted to 4 under this condition. Compound 2 was detected in several TTX-containing marine animals and a newt. Mice injected with 600 ng of 2 by intraperitoneal injection did not show any adverse symptoms, suggesting that the C-9 configuration in TTX is critical for its biological activity. Based on the structures, 2 and 4 were predicted to be shunt products for TTX biosynthesis.

Transcriptomic analysis reveals the genes involved in tetrodotoxin (TTX) accumulation, translocation, and detoxification in the pufferfish Takifugu rubripes

Tetrodotoxin (TTX) is a potent marine neurotoxin that exists in a variety of aquatic and terrestrial organisms. Pufferfish in different habitats show great variation in their TTX contents. Exploring the genes involved in TTX metabolism could contribute to our understanding of the molecular mechanisms underlying TTX accumulation, translocation, and detoxification in pufferfish. In this study, transcriptomic analysis was used to identify the functional genes related to TTX metabolism in the blood, liver, and muscle of the toxic and non-toxic tiger puffer (Takifugu rubripes). A total of 6101 differentially expressed genes (DEGs) were obtained after transcriptomic analysis; of these, 2401 were identified in the blood, 2262 in the liver, and 1438 in the muscle. After enrichment analysis, fourteen genes encoding glutathione S-transferases (GSTs), glutathione peroxidase (GPx), thioredoxins (TXNs), superoxide dismutase (SOD), ATP-binding cassettes (ABCs), apolipoproteins (APOs), inhibitors of apoptosis protein (IAP), and solute carrier (SLC), which are mainly antioxidant enzymes, membrane transporters, or anti-apoptotic factors, were revealed in the blood. Thirty-six genes encoding SLCs, ABCs, long-chain-fatty-acid-CoA ligases (ACSLs), interleukin 6 cytokine family signal transducer (IL6ST), endoplasmic reticulum (ER), and heat shock protein family A (Hsp70) were involved in transmembrane transporter activity and innate immune response. Notably, a large number of slc genes were found to play critical and diverse roles in TTX accumulation and translocation in the liver of T. rubripes. Nine genes from the slc, hsp70, complement C5 (c5), acsl, er, and serpin peptidase inhibitor (serpin) gene families were found to participate in the regulation of protein processing and anti-apoptosis. These results reflect the diverse functions of genes closely related to TTX accumulation, translocation, and detoxification in T. rubripes.

An Overview of the Anatomical Distribution of Tetrodotoxin in Animals

Tetrodotoxin (TTX), a potent paralytic sodium channel blocker, is an intriguing marine toxin. Widely distributed in nature, TTX has attracted attention in various scientific fields, from biomedical studies to environmental safety concerns. Despite a long history of studies, many issues concerning the biosynthesis, origin, and spread of TTX in animals and ecosystems remain. This review aims to summarize the current knowledge on TTX circulation inside TTX-bearing animal bodies. We focus on the advances in TTX detection at the cellular and subcellular levels, providing an expanded picture of intra-organismal TTX migration mechanisms. We believe that this review will help address the gaps in the understanding of the biological function of TTX and facilitate the development of further studies involving TTX-bearing animals.

A High Throughput Screening HPLC-FLD Method for Paralytic Shellfish Toxins (PSTs) Enabling Effective Official Control

Paralytic Shellfish Toxins (PSTs) are marine biotoxins, primarily produced by dinoflagellates of the genera Gymnodinium spp., Alexandrium spp. They can accumulate in shellfish and, through the food chain, be assimilated by humans, giving rise to Paralytic Shellfish Poisoning. The maximum permitted level for PSTs in bivalves is 800 μg STX·2HCl eqv/kg (Reg. EC N° 853/2004). Until recently, the reference analytical method was the Mouse Bioassay, but Reg. EU N° 1709/2021 entered into force on 13 October 2021 and identified in the Standard EN14526:2017 or in any other internationally recognized validated method not entailing the use of live animals as official methods. Then the official control laboratories had urgently to fulfill the new requests, face out the Mouse Bioassay and implement instrumental analytical methods. The “EURLMB SOP for the analysis of PSTs by pre-column HPLC-FLD according to OMA AOAC 2005.06” also introduced a simplified semiquantitative approach to discriminate samples above and below the regulatory limit. The aim of the present paper is to present a new presence/absence test with a cut-off at 600 μg STX·2HCl eqv/kg enabling the fast discrimination of samples with very low PSTs levels from those to be submitted to the full quantitative confirmatory EN14526:2017 method. The method was implemented, avoiding the use of a large number of certified reference standards and long quantification procedures, resulting in an efficient, economical screening instrument available for official control laboratories. The protocol was fully validated, obtaining good performances in terms of repeatability (<11%) and recovery (53−106%) and accredited according to ISO/IEC 17025. The method was applied to mollusks collected from March 2021 to February 2022 along the Marche region in the frame of marine toxins official control.

Inhalable particle-bound marine biotoxins in a coastal atmosphere: Concentration levels, influencing factors and health risks

Characterizing marine biotoxins (MBs) composition in coastal aerosol particles has become essential to tracking sources of atmospheric contaminants and assessing human inhalable exposure risks to air particles. Here, coastal aerosol particles were collected over an almost 3-year period for the analysis of eight representative MBs, including brevetoxin (BTX), okadaic acid (OA), pectenotoxin-2 (PTX-2), domoic acid (DA), tetrodotoxin (TTX), saxitoxin (STX), ciguatoxin (CTX) and ω-Conotoxin. Our data showed that the levels of inhalable airborne marine biotoxins (AMBs) varied greatly among the subcategories and over time. Both in daytime and nighttime, a predominance of coarse-mode AMB particles was found for all the target AMBs. Based on the experimental data, we speculate that an ambient AMB might have multiple sources/production pathways, which include air-sea aerosol production and direct generation and release from toxigenic microalgae/bacteria suspended in surface seawater or air, and different sources may make different contribution. Regardless of the subcategory, the highest deposition efficiency of an individual AMB was found in the head airway region, followed by the alveolar and tracheobronchial regions. This study provides new information about inhalable MBs in the coastal atmosphere. The coexistence of various particle-bound MBs raises concerns about potential health risks from exposure to coastal air particles.

Rising CO2 will increase toxicity of marine dinoflagellate Alexandrium minutum

Ocean acidification caused by increasing emission of carbon dioxide (CO₂) is expected to have profound impacts on marine ecological processes, including the formation and evolution of harmful algal blooms (HABs). We designed a set of experiments in the laboratory to examine the effects of increasing CO₂ on the growth and toxicity of a toxic dinoflagellate Alexandrium minutum producing paralytic shellfish toxins (PSTs). It was found that high levels of CO₂ (800 and 1200 ppm) significantly promoted the growth of A. minutum compared to the group (400 ppm) representing the current CO₂ level. The total yields of PSTs by A. minutum, including both intracellular and extracellular toxins, were significantly enhanced, probably due to the induction of core enzyme activity and key amino acids synthesis for PST production. More interestingly, high level of CO₂ promoted the transformation from gonyautoxin2&3 to gonyautoxin1&4 and depressed the release of PSTs from inside to outside of the cells. All these processes collectively led to an apparent increase of A. minutum toxicity. Our study demonstrated that rising CO₂ would increase the risk of toxic A. minutum based on the comprehensive analyses of different processes including algal growth and toxin synthesis, transformation and release.

Simultaneous Determination of Tetrodotoxin in the Fresh and Heat-Processed Aquatic Products by High-Performance Liquid Chromatography-Tandem Mass Spectrometry

Tetrodotoxin (TTX) was simultaneously detected in the fresh and heat-processed aquatic products by high-performance liquid chromatography-tandem mass spectrometry method. The detection conditions were investigated, including the chromatography column and mobile phase. Based on the optimized parameters, a sensitive determination method of TTX was established. The proposed method featured the merits of a good linear relationship between signal and TTX concentration (R2 = 0.9998), a wide detection matrix-based range of 0.2-100 ng/g, and a low detection limit of 0.2 ng/g, etc. The spiked assays evidenced its accuracy and reliability with recoveries of 90.5-107.2%. Finally, the developed method was simultaneously successfully applied in the determination of TTX in various fresh and heat-processed aquatic products.

An Updated Review of Tetrodotoxin and Its Peculiarities

Tetrodotoxin (TTX) is a crystalline, weakly basic, colorless organic substance and is one of the most potent marine toxins known. Although TTX was first isolated from pufferfish, it has been found in numerous other marine organisms and a few terrestrial species. Moreover, tetrodotoxication is still an important health problem today, as TTX has no known antidote. TTX poisonings were most commonly reported from Japan, Thailand, and China, but today the risk of TTX poisoning is spreading around the world. Recent studies have shown that TTX-containing fish are being found in other regions of the Pacific and in the Indian Ocean, as well as the Mediterranean Sea. This review aims to summarize pertinent information available to date on the structure, origin, distribution, mechanism of action of TTX and analytical methods used for the detection of TTX, as well as on TTX-containing organisms, symptoms of TTX poisoning, and incidence worldwide.

All-In-One: Microbial Response to Natural and Anthropogenic Forcings in a Coastal Mediterranean Ecosystem, the Syracuse Bay (Ionian Sea, Italy)

Bacterial and phytoplankton communities are known to be in close relationships, but how natural and anthropogenic stressors can affect their dynamics is not fully understood. To study the response of microbial communities to environmental and human-induced perturbations, phytoplankton and bacterial communities were seasonally monitored in a Mediterranean coastal ecosystem, Syracuse Bay, where multiple conflicts co-exist. Quali-quantitative, seasonal surveys of the phytoplankton communities (diatoms, dinoflagellates and other taxa), the potential microbial enzymatic activity rates (leucine aminopeptidase, beta-glucosidase and alkaline phosphatase) and heterotrophic culturable bacterial abundance, together with the thermohaline structure and trophic status in terms of nutrient concentrations, phytoplankton biomass (as Chlorophyll-a), and total suspended and particulate organic matter, were carried out. The aim was to integrate microbial community dynamics in the context of the environmental characterization and disentangle microbial patterns related to natural changes from those driven by the anthropic impact on this ecosystem. In spite of the complex relationships between the habitat characteristics, microbial community abundance and metabolic potential, in Syracuse Bay, the availability of organic substrates differently originated by the local conditions appeared to drive the distribution and activity of microbial assemblage. A seasonal pattern of microbial abundances was observed, with the highest concentrations of phytoplankton in spring and low values in winter, whereas heterotrophic bacteria were more abundant during the autumn period. The autumn peaks of the rates of enzymatic activities suggested that not only phytoplankton-derived but also allochthonous organic polymers strongly stimulated microbial metabolism. Increased microbial response in terms of abundance and metabolic activities was detected especially at the sites directly affected by organic matter inputs related to agriculture or aquaculture activities. Nitrogen salts such as nitrate, rather than orthophosphate, were primary drivers of phytoplankton growth. This study also provides insights on the different seasonal scenarios of water quality in Syracuse Bay, which could be helpful for management plans of this Mediterranean coastal environment.

Tetrodotoxin in live bivalve mollusks from Europe: Is it to be considered an emerging concern for food safety?

Tetrodotoxins (TTXs) are a group of potent neurotoxins named after the Tetraodontidae fish family (pufferfish). TTXs have been reported in several animal taxa, both terrestrial and marine. The ingestion of TTX-contaminated flesh can cause serious neurotoxic symptomatology and can eventually lead to death. Traditionally, TTXs have been associated with Asian countries, in particular with pufferfish consumption. However, they have also been reported in bivalve mollusks farmed in the Pacific area and, recently, in European seas. In Europe, different countries have reported TTXs, especially those bordering the Mediterranean Sea. As a consequence, in 2017 the European Food Safety Authority (EFSA) released an opinion with reference to TTX present in marine gastropods and bivalves, proposing a safety limit of 44 µg/kg TTXs in shellfish meat, below which no adverse effects should be observed in humans. Nevertheless, this limit has been exceeded on many occasions in European shellfish and, while for bivalves there have been no registered human intoxications, that is not the case for marine gastropods. However, TTXs have not yet been included in the list of marine biotoxins officially monitored in live bivalve mollusks within the European Union (EU). Thus, the aims of this manuscript are to discuss the increasing occurrence of TTXs in live bivalve mollusks from European sea waters, to acknowledge the still ongoing knowledge gaps that should be covered and to stimulate constructive debate on the eventuality of adopting a shared regulatory context, at least in the EU, for monitoring and managing this potential threat to food safety.

Hybrid Antibody-Aptamer Assay for Detection of Tetrodotoxin in Pufferfish

The marine toxin tetrodotoxin (TTX) poses a great risk to public health safety due to its severe paralytic effects after ingestion. Seafood poisoning caused by the consumption of contaminated marine species like pufferfish due to its expansion to nonendemic areas has increased the need for fast and reliable detection of the toxin to effectively implement prevention strategies. Liquid chromatography-mass spectrometry is considered the most accurate method, although competitive immunoassays have also been reported. In this work, we sought to develop an aptamer-based assay for the rapid, sensitive, and cost-effective detection of TTX in pufferfish. Using capture-SELEX combined with next-generation sequencing, aptamers were identified, and their binding properties were evaluated. Finally, a highly sensitive and user-friendly hybrid antibody–aptamer sandwich assay was developed with superior performance compared to several assays reported in the literature and commercial immunoassay kits. The assay was successfully applied to the quantification of TTX in pufferfish extracts, and the results obtained correlated very well with a competitive magnetic bead-based immunoassay performed in parallel for comparison. This is one of the very few works reported in the literature of such hybrid assays for small-molecule analytes whose compatibility with field samples is also demonstrated.

Tetrodotoxins in French Bivalve Mollusks-Analytical Methodology, Environmental Dynamics and Screening of Bacterial Strain Collections

Tetrodotoxins (TTXs) are potentially lethal paralytic toxins that have been identified in European shellfish over recent years. Risk assessment has suggested comparatively low levels (44 µg TTX-equivalent/kg) but stresses the lack of data on occurrence. Both bacteria and dinoflagellates were suggested as possible biogenic sources, either from an endogenous or exogenous origin. We thus investigated TTXs in (i) 98 shellfish samples and (ii) 122 bacterial strains, isolated from French environments. We optimized a method based on mass spectrometry, using a single extraction step followed by ultrafiltration without Solid Phase Extraction and matrix-matched calibration for both shellfish and bacterial matrix. Limits of detection and quantification were 6.3 and 12.5 µg/kg for shellfish and 5.0 and 10 µg/kg for bacterial matrix, respectively. Even though bacterial matrix resulted in signal enhancement, no TTX analog was detected in any strain. Bivalves (either Crassostrea gigas or Ruditapes philippinarum) were surveyed in six French production areas over 2.5-3 month periods (2018-2019). Concentrations of TTX ranged from 'not detected' to a maximum of 32 µg/kg (Bay of Brest, 17 June 2019), with events lasting 2 weeks at maximum. While these results are in line with previous studies, they provide new data of TTX occurrence and confirm that the link between bacteria, bivalves and TTX is complex.

Simultaneous determination of ten paralytic shellfish toxins and tetrodotoxin in scallop and short-necked clam by ion-pair solid-phase extraction and hydrophilic interaction chromatography with tandem mass spectrometry

Paralytic shellfish toxins and tetrodotoxin (puffer-fish toxin), the latter of which was recently found in bivalves from Europe, Japan, and New Zealand, are potent neurotoxins. A simple and effective clean-up procedure was developed for the simultaneous determination of ten paralytic shellfish toxins (gonyautoxins 1-6, decarbamoylgonyautoxins 2 and 3, and N-sulfocarbamoylgonyautoxins 2 and 3) and tetrodotoxin in the scallop, Mizuhopecten (Patinopecten) yessoensis, and the short-necked clam, Ruditapes philippinarum. To reduce matrix effects, 1% aqueous acetic acid extracts of the bivalves were cleaned up by ion-pair solid-phase extraction using a graphite carbon cartridge with tridecafluoroheptanoic acid as the volatile ion-pair reagent, followed by fourfold dilution. The ten paralytic shellfish toxins and tetrodotoxin were then separated on a hydrophilic interaction chromatography column and quantified by tandem mass spectrometry. The limits of detection and the limits of quantification for the ten PSTs ranged from 0.09 to 13.0 µg saxitoxin equivalents/kg and from 0.26 to 39.4 µg saxitoxin equivalents/kg, respectively. The limit of detection and the limit of quantification for tetrodotoxin ranged from 27.4 to 27.9 µg/kg and from 83.1 to 84.4 µg/kg, respectively. The proposed method yielded minimal matrix effects for the 11 analytes, thus allowing their quantification by simple external calibration. The proposed method also gave good mean recoveries of the 11 analytes ranging from 75.7 to 96.2% with relative standard deviations less than 16% at three fortification levels for the ten paralytic shellfish toxins (total concentrations of 277, 554, and 1107 µg saxitoxin equivalents/kg) and tetrodotoxin (100, 200, and 400 µg/kg) in the two bivalve samples. Finally, the proposed method was applied for the determination of the ten paralytic shellfish toxins and tetrodotoxin in scallop and short-necked clam samples.

Tetrodotoxins (TTXs) and Vibrio alginolyticus in Mussels from Central Adriatic Sea (Italy): Are They Closely Related?

Tetrodotoxins (TTXs), potent neurotoxins, have become an increasing concern in Europe in recent decades, especially because of their presence in mollusks. The European Food Safety Authority published a Scientific Opinion setting a recommended threshold for TTX in mollusks of 44 µg equivalent kg⁻¹ and calling all member states to contribute to an effort to gather data in order to produce a more exhaustive risk assessment. The objective of this work was to assess TTX levels in wild and farmed mussels (Mytilus galloprovincialis) harvested in 2018–2019 along the coastal area of the Marche region in the Central Adriatic Sea (Italy). The presence of Vibrio spp. carrying the non-ribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) genes, which are suspected to be involved in TTX biosynthesis, was also investigated. Out of 158 mussel samples analyzed by hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry (HILIC-MS/MS), 11 (7%) contained the toxins at detectable levels (8–26 µg kg⁻¹) and 3 (2%) contained levels above the EFSA safety threshold (61–76 µg kg⁻¹). Contaminated mussels were all harvested from natural beds in spring or summer. Of the 2019 samples, 70% of them contained V. alginolyticus strains with the NRPS and/or PKS genes. None of the strains containing NRPS and/or PKS genes showed detectable levels of TTXs. TTXs in mussels are not yet a threat in the Marche region nor in Europe, but further investigations are surely needed.

Algal blooms of Alexandrium spp. and Paralytic Shellfish Poisoning toxicity events in mussels farmed in Sicily

Marine biotoxins can accumulate in filter- feeders bivalve molluscs, that may represent a source of potential health problems being vectors of toxins, that are transferred to humans through their consumption. Harmful Algal Blooms impact on aquaculture may give also economic losses due to temporary closures of contaminated shellfish harvest and marketing. The presence of toxic algae for Paralytic Shellfish Poisoning (PSP), with recurrent toxic blooms of dinoflagellates, such as several Alexandrium species, been known since 2000 in the waters of an Ionian bay of Sicily, the Syracuse harbour, where shellfish farms are located. Our previous works reported in this area the positivity for PSP toxin in mussels (Mytilus galloprovincialis) with saxitoxin concentrations above the limit of the law and the simultaneous presence of toxic species of the genus Alexandrium in the waters. This work reports new recent episodes of algal blooms of Alexandrium minutum in the waters of the Syracuse harbour and PSP toxin contamination in farmed mussels, with values beyond the limits established by law, with the consequent immediate closure of the production area. PSP toxicity was detected with the MBA (Mouse Bioassay) with the confirm carried out with Lawrence method to quantify the total saxitoxin equivalents and characterize the toxic profile. Regular application of the implemented health plan is very important in order to prevent any risk and protect consumer health.

Distribution of Tetrodotoxin in Pacific Oysters (Crassostrea gigas)

A potent and heat-stable tetrodotoxin (TTX) has been found to accumulate in various marine bivalve species, including Pacific oysters (Crassostrea gigas), raising a food safety concern. While several studies on geographical occurrence of TTX have been conducted, there is a lack of knowledge about the distribution of the toxin within and between bivalves. We, therefore, measured TTX in the whole flesh, mantle, gills, labial palps, digestive gland, adductor muscle and intravalvular fluid of C. gigas using liquid chromatography-tandem mass spectrometry. Weekly monitoring during summer months revealed the highest TTX concentrations in the digestive gland (up to 242 µg/kg), significantly higher than in other oyster tissues. Intra-population variability of TTX, measured in the whole flesh of each of twenty animals, reached 46% and 32% in the two separate batches, respectively. In addition, an inter-population study was conducted to compare TTX levels at four locations within the oyster production area. TTX concentrations in the whole flesh varied significantly between some of these locations, which was unexplained by the differences in weight of flesh. This is the first study examining TTX distribution in C. gigas and the first confirmation of the preferential accumulation of TTX in oyster digestive gland.

Toxic marine microalgae and noxious blooms in the Mediterranean Sea: A contribution to the Global HAB Status Report

We review the spatial distribution of toxic marine microalgal species and the impacts of all types of harmful algal events (Harmful Algal Blooms, HABs) in the Mediterranean Sea (MS), including the Black Sea, the Sea of Marmara, coastal lagoons and transitional waters, based on two databases compiled in the Ocean Biogeographic Information System (OBIS). Eighty-four potentially toxic species have been detected in the MS (2,350 records), of which 16 described from these waters between 1860 and 2014 and a few suspected to have been introduced. More than half of these species (46) produce toxins that may affect human health, the remainders ichthyotoxic substances (29) or other types of toxins (9). Nevertheless, toxicity-related events are not frequent in the MS (308 records in 31 years), and mainly consist of impacts on aquaculture, caused by the dinoflagellates Dinophysis and Alexandrium, along with a few actual shellfish poisoning cases. Pseudo-nitzschia blooms are widespread, but domoic acid in shellfish rarely exceeds regulatory levels. Fish kills are probably less sporadic than reported, representing a problem at a few places along the southern MS coasts and in the Ebro River Delta. Since the last decade of the 20^th century, blooms of the benthic dinoflagellates Ostreopsis cf. ovata have regularly occurred all along rocky shores of the MS, at times with human health problems caused by toxic aerosol. New records of Gambierdiscus and Fukuyoa, until now reported for the westernmost and easternmost MS coasts, raise concerns about the risk of ciguatera, a syndrome so far known only for subtropical and tropical areas. Recent discoveries are the dinoflagellates Vulcanodinium rugosum, responsible for the presence of pinnatoxins in French lagoons' shellfish, and the azaspiracid-producers Azadinium spp. Mucilages and discolorations have a major impact on tourism in summer. Reports of toxic species and HABs have apparently increased in the MS over the last half century, which is likely related to the increased awareness and monitoring operations rather than to an actual increase of these phenomena. Indeed, while the case of Ostreopsis appears as a sudden upsurge rather than a trend, no actual increase of toxic or noxious events has so far emerged in intensively studied areas, such as the French and Spanish coasts or the Adriatic Sea. Moreover, some cases of decrease are reported, e.g., for Alexandrium minutum blooms disappearing from the Harbour of Alexandria. Overall, main HAB risks derive from cases of massive development of microalgal biomass and consequent impacts of reduced coastal water quality on tourism, which represents the largest part of the marine economy along the MS coasts.

First Detection of Tetrodotoxins in the Cotylean Flatworm Prosthiostomum trilineatum

Several polyclad flatworm species are known to contain high levels of tetrodotoxin (TTX), but currently TTX-bearing flatworms seem to be restricted to specific Planocera lineages belonging to the suborder Acotylea. During our ongoing study of flatworm toxins, high concentrations of TTXs were detected for the first time in the flatworm Prosthiostomum trilineatum, suborder Cotylea, from the coastal area of Hayama, Kanagawa, Japan. Toxin levels were investigated by high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS), revealing that this species contains comparable concentrations of toxins as seen in planocerid flatworms such as Planocera multitentaculata. This finding indicated that there may be other species with significant levels of TTXs. The distribution of TTXs among other flatworm species is thus of great interest.

Occurrence and persistence of enteric viruses, arsenic and biotoxins in Pacific oysters farmed in an Italian production site

The presence of Norovirus (NoV) and Hepatitis E virus (HEV) in non-depurated and depurated oysters raised in the north-west Italian coast was investigated by quantitative real-time RT-PCR. Total and inorganic arsenic (As) and the presence of marine biotoxins (DSP, ASP, PSP) by LC-MS were also investigated. NoV was detected through all the sampling period in non depurated and depurated oysters with highest levels during wintertime (>10⁴ genome copies per gram, gc/g) and minimum values in summer below the LOQ (<130/140 gc/g). HEV has never been found as well as biotoxins. Total As concentration was found in oysters in the range 0.45-3.0 mg/kg, while inorganic As was found in all samples in concentrations below the LOQ (<0.020 mg/kg). The study highlights how the 24 h depuration process didn't reduce significantly NoV levels and therefore the high concentration of NoV in oysters could represent a risk for consumers especially during winter and spring months.

First Detection of Tetrodotoxin in Bivalves and Gastropods from the French Mainland Coasts

In 2015, tetrodotoxins (TTXs) were considered a potential threat in Europe since several studies had shown the presence of these toxins in European bivalve molluscs. In this study, we investigated the occurrence of TTXs in 127 bivalve samples (mussels and oysters) and in 66 gastropod samples (whelks) collected all along the French mainland coasts in 2017 and 2018. Analyses were carried out after optimization and in-house validation of a performing hydrophilic interaction liquid chromatography associated with tandem mass spectrometry (HILIC-MS/MS) method. The concentration set by European Food Safety Authority (EFSA) not expected to result in adverse effects (44 µg TTX equivalent/kg) was never exceeded, but TTX was detected in three mussel samples and one whelk sample (1.7-11.2 µg/kg). The tissue distribution of TTX in this whelk sample showed higher concentrations in the digestive gland, stomach and gonads (7.4 µg TTX/kg) than in the rest of the whelk tissues (below the limit of detection of 1.7 µg TTX/kg). This is the first study to report the detection of TTX in French molluscs.

Establishment of double probes rolling circle amplification combined with lateral flow dipstick for rapid detection of Chattonella marina

Chattonella marina is one of the main algae that could cause harmful algal blooms. It has killed a large number of cultured fish in coastal areas of many countries, causing serious economic losses. Therefore, it is necessary to establish a method that can specifically detect C. marina at pre-bloom abundance, so that timely measures can be taken before this alga causes harm. In this study, a long probe, a short probe and a pair of amplification primers were first designed by using the internal transcribed spacer (ITS) sequence of C. marina as the target gene and using the CD74 gene of a distant species Gallus gallus as the base sequence. The double probes rolling circle amplification (dpRCA) system was then established with the designed probes and amplification primers. A novel detection protocol referred to as dpRCA-LFD by combining the dpRCA products and lateral flow dipstick (LFD) was finally established, which can make the detection results visible to the naked eyes. The reaction conditions of dpRCA were optimized and the optimal conditions were as follows: cycle number of ligation reaction, 12; ligation temperature, 58 °C; amplification temperature, 60 °C; and amplification time, 60 min. The specificity test that was performed using the optimized dpRCA conditions indicated that dpRCA-LFD was exclusively specific for the target alga. The tests with the genomic DNA of C. marina and the recombinant plasmid containing the ITS sequence of C. marina showed that the sensitivity of dpRCA-LFD was 100 times higher than that of conventional PCR. The detection limit (DL) for the genomic DNA was 8.3 × 10^-3 ng µL^-1 (8.3 × 10^-3 ng per reaction), and the DL for the recombinant plasmid DNA was 7.8 copies µL^-1 (7.8 copies per reaction). The practicality of the developed dpRCA-LFD was further validated by test with the spiked samples containing C. marina and field samples. The simulative test showed that the dpRCA-LFD has a DL of 10 cells mL^-1. The dpRCA-LFD could successfully recognize the target cells from the field samples. In summary, the dpRCA-LFD established in this study has advantages of good specificity, high sensitivity, and easily visible detection results, and therefore is promising for the analysis of C. marina in field samples.

Oral Chronic Toxicity of the Safe Tetrodotoxin Dose Proposed by the European Food Safety Authority and Its Additive Effect with Saxitoxin

Tetrodotoxin (TTX) is a potent natural toxin causative of human food intoxications that shares its mechanism of action with the paralytic shellfish toxin saxitoxin (STX). Both toxins act as potent blockers of voltage-gated sodium channels. Although human intoxications by TTX were initially described in Japan, nowadays increasing concern about the regulation of this toxin in Europe has emerged due to its detection in fish and mollusks captured in European waters. Currently, TTX is only regularly monitored in Dutch fishery products. However, the European Food Safety Authority (EFSA) has established a safety level of 44 µg/kg TTX as the amount of toxin that did not cause adverse effects in humans. This level was extrapolated considering initial data on its acute oral toxicity and EFSA remarked the need for chronic toxicity studies to further reduce the uncertainty of future toxin regulations. Thus, in this work, we evaluated the oral chronic toxicity of TTX using the safety levels initially recommended by EFSA in order to exclude potential human health risks associated with the worldwide expanding presence of TTX. Using internationally recommended guidelines for the assessment of oral chronic toxicity, the data provided here support the proposed safety level for TTX as low enough to prevent human adverse effects of TTX even after chronic daily exposure to the toxin. However, the combination of TTX with STX at doses above the maximal exposure level of 5.3 µg/kg body weight derived by EFSA increased the lethality of TTX, thus confirming that both TTX and paralytic shellfish toxins should be taken into account to assess human health risks.

Tetrodotoxin in marine bivalves and edible gastropods: A mini-review

Tetrodotoxin (TTX) is a potent neurotoxin responsible for countless human intoxications and deaths around the world. The distribution of TTX and its analogues is diverse and the toxin has been detected in organisms from both marine and terrestrial environments. Increasing detections seafood species, such as bivalves and gastropods, has drawn attention to the toxin, reinvigorating scientific interest and regulatory concerns. There have been reports of TTX in 21 species of bivalves and edible gastropods from ten countries since the 1980's. While TTX is structurally dissimilar to saxitoxin (STX), another neurotoxin detected in seafood, it has similar sodium channel blocking action and potency and both neurotoxins have been shown to have additive toxicities. The global regulatory level for the STX group toxins applied to shellfish is 800 μg/kg. The presence of TTX in shellfish is only regulated in one country; The Netherlands, with a regulatory level of 44 μg/kg. Due to the recent interest surrounding TTX in bivalves, the European Food Safety Authority established a panel to assess the risk and regulation of TTX in bivalves, and their final opinion was that a concentration below 44 μg of TTX per kg of shellfish would not result in adverse human effects. In this article, we review current knowledge on worldwide TTX levels in edible gastropods and bivalves over the last four decades, the different methods of detection used, and the current regulatory status. We suggest research needs that will assist with knowledge gaps and ultimately allow development of robust monitoring and management protocols.

Emerging Lyngbya wollei toxins: A new high resolution mass spectrometry method to elucidate a potential environmental threat

Mass spectrometric methods for the quantitative and qualitative analyses of algal biotoxins are often complicated by co-eluting compounds that present analytically as interferences. This issue is particularly critical for organic polyamines, where co-eluting materials can suppress the formation of cations during electrospray ionization. Here we present an extraction procedure designed specifically to overcome matrix-derived ion suppression of algal toxins in samples of Lyngbya wollei, a filamentous benthic algae known to produce several saxitoxin analogues. Lyngbya wollei samples were collected from a large, persistent harmful algal bloom in Lake Wateree, SC. Six known Lyngbya wollei-specific toxins (LWT1-6) were successfully resolved and quantified against saxitoxin using hydrophilic interaction liquid chromatography coupled with triple quadrupole and quadrupole time-of-flight mass spectrometry. The parent ions [M²⁺ - H⁺]⁺ were observed for LWTs 1-6 and the [M]²⁺ ion was observed for LWT5. High resolution mass spectra and unique fragmentation ions were obtained for LWTs 1-6. A dilution factor of 50 resulted in a linear calibration of saxitoxin in the algae matrix. Ion suppression was resolved by sample dilution, which led to linear, positive correlations between peak area and mass of the extracted sample (R² > 0.96). Optimized sample extraction method and instrument parameters are presented.

Temporal Variation of the Profile and Concentrations of Paralytic Shellfish Toxins and Tetrodotoxin in the Scallop, Patinopecten yessoensis, Cultured in a Bay of East Japan

Paralytic shellfish toxins (PSTs) are the major neurotoxic contaminants of edible bivalves in Japan. Tetrodotoxin (TTX) was recently detected in bivalve shellfish around the world, drawing widespread attention. In Japan, high levels of TTX were reported in the digestive gland of the scallop, Patinopecten yessoensis, in 1993; however, no new data have emerged since then. In this study, we simultaneously analyzed PSTs and TTX in scallops cultured in a bay of east Japan using hydrophilic interaction chromatography (HILIC)-MS/MS. These scallops were temporally collected from April to December 2017. The highest concentration of PSTs (182 µmol/kg, total congeners) in the hepatopancreas was detected in samples collected on May 23, lined to the cell density of the dinoflagellate, Alexandrium tamarense, in seawater around the scallops, whereas the highest concentration of TTX (421 nmol/kg) was detected in samples collected on August 22. Contrary to the previous report, temporal variation of the PSTs and TTX concentrations did not coincide. The highest concentration of TTX in the entire edible tissues was 7.3 µg/kg (23 nmol/kg) in samples obtained on August 22, which was lower than the European Food Safety Authority (EFSA)-proposed threshold, 44 µg TTX equivalents/kg shellfish meat. In addition, 12β-deoxygonyautoxin 3 was firstly identified in scallops.

Quantitation of Tetrodotoxin and Its Analogues with a Combination of Liquid Chromatography-Tandem Mass Spectrometry and Quantitative 1H-NMR Spectroscopy

Tetrodotoxin and its analogues are the causative toxins of pufferfish poisoning. Tetrodotoxin has been recently detected in bivalve mollusks collected in New Zealand and Europe, highlighting the need to include tetrodotoxin in monitoring programs for bivalves by instrumental methods. In the present study, tetrodotoxin and its analogues in commercially available tetrodotoxin reagents were quantitated accurately by quantitative ¹H-nuclear magnetic resonance (qNMR) spectroscopy. The results were applied to estimate relative molar responses of tetrodotoxin and its analogues in hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC/MS/MS). All four components (tetrodotoxin hemilactal form (1), tetrodotoxin 10,7-lactone form (2), 4-epitetrodotoxin (3), and 4,9-anhydrotetrodotoxin (4)) generated by equilibrating tetrodotoxin in aqueous solution were prepared as a mixture. From the HSQC spectrum of the mixture, the separated signals derived from three components, excluding 1, were selected and used for the quantitation. In addition, the relative molar responses of 3 and 4 on HILIC/MS/MS were calculated to be 0.73 and 0.46, respectively. These values could be useful for quantitation of 3 and 4 using the tetrodotoxin standard by HILIC/MS/MS. Our results also indicate that qNMR is useful for preparation of tetrodotoxin certified reference material.

Occurrence of Tetrodotoxin in Bivalves and Gastropods from Harvesting Areas and Other Natural Spaces in Spain

Tetrodotoxin (TTX) is a potent neurotoxin that is receiving increasing interest in the European Union because it has been found in different fishery products (fish, bivalves and gastropods) captured in European waters. Since available information is scarce, further analytical data regarding the incidence of this toxin in European fishery products is needed in order to perform an appropriate risk assessment devoted to protecting consumers' health. Hence, samples of bivalves and gastropods were collected at different points of the Spanish coast and analyzed by high-performance hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS) to evaluate the presence of TTX. None of the analyzed samples showed TTX above an internal threshold of 10 µg/kg or even showed a peak under it. Our results on TTX occurrence obtained in bivalve molluscs and gastropods did not show, at least in the studied areas, a risk for public health. However, taking into account previous positive results obtained by other research groups, and since we did not detect TTX in our samples, a more completed study increasing sampling frequency is needed to ensure proper risk evaluation towards the food safety of these products.