Update of risk assessments of main marine biotoxins in the European Union

The Temporal Distribution of Cyclic Imines in Shellfish in the Bays of Fangar and Alfacs, Northwestern Mediterranean Region

Spirolides (SPXs), gymnodimines (GYMs), and pinnatoxins (PnTXs) have been detected in shellfish from the northwestern Mediterranean coast of Spain. Several samples of bivalves were collected from Fangar Bay and Alfacs Bay in Catalonia over a period of over 7 years (from 2015 to 2021). Shellfish samples were analyzed for cyclic imines (CIs) on an LC1200 Agilent and 3200 QTrap triple-quadrupole mass spectrometer. In shellfish, SPX-1 was detected in two cases (of 26.5 µg/kg and 34 µg/kg), and GYM-A was only detected in trace levels in thirteen samples. Pinnatoxin G (PnTX-G) was detected in 44.6% of the samples, with its concentrations ranging from 2 µg/kg to 38.4 µg/kg. Statistical analyses revealed that seawater temperature influenced the presence or absence of these toxins. PnTX-G showed an extremely significant presence/temperature relationship in both bays in comparison to SPX-1 and GYM-A. The prevalence of these toxins in different bivalve mollusks was evaluated. A seasonal pattern was observed, in which the maximum concentrations were found in the winter months for SPX-1 and GYM-A but in the summer months for PnTX-G. The obtained results indicate that it is unlikely that CIs in the studied area pose a potential health risk through the consumption of a seafood diet. However, further toxicological information about CIs is necessary in order to perform a conclusive risk assessment.

A review on aquatic toxins - Do we really know it all regarding the environmental risk posed by phytoplankton neurotoxins?

Aquatic toxins are potent natural toxins produced by certain cyanobacteria and marine algae species during harmful cyanobacterial and algal blooms (CyanoHABs and HABs, respectively). These harmful bloom events and the toxins produced during these events are a human and environmental health concern worldwide, with occurrence, frequency and severity of CyanoHABs and HABs being predicted to keep increasing due to ongoing climate change scenarios. These contexts, as well as human health consequences of some toxins produced during bloom events have been thoroughly reviewed before. Conversely, the wider picture that includes the non-human biota in the assessment of noxious effects of toxins is much less covered in the literature and barely covered by review works. Despite direct human exposure to aquatic toxins and related deleterious effects being responsible for the majority of the public attention to the blooms' problematic, it constitutes a very limited fraction of the real environmental risk posed by these toxins. The disruption of ecological and trophic interactions caused by these toxins in the aquatic biota building on deleterious effects they may induce in different species is paramount as a modulator of the overall magnitude of the environmental risk potentially involved, thus necessarily constraining the quality and efficiency of the management strategies that should be placed. In this way, this review aims at updating and consolidating current knowledge regarding the adverse effects of aquatic toxins, attempting to going beyond their main toxicity pathways in human and related models' health, i.e., also focusing on ecologically relevant model organisms. For conciseness and considering the severity in terms of documented human health risks as a reference, we restricted the detailed revision work to neurotoxic cyanotoxins and marine toxins. This comprehensive revision of the systemic effects of aquatic neurotoxins provides a broad overview of the exposure and the hazard that these compounds pose to human and environmental health. Regulatory approaches they are given worldwide, as well as (eco)toxicity data available were hence thoroughly reviewed. Critical research gaps were identified particularly regarding (i) the toxic effects other than those typical of the recognized disease/disorder each toxin causes following acute exposure in humans and also in other biota; and (ii) alternative detection tools capable of being early-warning signals for aquatic toxins occurrence and therefore provide better human and environmental safety insurance. Future directions on aquatic toxins research are discussed in face of the existent knowledge, with particular emphasis on the much-needed development and implementation of effective alternative (eco)toxicological biomarkers for these toxins. The wide-spanning approach followed herein will hopefully stimulate future research more broadly addressing the environmental hazardous potential of aquatic toxins.

Characterisation and toxicological activity of three different Pseudo-nitzschia species from the northern Adriatic Sea (Croatia)

Diatoms of the genus Pseudo-nitzschia are cosmopolitans spread in seas and oceans worldwide, with more than 50 described species, dozens of which have been confirmed to produce domoic acid (DA). Here, we characterized and investigated the toxicological activity of secondary metabolites excreted into the growth media of different Pseudo-nitzschia species sampled at various locations in the northern Adriatic Sea (Croatia) using human blood cells under in vitro conditions. The results revealed that three investigated species of the genus Pseudo-nitzschia were capable of producing DA indicating their toxic potential. Moreover, toxicological data suggested all three Pseudo-nitzschia species can excrete toxic secondary metabolites into the surrounding media in addition to the intracellular pools of DA, raising concerns regarding their toxicity and environmental impact. In addition, all three Pseudo-nitzchia species triggered oxidative stress, one of the mechanisms of action likely responsible for the DNA damage observed in human blood cells. In line with the above stated, our results are of great interest to environmental toxicologists, the public and policy makers, especially in light of today's climate change, which favours harmful algal blooms and the growth of DA producers with a presumed negative impact on the public health of coastal residents.

Hazard Identification Related to the Presence of Vibrio spp., Biogenic Amines, and Indole-Producing Bacteria in a Non-Filter Feeding Marine Gastropod (Tritia mutabilis) Commercialized on the Italian Market

Tritia mutabilis is a carrion-feeder edible marine gastropod with an open circulatory system. Therefore, biological, and chemical contaminants associated with the feed can reach all body tissues. The aim of the present study was to investigate the possible association of these characteristics with some food safety hazards. Vibrio spp. load, and the prevalence of pathogenic V. parahaemolyticus, V. vulnificus, and V. cholerae, were investigated. Moreover, biogenic amines (BAs) and indole-producing bacteria (IPB), markers of seafood decomposition, were quantified for the first time in an edible carrion-feeder. Overall, 49 batches were analyzed (38 from retail, and 11 from primary production). The Vibrio spp. load resulted of 5.64 ± 0.69 log₁₀ CFU g⁻¹ at retail, and 5.27 ± 0.74 at harvest but all batches resulted negative for pathogenic Vibrio. Histamine, putrescine, cadaverine, and tyramine were detected both at harvest and at the retail level. Their sum (BAs Index) showed a mean value of 50.45 and 65.83 mg Kg⁻¹ in batches at harvest and at retail, respectively. IPB were detected at harvest and upon refrigeration for three days (T1–T3). The mean load resulted in 2.52 ± 0.85 log₁₀ MPN g⁻¹ at T0, 3.31 ± 1.23 at T3 in batches immediately refrigerated, and 3.22 ± 1.18 at T3 in batches previously immersed in clean seawater. Our results contribute to identifying food-borne hazards for T. mutabilis that may be related to the retention of biogenic amines and indole-producing bacteria due to carrion feeding.

Physiological changes induced by sodium chloride stress in Aphanizomenon gracile, Cylindrospermopsis raciborskii and Dolichospermum sp

Due to anthropogenic activities, associated with climate change, many freshwater ecosystems are expected to experience an increase in salinity. This phenomenon is predicted to favor the development and expansion of freshwater cyanobacteria towards brackish waters due to their transfer along the estuarine freshwater-marine continuum. Since freshwater cyanobacteria are known to produce toxins, this represents a serious threat for animal and human health. Saxitoxins (STXs) are classified among the most powerful cyanotoxins. It becomes thus critical to evaluate the capacity of cyanobacteria producing STXs to face variations in salinity and to better understand the physiological consequences of sodium chloride (NaCl) exposure, in particular on their toxicity. Laboratory experiments were conducted on three filamentous cyanobacteria species isolated from brackish (Dolichospermum sp.) and fresh waters (Aphanizomenon gracile and Cylindrospermopsis raciborskii) to determine how salinity variations affect their growth, photosynthetic activity, pigment composition, production of reactive oxygen species (ROS), synthesis of compatible solutes and STXs intracellular quotas. Salinity tolerance was found to be species-specific. Dolichospermum sp. was more resistant to salinity variations than A. gracile and C. raciborskii. NaCl variations reduced growth in all species. In A. gracile, carotenoids content was dose-dependently reduced by NaCl. By contrast, in C. raciborskii and Dolichospermum sp., variations in carotenoids content did not show obvious relationships with NaCl concentration. While in Dolichospermum sp. phycocyanin and phycoerythrin increased within the first 24 h exposure to NaCl, in both A. gracile and C. raciborskii, these pigments decreased proportionally to NaCl concentration. Low changes in salinity did not impact STXs production in A. gracile and C. raciborskii while higher increase in salinity could modify the toxin profile and content of C. raciborskii (intracellular STX decreased while dc-GTX2 increased). In estuaries, A. gracile and C. raciborskii would not be able to survive beyond the oligohaline area (i.e. salinity > 5). Conversely, in part due to its ability to accumulate compatible solutes, Dolichospermum sp. has the potential to face consequent salinity variations and to survive in the polyhaline area (at least up to salinity = 24).

Marine toxin domoic acid induces in vitro genomic alterations in human peripheral blood cells

Domoic acid (DA) is an excitatory marine neurotoxin produced by diatoms Pseudo-nitzschia spp. as a defence compound that accumulates in the food web and is associated with amnesic shellfish poisoning in humans. Although its toxicity has been well established in marine species, there is limited data on DA cytogenotoxicity in human non-target cells. Therefore, we aimed to investigate the cytogenotoxic potential of DA (0.01-10 μg/mL) in human peripheral blood cells (HPBCs) using a battery of bioassays in vitro. In addition, the influence of DA on oxidative stress parameters as a possible mechanism of action was assessed. Results revealed that DA induced dose- and time-dependent cytotoxic effects. DA significantly affected genomic instability by increasing the frequency of micronuclei and nuclear buds. Furthermore, a slight induction of primary DNA strand breaks was detected after 24 h of exposure accompanied by a significant increase in the number of abnormal size tailed nuclei. No induction of hOGG1 (human 8-oxoguanine DNA glycosylase) sensitive sites was determined upon exposure to DA. Additionally, DA induced oxidative stress by increased production of reactive oxygen species accompanied by changes in glutathione, superoxide dismutase, malondialdehyde and protein carbonyl levels. Overall, the obtained results showed adverse genotoxic effects of DA in non-target HPBCs.

Outbreak of diarrhetic shellfish poisoning associated with consumption of mussels, United Kingdom, May to June 2019

We report on six cases of diarrhetic shellfish poisoning following consumption of mussels harvested in the United Kingdom. Dinophysis spp. in the water column was found to have increased rapidly at the production site resulting in high levels of okadaic acid-group lipophilic toxins in the flesh of consumed mussels. Clinicians and public health professionals should remain aware of algal-derived toxins being a potential cause of illness following seafood consumption.

A Strategy to Replace the Mouse Bioassay for Detecting and Identifying Lipophilic Marine Biotoxins by Combining the Neuro-2a Bioassay and LC-MS/MS Analysis

Marine biotoxins in fish and shellfish can cause several symptoms in consumers, such as diarrhea, amnesia, or even death by paralysis. Monitoring programs are in place for testing shellfish on a regular basis. In some countries testing is performed using the so-called mouse bioassay, an assay that faces ethical concerns not only because of animal distress, but also because it lacks specificity and results in high amounts of false positives. In Europe, for lipophilic marine biotoxins (LMBs), a chemical analytical method using LC-MS/MS was developed as an alternative and is now the reference method. However, safety is often questioned when relying solely on such a method, and as a result, the mouse bioassay might still be used. In this study the use of a cell-based assay for screening, i.e., the neuro-2a assay, in combination with the official LC-MS/MS method was investigated as a new alternative strategy for the detection and quantification of LMBs. To this end, samples that had been tested previously with the mouse bioassay were analyzed in the neuro-2a bioassay and the LC-MS/MS method. The neuro-2a bioassay was able to detect all LMBs at the regulatory levels and all samples that tested positive in the mouse bioassay were also suspect in the neuro-2a bioassay. In most cases, these samples contained toxin levels (yessotoxins) that explain the outcome of the bioassay but did not exceed the established maximum permitted levels.

Magnetic Separation-Based Multiple SELEX for Effectively Selecting Aptamers against Saxitoxin, Domoic Acid, and Tetrodotoxin

In this study, a novel magnetic separation-based multiple systematic evolution of ligands by exponential enrichment (SELEX) was applied to select aptamers simultaneously against three kinds of marine biotoxins, including domoic acid (DA), saxitoxin (STX), and tetrodotoxin (TTX). Magnetic reduced graphene oxide (MRGO) was prepared to adsorb unbound ssDNAs and simplify the separation step. In the multiple SELEX, after the initial twelve rounds of selection against mixed targets and the subsequent four respective rounds of selection against each single target, the three resulting ssDNA pools were cloned, sequenced, and analyzed. Several aptamer candidates were selected and subjected to the binding affinity and specificity test. Finally, DA-06 ( K_d = 62.07 ± 19.97 nM), TTX-07 ( K_d = 44.12 ± 15.38 nM), and STX-41 ( K_d = 61.44 ± 23.18 nM) showed high affinity and good specificity for DA, TTX, and STX, respectively. They were also applied to detect and quantify DA, TTX, and STX successfully. The other two multitarget aptamers, DA-01 and TTX-27, were also obtained, which can bind with either DA or TTX. These aptamers provide alternative recognition molecules to antibodies for biosensor applications.

Screening for the presence of lipophilic marine biotoxins in shellfish samples using the neuro-2a bioassay

The neuro-2a bioassay is considered as one of the most promising cell-based in vitro bioassays for the broad screening of seafood products for the presence of marine biotoxins. The neuro-2a assay has been shown to detect a wide array of toxins like paralytic shellfish poisons (PSPs), ciguatoxins, and also lipophilic marine biotoxins (LMBs). However, the neuro-2a assay is rarely used for routine testing of samples due to matrix effects that, for example, lead to false positives when testing for LMBs. As a result there are only limited data on validation and evaluation of its performance on real samples. In the present study, the standard extraction procedure for LMBs was adjusted by introducing an additional clean-up step with n-hexane. Recovery losses due to this extra step were less than 10%. This wash step was a crucial addition in order to eliminate false-positive outcomes due to matrix effects. Next, the applicability of this assay was assessed by testing a broad range of shellfish samples contaminated with various LMBs, including diarrhetic shellfish toxins/poisons (DSPs). For comparison, the samples were also analysed by LC-MS/MS. Standards of all regulated LMBs were tested, including analogues of some of these toxins. The neuro-2a cells showed good sensitivity towards all compounds. Extracts of 87 samples, both blank and contaminated with various toxins, were tested. The neuro-2a outcomes were in line with those of LC-MS/MS analysis and support the applicability of this assay for the screening of samples for LMBs. However, for use in a daily routine setting, the test might be further improved and we discuss several recommended modifications which should be considered before a full validation is carried out.

A Rapid LC-HRMS Method for the Determination of Domoic Acid in Urine Using a Self-Assembly Pipette Tip Solid-Phase Extraction

In this study, we developed a self-assembly pipette tip solid-phase extraction (PTSPE) method using a high molecular weight polymer material (PAX) as the adsorbent for the determination of domoic acid (DA) in human urine samples by liquid chromatography high-resolution mass spectrometry (LC-HRMS) analysis. The PTSPE cartridge, assembled by packing 9.1 mg of PAX as sorbent into a 200 μL pipette tip, showed high adsorption capacity for DA owing to the strong cationic properties of PAX. Compared with conventional SPE, the PTSPE is simple and fast, and shows some advantages in the aspects of less solvent consumption, low cost, the absence of the evaporation step, and short time requirement. All the parameters influencing the extraction efficiency such as pH, the amount of sorbent, the number of aspirating/dispensing cycles, and the type and volume of eluent in PTSPE were carefully investigated and optimized. Under the optimized conditions, the limit of detection (LOD) and limit of quantification (LOQ) values of DA were 0.12 μg/L and 0.37 μg/L respectively. The extraction recoveries of DA from the urine samples spiked at four different concentrations were in a range from 88.4% to 102.5%. The intra- and inter-day precisions varied from 2.1% to 7.6% and from 2.6% to 12.7%, respectively. The accuracy ranged from -1.9% to -7.4%.

Potential Threats Posed by Tetrodotoxins in UK Waters: Examination of Detection Methodology Used in Their Control

Tetrodotoxin is a neurotoxin responsible for many human fatalities, most commonly following the consumption of pufferfish. Whilst the source of the toxin has not been conclusively proven, it is thought to be associated with various species of marine bacteria. Whilst the toxins are well studied in fish and gastropods, in recent years, there have been a number of reports of tetrodotoxin occurring in bivalve shellfish, including those harvested from the UK and other parts of Europe. This paper reviews evidence concerning the prevalence of tetrodotoxins in the UK together with methodologies currently available for testing. Biological, biomolecular and chemical methods are reviewed, including recommendations for further work. With the recent development of quantitative chromatographic methods for these and other hydrophilic toxins, as well as the commercial availability of rapid testing kits, there are a number of options available to ensure consumers are protected against this threat.

Environmental contaminants of emerging concern in seafood--European database on contaminant levels

Marine pollution gives rise to concern not only about the environment itself but also about the impact on food safety and consequently on public health. European authorities and consumers have therefore become increasingly worried about the transfer of contaminants from the marine environment to seafood. So-called "contaminants of emerging concern" are chemical substances for which no maximum levels have been laid down in EU legislation, or substances for which maximum levels have been provided but which require revision. Adequate information on their presence in seafood is often lacking and thus potential risks cannot be excluded. Assessment of food safety issues related to these contaminants has thus become urgent and imperative. A database (www.ecsafeseafooddbase.eu), containing available information on the levels of contaminants of emerging concern in seafood and providing the most recent data to scientists and regulatory authorities, was developed. The present paper reviews a selection of contaminants of emerging concern in seafood including toxic elements, endocrine disruptors, brominated flame retardants, pharmaceuticals and personal care products, polycyclic aromatic hydrocarbons and derivatives, microplastics and marine toxins. Current status on the knowledge of human exposure, toxicity and legislation are briefly presented and the outcome from scientific publications reporting on the levels of these compounds in seafood is presented and discussed.

Metal-organic framework UiO-66 modified magnetite@silica core-shell magnetic microspheres for magnetic solid-phase extraction of domoic acid from shellfish samples

Fe3O4@SiO2@UiO-66 core-shell magnetic microspheres were synthesized and characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectrometry, vibrating sample magnetometry, nitrogen adsorption porosimetry and zeta potential analyzer. The synthesized Fe3O4@SiO2@UiO-66 microspheres were first used for magnetic solid-phase extraction (MSPE) of domoic acid (DA) in shellfish samples. Combined with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), a fast, simple and sensitive method for the determination of DA was established successfully. Under the optimized conditions, the developed method showed short analysis time, good linearity (r(2) = 0.9990), low limit of detection (1.45 pg mL(-1); S/N = 3:1), low limit of quantification (4.82 pg mL(-1); S/N = 10:1), and good extraction repeatability (RSD ≤ 5.0%; n = 5). Real shellfish samples were processed using the developed method, and trace level of DA was detected. The results demonstrate that Fe3O4@SiO2@UiO-66 core-shell magnetic microspheres are the promising sorbents for rapid and efficient extraction of polar analytes from complex biological samples.

Potential threats posed by new or emerging marine biotoxins in UK waters and examination of detection methodology used in their control: brevetoxins

Regular occurrence of brevetoxin-producing toxic phytoplankton in commercial shellfishery areas poses a significant risk to shellfish consumer health. Brevetoxins and their causative toxic phytoplankton are more limited in their global distribution than most marine toxins impacting commercial shellfisheries. On the other hand, trends in climate change could conceivably lead to increased risk posed by these toxins in UK waters. A request was made by UK food safety authorities to examine these toxins more closely to aid possible management strategies, should they pose a threat in the future. At the time of writing, brevetoxins have been detected in the Gulf of Mexico, the Southeast US coast and in New Zealand waters, where regulatory levels for brevetoxins in shellfish have existed for some time. This paper reviews evidence concerning the prevalence of brevetoxins and brevetoxin-producing phytoplankton in the UK, together with testing methodologies. Chemical, biological and biomolecular methods are reviewed, including recommendations for further work to enable effective testing. Although the focus here is on the UK, from a strategic standpoint many of the topics discussed will also be of interest in other parts of the world since new and emerging marine biotoxins are of global concern.

In vitro detection of cardiotoxins or neurotoxins affecting ion channels or pumps using beating cardiomyocytes as alternative for animal testing

The present study investigated if and to what extent murine stem cell-derived beating cardiomyocytes within embryoid bodies can be used as a broad screening in vitro assay for neurotoxicity testing, replacing for example in vivo tests for marine neurotoxins. Effect of nine model compounds, acting on either the Na(+), K(+), or Ca(2+) channels or the Na(+)/K(+) ATP-ase pump, on the beating was assessed. Diphenhydramine, veratridine, isradipine, verapamil and ouabain induced specific beating arrests that were reversible and none of the concentrations tested induced cytotoxicity. Three K(+) channel blockers, amiodarone, clofilium and sematilide, and the Na(+)/K(+) ATPase pump inhibitor digoxin had no specific effect on the beating. In addition, two marine neurotoxins i.e. saxitoxin and tetrodotoxin elicited specific beating arrests in cardiomyocytes. Comparison of the results obtained with cardiomyocytes to those obtained with the neuroblastoma neuro-2a assay revealed that the cardiomyocytes were generally somewhat more sensitive for the model compounds affecting Na(+) and Ca(2+) channels, but less sensitive for the compounds affecting K(+) channels. The stem cell-derived cardiomyocytes were not as sensitive as the neuroblastoma neuro-2a assay for saxitoxin and tetrodotoxin. It is concluded that the murine stem cell-derived beating cardiomyocytes provide a sensitive model for detection of specific neurotoxins and that the neuroblastoma neuro-2a assay may be a more promising cell-based assay for the screening of marine biotoxins.

Cephalopods in neuroscience: regulations, research and the 3Rs

Cephalopods have been utilised in neuroscience research for more than 100 years particularly because of their phenotypic plasticity, complex and centralised nervous system, tractability for studies of learning and cellular mechanisms of memory (e.g. long-term potentiation) and anatomical features facilitating physiological studies (e.g. squid giant axon and synapse). On 1 January 2013, research using any of the about 700 extant species of "live cephalopods" became regulated within the European Union by Directive 2010/63/EU on the "Protection of Animals used for Scientific Purposes", giving cephalopods the same EU legal protection as previously afforded only to vertebrates. The Directive has a number of implications, particularly for neuroscience research. These include: (1) projects will need justification, authorisation from local competent authorities, and be subject to review including a harm-benefit assessment and adherence to the 3Rs principles (Replacement, Refinement and Reduction). (2) To support project evaluation and compliance with the new EU law, guidelines specific to cephalopods will need to be developed, covering capture, transport, handling, housing, care, maintenance, health monitoring, humane anaesthesia, analgesia and euthanasia. (3) Objective criteria need to be developed to identify signs of pain, suffering, distress and lasting harm particularly in the context of their induction by an experimental procedure. Despite diversity of views existing on some of these topics, this paper reviews the above topics and describes the approaches being taken by the cephalopod research community (represented by the authorship) to produce "guidelines" and the potential contribution of neuroscience research to cephalopod welfare.

Discovery of gymnodimine fatty acid ester metabolites in shellfish using liquid chromatography/mass spectrometry

RATIONALE

Gymnodimines (GYMs) are fast-acting toxins that belong to the cyclic imine group, a subclass of lipophilic marine toxins. GYMs are considered to be emerging toxins but have not yet been linked to incidents of human poisoning, Limited knowledge on the metabolism of GYMs means that a proper risk assessment has not been possible and caution must be taken when establishing the relevance of GYMs in terms of food safety of marine products.

METHODS

A series of mass spectrometric experiments involving precursor and product ion scans, selected reaction monitoring (SRM), and high-resolution mass spectrometry (MS) were used to detect and confirm 10-O-acyl esters of gymnodimine-A (1).

RESULTS

We have detected for the first time the presence of a range of acyl ester derivatives of GYMs in shellfish samples from the Gulf of Gabes, Tunisia. The MS fragmentation pathways of 1 and its esters were also elucidated. Partial synthesis of a palmitic acid ester of 1 facilitated confirmation of identity and calibration of SRM analyses. Evidence of acyl ester metabolites of gymnodimine-B and -C was also obtained.

CONCLUSIONS

A semi-quantitative analysis indicated that the majority of GYMs present in the sample were in the acylated form (>90%), suggesting that these compounds must not be neglected when trying to understand the risks associated with GYMs. There is a clear need for toxicology studies on these esters and assessment of bio-availability to humans.

Evaluation of seafood toxicity in the Australes archipelago (French Polynesia) using the neuroblastoma cell-based assay

Ciguatera fish poisoning (CFP), a disease caused by consuming fish that have accumulated ciguatoxins (CTXs) in their tissue, is regarded as the most prevalent form of intoxication in French Polynesia. Recently, the Australes, one of the least affected archipelago until the early 1980s, has shown a dramatic increase in its incidence rates in 2009 with unusual CFP cases. In the present work, potential health hazards associated with the proliferation of various marine phytoplankton species and the consumption of fish and marine invertebrates highly popular among local population were assessed in three Australes islands: Raivavae, Rurutu and Rapa. Extracts from the marine dinoflagellates Gambierdiscus, Ostreospis and mat-forming cyanobacteria as well as fish, giant clams and sea urchin samples were examined for the presence of CTXs and palytoxin (PLTX) by using the neuroblastoma cell-based assay (CBA-N2a). Cytotoxic responses observed with both standards (Pacific CTX-3C and PLTX) and targeted marine products indicate that CBA-N2a is a robust screening tool, with high sensitivity and good repeatability and reproducibility. In Rurutu and Raivavae islands, our main findings concern the presence of CTX-like compounds in giant clams and sea urchins, suggesting a second bio-accumulation route for CFP toxins in the ciguatera food chain. In Rapa, the potential CFP risk from Gambierdiscus bloom and fish was confirmed for the first time, with levels of CTXs found above the consumer advisory level of 0.01 ng Pacific CTX-1B g(-1) of flesh in three fish samples. However, despite the presence of trace level of PLTX in Ostreopsis natural assemblages of Rapa, no sign of PLTX accumulation is yet observed in tested fish samples. Because this multi-toxinic context is likely to emerge in most French Polynesian islands, CBA-N2a shows great potential for future applications in the algal- and toxin-based field monitoring programmes currently on hand locally.

Towards the standardisation of the neuroblastoma (neuro-2a) cell-based assay for ciguatoxin-like toxicity detection in fish: application to fish caught in the Canary Islands

The ouabain/veratridine-dependent neuroblastoma (neuro-2a) cell-based assay (CBA) was applied for the determination of the presence of ciguatoxin (CTX)-like compounds in ciguatera-suspected fish samples caught in the Canary Islands. In order to avoid matrix interferences the maximal concentration of wet weight fish tissue exposed to the neuro-2a cells was set at 20 mg tissue equivalent (TE) ml(-1) according to the sample preparation procedure applied. In the present study, the limit of quantification (LOQ) of CTX1B equivalents in fish extract was set at the limit of detection (LOD), being defined as the concentration of CTX1B equivalents inhibiting 20% cell viability (IC(20)). The LOQ was estimated as 0.0096 ng CTX1B eq.g TE(-1) with 23-31% variability between experiments. These values were deemed sufficient even though quantification given at the IC(50) (the concentration of CTX1B equivalents inhibiting 50% cell viability) is more accurate with a variability of 17-19% between experiments. Among the 13 fish samples tested, four fish samples were toxic to the neuro-2a cells with estimations of the content in CTX1B g(-1) of TE ranging from 0.058 (± 0.012) to 6.23 (± 0.713) ng CTX1B eq.g TE(-1). The high sensitivity and specificity of the assay for CTX1B confirmed its suitability as a screening tool of CTX-like compounds in fish extracts at levels that may cause ciguatera fish poisoning. Species identification of fish samples by DNA sequence analysis was conducted in order to confirm tentatively the identity of ciguatera risk species and it revealed some evidence of inadvertent misidentification. Results presented in this study are a contribution to the standardisation of the neuro-2a CBA and to the risk analysis for ciguatera in the Canary Islands.