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

An Update of Tetrodotoxins Toxicity and Risk Assessment Associated to Contaminated Seafood Consumption in Europe: A Systematic Review

Following the occurrence of Tetrodotoxins (TTXs) in Europe-a group of neurotoxins identified in Asia, where fatalities occurred after the ingestion of contaminated pufferfish-the EFSA proposed a limit of 44 µg of TTX/kg of shellfish meat in mollusks in 2017, to protect heavy consumers. The limit was based on an acute reference dose (ARfD) derived from the few available data on TTX toxicity. TTX is expected to increase with sea-surface warming; indeed, it has been found in spring/summer in mollusks in Europe, with concentrations often exceeding this limit. Due to the numerous uncertainties of the EFSA's ARfD, we conducted a systematic review to provide an update on TTX toxicity. Out of 12,741 articles retrieved from PubMed, Science Direct, and Scopus since 2017, only 17 were eligible for data extraction. Our results show that they are not sufficient to modify the EFSA's conclusions. Furthermore, our analysis of occurrence data in European seafood, to assess the current risk of exposure to TTX, reveals several gaps, such as different LODs/LOQs and seasonal monitoring not allowing comparisons between areas and too few analyzed sites. However, the presence of positive samples exceeding the EFSA limit indicates a potential risk even for general consumers, highlighting the urgency to address these knowledge gaps.

First data on tetrodotoxins in Cephalothrix mokievskii (palaeonemertea, nemertea) and possible involvement OF POISONOUS nemerteans in toxification of marine bioresources

We for the first time have recorded the presence of TTX and 11 of its analogues (TTXs) and determined the profile of these toxins by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) in Cephalothrix mokievskii, collected off the coast of Sakhalin Island and also revealed differences in the TTXs profile between C. mokievskii and sibling Cephalothrix cf, simula. We discuss the features of the TTXs profile in C. mokievskii, geographical distribution of TTX-containing nemerteans and its possible implication for toxification of marine bioresources.

Investigating Non-Native Ribbon Worm Cephalothrix simula as a Potential Source of Tetrodotoxin in British Bivalve Shellfish

Tetrodotoxin (TTX) is a potent marine neurotoxin found in several phylogenetically diverse organisms, some of which are sought as seafood. Since 2015, TTX has been reported in bivalve shellfish from several estuarine locations along the Mediterranean and European Atlantic coasts, posing an emerging food safety concern. Although reports on spatial and temporal distribution have increased in recent years, processes leading to TTX accumulation in European bivalves are yet to be described. Here, we explored the hypothesis that the ribbon worm species Cephalothrix simula, known to contain high levels of TTX, could play a role in the trophic transfer of the toxin into shellfish. During a field study at a single location in southern England, we confirmed C. simula DNA in seawater adjacent to trestle-farmed Pacific oysters Magallana gigas (formerly Crassostrea gigas) with a history of TTX occurrence. C. simula DNA in seawater was significantly higher in June and July during the active phase of toxin accumulation compared to periods of either no or continually decreasing TTX concentrations in M. gigas. In addition, C. simula DNA was detected in oyster digestive glands collected on 15 June 2021, the day with the highest recorded C. simula DNA abundance in seawater. These findings show evidence of a relationship between C. simula and TTX occurrence, providing support for the hypothesis that bivalves may acquire TTX through filter-feeding on microscopic life forms of C. simula present in the water column at particular periods each year. Although further evidence is needed to confirm such feeding activity, this study significantly contributes to discussions about the biological source of TTX in European bivalve shellfish.

Temporal variation in the concentrations and profiles of paralytic shellfish toxins and tetrodotoxin in scallop (Mizuhopecten yessoensis) and bloody clam (Anadara broughtonii) collected from the coast of Miyagi Prefecture, Japan

For food safety, the concentrations and profiles of paralytic shellfish toxins (PSTs) and tetrodotoxin were examined in economically important scallops and bloody clams collected from the coast of the Miyagi Prefecture, Japan. PSTs were the major toxins in both species. The tetrodotoxin concentration in scallops increased in summer, although the highest value (18.7 μg/kg) was lower than the European Food Safety Authority guideline threshold (44 μg/kg). This confirmed the safety for tetrodotoxin in this area.