Chitosan performance during Paralytic Shellfish Toxins (PST) depuration of Mytilus chilensis exposed to Alexandrium catenella

Marine toxins in environment: Recent updates on depuration techniques

Marine toxins pose a significant safety risk, leading to human intoxications and causing substantial economic losses in seafood-producing regions. The development of rapid, cost-effective, efficient, and reliable approaches for the containment of these substances is therefore crucial in order to mitigate the adverse impact of marine toxins. This research conducted a comprehensive review on the toxicity and influencing factors of marine toxins production. Additionally, depuration technologies, including adsorption, advanced oxidation processes, biodegradation, heating treatment, temporary maintenance and purification, and drug inhibition, were systematically summarized. The study also provided a comparative analysis of the advantages and disadvantages of various depuration technologies and proposed strategies for future development.

Immune and physiological responses of Mytilus unguiculatus to Alexandrium spp. with varying paralytic shellfish toxin profiles

The innate immunity of bivalves serves as the initial defense mechanism against environmental pollutants, ultimately impacting genetic regulatory networks through synergistic interactions. Previous research has demonstrated variations in the accumulation and tolerance capacities of bivalves; however, the specific mechanism underlying the low accumulation of PSTs in M. unguiculatus remains unclear. This study examined the alterations in feeding behavior and transcriptional regulation of M. unguiculatus following exposure to two Alexandrium strains with distinct toxin profiles, specifically gonyautoxin (AM) and N-sulfocarbamoyl toxin (AC). The total accumulation rate of PSTs in M. unguiculatus was 43.64 % (AC) and 27.80 % (AM), with highest PSTs content in the AM group (455.39 μg STXeq/kg). There were significant variations (P < 0.05) in physiological parameters, such as total hemocyte count, antioxidant superoxide activity and tissue damage in both groups. The absorption rate was identified as the key factor influencing toxin accumulation. Transcriptomic analyses demonstrated that PSTs triggered upregulation of endocytosis, lysosome, and immune-related signaling pathways. Furthermore, PSTs induced a nucleotide imbalance in the AC group, with total PSTs content serving as the most toxic indicator. These results suggested that protein-like substances had a crucial role in the stress response of M. unguiculatus to PSTs. This study provided novel perspectives on the impacts of intricate regulatory mechanisms and varying immune responses to PSTs in bivalves.

Cation-Exchange Resin Applied to Paralytic Shellfish Toxins Depuration from Bivalves Exposed to Gymnodinium catenatum

The accumulation of marine biotoxins in shellfish and their consumption causes serious food safety problems, threatening human health and compromising the availability of protein-based food. It is thus urgent to develop methodologies for the detoxification of live bivalves, avoiding their economic and nutritional devaluation. In this context, we tested an adsorption mechanism of paralytic shellfish toxins (PST) based on a cation-exchange resin. The first studies using cultures of Gymnodinium catenatum (natural producers of PST) showed a decrease of about 80% in overall toxicity after 48 h. Interestingly, we found that the toxins are adsorbed differently, with toxins' structural features playing a part in the adsorption capacity via steric hindrance, electronic effects, or the extent of positive charge density (e.g., dcSTX). The positive effect of the resin in accelerating PST clearance from live mussels (Mytilus edulis) is not evident when compared to resin-free clearance; nevertheless, relevant information could be gathered that will facilitate further in vivo studies. Several factors appear to be at play, namely the competition of natural substances (e.g., salts, organic matter) for the same binding sites, the blocking of pores due to interactions between molecules, and/or difficulties in resin absorption by mussels. Additionally, the present work revealed the ability of mussels to neutralize pH and proposes bioconversion reactions among the PST molecules.

Variations in the toxicity and condition index of five bivalve species throughout a red tide event caused by Alexandrium catenella: A field study

Harmful red tides in China have caused paralytic shellfish toxins (PSTs) pollution and led to severe socioeconomic effects in shellfish aquaculture. Although shellfish can survive harmful algal blooms, the effects on their Condition Index (CI) have been underestimated. This study sought to evaluate the effects of the profiles and levels of paralytic shellfish toxins on variations in the CI in bivalves under natural blooming conditions. We observed clear soft tissue lesions to varying degrees except in Mytilus galloprovincialis after toxin exposure. Among the five species of shellfish exposed in situ, only M. galloprovincialis accumulated PSTs content above the maximum permitted level (800 μg STX di-HCl eq./kg). The highest toxin content in all sample tissues was observed in Patinopecten yessoensis. Significant interspecies differences in PSTs accumulation among the five bivalve species were observed in the hepatopancreas. A total of nine PSTs components and four new C-11 hydroxyl metabolites (so-called M-toxins) toxins were detected, and detoxification diversity was observed among bivalves. We observed a higher proportion of M-toxin in early stages, and the proportions changed only slightly over time in M. galloprovincialis and Magallana gigas, thus accounting for the significantly higher metabolism rate. Notably, the CI in M. gigas and Argopecten irradians was positively correlated with lowest toxin accumulation of PSTs content, but significantly inhibited. In conclusion, our results revealed a significant inhibitory effect on the CI in shellfish, in a species specific manner, with distinct levels of inhibition correlated with different toxin metabolites. Our study revealed the toxin content of different bivalves exposed to a natural red tide environment and the consequent effects on growth, thus building a foundation for research on the mechanisms underlying the effects of PSTs on growth. These data establish the ecological and economic significance of the effects of harmful algal blooms on bivalves.

Feeding response and dynamic of intoxication and detoxification in two populations of the flat oyster Ostrea chilensis exposed to paralytic shellfish toxins (PST)

Juvenile oysters (Ostrea chilensis) from two populations (Quempillén estuary and Pullinque bay) were exposed to a toxic diet containing paralytic shellfish toxins (PST), produced by Alexandrium catenella, followed by a detoxification period. Feeding behaviour, toxin profile, dynamics of intoxication/detoxification, and survival were evaluated over the entire experimental period. Both populations reduced their feeding rates during the 30-day exposure to the toxic diet. This negative effect was reversible when the diet was switched to the non-toxic one. Oysters from the estuary accumulated PST more rapidly than the population from the bay, suggesting their increased ability to cope with more adverse conditions. Both populations showed low detoxification capacity. Survival was significantly higher in oysters from the estuary, compared to those from the bay. Due to the increasing frequency and intensity of A. catenella blooms in southern Chile, it is necessary to better understand the responses of O. chilensis in different environments. This is important not only because of the ecological and commercial relevance of the bivalve, but also in consideration of expected climate change scenarios, where the new environmental conditions could favour the frequency and intensity of harmful algal bloom events.