Concentrations of microcystins in tissues of several fish species from freshwater reservoirs and ponds

Blue revolution turning green? A global concern of cyanobacteria and cyanotoxins in freshwater aquaculture: A literature review

To enhance productivity, aquaculture is intensifying, with high-density fish ponds and increased feed input, contributing to nutrient load and eutrophication. Climate change further exacerbates cyanobacterial blooms and cyanotoxin production that affect aquatic organisms and consumers. A review was conducted to outline this issue from its inception - eutrophication, cyanobacterial blooms, their harmful metabolites and consequential effects (health and economic) in aquacultures. The strength of evidence regarding the relationship between cyanobacteria/cyanotoxins and potential consequences in freshwater aquacultures (fish production) globally were assessed as well, while identifying knowledge gaps and suggesting future research directions. With that aim several online databases were searched through June 2023 (from 2000), and accessible publications conducted in aquacultures with organisms for human consumption, reflecting cyanotoxin exposure, were selected. Data on cyanobacteria/cyanotoxins in aquacultures and its products worldwide were extracted and analyzed. Selected 63 papers from 22 countries were conducted in Asia (48%), Africa (22%), America (22%) and Europe (8%). Microcystis aeruginosa was most frequent, among over 150 cyanobacterial species. Cyanobacterial metabolites (mostly microcystins) were found in aquaculture water and fish from 18 countries (42 and 33 papers respectively). The most affected were small and shallow fish ponds, and omnivorous or carnivorous fish species. Cyanotoxins were detected in various fish organs, including muscles, with levels exceeding the tolerable daily intake in 60% of the studies. The majority of research was done in developing countries, employing less precise detection methods, making the obtained values estimates. To assess the risk of human exposure, the precise levels of all cyanotoxins, not just microcystins are needed, including monitoring their fate in aquatic food chains and during food processing. Epidemiological research on health consequences, setting guideline values, and continuous monitoring are necessary as well. Further efforts should focus on methods for elimination, prevention, and education.

Cyanotoxins in food: Exposure assessment and health impact

The intricate nature of cyanotoxin exposure through food reveals a complex web of risks and uncertainties in our dietary choices. With the aim of starting to unravel this intricate nexus, a comprehensive review of 111 papers from the past two decades investigating cyanotoxin contamination in food was undertaken. It revealed a widespread occurrence of cyanotoxins in diverse food sources across 31 countries. Notably, 68% of the studies reported microcystin concentrations exceeding established Tolerable Daily Intake levels. Cyanotoxins were detected in muscles of many fish species, and while herbivorous fish exhibited the highest recorded concentration, omnivorous species displayed a higher propensity for cyanotoxin accumulation, exemplified by Oreochromis niloticus. Beyond fish, crustaceans and bivalves emerged as potent cyanotoxin accumulators. Gaps persist regarding contamination of terrestrial and exotic animals and their products, necessitating further exploration. Plant contamination under natural conditions remains underreported, yet evidence underscores irrigation-driven cyanotoxin accumulation, particularly affecting leafy vegetables. Finally, cyanobacterial-based food supplements often harbored cyanotoxins (57 % of samples were positive) warranting heightened scrutiny, especially for Aphanizomenon flos-aquae-based products. Uncertainties surround precise concentrations due to methodological variations (chemical and biochemical) and extraction limitations, along with the enigmatic fate of toxins during storage, processing, and digestion. Nonetheless, potential health consequences of cyanotoxin exposure via contaminated food include gastrointestinal and neurological disorders, organ damage (e.g. liver, kidneys, muscles), and even elevated cancer risks. While microcystins received significant attention, knowledge gaps persist regarding other cyanotoxins' accumulation, exposure, and effects, as well as combined exposure via multiple pathways. Intriguing and complex, cyanotoxin exposure through food beckons further research for our safer and healthier diets.

A Feasibility Study into the Production of a Mussel Matrix Reference Material for the Cyanobacterial Toxins Microcystins and Nodularins

Microcystins and nodularins, produced naturally by certain species of cyanobacteria, have been found to accumulate in aquatic foodstuffs such as fish and shellfish, resulting in a risk to the health of the seafood consumer. Monitoring of toxins in such organisms for risk management purposes requires the availability of certified matrix reference materials to aid method development, validation and routine quality assurance. This study consequently targeted the preparation of a mussel tissue reference material incurred with a range of microcystin analogues and nodularins. Nine targeted analogues were incorporated into the material as confirmed through liquid chromatography with tandem mass spectrometry (LC-MS/MS), with an additional 15 analogues detected using LC coupled to non-targeted high resolution mass spectrometry (LC-HRMS). Toxins in the reference material and additional source tissues were quantified using LC-MS/MS, two different enzyme-linked immunosorbent assay (ELISA) methods and with an oxidative-cleavage method quantifying 3-methoxy-2-methyl-4-phenylbutyric acid (MMPB). Correlations between the concentrations quantified using the different methods were variable, likely relating to differences in assay cross-reactivities and differences in the abilities of each method to detect bound toxins. A consensus concentration of total soluble toxins determined from the four independent test methods was 2425 ± 575 µg/kg wet weight. A mean 43 ± 9% of bound toxins were present in addition to the freely extractable soluble form (57 ± 9%). The reference material produced was homogenous and stable when stored in the freezer for six months without any post-production stabilization applied. Consequently, a cyanotoxin shellfish reference material has been produced which demonstrates the feasibility of developing certified seafood matrix reference materials for a large range of cyanotoxins and could provide a valuable future resource for cyanotoxin risk monitoring, management and mitigation.

Determination of Cyanotoxins and Prymnesins in Water, Fish Tissue, and Other Matrices: A Review

Harmful algal blooms (HABs) and their toxins are a significant and continuing threat to aquatic life in freshwater, estuarine, and coastal water ecosystems. Scientific understanding of the impacts of HABs on aquatic ecosystems has been hampered, in part, by limitations in the methodologies to measure cyanotoxins in complex matrices. This literature review discusses the methodologies currently used to measure the most commonly found freshwater cyanotoxins and prymnesins in various matrices and to assess their advantages and limitations. Identifying and quantifying cyanotoxins in surface waters, fish tissue, organs, and other matrices are crucial for risk assessment and for ensuring quality of food and water for consumption and recreational uses. This paper also summarizes currently available tissue extraction, preparation, and detection methods mentioned in previous studies that have quantified toxins in complex matrices. The structural diversity and complexity of many cyanobacterial and algal metabolites further impede accurate quantitation and structural confirmation for various cyanotoxins. Liquid chromatography–triple quadrupole mass spectrometer (LC–MS/MS) to enhance the sensitivity and selectivity of toxin analysis has become an essential tool for cyanotoxin detection and can potentially be used for the concurrent analysis of multiple toxins.

Microcystins distribution, bioaccumulation, and Microcystis genotype succession in a fish culture pond

In freshwater aquaculture ponds, cyanobacterial blooms and microcystins (MCs) pollution have attracted considerable attention due to their toxic effects. To provide an insight into cyanobacterial problems in aquaculture ponds, MCs distribution, bioaccumulation, and Microcystis genotype succession in a fishpond were investigated from May 2017 to November 2017. The distribution of MCs in filtered water, seston, and sediment varied considerably among months. MCs concentrations in filtered water, seston, and sediment ranged from 1.16 to 3.66 μg/L, 0.64 to 13.98 μg/g DW, and 1.34 to 5.90 μg/g DW, respectively. In addition, chemical oxygen demand was positively correlated with sestonic MCs concentrations. MCs concentrations accumulated in different tissues of market-size fish were in the order of liver > kidney > intestine > muscle. MCs content in muscle was 4.3 times higher than the WHO recommended tolerable daily intake level. Twenty-four ITS genotypes of Microcystis were identified from a total of 653 sequences. During the survey period, considerable genotype variation and rapid genotype succession were observed and dominant genotype was absent. A redundancy analysis revealed that Microcystis genotypes could significantly influence the variations in the proportions of the potentially toxic Microcystis, which could in turn influence the MCs concentrations in seston.

Effects of dietary toxic cyanobacteria and ammonia exposure on immune function of blunt snout bream (Megalabrama amblycephala)

Cyanobacterial blooms caused by water eutrophication have become a worldwide problem. During the degradation of toxic cyanobacterial blooms, elevated ammonia and microcystins concentrations co-occur and exert toxicity on fish. Up to now, the combined effect of microcystins and ammonia on fish immunotoxicity has not been reported. The present study investigated immune responses of blunt snout bream (Megalabrama amblycephala) to dietary toxic cyanobacteria and ammonia exposure. Megalobrama amblycephala were exposed to solutions with different concentrations of NH₃-N (0, 0.06, 0.12 mg/L) and fed with diets containing 15% and 30% of toxic cyanobacteria lyophilized powder for 30 d. The microcystins concentration in different organs of Megalobrama amblycephala was in the following sequence: head kidney > liver > intestine > gonad > spleen > gill > trunk kidney > brain > muscle > heart. In both head kidney and spleen, the MC-LR and MC-RR concentration increased significantly with increasing NH₃-N concentration. It indicates that NH₃-N maybe promote the accumulation of microcystins in immune organs of Megalobrama amblycephala. Meanwhile, broadened peripheral interspace of lymphocytes, nucleus shrivel and edematous mitochondria were observed in head kidney lymphocyte of toxic treatment fish. Moreover, there were significant interactions between dietary toxic cyanobacteria and ammonia exposure on head kidney macrophage phagocytosis activity, respiratory burst activities, total number of white blood cells and the transcriptional levels of sIgM, mIgD and sIgZ genes. Our data clearly demonstrated that dietary toxic cyanobacteria combined with ammonia exposure showed a synergistic effect on Megalobrama amblycephala immunotoxicity.

Bioaccumulation of hepatotoxins - a considerable risk in the Latvian environment

The Gulf of Riga, river Daugava and several interconnected lakes around the City of Riga, Latvia, form adynamic brackish-freshwater system favouring occurrence of toxic cyanobacteria. We examined bioaccumulation of microcystins and nodularin-R in aquatic organisms in Latvian lakes, the Gulf of Riga and west coast of open Baltic Sea in 2002-2007. The freshwater unionids accumulated toxins efficiently,followed by snails. In contrast, Dreissena polymorpha and most lake fishes (except roach) accumulated much less hepatotoxins. Significant nodularin-R concentrations were detected also in marine clams and flounders. No transfer of nodularin-R and microcystins between lake and brackish water systems took place. Lake mussels can transfer hepatotoxins to higher organisms, and also effectively remove toxins from the water column. Obvious health risks to aquatic organisms and humans are discussed.