Freshwater neurotoxins and concerns for human, animal, and ecosystem health: A review of anatoxin-a and saxitoxin

A short-term exposure to saxitoxin triggers a multitude of deleterious effects in Daphnia magna at levels deemed safe for human health

Harmful algal blooms and the toxins produced during these events are a human and environmental health concern worldwide. Saxitoxin and its derivatives are potent natural aquatic neurotoxins produced by certain freshwater cyanobacteria and marine algae species during these bloom events. Saxitoxins effects on human health are well studied, however its effects on aquatic biota are still largely unexplored. This work aims at evaluating the effects of a pulse acute exposure (24 h) of the model cladoceran Daphnia magna to 30 μg saxitoxin L-1, which corresponds to the safety guideline established by the World Health Organization (WHO) for these toxins in recreational freshwaters. Saxitoxin effects were assessed through a comprehensive array of biochemical (antioxidant enzymes activity and lipid peroxidation), genotoxicity (alkaline comet assay), neurotoxicity (total cholinesterases activity), behavioral (swimming patterns), physiological (feeding rate and heart rate), and epigenetic (total 5-mC DNA methylation) biomarkers. Exposure resulted in decreased feeding rate, heart rate, total cholinesterases activity and catalase activity. Contrarily, other antioxidant enzymes, namely glutathione-S-transferases and selenium-dependent Glutathione peroxidase had their activity increased, together with lipid peroxidation levels. The enhancement of the antioxidant enzymes was not sufficient to prevent oxidative damage, as underpinned by lipid peroxidation enhancement. Accordingly, average DNA damage level was significantly increased in STX-exposed daphnids. Total DNA 5-mC level was significantly decreased in exposed organisms. Results showed that even a short-term exposure to saxitoxin causes significant effects on critical molecular and cellular pathways and modulates swimming patterns in D. magna individuals. This study highlights sub-lethal effects caused by saxitoxin in D. magna, suggesting that these toxins may represent a marked challenge to their thriving even at a concentration deemed safe for humans by the WHO.

New records on toxic cyanobacteria from Brazil: Exploring their occurrence and geography

Cyanobacterial Harmful Algal Blooms (CyanoHABs) pose a significant threat to communities globally, impacting ecosystems and public health. This study provides an in-depth review of the current state of cyanotoxins and the distribution of CyanoHABs species in Brazil, while also detailing the methods used for their detection. Four hundred and twenty-one incidents were analyzed from 1993 to 2021, compiling cyanotoxin records and toxic CyanoHABs occurrences. The investigation begins with the first detection of microcystins in 1994 and highlights pivotal moments, like the 1996 "Caruaru Syndrome" outbreak. This event encouraged research and updated cyanotoxin-monitoring guidelines. The Brazilian drought period of 2015-2016 exacerbated cyanobacterial growth and saxitoxin levels, coinciding with Zika-related microcephaly. This study delves into methods used for cyanotoxin analysis, including ELISA, bioassays, HPLC, and LC-MS. Additionally, we investigated the toxicity of 37 cyanobacterial strains isolated from various Brazilian environments. Extracts were tested against Artemia salina and analyzed by LC-MS. Results revealed toxicity in extracts from 49 % of cyanobacterial strains. LC-MS results were analyzed using GNPS MS/MS molecular networking for comparing experimental spectra with those of cyanotoxin standards against in-house databases and the existing literature. Our research underscores the variability in cyanotoxin production among species and over time, extending beyond microcystins. LC-MS results, interpreted through the GNPS platform, revealed six cyanotoxin groups in Brazilian strains. Yet, compounds present in 75 % of the toxic extracts remained unidentified. Further research is crucial for fully comprehending the impact of potentially harmful organisms on water quality and public health management strategies. The study highlights the urgent need for continuously monitoring cyanobacteria and the cyanotoxin inclusion of management in public health policies.

Development of a Multiplexed Electrochemical Aptasensor for the Detection of Cyanotoxins

In this study, we report a multiplexed platform for the simultaneous determination of five marine toxins. The proposed biosensor is based on a disposable electrical printed (DEP) microarray composed of eight individually addressable carbon electrodes. The electrodeposition of gold nanoparticles on the carbon surface offers high conductivity and enlarges the electroactive area. The immobilization of thiolated aptamers on the AuNP-decorated carbon electrodes provides a stable, well-orientated and organized binary self-assembled monolayer for sensitive and accurate detection. A simple electrochemical multiplexed aptasensor based on AuNPs was designed to synchronously detect multiple cyanotoxins, namely, microcystin-LR (MC-LR), Cylindrospermopsin (CYL), anatoxin-α, saxitoxin and okadaic acid (OA). The choice of the five toxins was based on their widespread presence and toxicity to aquatic ecosystems and humans. Taking advantage of the conformational change of the aptamers upon target binding, cyanotoxin detection was achieved by monitoring the resulting electron transfer increase by square-wave voltammetry. Under the optimal conditions, the linear range of the proposed aptasensor was estimated to be from 0.018 nM to 200 nM for all the toxins, except for MC-LR where detection was possible within the range of 0.073 to 150 nM. Excellent sensitivity was achieved with the limits of detection of 0.0033, 0.0045, 0.0034, 0.0053 and 0.0048 nM for MC-LR, CYL, anatoxin-α, saxitoxin and OA, respectively. Selectivity studies were performed to show the absence of cross-reactivity between the five analytes. Finally, the application of the multiplexed aptasensor to tap water samples revealed very good agreement with the calibration curves obtained in buffer. This simple and accurate multiplexed platform could open the window for the simultaneous detection of multiple pollutants in different matrices.

Cyanobacteria and Macroinvertebrate Relationships in Freshwater Benthic Communities beyond Cytotoxicity

Cyanobacteria are harmful algae that are monitored worldwide to prevent the effects of the toxins that they can produce. Most research efforts have focused on direct or indirect effects on human populations, with a view to gain easy accurate detection and quantification methods, mainly in planktic communities, but with increasing interest shown in benthos. However, cyanobacteria have played a fundamental role from the very beginning in both the development of our planet's biodiversity and the construction of new habitats. These organisms have colonized almost every possible planktic or benthic environment on earth, including the most extreme ones, and display a vast number of adaptations. All this explains why they are the most important or the only phototrophs in some habitats. The negative effects of cyanotoxins on macroinvertebrates have been demonstrated, but usually under conditions that are far from natural, and on forms of exposure, toxin concentration, or composition. The cohabitation of cyanobacteria with most invertebrate groups is long-standing and has probably contributed to the development of detoxification means, which would explain the survival of some species inside cyanobacteria colonies. This review focuses on benthic cyanobacteria, their capacity to produce several types of toxins, and their relationships with benthic macroinvertebrates beyond toxicity.

Blue Green Algae

Blue green algae cyanotoxins have become increasingly more prevalent due to environmental, industrial, and agricultural changes that promote their growth into harmful algal blooms. Animals are usually exposed via water used for drinking or bathing, though specific cases related to equines are very limited. The toxic dose for horses has not been determined, and currently only experimental data in other animals can be relied upon to aid in case interpretation and treatment. Treatment is mostly limited to supportive care, and preventative control methods to limit exposures are more likely to aid in animal health until more research has been performed.

Unveiling the link between Raphidiopsis raciborskii blooms and saxitoxin levels: Evaluating water quality in tropical reservoirs, Brazil

The proliferation of Raphidiopsis raciborskii blooms has sparked concerns regarding potential human exposure to heightened saxitoxins (STXs) levels. Thus, comprehending how environmental elements drive the proliferation of this STXs-producing species can aid in predicting human exposure risks. This study aimed to explore the link between cyanobacteria R. raciborskii, STXs cyanotoxins, and environmental factors in 37 public supply reservoirs in the tropical region and assess potential health hazards these toxins pose in the reservoir waters. A Structural Equation Model was used to assess the impact of environmental factors (water volume and physical and chemical variables) on R. raciborskii biomass and STXs levels. Furthermore, the potential risk of STXs exposure from consuming untreated reservoir water was evaluated. Lastly, the cumulative distribution function (CDF) of STXs across the reservoirs was computed. Our findings revealed a correlation between R. raciborskii biomass and STXs concentrations. Total phosphorus emerged as a critical environmental factor positively influencing species biomass and indirectly affecting STXs levels. pH significantly influenced STXs concentrations, indicating different factors influencing R. raciborskii biomass and STXs. Significantly, for the first time, the risk of STXs exposure was gauged using the risk quotient (HQ) for untreated water consumption from public supply reservoirs in Brazil's semi-arid region. Although the exposure risks were generally low to moderate, the CDF underscored the risk of chronic exposure due to low toxin concentrations in over 90% of samples. These outcomes emphasize the potential expansion of R. raciborskii in tropical settings due to increased phosphorus, amplifying waterborne STXs levels and associated intoxication risks. Thus, this study reinforces the importance of nutrient control, particularly phosphorus regulation, as a mitigation strategy against R. raciborskii blooms and reducing STXs intoxication hazards.

A fast and reliable LC-MS-MS method for the quantification of saxitoxin in blood plasma samples

Saxitoxins (STXs) are potent neurotoxins produced by marine dinoflagellates or freshwater cyanobacteria known to cause acute and eventually fatal human intoxications, which are classified as paralytic shellfish poisonings (PSPs). Rapid analysis of STXs in blood plasma can be used for a timely diagnosis and confirmation of PSPs. We developed a fast and simple method of STX extraction based on plasma sample acidification and precipitation by acetonitrile, followed by quantification using liquid chromatography-tandem mass spectrometry (LC-MS-MS). Our approach provides the results ≤30 min, with a limit of detection of 2.8 ng/mL and a lower limit of quantification of 5.0 ng/mL. Within-run and between-run precision experiments showed good reproducibility with ≤15% values. Standard curves for calibration were linear with correlation coefficients ≥0.98 across the assay calibration range (5-200 ng/mL). In an interlaboratory analytical exercise, the method was found to be 100% accurate in determining the presence or absence of STX in human plasma specimens, with recovery values of 86-99%. This simple method for STX determination in animal or human plasma can quickly and reliably diagnose STX exposures and confirm suspected PSP cases to facilitate patient treatment or expedite necessary public health or security actions.

What, How, When, and Where: Spatiotemporal Water Quality Hazards of Cyanotoxins in Subtropical Eutrophic Reservoirs

Though toxins produced during harmful blooms of cyanobacteria present diverse risks to public health and the environment, surface water quality surveillance of cyanobacterial toxins is inconsistent, spatiotemporally limited, and routinely relies on ELISA kits to estimate total microcystins (MCs) in surface waters. Here, we employed liquid chromatography tandem mass spectrometry to examine common cyanotoxins, including five microcystins, three anatoxins, nodularin, cylindrospermopsin, and saxitoxin in 20 subtropical reservoirs spatially distributed across a pronounced annual rainfall gradient. Probabilistic environmental hazard analyses identified whether water quality values for cyanotoxins were exceeded and if these exceedances varied spatiotemporally. MC-LR was the most common congener detected, but it was not consistently observed with other toxins, including MC-YR, which was detected at the highest concentrations during spring with many observations above the California human recreation guideline (800 ng/L). Cylindrospermopsin was also quantitated in 40% of eutrophic reservoirs; these detections did not exceed a US Environmental Protection Agency swimming/advisory level (15,000 ng/L). Our observations have implications for routine water quality monitoring practices, which traditionally use ELISA kits to estimate MC levels and often limit collection of surface samples during summer months near reservoir impoundments, and further indicate that spatiotemporal surveillance efforts are necessary to understand cyanotoxins risks when harmful cyanobacteria blooms occur throughout the year.

Sustainable bioremediation technologies for algal toxins and their ecological significance

The emergence of algal toxins in water ecosystems poses a significant ecological and human health concern. These toxins, produced by various algal species, can lead to harmful algal blooms, and have far-reaching consequences on biodiversity, food chains, and water quality. This review explores the types and sources of algal toxins, their ecological impacts, and the associated human health risks. Additionally, the review delves into the potential of bioremediation strategies to mitigate the effects of algal toxins. It discusses the role of microorganisms, enzymes, and algal-bacterial interactions in toxin removal, along with engineering approaches such as advanced oxidation processes and adsorbent utilization. Microbes and enzymes have been studied for their environmentally friendly and biocompatible properties, which make them useful for controlling or removing harmful algae and their toxins. The challenges and limitations of bioremediation are examined, along with case studies highlighting successful toxin control efforts. Finally, the review outlines future prospects, emerging technologies, and the need for continued research to effectively address the complex issue of algal toxins and their ecological significance.

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.

Harmful and beneficial properties of cyanotoxins: Two sides of the same coin

Cyanotoxins are by definition "harmful agents" produced by cyanobacteria. Their toxicity has been extensively studied and reviewed over the years. Cyanotoxins have been commonly classified, based on their poisonous effects on mammals, into three main classes, neurotoxins, hepatotoxins and dermatotoxins, and, considering their chemical features, mainly identified as peptides, alkaloids and lipopolysaccharides. Here we propose a broader subdivision of cyanotoxins into eight distinct classes, taking into account their molecular structures, biosynthesis and modes of action: alkaloids, non-ribosomal peptides, polyketides, non-protein amino acids, indole alkaloids, organophosphates, lipopeptides and lipoglycans. For each class, the structures and primary mechanisms of toxicity of the main representative cyanotoxins are reported. Despite their powerful biological activities, only recently scientists have considered the biotechnological potential of cyanotoxins, and their applications both in medical and in industrial settings, even if only a few of these have reached the biotech market. In this perspective, we discuss the potential uses of cyanotoxins as anticancer, antimicrobial, and biocidal agents, as common applications for cytotoxic compounds. Furthermore, taking into account their mechanisms of action, we describe peculiar potential bioactivities for several cyanotoxin classes, such as local anaesthetics, antithrombotics, neuroplasticity promoters, immunomodulating and antifouling agents. In this review, we aim to stimulate research on the potential beneficial roles of cyanotoxins, which require interdisciplinary cooperation to facilitate the discovery of innovative biotechnologies.

Recent Advances in Cyanotoxin Synthesis and Applications: A Comprehensive Review

Over the past few decades, nearly 300 known cyanotoxins and more than 2000 cyanobacterial secondary metabolites have been reported from the environment. Traditional studies have focused on the toxic cyanotoxins produced by harmful cyanobacteria, which pose a risk to both human beings and wildlife, causing acute and chronic poisoning, resulting in diarrhea, nerve paralysis, and proliferation of cancer cells. Actually, the biotechnological potential of cyanotoxins is underestimated, as increasing studies have demonstrated their roles as valuable products, including allelopathic agents, insecticides and biomedicines. To promote a comprehensive understanding of cyanotoxins, a critical review is in demand. This review aims to discuss the classifications; biosynthetic pathways, especially heterogenous production; and potential applications of cyanotoxins. In detail, we first discuss the representative cyanotoxins and their toxic effects, followed by an exploration of three representative biosynthetic pathways (non-ribosomal peptide synthetases, polyketide synthetases, and their combinations). In particular, advances toward the heterologous biosynthesis of cyanotoxins in vitro and in vivo are summarized and compared. Finally, we indicate the potential applications and solutions to bottlenecks for cyanotoxins. We believe that this review will promote a comprehensive understanding, synthetic biology studies, and potential applications of cyanotoxins in the future.

Present and future potential role of toxin-producing Synechococcus in the tropical region

As anthropogenic induced temperature rises and nutrient loadings increase in fresh and brackish environments, the ecological function of the phytoplankton community is expected to favour the picocyanobacteria, of the genus Synechococcus. Synechococcus is already a ubiquitous cyanobacterium found in both freshwater and marine environments, notwithstanding that the toxigenic species still remains unexplored in many freshwaters. Their fast growth rate and their ability to produce toxins make Synechococcus a potential dominant player in harmful algal blooms under climate change scenarios. This study examines the responses of a novel toxin-producing Synechococcus (i.e., one belonging to a freshwater clade; the other belonging to a brackish clade) to environmental changes that reflect climate change effects. We conducted a series of controlled experiments under present and predicted future temperatures, as well as under various N and P nutrients loadings. Our findings highlight how Synechococcus can be altered by the differing reactions to increasing temperature and nutrients, which resulted in considerable variations in cell abundance, growth rate, death rate, cellular stoichiometry and toxin production. Synechococcus had the highest growth observed at 28 °C, and further increases in temperature resulted in a decline for both fresh and brackish waters. Cellular stoichiometry was also altered, where more nitrogen (N) per cell was required, and the plasticity of N:P was more severe for the brackish clade. However, Synechococcus become more toxic under future scenario. Anatoxin-a (ATX) saw the greatest spike when temperature was at 34 °C especially under P-enrichment conditions. In contrast, Cylindrospermopsin (CYN) was promoted at the lowest tested temperature (25 °C) and under N-limitation. Overall, both temperature and external nutrients are the dominant control over Synechococcus toxins production. A model was also created to assess Synechococcus toxicity to zooplankton grazing. Zooplankton grazing was reduced by two folds under nutrient limitation, but temperature accounted for very insignificant change.

A rapid LC-MS/MS method for multi-class identification and quantification of cyanotoxins

Cyanobacteria can form harmful blooms in specific environmental conditions due to certain species producing toxic metabolites known as cyanotoxins. These toxins pose significant risks to public health and the environment, making it critical to identify and quantify them in food and water sources to avoid contamination. However, current screening methods only focus on a single class of cyanotoxins, limiting their effectiveness. Thus, fast and sensitive liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was developed to analyze eighteen cyanotoxins simultaneously. A simplified extraction procedure using lyophilized samples of cyanobacterial biomass was also used, eliminating the need for traditional solid-phase extraction methods. This method uses multiple reaction monitoring and allows accurate determination and quantification of eighteen cyanotoxins, including anatoxin-a, homoanatoxin-a, cylindrospermopsin, deoxy-cylindrospermopsin, nodularin, guanitoxin, seven microcystins (RR, [D-Asp3] RR, LA, LR, LY, LW, and YR), and five saxitoxins (gonyautoxins - GTX-1&4, GTX-2&3, GTX-5), decarbamoylgonyautoxin (dcGTX-2&3), and N-Sulfocarbamoylgonyautoxin (C1&C2), all in a short acquisition time of 8 min. Therefore, this method provides a simple and efficient approach to identify and quantify harmful compounds produced by cyanobacteria. Hence, this represents the first method to detecting guanitoxin among cyanotoxins. By expanding the range of toxins analyzed, this method can help ensure high-quality food and drinking water and protect recreational users from exposure to cyanotoxins.

Understanding the Risks of Diffusion of Cyanobacteria Toxins in Rivers, Lakes, and Potable Water

Blue-green algae, or cyanobacteria, may be prevalent in our rivers and tap water. These minuscule bacteria can grow swiftly and form blooms in warm, nutrient-rich water. Toxins produced by cyanobacteria can pollute rivers and streams and harm the liver and nervous system in humans. This review highlights the properties of 25 toxin types produced by 12 different cyanobacteria genera. The review also covered strategies for reducing and controlling cyanobacteria issues. These include using physical or chemical treatments, cutting back on fertilizer input, algal lawn scrubbers, and antagonistic microorganisms for biocontrol. Micro-, nano- and ultrafiltration techniques could be used for the removal of internal and extracellular cyanotoxins, in addition to powdered or granular activated carbon, ozonation, sedimentation, ultraviolet radiation, potassium permanganate, free chlorine, and pre-treatment oxidation techniques. The efficiency of treatment techniques for removing intracellular and extracellular cyanotoxins is also demonstrated. These approaches aim to lessen the risks of cyanobacterial blooms and associated toxins. Effective management of cyanobacteria in water systems depends on early detection and quick action. Cyanobacteria cells and their toxins can be detected using microscopy, molecular methods, chromatography, and spectroscopy. Understanding the causes of blooms and the many ways for their detection and elimination will help the management of this crucial environmental issue.

Transformation of Algal Toxins during the Oxidation/Disinfection Processes of Drinking Water: From Structure to Toxicity

With the increase of algal blooms worldwide, drinking water resources are threatened by the release of various algal toxins, which can be hepatotoxic, cytotoxic, or neurotoxic. Because of their ubiquitous occurrence in global waters and incomplete removal in conventional drinking water treatment, oxidation/disinfection processes have become promising alternative treatment options to destroy both the structures and toxicity of algal toxins. This Review first summarizes the occurrence and regulation of algal toxins in source water and drinking water. Then, the transformation kinetics, disinfection byproducts (DBPs)/transformation products (TPs), pathways, and toxicity of algal toxins in water oxidation/disinfection processes, including treatment by ozonation, chlorination, chloramination, ultraviolet-based advanced oxidation process, and permanganate, are reviewed. For most algal toxins, hydroxyl radicals (HO•) exhibit the highest oxidation rate, followed by ozone and free chlorine. Under practical applications, ozone and chlorine can degrade most algal toxins to meet water quality standards. However, the transformation of the parent structures of algal toxins by oxidation/disinfection processes does not guarantee a reduction in toxicity, and the formation of toxic TPs should also be considered, especially during chlorination. Notably, the toxicity variation of algal toxins is associated with the chemical moiety responsible for toxicity (e.g., Adda moiety in microcystin-LR and uracil moiety in cylindrospermopsin). Moreover, the formation of known halogenated DBPs after chlorination indicates that toxicity in drinking water may shift from toxicity contributed by algal toxins to toxicity contributed by DBPs. To achieve the simultaneous toxicity reduction of algal toxins and their TPs, optimized oxidation/disinfection processes are warranted in future research, not only for meeting water quality standards but also for effective reduction of toxicity of algal toxins.

Novel CRISPR/Cas technology in the realm of algal bloom biomonitoring: Recent trends and future perspectives

In conjunction with global climate change, progressive ocean warming, and acclivity in pollution and anthropogenic eutrophication, the incidence of harmful algal blooms (HABs) and cyanobacterial harmful algal blooms (CHABs) continue to expand in distribution, frequency, and magnitude. Algal bloom-related toxins have been implicated in human health disorders and ecological dysfunction and are detrimental to the national and global economy. Biomonitoring programs based on traditional monitoring protocols were characterised by some limitations that can be efficiently overdone using the CRISPR/Cas technology. In the present review, the potential and challenges of exploiting the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas technology for early detection of HABs and CHABs-associated toxigenic species were analysed. Based on more than 30 scientific papers, the main results indicate the great potential of CRISPR/Cas technology for this issue, even if the high sensitivity detected for the Cas12 and Cas13 platforms represents a possible interference risk.

Saxitoxin-Producing Raphidiopsis raciborskii (Cyanobacteria) Constrains Daphnia Fitness and Feeding Rate despite High Nutritious Food Availability

Changes in food quality can dramatically impair zooplankton fitness, especially in eutrophic water bodies where cyanobacteria are usually predominant. Cyanobacteria are considered a food with low nutritional value, and some species can produce bioactive secondary metabolites reported as toxic to zooplankton. Considering that cyanobacteria can limit the survival, growth and reproduction of zooplankton, we hypothesized that the dietary exposure of neotropical Daphnia species (D. laevis and D. gessneri) to saxitoxin-producing cyanobacteria impairs Daphnia feeding rates and fitness regardless of a high availability of nutritious algae. Life table and grazing assays were conducted with different diets: (1) without nutritional restriction, where neonates were fed with diets at a constant green algae biomass (as a nutritious food source), and an increasing cyanobacterial concentration (toxic and poor food source), and (2) with diets consisting of different proportions of green algae (nutritious) and cyanobacteria (poor food) at a total biomass 1.0 mg C L-1. In general, the presence of high proportions of cyanobacteria promoted a decrease in Daphnia somatic growth, reproduction and the intrinsic rate of population increase (r) in both diets with more pronounced effects in the nutritionally restricted diet (90% R. raciborskii). A two-way ANOVA revealed the significant effects of species/clone and treatments in both assays, with significant interaction between those factors only in the second assay. Regarding the grazing assay, only D. laevis was negatively affected by increased cyanobacterial proportions in the diet. In the life table assay with constant nutritious food, a reduction in the reproduction and the intrinsic rate of the population increase (r) of all species were observed. In conclusion, we found adverse effects of the toxic cyanobacterial strain R. raciborskii on Daphnia fitness, regardless of the constant amount of nutritious food available, proving the toxic effect of R. raciborskii and that the nutritional quality of the food has a greater influence on the fitness of these animals.

Occurrence, Distribution and Toxins of Benthic Cyanobacteria in German Lakes

Cyanobacteria are favored by climate change and global warming; however, to date, most research and monitoring programs have focused on planktic cyanobacteria. Benthic cyanobacteria blooms also increase and pose a risk to animal and human health; however, there is limited knowledge of their occurrence, distribution and the toxins involved, especially in relation to their planktic conspecifics. Therefore, we analyzed the benthic and planktic life forms of cyanobacterial communities in 34 lakes in Germany, including a monitoring of cyanotoxins. Community analyses were based on microscopic examination and Illumina sequencing of the 16S rRNA gene. The analyses of cyanotoxins were carried out using LC-MS/MS and ELISA. Observed benthic mats containing cyanobacteria consisted mainly of Nostocales and Oscillatoriales, being present in 35% of the lakes. Anatoxin was the most abundant cyanotoxin in the benthic samples, reaching maximum concentrations of 45,000 µg/L, whereas microcystin was the predominate cyanotoxin in the open-water samples, reaching concentrations of up to 18,000 µg/L. Based on the results, specific lakes at risk of toxic cyanobacteria could be identified. Our findings suggest that monitoring of benthic cyanobacteria and their toxins should receive greater attention, ideally complementing existing open-water sampling programs with little additional effort.

In Vitro Mutagenic and Genotoxic Assessment of Anatoxin-a Alone and in Combination with Cylindrospermopsin

Anatoxin-a (ATX-a) is a cyanobacterial toxin whose occurrence has been reported worldwide and has attracted increasing scientific interest due to its toxicity. Moreover, in nature, ATX-a usually appears together with other cyanotoxins, such as cylindrospermopsin (CYN), so possible interaction phenomena could happen and should be considered for risk assessment purposes. For this reason, the aim of this work was to explore the potential mutagenicity and genotoxicity of pure ATX-a and an ATX-a/CYN mixture using a battery of in vitro assays, including the bacterial reverse-mutation assay in Salmonella typhimurium (OECD 471) and the micronucleus test (MN) (OECD 487) on L5178Y Tk+/- cells. The results showed that ATX-a was not mutagenic either alone or in combination with CYN under the conditions tested. Nevertheless, genotoxic effects were observed for both ATX-a and its mixture with CYN following the in vitro MN assay. The genotoxicity exhibited by ATX-a was only observed in the absence of S9 mix, whereas in the cyanotoxin mixture the concentration-dependent genotoxicity of ATX-a/CYN in vitro was observed only in the presence of S9. Thus, the toxicity induced by cyanotoxin mixtures may vary from that produced by toxins alone, and consequently more studies are necessary in order to perform more realistic risk assessments.

Cyanotoxins, biosynthetic gene clusters, and factors modulating cyanotoxin biosynthesis

Cyanobacterial harmful algal blooms (CHABs) are a global environmental concern that encompasses public health issues, water availability, and water quality owing to the production of various secondary metabolites (SMs), including cyanotoxins in freshwater, brackish water, and marine ecosystems. The frequency, extent, magnitude, and duration of CHABs are increasing globally. Cyanobacterial species traits and changing environmental conditions, including anthropogenic pressure, eutrophication, and global climate change, together allow cyanobacteria to thrive. The cyanotoxins include a diverse range of low molecular weight compounds with varying biochemical properties and modes of action. With the application of modern molecular biology techniques, many important aspects of cyanobacteria are being elucidated, including aspects of their diversity, gene-environment interactions, and genes that express cyanotoxins. The toxicological, environmental, and economic impacts of CHABs strongly advocate the need for continuing, extensive efforts to monitor cyanobacterial growth and to understand the mechanisms regulating species composition and cyanotoxin biosynthesis. In this review, we critically examined the genomic organization of some cyanobacterial species that lead to the production of cyanotoxins and their characteristic properties discovered to date.

A carboxyl-functionalized covalent organic polymer for the efficient adsorption of saxitoxin

Saxitoxin (STX), the most widely distributed neurotoxin in marine waters and emerging cyanotoxin of concern in freshwaters, causes paralytic shellfish poisoning in humans upon consumption of contaminated shellfish. To allow for the efficient monitoring of this biotoxin, it is of high importance to find high-affinity materials for its adsorption. Herein, we report the design and synthesis of a covalent organic polymer for the efficient adsorption of STX. Two β-keto-enamine-based materials were prepared by self-assembly of 2,4,6-triformylphloroglucinol (Tp) with 2,5-diaminobenzoic acid (Pa-COOH) to give TpPa-COOH and with 2,5-diaminotoluene (Pa-CH₃) to give TpPa-CH₃. The carboxylic acid functionalized TpPa-COOH outperformed the methyl-bearing counterpart TpPa-CH₃ by an order of magnitude despite the higher long-range order and surface area of the latter. The adsorption of STX by TpPa-COOH was fast with equilibrium reached within 1 h, and the Langmuir adsorption model gave a calculated maximum adsorption capacity, Q_m, of 5.69 mg g^-1, making this material the best reported adsorbent for this toxin. More importantly, the prepared TpPa-COOH also showed good reusability and high recovery rates for STX in natural freshwater, thereby highlighting the material as a good candidate for the extraction and pre-concentration of STX from aquatic environments.

Removal of saxitoxin and anatoxin-a by PAC in the presence and absence of microcystin-LR and/or cyanobacterial cells

Cyanobacteria can produce cyanotoxins such as microcystin-LR (MC), saxitoxin (STX), and anatoxin-a (ANTX-a) which are harmful to humans and other animals. Individual removal efficiencies of STX and ANTX-a by powdered activated carbon (PAC) was investigated, as well as when MC-LR and cyanobacteria were present. Experiments were conducted with distilled water and then source water, using the PAC dosages, rapid mix/flocculation mixing intensities and contact times of two drinking water treatment plants in northeast Ohio. At pH 8 and 9, STX removal was 47%-81% in distilled water and 46%-79% in source water, whereas it was 0-28% for pH 6 in distilled water and 31%-52% in source water. When 1.6 µg/L or 20 µg/L MC-LR was present with STX, STX removal was increased with PAC simultaneously removing 45%-65% of the 1.6 µg/L MC-LR and 25%-95% of the 20 µg/L MC-LR depending on the pH. ANTX-a removal at pH 6 was 29%-37% for distilled water and 80% for source water, whereas it was 10%-26% for pH 8 in distilled water and 28% for pH 9 in source water. The presence of cyanobacteria cells decreased ANTX-a removal by at least 18%. When 20 µg/L MC-LR was present with ANTX-a in source water, 59%-73% ANTX-a and 48%-77% of MC-LR was removed at pH 9 depending on the PAC dose. In general, a higher PAC dose led to higher cyanotoxin removals. This study also documented that multiple cyanotoxins can be effectively removed by PAC for water at pH's between 6 and 9.

Design, synthesis and mechanism research of novel algicide based on bioactive fragments synthesis strategy

The frequency and intensity of harmful cyanobacterial blooms (HCBs) are increasing all over the world, their prevention and control have become a great challenge. In this paper, a series of 1,3,4-thiadiazole thioacetamides (T series) were designed and synthesized as potential algaecides. Among them, the compound T3 showed its best algacidal activity against Synechocystis sp. PCC 6803 (PCC 6803, EC₅₀ = 1.51 μM) and Microcystis aeruginosa FACHB 905 (FACHB905, EC₅₀ = 4.88 μM), which was more effective than the lead compound L1 (PCC6803, EC₅₀ = 7.7 μM; FACHB905, EC₅₀ = 8.8 μM) and the commercially available herbicide prometryn (PCC6803, EC₅₀ = 4.64 μM；FACHB905, EC₅₀ = 6.52 μM). Meanwhile, T3 showed a lower inhibitory activity (EC₅₀ = 12.76 μM) than prometryn (EC₅₀ = 7.98 μM) to Chlorella FACHB1227, indicating that T3 had selective inhibition to prokaryotic algae (PCC6803, FACHB905) and eukaryotic algae (FACHB1227). Furthermore, the algacidal and anti-algae activities of T3 were significantly better than those of prometryn, while the toxicity of zebrafish and human cells was less than prometryn. Electron microscope, physiological, biochemical and metabonomic analysis showed that T3 interfered with light absorption and light conversion during photosynthesis by significantly reducing chlorophyll content, thus inhibited metabolic pathways such as the Calvin cycle and TCA cycle, and eventually led to the cell rupture of cyanobacteria. These results afforded further development of effective and safe algaecides.

Freshwater Cyanobacterial Toxins, Cyanopeptides and Neurodegenerative Diseases

Cyanobacteria produce a wide range of structurally diverse cyanotoxins and bioactive cyanopeptides in freshwater, marine, and terrestrial ecosystems. The health significance of these metabolites, which include genotoxic- and neurotoxic agents, is confirmed by continued associations between the occurrence of animal and human acute toxic events and, in the long term, by associations between cyanobacteria and neurodegenerative diseases. Major mechanisms related to the neurotoxicity of cyanobacteria compounds include (1) blocking of key proteins and channels; (2) inhibition of essential enzymes in mammalian cells such as protein phosphatases and phosphoprotein phosphatases as well as new molecular targets such as toll-like receptors 4 and 8. One of the widely discussed implicated mechanisms includes a misincorporation of cyanobacterial non-proteogenic amino acids. Recent research provides evidence that non-proteinogenic amino acid BMAA produced by cyanobacteria have multiple effects on translation process and bypasses the proof-reading ability of the aminoacyl-tRNA-synthetase. Aberrant proteins generated by non-canonical translation may be a factor in neuronal death and neurodegeneration. We hypothesize that the production of cyanopeptides and non-canonical amino acids is a more general mechanism, leading to mistranslation, affecting protein homeostasis, and targeting mitochondria in eukaryotic cells. It can be evolutionarily ancient and initially developed to control phytoplankton communities during algal blooms. Outcompeting gut symbiotic microorganisms may lead to dysbiosis, increased gut permeability, a shift in blood-brain-barrier functionality, and eventually, mitochondrial dysfunction in high-energy demanding neurons. A better understanding of the interaction between cyanopeptides metabolism and the nervous system will be crucial to target or to prevent neurodegenerative diseases.

Cyanotoxins associated with macrophytes in Berlin (Germany) water bodies - Occurrence and risk assessment

Fatal dog poisoning after uptake of neurotoxic cyanobacteria associated with aquatic macrophytes in Tegeler See (Berlin, Germany) raised concerns about critical exposure of humans, especially children, to cyanotoxins produced by macrophyte associated cyanobacteria during recreational activity. From 2017 to 2021 a total of 398 samples of macrophytes washed ashore at bathing sites located at 19 Berlin lakes were analysed for anatoxins, microcystins, and cylindrospermopsins, as were 463 water samples taken in direct proximity to macrophyte accumulations. Cyanotoxins were detected in 66 % of macrophyte samples and 50 % of water samples, with anatoxins being the most frequently detected toxin group in macrophyte samples (58 %) and cylindrospermopsins in water samples (41 %). Microcoleus sp. associated with the water moss Fontinalis antipyretica was identified as anatoxin producing cyanobacterium in isolated strains as well as in field samples from Tegeler See. Anatoxin contents in macrophyte samples rarely exceeded 1 μg/g macrophyte fresh weight and peaked at 9. 2 μg/g f.w. Based on established toxicological points of departure, a critical anatoxin content of macrophyte samples of 3 μg/g f.w. is proposed. Five samples, all taken in Tegeler See and all associated with the water moss Fontinalis antipyretica, exceeded this value. Contents and concentrations of microcystins and cylindrospermopsins did not reach critical levels. The potential exposure risks to anatoxins for children and dogs are assessed and recommendations are given.

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 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.

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.

Toxic Effects Produced by Anatoxin-a under Laboratory Conditions: A Review

The presence of cyanotoxins and its bioaccumulation in the food chain is an increasingly common problem worldwide. Despite the toxic effects produced by Anatoxin-a (ATX-a), this neurotoxin has been less studied compared to microcystins (MCs) and cylindrospermopsin (CYN). Studies conducted under laboratory conditions are of particular interest because these provide information which are directly related to the effects produced by the toxin. Currently, the World Health Organization (WHO) considers the ATX-a toxicological database inadequate to support the publication of a formal guideline reference value. Therefore, the aim of the present work is to compile all of the in vitro and in vivo toxicological studies performed so far and to identify potential data gaps. Results show that the number of reports is increasing in recent years. However, more in vitro studies are needed, mainly in standardized neuronal cell lines. Regarding in vivo studies, very few of them reflect conditions occurring in nature and further studies with longer periods of oral exposure would be of interest. Moreover, additional toxicological aspects of great interest such as mutagenicity, genotoxicity, immunotoxicity and alteration of hormonal balance need to be studied in depth.

Molecularly imprinted polymers for environmental adsorption applications

Molecular imprinting polymers (MIPs) are synthetic materials with pores or cavities to specifically retain a molecule of interest or analyte. Their synthesis consists of the generation of three-dimensional polymers with specific shapes, arrangements, orientations, and bonds to selectively retain a particular molecule called target. After target removal from the binding sites, it leaves empty cavities to be re-occupied by the analyte or a highly related compound. MIPs have been used in areas that require high selectivity (e.g., chromatographic methods, sensors, and contaminant removal). However, the most widely used application is their use as a highly selective extraction material because of its low cost, easy preparation, reversible adsorption and desorption, and thermal, mechanical, and chemical stability. Emerging pollutants are traces of substances recently found in wastewater, river waters, and drinking water samples that represent a special concern for human and ecological health. The low concentration in which these pollutants is found in the environment, and the complexity of their chemical structures makes the current wastewater treatment not efficient for complete degradation. Moreover, these substances are not yet regulated or controlled for their discharge into the environment. According to the literature, MIPs, as a highly selective adsorbent material, are a promising approach for the quantification and monitoring of emerging pollutants in complex matrices. Therefore, the main objective of this work was to give an overview of the actual state-of-art of applications of MIPs in the recovery and concentration of emerging pollutants.

Transcriptional and toxic responses to saxitoxin exposure in the marine copepod Tigriopus japonicus

Saxitoxin (STX) is a highly toxic marine neurotoxin produced by phytoplankton and a growing threat to ecosystems worldwide due to the spread of toxic algae. Although STX is an established sodium channel blocker, the overall profile of transcriptional levels in STX-exposed organisms has yet to be described. Here, we describe a toxicity assay and transcriptome analysis of the copepod Tigriopus japonicus exposed to STX. The half-maximal lethal concentration of STX was 12.35 μM, and a rapid mortality slope was evident at concentrations between 12 and 13 μM. STX induced changes in swimming behavior among the copepods after 10 min of exposure. In transcriptome analysis, gene ontology revealed that the genes involved in nervous system and gene expression were highly enriched. In addition, the congenital neurological disorder and nuclear factor erythroid 2-related factor 2-mediated oxidative stress pathways were identified to be the most significant in network analysis and toxicity pathway analysis, respectively. This study provides valuable information about the effects of STX and related transcriptional responses in T. japonicus.

Review of harmful algal bloom effects on birds with implications for avian wildlife in the Chesapeake Bay region

The Chesapeake Bay, along the mid-Atlantic coast of North America, is the largest estuary in the United States and provides critical habitat for wildlife. In contrast to point and non-point source release of pesticides, metals, and industrial, personal care and household use chemicals on biota in this watershed, there has only been scant attention to potential exposure and effects of algal toxins on wildlife in the Chesapeake Bay region. As background, we first review the scientific literature on algal toxins and harmful algal bloom (HAB) events in various regions of the world that principally affected birds, and to a lesser degree other wildlife. To examine the situation for the Chesapeake, we compiled information from government reports and databases summarizing wildlife mortality events for 2000 through 2020 that were associated with potentially toxic algae and HAB events. Summary findings indicate that there have been few wildlife mortality incidents definitively linked to HABs, other mortality events that were suspected to be related to HABs, and more instances in which HABs may have indirectly contributed to or occurred coincident with wildlife mortality. The dominant toxins found in the Chesapeake Bay drainage that could potentially affect wildlife are microcystins, with concentrations in water approaching or exceeding human-based thresholds for ceasing recreational use and drinking water at a number of locations. As an increasing trend in HAB events in the U.S. and in the Chesapeake Bay have been reported, additional information on HAB toxin exposure routes, comparative sensitivity among species, consequences of sublethal exposure, and better diagnostic and risk criteria would greatly assist in predicting algal toxin hazard and risks to wildlife.

Elevated CO2 significantly increases N2 fixation, growth rates, and alters microcystin, anatoxin, and saxitoxin cell quotas in strains of the bloom-forming cyanobacteria, Dolichospermum

The effect of rising CO₂ levels on cyanobacterial harmful algal blooms (CHABs) is an emerging concern, particularly within eutrophic ecosystems. While elevated pCO₂ has been associated with enhanced growth rates of some cyanobacteria, few studies have explored the effect of CO₂ and nitrogen availability on diazotrophic (N₂-fixing) cyanobacteria that produce cyanotoxins. Here, the effects of elevated CO₂ and fixed nitrogen (NO₃^-) availability on the growth rates, toxin production, and N₂ fixation of microcystin, saxitoxin, and anatoxin-a - producing strains of the genus Dolichospermum were quantified. Growth rates of all Dolichospermum spp. were significantly increased by CO₂ or both CO₂ and NO₃^- with rates being highest in treatments with the highest levels of CO₂ and NO₃^-for all strains. While NO₃^- suppressed N₂ fixation, diazotrophy significantly increased when NO₃^--enriched Dolichospermum spp. were supplied with higher CO₂ compared to cultures grown under lower CO₂ levels. This suggests that diazotrophy will play an increasingly important role in N cycling in CO₂-enriched, eutrophic lentic systems. NO₃^- significantly increased quotas of the N-rich cyanotoxins, microcystin and saxitoxin, at ambient and enriched CO₂ levels, respectively. In contrast, elevated CO₂ significantly decreased cell quotas of microcystin and saxitoxin, but significantly increased cell quotas of the N-poor cyanotoxin, anatoxin. N₂ fixation was significantly negatively and positively correlated with quotas of N-rich and N-poor cyanotoxins, respectively. Findings suggest cellular quotas of N-rich toxins (microcystin and saxitoxin) may be significantly reduced, or cellular quotas of N-poor toxins (anatoxin) may be significantly enhanced, under elevated CO₂ conditions during diazotrophic cyanobacterial blooms. Finally, in the future, ecosystems that experience combinations of excessive N loading and CO₂ enrichment may become more prone to toxic blooms of Dolichospermum.

A Review of In Situ Methods-Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) for the Collection and Concentration of Marine Biotoxins and Pharmaceuticals in Environmental Waters

Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) are in situ methods that have been applied to pre-concentrate a range of marine toxins, pesticides and pharmaceutical compounds that occur at low levels in marine and environmental waters. Recent research has identified the widespread distribution of biotoxins and pharmaceuticals in environmental waters (marine, brackish and freshwater) highlighting the need for the development of effective techniques to generate accurate quantitative water system profiles. In this manuscript, we reviewed in situ methods known as Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) for the collection and concentration of marine biotoxins, freshwater cyanotoxins and pharmaceuticals in environmental waters since the 1980s to present. Twelve different adsorption substrates in SPATT and 18 different sorbents in POCIS were reviewed for their ability to absorb a range of lipophilic and hydrophilic marine biotoxins, pharmaceuticals, pesticides, antibiotics and microcystins in marine water, freshwater and wastewater. This review suggests the gaps in reported studies, outlines future research possibilities and guides researchers who wish to work on water contaminates using Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) technologies.

Cuspidothrix Is the First Genetically Proved Anatoxin A Producer in Bulgarian Lakes and Reservoirs

The paper presents the first proof of planktonic cyanoprokaryote genus Cuspidothrix as an anatoxin A (ATX) producer in Bulgarian wetlands. The results from polymerase chain reaction (PCR) obtained from two summer sampling campaigns in 26 selected lakes and reservoirs demonstrated presence of the anaC gene, responsible for ATX production in 21 strains of the genus. They were found in three waterbodies sampled in 2018 (coastal lake Vaya, coastal reservoir Poroy, inland reservoir Sinyata Reka) and in four waterbodies sampled in 2019 (inland reservoirs Duvanli, Koprinka, Plachidol 2, Sinyata Reka). The detected genetic diversity generally corresponds to the observations conducted by conventional light microscopy, by which we distinguished three species of Cuspidothrix (Cuspidothrix issatschenkoi, Cuspidothrix elenkinii and Cuspidothrix tropicalis, the latter considered alien in the country). Eleven strains showed high similarity to two sequences of C. issatschenkoi available from the National Centre for Biotechnology Information (NCBI). Ten other strains assembled in a group, which-in lack of available from NCBI genetic sequences-were presumed related to C. tropicalis and C. elenkinii after comparison with the results from light microscopy. Cuspidothrix strains found in Bulgarian waterbodies showed high genetic similarity to those isolated and sequenced from Asia (Japan, China) and Northern Europe (Norway, Finland).

Negative Effects of Cyanotoxins and Adaptative Responses of Daphnia

The plethora of cyanobacterial toxins are an enormous threat to whole ecosystems and humans. Due to eutrophication and increases in lake temperatures from global warming, changes in the distribution of cyanobacterial toxins and selection of few highly toxic species/ strains are likely. Globally, one of the most important grazers that controls cyanobacterial blooms is Daphnia, a freshwater model organism in ecology and (eco)toxicology. Daphnia-cyanobacteria interactions have been studied extensively, often focusing on the interference of filamentous cyanobacteria with Daphnia's filtering apparatus, or on different nutritional constraints (the lack of essential amino acids or lipids) and grazer toxicity. For a long time, this toxicity only referred to microcystins. Currently, the focus shifts toward other deleterious cyanotoxins. Still, less than 10% of the total scientific output deals with cyanotoxins that are not microcystins; although these other cyanotoxins can occur just as frequently and at similar concentrations as microcystins in surface water. This review discusses the effects of different cyanobacterial toxins (hepatotoxins, digestive inhibitors, neurotoxins, and cytotoxins) on Daphnia and provides an elaborate and up-to-date overview of specific responses and adaptations of Daphnia. Furthermore, scenarios of what we can expect for the future of Daphnia-cyanobacteria interactions are described by comprising anthropogenic threats that might further increase toxin stress in Daphnia.

Degradation of β-N-methylamino-l-alanine (BMAA) by UV/peracetic acid system: Influencing factors, degradation mechanism and DBP formation

β-N-methylamino-l-alanine (BMAA) is a cyanobacterial neurotoxin associated with human neurodegenerative diseases, and its removal in drinking water is receiving increasing attention. In this study, the degradation of BMAA in UV/peracetic acid (UV/PAA) system was investigated. BMAA degradation followed the pseudo-first-order kinetic model. The synergistic effect of UV and PAA exhibited a great potential for BMAA degradation, which was attributed to the generation of a large number of reactive radicals, of which R-C^• was the most dominant contributor. We also explored the effects of different factors on BMAA degradation. The results showed that there was a positive correlation between BMAA degradation and PAA dosage, and the optimal effect was achieved at pH 7. Notably, the existence of water matrices such as bicarbonate (HCO₃－), chloride ion (Cl－), humic acid (HA) and algal intracellular organic matter (IOM) all inhibited the degradation of BMAA. Based on the identified intermediates, this study suggested that reactive radicals degraded BMAA mainly by attacking the carbon-nitrogen bonds on BMAA. Besides, comparing the effect of Cl－ on disinfection byproduct (DBP) formation in UV/PAA-post-PAA oxidation and UV/chlorine-post-chlorination systems, it was found that the former was more sensitive to the presence of Cl－.

(Eco)Toxicology of Cyanobacteria and Cyanotoxins: From Environmental Dynamics to Adverse Effects

The problem of artificial eutrophication, together with the effects of climate changes has led to an increase in the frequency of the occurrence of cyanobacterial blooms [...].

Microcystis sp. AE03 strain in Dal Lake harbors cylindrospermopsin and microcystin synthetase gene cluster

Cyanobacterial harmful algal blooms (CHABs) are increasing at an alarming rate in different water bodies worldwide. In India, CHAB events in water bodies such as Dal Lake have been sporadically reported with no study done to characterize the cyanobacterial species and their associated toxins. We hypothesized that this Lake is contaminated with toxic cyanobacterial species with the possibility of the presence of cyanotoxin biosynthetic genes. We, therefore, used some of the molecular tools such as 16S ribosomal DNA, PCR, and phylogenetic analysis to explore cyanobacterial species and their associated toxins. A 3-year (2018–2020) survey was conducted at three different sampling sites of Dal Lake namely, Grand Palace Gath (S1), Nigeen basin (S2), and Gagribal basin (S3). Two strains of Dolichospermum sp. AE01 and AE02 (S3 and S1 site) and one strain of Microcystis sp. AE03 (S2 site) was isolated, cultured, and characterized phylogenetically by 16S ribosomal DNA sequencing. The presence of cyanotoxin genes from the isolates was evaluated by PCR of microcystins (mcyB), anatoxins (anaC), and cylindrospermopsins (pks) biosynthesis genes. Results revealed the presence of both mcyB and pks gene in Microcystis sp. AE03, and only anaC gene in Dolichospermum sp. AE02 strain. However, Dolichospermum sp. AE01 strain was not found to harbor any such genes. Our findings, for the first time, reported the coexistence of pks and mcyB in a Microcystis AE03 strain. This study has opened a new door to further characterize the unexplored cyanobacterial species, their associated cyanotoxin biosynthetic genes, and the intervention of high-end proteomic techniques to characterize the cyanotoxins.

An investigation on bloom dynamics of Alexandrium catenella and A. pacificum and toxin accumulation in shellfish along the coast of Qinhuangdao, China

The dinoflagellate genus Alexandrium comprises most of the toxic bloom-forming species producing paralytic shellfish toxins (PSTs) in the sea. Recently, repeated paralytic shellfish poisoning episodes have been recorded in Qinhuangdao located at the west coast of the Bohai Sea. To elucidate the relationship between toxic Alexandrium blooms and the poisoning episodes, a year-round investigation was carried out in this region from July 2020 to July 2021. Two qPCR assays were used to detect A. catenella and A. pacificum, and LC-MS/MS was applied to analyze PSTs in phytoplankton and shellfish samples. The blooms of A. catenella and A. pacificum were found in April and July, respectively, and PST content in three bivalves exhibited notable increase following the bloom of A. catenella. The results revealed bloom dynamics of the two toxic Alexandrium species in the Bohai Sea for the first time, and further confirmed A. catenella as the causative agent of poisoning episodes.

Triple immunochromatographic test system for detection of priority aquatic toxins in water and fish

Aquatic toxins are a group of toxic compounds produced by several types of freshwater and marine algae and cyanobacteria and transported through the food chains of water bodies. Potential contamination of aquaculture products (raw and processed fish and seafood) with aquatic toxins requires the use of efficient screening methods for their control. In this study, a multiplex immunochromatographic test system for the simultaneous detection of three aquatic toxins-phycotoxins domoic acid (DA) and okadaic acid (OA), and cyanotoxin microcystin-LR (MC-LR)-is for the first time developed. For this, a competitive indirect immunochromatographic analysis (ICA) based on gold-labeled secondary antibodies was carried out. The LODs/cutoffs/working ranges of the ICA were 0.05/0.3/0.07-0.29, 1.3/100/3.2-58.2, and 0.1/2.0/0.2-1.1 ng/mL for MC-LR, DA, and OA, respectively. The assay duration was 18 min. The developed test system was used to analyze water samples from natural sources (salt and fresh water) and fish samples. For sample preparation of water, simple dilution with a buffer was proposed; for fish samples, methanol-water extraction was utilized. It was demonstrated that the triple LFIA specifically detected target aquatic toxins with recoveries of 85.0-121.5%. The developed multiplex LFIA can be considered a promising analytical solution for the rapid, easy, and sensitive control of water and food safety.

Nitrogen and phosphorus significantly alter growth, nitrogen fixation, anatoxin-a content, and the transcriptome of the bloom-forming cyanobacterium, Dolichospermum

While freshwater cyanobacteria are traditionally thought to be limited by the availability of phosphorus (P), fixed nitrogen (N) supply can promote the growth and/or toxin production of some genera. This study characterizes how growth on N2 (control), nitrate (NO3 -), ammonium (NH4 +), and urea as well as P limitation altered the growth, toxin production, N2 fixation, and gene expression of an anatoxin-a (ATX-A) - producing strain of Dolichospermum sp. 54. The transcriptomes of fixed N and P-limited cultures differed significantly from those of fixed N-deplete, P-replete (control) cultures, while the transcriptomes of P-replete cultures amended with either NH4 + or NO3 - were not significantly different relative to those of the control. Growth rates of Dolichospermum (sp. 54) were significantly higher when grown on fixed N relative to without fixed N; growth on NH4 + was also significantly greater than growth on NO3 -. NH4 + and urea significantly lowered N2 fixation and nifD gene transcript abundance relative to the control while cultures amended with NO3 - exhibited N2 fixation and nifD gene transcript abundance that was not different from the control. Cultures grown on NH4 + exhibited the lowest ATX-A content per cell and lower transcript abundance of genes associated ATX-A synthesis (ana), while the abundance of transcripts of several ana genes were highest under fixed N and P - limited conditions. The significant negative correlation between growth rate and cellular anatoxin quota as well as the significantly higher number of transcripts of ana genes in cultures deprived of fixed N and P relative to P-replete cultures amended with NH4 + suggests ATX-A was being actively synthesized under P limitation. Collectively, these findings indicate that management strategies that do not regulate fixed N loading will leave eutrophic water bodies vulnerable to more intense and toxic (due to increased biomass) blooms of Dolichospermum.

Delineating the activity of the potent nicotinic acetylcholine receptor agonists (+)-anatoxin-a and (−)-hosieine-A

The affinity and thermodynamic parameters for the interactions of two naturally occurring neurotoxins, (+)-anatoxin-a and (−)-hosieine-A, with acetylcholine-binding protein were investigated using a fluorescence-quenching assay and isothermal titration calorimetry. The crystal structures of their complexes with acetylcholine-binding protein from Aplysia californica (AcAChBP) were determined and reveal details of molecular recognition in the orthosteric binding site. Comparisons treating AcAChBP as a surrogate for human α4β2 and α7 nicotinic acetylcholine receptors (nAChRs) suggest that the molecular features involved in ligand recognition and affinity for the protein targets are conserved. The ligands exploit interactions with similar residues as the archetypal nAChR agonist nicotine, but with greater affinity. (−)-Hosieine-A in particular has a high affinity for AcAChBP driven by a favorable entropic contribution to binding. The ligand affinities help to rationalize the potent biological activity of these alkaloids. The structural data, together with comparisons with related molecules, suggest that there may be opportunities to extend the hosieine-A scaffold to incorporate new interactions with the complementary side of the orthosteric binding site. Such a strategy may guide the design of new entities to target human α4β2 nAChR that may have therapeutic benefit.

A review and assessment of cyanobacterial toxins as cardiovascular health hazards

Eutrophicated waters frequently support bloom-forming cyanobacteria, many of which produce potent cyanobacterial toxins (cyanotoxins). Cyanotoxins can cause adverse health effects in a wide range of organisms where the toxins may target the liver, other internal organs, mucous surfaces and the skin and nervous system. This review surveyed more than 100 studies concerning the cardiovascular toxicity of cyanotoxins and related topics. Over 60 studies have described various negative effects on the cardiovascular system by seven major types of cyanotoxins, i.e. the microcystin (MC), nodularin (NOD), cylindrospermopsin (CYN), anatoxin (ATX), guanitoxin (GNTX), saxitoxin (STX) and lyngbyatoxin (LTX) groups. Much of the research was done on rodents and fish using high, acutely toxin concentrations and unnatural exposure routes (such as intraperitoneal injection), and it is thus concluded that the emphasis in future studies should be on oral, chronic exposure of mammalian species at environmentally relevant concentrations. It is also suggested that future in vivo studies are conducted in parallel with studies on cells and tissues. In the light of the presented evidence, it is likely that cyanotoxins do not constitute a major risk to cardiovascular health under ordinary conditions met in everyday life. The risk of illnesses in other organs, in particular the liver, is higher under the same exposure conditions. However, adverse cardiovascular effects can be expected due to indirect effects arising from damage in other organs. In addition to risks related to extraordinary concentrations of the cyanotoxins and atypical exposure routes, chronic exposure together with co-existing diseases could make some of the cyanotoxins more dangerous to cardiovascular health.

Response of Oreochromis niloticus (Teleostei: Cichlidae) exposed to a guanitoxin-producing cyanobacterial strain using multiple biomarkers

Changes in environmental conditions in aquatic ecosystems caused by anthropic actions can modify the composition of primary producers, promoting the excessive proliferation of cyanobacteria. These organisms can form cyanobacterial blooms, which directly affect aquatic life. The present study investigated the mutagenicity of the cyanobacterium Sphaerospermopsis torques-reginae (strain ITEP-024), guanitoxin-producing (natural organophosphate), and sublethal effects on fish in relevant environment concentrations. For this, the Ames test (Salmonella/microsome) was performed as a mutagenic assay for extracts of the ITEP-024 strain. Specimens of Oreochromis niloticus (Teleostei: Cichlidae) were subjected to acute 96 h exposure to different concentrations of aqueous extract of the strain: C = control group; T1 = 31.25 mg/L; T2 = 62.5 mg/L; T3 = 125 mg/L; and T4 = 250 mg/L. Genotoxic, biochemical, osmoregulatory, and physiologic biomarkers were analyzed. Our results showed that the cyanobacterium had a weak mutagenic response for the TA102 strain of Salmonella with and without metabolic activation by S9. Strains TA98 and TA100 were not affected. Fish from treatments T3 and T4 showed changes in oxidative stress (CAT, SOD, and GST enzymes), inhibition of the enzyme acetylcholinesterase activity, micronucleus formation, and osmoregulatory disorders. No guanitoxin accumulation was detected in the different tissues of O. niloticus by LC-MS/MS. Our results showed unprecedented mutagenicity data of the guanitoxin-producing cyanobacteria by the Ames test and biochemical, osmoregulatory, and genotoxic disorders in fish, providing efficient aquatic contamination biomarkers. Despite the great concern related to the presence of guanitoxin in blooms in freshwater ecosystems, its concentration is not yet regulated, and thus there is no monitoring agenda in current legislation.

Cyanotoxins and water quality parameters as risk assessment indicators for aquatic life in reservoirs

We assessed the extent of pollution in an essential public water supply reservoir (southeastern Brazil). An environmental monitoring study was performed at the Billings Reservoir (at the water catchment site) to assess the water quality in 2017, 2018, and 2019. Physicochemical parameters were analyzed, quantifying the total cyanobacteria and the cyanotoxins microcystins (MCs) and saxitoxins (SXTs), as well as their possible ecological risk to the aquatic environment. We also determined metals and metalloids (As, Ba, Cd, Pb, Cu, Cr, Fe, Mn, Ni, Zn, and Sb) and fecal bacteria (Escherichia coli). Monthly samplings were performed for 2017, 2018, and 2019 (totaling 36 sampling campaigns). Metals, metalloids, and E. coli values were below the maximum limit allowed by the Brazilian legislation. High concentrations of total cyanobacteria (3.07 × 10⁴ - 3.23 × 10⁵ cells/mL), microcystin variants MC-LR (0.67-23.63 μg/L), MC-LA (0.03-8.66 μg/L), MC-RR (0.56-7.92 μg/L), and MC-YR (0.04-1.24 μg/L), as well as the saxitoxins GTX2 (0.18-5.37 μg/L), GTX3 (0.13-4.40 μg/L), and STX (0.12-2.92 μg/L) were detected. From an ecotoxicological point of view, the estimated values for the risk quotient (RQ) for microcystins and saxitoxins were largely greater than 1, indicating a high risk to aquatic life. Therefore, further efforts need to be made to delay the eutrophication of the reservoir.

Permanent occurrence of Raphidiopsis raciborskii and cyanotoxins in a subtropical reservoir polluted by domestic effluents (Itupararanga reservoir, São Paulo, Brazil)

Toxic cyanobacteria blooms are a frequent problem in subtropical reservoirs and freshwater systems. The purpose of this study was to investigate the occurrence of potentially toxic cyanobacteria and the environmental conditions associated with the presence of cyanotoxins in a Brazilian subtropical reservoir. Five collections were carried out at seven sampling locations in the reservoir, during the rainy and dry seasons, between the years 2016 and 2017. There was permanent occurrence of Raphidiopsis raciborskii (Woloszynska) Aguilera, Berrendero Gómez, Kastovsky, Echenique & Salerno (Phycologia 57(2):130-146, 2018), ranging between dominant and abundant, with an average biomass of 38.8 ± 29.9 mg L^-1. Also abundant were Dolichospermum solitarium, D. planctonicum, Planktothrix isothrix, and Aphanizomenon gracile. Saxitoxin (STX) was detected in all the collected samples (0.11 ± 0.05 µg L^-1). Microcystin (MC) was also detected, but at lower concentrations (0.01 ± 0.0 µg L^-1). Low availability of NO₃^- and phosphorus limitation had significant effects on the R. raciborskii biomass and the levels of STX and MC. It was observed that R. raciborskii was sensitive to thermal stratification, at the same time that STX levels were higher. This suggested that STX was produced under conditions that restricted the growth of R. raciborskii. These are important findings, because they add information about the permanent occurrence of STX and R. raciborskii in an aquatic ecosystem limited by phosphorus, vulnerable to climatic variations, and polluted by domestic effluents.