Microcystins in potable surface waters: toxic effects and removal strategies

Magnetic nanostructured agents for the mitigation of mycotoxins and cyanotoxins in the food chain

Natural toxins, such as mycotoxins and cyanotoxins, can contaminate food and feed, leading to toxicity in humans and animals. This study focused on using nine magnetic nanostructured agents to remove the main types of toxins. Initially, the efficacy of these materials was evaluated in water solutions, revealing that composites with sizes below 3 mm, containing magnetite, activated carbon, esterified pectin, and sodium alginate, removed up to 90% of mycotoxins and cyanotoxins with an adsorption of 873 ng/g. The application of the nanostructures was then assessed in beer, milk, Distillers Dried Grains with Solubles and water contaminated with cyanobacteria. The presence of matrix slightly decreases the adsorption capacity for some toxins. The maximum toxin removal capacity was calculated with cyanotoxins, composites achieved a removal of up to 0.12 mg/g, while nanocomposites (15 μm) reached 36.6 mg/g. Therefore, these findings point out the potential for using nanotechnology in addressing natural toxins contamination.

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.

Biofilm community composition is changing in remote mountain lakes with a relative increase in potentially toxigenic algae

Mountain lakes provide clear drinking water to humankind but are strongly impacted by global change. Benthic biofilms are crucial for maintaining water quality in these oligotrophic lakes, yet little is known about the effects of global change on mountain biofilm communities. By combining analyses of metabarcoding data on 16S and 18S rRNA genes with climatic and environmental data, we investigated global change effects on the composition of biofilm prokaryotic and micro-eukaryotic assemblages in a five-year monitoring program of 26 Pyrenean lakes (2016-2020). Using time-decay relationships and within-lake dissimilarity modelling, we show that the composition of both prokaryotic and micro-eukaryotic biofilm communities significantly shifted and their biodiversity declined from 2016 to 2020. In particular, analyses of temporal trends with linear mixed models indicated an increase in the richness and relative abundance of cyanobacteria, including potentially toxigenic cyanobacteria, and a concomitant decrease in diatom richness and relative abundance. While these compositional shifts may be due to several drivers of global change acting simultaneously on mountain lake biota, water pH and hardness were, from our data, the main environmental variables associated with changes for both prokaryotic and micro-eukaryotic assemblages. Water pH and hardness increased in our lakes over the study period, and are known to increase in Pyrenean lakes due to the intensification of rock weathering as a result of climate change. Given predicted climate trends and if water pH and hardness do cause some changes in benthic biofilms, those changes might be further exacerbated in the future. Such biofilm compositional shifts may induce cascading effects in mountain food webs, threatening the resilience of the entire lake ecosystem. The rise in potentially toxigenic cyanobacteria also increases intoxication risks for humans, pets, wild animals, and livestock that use mountain lakes. Therefore, our study has implications for water quality, ecosystem health, public health, as well as local economies (pastoralism, tourism), and highlights the possible impacts of global change on mountain lakes.

Photocatalytic degradation of organic pollutants by carbon quantum dots functionalized g-C3N4: A review

Graphitic carbon nitride (g-C₃N₄) has received much attention due to its unique characteristics of stable physicochemical features, facile preparation, and inexpensive cost. However, the bulk g-C₃N₄ has a weak capacity for pollutant degradation and needs to be modified for real application. Therefore, extensive research has been done on g-C₃N₄, and the discovery of the novel zero-dimensional nanomaterials known as carbon quantum dots (CQDs) provided it with a unique modification option. In this review, the development for the removal of organic pollutants by g-C₃N₄/CQDs was discussed. Firstly, the preparation of g-C₃N₄/CQDs were introduced. Then, the application and the degradation mechanism of g-C₃N₄/CQDs were briefly described. And the discussion of the influencing factors on g-C₃N₄/CQDs' ability to degrade organic pollutants came in third. Finally, the conclusions of photocatalytic degradation of organic pollutants by g-C₃N₄/CQDs and future perspectives followed. This review will strengthen the understanding of the photocatalytic degradation of real organic wastewater by g-C₃N₄/CQDs, including their preparation, application, mechanism, and influencing factors.

Research progress on influencing factors on compost maturity and cyanobacteria toxin degradation during aerobic cyanobacteria composting: a review

Cyanobacterial bloom is by far one of the most common water quality hazards. As cyanobacteria are rich in nitrogen, phosphorus, and other organic matter, the potential for beneficial use of cyanobacteria is promising. Aerobic composting is currently a hot topic of research in cyanobacteria treatment, which can effectively achieve reduction, recycling, and removal of the harmful impact of cyanobacteria. In this review, the characteristics of cyanobacteria in aerobic composting processes, the effects of physical, chemical, and biological factors on the composting process, and the degradation of microcystic toxins were systematically discussed and summarized. This review epitomizes the large quantities of research data collected by many scholars around the world to address the characteristics of "one low and five highs" in the aerobic cyanobacterial composting process. The composting techniques developed are effective and easy to adopt in the real world, such as adjusting the substrate C/N ratio and moisture content and use of chemical and biological additives to achieve reduction, recycling, and detoxication of the cyanobacterial wastes. The aim of this comprehensive review is to provide theoretical guidance and reference for further development and application of aerobic cyanobacteria composting technology.

Heterotrophic Bacteria Dominate Catalase Expression during Microcystis Blooms

In the oligotrophic oceans, key autotrophs depend on "helper" bacteria to reduce oxidative stress from hydrogen peroxide (H₂O₂) in the extracellular environment. H₂O₂ is also a ubiquitous stressor in freshwaters, but the effects of H₂O₂ on autotrophs and their interactions with bacteria are less well understood in freshwaters. Naturally occurring H₂O₂ in freshwater systems is proposed to impact the proportion of microcystin-producing (toxic) and non-microcystin-producing (nontoxic) Microcystis in blooms, which influences toxin concentrations and human health impacts. However, how different strains of Microcystis respond to naturally occurring H₂O₂ concentrations and the microbes responsible for H₂O₂ decomposition in freshwater cyanobacterial blooms are unknown. To address these knowledge gaps, we used metagenomics and metatranscriptomics to track the presence and expression of genes for H₂O₂ decomposition by microbes during a cyanobacterial bloom in western Lake Erie in the summer of 2014. katG encodes the key enzyme for decomposing extracellular H₂O₂ but was absent in most Microcystis cells. katG transcript relative abundance was dominated by heterotrophic bacteria. In axenic Microcystis cultures, an H₂O₂ scavenger (pyruvate) significantly improved growth rates of one toxic strain while other toxic and nontoxic strains were unaffected. These results indicate that heterotrophic bacteria play a key role in H₂O₂ decomposition in Microcystis blooms and suggest that their activity may affect the fitness of some Microcystis strains and thus the strain composition of Microcystis blooms but not along a toxic versus nontoxic dichotomy. IMPORTANCE Cyanobacterial harmful algal blooms (CHABs) threaten freshwater ecosystems globally through the production of toxins. Toxin production by cyanobacterial species and strains during CHABs varies widely over time and space, but the ecological drivers of the succession of toxin-producing species remain unclear. Hydrogen peroxide (H₂O₂) is ubiquitous in natural waters, inhibits microbial growth, and may determine the relative proportions of Microcystis strains during blooms. However, the mechanisms and organismal interactions involved in H₂O₂ decomposition are unexplored in CHABs. This study shows that some strains of bloom-forming freshwater cyanobacteria benefit from detoxification of H₂O₂ by associated heterotrophic bacteria, which may impact bloom development.

Low-Resolution Raman Spectroscopy for the detection of contaminant species in algal bioreactors

Fouling of aquatic systems by harmful microalgal and cyanobacterial species is an environmental and public health concern. Microalgal bioreactors are engineered ecosystems for the cultivation of algal biomass to meet the increasing demand for alternative protein sources and algae-derived products. Such bioreactors are often open or semi-open ponds or raceways that are prone to contamination by contaminant photosynthetic microorganisms, including harmful cyanobacterial species (HCBs). HCBs affect the quality of products through the accumulation of off-flavours, reducing their acceptance by consumers, and through the production of several different toxins collectively known as cyanotoxins. The density of cultured species within the bioreactor environment creates difficulty in detecting low concentrations of contaminant cells, and there is currently no technology enabling rapid monitoring of contaminations. The present study demonstrates the potential of Low-Resolution Raman Spectroscopy (LRRS) as a tool for rapid detection of low concentrations of HCBs within dense populations of the spirulina (Arthrospira platensis) cultures. An LRRS system adapted for the direct measurement of raw biomass samples was used to assemble a database of Raman spectral signatures, from eight algal and cyanobacterial strains. This dataset was used to develop both quantitative and discriminative chemometric models. The results obtained from the chemometric analyses demonstrate the ability of the LRRS to detect and quantify algal and cyanobacterial species at concentrations as low as 10³ cells/mL and to robustly discriminate between species at concentrations of 10⁴ cells/mL. The LRRS and chemometric analyses were further able to detect the presence of low concentrations (10³cells/mL) of contaminating species, including the toxic cyanobacterium Microcystis aeruginosa, within dense (>10⁷ cells/mL) spirulina cultures. The results presented provide a first demonstration of the potential of LRRS technology for real-time detection of contaminant species within microalgal bioreactors, and possibly for early detection of developing harmful algal blooms in other aquatic ecosystems.

Using soil amendments to reduce microcystin-LR bioaccumulation in lettuce

Contamination of microcystins (MCs) in plant-soil system have become a serious problem worldwide, however, it remains largely unknown how to alleviate the potential risk of consuming MCs-contaminated plants. In the present study, attapulgite, biochar and peat were used as soil amendments to reduce MCs bioaccumulation in lettuce. Lettuce irrigated with 10 μg L-1 microcystin-LR (MC-LR) were growing in two different kinds of soils with or without soil amendments. Results showed that all soil amendments effectively reduced MC-LR bioaccumulation in lettuce roots and leaves. Compared with the control treatment, the MC-LR concentrations in leaves in treatments with attapulgite, biochar and peat decreased by 41.5%, 30.6%, 57.0% in soil A and 38.9%, 43.2%, 54.7% in soil B, respectively. Peat application was most effective in reducing MC-LR bioaccumulation. The decreased soil free MC-LR concentrations were positively correlated with MC-LR concentrations in lettuce, indicating decreased bioavailability of MC-LR by soil amendments. It is noteworthy that soil total MC-LR concentration in peat treatment significantly decreased by 33.3% and 29.4% in soil A and soil B, respectively, compared with the controls. According to the results from high-throughput sequencing, peat amendment increased the α-diversity of soil bacterial community and boosted the abundance of Sphingomonas and Methylobacillus (dozens of MC-degrading bacteria belong to these genera). This was in line with the results of soil total MC-LR concentration. It can be speculated that peat application directly and/or indirectly promoted microbial degradation of MC-LR in soils. This work proposed an effective way to alleviate the potential risks of MCs contamination in plant-soil system.

Cyanotoxins and Food Contamination in Developing Countries: Review of Their Types, Toxicity, Analysis, Occurrence and Mitigation Strategies

Cyanotoxins have gained global public interest due to their potential to bioaccumulate in food, which threatens human health. Bloom formation is usually enhanced under Mediterranean, subtropical and tropical climates which are the dominant climate types in developing countries. In this context, we present an up-to-date overview of cyanotoxins (types, toxic effects, analysis, occurrence, and mitigation) with a special focus on their contamination in (sea)food from all the developing countries in Africa, Asia, and Latin America as this has received less attention. A total of 65 publications have been found (from 2000 until October 2021) reporting the contamination by one or more cyanotoxins in seafood and edible plants (five papers). Only Brazil and China conducted more research on cyanotoxin contamination in food in comparison to other countries. The majority of research focused on the detection of microcystins using different analytical methods. The detected levels mostly surpassed the provisional tolerable daily intake limit set by the World Health Organization, indicating a real risk to the exposed population. Assessment of cyanotoxin contamination in foods from developing countries still requires further investigations by conducting more survey studies, especially the simultaneous detection of multiple categories of cyanotoxins in food.

Repeated exposure to microcystin-leucine-arginine potentiates excitotoxicity induced by a low dose of kainate

Microcystin-leucine-arginine (MLCR) is a cyanobacterial toxin, and has been demonstrated to cause neurotoxicity. In addition, MCLR has been identified as an inhibitor of protein phosphatase (PP)1 and PP2A, which are known to regulate the phosphorylation of various molecules related to synaptic excitability. Thus, in the present study, we examined whether MCLR exposure affects seizures induced by a low dose of kainic acid (KA; 0.05 μg, i.c.v.) administration. KA-induced seizure occurrence and seizure score significantly increased after repeated exposure to MCLR (2.5 or 5.0 μg/kg, i.p., once a day for 10 days), but not after acute MCLR exposure (2.5 or 5.0 μg/kg, i.p., 2 h and 30 min prior to KA administration), and hippocampal neuronal loss was consistently facilitated by repeated exposure to MCLR. In addition, repeated MCLR significantly elevated the membrane expression of kainate receptor GluK2 subunits, p-pan-protein kinase C (PKC), and p-extracellular signal-related kinase (ERK) at 1 h after KA. However, KA-induced membrane expression of Ca²⁺/calmodulin-dependent kinase II (CaMKII) was significantly reduced by repeated MCLR exposure. Consistent with the enhanced seizures and neurodegeneration, MCLR exposure significantly potentiated KA-induced oxidative stress and microglial activation, which was accompanied by increased expression of p-ERK and p-PKCδ in the hippocampus. The combined results suggest that repeated MCLR exposure potentiates KA-induced excitotoxicity in the hippocampus by increasing membrane GluK2 expression and enhancing oxidative stress and neuroinflammation through the modulation of p-CaMKII, p-PKC, and p-ERK.

Harmful algal bloom resources for livestock veterinarians

Harmful algal blooms can have deleterious effects on animal and human health as well as the environment and are anticipated to become more frequent and intensified in the future because of climate change. Veterinarians are well positioned to diagnose and treat animals affected by HABs and to educate livestock owners and the public about health risks and environmental issues associated with those toxic events. Pets, livestock, wildlife, and marine life can all be affected by HABs. Information about HABs is becoming increasingly assessable as a result of ongoing research into the structure, properties, toxic mechanisms, and geographic distribution of toxins found in HABs. The AVMA's multi-entity working group on HABs is comprised of members from the Aquatic Veterinary Medicine Committee, Committee on Environmental Issues, and Council on Public Health and is working to make more information and resources regarding HABs available to practicing veterinarians. The present article is the first of those resources and provides a review of HABs, with a focus on livestock. It includes background material about bloom formation, appearance, and persistence as well as descriptions of clinical observations from early field cases and more recent information about the causative organisms and toxins to provide livestock veterinarians a foundation for understanding HABs. Reporting of HABs and prevention and mitigation strategies for livestock owners are also discussed.

Association of serum microcystin levels with neurobehavior of school-age children in rural area of Southwest China: A cross-sectional study

To investigate whether microcystin-LR (MC-LR) influences children's cognitive function and memory ability, we measured serum MC-LR and whole blood lead levels in 697 primary students, and collected their academic and neurobehavioral test scores. The median of serum MC-LR levels was 0.80 µg/L (the value below the limit of detection to 1.67 µg/L). The shapes of the associations of serum MC-LR levels (cut-point: 0.95 µg/L) with scores on academic achievements, digit symbol substitution test and long-term memory test were parabolic curves. Logistic regression analysis showed that MC-LR at concentrations of 0.80-0.95 µg/L was associated with the increased probability of higher achievements on academic achievements [odds ratio (OR) = 2.20, 95% confidence interval (CI): 1.28-3.79], and also with scores on digit symbol substitution test (OR = 1.73, 95% CI: 1.05-2.86), overall memory quotient (OR = 2.27, 95% CI: 1.21-4.26), long-term memory (OR = 1.85, 95% CI: 1.01-3.38) and short-term memory (OR = 2.13, 95% CI: 1.14-3.98) after adjustment for confounding factors. Antagonism of MC-LR and lead on long-term memory was observed (synergism index = 0.15, 95% CI: 0.03-0.74). In conclusion, serum MC-LR at concentrations of 0.80-0.95 µg/L was positively associated with higher scores on cognitive and neurobehavioral tests, and antagonism between MC-LR at concentrations of 0.80-1.67 µg/L and lead exposure was obviously observed on long-term memory in children. Concerning that MC-LR is a neurotoxin at high doses, our observation is interesting and need further investigation.

Metabolomics safety assessments of microcystin exposure via drinking water in rats

Drinking water exposure to microcystin-leucine-arginine (MC-LR), the most widely occurring cyanotoxins, poses a highly potential risk for human health. However, the health risk of MC-LR exposure at current guideline value in drinking water has not yet entirely evaluated. In the current study, we used ¹H NMR-based metabolomics combined with targeted metabolic profiling by GC/LC-MS to explore the toxic effects of MC-LR exposure at environmentally relevant concentrations via drinking water in rats. The results revealed that multiple biological consequences of MC-LR exposure on host metabolism in rats. Both relatively low and high doses of MC-LR used here induced hepatic lipogenesis and inflammation. While only relatively high dose MC-LR (10 μg/L) in drinking water caused more metabolic disorders including inhibition of gluconeogenesis and promotion of β-oxidation of fatty acid. Although the dose of 1.0 μg/L MC-LR is extremely low for rats, alterations of metabolic profiles were unexpectedly found in rat liver and serum, alarming potential health risk of MC-LR at the WHO guideline level.

Removal of Dolichospermum circinale, Microcystis aeruginosa, and their metabolites using hydrogen peroxide and visible light

Frequent cyanobacterial blooms in reservoirs used for human supply increase the risk of noxious secondary metabolites, endangering human health and ecological balance, and requiring constant monitoring by water companies. Although hydrogen peroxide (H2O2) has been widely reported as an effective agent for the control of cyanobacteria, being Microcystis aeruginosa one of the most studied species, very limited data is available on its effects over Dolichospermum circinale. Therefore, this study aimed to evaluate the impact of H2O2 on D. circinale and comparing it to the effects over the M. aeruginosa. The treatment was performed in cyanobacterial cultures with the application of 2 and 5 mg L-1 of H2O2 under visible light. To measure the impact of the treatment, intact cells were counted and cell re-growth monitored. Geosmin and microcystin, cell pigments, color, and organic matter in water were also analyzed during the treatment. The results showed that even the smallest H2O2 concentration (2 mg L-1) was able to completely remove D. circinale cells. Although M. aeruginosa could only be completely removed using 5 mg L-1, the few cells remaining after the application of 2 mg L-1 were not viable and did not re-grew after 15 days. Total microcystin concentration increased after M. aeruginosa was exposed to H2O2, suggesting that oxidative stress may increase the detection of this metabolite when the cells are lysed. While 2 mg L-1 was able to significantly decrease total geosmin, the addition of 5 mg L-1 did not improve removal. Chlorophyll-a was readily degraded after cell rupture but the same did not happen to phycocyanin, demonstrating its high resilience to this oxidant. Color and organic matter increased for the M. aeruginosa but decreased for the D. circinale suspension, probably because the higher concentration of the M. aeruginosa yielded more extracellular content to the water which was not able to be degraded by the amount of H2O2 applied.

Harmful Algal Blooms Threaten the Health of Peri-Urban Fisher Communities: A case study in Kisumu Bay, Lake Victoria, Kenya

Available guidance to mitigate health risks from exposure to freshwater harmful algal blooms (HABs) is largely derived from temperate ecosystems. Yet in tropical ecosystems, HABs can occur year-round, and resource-dependent populations face multiple routes of exposure to toxic components. Along Winam Gulf, Lake Victoria, Kenya, fisher communities rely on lake water contaminated with microcystins (MCs) from HABs. In these peri-urban communities near Kisumu, we tested hypotheses that MCs exceed exposure guidelines across seasons, and persistent HABs present a chronic risk to fisher communities through ingestion with minimal water treatment and frequent, direct contact. We tested source waters at eleven communities across dry and rainy seasons from September 2015 through May 2016. We measured MCs, other metabolites, physicochemical parameters, chlorophyll a, phytoplankton abundance and diversity, and fecal indicators. We then selected four communities for interviews about water sources, usage, and treatment. Greater than 30% of source water samples exceeded WHO drinking water guidelines for MCs (1μg/L), and over 60% of source water samples exceeded USEPA guidelines for children and immunocompromised individuals. 50% of households reported sole use of raw lake water for drinking and household use, with alternate sources including rain and boreholes. Household chlorination was the most widespread treatment utilized. At this tropical, eutrophic lake, HABs pose a year-round health risk for fisher communities in resource -limited settings. Community-based solutions and site-specific guidance for Kisumu Bay and similarly impacted regions is needed to address a chronic health exposure likely to increase in severity and duration with global climate change.

Ecological models for estimating breakpoints and prediction intervals

The relationships between an environmental variable and an ecological response are usually estimated by models fitted through the conditional mean of the response given environmental stress. For example, nonparametric loess and parametric piecewise linear regression model (PLRM) are often used to represent simple to complex nonlinear relationships. In contrast, piecewise linear quantile regression models (PQRM) fitted across various quantiles of the response can reveal nonlinearities in its range of variation across the explanatory variable.We assess the number and positions of candidate breakpoints using loess and compare the relative efficiencies of PLRM and PQRM to quantitatively determine the breakpoints' location and precision. We propose a nonparametric method to generate bootstrap confidence intervals for breakpoints using PQRM and prediction bands for loess and PQRM. We illustrated the applications using data from two aquatic studies suspected to exhibit multiple environmental breakpoints: relating a fish multimetric index of community health (MMI) to agricultural activity in wetlands' adjacent drainage basins; and relating cyanobacterial biomass to total phosphorus concentration in Canadian lakes.Two statistically significant breakpoints were detected in each dataset, demarcating boundaries of three linear segments, each with markedly different slopes. PQRM generated less biased, more accurate, and narrower confidence intervals for the breakpoints and narrower prediction bands than PLRM, especially for small samples and large error variability. In both applications, the relationship between the response and environmental variables was weak/nonsignificant below the lower threshold, strong through the midrange of the environmental gradient, and weak/nonsignificant beyond the upper threshold.We describe several advantages of PQRM over PLRM in characterizing environmental relationships where the scatter of points represents natural environmental variation rather than measurement error. The proposed methodology will be useful for detecting multiple breakpoints in ecological applications where the limits of variation are as important as the conditional mean of a function.

The Use of Biochar and Pyrolysed Materials to Improve Water Quality through Microcystin Sorption Separation

Harmful algal blooms have increased globally with warming of aquatic environments and increased eutrophication. Proliferation of cyanobacteria (blue-green algae) and the subsequent flux of toxic extracellular microcystins present threats to public and ecosystem health and challenges for remediation and management. Although methods exist, there is currently a need for more environmentally friendly and economically and technologically feasible sorbents. Biochar has been proposed in this regard because of its high porosity, chemical stability, and notable sorption efficiency for removing of cyanotoxins. In light of worsening cyanobacterial blooms and recent research advances, this review provides a timely assessment of microcystin removal strategies focusing on the most pertinent chemical and physical sorbent properties responsible for effective removal of various pollutants from wastewater, liquid wastes, and aqueous solutions. The pyrolysis process is then evaluated for the first time as a method for sorbent production for microcystin removal, considering the suitability and sorption efficiencies of pyrolysed materials and biochar. Inefficiencies and high costs of conventional methods can be avoided through the use of pyrolysis. The significant potential of biochar for microcystin removal is determined by feedstock type, pyrolysis conditions, and the physiochemical properties produced. This review informs future research and development of pyrolysed materials for the treatment of microcystin contaminated aquatic environments.

Simultaneous control of algal micropollutants based on ball-milled powdered activated carbon in combination with permanganate oxidation and coagulation

This study reports application of KMnO₄ pre-oxidation and engineered powdered activated carbon (PAC) adsorption to simultaneously control geosmin, 2-methylisoborneol (2-MIB), and microcystin-LR (MC-LR) in conventional drinking water treatment plants (DWTPs). Pulverization of commercial wood-based PAC (1 mm ZrO₂ ball, 12 h) reduced the median size to ~6 μm and resulted in overall enhanced kinetics for adsorption of the algal micropollutants. A series of parametric experiments were performed to estimate minimal contact for KMnO₄ (1 mg L^-1, 10 minutes) and PAC (20 mg L^-1, 40 minutes) prior to coagulation, with the aim to meet guidelines (0.02, 0.02, and 1 μg L^-1 for geosmin, 2-MIB, and MC-LR, respectively) at specific influent concentrations (0.1, 0.1, and 100 μg L^-1) in surface water matrix. Ball-milling of parent PAC with a low oxygen content (~2.5 w/w%) could avoid interferences from/to the KMnO₄ pre-oxidation and subsequent coagulation. Pilot-scale experiments confirmed the compatibility of the combined KMnO₄ and PAC at existing DWTPs.

Vitamin C Protects Porcine Oocytes From Microcystin-LR Toxicity During Maturation

Microcystin-leucine arginine (MC-LR) is the most toxic cyanotoxin found in water bodies. Microcystins are produced as secondary products of cyanobacteria metabolism. They have a stable structure, and can bioaccumulate in living organisms. Humans and livestock who drink fresh water containing MC-LR can be poisoned. However, few studies have reported the effects of MC-LR exposure on livestock or human reproduction. In this study, we used porcine oocytes as a model to explore the effects of MC-LR on oocyte maturation, and studied the impact of vitamin C (VC) administration on MC-LR-induced meiosis defects. Exposure to MC-LR significantly restricted cumulus cell expansion and decreased first polar body extrusion. Further studies showed that MC-LR exposure led to meiosis arrest by disturbing cytoskeleton dynamics with MC-LR exposed oocytes displaying aberrant spindle organization, low levels of acetylate α-tubulin, and disturbed actin polymerization. Additionally, MC-LR exposure impaired cytoplasmic maturation by inducing mitochondria dysfunction. Moreover, MC-LR also produced abnormal epigenetic modifications, and induced high levels of oxidative stress, caused DNA damage and early apoptosis. The administration of VC provided partial protection from all of the defects observed in oocytes exposed to MC-LR. These results demonstrate that MC-LR has a toxic effect on oocyte meiosis through mitochondrial dysfunction-induced ROS, DNA damage and early apoptosis. Supplementation of VC is able to protect against MC-LR-induced oocyte damage and represents a potential therapeutic strategy to improve the quality of MC-LR-exposed oocytes.

Recent Advancements in the Removal of Cyanotoxins from Water Using Conventional and Modified Adsorbents—A Contemporary Review

The prevalence of cyanobacteria is increasing in freshwaters due to climate change, eutrophication, and their ability to adapt and thrive in changing environmental conditions. In response to various environmental pressures, they produce toxins known as cyanotoxins, which impair water quality significantly. Prolonged human exposure to cyanotoxins, such as microcystins, cylindrospermopsin, saxitoxins, and anatoxin through drinking water can cause severe health effects. Conventional water treatment processes are not effective in removing these cyanotoxins in water and advanced water treatment processes are often used instead. Among the advanced water treatment methods, adsorption is advantageous compared to other methods because of its affordability and design simplicity for cyanotoxins removal. This article provides a current review of recent developments in cyanotoxin removal using both conventional and modified adsorbents. Given the different cyanotoxins removal capacities and cost of conventional and modified adsorbents, a future outlook, as well as suggestions are provided to achieve optimal cyanotoxin removal through adsorption.

Magnetic nanostructures for marine and freshwater toxins removal

Marine and freshwater toxins contaminate water resources, shellfish and aquaculture products, causing a broad range of toxic effects in humans and animals. Different core-shell nanoparticles were tested as a new sorbent for removing marine and freshwater toxins from liquid media. Water solutions were contaminated with 20 μg/L of marine toxins and up to 50 μg/L of freshwater toxins and subsequently treated with 250 or 125 mg/L of nanoparticles. Under these conditions, carbon nanoparticles removed around 70% of saxitoxins, spirolides, and azaspiracids, and up to 38% of diarrheic shellfish poisoning toxins. In the case of freshwater toxins, the 85% of microcystin LR was eliminated; other cyclic peptide toxins were also removed in a high percentage. Marine toxins were adsorbed in the first 5 min of contact, while for freshwater toxins it was necessary 60 min to reach the maximum adsorption. Toxins were recovered by extraction from nanoparticles with different solvents. Gymnodinium catenatum, Prorocentrum lima, and Microcystis aeruginosa cultures were employed to test the ability of nanoparticles to adsorb toxins in a real environment, and the same efficacy to remove toxins was observed in these conditions. These results suggest the possibility of using the nanotechnology in the treatment of contaminated water or in chemical analysis applications.

Microcystins: Biogenesis, Toxicity, Analysis, and Control

Microcystins are cyclic peptide toxins formed by cyanobacteria. These toxins are recognized for their association with algal blooms, posing a significant threat to ecosystems and drinking water quality. Due to the growing environmental concerns they raise, a comprehensive review on microcystins' genesis, toxicity, and analytical methods for their quantitative determination is outlined. Genes, including the mcyABC cluster, regulate microcystin biogenesis. Bioanalytical experiments have identified key environmental factors, such as temperature and nitrogen availability, that promote microcystin production. Microcystin toxicity is explored based on its modulatory effects on protein phosphatases 1 and 2A in specific tissues and organs. Additionally, biochemical mechanisms of chelation, transportation, resultant oxidative stress, and tumor promotion abilities of microcystins are also discussed. Various analytical methods to separate, detect, and quantify microcystins, including the quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, nuclear magnetic resonance spectroscopy, and chromatographic platforms-linked tandem mass spectrometry (LC-MS) for unequivocal structural identification, are also reviewed. Since control of microcystins in water is of great necessity, both water treatment and mechanisms of abiotic transformation and microbial degradation are also discussed.

Limnological Differences in a Two-Basin Lake Help to Explain the Occurrence of Anatoxin-a, Paralytic Shellfish Poisoning Toxins, and Microcystins

Chautauqua Lake, New York, is a two-basin lake with a deeper, cooler, and less nutrient-rich Northern Basin, and a warmer, shallower, nutrient-replete Southern Basin. The lake is populated by a complex mixture of cyanobacteria, with toxigenic strains that produce microcystins, anatoxins, and paralytic shellfish poisoning toxins (PSTs). Samples collected from 24 sites were analyzed for these three toxin classes over four years spanning 2014-2017. Concentrations of the three toxin groups varied widely both within and between years. During the study, the mean and median concentrations of microcystins, anatoxin-a, and PSTs were 91 and 4.0 μg/L, 0.62 and 0.33 μg/L, and 32 and 16 μg/L, respectively. Dihydro-anatoxin was only detected once in Chautauqua Lake, while homo-anatoxin was never detected. The Northern Basin had larger basin-wide higher biomass blooms with higher concentrations of toxins relative to the more eutrophied Southern Basin, however blooms in the North Basin were infrequent. Chlorophyll concentrations and toxins in the two basins were correlated with different sets of environmental and physical parameters, suggesting that implementing controls to reduce toxin loads may require applications focused on more than reductions in cyanobacterial bloom density (e.g., reduction of phosphorus inputs), and that lake limnological factors and morphology are important determinants in the selection of an appropriate management strategy. Chautauqua Lake is a drinking water source and is also heavily used for recreation. Drinking water from Chautauqua Lake is unlikely to be a significant source of exposure to cyanotoxins due to the location of the intakes in the deeper North Basin, where there were generally low concentrations of toxins in open water; however, toxin levels in many blooms exceeded the US Environmental Protection Agency's recreational guidelines for exposure to cyanotoxins. Current cyanotoxin monitoring in Chautauqua Lake is focused on microcystins. However, the occurrence of blooms containing neurotoxic cyanotoxins in the absence of the microcystins indicates this restricted monitoring may not be sufficient when aiming to protect against exposure to cyanotoxins. The lake has a large number of tourist visitors; thus, special care should be taken to prevent recreational exposure within this group.

Biotransformations, Antioxidant System Responses, and Histopathological Indexes in the Liver of Fish Exposed to Cyanobacterial Extract

Radiocystis fernandoi, a microcystin (MC) producer, has been common in cyanobacterial blooms in tropical regions. Microcystin is a hepatotoxin that causes tissue damage and even death in animals, including humans; its detoxification process may involve biotransformation and activation of the antioxidant defense system. We evaluated the detoxification pathway, examined the antioxidant defense system responses, and determined the alterations and the organ histopathological indexes in the liver of the tropical fish Hoplias malabaricus after acute and subchronic intraperitoneal exposure to microcystin. The crude microcystin extract of R. fernandoi had predominantly MC-RR and MC-YR. The detoxification process was activated by increasing ethoxyresorufin-O-deethylase activity, whereas glutathione S-transferase was inhibited. The activity of the antioxidant defense enzymes superoxide dismutase (SOD) and glutathione peroxidase decreased after acute exposure; the SOD-catalase system and the glutathione level increased after subchronic exposure. The carbonyl protein level, lipid peroxidation (LPO), and DNA damage were unchanged after acute exposure, whereas protein carbonyl was unchanged, LPO decreased, and DNA damage increased after subchronic exposure. Histopathological alteration indexes differed between acute and subchronic exposure, but the histopathological organ indexes indicate liver dysfunction in both exposure periods. We conclude that MC-RR and MC-YR induce different liver responses depending on the time of exposure, and the antioxidant defense responses after subchronic exposure may help to partially restore the liver function. Environ Toxicol Chem 2020;39:1041-1051. © 2020 SETAC.

Elimination of cyanobacteria and microcystins in irrigation water-effects of hydrogen peroxide treatment

Cyanobacterial blooms pose a risk to wild and domestic animals as well as humans due to the toxins they may produce. Humans may be subjected to cyanobacterial toxins through many routes, e.g., by consuming contaminated drinking water, fish, and crop plants or through recreational activities. In earlier studies, cyanobacterial cells have been shown to accumulate on leafy plants after spray irrigation with cyanobacteria-containing water, and microcystin (MC) has been detected in the plant root system after irrigation with MC-containing water. This paper reports a series of experiments where lysis of cyanobacteria in abstracted lake water was induced by the use of hydrogen peroxide and the fate of released MCs was followed. The hydrogen peroxide-treated water was then used for spray irrigation of cultivated spinach and possible toxin accumulation in the plants was monitored. The water abstracted from Lake Köyliönjärvi, SW Finland, contained fairly low concentrations of intracellular MC prior to the hydrogen peroxide treatment (0.04 μg L^-1 in July to 2.4 μg L^-1 in September 2014). Hydrogen peroxide at sufficient doses was able to lyse cyanobacteria efficiently but released MCs were still present even after the application of the highest hydrogen peroxide dose of 20 mg L^-1. No traces of MC were detected in the spinach leaves. The viability of moving phytoplankton and zooplankton was also monitored after the application of hydrogen peroxide. Hydrogen peroxide at 10 mg L^-1 or higher had a detrimental effect on the moving phytoplankton and zooplankton.

Responses of the proteome in testis of mice exposed chronically to environmentally relevant concentrations of Microcystin-LR

Microcystin-LR (MC-LR), a widespread environmental contaminant, has been shown to have potent acute testicular toxicity. However, magnitudes of toxic effects, induced by MCs, depend on route and magnitude of exposure to the toxin. In the present study, male mice were orally exposed 1, 10 or 100 μg/L MC-LR for 90 or 180 days, and pathological approach and the isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomics were employed with testes. Proteomics revealed that a number of differentially altered proteins may be involved in MC-LR-induced chronic testicular toxicity. The biological process analysis indicated the altered proteins played an important role in biological adhesion, cellular process, response to stimulus or rhythmic process. The cellular component analysis revealed that most of the proteins with altered expression associated with cell part, extracellular region, extracellular region part, membrane, membrane part, organelle or organelle part. The molecular function showed that these proteins were critical in molecular transducer activity. Integrity analyses provide first compelling evidence that MC-LR significantly cause dysfunction of blood-testis barrier (BTB) through affecting tight junctions and gap junctions. Moreover, phosphatidylinositol 3-kinase (PI3K)/AKT eventually contributed to injury result from chronic low-level MC-LR treatment. Identification of proteins in testis responsive to MC-LR provides insights into molecular mechanisms of chronic toxicity of MCs.

Degradation of cyanotoxin microcystin-LR in synthetic and natural waters by chemical-free UV/VUV radiation

This study investigated the capability of ultraviolet radiation at 254 nm and 185 nm (UV/VUV) to degrade cyanotoxin microcystin-LR (MC-LR). Results showed 70% toxin reduction solely by 254 nm direct photolysis (ε₂₅₄ = 13,225 ± 814 M^-1cm^-1; Φ₂₅₄ = 0.29 ± 0.03 mol/Einstein). The addition of 185 nm increased MC-LR degradation through advanced oxidation by ^•OH (k_•OH,MC-LR = 2.25 ± 0.39 × 10¹⁰ M^-1s^-1). Alkalinity and organics (DOC) reduced MC-LR degradation by scavenging ^•OH (k_obs,MilliQ = 0.117 cm²/mJ; k_{obs,50ppmAlk.} = 0.0497 cm²/mJ; k_obs,6ppmDOC = 0.019 cm²/mJ). Chloride absorbed 185 nm, impacting ^•OH formation and generating Cl^•, while also scavenging ^•OH. However, Cl^• is reactive and ^•OH scavenging is reversible, resulting in relatively low impact on MC-LR degradation (k_obs,50ppmCl = 0.0939 cm²/mJ). In natural water, MC-LR could be degraded from a typical concentration (˜15 μg/L) to below detection (<0.5 μg/L) with a UV₂₅₄ fluence of 200 mJ/cm² using UV/VUV. The presence of cyanobacterial cells impeded MC-LR degradation; however, 90% MC-LR degradation could still be achieved. UV/VUV is a promising chemical-free technology capable of MC-LR degradation in a variety of water conditions, and a potentially suitable treatment option for small, remote communities.

Combined Danio rerio embryo morbidity, mortality and photomotor response assay: A tool for developmental risk assessment from chronic cyanoHAB exposure

Freshwater harmful algal blooms produce a broad array of bioactive compounds, with variable polarity. Acute exposure to cyanotoxins can impact the liver, nervous system, gastrointestinal tract, skin, and immune function. Increasing evidence suggests chronic effects from low-level exposures of cyanotoxins and other associated bioactive metabolites of cyanobacterial origin. These sundry compounds persist in drinking and recreational waters and challenge resource managers in detection and removal. A systematic approach to assess the developmental toxicity of cyanobacterial metabolite standards was employed utilizing a robust and high throughput developmental Danio rerio embryo platform that incorporated a neurobehavioral endpoint, photomotor response. Subsequently, we applied the platform to cyanobacterial bloom surface water samples taken from temperate recreational beaches and tropical lake subsistence drinking water sources as a model approach. Dechorionated Danio rerio embryos were statically immersed beginning at four to six hours post fertilization at environmentally relevant concentrations, and then assessed at 24 h and 5 days for morbidity, morphological changes, and photomotor response. At least one assessed endpoint deviated significantly for exposed embryos for 22 out of 25 metabolites examined. Notably, the alkaloid lyngbyatoxin-a resulted in profound, dose-dependent morbidity and mortality beginning at 5 μg/L. In addition, hydrophobic components of extracts from beach monitoring resulted in potent morbidity and mortality despite only trace cyanotoxins detected. The hydrophilic extracts with several order of magnitude higher concentrations of microcystins resulted in no morbidity or mortality. Developmental photomotor response was consistently altered in environmental bloom samples, independent of the presence or concentration of toxins detected in extracts. While limited with respect to more polar compounds, this novel screening approach complements specific fingerprinting of acutely toxic metabolites with robust assessment of developmental toxicity, critical for chronic exposure scenarios.

Efficient degradation of microcystin-LR by BiVO4/TiO2 photocatalytic nanocomposite under visible light

Microcystin-Leucine Arginine (MC-LR) is one of the most studied cyanotoxins due to its toxicity and abundant that cause health hazards for humans through of the drinking water. In this study, BiVO₄/TiO₂ nanocomposite was synthesized by hydrothermal method and employed for the removal of MC-LR. The characteristics of the catalysts were determined by FESEM, XRD and FTIR spectra. Response surface methodology (RSM) was applied to assess the effects of operating variables (pH, contact time, and catalyst dose) on the MC-LR removal. The coefficient of determination (R²) was calculated 98.7% for the response. The residual concentration of MC-LR was measured by high-performance liquid chromatography (HPLC). The results show that the highest removal efficiency of MC-LR was 98% under the optimum conditions (pH = 5, contact time = 90 min, and catalyst dose = 0.5 g/l). MC-LR decomposition efficiency by BiVO₄/TiO₂ nanocomposite was enhanced by pH reduction and increasing of contact time and catalyst dose. The prepared BiVO₄/TiO₂ nanocomposite with technological potential can be used directly in environmental preservation, specifically in the decontamination of MC-LR from aqueous solutions.

Icariin attenuate microcystin-LR-induced gap junction injury in Sertoli cells through suppression of Akt pathways

Microcystin-leucine-arginine (MC-LR) can cause male reproductive disorder. However, the underlying mechanism are not yet entirely elucidated. In this study, we aimed to investigated the effects of MC-LR on the integrity of blood-testis barrier (BTB) and the related molecular mechanisms. Both in vivo and in vitro experiments revealed that MC-LR caused disruption of BTB and gap junctions between Sertoli cells respectively, which was paralleled by the alteration of connexin43 (Cx43). Our data demonstrated that MC-LR decreased gap junction intercellular communication (GJIC) and impaired Cx43 expression by activating the phosphatidylinositol 3-kinase/Akt cascades. In addition, a possible protective effect of Icariin (ICA), a flavonoid isolated from Chinese medicinal herb, against MC-LR toxicity was investigated. The ICA prevented the degradation of GJIC and impairment of Cx43 induced by MC-LR via suppressing the Akt pathway. Together, our results confirmed that the expression of Cx43 induced by MC-LR was regulated in vivo and in vitro, which was involved in the destruction of BTB. Additionally, ICA seems to be able to mitigate the MC-LR toxic effects.

Prodigiosin Promotes Nrf2 Activation to Inhibit Oxidative Stress Induced by Microcystin-LR in HepG2 Cells

Microcystin-LR (MC-LR), a cyanotoxin produced by cyanobacteria, induces oxidative stress in various types of cells. Prodigiosin, a red linear tripyrrole pigment, has been recently reported to have antimicrobial, antioxidative, and anticancer properties. How prodigiosin reacts to reactive oxygen species (ROS) induced by MC-LR is still undetermined. This study aimed to examine the effect of prodigiosin against oxidative stress induced by MC-LR in HepG2 cells. Ros was generated after cells were treated with MC-LR and was significantly inhibited with treatment of prodigiosin. In prodigiosin-treated cells, the levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and Nrf2-related phase II enzyme heme oxygenase-1 (HO-1) were increased. Besides, prodigiosin contributed to enhance nuclear Nrf2 level and repressed ubiquitination. Furthermore, prodigiosin promoted Nrf2 protein level and inhibited ROS in Nrf2 knocked down HepG2 cells. Results indicated that prodigiosin reduced ROS induced by MC-LR by enhancing Nrf2 translocation into the nucleus in HepG2 cells. The finding presents new clues for the potential clinical applications of prodigiosin for inhibiting MC-LR-induced oxidative injury in the future.

The Efficiency of Microstrainers Filtration in the Process of Removing Phytoplankton with Special Consideration of Cyanobacteria

The research presented in this manuscript concerns the evaluation of the effectiveness of microstrainers, which are designed to reduce the amount of plankton in treated surface water. The efficiency of microstrainer filtration analysis is very important for the proper course of the water-treatment process not only in the Water-Treatment Plant (WTP) in Zielona Góra (central western Poland) but also in other WTPs around the world. The qualitative and quantitative monitoring of the abundance of plankton including cyanobacteria during the particle-filtration process allows not only for the assessment of the potential cyanotoxic risk in surface water providing a source of drinking water, but also allows the evaluation of the action and the prevention of adverse impacts of microstrainers. Over four years of research, it was observed that the largest amount of cyanobacteria before microstrainer filtration took place in May. The dominant species was Limnothrix redeckei. The microstrainer removal of plankton and cyanobacteria was statistically significant. The quantity of removed plankton increased with its increasing content in raw water. The particle-filtration process, by reducing the amount of cyanobacteria, contributes to a decrease in intracellular microcystins.

The chemodiversity of algal dissolved organic matter from lysed Microcystis aeruginosa cells and its ability to form disinfection by-products during chlorination

Algal-derived dissolved organic matter (ADOM) originating from lysed Microcystis aeruginosa cells was investigated as precursor material to form disinfection by-products upon disinfection with free chlorine. Non-targeted ultrahigh resolution 12 T negative mode electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed high molecular diversity in solid-phase extracted and ionizable components of Microcystis aeruginosa ADOM. The toxin microcystin LR was effectively degraded by free chlorine, which was expected. However, we found a high diversity of disinfection by-products associated with the addition of free chlorine to the water-soluble and solid-phase extractable fraction of ADOM and of double-bond moieties in abundant and known unsaturated fatty acids. Aromatic DOM precursors were absent from known metabolites of Microcystis aeruginosa and no evidence for aromatic disinfection by-products (DBPs) was found, despite N-containing compounds. A large diversification of N-containing molecular formulas was observed after chlorination, which seems indicative for the breakdown and oxidation of larger peptides. Additionally, a diverse group of N-compounds with presumed chloramine functional groups was observed. This study highlights the importance to evaluate ADOM and its ability to form different DBPs when compared to allochthonous or terrestrially-derived DOM.

Adsorption of microcystin-LR onto kaolinite, illite and montmorillonite

In this study, microcystin-LR (MCLR) interactions with three representative silicate clays were studied using equilibrium batch experiments in order to provide insight into the role of clays on determining MCLR fate. The three tested clay minerals (kaolinite, montmorillonite and illite), saturated with sodium or calcium ions, were equilibrated with MCLR across a range of toxin concentrations at pH 5, 7 or 9. The results were fit to Freundlich and linear isotherm models, with the linear isotherm fits deemed most appropriate. In general, adsorption of MCLR was greater in the systems with Ca than in those with Na, however, regardless of the cation present, montmorillonite had the highest adsorption affinity for MCLR. Furthermore, except for Ca-montmorillonite, MCLR adsorption decreased with increasing pH. The pH-dependence of adsorption suggests the polar groups of MCLR, carboxylate associated with the glutamic acid and methylaspartic acid groups and amine associated with the arginine group, were more important in determining MCLR interactions with clays than the nonpolar ADDA group. Increased adsorption in systems enriched with calcium suggests Ca modified the clay interfacial properties and the availability of MCLR groups in a manner that increased MCLR affinity. Overall, the results suggest clays are capable of adsorbing MCLR from the aqueous phase, particularly at low pH and when saturated with Ca²⁺.

Occurrence and toxicity of microcystin congeners other than MC-LR and MC-RR: A review

The occurrence of cyanobacterial toxins is being increasingly reported. This is a reason for concern as they can induce toxic effects both in humans and in the environment. Among them, microcystins (MCs) are the best described and most diverse group of cyanobacterial toxins, and MC-LR and MC-RR are the congeners most widely investigated. However, the number of MC variants has also increased in recent years. Some of these minority variants have been shown to have a different toxicokinetic and toxicodynamic profile, but research focused on them is still limited. Moreover, in some water bodies these minority variants can be the predominant toxins. Nonetheless, MC-LR is the only one used for risk evaluation purposes at present. In order to contribute to more realistic risk assessments in the future, the aim of this review was to compile the available information in the scientific literature regarding the occurrence and concentration of minority MCs in water and food samples, and their toxic effects. The data retrieved demonstrate the congener-specific toxicity of MCs, as well as many data gaps in relation to analytical or mechanistic aspects, among others. Therefore, further research is needed to improve the toxicological characterization of these toxins and the exposure scenarios.

Single and combined exposure of microcystin-LR and nitrite results in reproductive endocrine disruption via hypothalamic-pituitary-gonadal-liver axis

Microcystin-LR (MC-LR) released by Microcystis blooms degradation usually co-exists with a chemical called nitrite, posing a serious harm to aquatic organisms. To assess the single and combined effects of MC-LR and nitrite on the reproductive endocrine system, a fully factorial experiment was designed and adult male zebrafish (Danio rerio) were exposed to 9 treatment combinations of MC-LR (0, 3, 30 μg/L) and nitrite (0, 2, 20 mg/L) for 30 d. The results showed that both MC-LR and nitrite caused concentration-dependent effects including the growth inhibition, decreased gonad index as well as testicular injuries with widen intercellular spaces and seminiferous epithelium deteriorations. And testicular pathological changes in the co-exposure groups of MC-LR and nitrite were similar but more serious than those in single-factor exposure groups. Concurrently, exposure to MC-LR or nitrite alone could significantly decrease T levels by downregulating gene expressions (gnrh2, lhβ, ar, lhr) in the hypothalamic-pituitary-gonadal-liver-axis (HPGL-axis), and there were significant interactions between MC-LR and nitrite on them. In contrast, E2 levels as well as transcriptional levels of cyp19a1b, cyp19a1a and vtg1 showed significant inductions with increasing MC-LR concentrations, indicating an estrogen-like effect of MC-LR. Our findings illustrated that co-exposure of MC-LR and nitrite synergistically cause reproductive dysfunction by interfering with the HPGL axis in male fish, which prompt us to focus more on the potential risks in fish reproduction and even population dynamics due to the wide occurrence of toxic cyanobacterial blooms.

Glutathione peroxidase-1 overexpressing transgenic mice are protected from neurotoxicity induced by microcystin-leucine-arginine

Although it has been well-recognized that microcystin-leucine-arginine (MCLR), the most common form of microcystins, induces neurotoxicity, little is currently known about the underlying mechanism for this neurotoxicity. Here, we found that MCLR (10 ng/μL/mouse, i.c.v.) induces significant neuronal loss in the hippocampus of mice. MCLR-induced neurotoxicity was accompanied by oxidative stress, as shown by a significant increase in the level of 4-hydroxynonenal, protein carbonyl, and reactive oxygen species (ROS). Superoxide dismutase-1 (SOD-1) activity was significantly increased, but glutathione peroxidase (GPx) level was significantly decreased following MCLR insult. In addition, MCLR significantly inhibited GSH/GSSG ratio, and significantly induced NFκB DNA binding activity. Because reduced activity of GPx appeared to be critical for the imbalance between activities of SODs and GPx, we utilized GPx-1 overexpressing transgenic mice to ascertain the role of GPx-1 in this neurotoxicity. Genetic overexpression of GPx-1 or NFκB inhibitor pyrrolidine dithiocarbamate (PDTC) significantly attenuated MCLR-induced hippocampal neuronal loss in mice. However, PDTC did not exert any additive effect on neuroprotection mediated by GPx-1 overexpression, indicating that NFκB is a neurotoxic target of MCLR. Combined, these results suggest that MCLR-induced neurotoxicity requires oxidative stress associated with failure in compensatory induction of GPx, possibly through activation of the transcription factor NFκB.

Genetic overexpression of glutathione peroxidase-1 attenuates microcystin-leucine-arginine-induced memory impairment in mice

Microcystin-leucine-arginine (MCLR) is the most common form of microcystins, which are environmental toxins produced by cyanobacteria, and its hepatotoxicity has been well-documented. However, the neurotoxic potential of MCLR remains to be further elucidated. In the present study, we investigated whether intracerebroventricular (i.c.v.) infusion of MCLR induces mortality and neuronal loss in the hippocampus of mice. Because we found that MCLR impairs memory function in the hippocampus at a low dose (4 ng/μl/mouse, i.c.v.) without a significant neuronal loss, we focused on this dose for further analyses. Results showed that MCLR (4 ng/μl/mouse, i.c.v.) significantly increased oxidative stress (i.e., malondialdehyde, protein carbonyl, and synaptosomal ROS) in the hippocampus. In addition, MCLR significantly increased superoxide dismutase (SOD) activity without corresponding induction of glutathione peroxidase (GPx) activity, and thus led to significant decrease in the ratio of GPx/SODs activity. The GSH/GSSG ratio was also significantly reduced after MCLR treatment. GPx-1 overexpressing transgenic mice (GPx-1 Tg) were significantly protected from MCLR-induced memory impairment and oxidative stress. The DNA binding activity of nuclear factor erythroid-derived 2-related factor 2 (Nrf2) in these mice was significantly enhanced, and the ratios of GPx/SODs activity and GSH/GSSG returned to near control levels in the hippocampus. Importantly, memory function exhibited a significant positive correlation with the ratios of GPx/SODs activity and GSH/GSSG in the hippocampus of MCLR-treated non-transgenic (non-Tg)- and GPx-1 Tg-mice. Combined, our results suggest that MCLR induces oxidative stress and memory impairment without significant neuronal loss, and that GPx-1 gene constitutes an important protectant against MCLR-induced memory impairment and oxidative stress via maintaining antioxidant defense system homeostasis, possibly through the induction of Nrf2 transcription factor.

Essential roles of Akt/Snail pathway in microcystin-LR-induced tight junction toxicity in Sertoli cell

Microcystin (MC)-LR is a cyclic heptapeptide that acts as a potent reproductive system toxin. However, the underlying pathways of MCLR-induced reproductive system toxicity have not been well elucidated. The blood-testis barrier is mainly constituted by tight junctions (TJs) between adjacent Sertoli cells in the seminiferous epithelium near the basement membrane. The present study was designed to investigate changes in TJs and the underlying pathway in MC-LR-induced TJs toxicity in Sertoli cell. In our study, the transepithelial electrical resistance (TER) value was decreased in a dose dependent manner due to the markers of TJs occludin, claudin and zonula occludens-1 (ZO-1) expression decline. MC-LR is shown to induce cytotoxicity by inhibiting protein phosphatase 2A (PP2A) activity. Our results also showed that the PP2A activity presented a dose-dependent decline. Moreover, MC-LR stimulated protein expression of snail by Akt/GSK-3β activation. The activated Akt/GSK-3β and snail signaling pathway largely accounted for MC-LRinduced TJs toxicity, which could be partially reversed by snail siRNA interference or AKT chemical inhibitor in TM4 cells. These findings indicated that MC-LR inhibit the protein expression of TJs, and the activation of Akt/Snail signaling pathways due to PP2A inhibition is proposed to participate in this process.

Development and single-laboratory validation of a UHPLC-MS/MS method for quantitation of microcystins and nodularin in natural water, cyanobacteria, shellfish and algal supplement tablet powders

A simple, rapid UHPLC-MS/MS method has been developed and optimised for the quantitation of microcystins and nodularin in wide variety of sample matrices. Microcystin analogues targeted were MC-LR, MC-RR, MC-LA, MC-LY, MC-LF, LC-LW, MC-YR, MC-WR, [Asp3] MC-LR, [Dha7] MC-LR, MC-HilR and MC-HtyR. Optimisation studies were conducted to develop a simple, quick and efficient extraction protocol without the need for complex pre-analysis concentration procedures, together with a rapid sub 5min chromatographic separation of toxins in shellfish and algal supplement tablet powders, as well as water and cyanobacterial bloom samples. Validation studies were undertaken on each matrix-analyte combination to the full method performance characteristics following international guidelines. The method was found to be specific and linear over the full calibration range. Method sensitivity in terms of limits of detection, quantitation and reporting were found to be significantly improved in comparison to LC-UV methods and applicable to the analysis of each of the four matrices. Overall, acceptable recoveries were determined for each of the matrices studied, with associated precision and within-laboratory reproducibility well within expected guidance limits. Results from the formalised ruggedness analysis of all available cyanotoxins, showed that the method was robust for all parameters investigated. The results presented here show that the optimised LC-MS/MS method for cyanotoxins is fit for the purpose of detection and quantitation of a range of microcystins and nodularin in shellfish, algal supplement tablet powder, water and cyanobacteria. The method provides a valuable early warning tool for the rapid, routine extraction and analysis of natural waters, cyanobacterial blooms, algal powders, food supplements and shellfish tissues, enabling monitoring labs to supplement traditional microscopy techniques and report toxicity results within a short timeframe of sample receipt. The new method, now accredited to ISO17025 standard, is simple, quick, applicable to multiple matrices and is highly suitable for use as a routine, high-throughout, fast turnaround regulatory monitoring tool.

Temporal Dynamics of the Microbial Community Composition with a Focus on Toxic Cyanobacteria and Toxin Presence during Harmful Algal Blooms in Two South German Lakes

Bacterioplankton plays an essential role in aquatic ecosystems, and cyanobacteria are an influential part of the microbiome in many water bodies. In freshwaters used for recreational activities or drinking water, toxic cyanobacteria cause concerns due to the risk of intoxication with cyanotoxins, such as microcystins. In this study, we aimed to unmask relationships between toxicity, cyanobacterial community composition, and environmental factors. At the same time, we assessed the correlation of a genetic marker with microcystin concentration and aimed to identify the main microcystin producer. We used Illumina MiSeq sequencing to study the bacterioplankton in two recreational lakes in South Germany. We quantified a microcystin biosynthesis gene (mcyB) using qPCR and linked this information with microcystin concentration to assess toxicity. Microcystin biosynthesis gene (mcyE)-clone libraries were used to determine the origin of microcystin biosynthesis genes. Bloom toxicity did not alter the bacterial community composition, which was highly dynamic at the lowest taxonomic level for some phyla such as Cyanobacteria. At the OTU level, we found distinctly different degrees of temporal variation between major bacteria phyla. Cyanobacteria and Bacteroidetes showed drastic temporal changes in their community compositions, while the composition of Actinobacteria remained rather stable in both lakes. The bacterial community composition of Alpha- and Beta-proteobacteria remained stable over time in Lake Klostersee, but it showed temporal variations in Lake Bergknappweiher. The presence of potential microcystin degraders and potential algicidal bacteria amongst prevalent Bacteroidetes and Alphaproteobacteria implied a role of those co-occurring heterotrophic bacteria in cyanobacterial bloom dynamics. Comparison of both lakes studied revealed a large shared microbiome, which was shaped toward the lake specific community composition by environmental factors. Microcystin variants detected were microcystin-LR, -RR, and -YR. The maximum microcystin concentrations measured was 6.7 μg/L, a value still acceptable for recreational waters but not drinking water. Microcystin concentration correlated positively with total phosphorus and mcyB copy number. We identified low abundant Microcystis sp. as the only microcystin producer in both lakes. Therefore, risk assessment efforts need to take into account the fact that non-dominant species may cause toxicity of the blooms observed.

Management of toxic cyanobacteria for drinking water production of Ain Zada Dam

Blooms of toxic cyanobacteria in Algerian reservoirs represent a potential health problem, mainly from drinking water that supplies the local population of Ain Zada (Bordj Bou Arreridj). The objective of this study is to monitor, detect, and identify the existence of cyanobacteria and microcystins during blooming times. Samples were taken in 2013 from eight stations. The results show that three potentially toxic cyanobacterial genera with the species Planktothrix agardhii were dominant. Cyanobacterial biomass, phycocyanin (PC) concentrations, and microcystin (MC) concentrations were high in the surface layer and at 14 m depth; these values were also high in the treated water. On 11 May 2013, MC concentrations were 6.3 μg/L in MC-LR equivalent in the drinking water. This study shows for the first time the presence of cyanotoxins in raw and treated waters, highlighting that regular monitoring of cyanobacteria and cyanotoxins must be undertaken to avoid potential health problems.

Detection of freshwater cyanotoxins and measurement of masked microcystins in tilapia from Southeast Asian aquaculture farms

Recently, there has been a rise in freshwater harmful algal blooms (HABs) globally, as well as increasing aquaculture practices. HABs can produce cyanotoxins, many of which are hepatotoxins. An ultra-performance liquid chromatography tandem mass spectrometry method was developed and validated for nine cyanotoxins across three classes including six microcystins, nodularin, cylindrospermopsin and anatoxin-a. The method was used to analyse free cyanotoxin(s) in muscle (n = 34), liver (n = 17) and egg (n = 9) tissue samples of 34 fish sourced from aquaculture farms in Southeast Asia. Conjugated microcystin was analysed by Lemieux oxidation to ascertain the total amount of microcystin present in muscle. Some tilapia accumulated free microcystin-LR in the muscle tissue at a mean of 15.45 μg/kg dry weight (dw), with total microcystin levels detected at a mean level of 110.1 μg/kg dw, indicating that the amount of conjugated or masked microcystin present in the fish muscle accounted for 85% of the total. Higher levels of cyanotoxin were detected in the livers, with approximately 60% of those tested being positive for microcystin-LR and microcystin-LF, along with cylindrospermopsin. Two fish from one of the aquaculture farms contained cylindrospermopsin in the eggs; the first time this has been reported. The estimated daily intake for free and total microcystins in fish muscle tissue was 2 and 14 times higher, respectively, than the tolerable daily intake value. This survey presents the requirement for further monitoring of cyanotoxins, including masked microcystins, in aquaculture farming in these regions and beyond, along with the implementation of guidelines to safeguard human health. Graphical abstract ᅟ.

Adsorption of microcystin-LR on mesoporous carbons and its potential use in drinking water source

Microcystin-LR (MC-LR) is a common toxin derived from cyanobacterial blooms an effective, rapid and non-toxic method needs to be developed for its removal from drinking water treatment plants (DWTP). For an adsorption-based method, mesoporous carbon can be a promising supplemental adsorbent. The effect of mesoporous carbon (MC1, MC2, and MC3) properties and water quality parameters on the adsorption of MC-LR were investigated and the results were analyzed by kinetic, isotherm, thermodynamic, Derjaguin-Landau-Verwey-Overbeek (DLVO), and intraparticle diffusion models. MC1 was the most appropriate type for the removal of MC-LR with a maximum adsorption capacity of 35,670.49 μg/g. Adsorption of MC-LR is a spontaneous reaction dominated by van der Waals interactions. Pore sizes of 8.5-14 nm enhance the pore diffusion of MC-LR from the surface to the mesopores of MC1. The adsorption capacity was not sensitive to changes in the pH (3.2-8.0) and the existence of organic matter (2-5 mg/L). Furthermore, the final concentration of MC-LR was below the WHO guideline level after a 10-min reaction with 20 mg/L of MC1 in the Nak-Dong River, a drinking water source. The MC-LR adsorption mainly competed with humic substances (500-1000 g/mole); however, they did not have a great effect on adsorption.

Elimination of microcystin-LR and residual Mn species using permanganate and powdered activated carbon: Oxidation products and pathways

The oxidation of microcystin-LR (MC-LR) in deionized water (DI) and river water using potassium permanganate (KMnO₄) at a neutral pH and at 23 ± 2 °C was investigated. These two aqueous systems (i.e., DI and river water) gave comparable second-order rate constants (289.9 and 285.5 M^-1s^-1 (r² > 0.99), respectively), which confirmed the effectiveness of this oxidation process for the treatment of natural surface water. The presence of either humic or fulvic acid reduced the removal efficiency of MC-LR, with the latter exhibiting a greater inhibitory effect. Monitoring of MC-LR and residual Mn²⁺ levels with adding KMnO₄ (1 mg/L) and powdered activated carbon (PAC, 5-20 mg L^-1) before and during coagulation, respectively, revealed that 60 min of permanganate pre-oxidation followed by coagulant addition with PAC was the most effective approach for reducing both levels below limits stated by WHO guidelines. The MC-LR degradation products were the result of oxidation occurring at the diene and aromatic moieties of the Adda (3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid) side-chain, in addition to amine bond hydrolysis of the Mdha (N-methyldehydroalanine) moiety. Several toxic by-products with an intact Adda chain were observed during the reaction, but completely disappeared after 60 min. This further supports the conclusion that sufficient contact time with permanganate (i.e., >60 min) is essential to reducing the residual toxicity and maximizing the efficiency of MC-LR oxidation when treating raw water.

Employing CBPR to investigate function, utility, and longevity of household filters to improve potable water quality for indigenous peoples at Lake Atitlán, Guatemala: a pilot study with San Pedro de La Laguna

Cyanobacterial blooms at Lake Atitlán in Guatemala threaten and compromise the livelihood and health of local residents. Indigenous Tz'utujil, Kaqchikel, and K'iche' rely directly on lake water for drinking, bathing, cleaning, cooking, and fishing. Nonpoint source runoff and untreated wastewater pumped directly into the lake contribute to high fecal pathogen loads into source waters. Concurrent nutrient loading results in cyanobacterial blooms further compromising water quality. A lakeside municipality facing high rates of childhood gastrointestinal illness volunteered to engage in community-based participatory research (CBPR) to evaluate efficacy, utility, and longevity of filters in households. The filters consistently reduced the risk of coliforms and E. coli in household water drawn from the lake based on World Health Organization guidelines. Household surveys were simultaneously administered through a student leadership group regarding water usage, water quality, and community health. Filters demonstrated ability to reduce high loads of fecal indicators from source waters and ability to remove a cyanobacterial toxin (microcystin) at 10 μg/L in deionized water. Further studies are imperative to determine longevity of use in households and CBPR provides a powerful avenue to test efficacy of a possible intervention while engaging stakeholders and empowering community members with sustainable solutions.

A Bacillus sp. strain with antagonistic activity against Fusarium graminearum kills Microcystis aeruginosa selectively

Cyanobacterial harmful algal blooms (CyanoHABs) cause severe environmental problems, economic losses and threaten human health seriously. In the present study, a Bacillus sp. strain, designated as AF-1, with strong antagonistic activity against plant pathogenic fungus Fusarium graminearum was isolated from purple soil. Bacillus sp. AF-1 selectively killed Microcystis aeruginosa at low cell density (1.6×10³cfu/mL), and showed the strongest bactericidal activity against M. aeruginosa NIES-843 (A_e=93%, t=6d). The algicidal substances originated from strain AF-1 were stable in the temperature range of 35-100°C, and pH range of 3-11. Cell-free filtrate of AF-1 culture caused excessive accumulation of intracellular reactive oxygen species (ROS), cell death and the efflux of intracellular components of M. aeruginosa NIES-843 cells. The expression of genes recA, psbA1, psbD1, rbcL and mcyB, involved in DNA repair, photosynthesis and microcystin synthesis of NIES 843, were significantly influenced by the cell-free filtrate of AF-1 culture. Bacillus sp. AF-1 has the potential to be developed as a bifunctional biocontrol agent to control CyanoHABs and F. graminearum caused plant disease.

Microcystins affect zooplankton biodiversity in oxbow lakes

The authors tested the hypothesis that zooplankton diversity and density are affected by the presence of cyanotoxins in the water. The authors focused on 4 oxbow lakes of the Vistula River in southern Poland, which are subjected to mass cyanobacterial development. In 2 of the oxbows (Piekary and Tyniec), microcystins released into the water were found. The highest concentration of microcystins (0.246 μg/L) was observed for microcystins LR. Zooplankton diversity showed a weak response to the presence of microcystins released into the water. The Shannon index (H') of total zooplankton diversity decreased in the Piekary and Tyniec oxbows during periods when the microcystin concentrations were highest. The same trend was noted for diversity of rotifers in both oxbows and for diversity of copepods in Piekary, but not for copepods in Tyniec. No such trends were found for the diversity of cladocerans in any of the oxbows, nor was a relationship found between density of zooplankton and microcystins. Statistical analyses showed that the number of species in individual samples was negatively correlated with the levels of sulfates, phosphates, and ammonia, but the microcystin concentration was positively related to those levels. This points to the complexity of the interactions and synergies among toxins, abiotic factors, and zooplankton biodiversity. In focusing on the problem of cyanotoxins, conservation studies should pay attention to this complexity. Environ Toxicol Chem 2017;36:165-174. © 2016 SETAC.