Estimation of microcystins in the freshwater fish Oreochromis niloticus in an Egyptian fish farm containing a Microcystis bloom

Rice Straw-Derived Biochar Mitigates Microcystin-LR-Induced Hepatic Histopathological Injury and Oxidative Damage in Male Zebrafish via the Nrf2 Signaling Pathway

Microcystin-leucine arginine (MC-LR) poses a serious threat to aquatic animals during cyanobacterial blooms. Recently, biochar (BC), derived from rice straw, has emerged as a potent adsorbent for eliminating hazardous contaminants from water. To assess the joint hepatotoxic effects of environmentally relevant concentrations of MC-LR and BC on fish, male adult zebrafish (Danio rerio) were sub-chronically co-exposed to varying concentrations of MC-LR (0, 1, 5, and 25 μg/L) and BC (0 and 100 μg/L) in a fully factorial experiment. After 30 days exposure, our findings suggested that the existence of BC significantly decreased MC-LR bioavailability in liver. Furthermore, histopathological analysis revealed that BC mitigated MC-LR-induced hepatic lesions, which were characterized by mild damage, such as vacuolization, pyknotic nuclei, and swollen mitochondria. Compared to the groups exposed solely to MC-LR, decreased malondialdehyde (MDA) and increased catalase (CAT) and superoxide dismutase (SOD) were noticed in the mixture groups. Concurrently, significant changes in the mRNA expression levels of Nrf2 pathway genes (cat, sod1, gstr, keap1a, nrf2a, and gclc) further proved that BC reduces the oxidative damage induced by MC-LR. These findings demonstrate that BC decreases MC-LR bioavailability in the liver, thereby alleviating MC-LR-induced hepatotoxicity through the Nrf2 signaling pathway in zebrafish. Our results also imply that BC could serve as a potentially environmentally friendly material for mitigating the detrimental effects of MC-LR on fish.

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

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

Cyanotoxins in food: Exposure assessment and health impact

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

Effects of Astaxanthin on Growth Performance, Gut Structure, and Intestinal Microorganisms of Penaeus vannamei under Microcystin-LR Stress

Microcystin-LR (MC-LR) are biologically active cycloheptapeptide compounds that are released by cyanobacteria during water blooms and are extensively found in aquatic ecosystems. The Penaeus vannamei is a significant species in global aquaculture. However, the high level of eutrophication in aquaculture water frequently leads to outbreaks of cyanobacterial blooms, posing a significant threat to its sustainable cultivation. Astaxanthin (AX) is commonly utilized in aquaculture for its physiological benefits, including promoting growth and enhancing immune function in cultured organisms. This study aimed to examine the protective effect of astaxanthin on P. vannamei exposed to microcystin-induced stress. The experiment consisted of three groups: one group was fed formulated feed containing MC (100 μg/kg), another group was fed formulated feed containing MC (100 μg/kg) + AX (100 mg/kg), and the third group was fed basic feed (control group). After 15 days of feeding, the specific growth rate (SGR) was significantly higher in the MCAX group (2.21% day-1) compared to the MC group (0.77% day-1), and there was no significant difference between the MCAX group (2.21% day-1) and the control group (2.24% day-1). Similarly, the percent of weight gain (PWG) was also significantly higher in the MCAX group (14.61%) compared to the MC group (13.44%) and the control group (16.64%). Compared to the control group, the epithelial cells in the MC group suffered severe damage and detachment from the basement membrane. However, in the MCAX group, although there was still a gap between the intestinal epithelial cells and the basement membrane, the overall intestinal morphology was slightly less impaired than it was in the MC group. The analysis of the intestinal microbiota revealed a significant disparity in the community composition (chao 1 and ACE) between the MC and MCAX groups. When comparing the various bacterial genera, the MC group exhibited an increase in Vibrio abundance, whereas the MCAX group showed a decrease in both Shewanella and Vibrio abundance. The results indicate that AX has a positive impact on the growth performance and resistance of P. vannamei against MC by regulating the composition of the intestinal microbiota. AX can be utilized to mitigate the detrimental effects of MC in aquaculture practices. This function could be attributed to the role of AX in preserving the structural integrity of the intestinal mucosa and regulating the composition of the intestinal microbiota.

Cyanotoxins in African waterbodies: occurrence, adverse effects, and potential risk to animal and human health

Public concerns about cyanotoxins production in water and its detrimental impacts on human and animal health are growing primarily due to the widespread eutrophication observed in aquatic ecosystems. A review of relevant literature was done to determine the degree of cyanotoxin occurrence and its harmful effects in African waterbodies. Data were extracted from 64 published studies from 1990 to 2022 that quantified the concentration of cyanotoxins in African aquatic ecosystems. Cyanotoxins have been reported in 95 waterbodies (29 lakes, 41 reservoirs, 10 ponds, 9 rivers, 5 coastal waters, and 1 irrigation canal) from 15 African countries. Cyanotoxins were documented in all the regions of Africa except the central region. Microcystins have been reported in nearly all waterbodies (98.9%), but anatoxin-a (5.3%), cylindrospermopsin (2.1%), nodularins (2.1%), homoanatoxin-a (1.1%), and β-N-methylamino-L-alanine (1.1%) were encountered in a small number of water ecosystems, homoanatoxin-a and β-N-methylamino-L-alanine each occurred in one waterbody. The largest concentrations of microcystins and nodularins were reported in South African Lakes Nhlanganzwani (49,410 μg L-1) and Zeekoevlei (347,000 μg g-1). Microcystin concentrations exceeding the WHO guideline for lifetime drinking water (1 μg L-1) were reported in 63% of the aquatic ecosystems surveyed. The most frequently reported toxin-producing cyanobacteria genus is Microcystis spp. (73.7%), followed by Oscillatoria spp. (35.8%) and Dolichospermum spp. (33.7%). Cyanotoxin-related animal mortality and human illness were reported in the continent. Consequently, it is necessary to regularly monitor the level of nutrients, cyanobacteria, and cyanotoxins in African waterbodies in an integrated manner to devise a sustainable water resources management.

Effects of Algicidal Macrophyte Metabolites on Cyanobacteria, Microcystins, Other Plankton, and Fish in Microcosms

To control harmful algae blooms (HABs), methods based on natural mechanisms are now required. We investigated the effects of an algicide derived from macrophyte metabolites, namely mixtures of gallic, tetradecanoic, heptanoic, and octanoic acids (1:1:1:1 mass ratio, a total concentration of 14 mg/L), on the biomass of cyanobacteria and other plankton and the production of microcystins under experimental conditions. Two types of microcosms have been created: simple (microalgae, cyanobacteria, and zooplankton) and complex (microalgae, cyanobacteria, zooplankton, and planktivorous fish). We observed the dynamics of the phytoplankton structure, the concentrations of microcystins and chlorophyll-a, hydrochemistry, and the status of zooplankton and fish in both types of microcosms with and without algicide for one month (from 19 July to 19 August 2021). The introduction of algicide caused changes in phytoplankton structure, a drop in cyanobacterial biomass, and a decrease in the total concentration of microcystins. Surprisingly, the contributions of the most toxic microcystins (LR form) were higher in both types of microcosms exposed to algicide than in microcosms without algicide. The inhibitory effect on the cyanobacterial biomass was most significant in complex ecosystems (containing fish), while it was only observed at the end of the exposure in simple ecosystems. Not only algicide but also phytoplankton consumed by fish and zooplankton, as well as nutrient excretory activity by both consumers, seem to have impact on cyanobacterial biomass. This study found that the using chemical substances similar to macrophyte metabolites can help regulate HABs and cyanotoxins. However, the results differ depending on ecosystem type.

Metabolomics Applied to Cyanobacterial Toxins and Natural Products

The biological and chemical diversity of Cyanobacteria is remarkable. These ancient prokaryotes are widespread in nature and can be found in virtually every habitat on Earth where there is light and water. They are producers of an array of secondary metabolites with important ecological roles, toxic effects, and biotechnological applications. The investigation of cyanobacterial metabolites has benefited from advances in analytical tools and bioinformatics that are employed in metabolomic analyses. In this chapter, we review selected articles highlighting the use of targeted and untargeted metabolomics in the analyses of secondary metabolites produced by cyanobacteria. Here, cyanobacterial secondary metabolites have been didactically divided into toxins and natural products according to their relevance to toxicological studies and drug discovery, respectively. This review illustrates how metabolomics has improved the chemical analysis of cyanobacteria in terms of speed, sensitivity, selectivity, and/or coverage, allowing for broader and more complex scientific questions.

Morphological, molecular, and biochemical study of cyanobacteria from a eutrophic Algerian reservoir (Cheffia)

The cyanobacteria management in water bodies requires a deep knowledge of the community composition. Considering the reliable and thorough information provided by the polyphasic approach in cyanobacteria taxonomy, here we assess the cyanobacterial community structure of the Cheffia reservoir from Algeria. Cyanobacteria were identified on the basis of morphological traits and next-generation sequencing (NGS); toxins-related genes were localized in addition to the identification of toxins; temperature and nutrient level of water samples were also determined. The polyphasic approach was essential for cyanobacteria investigation; 28 genera were identified through 16S rRNA metabarcoding with the dominance of taxa from Microcystis (34.2%), Aphanizomenon (20.1%), and Planktothrix (20.0%), and morphological analysis revealed the association in this water body of five species within the genus Microcystis: M. aeruginosa, M. novacekii, M. panniformis, M. ichthyoblabe, and M. flos-aquae. The presence of mcyE genotypes was detected; moreover, HPLC-PDA and LC-ESI-MS/MS revealed the production of microcystin-LR. Results obtained in our study are very important since this ecosystem is used for water supply and irrigation; as a consequence, a good water management plan is essential.

Spirulina platensis protects against microcystin-LR-induced toxicity in rats

Microcystis aeruginosa produces an abundant cyanotoxin (microcystins (MCs) in freshwater supplies. MCs have adverse health hazards to animals and humans. Microcystin-leucine-arginine (microcystin-LR or MC-LR) is the most studied among these MCs due to their high toxicity. So, this study was designed to evaluate the possible therapeutic role of the natural algal food supplement, Spirulina platensis (SP), against MC-LR-induced toxic effects in male Wistar rats. Forty rats were randomly divided into five groups. Control and SP groups orally administered distilled water and SP (1000 mg/kg/daily), respectively, for 21 days. MC-LR group was intraperitoneally injected with MC-LR (10 μg/kg/day) for 14 days. MC-LR-SP500 and MC-LR-SP1000 groups were orally treated with SP (500 and 1000 mg/kg, respectively) for 7 days and concomitantly with MC-LR for 14 days. MC-LR induced oxidative hepatorenal damage, cardiotoxicity, and neurotoxicity greatly, which was represented by reduction of reduced glutathione content and the activities of glutathione peroxidase, catalase, and superoxide dismutase and elevation of concentrations of nitric oxide and malondialdehyde in renal, hepatic, brain, and heart tissues. In addition, it increased serum levels of urea, creatinine, tumor necrosis factor-alfa, interleukin-1beta and interleukin-6 and serum activities of alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, creatine kinase, and creatine kinase-MB. However, S. platensis restored normal levels of measured serum parameters, ameliorated MC-LR-induced oxidative damage, and normalized tissue antioxidant biomarkers. In conclusion, SP alleviated MC-induced organ toxicities by mitigating oxidative and nitrosative stress and lipid peroxidation.

Energy-effective elimination of harmful microcystins by a non-thermal plasma process

Some cyanobacteria produce toxins that threaten the aquatic ecosystem and human health. To prevent serious consequences, this study suggests a potential means of reducing microalgal toxins, microcystins (MCs) by applying non-thermal plasma (NTP) process. Quantified MC-RR, -LR, and -YR were drastically degraded and removed as much as 99.9% by reactive species generated by NTP. Results further demonstrate that NTP uses less energy based on estimated energy per order (EEO kWh m^-3 order^-1) than other advanced oxidation processes and requires relatively less time to remove the MCs. As a result, NTP may be a viable management option for effective MC control during severe surface water blooms.

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.

Microcystin-Induced Immunotoxicity in Fishes: A Scoping Review

Cyanobacteria (blue-green algae) have been present on Earth for over 2 billion years, and can produce a variety of bioactive molecules, such as cyanotoxins. Microcystins (MCs), the most frequently detected cyanotoxins, pose a threat to the aquatic environment and to human health. The classic toxic mechanism of MCs is the inhibition of the protein phosphatases 1 and 2A (PP1 and PP2A). Immunity is known as one of the most important physiological functions in the neuroendocrine-immune network to prevent infections and maintain internal homoeostasis in fish. The present review aimed to summarize existing papers, elaborate on the MC-induced immunotoxicity in fish, and put forward some suggestions for future research. The immunomodulatory effects of MCs in fish depend on the exposure concentrations, doses, time, and routes of exposure. Previous field and laboratory studies provided strong evidence of the associations between MC-induced immunotoxicity and fish death. In our review, we summarized that the immunotoxicity of MCs is primarily characterized by the inhibition of PP1 and PP2A, oxidative stress, immune cell damage, and inflammation, as well as apoptosis. The advances in fish immunoreaction upon encountering MCs will benefit the monitoring and prediction of fish health, helping to achieve an ecotoxicological goal and to ensure the sustainability of species. Future studies concerning MC-induced immunotoxicity should focus on adaptive immunity, the hormesis phenomenon and the synergistic effects of aquatic microbial pathogens.

Analysis of bacterial communities in a municipal duck pond during a phytoplankton bloom and isolation of Anatilimnocola aggregata gen. nov., sp. nov., Lacipirellula limnantheis sp. nov. and Urbifossiella limnaea gen. nov., sp. nov. belonging to the phylum Planctomycetes

Waterbodies such as lakes and ponds are fragile environments affected by human influences. Suitable conditions can result in massive growth of phototrophs, commonly referred to as phytoplankton blooms. Such events benefit heterotrophic bacteria able to use compounds secreted by phototrophs or their biomass as major nutrient source. One example of such bacteria are Planctomycetes, which are abundant on the surfaces of marine macroscopic phototrophs; however, less data are available on their ecological roles in limnic environments. In this study, we followed a cultivation-independent deep sequencing approach to study the bacterial community composition during a cyanobacterial bloom event in a municipal duck pond. In addition to cyanobacteria, which caused the bloom event, members of the phylum Planctomycetes were significantly enriched in the cyanobacteria-attached fraction compared to the free-living fraction. Separate datasets based on isolated DNA and RNA point towards considerable differences in the abundance and activity of planctomycetal families, indicating different activity peaks of these families during the cyanobacterial bloom. Motivated by the finding that the sampling location harbours untapped bacterial diversity, we included a complementary cultivation-dependent approach and isolated and characterized three novel limnic strains belonging to the phylum Planctomycetes.

Rainbow darter (Etheostoma caeruleum) from a river impacted by municipal wastewater effluents have altered gut content microbiomes

Municipal wastewater treatment plant (WWTP) effluent contains pharmaceuticals and personal care products known to affect fish health and reproduction. The microbiome is a community of bacteria integral in maintaining host health and is influenced by species, diet, and environment. This study investigated changes in the diversity and composition of the gut content microbiome of rainbow darter (Etheostoma caeruleum) at ten sites on the Grand River, Ontario, Canada. Gut contents were collected in fall 2018 from these fish at sites upstream and downstream of two municipal wastewater treatment plants (WWTPs; Waterloo and Kitchener). 16S rRNA genes were sequenced to determine the composition and diversity (alpha and beta) of microbial taxa present. Gut content bacterial alpha diversity increased downstream of both WWTP outfalls; dominance of bacterial amplicon sequence variants decreased compared to upstream fish. Fish collected at different sites had distinct bacterial communities, with upstream samples dominant in Proteobacteria and Firmicutes, and downstream samples increasingly abundant in Proteobacteria and Cyanobacteria. In mammals, increased abundance of Proteobacteria is indicative of microbial dysbiosis and has been linked to altered health outcomes, but this is not yet known for fish. This research indicates that the fish gut content microbiome was altered downstream of WWTP effluent outfalls and could lead to negative health outcomes.

A superoxide dismutase (MnSOD) with identification and functional characterization from the freshwater mussel Cristaria plicata

Manganese superoxide dismutase (MnSOD) is a sort of important metalloenzyme that can catalyze ROS in the organisms. In this study, MnSOD cDNA of C. plicata, designated as CpMnSOD (accession no. MK465057), was cloned from hemocytes. The full-length cDNA of MnSOD was 1096 bp with a 672 bp open reading frame encoding 223 amino acids. The deduced amino acid sequence contained a mitochondrial-targeting sequence (MTS) of 18 amino acids in the N-terminus, and four conserved amino acids for manganese binding (H⁴⁹, H⁹⁷, D¹⁸², H¹⁸⁶). CpMnSOD showed a high level (65-73%) of sequence similarity to MnSODs from other species. The results of Real-time quantitative PCR revealed that CpMnSOD mRNA constitutively expressed in tissues. The highest expression level was in hepatopancreas, followed by muscle, mantle and gill, and the lowest expression level was in hemocytes. After microcystin challenge, the expression levels of CpMnSOD mRNA were up-regulated in hemocytes and hepatopancreas. The cDNA of CpMnSOD was cloned into the plasmid pColdI-ZZ, and the recombinant protein was expressed in Escherichia coli BL21 (DE3). The enzyme stability assay showed that the purified CpMnSOD protein maintained more than 80% enzyme activity at temperature up to 70 °C, at pH 2.0-10.0, and resistant to 8 mol/L urea or 8% SDS.

Bioaccumulation of microcystins in seston, zooplankton and fish: A case study in Lake Zumpango, Mexico

Cyanotoxins from toxic blooms in lakes or eutrophic reservoirs are harmful to several organisms including zooplankton, which often act as vectors of these secondary metabolites, because they consume cyanobacteria, bioaccumulate the cyanotoxins and pass them on along the food chain. Microcystins are among the most commonly found cyanotoxins and often cause zooplankton mortality. Although cyanobacterial blooms are common and persistent in Mexican water bodies, information on the bioaccumulation of cyanotoxins is scarce. In this study we present data on the bioaccumulation of cyanotoxins from Planktothrix agardhii, Microcystis sp., Cylindrospermopsis raciborskii and Dolichospermum planctonicum blooms in the seston (suspended particulate matter more than 1.2 μm) by zooplankton and fish (tilapia (Oreochromis niloticus) and mesa silverside (Chirostoma jordani) samples from Lake Zumpango (Mexico City). The cyanotoxins were extracted from the seston, zooplankton and fish tissue by disintegration using mechanical homogenization and 75% methanol. After extraction, microcystins were measured using an ELISA kit (Envirologix). Concentration of microcystins expressed as equivalents, reached a maximum value of 117 μg g^-1 on sestonic samples; in zooplankton they were in the range of 0.0070-0.29 μg g^-1. The dominant zooplankton taxa included Acanthocyclops americanus copepodites, Daphnia laevis and Bosmina longirostris. Our results indicate twice the permissible limits of microcystins (0.04 μg kg^-1 d^-1) for consumption of cyanobacterial products in whole fish tissue of Chirostoma jordani. The data have been discussed with emphasis on the importance of regular monitoring of water bodies in Mexico to test the ecotoxicological impacts of cyanobacterial blooms and the risk that consumption of products with microcystins could promote.

Stable-isotope dilution LC-MS/MS method for quantitative determination of microcystin conjugates with cysteine and glutathione in biotic matrices

Microcystins are cyclic peptide toxins with hepatotoxic and tumor-promoting properties, which are produced in significant quantities (up to tens of μg/L) in freshwater cyanobacterial water blooms. Several studies reported microcystin accumulation in fish with possible food transfer to humans. These compounds are further metabolized to cysteine and glutathione conjugates which can be present in tissues in significant concentrations. In this study, we focused on the development and evaluation of robust and highly sensitive SPE-LC-MS/MS method for the analysis of microcystin conjugates in fish tissue samples. For the first time, we demonstrate the use of isotopically labeled internal standards which are essential for accurate and precise determination of analytes in complex biotic matrices. LLOQs of respective microcystin conjugates (signal-to-noise ratio; S/N > 10, peak-to-peak method) ranged from 3.3 to 5.0 ng/g of tissue fresh weight (FW). The calibration was linear within a range of concentrations from 1 to 70 ng/mL for all analyzed conjugates. The precision and repeatability of the method were very good with recoveries in the range of 88.5-107.6% and relative standard deviations between 8.8 and 13.2% for all analytes. In the follow-up study, fully validated method was used for the determination of microcystin conjugate levels in common carp exposed to microcystin-containing cyanobacterial biomass under controlled conditions. Significant amounts of microcystin conjugates (up to 55 ng/g) were found in the tissues of fish after 7 weeks of exposure. Our method was shown to be robust, sensitive, selective, and suitable for the determination of trace levels of microcystin conjugates in fish tissues.

Molecular effects of Microcystin-LA in tilapia (Oreochromis niloticus)

Nile tilapia (Oreochromis niloticus) is a freshwater phytoplanktivorous fish species reported to accumulate and tolerate large amounts of cyanotoxins such as microcystins (MCs). The present study aimed to investigate molecular responses to the acute exposure of Nile tilapia to the Microcystin-LA analogue (MC-LA). Thus, the specimens were sublethally exposed to 1000 μg kg^-1 of MC-LA for 12, 24, 48, and 96 h. Gene expression of PP1, PP2A, GST, GPX and actin was analyzed by quantitative PCR. The protein abundance profile of PP2A was determined by immunoblotting, while the integrity of its biological function was assessed by a phosphatase enzymatic assay. PP2A activity was significantly and strongly reduced by MC-LA. A resulting feedback mechanism significantly increased PP2A gene expression and protein abundance in all assessed times. However, a recovery of that phosphatase activity was not observed. In this study, the observed increase in GPX gene expression was the only response that could be directly related to the unknown factors associated to the fish survival to such high dose exposure.

Piperine Enhances the Antioxidant and Anti-Inflammatory Activities of Thymoquinone against Microcystin-LR-Induced Hepatotoxicity and Neurotoxicity in Mice

Microcystin- (MC-) LR is the most frequent cyanotoxin produced by Microcystis aeruginosa cyanobacteria in the contaminated freshwater environment. MC represents a health hazard to humans and animals. Therefore, the present study was designed to evaluate the potential ameliorative effect of thymoquinone (TQ) and/or piperine (PP) against MC toxicity in mice. Fifty-six mice were randomly divided into seven experimental groups. Group I is the normal control that received distilled water for 21 days; Group II (TQ) was treated with TQ (10 mg/kg, i.p) for 21 days; Group III (PP) was treated with PP (25 mg/kg, i.p) for 21 days; Group IV (MC) was treated with MC (10 μg/kg, i.p) for 14 days and served as the toxic control; and Groups V, VI, and VII received TQ and/or PP 7 days prior to MC and continued for 14 days with MC. The results revealed that MC elicited hepatotoxicity and neurotoxicity which was evident due to the significant elevation of serum AST, ALT, γGT, ALP, LDH, IL-1β, IL-6, and TNF-α levels. Furthermore, MC markedly increased MDA and NO contents along with reduction of GSH, SOD, CAT, and GSH-Px in liver and brain tissues. The electron transport chain may be a possible target for MC. TQ and/or PP ameliorated the MC-mediated oxidative damage in the liver and brain which might be attributed to their antioxidant properties. However, the concurrent treatment of TQ and PP showed the best regimen as a result of the PP-enhanced bioavailability of TQ.

Concentrations of cylindrospermopsin toxin in water and tilapia fish of tropical fishponds in Egypt, and assessing their potential risk to human health

Unlike microcystin, cylindrospermospin (CYN) concentrations in fishpond water and their accumulation in fish tissues have been largely unexplored. This study determined CYN levels in water and tilapia fish organs from three tropical fishponds in southern Egypt. Water and fish samples were collected monthly from fishponds for 12 months (Oct 2012 to Sep 2013). The results revealed that six CYN-producing species of cyanobacteria dominated phytoplankton populations and formed blooms in these fishponds during warm months. Among these species, Anabaena affinis, Planktothrix agardhii, Cylindrospermopsis catemaco, and C. philippinensis were assigned as CYN producers for the first time in the present study. The highest cell densities of CYN-producing species in fishponds were recorded in August and September 2013, correlating with high temperature, pH and nutrient concentrations. Dissolved CYN was found in fishpond waters at levels (0.3-2.76 μg L^-1) very close to those of particulate CYN (0.4-2.37 μg L^-1). CYN was also estimated in tilapia fish organs at levels up to 417 ng g^-1 in the intestines, 1500 ng g^-1 in the livers, and 280 ng g^-1in edible muscles. Compared to the recommended guideline (0.03 μg kg^-1 day^-1), the estimated daily intake (EDI) of CYN in our samples of edible muscles exceeded this limit by a factor of 1.3-14 during summer and autumn. This might represent a risk to human health upon consumption of such contaminated fish muscles. Therefore, fishponds worldwide should be monitored for the presence toxic cyanobacteria to protect humans from their potent toxins.

Cyanobacterial effects in Lake Ludoš, Serbia - Is preservation of a degraded aquatic ecosystem justified?

Cyanobacteria are present in many aquatic ecosystems in Serbia. Lake Ludoš, a wetland area of international significance and an important habitat for waterbirds, has become the subject of intense research interest because of practically continuous blooming of cyanobacteria. Analyses of water samples indicated a deterioration of ecological condition and water quality, and the presence of toxin-producing cyanobacteria (the most abundant Limnothrix redekei, Pseudanabaena limnetica, Planktothrix agardhii and Microcystis spp.). Furthermore, microcystins were detected in plants and animals from the lake: in macrophyte rhizomes (Phragmites communis, Typha latifolia and Nymphaea elegans), and in the muscle, intestines, kidneys, gonads and gills of fish (Carassius gibelio). Moreover, histopathological deleterious effects (liver, kidney, gills and intestines) and DNA damage (liver and gills) were observed in fish. A potential treatment for the reduction of cyanobacterial populations employing hydrogen peroxide was tested during this study. The treatment was not effective in laboratory tests although further in-lake trials are needed to make final conclusions about the applicability of the method. Based on our observations of the cyanobacterial populations and cyanotoxins in the water, as well as other aquatic organisms and, a survey of historical data on Lake Ludoš, it can be concluded that the lake is continuously in a poor ecological state. Conservation of the lake in order to protect the waterbirds (without urgent control of eutrophication) actually endangers them and the rest of the biota in this wetland habitat, and possibly other ecosystems. Thus, urgent measures for restoration are required, so that the preservation of this Ramsar site would be meaningful.

Microcystin induction small Maf protein involve in transcriptional regulation of GST from freshwater mussel Cristaria plicata

The small Mafs, MafF, MafG and MafK play critical roles in morphogenesis and homeostasis through associating with Cap "n" Collar family of transcription factors. In this study, we tried to identify a small Maf protein in the freshwater mussel Cristaria plicata. The MafK cDNA of C. plicata, designated as CpMafK, was cloned from the hemocytes using degenerate primers by the rapid amplification of cDNA ends PCR. The full length cDNA of CpMafK is 2170 bp, which includes an open reading frame of 570 bp, encoding 189 amino acids. CpMafK possesses four conserved domains and shows a low level (54-63%) of sequence similarity to small Mafs from other species. The results of Real-time quantitative PCR revealed that CpMafK mRNA was constitutively expressed in tissues, and the highest expression level was in hepatopancreas. After microcystin challenge, the expression levels of CpMafK mRNA were up-regulated in hemocytes and hepatopancreas. The cDNA of CpMafK was cloned into the plasmid pET-32, and the recombinant protein was expressed in Escherichia coli BL21(DE3). CpMafK could combine to the promoters of CpGST1 and CpGST2 with high-affinity in vitro. Therefore, CpMafK could regulate the expression of detoxification.

Subchronic toxicity of Nile tilapia with different exposure routes to Microcystis aeruginosa: Histopathology, liver functions, and oxidative stress biomarkers

BACKGROUND

Toxic cyanobacterial blooms (Microcystis aeruginosa contains microcystins [MCs]) have been reported to induce clinicopathological alterations as well as different oxidative stress in aquatic biota.

AIM

Three-week subchronic exposure experiment was carried out on Nile tilapia, to determine their effects on fish behavior, tissues, liver functions, antioxidant enzymes, and lipid peroxidation.

MATERIALS AND METHODS

Fish were exposed to four main treatments; orally fed diet plus toxic cells of M. aeruginosa (containing 3500 µg/g MC-LR), immersion in 500 µg MC-LR/L, intraperitoneal injection of M. aeruginosa MC-LR with a dose of 0.1 ml of extracted toxin at a dose of 200 μg/kg bwt, and the fourth one served as a control group, then the fish were sacrificed at the end of 3^rd week of exposure.

RESULTS

The results revealed no recorded mortality with obvious behavioral changes and an enlarged liver with the congested gall bladder. Histopathology demonstrated fragmentation, hyalinization, and necrosis of the subcutaneous musculature marked fatty degeneration, and vacuolation of hepatopancreatic cells with adhesion of the secondary gill lamellae associated with severe leukocytic infiltration. Furthermore, liver functions enzymes (aspartate aminotransferase and alanine aminotransferase, and the activities of glutathione peroxidase, glutathione reductase, lipid peroxidase, and catalase enzymes) were significantly increased in all treatments starting from the 2^nd week as compared to the control levels.

CONCLUSION

In this context, the study addresses the possible toxicological impacts of toxic M. aeruginosa contain MC-LR to Nile tilapia, and the results investigated that MC-LR is toxic to Nile tilapia in different routes of exposure as well as different doses.

Accumulation of Microcystin (LR, RR and YR) in Three Freshwater Bivalves in Microcystis aeruginosa Bloom Using Dual Isotope Tracer

Abstract: Stable isotope tracers were first applied to evaluate the Microcystis cell assimilation efficiency of Sinanodonta bivalves, since the past identification method has been limited to tracking the changes of each chl-a, clearity, and nutrient. The toxicity profile and accumulation of MC-LR, -RR and -YR in different organs (foot and digestive organs) from the three filter-feeders (Sinanodonta woodina, Sinanodonta arcaeformis, and Unio douglasiae) were assessed under the condition of toxigenic cyanobacteria (Microcystis aeruginosa) blooms through an in situ pond experiment using ¹³C and ¹⁵N dual isotope tracers. Chl-a concentration in the manipulated pond was dramatically decreased after the beginning of the second day, ranging from 217.5 to 15.6 μg·L^-1. The highest amount of MCs was incorporated into muscle and gland tissues in U. douglasiae during the study period, at nearly 2 or 3 times higher than in S.woodiana and S. arcaeformis. In addition, the incorporated ¹³C and ¹⁵N atom % in the U. douglasiae bivalve showed lower values than in other bivalves. The results demonstrate that U. douglasiae has less capacity to assimilate toxic cyanobacteria derived from diet. However, the incorporated ¹³C and ¹⁵N atom % of S. arcaeformis showed a larger feeding capacity than U. douglasiae and S. wodiana. Our results therefore also indicate that S. arcaeformis can eliminate the toxin more rapidly than U. douglasiae, having a larger detoxification capacity.

Bioconcentration and multi-biomarkers of organic UV filters (BM-DBM and OD-PABA) in crucian carp

Organic UV filters (OUV-Fs) are increasingly used in sunscreens and personal care products. In the present work, the bioconcentration and multi-biomarker effects of butyl methoxydibenzoylmethane (BM-DBM) and ethylhexyl dimethyl p-aminobenzoate (OD-PABA) were investigated in crucian carp (Carassius auratus). The fish were exposed to various concentrations of BM-DBM (3.88, 35.61, 181.85 and 337.15μg/L), OD-PABA (4.66, 53.83, 264.22 and 459.32μg/L) and their mixture (2.31+2.79, 23.69+26.18, 97.37+134.81 and 193.93+246.08μg/L) for 28 days. The maximal concentrations of two OUV-Fs were detected in the fish liver, followed by the brain, kidney, gill and muscle in most cases. The maximal BCF values of OD-PABA calculated in various exposure concentrations were 0.37 - 101.21 in single exposure groups and 0.11 - 31.09 in mixed exposure groups. Acetylcholinesterase (AChE) activity was significantly inhibited by BM-DBM as well as the mixtures at all of the exposure concentrations and by OD-PABA at higher concentrations (≥264.22μg/L) during 28 days of exposure. The maximal inhibition rates of AChE activity reached 64.04% for BM-DBM, 41.05% for OD-PABA and 61.50% for the mixtures at the highest concentration, which indicated that these two OUV-Fs might damage the central nervous system. Concerning oxidative stress status, BM-DBM and the mixtures significantly increased superoxide dismutase (SOD) and glutathione reductase (GR) activities and inhibited catalase (CAT) activity, while OD-PABA caused a significant increase of GR and CAT activities. AChE and GR activities seemed to be more sensitive biomarkers for BM-DBM and OD-PABA.

Microcystin accumulation in bighead carp (Aristichthys nobilis) during a Microcystis-dominated bloom and risk assessment of the dietary intake in a fish pond in China

Microcystins (MCs) produced by cyanobacteria can accumulate in freshwater fish tissues and pose potential risk to human health. In this study, variations in MC content were examined in water samples and fish tissues during a Microcystis aeruginosa-dominated bloom in a fish pond in China, from June 2009 to August 2009. A total of ten microcystin variants were detected in water samples in the fish pond, including MCLR, MCRR, MCYR, MCLF, MCLY, MCLA, and MCLW, and other three undefined MC variants. MCLR was the dominant variant in the water samples, followed by MCLF and MCLY. The highest MC concentration in the common carp (Aristichthys nobilis) was found in the order intestine > spleen > muscle; however, the order with the most MC variants detected was muscle > spleen = kidney = gallbladder > liver = intestine. The highest overall MC concentration detected in the water samples was 12.24 μg L^-1, and the estimated daily intake for humans from the consumption of fish was about 0.48 μg MCLR eq kg^-1 body weight (BW), 12-fold the tolerable daily intake (TDI) proposed by the World Health Organization. Therefore, the combined risks from skin exposure and food intake in this fish pond should not be overlooked.

Cyanobacterial Toxins in Water Sources and Their Impacts on Human Health

Cyanobacteria are a group of phytoplankton of marine and freshwaters. The accelerated eutrophication of water sources by agricultural and industrial run-off has increased the occurrence and intensity of cyanobacterial blooms. They are of particular concern because of their production for potent hepato-, neuro-, and dermatoxins, being hazardous to human health. Dissemination of knowledge about cyanobacteria and their cyanotoxins assists water supply authorities in developing monitoring and management plans, and provides the public with appropriate information to avoid exposure to these toxins. This chapter provides a broad overview and up-to-date information on cyanobacteria and their toxins in terms of their occurrence, chemical and toxicological characteristics, fate in the environment, guideline limits, and effective treatment techniques to remove these toxins from drinking water. Future research directions were also suggested to fill knowledge and research gaps, and advance the abilities of utilities and water treatment plant designers to deal with these toxins.

Transfer, tissue distribution and bioaccumulation of microcystin LR in the phytoplanktivorous and carnivorous fish in Anzali wetland, with potential health risks to humans

This study was conducted to determine Microcystin LR concentration in the aquatic ecosystem of the Anzali wetland in Iran. Extraction and detection of MC-LR from the water and fish samples was conducted by the SPE and HPLC-UV apparatus. Our results showed that among toxic cyanobacteria, Anabaena was the dominant genera during the study period. The results indicated that MC-LR content in water ranged from 0.18 to 3.02μg/L in dissolved fraction and undetectable level to 1.13μg/L in cellular fraction, in all three seasons. The results of PCA revealed that the environmental parameters including EC, Chl-a, PO₄^3-, pH and temperature were the most effective factors influencing the MC-LR production. Results further showed the mean concentration of MC-LR in muscle and liver of silver carp ranged from 10.12 to 40.98 and from undetectable to 44.34μg/kg w.w, respectively. The mean concentration of MC-LR in northern pike was 15.18 to 35.1μg/kg w.w in muscle and undetectable to 51.91μg/kg w.w in liver samples. Our results suggest that consumption of fish harvested from the Anzali wetland seems to be unsafe for humans, based on obtained estimated daily intake values which were higher than the tolerable daily intake value recommended by WHO. In addition, bioaccumulation factor of MC-LR in edible tissues of fish was estimated based on lipid normalization. The results showed that the BAF of MC-LR in silver carp (1047±185L/kg of lipid) was lower than the northern pike (1272±185L/kg of lipid), although the difference was not significant.

Does anatoxin-a influence the physiology of Microcystis aeruginosa and Acutodesmus acuminatus under different light and nitrogen conditions?

Due to changing global climatic conditions, a lot of attention has been given to cyanobacteria and their bioactive secondary metabolites. These conditions are expected to increase the frequency of cyanobacterial blooms, and consequently, the concentrations of cyanotoxins in aquatic ecosystems. Unfortunately, there are very few studies that address the effects of cyanotoxins on the physiology of phytoplankton species under different environmental conditions. In the present study, we investigated the effect of the cyanotoxin anatoxin-a (ATX-A) on Microcystis aeruginosa (cyanobacteria) and Acutodesmus acuminatus (chlorophyta) under varying light and nitrogen conditions. Low light (LL) and nitrogen limitation (LN) resulted in significant cell density reduction of the two species, while the effect of ATX-A on M. aeruginosa was not significant. However, under normal (NN) and high nitrogen (HN) concentrations, exposure to ATX-A resulted in significantly (p < 0.05) lower cell density of A. acuminatus. Pigment content of M. aeruginosa significantly (p < 0.05) declined in the presence of ATX-A, regardless of the light condition. Under each light condition, exposure to ATX-A caused a reduction in total microcystin (MC) content of M. aeruginosa. The detected MC levels varied as a function of nitrogen and ATX-A concentrations. The production of reactive oxygen species (H₂O₂) and antioxidant enzyme activities of both species were significantly altered by ATX-A under different light and nitrogen conditions. Our results revealed that under different light and nitrogen conditions, the response of M. aeruginosa and A. acuminatus to ATX-A was variable, which demonstrated the need for different endpoints of environmental factors during ecotoxicological investigations.

Occurrence of microcystins in water, bloom, sediment and fish from a public water supply

Microcystin (MC) accumulation was determined in the liver and muscle of two omnivorous fish species which are consumed and are economically important, and in a planktivorous-carnivorous fish from Lake Eğirdir, Turkey. Free extractable MCs in fish tissue samples were detected by enzyme-linked immunosorbent assay (ELISA) with confirmation by high performance liquid chromatography with photodiode array detection (HPLC-PDA). MC-LA and -YR, were detected in both liver and muscle, followed by MCs -LY, -LF, -RR and -LR respectively. The MC concentrations varied between 0.043 and 1.72μg/g dry weight in liver and muscle tissues. MCs were also determined in samples of water, sediment and a bloom sample of Microcystis aeruginosa from the lake by HPLC-PDA. MC-LY and -YR were most commonly identified in water samples, with total MC concentrations ranging from 2.9±0.05 to 13.5±2.3μg/L. Sediment analyses, showed that MC-YR was present in samples between 7.0 and 17.6μg/g dw, especially in October, November and December when no MC-YR was recorded in water, followed by MC-LW. The findings indicate that water and sediment contained MCs, and more importantly that fish were contaminated with MCs that may pose an MC-associated human health risk.

Microcystin-LR induced developmental toxicity and apoptosis in zebrafish (Danio rerio) larvae by activation of ER stress response

Recent studies have demonstrated that cyanobacteria-derived Microcystin-LR (MC-LR) can cause developmental toxicity and trigger apoptosis in zebrafish (Danio rerio) larvae, but the underlying mechanisms remain largely unknown. In this study, we tested the hypothesis that the mechanism by which MC-LR induces developmental toxicity is through activation of endoplasmic reticulum (ER) stress. MC-LR (4.0 μM) exposure through submersion caused serious developmental toxicity, such as malformation, growth delay and decreased heart rates in zebrafish larvae, which could be inhibited by ER stress blocker, tauroursodeoxycholic acid (TUDCA, 20 μM). Meanwhile, acridine orange (AO) staining showed TUDCA could rescue cell apoptosis in heart area in zebrafish larvae resulted by MC-LR exposure. Real-time polymerase chain reaction (real-time PCR) analysis demonstrated that MC-LR induced activation of ER stress which consequently triggered apoptosis in zebrafish larvae. Protein expression examined by western blot indicated that MC-LR could activate MAPK8/Bcl-2/Bax pathway and caspase-dependent apoptotic pathway in zebrafish larva and the effects were mitigated by inhibition of ER stress. Taken together, the results observed in this study suggested that ER stress plays a critical role in developmental toxicity and apoptosis in zebrafish embryos exposed to MC-LR.

Determination of Environmental Exposure to Microcystin and Aflatoxin as a Risk for Renal Function Based on 5493 Rural People in Southwest China

Although the nephrotoxicity of microcystin and aflatoxin has been observed in animal and clinical cases, few population data are available. We conducted a cross-sectional study in Southwest China to investigate the association of renal function indicators (RFIs, including BUN, SCr, and eGFR) with exposure to microcystin and aflatoxin in 5493 members of the general population. Microcystin-LR levels in water and aquatic products and aflatoxin B1 levels in daily foods were measured by ELISA, and individual estimated daily intake (EDI) was assessed on the basis of the measurement and questionnaire. We found that participants with abnormal RFIs had a much higher mean level of microcystin-LR EDI than those with normal RFIs and that there was a significant increasing trend for abnormal rates and odds ratios of RFIs with increasing microcystin-LR EDI quartiles (p for trend = 0.000). Compared with the lowest quartile of microcystin-LR exposure, those in the highest quartile had significantly higher risks of abnormal BUN (OR = 1.80, 95% CI = 1.34-2.42), SCr (OR = 4.58, 95% CI = 2.92-7.21), and eGFR (OR = 4.41, 95% CI = 2.55-7.63), respectively, but no higher risk was found in subjects with higher AFB1 exposure. After adjustment for confounding factors, risk associations with microcystin-LR persisted. Consequently, our results suggest that microcystin, rather than aflatoxin, might be one important risk of renal-function impairment.

Cyanobacteria and cyanotoxins in fishponds and their effects on fish tissue

Cyanobacteria can produce toxic metabolites known as cyanotoxins. Common and frequently investigated cyanotoxins include microcystins (MCs), nodularin (NOD) and saxitoxins (STXs). During the summer of 2011 extensive cyanobacterial growth was found in several fishponds in Serbia. Sampling of the water and fish (common carp, Cyprinus carpio) was performed. Water samples from 13 fishponds were found to contain saxitoxin, microcystin, and/or nodularin. LC-MS/MS showed that MC-RR was present in samples of fish muscle tissue. Histopathological analyses of fish grown in fishponds with cyanotoxin production showed histopathological damage to liver, kidney, gills, intestines and muscle tissues. This study is among the first so far to report severe hyperplasia of intestinal epithelium and severe degeneration of muscle tissue of fish after cyanobacterial exposure. These findings emphasize the importance of cyanobacterial and cyanotoxin monitoring in fishponds in order to recognize cyanotoxins and their potential effects on fish used for human consumption and, further, on human health.

A review of neurotoxicity of microcystins

Cyanobacterial blooms-produced microcystins are secondary metabolites which can accumulate in the food chain and contaminate water, thus posing a potential threat to the health of aquatic animals and even humans. Microcystin toxicity affects not only the liver but also the other organs, i.e., the brain. The serious neurotoxicity effects caused by microcystins then lead to various symptoms. This review focuses on the neurotoxicity of microcystins. Microcystins can cross blood-brain barrier with the transport of Oatps/OATPs, causing neurostructural, functional, and behavioral changes. In this review, potential uptake mechanisms and neurotoxicity mechanisms are summarized, including neurotransmissions, neurochannels, signal transduction, oxidative stress, and cytoskeleton disruption. However, further researches are needed for detailed studies on signaling pathways and the downstream pathways of neurotoxicity of microcystins.

Occurrence of cyanobacteria and microcystin toxins in raw and treated waters of the Nile River, Egypt: implication for water treatment and human health

Monitoring of cyanobacteria and their associated toxins has intensified in raw water sources of drinking water treatment plants (WTPs) in most countries of the world. However, it is not explored yet for Egyptian WTPs. Therefore, this study was undertaken to investigate the occurrence of cyanobacteria and their microcystin (MC) toxins in the Nile River source water of Damietta WTP during warm months (April-September 2013) and to evaluate the removal efficiency of both cyanobacterial cells and MCs by conventional methods used in this plant as a representative of Egyptian drinking WTPs. The results showed that the source water at the intake of Damietta WTP contained dense cyanobacterial population (1.1-6.6 × 107 cells L(-1)) dominated by Microcystis aeruginosa. This bloom was found to produce MC-RR and MC-LR. Both cyanobacterial cell density and intracellular MCs in the intake source water increased with the increase in temperature and nutrients during the study period, with maximum values obtained in August. During treatment processes, cyanobacterial cells were incompletely removed by coagulation/flocculation/sedimentation (C/F/S; 91-96.8%) or sand filtration (93.3-98.9%). Coagulation/flocculation induced the release of MCs into the ambient water, and the toxins were not completely removed or degraded during further treatment stages (filtration and chlorination). MCs in outflow tank water were detected in high concentrations (1.1-3.6 μg L - 1), exceeding WHO provisional guideline value of 1 μg L - 1 for MC-LR in drinking water. Based on this study, regular monitoring of cyanobacteria and their cyanotoxins in the intake source water and at different stages at all WTPs is necessary to provide safe drinking water to consumers or to prevent exposure of consumers to hazardous cyanobacterial metabolites.

Identifying best methods for routine ELISA detection of microcystin in seafood

Ingestion of water contaminated with the cyanotoxin, microcystin (MC), can pose serious health risks to humans. MC is also known to accumulate in seafood; however, this exposure pathway is much less understood. A fundamental element of this uncertainty is related to analytical difficulties. Commercially available enzyme-linked immunosorbent assays (ELISAs) offer one of the best options for routine MC detection, but methods of detecting MC in tissue are far from standardized. We spiked freshwater finfish and marine mussel tissues with MC, then compared recovery rates using four different preparation protocols and two ELISA types (polyclonal anti-MC-ADDA/direct monoclonal (DM)). Preparation protocol, type of ELISA, and seafood tissue variety significantly affected MC detection. This is the first known study to use DM ELISA for tissue analyses, and our findings demonstrate that DM ELISA combined with a short solvent extraction results in fewer false positives than other commonly used methods. This method can be used for rapid and reliable MC detection in seafood.

Life history responses of Daphnia similoides simultaneously exposed to microcystin-LR and ammonia and their postexposure recovery

Aquatic organisms often suffer episodic stress from cyanobacterial bloom-derived concomitants and sometimes interactive stressors, and they may recover when stressors terminate. To assess whether exposed Daphnia can quickly recover from combined toxicity of bloom-derived stressors, Daphnia similoides were exposed to mixtures of ammonia (0 mg L(-1) , 0.37 mg L(-1) , and 0.58 mg L(-1) ) and dissolved microcystin-LR (0 µg L(-1) , 10 µg L(-1) , 30 µg L(-1) , and 100 µg L(-1) ) in a full factorial design for 14 d and subsequently allowed to recover for 7 d. During the exposure, the mixtures of ammonia and microcystin-LR showed different effects on the selected variables. Ammonia delayed the time to maturation, but microcystin-LR was not negative to the development of the tested daphnids. Furthermore, microcystin-LR reduced the prolonged developmental time to first eggs and first clutch caused by high ammonia. The total reproduction of D. similoides was dramatically reduced by 64% to 79% by both toxicants and their combinations, but there were no interactive effects. After the recovery period, organisms under most treatments did not recover completely from the combined stress but showed positive signs of recovery, based on the size of the last clutch and the mean number of clutches during recovery; thus the affected D. similoides have the potential to quickly recover from the combined toxic stressors.

Bioaccumulation of microcystins (MCs) in four fish species from Lake Taihu, China: assessment of risks to humans

Microcystins (MCs) are the toxic products of harmful algal blooms and they accumulate in fish. The accumulation of MCs in fish living in different trophic levels from different parts of Lake Taihu was determined. This information was then used to evaluate the risks posed by the MCs in fish to human health. The concentrations of three MCs, MC-LR, MC-YR and MC-RR, were quantified in the following four fish species: silver carp (Hypophthalmichthys molitrix), bighead carp (Aristichthys nobilis), crucian carp (Carassius auratus) and common carp (Cyprinus carpio), using high performance liquid chromatography interfaced with tandem (triple quadrupole) mass spectrometry. The mean concentrations of MCs in the muscle, the kidney, the intestinal wall and the heart were significantly different among the four fishes except in the liver. C. carpio contained the highest mean concentration of MCs in the muscle (31.7 ± 12.1 ng/g, dry mass (dm)), whereas C. auratus had the highest mean concentrations of MCs in the liver (45.4 ± 44.5 ng/g, dm), kidney (114 ± 51.1 ng/g, dm), intestinal wall (2.04 × 10(3)± 4.43 × 10(3)ng/g, dm) and heart (59.5 ± 26.7 ng/g, dm). The mean concentration of MCs in the intestinal walls of the fish species was significantly higher than in other organs (p<0.01). The fish from Meiliang Bay had significantly higher concentrations of MCs than those from the centre, west or south banks of the lake (p<0.01). The body lengths and masses of the fish were negatively correlated with the concentrations of MCs in the kidney (p<0.05) and heart (p<0.01). The average daily intake (ADI) of MCs in the muscle of all fishes exceeded the provisional tolerable daily intake (TDI) set by World Health Organization. The estimated daily intakes of MCs in 55.6% of the muscle samples exceeded the TDI. The MCs in the tissues of the fish from Lake Taihu pose potential risks to the health of humans who consume these four fish species.

The role of apoptosis in MCLR-induced developmental toxicity in zebrafish embryos

We previously demonstrated that cyanobacteria-derived microcystin-leucine-arginine (MCLR) is able to induce developing toxicity, such as malformation, growth delay and also decreased heart rates in zebrafish embryos. However, the molecular mechanisms by which MCLR induces its toxicity during the development of zebrafish remain largely unknown. Here, we evaluate the role of apoptosis in MCLR-induced developmental toxicity. Zebrafish embryos were exposed to various concentrations of MCLR (0, 0.2, 0.5, 2, and 5.0 mg L(-1)) for 96 h, at which time reactive oxygen species (ROS) was significantly induced in the 2 and 5.0 mg L(-1) MCLR exposure groups. Acridine orange (AO) staining and terminal deoxynucleotide transferase-mediated deoxy-UTP nick end labelling (TUNEL) assay showed that MCLR exposure resulted in cell apoptosis. To test the apoptotic pathway, the expression pattern of several apoptotic-related genes was examined for the level of enzyme activity, gene and protein expression, respectively. The overall results demonstrate that MCLR induced ROS which consequently triggered apoptosis in the heart of developing zebrafish embryos. Our results also indicate that the p53-Bax-Bcl-2 pathway and the caspase-dependent apoptotic pathway play major roles in MCLR-induced apoptosis in the developing embryos.

Variation in cyanobacterial hepatotoxin (microcystin) content of water samples and two species of fishes collected from a shallow lake in Algeria

Microcystins (MCs) produced from cyanobacteria can accumulate in freshwater fish tissues. In this study, variations in these toxins content were examined monthly in water samples and two species of fish in Lake Oubeira, Algeria, from April 2010 to March 2011. During the study period, MCs were analyzed using protein phosphatase type 2A (PP2A) inhibition assay. In lake water, total (dissolved and intracellular toxins) MC concentrations by PP2A ranged from 0.028 to 13.4 μg equivalent MC-LR/l, with a peak in September 2010. MC-LR was the dominant variant (90 % of the total) in water samples, followed by MC-YR and MC-(H4)YR. The highest MC concentration in the omnivorous common carp (Cyprinus carpio) was found in the order intestine > hepatopancreas > muscle; however, in the carnivorous European eel (Anguilla anguilla) the order was liver > intestine > muscle. Highest MC concentrations in the intestine tissue of the common carp were found between August and November 2010 where high MC concentrations were detected in water samples, whereas high levels of MCs in the liver of the European eel were found later between January and February 2011. During the entire period of study, the World Health Organization (WHO) lifetime limit for tolerable daily intake was exceeded only in common carp muscle.

Microcystin Contamination in Sea Mussel Farms from the Italian Southern Adriatic Coast following Cyanobacterial Blooms in an Artificial Reservoir

An experimental study was performed in 2009-2010 to investigate the polluting effect of eutrophic inland waters communicating with the sea coast. The study was planned after a heavy and long-lasting Planktothrix rubescens bloom occurred in the Lake Occhito, an artificial reservoir. The waters of the reservoir flow into the southern Adriatic Sea, near several marine breeding of Mytilus galloprovincialis mussels, a typical seafood from the Apulia region (Southern Italy). A monitoring study of water and mussels from the sea coast of northern Apulia region and on the Occhito reservoir was carried out over twelve months, to get more information regarding the contamination by cyanobacteria and related cyanotoxins. Elisa immunoassay analyses estimated total microcystin amounts from 1.73 to 256 ng/g in mussels, up to 0.61 μg/L in sea water and up to 298.7 μg/L in lake water. Analyses of some samples of free-living marine clams as well as of marine and freshwater fish proved microcystin contamination. Selective confirmatory analyses by LC/ESI-Q-ToF-MS/MS on some mussel samples identified the microcystin desMe-MC-RR as the major toxin; this compound has been reported in the literature as a specific marker toxin of Planktothrix rubescens blooms. Our study describes for the first time the direct relationship between environmental pollution and food safety, caused by seafood contamination from freshwater toxic blooms.

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

The aim of this study is to summarise the determination of concentrations of microcystins (MCs) in muscle and liver of freshwater fish species caught in stagnant waters of the Czech Republic. Within the years 2007-2009, 351 muscle samples and 291 liver samples of 16 freshwater fish species derived from four fishponds, and four water reservoirs were analysed. MCs were detected in 53 liver samples. The highest concentrations of microcystins were determined in liver samples of carnivorous fish species; 50.3 ng/g of fresh weight (FW) in perch (Perca fluviatilis) and 22.7 ng/g FW in pikeperch (Sander lucioperca). MCs in liver were detected in other five fish species; asp (Aspius aspius), pike (Esox lucius), common carp (Cyprinus carpio), grass carp (Ctenopharyngodon idella) and European eel (Anguilla anguilla). Concentrations of MCs in liver of nine fish species (European bream, whitefish, tench, silver carp, European catfish, roach, chub, crucian carp and rudd) were below the detection limit of 1.2-5.4 ng/g FW for different MC congeners. However, the concentrations of MCs in all muscle samples were below the detection limit. The assessment of MCs concentrations might be influenced by the detection method used. Due to the concentrations of MCs being below the detection limit in muscle samples of all fish species analysed, it seems that there might be a low potential threat for human health in case of fish muscle consumption.

Grazing on Microcystis aeruginosa and degradation of microcystins by the heterotrophic flagellate Diphylleia rotans

Cyanobacterial toxins can cause damage in aquatic ecosystems worldwide, as well as the poisoning of livestock, plants and humans when ingested in large amounts. Although many studies investigated grazing of harmful cyanobacteria by metazoan plankton, grazing of cyanobacteria by hetertophic flagellates is largely unexplored. This laboratory study investigated grazing of toxic Microcystis aeruginosa by the heterotrophic flagellate Diphylleia rotans isolated from a Saudi hypertrophic lake. D. rotans was able to feed on M. aeruginosa with estimated ingestion (10.2 to 16.5 prey flagellate (-1)d(-1)) and specific growth rates (0.71 to 0.99d(-1)) differed with the increase in the initial density of the flagellate. Grazing increased microcystin production within Microcystis cells during first two days of incubation, and afterwards induced the release of these toxins into the medium. The concentrations of releasing microcystin were strongly reduced in grazing-treated cultures compared to controls, indicating the degradation of microcystins by D. rotans growing under axenic conditions. Taken these results, D. rotans can play an important role in the reduction of Microcystis biomass and microcystin toxins, and thus could be used as a safe bioagent for the biocontrol of harmful algal blooms in aquatic environments.