Variations in the microcystin content of different fish species collected from a eutrophic lake

Insights in Pharmaceutical Pollution: The Prospective Role of eDNA Metabarcoding

Environmental pollution is a growing threat to natural ecosystems and one of the world's most pressing concerns. The increasing worldwide use of pharmaceuticals has elevated their status as significant emerging contaminants. Pharmaceuticals enter aquatic environments through multiple pathways related to anthropogenic activity. Their high consumption, insufficient waste treatment, and the incapacity of organisms to completely metabolize them contribute to their accumulation in aquatic environments, posing a threat to all life forms. Various analytical methods have been used to quantify pharmaceuticals. Biotechnology advancements based on next-generation sequencing (NGS) techniques, like eDNA metabarcoding, have enabled the development of new methods for assessing and monitoring the ecotoxicological effects of pharmaceuticals. eDNA metabarcoding is a valuable biomonitoring tool for pharmaceutical pollution because it (a) provides an efficient method to assess and predict pollution status, (b) identifies pollution sources, (c) tracks changes in pharmaceutical pollution levels over time, (d) assesses the ecological impact of pharmaceutical pollution, (e) helps prioritize cleanup and mitigation efforts, and (f) offers insights into the diversity and composition of microbial and other bioindicator communities. This review highlights the issue of aquatic pharmaceutical pollution while emphasizing the importance of using modern NGS-based biomonitoring actions to assess its environmental effects more consistently and effectively.

Bio-fabricated bismuth-based materials for removal of emerging environmental contaminants from wastewater

Although rapid industrialization has made life easier for humans, several associated issues are emerging and harming the environment. Wastewater is regarded as one of the key problems of the 21st century due to its massive production every year and requires immediate attention from all stakeholders to protect the environment. Since the introduction of nanotechnology, bismuth-based nanomaterials have been used in variety of applications. Various techniques, such as hydrothermal, solvo-thermal and biosynthesis, have been reported for synthesizing these materials, etc. Among these, biosynthesis is eco-friendly, cost-effective, and less toxic than conventional chemical methods. The prime focuses of this review are to elaborate biosynthesis of bismuth-based nanomaterials via bio-synthetic agents such as plant, bacteria and fungi and their application in wastewater treatment as anti-pathogen/photocatalyst for pollutant degradation. Besides this, future perspectives have been presented for the upcoming research in this field, along with concluding remarks.

Cyanotoxins Increase Cytotoxicity and Promote Nonalcoholic Fatty Liver Disease Progression by Enhancing Cell Steatosis

Freshwater prokaryotic cyanobacteria within harmful algal blooms produce cyanotoxins which are considered major pollutants in the aquatic system. Direct exposure to cyanotoxins through inhalation, skin contact, or ingestion of contaminated drinking water can target the liver and may cause hepatotoxicity. In the current study, we investigated the effect of low concentrations of cyanotoxins on cytotoxicity, inflammation, modulation of unfolded protein response (UPR), steatosis, and fibrosis signaling in human hepatocytes and liver cell models. Exposure to low concentrations of microcystin-LR (MC-LR), microcystin-RR (MC-RR), nodularin (NOD), and cylindrospermopsin (CYN) in human bipotent progenitor cell line HepaRG and hepatocellular carcinoma (HCC) cell lines HepG2 and SK-Hep1 resulted in increased cell toxicity. MC-LR, NOD, and CYN differentially regulated inflammatory signaling, activated UPR signaling and lipogenic gene expression, and induced cellular steatosis and fibrotic signaling in HCC cells. MC-LR, NOD, and CYN also regulated AKT/mTOR signaling and inhibited autophagy. Chronic exposure to MC-LR, NOD, and CYN upregulated the expression of lipogenic and fibrosis biomarkers. Moreover, RNA sequencing (RNA seq) data suggested that exposure of human hepatocytes, HepaRG, and HCC HepG2 cells to MC-LR and CYN modulated expression levels of several genes that regulate non-alcoholic fatty liver disease (NAFLD). Our data suggest that low concentrations of cyanotoxins can cause hepatotoxicity and cell steatosis and promote NAFLD progression.

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

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

Massive fish death associated with the toxic cyanobacterial Planktothrix sp. bloom in the Béni-Haroun Reservoir (Algeria)

In July 2017, a massive bloom of the potentially toxic cyanobacterial species Planktothrix sp. was observed in the Béni-Haroun Reservoir (Algeria), which was followed by a massive fish death. Many questions were raised in association with the role of cyanotoxins and the fish massive mortality. The objective of this paper is twofold: (1) to investigate the variability of physicochemical and cyanobacterial parameters (chlorophyll-a, phycocyanin, allophycocyanin, and microcystins) throughout the period of July 2017 to June 2018; and (2) to determine the free and total MC levels in viscera and muscle tissues of the common carp (Cyprinus carpio), which are found dead in the considered reservoir in October 2017. Our results showed microcystin (MC) concentrations in water samples (by the protein phosphatase PP2A assay) had reached 651.2 ng MC-LR equiv./L. Total MC levels (free + bound) in the viscera and muscle tissues of sampled dead fish were at 960.24 and 438.54 µg MC-LR equiv./kg dw, respectively. It is assumed that high concentrations of MC observed in the tissues of common carp induced a strong degradation of the visceral contents resulting in the complete lysis of the hepatopancreas, and presumably the massive fish death.

Examination of Microcystin Adsorption by the Type of Plastic Materials Used during the Procedure of Microcystin Analysis

The incidence of eutrophication is increasing due to fertilizer abuse and global warming. Eutrophication can induce the proliferation of cyanobacteria such as Microcystis, which produces microcystins. Microcystins are toxic to specific organs such as the liver and the heart. Thus, monitoring of microcystins is strongly required to control drinking water and agricultural product qualities. However, microcystins could be adsorbed by plastic materials during sample storage and preparation, hindering accurate analysis. Therefore, the current study examined the recovery rate of microcystins from six plastics used for containers and eight plastics used for membrane filters. Among the six plastics used for containers, polyethylene terephthalate showed the best recovery rate (≥81.3%) for 48 h. However, polypropylene, polystyrene, and high- and low-density polyethylenes showed significant adsorption after exposure for 1 hr. For membrane materials, regenerated cellulose (≥99.3%) showed the highest recovery rate of microcystins, followed by polyvinylidene fluoride (≥94.1%) and polytetrafluoroethylene (≥95.7%). The adsorption of microcystins appeared to be strongly influenced by various molecular interactions, including hydrophobic interaction, hydrogen bonding, and electrostatic interaction. In addition, microcystins’ functional residues seemed to be critical factors affecting their adsorption by plastic materials. The present study demonstrates that polyethylene terephthalate and regenerated cellulose membrane are suitable plastic materials for the analysis of microcystins.

Microcystin accumulation in Sportfish from an agricultural reservoir differs among feeding guild, tissue type, and time of sampling

Cyanobacterial blooms sometimes create secondary metabolites that can be transferred between trophic levels and accumulate in fish, but little is known about what time of year fish are most susceptible. Here, we examine microcystin in the muscle, liver, and kidney of bluegill and largemouth bass from an agricultural reservoir over 12 months. We identify which fish characteristics and water parameters best explain microcystin accumulation in fish tissues. Microcystin in bluegill was significantly higher than largemouth bass. In both species, microcystin was highest in livers (bluegill mean = 57.6 ng g ^- 1, largemouth bass mean = 71.8 ng g ^- 1 wet weight [ww]), then kidneys (bluegill mean = 27.1, largemouth bass mean = 22.7 ng g ^- 1 ww), followed by muscles (bluegill mean = 7.6, largemouth bass mean = 5.7 ng g ^- 1 ww). Adult bluegill feed on benthic macroinvertebrates and zooplankton, which may explain their higher microcystin concentrations compared to largemouth bass, which are primarily piscivorous. Harvest date emerged as the best predictor of microcystin in muscles and kidneys, with the highest concentrations occurring in April. Microcystin in water also emerged as a significant predictor, albeit much lower than harvest date, suggesting that low but persistent microcystin concentrations in water may result in accumulation of this cyanotoxin in fish. This study is the first to examine microcystin in fish from the North American Great Plains and one of only 5 studies that investigate microcystin in bluegill and largemouth bass. Additional investigation into the relationship between cyanobacteria and fish health is warranted, especially during spring when fish microcystin concentrations were highest.

Hepatic nodular alterations in wild fish from a hyper-eutrophic freshwater system with cyanobacterial blooms: a species and seasonal comparison

This paper reports on the seasonal and species comparison of hepatic nodular alterations in two indicator fish species from the hyper-eutrophic Roodeplaat Dam in South Africa. This freshwater system is characterized by seasonal cyanobacterial algal blooms which release bio-toxins, including hepato-toxins, which can have negative effects on the health of the resident fish population. A total of 115 Clarias gariepinus (Burchell) and 98 Oreochromis mossambicus (Peters) were collected seasonally across six different surveys over a period of 3 years. Nodular alterations in livers were assessed both macroscopically and microscopically. We found a species difference with a 48% prevalence of nodular alterations in C. gariepinus and no macroscopically visible alterations in O. mossambicus. Affected fish also showed an increase in the ratio of liver mass to body mass, i.e., the hepatosomatic index. The microscopic characteristics of the nodules were primarily associated with pre-neoplastic, focal areas of cellular alterations; most prevalent were focal areas of steatosis. However, we could not establish a seasonal pattern regarding the occurrence of these alterations and therefore no association between the occurrence of the liver pathology and the cyanobacterial blooms. Our results therefore suggest that the occurrence of nodular alterations is not an acute, seasonal response, but rather a chronic, and possibly, and more interestingly, a species-specific, pathological response.

Toxic effects of cyanotoxins in teleost fish: A comprehensive review

The phenomenon of eutrophication leads to the global occurrence of algal blooms. Cyanotoxins as produced by many cyanobacterial species can lead to detrimental effects to the biome due to their stability and potential biomagnification along food webs. Therefore, understanding of the potential risks these toxins pose to the most susceptible organisms is an important prerequisite for ecological risks assessment of cyanobacteria blooms. Fishes are an important component of aquatic ecosystems that are prone to direct exposure to cyanotoxins. However, relatively few investigations have focused on measuring the toxic potentials of cyanotoxins in teleost fishes. This review comprehensively describes the major toxicological impacts (such as hepatotoxicity, neurotoxicity, immune toxicity, reproductive toxicity and cytogenotoxicity) of commonly occurring cyanotoxins in teleost fishes. The present work encompasses recent research progresses with special emphasis on the basic molecular mechanisms by which different cyanotoxins impose their toxicities in teleost fishes. The major research areas, which need to be focused on in future scientific investigations, have also been highlighted. Protein kinase inhibition, transcriptional dysregulation, disruption of redox homeostasis and the induction of apoptotic pathways appear to be the key drivers of the toxicological effects of cyanotoxins in fish. Analyses also showed that the impacts of cyanotoxins on specific reproductive processes are relatively less described in teleosts in comparison to mammalian systems. In fact, as compared to other toxicological effects of cyanotoxins, their reproductive toxicity (such as impacts on oocyte development, maturation and their hormonal regulation) is poorly understood in fish, and thus requires further studies. Furthermore, additonal studies characterizing the molecular mechanisms responsible for the cellular uptake of cyanotoxins need to be investigated.

Mechanisms and risks of joint control of nitrogen and phosphorus through sediment capping technology in a pilot-scale study

Purpose

Nitrogen (N) and phosphorus (P) are the key elements leading to eutrophication, and it is important to jointly control N and P release from sediments into the water column.

Methods

Different mixed materials including P sorbent, natural organic carbon (C), and an oxidizing agent were applied in a 1-year pilot-scale experiment.

Results

The addition of iron-rich (IR) clay and Phoslock agent promoted the formation of iron bound P (Fe(OOH)~P) and calcium bound P (CaCO3~P) in sediments, respectively. IR clay offered more advantages in immobilization of phosphorus as refractory P, and the Phoslock agent more effectively reduced the risk of P release into water, which was expressed as a low equilibrium P concentration (EPC0). Mixtures of sugarcane (SU) detritus and IR clay exhibited high carbohydrate (CHO) contents, which further fuelled both denitrification and dissimilatory nitrate reduction to ammonium (DNRA). This indicated that the SU dosage should be controlled to avoid DNRA over denitrification. Attention should be given to the fact that SU introduction significantly promoted the generation of an anaerobic state, leading to the desorption and release of Fe(OOH)~P, which could be alleviated by using Oxone. Multienzyme activity analysis showed that P and N transformation shifted from P desorption to organic P hydrolysis and from ammonification to denitrification and DNRA, respectively.

Conclusion

We recommend the use of P sorbent and organic C combined with oxidizing agents as effective mixed materials for sediment remediation, which could enhance P adsorption and provide electron donors for denitrification, while also avoiding the generation of anoxia.

Predicting Cyanobacterial Harmful Algal Blooms (CyanoHABs) in a Regulated River Using a Revised EFDC Model

Cyanobacterial Harmful Algal Blooms (CyanoHABs) produce toxins and odors in public water bodies and drinking water. Current process-based models predict algal blooms by modeling chlorophyll-a concentrations. However, chlorophyll-a concentrations represent all algae and hence, a method for predicting the proportion of harmful cyanobacteria is required. We proposed a technique to predict harmful cyanobacteria concentrations based on the source codes of the Environmental Fluid Dynamics Code from the National Institute of Environmental Research. A graphical user interface was developed to generate information about general water quality and algae which was subsequently used in the model to predict harmful cyanobacteria concentrations. Predictive modeling was performed for the Hapcheon-Changnyeong Weir–Changnyeong-Haman Weir section of the Nakdong River, South Korea, from May to October 2019, the season in which CyanoHABs predominantly occur. To evaluate the success rate of the proposed model, a detailed five-step classification of harmful cyanobacteria levels was proposed. The modeling results demonstrated high prediction accuracy (62%) for harmful cyanobacteria. For the management of CyanoHABs, rather than chlorophyll-a, harmful cyanobacteria should be used as the index, to allow for a direct inference of their cell densities (cells/mL). The proposed method may help improve the existing Harmful Algae Alert System in South Korea.

Interannual and Spatial Variability of Cyanotoxins in the Prespa Lake Area, Greece

The Prespa Lakes area in Greece—comprised partly of lake Great and lake Lesser Prespa and the Vromolimni pond—has a global importance for biodiversity. Although the waters show regular cyanobacteria blooms, assessments of water quality threats are limited. Samples collected in 2012 revealed scattered and low microcystin (MC) concentrations in Great Prespa (<0.2 μg MC L−1) whereas considerable spatial heterogeneity in both total chlorophyll (2.4–93 µg L−1) and MC concentrations (0.04–52.4 µg MC L−1) was detected in Lesser Prespa. In 2013, there was far less spatial variability of MC concentrations in Lesser Prespa (0.4–1.53 µg L−1), however in 2014, increased concentrations were detected near the lakeshore (25–861 µg MC L−1). In Vromolimni pond the MC concentrations were on average 26.6 (±6.4) µg MC L−1 in 2012, 2.1 (±0.3) µg MC L−1 in 2013 and 12.7 (±12.5) µg MC L−1 in 2014. In 2013, no anatoxins, saxitoxins, nor cylindrospermopsins were detected in Lesser Prespa and Vromolimni waters. Tissue samples from carps, an otter and Dalmatian Pelicans contained 0.4–1.9 µg MC g−1 dry weight. These results indicate that cyanotoxins could be a threat to the ecosystem functions of particularly Lesser Prespa and Vromolimni.

A Mini-Review on Detection Methods of Microcystins

Cyanobacterial harmful algal blooms (CyanoHABs) produce microcystins (MCs) which are associated with animal and human hepatotoxicity. Over 270 variants of MC exist. MCs have been continually studied due of their toxic consequences. Monitoring water quality to assess the presence of MCs is of utmost importance although it is often difficult because CyanoHABs may generate multiple MC variants, and their low concentration in water. To effectively manage and control these toxins and prevent their health risks, sensitive, fast, and reliable methods capable of detecting MCs are required. This paper aims to review the three main analytical methods used to detect MCs ranging from biological (mouse bioassay), biochemical (protein phosphatase inhibition assay and enzyme linked immunosorbent assay), and chemical (high performance liquid chromatography, liquid chromatography-mass spectrometry, high performance capillary electrophoresis, and gas chromatography), as well as the newly emerging biosensor methods. In addition, the current state of these methods regarding their novel development and usage, as well as merits and limitations are presented. Finally, this paper also provides recommendations and future research directions towards method application and improvement.

Optimization of an MMPB Lemieux Oxidation method for the quantitative analysis of microcystins in fish tissue by LC-QTOF MS

Microcystins are toxic heptapeptides produced by cyanobacteria in marine and freshwater environments. In biological samples such as fish, microcystins can be found in the free form or covalently bound to protein phosphatases type I and II. Total microcystins in fish have been quantified in the past using the Lemieux Oxidation approach, where all toxins are oxidated to a common fragment (2-methyl-3-methoxy-4-phenylbutyric acid, MMPB) regardless of their initial amino acid configuration or form (free or protein bound). These studies have been carried out using different experimental conditions and employed different quantification strategies. The present study has further investigated the oxidation step using a systematic approach, to identify the most important factors leading to a higher, more robust MMPB generation yield from fish tissue in order to reduce the method detection limit. Field samples were quantified using an in-situ generated MMPB matrix matched calibration curve by isotope dilution with d₃-MMPB via liquid chromatography coupled to time-of-flight mass spectrometry (LC-QTOF MS). This approach improves method's accuracy by taking into account of potential matrix effects that could affect the derivatization, sample prepation and instrumental analysis steps. The validated method showed 16.7% precision (RSD) and +6.7% accuracy (bias), with calculated method detection limits of 7.28 ng g^-1 Performance of the method was assessed with the analysis of laboratory exposed Rainbow Trout (Oncorhynchus mykiss) to cyanobacteria as a positive control, where no microcystins were detected in the pre-exposure fish liver and fillet, low levels in the exposed fillet (65.0 ng g^-1) and higher levels in the exposed liver (696 ng g^-1). Finally, the method was employed for the analysis of 26 fillets (muscle) and livers of Walleye (Sander vitreus) and Yellow Perch (Perca flavescens) from Lake Erie, showing very low concentrations of microcystins in the fillet and higher concentrations in liver, up to 3720 ng g^-1.

Quantifying the Human Health Benefits of Using Satellite Information to Detect Cyanobacterial Harmful Algal Blooms and Manage Recreational Advisories in U.S. Lakes

Significant recent advances in satellite remote sensing allow environmental managers to detect and monitor cyanobacterial harmful algal blooms (cyanoHAB), and these capabilities are being used more frequently in water quality management. A quantitative estimate of the socioeconomic benefits generated from these new capabilities, known as an impact assessment, was missing from the growing literature on cyanoHABs and remote sensing. In this paper, we present an impact assessment framework to characterize the socioeconomic benefits of satellite remote sensing for detecting cyanoHABs and managing recreational advisories at freshwater lakes. We then apply this framework to estimate the socioeconomic benefits of satellite data that were used to manage a 2017 cyanoHAB event in Utah Lake. CyanoHAB events on Utah Lake can pose health risks to people who interact with the blooms through recreation. We find that the availability of satellite data yielded socioeconomic benefits by improving human health outcomes valued at approximately $370,000, though a sensitivity analysis reveals that this central estimate can vary significantly ($55,000-$1,057,000 in benefits) as a result of different assumptions regarding the time delay in posting a recreational advisory, the number of people exposed to the cyanoHAB, the number of people who experience gastrointestinal symptoms, and the cost per case of illness.

Analysis of Covalently Bound Microcystins in Sediments and Clam Tissue in the Sacramento-San Joaquin River Delta, California, USA

Harmful cyanobacterial blooms compromise human and environmental health, mainly due to the cyanotoxins they often produce. Microcystins (MCs) are the most commonly measured group of cyanotoxins and are hepatotoxic, neurotoxic, and cytotoxic. Due to MCs ability to covalently bind to proteins, quantification in complex matrices is difficult. To analyze bound and unbound MCs, analytical methods were optimized for analysis in sediment and clam tissues. A clean up step was incorporated to remove lipids, improving percent yield. This method was then applied to sediment and clam samples collected from the Sacramento-San Joaquin River Delta (Delta) in the spring and fall of 2017. Water samples were also tested for intracellular and extracellular MCs. These analyses were used to quantify the partitioning of MCs among sediment, clams, and water, and to examine whether MCs persist during non-summer months. Toxin analysis revealed that multiple sediment samples collected in the Delta were positive for MCs, with a majority of the positive samples from sites in the San Joaquin River, even while water samples from the same location were below detection limit. These data highlight the importance of analyzing MCs in complex matrices to accurately evaluate environmental risk.

Microcystin concentrations and liver histopathology in Clarias gariepinus and Oreochromis mossambicus from three impacted rivers flowing into a hyper-eutrophic freshwater system: A pilot study

The Roodeplaat Dam and its three inflowing rivers are highly impacted by surrounding anthropogenic activities. The system is hyper-eutrophic and characterized by seasonal algal blooms and previous studies have reported levels of the hepatotoxin microcystin in the water of the impoundment. Limited information is available on the microcystin concentrations in the inflowing rivers and no information is available on the bioaccumulated levels and potential health effects in fish inhabiting these rivers. The aim of this study was to do a histopathological assessment and to determine the concentrations of bioaccumulated microcystins in the livers of two indicator fish species Clarias gariepinus and Oreochromis mossambicus. The results showed that the two species bioaccumulate microcystins at different concentrations and that their hepatic health response varied. The liver index was significantly higher for C. gariepinus compared to O. mossambicus. No significant positive correlation was found between the bioaccumulated microcystin levels and the liver histology index. It is recommended that this pilot study be followed by a controlled exposure study to confirm a possible cause and effect relationship between microcystin exposure and the specific liver alterations identified.

Microcystin Content in Phytoplankton and in Small Fish from Eutrophic Nyanza Gulf, Lake Victoria, Kenya

The human health risks posed by exposure to cyanobacterial toxins such as microcystin (MC) through water and fish consumption remain poorly described. During the last two decades, coastal regions of Lake Victoria such as Nyanza Gulf (Kisumu Bay) have shown severe signs of eutrophication with blooms formed by Microcystis producing MC. In this study, the spatial variability in MC concentration in Kisumu Bay was investigated which was mostly caused by Microcystis buoyancy and wind drifting. Small fish (<6 cm) mainly composed of Rastrineobola argentea were examined for MC content by means of biological methods such as ELISA and protein phosphatase inhibition assay (PPIA) and partly by chemical-analytical methods such as LC-MS/MS. Overall, the MC content in small fish was related to the MC content observed in the seston. When comparing the MC content in the seston in relation to dry weight with the MC content in small fish the latter was found three orders of magnitude decreased. On average, the ELISA-determined MC contents exceeded the PPIA-determined MC contents by a factor of 8.2 ± 0.5 (SE) while the MC contents as determined by LC-MS/MS were close to the detection limit. Using PPIA, the MC content varied from 25–109 (mean 62 ± 7) ng/g fish dry weight in Kisumu Bay vs. 14 ± 0.8 ng MC/g in the more open water of L. Victoria at Rusinga channel. Drying the fish under the sun showed little effect on MC content, although increased humidity might indirectly favor photocatalyzed MC degradation.

Optimization of extraction methods for quantification of microcystin-LR and microcystin-RR in fish, vegetable, and soil matrices using UPLC-MS/MS

Human-driven environmental change has increased the occurrence of harmful cyanobacteria blooms in aquatic ecosystems. Concomitantly, exposure to microcystin (MC), a cyanobacterial toxin that can accumulate in animals, edible plants, and agricultural soils, has become a growing public health concern. For accurate estimation of health risks and timely monitoring, availability of reliable detection methods is imperative. Nonetheless, quantitative analysis of MCs in many types of biological and environmental samples has proven challenging because matrix interferences can hinder sample preparation and extraction procedures, leading to poor MC recovery. Herein, controlled experiments were conducted to enhance the use of ultra-performance liquid-chromatography tandem-mass spectrometry (UPLC-MS/MS) to recover MC-LR and MC-RR at a range of concentrations in seafood (fish), vegetables (lettuce), and environmental (soil) matrices. Although these experiments offer insight into detailed technical aspects of the MC homogenization and extraction process (i.e., sonication duration and centrifugation speed during homogenization; elution solvent to use during the final extraction), they centered on identifying the best (1) solvent system to use during homogenization (2-3 tested per matrix) and (2) single-phase extraction (SPE) column type (3 tested) to use for the final extraction. The best procedure consisted of the following, regardless of sample type: centrifugation speed = 4200 × g; elution volume = 8 mL; elution solvent = 80% methanol; and SPE column type = hydrophilic-lipophilic balance (HLB), with carbon also being satisfactory for fish. For sonication, 2 min, 5 min, and 10 min were optimal for fish, lettuce, and soil matrices, respectively. Using the recommended HLB column, the solvent systems that led to the highest recovery of MCs were methanol:water:butanol for fish, methanol:water for lettuce, and EDTA-Na₄P₂O₇ for soils. Given that the recommended procedures resulted in average MC-LR and MC-RR recoveries that ranged 93 to 98%, their adoption for the preparation of samples with complex matrices before UPLC-MS/MS analysis is encouraged.

An overview of the accumulation of microcystins in aquatic ecosystems

Cyanotoxins produced by toxic cyanobacteria pose a major, worldwide environmental threat to freshwater ecosystems. Microcystins (MCs) are considered to be the most hazardous groups. Indeed, some of the largest aquatic ecosystems on the earth are being contaminated with MCs. Questions have arisen regarding their transfer and bioaccumulation in natural environment. This review summarizes the present state of knowledge regarding toxic cyanobacteria and MCs, with a specific focus on their distribution in different components of aquatic ecosystems. Their accumulation in water columns, aquatic animals, plants, and sediments is summarized. MCs have been contaminating all areas of the aquatic ecosystems. Of these, the water column was the most contaminated with MCs and served as an intermediate transmission substation. Via this route, MCs could enter to other stations such as sediment, animals, aquatic and terrestrial plants. Therefore, the use of water contaminated with MCs may induce food chain contaminations with considerable health risks.

Developmental neurotoxicity of Microcystis aeruginosa in the early life stages of zebrafish

Accumulating evidence suggests that cyanotoxins can exert neurotoxic effects on exposed aquatic organisms but most studies have focused on purified toxins rather than on the more complex effects of cyanobacterial blooms. To evaluate this issue in an environmentally relevant model, we assessed the developmental neurotoxicity induced by Microcystis aeruginosa on newly hatched zebrafish. After four days of exposure, the locomotor activity of zebrafish larvae was significantly decreased with increasing algae concentration. The levels of both acetylcholinesterase (AChE) and dopamine (DA) were decreased, accompanied by a decline in ache, chrna7 and manf and a compensatory increase in nr4a2b transcription. Furthermore, the expression of nine marker genes for nervous system function or development, namely, elavl3, gap43, gfap, mbp, nestin, ngn1, nkx2.2a, shha and syn2a, similarly decreased after algal exposure. These results demonstrated that Microcystis aeruginosa exposure affected cholinergic and dopaminergic neurotransmitter systems, the transcription of key nervous system genes, and consequently the activity level of larval zebrafish. Importantly, discrepancies in the neurotoxic effects observed in this study and in previous reports that were based on exposure to pure cyanotoxin highlight the necessity for further investigation of cyanobacterial bloom mixtures when assessing the ecotoxicity of cyanobacteria.

First report on free and covalently bound microcystins in fish and bivalves from Vietnam: Assessment of risks to humans

The free and covalently bound microcystins (MCs) in 3 fish and 2 bivalves from the Dau Tieng Reservoir in Vietnam were investigated for the first time in the present study. The results showed that all species were contaminated with MCs. Our findings indicate that eating the muscle of fish from the Dau Tieng Reservoir is safe but that eating the bivalves is not safe during toxic cyanobacterial bloom episodes. Environ Toxicol Chem 2017;36:2953-2957. © 2017 SETAC.

Fresh produce and their soils accumulate cyanotoxins from irrigation water: Implications for public health and food security

Microcystin (MC), a hepatotoxin that can adversely affect human health, has become more prevalent in freshwater ecosystems worldwide, owing to an increase in toxic cyanobacteria blooms. While consumption of water and fish are well-documented exposure pathways of MCs to humans, less is known about the potential transfer to humans through consumption of vegetables that have been irrigated with MC-contaminated water. Likewise, the impact of MC on the performance of food crops is understudied. To help fill these information gaps, we conducted a controlled laboratory experiment in which we exposed lettuce, carrots, and green beans to environmentally relevant concentrations of MC-LR (0, 1, 5, and 10μg/L) via two irrigation methods (drip and spray). We used ELISA and LC-MS/MS to quantify MC-LR concentrations and in different parts of the plant (edible vs. inedible fractions), measured plant performance (e.g., size, mass, edible leaves, color), and calculated human exposure risk based on accumulation patterns. MC-LR accumulation was positively dose-dependent, with it being greater in the plants (2.2-209.2μg/kg) than in soil (0-19.4μg/kg). MC-LR accumulation varied among vegetable types, between plant parts, and between irrigation methods. MC-LR accumulation led to reduced crop growth and quality, with MC-LR persisting in the soil after harvest. Observed toxin accumulation patterns in edible fractions of plants also led to estimates of daily MC-LR intake that exceeded both the chronic reference dose (0.003μg/kg of body weight) and total daily intake guidelines (0.04μg/kg of body weight). Because the use of MC-contaminated water is common in many parts of the world, our collective findings highlight the need for guidelines concerning the use of MC-contaminated water in irrigation, as well as consumption of these crops.

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.

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.

Toxicology of freshwater cyanobacteria

Many chemical contaminants in drinking water have been shown to cause adverse health effects in humans after prolonged exposure. Cyanobacteria are one of the most potent and diverse groups of photosynthetic prokaryotes. One key component of cyanobacterial success in the environment is the production of potent toxins as secondary metabolites, which have been responsible for numerous adverse health impacts in humans. Anthropogenic activities have led to the increase of eutrophication in freshwater bodies' worldwide, causing cyanobacterial blooms to become more frequent. The present article will discuss about harmful cyanobacteria and their toxicology with special references to microcystin, nodularin, and cylindrospermopsin.

Health impacts from cyanobacteria harmful algae blooms: Implications for the North American Great Lakes

Harmful cyanobacterial blooms (cHABs) have significant socioeconomic and ecological costs, which impact drinking water, fisheries, agriculture, tourism, real estate, water quality, food web resilience and habitats, and contribute to anoxia and fish kills. Many of these costs are well described, but in fact are largely unmeasured. Worldwide cHABs can produce toxins (cyanotoxins), which cause acute or chronic health effects in mammals (including humans) and other organisms. There are few attempts to characterize the full health-related effects other than acute incidences, which may go unrecorded. At present these are difficult to access and evaluate and may be ascribed to other causes. Such information is fundamental to measure the full costs of cHABs and inform the need for often-costly management and remediation. This paper synthesizes information on cHABs occurrence, toxicology and health effects, and relates this to past and current conditions in the Great Lakes, a major global resource which supplies 84% of the surface water in North America. This geographic region has seen a significant resurgence of cHABs since the 1980s. In particular we focus on Lake Erie, where increased reporting of cHABs has occurred from the early 1990's. We evaluate available information and case reports of cHAB-related illness and death and show that cHABs occur throughout the basin, with reports of animal illness and death, especially dogs and livestock. Lake Erie has consistently experienced cHABs and cyanotoxins in the last decade with probable cases of human illness, while the other Great Lakes show intermittent cHABs and toxins, but no confirmed reports on illness or toxicity. The dominant toxigenic cyanobacterium is the genus Microcystis known to produce microcystins. The presence of other cyanotoxins (anatoxin-a, paralytic shellfish toxins) implicates other toxigenic cyanobacteria such as Anabaena (Dolichospermum) and Lyngbya.

Evaluation of the transfer and the accumulation of microcystins in tomato (Solanum lycopersicum cultivar MicroTom) tissues using a cyanobacterial extract containing microcystins and the radiolabeled microcystin-LR ((14)C-MC-LR)

Microcystins are the most common cyanotoxins and may be expected wherever blooms of cyanobacteria occur in surface waters. Their persistence both in the irrigation water and in the soil can lead to their transfer and bioaccumulation into agricultural plants. The aim of this work was to investigate microcystin accumulation in Solanum lycopersicum cultivar MicroTom. The plant was exposed to either Microcystis aeruginosa crude extracts containing up to 100 μg eq.MC-LRL(-1) in a soil-plant system for 90 days or pure radiolabeled (14)C-MC-LR in a hydroponic condition for 48 h. Toxin bioaccumulation in the soil and different plant tissues was assessed both by the PP2A inhibition assay and by liquid chromatography-mass spectrometry (LC/MS/MS). After 90 days of exposure, microcystins persisted in the soil and their free extractable concentrations accumulated were very low varying between 1.6 and 3.9 μg eq.MC-LR kg(-1) DW. Free MC-LR was detected only in roots and leaves with concentrations varying between 4.5 and 8.1 μg kg(-1) DW and between 0.29 and 0.55 μg kg(-1) DW, respectively. By using radioactivity ((14)C-MC-LR), the results have reported a growing accumulation of toxins within the organs roots>leaves>stems and allowed them to confirm the absence of MC-LR in fruits after 48 h of exposure. The bioconcentration factor (BCF) was 13.6 in roots, 4.5 in leaves, and 1.4 in stems. On the other hand, the results highlight the presence of two radioactive fractions in different plant tissues. The non-extractable fraction of radioactivity, corresponding to the covalently bound MC-LR, was higher than that of the extractable fraction only in roots and leaves reaching 56% and 71% of the total accumulated toxin, respectively. Therefore, results raise that monitoring programs must monitor the presence of MCs in the irrigation water to avoid the transfer and accumulation of these toxins in crops.

Maternal repeated oral exposure to microcystin-LR affects neurobehaviors in developing rats

Microcystins are toxic peptides secreted by certain water blooms of toxic cyanobacteria. The most widely studied microcystin is microcystin-LR (MC-LR), which exhibits hepatotoxicity and neurotoxicity. However, limited information is available regarding the effects on offspring following maternal exposure. The present study was conducted to observe the effects of progestational exposure to MC-LR on postnatal development in rats. Female Sprague-Dawley rats (28 d old) were randomly divided into a control group and 3 treatment groups (1.0 µg MC-LR/kg body wt, 5.0 µg MC-LR/kg body wt, and 20.0 µg MC-LR/kg body wt), with 7 rats per group. The MC-LR was administered through gavage once every 48 h for 8 wk. Pure water was used as control. Each female rat was mated with an unexposed adult male rat. Motor development, behavioral development, and learning ability of pups were detected using surface righting reflex, negative geotaxis, and cliff avoidance tests on postnatal day 7. Open-field and Morris water maze tests were performed on postnatal day 28 and day 60. The levels of lipid peroxidation products and antioxidant indices in the rat hippocampus were also detected. Pups from the MC-LR-treated groups had significantly lower scores than controls in the cliff avoidance test (p < 0.05). Cognitive impairment, malondialdehyde level, and total superoxide dismutase activity significantly increased in MC-LR-exposed pups compared with controls (p < 0.05). Therefore, the present study reveals that maternal exposure to MC-LR has adverse effects on neurodevelopment in rat offspring.

The fate of microcystins in the environment and challenges for monitoring

Microcystins are secondary metabolites produced by cyanobacteria that act as hepatotoxins in higher organisms. These toxins can be altered through abiotic processes, such as photodegradation and adsorption, as well as through biological processes via metabolism and bacterial degradation. Some species of bacteria can degrade microcystins, and many other organisms metabolize microcystins into a series of conjugated products. There are toxicokinetic models used to examine microcystin uptake and elimination, which can be difficult to compare due to differences in compartmentalization and speciation. Metabolites of microcystins are formed as a detoxification mechanism, and little is known about how quickly these metabolites are formed. In summary, microcystins can undergo abiotic and biotic processes that alter the toxicity and structure of the microcystin molecule. The environmental impact and toxicity of these alterations and the metabolism of microcystins remains uncertain, making it difficult to establish guidelines for human health. Here, we present the current state of knowledge regarding the alterations microcystins can undergo in the environment.

Alterations in neurobehaviors and inflammation in hippocampus of rats induced by oral administration of microcystin-LR

Microcystin-LR (MC-LR) is a widely studied toxic peptide secreted by certain water blooms of cyanobacteria that exhibit hepatotoxicity and neural toxicity. This study aimed to observe the neurotoxic effects of low-dose MC-LR exposure by oral administration. Male Sprague-Dawley (SD) rats were administered orally every 2 days for 8 weeks with pure water and 0.2, 1.0, and 5.0 μg/kg MC-LR. The Morris water maze test was used to assess the spatial learning and memory capability of rats. The activation of astrocytes and nitric oxide synthase (NOS) was evaluated by immunohistochemistry, and concentrations of nitric oxide (NO) in rat hippocampus were analyzed. Slight liver dysfunction was observed in the 5.0 μg/kg MC-LR-treated rats. Impairment of spatial learning and memory was also observed in the 5.0 μg/kg MC-LR-treated rats. Astrocytes in the hippocampus of the 5.0 μg/kg MC-LR-treated rats showed enhanced activation and cell density; the inflammatory indicators, NOS and NO, increased in accordance with astrocyte activation. This study showed that oral exposure of MC-LR had adverse affects on neurobehaviors, and induced inflammation in memory-related brain regions.

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.