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

Probiotic Lactobacillus rhamnosus modulates MCLR-induced oogenesis disorders in zebrafish: Evidence from the transcriptome

Microcystin-LR (MCLR) produced by cyanobacterial blooms have received global attention. MCLR has been recognized as a reproductive toxin to fish and poses a threat to ecosystem stability. It has been proven that probiotic dietary management can improve reproductive performance of fish. It is worth paying attention to exploring whether probiotic management can alleviate the reproductive toxicity caused by MCLR. In this investigation, adult zebrafish were exposed to different doses of MCLR solution (0, 2.2, and 22 μg/L) with or without the Lactobacillus rhamnosus GG supplementation for a duration of 28 days. The results showed that female zebrafish spawning was reduced after exposure to MCLR, but this reduction was reversed when L. rhamnosus GG was added. To elucidate how L. rhamnosus GG mitigates reproductive toxicity caused by MCLR, we examined a series of indicators of MCLR accumulation, ovarian histology, hormones, and transcriptome levels. Our study showed that L. rhamnosus GG could alleviate oogenesis disorders and ultimately attenuate MCLR-induced reproductive toxicity by reducing MCLR accumulation in the gonads, modulating the expression of endocrine system and auto/paracrine factors. The transcriptome results revealed that single or combined exposure of MCLR and L. rhamnosus GG mainly affected the endocrine system, energy metabolism, and RNA degradation and translation. Overall, our results provide new insights for alleviating MCLR-induced reproductive toxicity and help promote healthy aquaculture.

Microcystin exposure alters gut microbiota composition in fish: An in-Situ analysis of post-bloom effects in Hulun Lake, China

Cyanobacterial blooms are one of the most common stressors aquatic plants and animals encounter in freshwater ecosystems such as rivers and lakes. Following such outbreaks, some cyanobacteria release toxins, notably microcystins, which are highly toxic. Although numerous studies have explored the effects of microcystins on fish, their in-situ effects on the fish gut microbiome remain unexamined. Our objectives were to examine the fish gut microbiome before (Ju) and after (Au) cyanobacterial blooms and to monitor water quality. We collected Ju and Au fish gut and water samples from Hulun Lake. Using 16S rRNA full-length sequencing, we analyzed the composition, structure, and function of the fish gut microbiome. Results revealed significant disparities in microcystin concentrations between the Ju and Au water samples. In addition, the microcystin concentration in the carp gut was significantly higher than that in its muscle after the cyanobacterial bloom outbreak. Notably, the Au group demonstrated an increase in the microcystin level in water and a marked reduction in fish gut microbiota diversity compared with the Ju group. The cyanobacterial bloom decreased gut microbiome diversity in fish, with the Au group exhibiting a significantly reduced abundance of bacteria related to gut stability and microcystin degradation compared to the Ju group. Furthermore, we observed an upregulation of disease-associated bacterial metabolic functions in the Au group. In conclusion, these findings suggest that microcystins influence the composition and function of fish gut microbiota, improving our understanding of the interaction between fish gut microbiome and their environment. This study offers new perspectives on the adaptive mechanisms of aquatic organisms to cyanobacterial blooms.

Early pregnancy exposure to Microcystin-LR compromises endometrial decidualization in mice via the PI3K/AKT/FOXO1 signaling pathway

Previous experimental studies have found that exposure to Microcystin-leucine arginine can impact pregnancy outcomes in female mice. The impact of MC-LR on early pregnancy in mammals is not yet well understood. Both mice and humans need to undergo decidualization to maintain pregnancy. In this study, we tried to evaluate whether MC-LR affects decidualization process in mice. Our research showed that MC-LR decreased maternal weight gain, uterine weight, and implantation site weight. These findings suggested that MC-LR exerted adverse effects on decidualization. In mice, we examined decreased number of polyploid decidual cells, but marked proliferation of mouse endometrial stromal cells the expression levels of prolactin (PRL)and insulin-like growth factor binding protein 1 (IGFBP1) were significantly downregulated in the decidual tissue and primary endometrial stromal cells following MC-LR treatment. Furthermore, further in vitro experiments identified that MC-LR promoted endometrial stromal cell division and cycle transition. Lastly, our study demonstrated that MC-LR impaired decidualization through the PI3K/AKT/FOXO1 pathway. Collectively, these data suggested that exposure to MC-LR impaired decidualization during early pregnancy.

A systematic review on aquaculture wastewater: Pollutants, impacts, and treatment technology

Aquaculture is the major way to solve the global food sacrcity. As the global population increases, the demand for aquaculture increases. Fish feed, drugs and chemicals, and metabolic waste or mortalities of aquatic organisms also increase, eventually resulting in the production of a large amount of aquaculture wastewater. These aquaculture discharges contain a variety of pollutants, such as conventional pollutants, organic compounds, heavy metals, and biological contaminants, inducing occupational hazards and risks, food security, the environment pollution. Proper wastewater treatment technologies are required to remove hazardous pollutants for minimizing their impacts on environmental and human health. Recirculating aquaculture systems, some biological and physicochemical methods have been applied to remove some pollutants from the aquaculture wastewater, but their efficiency in removing pollutants still requires to be further improved for achieving zero-waste discharge and ensuring sustainable aquaculture development. Meanwhile, sound regulation and legislation needs to be established for ensuring the normal operation of aquaculture industries and the standard discharge of wastewater. This review aims to provide comprehensive information of aquaculture wastewater for the researchers and promote the healthy development of aquaculture.

Toxic effects of nanoplastics and microcystin-LR coexposure on the liver-gut axis of Hypophthalmichthys molitrix

Plastic products and nutrients are widely used in aquaculture facilities, resulting in copresence of nanoplastics (NPs) released from plastics and microcystins (MCs) from toxic cyanobacteria. The potential effects of NPs-MCs coexposure on aquatic products require investigation. This study investigated the toxic effects of polystyrene (PS) NPs and MC-LR on the gut-liver axis of silver carp Hypophthalmichthys molitrix, a representative commercial fish, and explored the effects of the coexposure on intestinal microorganism structure and liver metabolic function using traditional toxicology and multi-omics association analysis. The results showed that the PS-NPs and MC-LR coexposure significantly shortened villi length, and the higher the concentration of PS-NPs, the more obvious the villi shortening. The coexposure of high concentrations of PS-NPs and MC-LR increased the hepatocyte space in fish, and caused obvious loss of gill filaments. The diversity and richness of the fish gut microbes significantly increased after the PS-NPs exposure, and this trend was amplified in the copresence of MC-LR. In the coexposure, MC-LR contributed more to the alteration of fish liver metabolism, which affected the enrichment pathway in glycerophospholipid metabolism and folic acid biosynthesis, and there was a correlation between the differential glycerophospholipid metabolites and affected bacteria. These results suggested that the toxic mechanism of PS-NPs and MC-LR coexposure may be pathological changes of the liver, gut, and gill tissues, intestinal microbiota disturbance, and glycerophospholipid metabolism imbalance. The findings not only improve the understanding of environmental risks of NPs combined with other pollutants, but also provide potential microbiota and glycerophospholipid biomarkers in silver carp.

Microcystin concentrations and congener composition in relation to environmental variables across 440 north-temperate and boreal lakes

Understanding the environmental conditions and taxa that promote the occurrence of cyanobacterial toxins is imperative for effective management of lake ecosystems. Herein, we modeled total microcystin presence and concentrations with a broad suite of environmental predictors and cyanobacteria community data collected across 440 Canadian lakes using standardized methods. We also conducted a focused analysis targeting 14 microcystin congeners across 190 lakes, to examine how abiotic and biotic factors influence their relative proportions. Microcystins were detected in 30 % of lakes, with the highest total concentrations occurring in the most eutrophic lakes located in ecozones of central Canada. The two most commonly detected congeners were MC-LR (61 % of lakes) and MC-LA (37 % of lakes), while 11 others were detected more sporadically across waterbodies. Congener diversity peaked in central Canada where cyanobacteria biomass was highest. Using a zero-altered hurdle model, the probability of detecting microcystin was best explained by increasing Microcystis biomass, Daphnia and cyclopoid biomass, soluble reactive phosphorus, pH and wind. Microcystin concentrations increased with the biomass of Microcystis and other less dominant cyanobacteria taxa, as well as total phosphorus, cyclopoid copepod biomass, dissolved inorganic carbon and water temperature. Collectively, these models accounted for 34 % and 70 % of the variability, respectively. Based on a multiple factor analysis of microcystin congeners, cyanobacteria community data, environmental and zooplankton data, we found that the relative abundance of most congeners varied according to trophic state and were related to a combination of cyanobacteria genera biomasses and environmental variables.

Microcystin-LR Induces and Aggravates Colitis through NLRP3 Inflammasome-Mediated Pyroptosis in Mice

Inflammatory bowel disease (IBD) is a chronic, lifelong gastrointestinal disease, characterized by periods of activity and remission. The etiology of IBD is closely related to environmental factors. Previous studies have shown that the cyanotoxin microcystin-LR (MC-LR) causes intestinal damage, even IBD. To explore MC-LR's effects and potential mechanisms on IBD occurrence and development, we used dextran-sulfate sodium gavage (DSS) and MC-LR together for the first time in mice. There were four groups of mice: (A) mice given PBS gavage (control, CT); (B) mice given 3% DSS gavage (DSS); (C) mice given 200 µg/kg MC-LR gavage (MC-LR); and (D) mice given 3% DSS + 200 µg/kg MC-LR gavage (DSS + MC-LR). Compared with the CT group, the MC-LR group and the DSS group demonstrated more severe colitis results, which presented as higher weight loss, an increased Disease Activity Index (DAI) score, shorter colon length, a higher degree of tissue structural damage, more apoptotic cells, and greater pro-inflammatory cytokines. Similarly, the DSS + MC-LR group showed more severe colitis compared with the DSS group. Subsequent experiments confirmed that MC-LR or DSS increased the expression of pyroptosis-related proteins mediated by the nucleotide-binding domain-like receptor protein 3 (NLRP3). Likewise, compared with the DSS group, the DSS + MC-LR group expressed these proteins at a higher level. In conclusion, our research is the first to show that MC-LR may induce colitis, and even IBD, through NLRP3 inflammasome-mediated pyroptosis, and it could aggravate DSS-induced colitis in the same way.

Transmission of Microcystins in Natural Systems and Resource Processes: A Review of Potential Risks to Humans Health

The rapid rise of microcystins (MCs) poses a serious threat to global freshwater ecosystems and has become an important issue of global public health. MCs have considerable stability and are the most widely distributed hepatotoxins. It cannot only accumulate in aquatic organisms and transfer to higher nutrients and levels, but also be degraded or transferred during the resource utilization of cyanobacteria. No matter which enrichment method, it will lead to the risk of human exposure. This review summarizes the research status of MCs, and introduces the distribution of MCs in different components of aquatic ecosystems. The distribution of MCs in different aquatic organisms was summarized, and the potential risks of MCs in the environment to human safety were summarized. MCs have polluted all areas of aquatic ecosystems. In order to protect human life from the health threats caused by MCs, this paper also proposes some future research directions to promote MCs control and reduce human exposure to MCs.

Microcystin pollution in lakes and reservoirs: A nationwide meta-analysis and assessment in China

The frequent occurrence of microcystins (MCs) has caused a series of water security issues worldwide. Although MC pollution in natural waters of China has been reported, a systematic analysis of the risk of MCs in Chinese lakes and reservoirs is still lacking. In this study, the distribution, trend, and risk of MCs in Chinese lakes and reservoirs were comprehensively revealed through meta-analysis for the first time. The results showed that MC pollution occurrence in numerous lakes and reservoirs have been reported, with MC pollution being distributed in the waters of 15 provinces in China. For lakes, the maximum mean total MC (TMC) and dissolved MC (DMC) concentrations occurred in Lake Dianchi (23.06 μg/L) and Lake Taihu (1.00 μg/L), respectively. For reservoirs, the maximum mean TMC and DMC concentrations were detected in Guanting (4.31 μg/L) and Yanghe reservoirs (0.98 μg/L), respectively. The TMC concentrations in lakes were significantly higher than those in the reservoirs (p < 0.05), but no difference was observed in the DMC between the two water bodies (p > 0.05). Correlation analysis showed that the total phosphorus concentrations, pH, transparency, chlorophyll a, and dissolved oxygen were significantly related to the DMC in lakes and reservoirs. The ecological risks of DMC in Chinese lakes and reservoirs were generally at low levels, but high or moderate ecological risks of TMC had occurred in several waters, which were not negligible. Direct drinking water and consumption of aquatic products in several MC-polluted lakes and reservoirs may pose human health risks. This study systematically analyzed the pollution and risk of MCs in lakes and reservoirs nationwide in China and pointed out the need for further MC research and management in waters.

Microplastics benefit bacteria colonization and induce microcystin degradation

Microplastics (MPs) can sorb toxic substances and be colonized by microorganisms. However, the interactions between the adsorbed toxic substances and the MPs biofilm remains inadequately understood. Here, a 37-days microcosm experiment was conducted to investigate the influence of polystyrene microplastics (PS-MPs) on microcystin (MC-LR) behavior in turbulent scenarios. The results revealed that adsorption by PS-MPs was the primary process that led to a quick reduction of aquatic MC-LR concentrations. With the colonization of microorganisms on the PS-MPs, the attached biofilm altered the surface properties of PS-MPs, which enhanced the bio-adsorption of MC-LR. Meanwhile, microcystins degrading bacteria, such as Sphingomonadaceae and Methylophilaceae, inhabited in the biofilm, which facilitated the MC-LR biodegradation; this was also demonstrated by the identified MC-LR degradation products. Thus, the MC-LR concentration in water was constantly decreased, with a maximum removal capability of 35.8% in PS-MPs added groups. In addition, a 25% reduction of MC-LR was recorded in PS-MPs added static water. This suggested that the interaction between PS-MPs, biofilm, and MC-LR may be prevalent in natural waters. Our results indicate MPs as vectors for toxic substances could be a double-edged sword (adsorption and biodegradation), which provides new insights for understanding the ecological risks of microplastics.

Phytoplankton Composition and Their Related Factors in Five Different Lakes in China: Implications for Lake Management

In this paper, two trophic lakes: Lake Taihu and Lake Yanghe, and three alpine lakes: Lake Qinghai, Lake Keluke, and Lake Tuosu, were investigated to discover the connections between environmental factors and the phytoplankton community in lakes with differences in trophic levels and climatic conditions. Three seasonal data, including water quality and phytoplankton, were collected from the five lakes. The results demonstrated clear differences in water parameters and phytoplankton compositions in different lakes. The phytoplankton was dominated by Bacillariophyta, followed by Cyanobacteria and Chlorophyta in Lake Qinghai, Lake Keluke, and Lake Tuosu. It was dominated by Cyanobacteria (followed by Chlorophyta and Bacillariophyta in Lake Yanghe) and Cyanobacteria (followed by Chlorophyta and Cryptophyta in Lake Taihu). The temperature was an essential factor favoring the growth of Cyanobacteria, Chlorophyta, and Bacillariophyta, especially Cyanobacteria and Chlorophyta. The pH had significantly negative relationships with Cyanobacteria, Chlorophyta, and Bacillariophyta. Particularly, a high pH might be a strong and negative factor for phytoplankton growth in alpine lakes. A high salinity was also an adverse factor for phytoplankton. Those results could provide fundamental information about the phytoplankton community and their correlated factors in the alpine lakes of the Tibetan Plateau, contributing to the protection and management of alpine lakes.

Microplastic contamination assessment in water and economic fishes in different trophic guilds from an urban water supply reservoir after flooding

Rain and floods events are responsible for the transport of microplastics in freshwater ecosystems, yet to date, rare study has examined microplastics pollution in urban water supply reservoirs during such events. In this study, we investigated the concentrations and characteristics of microplastic in water and economic fish species with different feeding guilds in the Dafangying Reservoir, an important source of drinking water for Hefei city. Microplastic concentrations in water were relatively higher than that in natural lakes, indicating abundant microplastic contaminants input through overland runoff triggered by flooding. Our results detected five types (fiber, debris, film, microbead and particle) and six colors (black, transparent, blue, yellow, red and green) of microplastics in water samples. Fiber accounted for the dominant shape, which may result from the household sewage from washing clothes and desquamated fiber transported by wind and overland runoff. Meanwhile, transparent was the predominant microplastic color, which can be ascribe to the widely use of intentionally manufactured transparent disposable plastic commodities in cities. Then in fish samples, the microplastic concentrations ranged from 8.75 to 51.3 items/individual in fish guts, and 9.5-52.6 items/individual in fish gills. Our results demonstrated significant higher microplastic concentrations in planktivorous and herbivorous species. The filter feeding capture mode, i.e., engulfing floating prey through frequently drawing in large volume of water confused with microplastics, may result in the higher microplastic concentrations of planktivorous fishes. Due to the dense microplastics adhering on plant surface, herbivorous fishes can concentrate higher microplastics abundance through the ingestion of macrophytes. According to the biological concentration factor (BCF), all the determined microplastics gave BCF far below 1, suggesting the low bioaccumulation capacity of microplastics in fish species.

Plant-cyanobacteria interactions: Beneficial and harmful effects of cyanobacterial bioactive compounds on soil-plant systems and subsequent risk to animal and human health

Plant-cyanobacteria interactions occur in different ways and at many different levels, both beneficial and harmful. Plant-cyanobacteria interactions, as a beneficial symbiosis, have long been demonstrated in rice-growing areas (Poaceae) where the most efficient nitrogen-fixing cyanobacteria are present in paddies. Moreover, cyanobacteria may in turn produce and/or secrete numerous bioactive compounds that have plant growth-promoting abilities or that may make the plant more resistant to abiotic or biotic stress. In recent years, there has been a growing worldwide interest in the use of cyanobacterial biomass as biofertilizers to replace chemical fertilizers, in part to overcome increasing organic-farming demands. However, the potential presence of harmful cyanotoxins has delayed the use of such cyanobacterial biomass, which can be found in large quantities in freshwater ecosystems around the world. In this review, we describe the existing evidence for the positive benefit of plant-cyanobacteria interactions and discuss the use of cyanobacterial biomass as biofertilizers and its growing worldwide interest. Although mass cyanobacterial blooms and scums are a current and emerging threat to the degradation of ecosystems and to animal and human health, they may serve as a source of numerous bioactive compounds with multiple positive effects that could be of use as an alternative to chemical fertilizers in the context of sustainable development.

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.

Advances in the toxicology research of microcystins based on Omics approaches

Microcystins (MCs) are the most widely distributed cyanotoxins, which can be ingested by animals and human body in multiple ways, resulting in a threat to human health and the biodiversity of wildlife. Therefore, the study on toxic effects and mechanisms of MCs is one of the focuses of attention. Recently, the Omics techniques, i.e. genomics, transcriptomics, proteomics and metabolomics, have significantly contributed to the comprehensive understanding and revealing of the molecular mechanisms about the toxicity of MCs. This paper mainly reviews current literature using the Omics approaches to explore the toxicity mechanism of MCs in liver, gonad, spleen, brain, intestine and lung of multiple species. It was found that MCs can exert strong toxic effects on various metabolic activities and cell signal transduction in cell cycle, apoptosis, destruction of cell cytoskeleton and redox disorder, at protein, transcription and metabolism level. Meanwhile, it was also revealed that the alteration of non-coding RNAs (miRNA, circRNA and lncRNA, etc.) and gut microbiota plays an essential regulatory role in the toxic effects of MCs, especially in hepatotoxicity and reproductive toxicity. In addition, we summarized current research gaps and pointed out the future directions for research. The detailed information in this paper shows that the application and development of Omics techniques have significantly promoted the research on MCs toxicity, and it is also a valuable resource for exploring the toxic mechanism of MCs.

The joint effect of parental exposure to microcystin-LR and polystyrene nanoplastics on the growth of zebrafish offspring

The coexistence of nanoplastics (NPs) and various pollutants in the environment has become a problem that cannot be ignored. In order to identify the microcystin-LR (MCLR) bioaccumulation and the potential impacts on the early growth of F1 zebrafish (Danio rerio) offspring in the presence of polystyrene nanoplastics (PSNPs), PSNPs and MCLR were used to expose adult zebrafish for 21days. The exposure groups divided into MCLR (0, 0.9, 4.5 and 22.5μgL^-1) alone groups and PSNP (100μgL^-1) and MCLR co-exposure groups. F1 embryos were collected and developed to 120 h post-fertilization (hpf) in clear water. Compared with the exposure to MCLR only, the combined exposure increased the parental transfer of MCLR to the offspring and subsequently exacerbated the growth inhibition of F1 larvae. Further research clarified that combined exposure of PSNPs and MCLR could reduce the levels of thyroxine (T4) and 3, 5, 3'-triiodothyronine (T3) by altering the expression of hypothalamus-pituitary-thyroid (HPT) axis-related genes, eventually leading to growth inhibition of F1 larvae. Our results also exhibited combined exposure of PSNPs and MCLR could change the transcription of key genes of the GH/IGF axis compared with MCLR single exposure, suggesting the GH/IGF axis was a potential target for the growth inhibition of F1 larvae in PSNPs and MCLR co-exposure groups. The present study highlights the potential risks of coexistence of MCLR and PSNPs on development of fish offspring, and the environmental risks to aquatic ecosystems.

Occurrence of microcystins, anabaenopeptins and other cyanotoxins in fish from a freshwater wildlife reserve impacted by harmful cyanobacterial blooms

Harmful algal blooms of cyanobacteria (CyanoHABs) can lead to the release of potent toxins that can seriously affect ecosystem integrity. Some freshwater watersheds are particularly at risk considering the threats to already imperiled wildlife. The consumption of tainted drinking water and contaminated food also raises concerns for human health. In the present study, a pilot survey was conducted in the riverine ecosystem of the Pike River Ecological Reserve (QC, Canada) near Missisquoi Bay, Lake Champlain. We examined the occurrence of multiclass cyanotoxins including 12 microcystins, anatoxins, cylindrospermopsin (CYN), anabaenopeptins (AP-A, AP-B), and cyanopeptolin-A in surface waters and wild-caught fish during the summer 2018. Out of the 18 targeted cyanotoxins, 14 were detected in bloom-impacted surface water samples; toxins peaked during early-mid September with the highest concentrations for MC-LR (3.8 μg L^-1) and MC-RR (2.9 μg L^-1). Among the 71 field-collected fish from 10 species, 30% had positive detections to at least one cyanotoxin. In positive samples, concentration ranges in fish muscle were as follows for summed microcystins (∑MCs: 0.16-9.2 μg kg^-1), CYN (46-75 μg kg^-1), AP-A (1.1-5.4 μg kg^-1), and AP-B (0.12-5.0 μg kg^-1). To the best of our knowledge, this is one the first reports of anabaenopeptins occurrence in wildlife. The maximum ∑MCs in fish was 1.15-fold higher than the World Health Organization (WHO) daily intake recommendation for adults and nearly equated the derived value for young children. The concentration of CYN was also about 3-fold higher than the limit derived from the human health guideline values.

Mercury, microcystins and Omega-3 polyunsaturated fatty acids in farmed fish in eutrophic reservoir: Risk and benefit assessment

Fish is an important source of nutritional omega-3 (n-3) polyunsaturated fatty acids, but it also readily accumulates toxic mercury (Hg) and microcystins (MC) in eutrophic aquatic systems. In China, farmed fish was widely consumed, and aquaculture has caused pervasive eutrophication of freshwater lakes, resulting in the increasing accumulation of MC in fish tissue. To assess the risk-benefit of consuming farmed fish, 205 fish samples of 10 primary species were collected from the eutrophic Wujiangdu (WJD) Reservoir, SW China. The contents of Hg, microcystin-RR (MC-RR), microcystin-LR (MC-LR), and polyunsaturated fatty acids (PUFA) in fish were analyzed. The results showed that THg and MeHg concentrations in all fish sampls were well below the safety limit (500 ng/g w.w) established by the Standardization Administration of China, with average values of 22.9 ± 22.8 and 6.0 ± 6.6 ng/g wet weight (w.w.), respectively. Average concentrations of MC-RR and MC-LR were 40 ± 80 and 50 ± 80 ng/g w.w., respectively. MC-RR and MC-LR concentrations in fish were significantly higher in silver carp and black carp than in perch and catfish (p < 0.05). In nutritional terms, average concentrations of n-3 PUFA and the eicosapentaenoic (EPA) + docosahexaenoic acids (DHA) of fish were 2.0 ± 2.5 and 1.4 ± 0.5 mg/g w.w., respectively. The risk-benefit assessment suggests that the n-3 PUFA benefits from consuming all farmed fish species in the WJD Reservoir outweigh the adverse effects of MeHg. However, except for perch, most fish species still pose a high MC-LR exposure risk that created a requirement for fish consumption advisories and monitoring. Consequently, more attention should be paid on the health risk of combined exposure to pollutants by aquatic product consumption.

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.

Effects of MC-LR on histological structure and cell apoptosis in the kidney of grass carp (Ctenopharyngodon idella)

Microcystin-LR (MC-LR) is a well-known hepatotoxin; however, increasing evidence suggests that it might induce kidney injury. Grass carp (Ctenopharyngodon idella) is one of the most important farmed species and may be affected by MC-LR releasing into waterbody during cyanobacterial bloom. Here, this present study aimed to explore the nephrotoxicity of grass carp by MC-LR. The grass carp received a single intraperitoneal injection of different doses of MC-LR (0, 25, 75, and 100 μg/kg body weight (BW)), and the kidneys were isolated at 24 and 96 h post-injection (hpi). Histopathological examination revealed kidney lesions, with severe hemorrhage, necrosis of the interstitium, and dilation of Bowman's capsule in the 75 and 100 μg MC-LR/kg BW groups. Under transmission electron microscopy, a larger number of swelling and vacuolated degeneration of mitochondria were observed; moreover, apoptotic features, such as condensed chromatin and shrinkage of cells, were observed in the 75 and 100 μg MC-LR/kg BW groups at 96 hpi. MC-LR significantly upregulated the number of apoptotic cells in the 75 and 100 μg/kg BW groups at 96 hpi as indicated by terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) assay (P < 0. 05). The results of quantitative assays showed that the mRNA expression of Bax, caspase-9, and caspase-3 in grass carp kidney were significantly increased at 96 hpi in the 75 and 100 μg MC-LR/kg BW groups compared with that in the control group, but Bcl-2 mRNA expression was significantly decreased in all the treatment groups at 24 and 96 hpi. Taken together, these results indicated that MC-LR damaged the kidney structure and resulted in renal apoptosis which may occur via the mitochondrial pathway.

A Review of Nephrotoxicity of Microcystins

Cyanobacterial blooms triggered by eutrophication and climate change have become a global public health issue. The toxic metabolites microcystins (MCs) generated by cyanobacteria can accumulate in food chain and contaminate water, thus posing a potential threat to human and animals health. Studies have suggested that aside liver, the kidney may be another target organ of MCs intoxication. Therefore, this review provides various evidences on the nephrotoxicity of MCs. The review concludes that nephrotoxicity of MCs may be related to inhibition of protein phosphatases and excessive production of reactive oxygen species, cytoskeleton disruption, endoplasmic reticulum stress, DNA damage and cell apoptosis. To protect human from MCs toxic consequences, this paper also puts forward some directions for further research.

Mixotrophic Ochromonas Addition Improves the Harmful Microcystis-Dominated Phytoplankton Community in In Situ Microcosms

Driven by global warming and eutrophication, outbreaks of cyanobacterial blooms have severely impacted ecosystem stability and water safety. Of the organisms used to control cyanobacteria, protozoa can highly resist cyanotoxins, efficiently control cyanobacterial populations, and show considerably different feeding strategies from those of metazoans. Thus, protozoa have great potential to control harmful cyanobacteria and improve phytoplankton composition in eutrophic waters. To evaluate the actual effects of protozoa in controlling cyanobacteria and improving the phytoplankton community structure in the field, an in situ microcosm study was performed using a flagellate Ochromonas gloeopara that ingests Microcystis. Results showed that adding Ochromonas reduced the cyanobacterial populations and increased the chlorophyte and diatom proportions. Furthermore, the species richness and diversity of the phytoplankton community were enhanced in microcosms with Ochromonas. Additionally, there was a gradual increase in the chlorophyte population in the unicellular Microcystis control, while Ochromonas addition significantly accelerated the replacement of dominant species. This study was the first to show the practical effects of protozoa on controlling cyanobacteria in the field, highlighting that a reduction in in situ cyanobacteria via protozoa can improve the phytoplankton community structure, dredge the toxic cyanobacteria-dominated microbial food web, and mitigate harmful cyanobacteria risks in fresh waters.

Acute microcystin-LR exposure interfere thyroid hormones homeostasis in adult zebrafish (Danio rerio)

Microcystin-LR (MC-LR) in the aquatic environment may disturb thyroid hormone (TH) homeostasis. It is not clear how MC-LR affects downstream biological processes after TH disturbance. After exposure to 50, 100, 200 and 400 μg/L MC-LR for 24, 48, 72, or 96 h, alterations of the TH metabolism of adult zebrafish at thyroxine (T4), triiodothyronine (T3) levels, and iodothyronine deiodinase (Dio) activity, were observed. After exposure to MC-LR at 400 μg/L, T3 and T4 levels decreased significantly in females (p < 0.05) and returned to normal levels at 96 h. In males, T4 levels were not significantly different between groups. The expression of corticotropin releasing hormone, thyroid-stimulating hormone beta subunit, transthyretin, sodium/iodide cotransporter, thrombopoietin, thyroid hormone receptor alpha and beta changed, but not in a dose-dependent manner. Acute MC-LR exposure induced a negative feedback regulation of the hypothalamic-pituitary-thyroid axis in adult zebrafish, and females were more sensitive than males. In conclusion, acute MC-LR exposure disrupted the TH metabolism by altering Dio activity and gene expression of the HPT axis; these changes may affect the complement system through regulation of c9 mRNA synthesis.

Cyanobacterial blooms modify food web structure and interactions in western Lake Erie

With anthropogenic eutrophication and climate change causing an increase in cyanobacterial blooms worldwide, the need to understand the consequences of these blooms on aquatic ecosystems is paramount. Key questions remain unanswered with respect to how cyanobacteria blooms affect the structure of aquatic food webs, the foraging abilities of higher consumers, and the potential for cyanotoxins (e.g., microcystins [MCs]) to accumulate in fish. Toward addressing these uncertainties, physicochemical attributes, water (for MCs), phytoplankton, zooplankton, and epipelagic and benthic age-0 fish were sampled at 75 sites (44 sites for fish) of varying cyanobacteria concentration (0.1-44 μg/L) in western Lake Erie during the cyanobacteria bloom season, 2013-2014. Sites with high cyanobacteria biomass were characterized by Microcystis spp. (84-100% of biomass), detectible levels of MCs (maximum = 10.8 μg/L), and low water transparency (minimum = 0.25 m). Counter to expectations, strong positive relationships were found between cyanobacteria concentration and the biomass of several herbivorous zooplankton taxa (e.g., Daphnia, Diaphanosoma spp., Bosmina (formerly Eubosmina) coregoni, and Calanoida spp.). Expectations regarding fish were partly supported (e.g., diet selectivity varied across a cyanobacteria gradient) and partly not (e.g., consumption of zooplankton did not differ between bloom and non-bloom sites). These findings show that cyanobacterial blooms can strongly affect the distribution, composition, and interactions of zooplankton and fish, sometimes in surprising ways, highlighting the need to further explore their impact on aquatic food webs.

Effects of Chronic Exposure to Microcystin-LR on Kidney in Mice

Microcystin-LR (MC-LR) is a potent hepatotoxin, but a few studies suggested that it might also induce nephrotoxicity. However, nephrotoxicity induced by prolonged oral exposure to MC-LR is unknown. The aim of this study was to evaluate the potential influence of MC-LR on the kidney in mice following chronic exposure to MC-LR. In this study, we evaluated the nephrotoxicity of MC-LR in mice drinking water at different concentrations (1, 30, 60, 90, and 120 μg/L) for 6 months for the first time. The results showed that the kidney weights and the kidney indexes of mice were not altered in the MC-LR treated mice, compared with the control group. In addition, the renal function indicators revealed that the serum creatinine (SCr) levels were not significant changes after exposure to MC-LR. The blood urea nitrogen (BUN) levels were markedly decreased after exposure to 90 and 120 μg/L MC-LR for 3 months. The BUN levels were lower than that of the control group after exposure to 120 μg/L MC-LR for 6 months. The histopathological investigation revealed enlarged renal corpuscles, widened of kidney tubules, and lymphocyte infiltration in the interstitial tissue and the renal pelvis after exposure to 60, 90, and 120 μg/L MC-LR. Consequently, our results suggested that long-term exposure to MC-LR might be one important risk of kidney injury, which will provide important clues for the prevention of renal impairment.

Broad-specificity ELISA with a heterogeneous strategy for sensitive detection of microcystins and nodularin

A highly sensitive and broadly specific competitive indirect enzyme-linked immunosorbent assay (ciELISA) method was developed for the simultaneous detection of nine microcystins (MCs) and nodularin (NOD) using MC-LR-keyhole limpet hemocyanin (KLH) for New Zealand white rabbit immunization to produce antibodies. The MC-LR-bovine serum albumin (BSA) and NOD-BSA coating antigens were compared and heterogeneous coating strategy was found to significantly improve the sensitivity of detection, as evident from the appropriate structure. Comparison of the half-maximum inhibitory concentration (IC50) with MC-LR and MC-LR-BSA coating techniques (0.29 ng/mL) revealed the superior performance of 0.054 ng/mL for NOD-BSA coating. NOD-BSA was selected as the coating antigen, because it showed ultrahigh sensitivity for the detection of MC-LR with a limit of detection (LOD) of 0.0016 ng/mL, which was below the maximum residue level (MRL) of 1 ng/mL. In addition, high reproducibility, good stability, and acceptable spiked sample detection, as validated by liquid chromatography tandem mass spectrometry (LC-MS/MS), indicated the possible application of this method for the analysis of MCs and NOD in water sample.

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.

Epigenetic inactivation of LHX6 mediated microcystin-LR induced hepatocarcinogenesis via the Wnt/β-catenin and P53 signaling pathways

Microcystins (MCs) have been shown to be carcinogenic by animal and cellular experiments and found to be associated with the development of human hepatocellular carcinoma (HCC) through epidemiological studies. However, the molecular mechanism of microcystin-LR (MC-LR) induced HCC is still unclear. This study is determined to clarify the role and mechanism of LHX6 in MC-LR-induced hepatocarcinogenesis. Using the previously established MC-LR-induced malignant transformation model in L02 cells, we screened out LHX6, homeobox gene that was significantly changed. We found that LHX6 was significantly down-regulated in MC-LR treated L02 cells and the liver tissue of rats treated for 35 weeks with 10 μg/kg body weight of MC-LR. Expression of LHX6 in human tumor tissue was significantly down-regulated in high MC-LR-exposure group. LHX6 was hypermethylated in MC-LR treated L02 cells and up-regulated after treatment with 10 μM of 5-aza-2'-deoxycytidine. Furthermore, overexpression of LHX6 inhibited proliferation, invasion and migration of malignantly transformed L02 cells in vitro and in vivo, while knockdown of LHX6 resulted in an opposite phenotype. In addition, we found that up-regulation of P53 and Bax resulted in apoptosis, and that down-regulation of CTNNB1 and MMP7 led to migration of MC-LR treated L02 cells. Blockade of P53 and CTNNB1 by its inhibitor significantly diminished the effect of LHX6. These genes were working together during the process of MC-LR-induced hepatocarcinogenesis. Our study demonstrated for the first time that LHX6 gene expression is regulated by DNA methylation and can inhibit the proliferation, invasion and migration through Wnt/β-catenin and P53 signaling pathways during the MC-LR-induced hepatocarcinogenesis. This result may suggest that LHX6 gene can be used as a potential target gene and a biomarker for liver cancer treatment.

A Review of Cardiovascular Toxicity of Microcystins

The mortality rate of cardiovascular diseases (CVD) in China is on the rise. The increasing burden of CVD in China has become a major public health problem. Cyanobacterial blooms have been recently considered a global environmental concern. Microcystins (MCs) are the secondary products of cyanobacteria metabolism and the most harmful cyanotoxin found in water bodies. Recent studies provide strong evidence of positive associations between MC exposure and cardiotoxicity, representing a threat to human cardiovascular health. This review focuses on the effects of MCs on the cardiovascular system and provides some evidence that CVD could be induced by MCs. We summarized the current knowledge of the cardiovascular toxicity of MCs, with regard to direct cardiovascular toxicity and indirect cardiovascular toxicity. Toxicity of MCs is mainly governed by the increasing level of reactive oxygen species (ROS), oxidative stress in mitochondria and endoplasmic reticulum, the inhibition activities of serine/threonine protein phosphatase 1 (PP1) and 2A (PP2A) and the destruction of cytoskeletons, which finally induce the occurrence of CVD. To protect human health from the threat of MCs, this paper also puts forward some directions for further research.

Microcystin-LR promotes necroptosis in primary mouse hepatocytes by overproducing reactive oxygen species

Microcystin-LR (MC-LR) is a type of cyclic heptapeptide toxin produced by cyanobacteria during bloom events. MC-LR-induced cell death is critically involved in its potent specific hepatotoxicity. Many studies have demonstrated that prototypical apoptosis as a form of programmed cell death after MC-LR is associated with liver injury. However, whether another form of programmed cell death exists and the underlying mechanism have not been reported. Here, we demonstrate that MC-LR can induce necroptosis via ROS overactivation in primary mouse hepatocytes. Various potential pathways of programmed cell death induced by MC-LR were evaluated by annexin V/PI dual staining for flow cytometric analysis, image-based PI staining analysis and western blot analysis. Cell viability was determined by the CCK8 assay. Rupture of the plasma membrane was indicated by lactate dehydrogenase release. ROS was evaluated with the carboxy-H2DCFDA fluorescent probe. It was found that in MC-LR-treated cells, as the plasma membrane was damaged, annexin V/PI-stained double-positive cells were significantly induced and PI-stained nuclei were more diffuse. Western blot analysis showed that MC-LR treatment significantly upregulated the expression of necroptotic and apoptotic proteins. Mechanistically, MC-LR induced ROS overproduction by dysregulating the expression and activity of the pro-oxidants SOD1, MAOA, and NOX4 and the antioxidant GPX1. These results indicate the presence of a novel mechanism for MC-LR-mediated liver injury and present a novel target in the treatment of MC-LR-exposed patients.

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.

Chronic exposure to microcystin-LR reduces thyroid hormone levels by activating p38/MAPK and MEK/ERK signal pathway

Microcystin-LR (MC-LR) is the most toxic and abundant microcystin that produced by cyanobacteria. Previous studies have shown MC-LR had acute toxic to thyroid, however, the mechanism is still unclear, and the effect of long-term, low-dose MC-LR on thyroid remains uncertain. In this study, we investigated the chronic, low-dose effect of MC-LR on mouse thyroid tissues and thyroid hormone metabolism. MC-LR was orally administered to mice at 0, 1, 10, 20 and 40 μg/L for 6 consecutive months for histopathological and immunoblot analysis. Nthy-ori 3-1 cells were cultured in various concentrations of MC-LR (0, 0.5, 5, 50, 500 nmol/L) for indicated time, meanwhile the cell viability and proteins change were tested. From our study, the chronic, low-dose MC-LR exposure can disturb thyroid hormone synthesis and metabolism through activating the p38/MAPK and MEK/ERK signaling pathways, then up-regulating the expression of type 3 deiodinase. These data support the potential toxic effects of MC-LR on thyroid tissue and thyroid hormone metabolism.

Microcystin-LR exposure induced nephrotoxicity by triggering apoptosis in female zebrafish

Recently, several studies showed that microcystin-LR (MCLR) can accumulate and induce toxicity in kidney. However, the exact mechanism is unknown. The aim of this study was to explore the mechanism of MCLR-induced nephrotoxicity. To this end, adult zebrafish were exposed to MCLR (0, 1, 5 and 25 μg/L) for 60 days. Exposure to MCLR caused histopathological lesions, which were characterized by renal tubules filled with eosinophilic casts, abnormal renal tubules, intertubular space decrease, and blood infiltration in renal cells. RNA-Seq analysis indicated that exposure to MCLR significantly interfered with renal gene expressions, and these genes were enriched in various pathways, such as oxidative phosphorylation, cell cycle, and protein processing in endoplasmic reticulum, which were related to apoptosis. Furthermore, terminal deoxynucleotide transferase-mediated deoxy-UTP nick end labelling (TUNEL) assay showed that MCLR exposure induced renal cell apoptosis. In addition, negative changes of the reactive oxygen species (ROS) level as well as apoptotic-related gene, protein expressions and enzyme activities suggested that MCLR could induce production of ROS, subsequently triggering apoptosis via p53-bcl-2 and caspase-dependent pathway in the kidney of zebrafish. Therefore, it can be concluded that apoptosis is a primary case of MCLR-induced nephrotoxicity.

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

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

Cyanobacterial Blooms and Microcystins in Southern Vietnam

Studies on cyanobacteria in Vietnam are limited and mainly restricted to large reservoirs. Cyanobacterial blooms in small water bodies may pose a health risk to local people. We sampled 17 water bodies in the vicinity of urban settlements throughout the Mekong basin and in southeast Vietnam. From these, 40 water samples were taken, 24 cyanobacterial strains were isolated and 129 fish, 68 snail, 7 shrimp, 4 clam, and 4 duck samples were analyzed for microcystins (MCs). MCs were detected up to 11,039 µg/L or to 4033 µg/g DW in water samples. MCs were detected in the viscera of the animals. MC-LR and MC-RR were most frequently detected, while MC-dmLR, MC-LW, and MC-LF were first recorded in Vietnam. Microcystis was the main potential toxin producer and the most common bloom-forming species. A potential health hazard was found in a duck⁻fish pond located in the catchment of DauTieng reservoir and in the DongNai river where raw water was collected for DongNai waterwork. The whole viscera of fish and snails must be completely removed during food processing. Cyanobacterial monitoring programs should be established to assess and minimize potential public health risks.

Chlorophytes prolong mixotrophic Ochromonas eliminating Microcystis: Temperature-dependent effect

Cyanobacterial blooms, caused by eutrophication and climate warming, exert severely negative effects on aquatic ecosystem. Some species of protozoans can graze on toxic cyanobacteria and degrade microcystins highly efficiently, which shows a promising way to control the harmful algae. However, in the field, many different species of algae coexist with Microcystis and may affect protozoans eliminating Microcystis. Therefore, in this study, we assessed the impacts of chlorophytes, a type of beneficial algae for zooplankton and common competitors of cyanobacteria, on flagellate Ochromonas eliminating toxin-producing Microcystis at different temperatures. Our results showed that Ochromonas still eliminated Microcystis population and degraded the total microcystins with the addition of chlorophytes, although the time of eliminating Microcystis was prolonged and temperature-dependent. Additionally, in the grazing treatments, chlorophytes populations gradually increased with the depletion of Microcystis, whereas Microcystis dominated in the mixed algal cultures without Ochromonas. The findings indicated that although chlorophytes prolong mixotrophic Ochromonas eliminating Microcystis, the flagellate grazing Microcystis helps chlorophytes dominating in the primary producers, which is significant in improving water quality and reducing aquatic ecosystem risks.

The production and release of microcystin related to phytoplankton biodiversity and water salinity in two cyanobacteria blooming lakes

To find the connections between microcystins and the phytoplankton community, coupled with environmental factors, we investigated 2 cyanobacteria blooming lakes, Lake Taihu (at the center of the Yangtze River Delta, eastern China) and Lake Yanghe (near Qinhuangdao City, northern China). Two years of data, including water quality and the amounts of phytoplankton, microcystins, and the congeners in both algal cells and water, were collected from the 2 lakes during 2013 and 2014. The results showed that both the microcystin quota and release percentage were positively correlated with biodiversity of phytoplankton and the Chlorophyta to phytoplankton ratio, but were negatively correlated with cyanobacteria abundance and the cyanobacteria to phytoplankton ratio; both the microcystin quota and release percentage were closely related to the intensity of competition between cyanobacteria and other phytoplankton; meanwhile, microcystins played a role in the competition between cyanobacteria and other phytoplankton. Salinity had a significantly negative relationship with both cellular and total microcystins, but a significantly positive relationship with the microcystin releasing percentage, indicating that an increase in salinity inhibited the production of microcystins but promoted their release into the aquatic environment. In addition, the average number of microcystins in Lake Yanghe was several times higher than the provisional guideline value adopted by the World Health Organization, indicating a possible health risk to local people. Environ Toxicol Chem 2018;37:2312-2322. © 2018 SETAC.

Exposure routes and health effects of microcystins on animals and humans: A mini-review

Microcystins (MCs) pollution has quickly risen in infamy and has become a major problem to public health worldwide. MCs are a group of monocyclic hepatotoxic peptides, which are produced by some bloom-forming cyanobacteria in water. More than 100 different MCs variants posing a great threat to animals and humans due to their potential carcinogenicity have been reported. To reduce MCs risks, the World Health Organization has set a provisional guideline of 1 μg/L MCs in human's drinking water. This paper provides an overview of exposure routes of MCs into the human system and health effects on different organs after MCs exposure including the liver, intestine, brain, kidney, lung, heart and reproductive system. In addition, some evidences on human poisoning and deaths associated with MCs exposure are presented. Finally, in order to protect human life against the health threats posed by MCs, this paper also suggests some directions for future research that can advance MCs control and minimize human exposure to MCs.

P44/42 MAPK signal pathway-mediated hyperphosphorylation of paxillin and redistribution of E-cadherin was involved in microcystin-LR-reduced cellular adhesion in a human liver cell line

Microcystin-LR (MC-LR) is the most common and toxic variant of microcystins. We hypothesize that p44/42 MAPK (ERK1/2) signal pathway is involved in MC-LR-induced cell adhesion alteration in a human liver cell line-HL7702. We identified that MC-LR constantly activated MEK1/2-ERK1/2 signal pathway for 24 h, 48 h and 72 h in vitro. MC-LR reduced hepatocytes adhesion efficiency. Furthermore, as the focal adhesion biomarker, hyperphosphorylation of paxillin (ser83) was induced by MC-LR, which can be blocked by ERK1/2 pathway inhibitor (U0126) and was enhanced after hepatocytes transfected with pCMV6-MAPK plasmid. E-cadherin, as a biomarker which reflects the dynamic of cell-cell adhesion, its redistribution in hepatocytes was induced by MC-LR, and these redistribution and colocalization can be attenuated by U0126. Furthermore, MC-LR increased the co-localization efficiency of p-ERK1/2 with E-cadherin and paxillin. Finally, MC-LR-induced adhesive alteration of hepatocytes can be blocked by ERK1/2 signal pathway inhibitor. These data suggest ERK1/2-phospho-paxillin (ser83)/E-cadherin axis is involved in MC-LR toxic mechanism, which probably provides adaptive protection against MC-LR-induced hepatocytes adhesion changes.

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.

Uptake and accumulation of Microcystin-LR based on exposure through drinking water: An animal model assessing the human health risk

Harmful Algal Blooms (HABs) in freshwater systems and intensified aquaculture have increased the risk to human health through exposure to cyanotoxins such as microcystin-LR (MC-LR). To understand the uptake and processing of MC-LR in humans, the pig was chosen as an animal model. This was assessed by repeated exposure for 13 weeks of eight animals dosed daily with MC-LR at 0.04 µg/kg bw, repeated with six animals over five weeks at a dose 50 times higher at 2 µg/kg bw. An analytical method was developed for MC-LR in porcine serum and also to analyse levels of free MC-LR in harvested porcine tissues, with Lemieux Oxidation employed to determine bound MC-LR in these tissues. MC-LR was not detected in the serum of treated animals from either experiment but free MC-LR was observed in the large intestine and kidney from two animals from the higher dosed group at levels of 1.4 and 1.9 µg/kg dry weight (dw) respectively. The results indicated 50% of higher dosed animals accumulated bound MC-LR in liver tissue, averaging 26.4 µg, approximately 1.1% of the dose administered. These results point to the potential uptake and accumulation of MC-LR in human liver tissue exposed chronically to sub-acute doses.

Chronic exposure of nanomolar MC-LR caused oxidative stress and inflammatory responses in HepG2 cells

Low dose but long-term exposure of microcystin-LR (MC-LR) could induce human hepatitis and promote liver cancer according to epidemiological investigation results, but the exact mechanism has not been completely elucidated. In the present study, a chronic toxicity test of MC-LR exposure on HepG2 cells at 0.1-30 nM for 83 d was conducted under laboratory conditions. The western blot assay result revealed that MC-LR entered HepG2 cells, even at the concentration of 0.1 nM, after 83 d of exposure, but no cytotoxicity was observed in the HepG2 cells, as determined by the CCK-8 and LDH tests. However, the results of the DCF fluorescence assay showed that the intracellular ROS level in the 30 nM MC-LR-treated cells was significantly higher than that of the control cells, and 5 and 10 nM of MC-LR exposure totally increased the activity of SOD in HepG2 cells. These results indicate that MC-LR exposure at low concentration also induced excessive ROS in HepG2 cells. Additionally, long-term exposure of MC-LR at low concentration remarkably promoted the expression of NF-κB p65, COX-2, iNOS, TNF-α, IL-1β, and IL-6 in the cells, suggesting that long-term MC-LR exposure at low concentration can induce inflammatory reaction to HepG2 cells, which might account for MC-induced human hepatitis. Thus, we hypothesized that the pathogenesis of human hepatitis and hepatocarcinoma caused by MCs might be closely associated with oxidative stress and inflammation.

Monitoring and research of microcystins and environmental factors in a typical artificial freshwater aquaculture pond

Freshwater aquaculture ponds are important artificially regulated aquatic ecosystems which provide a large number of freshwater fish products in China. The cyanobacteria bloom and microcystin (MC) pollution caused by anthropogenic eutrophication have attracted much attention due to their toxic effects. To provide an insight into the cyanobacterial problem in the ponds, the environmental parameters and MCs of a typical artificial pond in the Yangtze River Delta region of China were monitored and studied from May to December 2015. During the monitoring period, the ponds were in serious eutrophication with total phosphorus (TP) concentrations between 0.95 and 1.80 μg/L, and total nitrogen (TN) concentrations between 1.1 and 4.86 μg/L. High feed coefficient and high fish stock were the main reasons for the eutrophication. The results showed that the water temperature was the key factor that affected the cyanobacteria blooming in the pond. The chlorophyll a concentration was significantly positively correlated with the cyanobacteria density during the blooming season. MC-LR and MC-RR existed simultaneously and showed a significant positive correlation. The peak concentrations of dissolved MC-LR and MC-RR in the pond water were 40.6 and 4.7 μg/L, respectively, which is considered highly toxic. Free MC-LR and MC-RR were also found in the aquaculture products. MC-LR concentrations in the bighead carp (Aristichthys nobilis) liver and shrimp (Macrobrachium nipponense) muscle were up to 2.64 and 4.17 μg/kg, respectively. MC-RR concentration was up to 1.89 μg/kg in the black carp (Mylopharyngodon piceus) liver. The results implied the potential health risks for citizens and pets caused by current artificial freshwater aquaculture pond systems.

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.

Toxic mechanisms of microcystins in mammals

Microcystins, such as microcystin-leucine arginine (MC-LR), are some of the most toxic and prevalent cyanotoxins produced by cyanobacteria in freshwater and saltwater algal blooms worldwide. Acute and chronic exposures to microcystins are primarily known to cause hepatotoxicity; cellular damage and genotoxicity within mammalian livers. However, in vivo studies indicate that similar damage may occur in other mammalian organs and tissues, such as the kidney, heart, reproductive systems, and lungs - particularly following chronic low-dose exposures. Mechanisms of toxicity of mycrocystins are reviewed herein; including cellular uptake, interaction with protein phosphatases PP1 and PP2A, cytoskeletal effects, formation of oxidative stress and induction of apoptosis. In general, the mode of action of toxicity by MCs in mammalian organs are similar to those that have been observed in liver tissues. A comprehensive understanding of the toxic mechanisms of microcystins in mammalian tissues and organs will assist in the development of risk assessment approaches to public health protection strategies and the development of robust drinking water policies.

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

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

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

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