Concentrations Of microcystin-LR Research Articles

Study of Seasonal Dynamics of Microcystins and Nutrients in Studena Reservoir in 2023

This paper is a synthesis of data from studies conducted in 2023 on the seasonal dynamics of the presence of microcystin-LR and its homologues in water samples from Studena reservoir. A total of ten samples were collected from June to October 2023. The species composition of phytoplankton and the nutrients total nitrogen and total phosphorus were determined. The presence of microcystins was detected in three samples from the months of September and October (microcystin-LR concentration 0.38 and 0.75 μg/L in the water sample and in a scum at the reservoir wall in October; microcystin-RR 0.10 μg/L in September and 0.55 and 0.70 μg/L in the water sample and in a scum at the reservoir wall in October; microcystin-YR 0.27 and 0.48 μg/L in the water sample and in a scum at the reservoir wall in October). Trace amounts of microcystin-LR equivalents other than microcystin-RR and microcystin-YR were observed in water samples in June and July. The phytoplankton communities in the reservoir are persistently inhabited by blue-green algae. The presence of microcystins at concentrations close to the permissible level in the autumn sample indicates that at the time of sampling the bloom of cyanobacteria that produced the microcystins had passed and the toxins released remained in the water. Due to the near acceptable concentration of MC-LR in the autumn sample, serious consideration should be given to monitoring the reservoir during periods favourable for bloom formation.

Seasonal Rise in the Contents of Microcystin-LR and Odorous Substances Due to Cyanobacterial Blooms in a Drinking Water Reservoir Supplying Xinyang City, China.

Cyanobacterial blooms have become a serious water pollution problem in many parts of the world, and the monitoring and study of the impacts of biotoxins on human health are of vital importance. In this study, the contents of microcystin-LR, 2-methylisoborneol, and geosmin were measured in water and sediment samples from Nanwan Reservoir, China, by means of bimonthly sampling between February and December 2023. The physicochemical and hydrochemical factors and phytoplankton dynamics in the reservoir were also investigated. The results showed that the overall mean concentration of microcystin-LR (0.729 μg/L) in summer approached the guiding standard (1 μg/L) set by the WHO for drinking water. Furthermore, the content of 2-methylisoborneol (143.5 ng/L) was 14 times higher than the national standard (10 ng/L). The results of laboratory cultures showed that lower light levels and medium temperatures were suitable for the growth of Microcystis and Planktothricoides but higher temperatures promoted the synthesis and release of microcystin-LR and 2-methylisoborneol. In addition, the results of co-cultures showed that the growth of Planktothricoides was inhibited by Microcystis. Our results suggest that cyanobacterial bloom and the presence of the metabolites 2-methylisoborneol and microcystin-LR can decrease the drinking water quality of Nanwan Reservoir.

Nicotinamide Alleviates Synergistic Impairment of Intestinal Barrier Caused by MC-LR and NaNO2 Coexposure.

Microcystin-LR (MC-LR) and nitrites from the environment and daily life can be ingested and absorbed by humans via the digestive tract. However, their combined effects on intestinal health remain unclear. Here, the combined impact of MC-LR and sodium nitrite (NaNO2) on the intestines of mice was investigated under actual human exposure conditions. After mice were exposed to MC-LR (10, 100 μg/L) and NaNO2 (30, 300 mg/L) individual and in combination for 6 months, it was found that MC-LR and NaNO2 synergistically decreased intestinal permeability and disrupted intestinal physical, chemical, immune, and microbial barriers. In the coexposure groups, the synergistic impairment to the intestinal barrier was noted with increasing concentrations of MC-LR or NaNO2, but this adverse effect was alleviated by nicotinamide supplementation. This study underscores the potential risks of simultaneous ingestion of MC-LR and nitrite on intestinal health. The protective role of nicotinamide suggests avenues for therapeutic intervention against environmental toxin-induced intestinal impairment.

Nanozyme and bifunctional nanobody-based colorimetric-SERS dual-mode Immunosensor for microcystin-LR detection

Microcystin-LR (MC-LR), a potent cyanotoxin in freshwater, poses a risk of severe liver damage and other health issues, making its detection vital. However, the detection capabilities of conventional antibodies are constrained, which limited their use in immunoassays. In this work, we designed a new bifunctional nanobody, named A2.3-SBP (comprised of nanobody and streptavidin binding peptide), capable of binding with MC-LR and streptavidin. Based on A2.3-SBP and Fe3O4@Au-Pt nanozyme, we introduced an enzyme-free immunosensor that operated in microplate with colorimetric and surface-enhanced Raman scattering (SERS) detection modes. The dual-mode assay showed color changes and SERS intensity directly correlating to MC-LR concentrations with a range from 1.0 to 500 ng/mL and a limit of detection of 0.26 and 0.032 ng/mL, respectively. This strategy eliminated the need for complex enzymatic reactions and realized dual-signal detection of MC-LR in 96 water samples (0.03 μg/kg) within 30 min, suggesting its potential in drinking water detection.

Assessing the response lettuce and arugula to MC-LR-contaminated water irrigation: photosynthetic changes and antioxidant defense.

Irrigation of crops with cyanotoxin-contaminated water poses a significant risk to human health. The direct phytotoxic effects of microcystin-LR (MC-LR), one of the most toxic and prevalent microcystin variants in water bodies, can induce physiological stress and hinder crop development and production. This study investigated the impact of environmentally relevant concentrations of MC-LR (1 to 10µg L-1) on photosynthetic parameters and antioxidant response of lettuce (Lactuca sativa L.) and arugula (Eruca sativa L.) following irrigation with contaminated water. During the 15-day experiment, lettuce and arugula were exposed to various concentrations of MC-LR, and their photosynthetic rates, stomatal conductance, leaf tissue transpiration, and intercellular CO2 concentrations were measured using an infrared gas analyzer. These results suggest that the influence of MC-LR on gas exchange in crops is concentration-dependent, with notable disruptions during exposure and recovery tendency during detoxification. Antioxidant response analysis revealed that glutathione S-transferase (GST) and superoxide dismutase (SOD) activities were upregulated during the exposure phase in the presence of MC-LR. However, GST activity decreased during the detoxification phase in both crops, although the effects of the toxin at 10µg L-1 were still evident in arugula. The internal H2O2 concentration in the crops increased after exposure to MC-LR, showing a time- and concentration-dependent pattern, with an increase during the exposure phase (days 1-7) and a decrease during the detoxification phase (days 8-15). Irrigation of lettuce and arugula with MC-LR-contaminated water affected various aspects of the photosynthetic apparatus and antioxidant responses, which could influence the general health and productivity of exposed crops at environmentally relevant microcystin concentrations. Furthermore, investigation of additional vegetable species and long-term MC-LR exposure can be crucial for understanding the extent of contamination risk, detoxification mechanisms, and other parameters affecting these crops.

Nephrotoxicity of Cylindrospermopsin (CYN) and Microcystin-LR (MC-LR) on Mammalian Kidney: Wistar Rat as a Model Assessment

Naturally derived cyanotoxins, cylindrospermopsin (CYN), and microcystin-LR (MC-LR) have shown hepatotoxic and nephrotoxic effects in several studies. The present study aimed to determine the possible nephrotoxicity of MC-LR and CYN on mammalian kidneys using male Wistar rats as an animal model. Potential nephrotoxicity was evaluated at different doses of CYN (0.175 μg.kg-1, 0.140 μg.kg-1, 0.105 μg.kg-1) and MC-LR (0.105 μg.kg-1, 0.070 μg.kg-1, 0.035 μg.kg-1) was observed. Water samples from dug wells contaminated with CYN (0.161 μg.kg-1) and MC-LR (0.091 μg.kg-1) from the Padaviya area in Anuradhapura, Sri Lanka were used as environmental samples. The control groups were treated with distilled water. The exposure time of rats to the toxin was 90 days. Evaluation of urinary creatinine, serum creatinine, and Kidney Injury Molecule-1 (KIM-1) were estimated using standard protocols. A significant increase in serum creatinine levels was observed in all CYN and MC-LR treated groups (p<0.05) after 7 and 42 days of exposure, respectively, compared to control. It was found a decrease of urine creatinine when rats were treated with different concentrations of CYN and MC-LR (p<0.05) after 7 days compared to the control. The highest KIM-1 concentrations were recorded at 0.175 μg.kg-1 of CYN and 0.105 μg.kg-1 of MC-LR. The concentrations of KIM-1 in the control groups for CYN-treated and MC-LR-treated were not detected. Luminal protein, nuclear pyknosis, mild tubular epithelial swelling, vascular congestion, and interstitial inflammation in CYN and MC-LR treated groups were common. No predominant changes were observed in the control groups treated with CYN and MC-LR. The results of the present study confirm that the consumption of CYN and MC-LR-contaminated water may lead to kidney injury in Wistar rats.

New Report of Cyanobacteria and Cyanotoxins in El Pañe Reservoir: A Threat for Water Quality in High-Andean Sources from PERU.

Cyanobacteria are cosmopolitan organisms; nonetheless, climate change and eutrophication are increasing the occurrence of cyanobacteria blooms (cyanoblooms), thereby raising the risk of cyanotoxins in water sources used for drinking, agriculture, and livestock. This study aimed to determine the presence of cyanobacteria, including toxigenic cyanobacteria and the occurrence of cyanotoxins in the El Pañe reservoir located in the high-Andean region, Arequipa, Peru, to support water quality management. The study included morphological observation of cyanobacteria, molecular determination of cyanobacteria (16S rRNA analysis), and analysis of cyanotoxins encoding genes (mcyA for microcystins, cyrJ for cylindrospermopsins, sxtl for saxitoxins, and AnaC for anatoxins). In parallel, chemical analysis using Liquid Chromatography coupled with Mass Spectrometry (LC-MS/MS) was performed to detect the presence of cyanotoxins (microcystins, cylindrospermopsin, saxitoxin, and anatoxin, among others) and quantification of Microcystin-LR. Morphological data show the presence of Dolichospermum sp., which was confirmed by molecular analysis. Microcystis sp. was also detected through 16S rRNA analysis and the presence of mcyA gene related to microcystin production was found in both cyanobacteria. Furthermore, microcystin-LR and demethylated microcystin-LR were identified by chemical analysis. The highest concentrations of microcystin-LR were 40.60 and 25.18 µg/L, in May and November 2022, respectively. Microcystins were detected in cyanobacteria biomass. In contrast, toxins in water (dissolved) were not detected. Microcystin concentrations exceeded many times the values established in Peruvian regulation and the World Health Organization (WHO) in water intended for human consumption (1 µg/L). This first comprehensive report integrates morphological, molecular, and chemical data and confirms the presence of two toxigenic cyanobacteria and the presence of microcystins in El Pañe reservoir. This work points out the need to implement continuous monitoring of cyanobacteria and cyanotoxins in the reservoir and effective water management measures to protect the human population from exposure to these contaminants.

Insights into the interaction mechanisms between Microcystin-degrading bacteria and Microcystis aeruginosa

Interactions between bacteria and cyanobacteria influence the occurrence and development of harmful cyanobacterial blooms (HCBs). Bloom-forming cyanobacteria and cyanotoxin-degrading bacteria are essential in HCBs, nonetheless, their interactions and the underlying mechanisms remain unclear. To address this gap, a typical microcystin-LR (MC-LR)-degrading bacterium and a toxic Microcystis aeruginosa strain were co-cultivated to investigate their interactions. The cyanobacterial growth was enhanced by 24.8 %-44.3 % in the presence of the bacterium in the first 7 days, and the cyanobacterium enhanced the bacterial growth by 59.2 %-117.5 % throughout the growth phases, suggesting a mutualistic relationship between them. The presence of the bacterium increased cyanobacterial intracellular MC-LR content on days 4, 8, and 10 while reducing the extracellular MC-LR concentration, revealing the dual roles of the bacterium in enhancing cyanotoxin production and degrading cyanotoxins. The bacterium alleviated the oxidative stress, which may be crucial in promoting cyanobacterial growth. Critical functional genes related to cyanobacterial photosynthesis and MC-LR synthesis, and bacterial MC-LR degradation were up-regulated in the presence of the bacterium and cyanobacterium, respectively. Moreover, extracellular polymeric substances (EPS) were produced at the cell interface, implying EPS play a role in cyanobacterial-bacterial interactions. This study is the first to unveil the interaction mechanisms between cyanotoxin-degrading bacteria and bloom-forming cyanobacteria, shedding light on the dynamics of HCBs.

Suspended particulate matter-biofilm aggregates benefit microcystin removal in turbulent water but trigger toxicity toward Daphnia magna

Suspended particulate matter (SPM) and biofilm are critical in removing contaminants in aquatic environments, but the environmental behavior and ecological toxicity of SPM-biofilm aggregates modulated by turbulence intensities are largely unknown. This study determined the removal pathways of microcystin-LR (MC-LR) by SPM and its biofilm under different turbulence intensities (2.25 × 10–3, 1.01 × 10–2, and 1.80 × 10–2 m2/s3). Then, we evaluated the toxicity of SPM-biofilm aggregates to Daphnia magna. The results revealed that SPM contributed to the adsorption of MC-LR, and the removal of MC-LR can be accelerated with biofilm formation on SPM, with 95.66 % to 97.45 % reduction in MC-LR concentration under the studied turbulence intensities. Higher turbulence intensity triggered more frequent contact of SPM and MC-LR, formed compact but smaller clusters of SPM-biofilm aggregates, and enhanced the abundance of mlrA and mlrB; thus benefiting the adsorption, biosorption, and biodegradation of MC-LR. Furthermore, the SPM-biofilm aggregates formed in turbulent water triggered oxidative stress to Daphnia magna, while a weak lethal toxic effect was identified under moderate turbulence intensity. The results indicate that the toxicity of SPM-biofilm aggregates fail to display a linear relationship with turbulence intensity. These findings offer new perspectives on understanding the environmental behavior and ecological outcomes of SPM and its biofilms in turbulent aquatic environments.

Probiotics Alleviate Microcystin-LR-Induced Developmental Toxicity in Zebrafish Larvae.

Microcystin-LR (MCLR) poses a significant threat to aquatic ecosystems and public health. This study investigated the protective effects of the probiotic Lactobacillus rhamnosus against MCLR-induced developmental toxicity in zebrafish larvae. Zebrafish larvae were exposed to various concentrations of MCLR (0, 0.9, 1.8, and 3.6 mg/L) with or without L. rhamnosus from 72 to 168 h post-fertilization (hpf). Probiotic supplementation significantly improved survival, hatching, and growth rates and reduced malformation rates in MCLR-exposed larvae. L. rhamnosus alleviated MCLR-induced oxidative stress by reducing reactive oxygen species (ROS) levels and enhancing glutathione (GSH) content and catalase (CAT) activity. Probiotics also mitigated MCLR-induced lipid metabolism disorders by regulating key metabolites (triglycerides, cholesterol, bile acids, and free fatty acids) and gene expression (ppara, pparb, srebp1, and nr1h4). Moreover, 16S rRNA sequencing revealed that L. rhamnosus modulated the gut microbiome structure and diversity in MCLR-exposed larvae, promoting beneficial genera like Shewanella and Enterobacter and inhibiting potential pathogens like Vibrio. Significant correlations were found between gut microbiota composition and host antioxidant and lipid metabolism parameters. These findings suggest that L. rhamnosus exerts protective effects against MCLR toxicity in zebrafish larvae by alleviating oxidative stress, regulating lipid metabolism, and modulating the gut microbiome, providing insights into probiotic-based strategies for mitigating MCLR toxicity in aquatic organisms.

Metabolomics reveals the lipid metabolism disorder in Pelophylax nigromaculatus exposed to environmentally relevant levels of microcystin-LR

Cyanobacterial blooms have emerged as a significant environmental issue worldwide in recent decades. However, the toxic effects of microcystin-LR (MC-LR) on aquatic organisms, such as frogs, have remained poorly understood. In this study, frogs (Pelophylax nigromaculatus) were exposed to environmentally relevant concentrations of MC-LR (0, 1, and 10 μg/L) for 21 days. Subsequently, we assessed the impact of MC-LR on the histomorphology of the frogs' livers and conducted a global MS-based nontarget metabolomics analysis, followed by the determination of substances involved in lipid metabolism. Results showed that MC-LR significantly induced histological alterations in the frogs' hepatopancreas. Over 200 differentially expressed metabolites were identified, primarily enriched in lipid metabolism. Biochemical analysis further confirmed that MC-LR exposure led to a disorder in lipid metabolism in the frogs. This study laid the groundwork for a mechanistic understanding of MC-LR toxicity in frogs and potentially other aquatic organisms.

Co-exposure of microcystin-LR and nitrite induced kidney injury through TLR4/NLRP3/GSDMD-mediated pyroptosis

The degradation of cyanobacterial blooms releases hazardous contaminants such as microcystin-LR (MC-LR) and nitrite, which may collectively exert toxicity on various bodily systems. To evaluate their individual and combined toxicity in the kidney, mice were subjected to different concentrations of MC-LR and/or nitrite over a 6-month period in this study. The results revealed that combined exposure to MC-LR and nitrite exacerbated renal pathological alterations and dysfunction compared to exposure to either compound alone. Specifically, the protein and mRNA expression of kidney injury biomarkers, such as kidney injury molecule 1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL), were notably increased in combined exposure group. Concurrently, co-exposure to MC-LR and nitrite remarkedly upregulated levels of proinflammatory cytokines TNF-α, IL-6 and IL-1β, while decreasing the anti-inflammatory cytokine IL-10. Notably, MC-LR and nitrite exhibited synergistic effects on the upregulation of renal IL-1β levels. Moreover, MC-LR combined with nitrite not only elevated mRNA levels of proinflammatory cytokines but also increased protein levels of pyroptosis biomarkers such as IL-1β, Gasdermin D (GSDMD), and Cleaved-GSDMD. Mechanistic investigations revealed that co-exposure to MC-LR and nitrite promoted pyroptosis both in vivo and in vitro, possibly through the activation of the TLR4/NLRP3/GSDMD pathway. Pretreatment with TLR4 inhibitor and NLRP3 inhibitor effectively suppressed pyroptosis induced by the co-exposure of these two toxins in HEK293T cells. These findings provide compelling evidence that MC-LR combined with nitrite synergistically induces pyroptosis in the kidney by activating the TLR4/NLRP3/GSDMD pathway. Overall, this study significantly enhances our comprehension of how environmental toxins interact and induce harm to the kidneys, offering promising avenues for identifying therapeutic targets to alleviate their toxic effects on renal health.

Environmentally Friendly and Cost-Effective Approaches to Reduce Toxin Content in Toxic Cyanobacterial Biomasses

Cyanobacterial outgrowths are naturally occurring processes in eutrophic aquatic ecosystems. Furthermore, as a result of climate change and anthropogenic pollution, cyanobacteria harmful algal blooms (CyanoHABs) are expanding worldwide. CyanoHABs are considered a threat to human health and environment due to the production of potent toxic substances, but at the same time, valuable products can be obtained from these microorganisms. The main objective of this study was to test straightforward and cost-effective methods to reduce the toxin content of cyanobacterial biomass for the exploitation of this important biological resource. To carry out this study, lyophilized or hydrated biomass from microcystin-LR (MC-LR) producing Microcystis aeruginosa and cylindrospermopsin (CYN) producing Chrysosporum ovalisporum strains were subjected to the following treatments: (1) thermal (50 °C); (2) ultraviolet (UV) radiation; (3) ozone; and (4) sunlight, for periods varying between 2 and 12 h. MC-LR and CYN concentrations were quantified by LC-MS and compared between experimental groups. The results show a significant reduction in the amount of MC-LR in M. aeruginosa biomass (lyophilized and hydrated) exposed to sunlight. Since no other treatment reduced MC-LR in M. aeruginosa biomass, this molecule was demonstrated to be very stable. Regarding CYN, the concentration of this toxin in C. ovalisporum biomass was significantly reduced with the exposure to UV radiation, to approximately 51% of the initial concentration after 2 h of exposure; 86% reduction after 5 h of exposure; and 77% reduction after 12 h of exposure. Overall, this study demonstrates that the toxicity of cyanobacterial biomass can be reduced by employing environmentally friendly and cost-effective treatments with sunlight and UV radiation.

Control of Microcystis aeruginosa by Daphnia: Experimental evidence and identification of involved infochemicals.

Infochemicals refer to chemicals responsible for information exchange between organisms. We evaluated the effects of Daphnia magna and Daphnia galeata infochemicals on Microcystis aeruginosa for 15d. The Daphnia infochemicals were obtained from spent medium after culturing Daphnia in Elendt M4 medium for 48 h. Both Daphnia infochemicals significantly increased (p < 0.05) the intracellular reactive oxygen species level and microcystin-LR concentration in M. aeruginosa. This cellular effect increased colony formation of M. aeruginosa, thereby inhibiting the growth of M. aeruginosa. D. galeata infochemicals provoked significantly greater (p < 0.05) adverse effects on M. aeruginosa than those of D. magna infochemicals, which were further exaggerated by pre-exposure of Daphnia to M. aeruginosa. This result seems to be related to the different compositions and concentrations of Daphnia infochemicals. Several Daphnia infochemicals, such as methyl ferulate, cyclohexanone, 3, 5-dimethyl, hexanedioic acid, and bis(2-ethylhexyl) ester, showed a high correlation with M. aeruginosa cell concentration (|r | >0.6), suggesting that they may play a key role in controlling harmful cyanobacteria. Additionally, pre-exposure of D. magna and D. galeata to M. aeruginosa produced oleic acid, methyl ester, and n-hexadecanoic acid, with a highly correlation with M. aeruginosa cell concentration (|r | >0.6). p-tolyl acetate and linoleic acid were detected only in the pre-exposed D. galeata infochemicals. These findings suggest that some of Daphnia infochemicals identified in this study can be a promising tool to control M. aeruginosa growth. However, further studies are required to verify the specific actions of these infochemicals against cyanobacteria.

Microcystin-LR Induces Estrogenic Effects at Environmentally Relevant Concentration in Black-Spotted Pond Frogs (Pelophylax nigromaculatus): In Situ, In Vivo, In Vitro, and In Silico Investigations.

Harmful cyanobacterial blooms are frequent and intense worldwide, creating hazards for aquatic biodiversity. The potential estrogen-like effect of Microcystin-LR (MC-LR) is a growing concern. In this study, we assessed the estrogenic potency of MC-LR in black-spotted frogs through combined field and laboratory approaches. In 13 bloom areas of Zhejiang province, China, the MC-LR concentrations in water ranged from 0.87 to 8.77 μg/L and were correlated with sex hormone profiles in frogs, suggesting possible estrogenic activity of MC-LR. Tadpoles exposed to 1 μg/L, an environmentally relevant concentration, displayed a female-biased sex ratio relative to controls. Transcriptomic results revealed that MC-LR induces numerous and complex effects on gene expression across multiple endocrine axes. In addition, exposure of male adults significantly increased the estradiol (E2)/testosterone (T) ratio by 3.5-fold relative to controls. Downregulation of genes related to male reproductive endocrine function was also identified. We also showed how MC-LR enhances the expression of specific estrogen receptor (ER) proteins, which induce estrogenic effects by activating the ER pathway and hypothalamic-pituitary-gonadal (HPG) axis. In aggregate, our results reveal multiple lines of evidence demonstrating that, for amphibians, MC-LR is an estrogenic endocrine disruptor at environmentally relevant concentrations. The data presented here support the need for a shift in the MC-LR risk assessment. While hepatoxicity has historically been the focus of MC-LR risk assessments, our data clearly demonstrate that estrogenicity is a major mode of toxicity at environmental levels and that estrogenic effects should be considered for risk assessments on MC-LR going forward.

Magnetic recyclable visible light-driven Bi2WO6/Fe3O4/RGO for photocatalytic degradation of Microcystin-LR: Mechanism, pathway, and influencing factors

Photocatalysis was an attractive strategy that had potential to tackle the Microcystin-LR (MC-LR) contamination of aquatic ecosystems. Herein, magnetic photocatalyst Fe3O4/Bi2WO6/Reduced graphene oxide composites (Bi2WO6/Fe3O4/RGO) were employed to degrade MC-LR. The removal efficiency and kinetic constant of the optimized Bi2WO6/Fe3O4/RGO (Bi2WO6/Fe3O4-40%/RGO) was 1.8 and 2.3 times stronger than the pure Bi2WO6. The improved activity of Bi2WO6/Fe3O4-40%/RGO was corresponded to the expanded visible light adsorption ability and reduction of photogenerated carrier recombination efficiency through the integration of Bi2WO6 and Fe3O4-40%/RGO. The MC-LR removal efficiency exhibited a positive tendency to the initial density of algae cells, fulvic acid, and the concentration of MC-LR decreased. The existed anions (Cl−, CO3−2, NO3−, H2PO4−) reduced MC-LR removal efficiency of Bi2WO6/Fe3O4-40%/RGO. The Bi2WO6/Fe3O4-40%/RGO could degrade 79.3% of MC-LR at pH = 7 after 180 min reaction process. The trapping experiments and ESR tests confirmed that the h+, ∙OH, and ∙O2− played a significant role in MC-LR degradation. The LC-MS/MS result revealed the intermediates and possible degradation pathways.

Changes in physiology, antioxidant system, and gene expression in Microcystis aeruginosa under fenoxaprop-p-ethyl stress.

Fenoxaprop-p-ethyl (FE) is one of the typical aryloxyphenoxypropionate herbicides. FE has been widely applied in agriculture in recent years. Human health and aquatic ecosystems are threatened by the cyanobacteria blooms caused by Microcystis aeruginosa, which is one of the most common cyanobacteria responsible for freshwater blooming. Few studies have been reported on the physiological effects of FE on M. aeruginosa. This study analyzed the growth curves, the contents of chlorophyll a and protein, the oxidative stress, and the microcystin-LR (MC-LR) levels of M. aeruginosa exposed to various FE concentrations (i.e., 0, 0.5, 1, 2, and 5mg/L). FE was observed to stimulate the cell density, chlorophyll a content, and protein content of M. aeruginosa at 0.5- and 1-mg/L FE concentrations but inhibit them at 2 and 5mg/L FE concentrations. The superoxide dismutase and catalase activities were enhanced and the malondialdehyde concentration was increased by FE. The intracellular (intra-) and extracellular (extra-) MC-LR contents were also affected by FE. The expression levels of photosynthesis-related genes psbD1, psaB, and rbcL varied in response to FE exposure. Moreover, the expressions of microcystin synthase-related genes mcyA and mcyD and microcystin transportation-related gene mcyH were significantly inhibited by the treatment with 2 and 5mg/L FE concentrations. These results might be helpful in evaluating the ecotoxicity of FE and guiding the rational application of herbicides in modern agriculture.

Experimental accumulation and depuration kinetics and natural occurrence of microcystin-LR in basil (Ocimum basilicum L.)

Microcystin-LR (MC-LR) is a hepatotoxic metabolite that naturally occurs during some cyanobacterial blooms in eutrophic waterbodies, and irrigation of edible plants with MC-LR-contaminated water causes bioaccumulation of the toxin. However, sufficient information about accumulation and depuration mechanics in hydroculture-grown herb plants is still lacking. This work aimed at 1) investigating bioaccumulation and depuration of MC-LR in basil, 2) verifying the possible MC-LR detoxification mechanisms in the plant, and 3) detecting the natural occurrence of MC-LR in basil (n = 50) collected from the Belgian market. Basil plants grown in a hydroculture were exposed to MC-LR (5, 20, and 50 μg L−1) spiked in a Hoagland solution for seven days. MC-LR depuration was also studied by transferring the plants to a non-contaminated Hoagland solution after exposure to MC-LR for another seven days. MC-LR concentrations in Hoagland solution, basil leaves, and roots were quantified using a validated UHPLC–MS/MS method. In addition, ELISA and LC–HRMS (only basil leaves) were used for confirmation. The results showed an increase in the accumulated levels of MC-LR at higher exposure doses, with higher MC-LR levels in roots than in leaves for all the treatment conditions. For MC-LR depuration, significant reductions were observed in all the treatment conditions for roots only. No MC-LR conjugates, potentially related to metabolism, were detected by LC–HRMS. Finally, MC-LR was detected in one store-bought basil sample, representing the first occurrence of cyanotoxins in an edible crop from Belgium.

Degradation performance and mechanism of microcystins in aquaculture water using low-temperature plasma technology

The eutrophication of aquaculture water bodies seriously restricts the healthy development of the aquaculture industry. Among them, microcystins are particularly harmful. Therefore, the development of technologies for degrading microcystins is of great significance for maintaining the healthy development of the aquaculture industry. The feasibility and mechanism of removing microcystins-LR by dielectric barrier discharge (DBD) plasma were studied. DBD discharge power of 49.6 W and a treatment time of 40 min were selected as the more suitable DBD parameters, resulting in microcystin-LR removal efficiency of 90.4%. Meanwhile, the effects of initial microcystin-LR concentration, initial pH value, turbidity, anions on the degradation effect of microcystin-LR were investigated. The removal efficiency of microcystin-LR decreased with the increase of initial microcystin-LR concentration and turbidity. The degradation efficiency of microcystin-LR at pH 4.5 and 6.5 is significantly higher than that at pH 8.5 and 3.5. HCO3− can inhibit the removal efficiency of microcystin-LR. Furthermore, five intermediates products (m/z = 1029.5, 835.3, 829.3, 815.4, 642.1) were identified in this study, and the toxicity analysis of these degradation intermediates indicated that DBD treatment can reduce the toxicity of microcystin-LR. e－aq, •OH, H2O2, and O3 have been shown to play a major role in the degradation of microcystin-LR, and the contribution ranking of these active species is e－aq > •OH > H2O2 > O3. The application of DBD plasma technology in microcystin-LR removal and detoxification has certain development potential.

Effects of the catastrophic 2020 Yangtze River seasonal floods on microcystins and environmental conditions in Three Gorges Reservoir Area, China.

During July and August 2020, Three Gorges Reservoir Area (TGRA) suffered from catastrophic seasonal floods. Floods changed environmental conditions and caused increase in concentration of microcystins (MCs) which is a common and potent cyanotoxin. However, the effects and seasonal variations of MCs, cyanobacteria, and environmental conditions in TGRA after the 2020 Yangtze River extreme seasonal floods remain largely unclear, and relevant studies are lacking in the literature. A total of 12 representative sampling sites were selected to perform concentration measurement of relevant water quality objectives and MCs in the representative area of the TGRA. The sampling period was from July 2020 to October 2021, which included the flood period. Organic membrane filters were used to perform the DNA extraction and analyses of the 16S rRNA microbiome sequencing data. Results showed the seasonal floods result in significant increases in the mean values of microcystin-RR (MCRR), microcystin-YR (MCYR), and microcystin-LR (MCLR) concentration and some water quality objectives (i.e., turbidity) in the hinterland of TGRA compared with that in non-flood periods (p < 0.05). The mean values of some water quality objectives (i.e., total nitrogen (TN), total phosphorus (TP), total dissolved phosphorus (TDP), and turbidity), MC concentration (i.e., MCRR, MCYR, and MCLR), and cyanobacteria abundance (i.e., Cyanobium_PCC-6307 and Planktothrix_NIVA-CYA_15) displayed clear tendency of increasing in summer and autumn and decreasing in winter and spring in the hinterland of TGRA. The results suggest that seasonal floods lead to changes in MC concentration and environmental conditions in the hinterland of TGRA. Moreover, the increase in temperature leads to changes in water quality objectives, which may cause water eutrophication. In turn, water eutrophication results in the increase in cyanobacteria abundance and MC concentration. In particular, the increased MC concentration may further contribute to adverse effects on human health.