Degradation Of microcystin-LR Research Articles

S-scheme carbon doped-TiO2/ZnIn2S4 heterojunction for enhanced photocatalytic degradation of microcystin-LR and hydrogen evolution

Photocatalytic degradation of pollutants coupled with hydrogen (H2) evolution has emerged as a promising solution for environmental and energy crises. However, the fast recombination of photoexcited electrons and holes limits photocatalytic activities. Herein, an S-scheme heterojunction carbon doped-TiO2/ZnIn2S4 (C–TiO2/ZnIn2S4) was designed by substituting oxygen sites within C–TiO2 by ZnIn2S4. Under visible light irradiation, the optimal C–TiO2/ZnIn2S4 exhibits a higher degradation efficiency (88.6%) of microcystin-LR (MC-LR), compared to pristine C–TiO2 (72.9%) and ZnIn2S4 (66.8%). Furthermore, the H2 yield of the C–TiO2/ZnIn2S4 reaches 1526.9 μmol g−1 h−1, which is 3.83 times and 2.87 times that of the C–TiO2 and ZnIn2S4, respectively. Experimental and theoretical investigations reveal that an internal electric field (IEF) informed in the C–TiO2/ZnIn2S4 heterojunction, accelerates the separation of photogenerated charge pairs, thereby enhancing photocatalytic efficiency of MC-LR degradation and H2 production. This work highlights a new perspective on the development of high-performance photocatalysts for wastewater treatment and H2 generation.

Simultaneous inactivation of Microcystis aeruginosa and degradation of microcystin-LR in water by activation of periodate with sunlight

Harmful algal blooms pose tremendous threats to ecological safety and human health. In this study, simulated solar light (SSL) irradiation was used to activate periodate (PI) for the inactivation of Microcystis aeruginosa and degradation of microcystin-LR (MC-LR). We found that PI-SSL system could effectively inactivate 5 × 106 cells·mL−1 algal cells below the limit of detection within 180 min. ·OH and iodine (IO3· and IO4·) radicals generated in PI-SSL system could rupture cell membranes, releasing intracellular substances including MC-LR into the reaction system. However, the released MC-LR could be degraded into non-toxic small molecules via hydroxylation and ring cleavage processes in PI-SSL system, reducing their environmental risks. High algae inactivation performance of PI-SSL system in solution with a wide pH range (3–9), with the coexisting anions (Cl−, NO3− and SO42−) and the copresence of natural organic matters (humic acid and fulvic acid), real water (lake water and river water), as well as in continuous-flow reactor (14 h) were also achieved. In addition, under natural sunlight irradiation, effective algae inactivation could also be achieved in an enlarged reactor (1 L). Overall, our study showed that PI-SSL system could avoid the inference by the background substances and could be employed as a feasible technique to treat algal bloom water.

Decoration of CeO2 nanoparticles on g-C3N4 for degradation of microcystins through photocatalytic activation of peroxymonosulfate

As the most common cyanobacterial toxin, microcystin LR (MC-LR) has dangerous neurotoxicity and hepatotoxicity, posing a serious threat to human and ecosystem health. Therefore, we constructed a type-II CeO2/g-C3N4 heterojunction for highly efficient degradation of MC-LR via peroxymonosulfate (PMS) assisted-visible light-driven photocatalysis process. Multi techniques were conducted to analyze the microstructures, optical and electrochemical properties of CeO2/g-C3N4. The experimental results indicate that the composite material has appropriate energy levels and establishes a well-established interfacial band structure, facilitating the migration and separation of photogenerated electron-hole pairs. The coupled photocatalysis and PMS activation system presented a dramatically enhanced catalytic performance. Within 60 min, 10% CeO2/g-C3N4/PMS could degrade 99% of the MC-LR present in the solution under visible light irradiation, which was about 3.8 times higher than that in a single photocatalytic system. The optimal conditions for this degradation process were a PMS dosage of 3.0 mM and an initial pH of 2.5. EPR analysis revealed that SO4•ˉ, O2•ˉ, h+, and 1O2 were involved in the degradation process. Moreover, the intermediates of its degradation were analyzed through UPLC-MS. This study provides a valuable resource for the intelligent development of type-II heterojunction and its practical implications in the photodegradation of MC-LR through synergistic activation with PMS.

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.

Metabolomic and gut-microbial responses of earthworms exposed to microcystins and nano zero-valent iron in soil

The earthworm-based vermiremediation facilitated with benign chemicals such as nano zero-valent iron (nZVI) is a promising approach for the remediation of a variety of soil contaminants including cyanotoxins. As the most toxic cyanotoxin, microcystin-LR (MC-LR) enter soil via runoff, irrigated surface water and sewage, and the application of cyanobacterial biofertilizers as part of the sustainable agricultural practice. Earthworms in such remediation systems must sustain the potential risk from both nZVI and MC-LR. In the present study, earthworms (Eisenia fetida) were exposed up to 14 days to MC-LR and nZVI (individually and in mixture), and the toxicity was investigated at both the organismal and metabolic levels, including growth, tissue damage, oxidative stress, metabolic response and gut microbiota. Results showed that co-exposure of MC-LR and nZVI is less potent to earthworms than that of separate exposure. Histological observations in the co-exposure group revealed only minor epidermal brokenness, and KEGG enrichment analysis showed that co-exposure induced earthworms to regulate glutathione biosynthesis for detoxification and reduced adverse effects from MC-LR. The combined use of nZVI promoted the growth and reproduction of soil and earthworm gut bacteria (e.g., Sphingobacterium and Acinetobacter) responsible for the degradation of MC-LR, which might explain the observed antagonism between nZVI and MC-LR in earthworm microcosm. Our study suggests the beneficial use of nZVI to detoxify pollutants in earthworm-based vermiremediation systems where freshwater containing cyanobacterial blooms is frequently used to irrigate soil and supply water for the growth and metabolism of earthworms.

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.

Feasibility and mechanism of removing Microcystis aeruginosa and degrading microcystin-LR by dielectric barrier discharge plasma

Harmful cyanobacterial bloom is one of the serious environmental problems worldwide. Microcystis aeruginosa is a representative harmful alga in cyanobacteria bloom. It is of great significance to develop new technologies for the removal of Microcystis aeruginosa and microcystins. The feasibility and mechanism of removing microcystis aeruginosa and degrading microcystins by dielectric barrier discharge (DBD) plasma were studied. The suitable DBD parameters obtained in this study are DBD (41.5 W, 40 min) and DBD (41.5 W, 50 min), resulting in algae removal efficiency of 77.4% and 80.4%, respectively; scanning electron microscope and LIVE-DEATH analysis demonstrate that DBD treatment can disrupt cell structure and lead to cell death; analysis of elemental composition and chemical state indicated that there are traces of oxidation of organic nitrogen and organic carbon in microcystis aeruginosa; further intracellular ROS concentration and antioxidant enzyme activity analysis confirm that DBD damage microcystis aeruginosa through oxidation. Meanwhile, DBD can effectively degrade the microcystin-LR released after cell lysis, the extracellular microcystin-LR concentration in the DBD (41.5 W) group decreased by 88.7% at 60 min compared to the highest concentration at 20 min; further toxicity analysis of degradation intermediates indicated that DBD can reduce the toxicity of microcystin-LR. The contribution of active substances to the inactivation of microcystis aeruginosa is eaq− >•OH > H2O2 > O3 > 1O2 >•O2− >ONOO−, while on the degradation of microcystin-LR is eaq− >•OH > H2O2 > O3 >•O2− >1O2 > ONOO−. The application of DBD plasma technology in microcystis aeruginosa algae removal and detoxification has certain prospects for promotion and application.

Screening of the Bacterial Consortium Related to the Microcystin-LR Degradation Isolated From the Marine Area, Isahaya-Bay, and the Freshwater Area, Isahaya-Shin-ike-Pond, Japan

Eutrophication is still a severe global problem, and cyanobacterial microcystins (MCs) have been detected in sea areas such as harbors and coastal regions in addition to freshwater areas. Therefore, it is necessary to clarify the fate of MCs in sea areas. In Japan, Isahaya-Shin-ike-Pond, a freshwater area divided by the dike from Isahaya-bay, Nagasaki-prefecture, has eutrophicated, and cyanobacterial blooms have occurred sometimes. Water in Isahaya-Shin-ike-Pond is regularly discharged to Isahaya-bay to control the water levels in Isahaya-Shin-ike-Pond. Some researchers in Japan detected MCs from the sediment sample of Isahaya-bay; thus, MCs discharged from Isahaya-Shin-ike-Pond could be threatening the environment in Isahaya-bay. In this regard, some bacterial consortiums were isolated from Isahaya-Shin-ike-Pond and Isahaya-bay, which might degrade Microcystin-LR (MC-LR), the highly toxic representative MCs. In this report, we screened and determined the MCs degradation activity in these bacterial consortiums. As a result, we found that all bacterial consortiums degrade MC-LR. Furthermore, the HPLC chromatogram had the peak of substance-like intermediate of MC-LR decomposition. Consortium collected from approximately 4,900 m offshore from the dike degraded 97% of MC-LR. Although the bacterial communities in these consortiums differed, Bacillus sp. was in both consortiums collected from Isahaya-Shin-ike-Pond and Isahaya-bay. Because some strain of Bacillus sp. has the potential for MCs degradation, it might play an essential role in these bacterial consortiums. These results indicate that the bacteria degrade MCs even though MCs are discharged from the Isahaya-Shin-ike-Pond to Isahaya-bay.

Constructed wetland mesocosms improve the biodegradation of microcystin-LR and cylindrospermopsin by indigenous bacterial consortia

Cyanobacterial blooms releasing harmful cyanotoxins, such as microcystin (MC) and cylindrospermopsin (CYN), are prominent threats to human and animal health. Constructed wetlands (CW) may be a nature-based solution for bioremediation of lake surface water containing cyanotoxins, due to its low-cost requirement of infrastructure and environmentally friendly operation. There is recent evidence that microcystin-LR (MC-LR) can efficiently be removed in CW microcosms where CYN degradation in CW is unknown. Likewise, the mechanistic background regarding cyanotoxins transformation in CW is not yet elucidated. In the present study, the objective was to compare MC-LR and CYN degradation efficiencies by two similar microbial communities obtained from CW mesocosms, by two different experiments setup: 1) in vitro batch experiment in serum bottles with an introduced CW community, and 2) degradation in CW mesocosms. In experiment 1) MC-LR and CYN were spiked at 100 µg L−1 and in experiment 2) 200 µg L−1 were spiked. Results showed that MC-LR was degraded to ≤1 µg L−1 within seven days in both experiments. However, with a markedly higher degradation rate constant in the CW mesocosms (0.18 day−1 and 0.75 day−1, respectively). No CYN removal was detected in the in vitro incubations, whereas around 50 % of the spiked CYN was removed in the CW mesocosms. The microbial community responded markedly to the cyanotoxin treatment, with the most prominent increase of bacteria affiliated with Methylophilaceae (order: Methylophilales, phylum: Proteobacteria). The results strongly indicate that CWs can develop an active microbial community capable of efficient removal of MC-LR and CYN. However, the CW operational conditions need to be optimized to achieve a full CYN degradation. To the best of our knowledge, this study is the first to report the ability of CW mesocosms to degrade CYN.

Microcystin-LR Biodestruction by Autochthonous Microbiota of Different Water Bodies in the North-West of Russia

The ability of the autochthonous microbiota of different water bodies in the North-West of the Russian Federation to degrade the highly toxic microcystin-LR (MC-LR) was shown for the first time. The maximum rate of degradation of MC-LR was noted in water samples from the Sestroretskij Razliv Lake and the Lower Suzdal Lake during the period of mass development of cyanobacteria. In water samples from Lake Ladoga, where no toxic cyanobacterial blooms were previously noted, MC-LR biodegradation proceeded at a much lower rate and with a longer lag phase. The composition of MC-LR biodegradation products indicates the presence in the autochthonous microbiota of the studied objects of microorganisms capable of degrading microcystins both by the mlr mechanism and by the biochemical pathway involving glutathione.

Elucidating microbial mechanisms of microcystin-LR degradation in Lake Erie beach sand through metabolomics and metatranscriptomics

As one of five Laurentian Great Lakes, Lake Erie ranks among the top freshwater drinking sources and ecosystems globally. Historical and current agriculture mismanagement and climate change sustains the environmental landscape for late summer cyanobacterial harmful algal blooms, and consequently, cyanotoxins such as microcystin (MC). Microcystin microbial degradation is a promising mitigation strategy, however the mechanisms controlling the breakdown of MCs in Lake Erie are not well understood. Pelee Island, Ontario, Canada is located in the western basin of Lake Erie and the bacterial community in the sand has demonstrated the capacity of metabolizing the toxin. Through a multi-omic approach, the metabolic, functional and taxonomical signatures of the Pelee Island microbial community during MC-LR degradation was investigated over a 48-hour period to comprehensively study the degradation mechanism. Cleavage of bonds surrounding nitrogen atoms and the upregulation of nitrogen deamination (dadA, alanine dehydrogenase, leucine dehydrogenase) and assimilation genes (glnA, gltB) suggests a targeted isolation of nitrogen by the microbial community for energy production. Methylotrophic pathways RuMP and H4MPT control assimilation and dissimilation of carbon, respectively and differential abundance of Methylophilales indicates an interconnected role through electron exchange of denitrification and methylotrophic pathways. The detected metabolites did not resolve a clear breakdown pathway, but rather the diversity of products in combination with taxonomic and functional results supports that a variety of strategies are applied, such as epoxidation, hydroxylation, and aromatic degradation. Annual repeated exposure to the toxin may have allowed the community to adaptatively establish a novel pathway through functional plasticity and horizontal gene transfer. The culmination of these results reveals the complexity of the Pelee Island sand community and supports a dynamic and cooperative metabolism between microbial species to achieve MC degradation.

Highly efficient photocatalytic degradation of microcystin-LR with permonosulfate activated by visible-light over Z-scheme ZnO/g-C3N4: Degradation pathways and mechanism

Harmful algal blooms and the release of cyanotoxins pose a significant threat to aquatic life. This study aimed to develop a high efficient way to degrade microcystin-LR (MC-LR), a most common and highly toxic cyanotoxin in cyanobacterial blooms, by constructing a Z-scheme ZnO-g-C3N4 heterojunction for photocatalysis integrated with permonosulfate (PMS) activation process. The formation of the Z-scheme heterojunction facilitated the separation of photogenerated carriers and generated more active species with strong oxidative potential, resulting in more efficient degradation of MC-LR. Under visible light, the ZnO/g-C3N4/PMS photocatalyst successfully removed 97% of MC-LR (500 µg·L−1) within 120 min. In comparison, the ZnO/g-C3N4/PMS (k = 0.074 min−1) system exhibited degradation rate constants of 8.6 and 11.7 times higher than that of g-C3N4/PMS (k = 0.0086 min−1) and ZnO/PMS (k = 0.0063 min−1) systems, respectively. Chemical trapping experiments and EPR tests revealed that the predominant active species were •O2−, SO4•-, and •OH. The degradation route of MC-LR by ZnO/g-C3N4/PMS/Vis process was proposed based on the intermediate products analysis by UPLC-MS, wherein the addition of •OH and the oxidative cleavage by •O2− and SO4•- were the main degradation pathways. This study developed a prospective way to design Z-scheme heterojunction photocatalyst constructing with PMS activation for highly efficient prevention of harmful algal blooms.

Easily hydroxylated PtxPd1-x-TiO2 nanotube arrays: An energetic Schottky photocatalyst for synergistically boosted degradation of Microcystin-LR

The metal co-catalyst-based photocatalytic oxidation technology provides a promising approach to eliminate contaminants from water. However, the applicability of these catalysts often suffer from severe carrier recombination and high activation energy barriers of reactive oxygen species (ROS). Herein, self-supporting TiO2 nanotube arrays were engineered with PtPd atom clusters having atomically controlled molar ratio, assembling a dynamic Mott-Schottky catalyst for photocatalytic removal of Microcystin-LR, a toxin produced by cyanobacteria. The separation of photogenerated carriers and the creation of reactive oxygen species (ROS) are optimized by regulating electronic construction via tailoring the Pd ratio in PtPd atom clusters (ca. 4.6 nm in size). The exciton lifetime of the optimum Pt0.9Pd0.1-TiO2 is shortened from 2.51 ns on pure TiO2 to 1.16 ns, and the Gibbs free energy for forming hydroxyl radicals (•OH) varies from −0.826 eV (pure TiO2) to −2.576 eV, powering plentiful •OH when Pt0.9Pd0.1-TiO2 illuminated under solar lights. The kinetic constant of Pt0.9Pd0.1-TiO2 for MC-LR removal is 12.7 times higher than that of the pristine TiO2, presenting exceptional photocatalytic capacity in turning Microcystin-LR into harmless chemicals.

Feasibility and mechanism of recycling carbon resources from waste cyanobacteria and reducing microcystin toxicity by dielectric barrier discharge plasma

Recycling carbon resources from discarded cyanobacteria is a worthwhile research topic. This study focuses on the use of dielectric barrier discharge (DBD) plasma technology as a pretreatment for anaerobic fermentation of cyanobacteria. The DBD group (58.5 W, 45 min) accumulated the most short chain fatty acids (SCFAs) along with acetate, which were 3.0 and 3.3 times higher than the control. The DBD oxidation system can effectively collapse cyanobacteria extracellular polymer substances and cellular structure, improve the biodegradability of dissolved organic matter, enrich microorganisms produced by hydrolysis and SCFAs, reduce the abundance of SCFAs consumers, thereby promoting the accumulation of SCFAs and accelerating the fermentation process. The microcystin-LR removal rate of 39.8% was obtained in DBD group (58.5 W, 45 min) on day 6 of anaerobic fermentation. The toxicity analysis using the ECOSAR program showed that compared to microcystin-LR, the toxicity of degradation intermediates was reduced. The contribution order of functional active substances to cyanobacteria cracking was obtained as eaq− > •OH > 1O2 > •O2− > ONOO−, while the contribution order to microcystin-LR degradation was eaq− > •OH > •O2− > 1O2 > ONOO−. DBD has the potential to be a revolutionary pretreatment method for cyanobacteria anaerobic fermentation.

Coating TiO2 with MIL-101(Fe) to decarboxylate D-Glu and D-MeAsp of microcystin-LR from HA-rich water: Diminishing the inhibitory effect of humic acids

Humic acids (HA) released during algal bloom poses a key challenge for efficient photocatalytic degradation of Microcystin-LR (MC-LR) due to their scavenging function on active species. Herein, MIL-101(Fe)/TiO2-P25 (M/P) was constructed to diminish the inhibitory effect of HA on the photocatalytic degradation of MC-LR. Results showed that MC-LR could be efficiently removed assigning to the photogenerated holes (h+) and superoxide radical (O2•−) oxidation under visible light irradiation, where the carboxy groups of D-glutamic acid (Glu) and methyl-D-aspartic acid (MeAsp), and Adda side chain related to MC-LR biotoxicity were selectively destroyed to achieve MC-LR detoxication. More importantly, HA exerted non-inhibitory effect on MC-LR removal by M/P. The counteracting mechanisms were studied. Firstly, the location of TiO2 in the pore structure of MIL-101(Fe) could occupy the adsorption sites of HA, and decrease the HA adsorption on M/P. Furthermore, XPS analyses suggested the coordination of unsaturated Fe metal sites on the surface of M/P hybrids complexed with –OH and –COOH of HA, which could accelerate the electron transfer and reduce hole consumption. Thus, the inhibitory effect of HA was alleviated during photocatalytic MC-LR treatment. This work offers a possible way to remove MC-LR in an abundant HA matrix water system efficiently.

Developing self-floating N-defective graphitic carbon nitride photocatalyst for efficient photodegradation of Microcystin-LR under visible light

The frequent occurrence of algal blooms in water bodies leads to a significant accumulation of microcystin-LR (MC-LR). In this study, we developed a porous foam-like self-floating N-deficient g-C3N4 (SFGN) photocatalyst for efficient photocatalytic degradation of MC-LR. Both the characterization results and DFT calculations indicate that the surface defects and floating state of SFGN synergistically enhance light harvesting and photogenerated carrier migration rate. The photocatalytic process achieved a nearly 100 % removal rate of MC-LR within 90 min, while the self-floating state of SFGN maintained good mechanical strength. ESR and radical capture experiments revealed that the primary active species responsible for the photocatalytic process was OH. This finding confirmed that the fragmentation of MC-LR occurs as a result of OH attacking the MC-LR ring. LC–MS analysis indicated that majority of the MC-LR molecules were mineralized into small molecules, allowing us to infer possible degradation pathways. Furthermore, after four consecutive cycles, SFGN exhibited remarkable reusability and stability, highlighting the potential of floating photocatalysis as a promising technique for MC-LR degradation.

Modeling of the Atmospheric Process of Cyanobacterial Toxins in Algal Aerosol

The degradation of microcystin-LR (MC-LR) in cyanobacterial aerosol with atmospheric oxidants, such as ozone and OH radicals, was predicted by the Harmful Algal Aerosol Reaction (HAAR) model. The ozonolysis of MC-LR in cyanobacterial aerosol at nighttime and its photooxidation during the daytime was observed in an outdoor chamber. The HAAR model simulates the impact of humidity and aerosol compositions on MC-LR decay. In the model, gas-particle partitioning of atmospheric oxidants onto algal aerosol was kinetically treated using the absorption and desorption processes. In the model simulation, the half-life of MC-LR estimated with its ozonolysis rate constant (3 × 10–11cc/molecules/s) is 4.6 h ± 0.92 at 66 ppb ozone. With the reaction rate constant for MC-LR with OH radicals (6 × 10–7 cc/molecules/s), the estimated half-life of MC-LR during daytime under Florida’s typical summer sunlight is 6 minutes, suggesting that the reaction with OH radicals dominates daytime MC-LR decay. Under moderate sunlight with a typical wind speed (9.2 km/h), the dispersion and HAAR models predict that 25% of aerosolized MC-LR undergoes the atmospheric process within 0.92 km from a bloom source in Florida’s largest lake, suggesting the critical role of the atmospheric oxidation of MC-LR decay.

Evaluating the microcystin-LR-degrading potential of bacteria growing in extreme and polluted environments

Inhabitants of extreme and polluted environments are attractive as candidates for environmental bioremediation. Bacteria growing in oil refinery effluents, tannery dumpsite soils, car wash effluents, salt pans and hot springs were screened for microcystin-LR biodegradation potentials. Using a colorimetric BIOLOG MT2 assay; Arthrobacter sp. B105, Arthrobacter junii, Plantibacter sp. PDD-56b-14, Acinetobacter sp. DUT-2, Salinivibrio sp. YH4, Bacillus sp., Bacillus thuringiensis and Lysinibacillus boronitolerans could grow in the presence of microcystin-LR at 1, 10 and 100 µg L−1. Most bacteria grew optimally at 10 µg L−1 microcystin-LR under alkaline pH (8 and 9). The ability of these bacteria to use MC-LR as a growth substrate depicts their ability to metabolize the toxin, which is equivalent to its degradation. Through PCR screening, these bacteria were shown to lack the mlr genes implying possible use of a unique microcystin-LR degradation pathway. The study highlights the wide environmental and taxonomic distribution of microcystin-LR degraders.

Applicability of Electron Beam Technology for the Degradation of Microcystin-LR in Surface Waters.

Studies were performed to investigate the effects of surface water quality parameters on the degradation of microcystin-LR (MC-LR) using high-energy electron beam (eBeam) technology. Surface water samples were collected across different geographic locations in the United States. Water quality parameters including pH, alkalinity, TDS, and dissolved oxygen were measured in all samples. Degradation of MC-LR in all samples, regardless of parameter concentrations, was above 99%. The effect of natural organic matter (NOM) on MC-LR degradation was also investigated in the presence of fulvic acid. Similarly, the degradation efficiency of MC-LR exceeded 99% for all concentrations of fulvic acid at 5 kGy. This study suggests that surface water quality has a negligible effect on the degradation of MC-LR via eBeam treatment. The results indicate that eBeam technology is a promising technique for the treatment of water contaminated with microcystins.

Visible light-driven photocatalytic degradation of Microcystin-LR by Bi2WO6/Reduced graphene oxide heterojunctions: Mechanistic insight, DFT calculation and degradation pathways

Developing heterostructure photocatalysts for removing Microcystin-LR (MC-LR) under visible light was of positive significance to control the risk of Microcystins and ensure the safety of water quality. Herein, the Bi2WO6/Reduced graphene oxide (RGO) nanocomposites were prepared via a simple one-spot hydrothermal method for the first time to degrade MC-LR. The optimized Bi2WO6/RGO (Bi2WO6/RGO3%) achieved a removal efficiency of 82.3% toward MC-LR, with 1.9-fold higher efficiencies than Bi2WO6, and it showed superior reusability and high stability after 5 cycles. The degradation efficiency of MC-LR demonstrated a negative trend with the initial concentration of MC-LR, fulvic acid, and initial algal density increased, while MC-LR removal rate for the presence of anions was in the order of Cl− > CO3−2 > NO3− > H2PO4−. The degradation efficiency of MC-LR could reach up to 82.3% within 180 min in the neutral condition. The active species detection experiments and EPR measurements demonstrated that the holes (h+), hydroxide radicals (∙OH), and superoxide radicals (∙O2−) participated in the degradation of MC-LR. The DFT calculations showed that 0.56 of electron transferred from Bi2WO6 to RGO, indicating RGO introduction could prevent the recombination of photoelectrons and holes and was beneficial for MC-LR degradation. Finally, the possible intermediate products and degradation pathways were also proposed by the LC-MS/MS analysis.