Analysis of trace microcystins in vegetables using matrix solid-phase dispersion followed by high performance liquid chromatography triple-quadrupole mass spectrometry detection

Capillary electrophoresis tandem mass spectrometry to determine multiclass cyanotoxins in reservoir water and spinach samples

Cyanotoxins constitute a group of toxic secondary metabolites, the presence of which in any water body poses a major health risk. Moreover, advanced organisms such as edible plants exposed to these toxins, are a possible pathway for human exposure. Green analytical chemistry is demanding environmentally friendly analytical techniques. In this sense, we propose the use of capillary electrophoresis coupled to tandem mass spectrometry (CE-MS/MS) to determine a mixture of eight cyanotoxins belonging to three different classes: cyclic peptides (microcystin-LR, microcystin-RR and nodularin), alkaloids (cylindrospermopsin and anatoxin-a) and three isomeric non-protein amino acids (β-methylamino-l-alanine, 2,4-diaminobutyric acid and N-(2-aminoethyl)glycine). Separation was achieved by using an acidic background electrolyte consisting of 2 M formic acid and 20% acetonitrile in water. Parameters affecting MS/MS detection and the sheath-liquid interface were also studied. Finally, a combination of pH-junction, field-amplified sample stacking (FASS) and acid barrage as online preconcentration strategies, was employed to improve sensitivity and efficiency. The online preconcentration applied, in combination with a dual cartridge solid-phase extraction (SPE) system, allows to obtain limits of detection in the very low range of µg·L-1 for these multiclass cyanotoxins in reservoir water samples (from 0.005 to 0.10 µg·L-1). Furthermore, for the first time cyanotoxins are analysed in spinach samples through CE-MS/MS using the same SPE procedure, following lyophilisation and solid-liquid extraction with 6 mL 80 % aqueous MeOH.

Application of aptamer-conjugated graphene oxide for specific enrichment of microcystin-LR in Achatina fulica prior to matrix-assisted laser desorption ionization mass spectrometry

Microcystin-LR (MC-LR), as a hepatotoxin, can cause liver swelling, hepatitis, and even liver cancer. In this study, MC-LR aptamer (Apt-3) modified graphene oxide (GO) was designed to enrich MC-LR in white jade snail (Achatina fulica) and pond water, followed by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) analysis. Results indicated that the Apt-3/PEG/GO nanocomposites were highly specific to MC-LR, and the detection limit of MALDI-MS was 0.50 ng/mL. Moreover, the MC-LR can be released from nanocomposites at 75°C, thus, the reuse of Apt-3/PEG/GO is realized. Real sample analysis indicated that the Apt-3/PEG/GO nanocomposites coupled with MALDI-MS were efficient in detecting trace amounts of MC-LR in real samples. With the merits of being low cost, reusable, and easy to besynthesized, this Apt-3/PEG/GO MALDI-MS is expected to be comprehensively applied by anchoring suitable aptamers for different targets.

Fast cathodic electrodeposition of ZnTCPP-functionalized metal-organic framework films for preparation of a fluorescent aptamer sensor for microcystin determination

A one-step electrodeposition-assisted self-assembly technique has been developed for preparation of ZnTCPP@MOF films with three-dimensional mesoporous structure in a three-electrode system. The internal structure of the ZnTCPP@MOF films was tuned by adjusting the electrochemical deposition voltage, deposition time, and the concentration of ZnTCPP at room temperature. The ZnTCPP@MOF films under different deposition conditions were characterized by scanning electron microscopy, Fourier transformation infrared spectroscopy, and X-ray photoelectron spectroscopy. The prepared ZnTCPP@MOF films exhibited excellent fluorescence properties, in which ZnTCPP molecules were encapsulated inside the MOF as fluorescent signal probes and structure-directing agents, which affected the electrochemical response of the ZnTCPP@MOF films. The sensing platform based on ZnTCPP@MOF film was used to detect microcystin with a wide determination range (1.0 × 10^-12 mol/L ~ 1.0 × 10^-5 mol/L), low determination limit (3.8 × 10^-13 mol/L), and high sensitivity. More importantly, the strategy is simple, low-cost, green, and environmentally friendly, and it provides a new strategy for the direct use of MOFs films as signaling components.

Ionic liquid assisted in situ growth of nano-confined ionic liquids/metal-organic frameworks nanocomposites for monolithic capillary microextraction of microcystins in environmental waters

A facile in-situ ionothermal synthesis strategy for fabrication of ionic liquids/metal-organic frameworks (MOFs) (ILs@ZIF-8) nanocomposites hybrid monolith has been proposed to facilitate highly effective capillary microextraction (CME) of ultra-trace microcystins (MCs) in environmental waters. The ZnO nanoparticles (ZnO-NPs) were initially introduced into a precursor polymer monolith, and acted as the metal sources and anchoring seeds to construct ILs@ZIF-8 nanocomposites hybrid monolith via a nanoparticle-directed in-situ growth route in confined imidazolium ionic liquids. Detailed characterization based on scanning electron microscopy (SEM), X-ray diffraction (XRD) and N₂ adsorption-desorption isotherms confirmed that both the morphology and porous structure of ZIF-8 were finely tuned by the incorporation of ILs, which acted as solvents and structure directing agent. The confinement of ILs in ZIF-8 framework endows the ILs@ZIF-8 hybrid monolith additional adsorption sites and satisfied water stability for the synergistic enhancement of adsorption efficiency of MCs via multiple interactions (including π-π stacking, hydrogen bonding, hydrophobic and electrostatic interactions). Coupling ILs@ZIF-8 hybrid monolith-based CME to LC-MS enabled an efficient and sensitive analysis of MCs in surface waters with ultra-low detection limits (LOD ≤ 1.4 ng L^-1) and satisfactory recoveries (70.2%-107.0%). This study showed great potential for feasible design and fabrication of ILs@MOFs composites with synergistic and tunable structures toward efficient sample preparation applications.

Recent advancements in LC-MS based analysis of biotoxins: Present and future challenges

There has been a rising concern regarding the harmful impact of biotoxins, source of origin, and the determination of the specific type of toxin. With numerous reports on their extensive spread, biotoxins pose a critical challenge to figure out their parent groups, metabolites, and concentration. In that aspect, liquid chromatography-mass spectrometry (LC-MS) based analysis paves the way for its accurate identification and quantification. The biotoxins are ideally categorized as phytotoxins, mycotoxins, shellfish-toxins, ciguatoxins, cyanotoxins, and bacterial toxins such as tetrodotoxins. Considering the diverse nature of biotoxins, both low-resolution mass spectrometry (LRMS) and high-resolution mass spectrometry (HRMS) methods have been implemented for their detection. The sample preparation strategy for complex matrix usually includes "QuEChERS" extraction or solid-phase extraction coupled with homogenization and centrifugation. For targeted analysis of biotoxins, the LRMS consisting of a tandem mass spectrometer operating in multiple reaction monitoring mode has been widely implemented. With the help of the reference standard, most of the toxins were accurately quantified. At the same time, the suspect screening and nontarget screening approach are facilitated by the HRMS platforms during the absence of reference standards. Significant progress has also been made in sampling device employment, utilizing novel sample preparation strategies, synthesizing toxin standards, employing hybrid MS platforms, and the associated data interpretation. This critical review attempts to elucidate the progress in LC-MS based analysis in the determination of biotoxins while pointing out major challenges and suggestions for future development.

Immunoassay technology: Research progress in microcystin-LR detection in water samples

Increasing global warming and eutrophication have led to frequent outbreaks of cyanobacteria blooms in freshwater. Cyanobacteria blooms cause the death of aquatic and terrestrial organisms and have attracted considerable attention since the 19th century. Microcystin-LR (MC-LR) is one of the most typical cyanobacterial toxins. Therefore, the fast, sensitive, and accurate determination of MC-LR plays an important role in the health of humans and animals. Immunoassay refers to a method that uses the principle of immunology to determine the content of the tested substance in a sample using the tested substance as an antigen or antibody. In analytical applications, the immunoassay technology could use the specific recognition of antibodies for MC-LR detection. In this review, we firstly highlight the immunoassay detection of MC-LR over the past two decades, including classical enzyme-link immunosorbent assay (ELISA), modern immunoassay with optical signal, and modern immunoassay with electrical signal. Among these detection methods, the water environment was used as the main detection system. The advantages and disadvantages of the different detection methods were compared and analyzed, and the principles and applications of immunoassays in water samples were elaborated. Furthermore, the current challenges and developmental trends in immunoassay were systematically introduced to enhance MC-LR detection performance, and some critical points were given to deal with current challenges. This review provides novel insight into MC-LR detection based on immunoassay method.

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.

Multiplexed SERS Detection of Microcystins with Aptamer-Driven Core-Satellite Assemblies

We describe surface-enhanced Raman spectroscopy (SERS) aptasensors that can indirectly detect MC-LR and MC-RR, individually or simultaneously, in natural water and in algal culture. The sensor is constructed from nanoparticles composed of successive layers of Au core-SERS label-silver shell-gold shell (Au@label@Ag@Au NPs), functionalized on the outer Au surface by MC-LR and/or MC-RR aptamers. These NPs are immobilized on asymmetric Au nanoflowers (AuNFs) dispersed on planar silicon substrates through DNA hybridization of the aptamers and capture DNA sequences with which the AuNFs are functionalized, thereby forming core-satellite nanostructures on the substrates. This construction led to greater electromagnetic (EM) field enhancement of the Raman label-modified region, as supported by finite-difference time-domain (FDTD) simulations of the core-satellite assembly. In the presence of MC-LR and/or MC-RR, the aptamer-functionalized NPs dissociate from the AuNFs because of the stronger affinity of the aptamers with the MCs, which decreases the SERS signal, thus allowing indirect detection of the MCs. The improved SERS sensitivity significantly decreased the limit of detection (LOD) for separate MC-LR detection (0.8 pM) and for multiplex detection (1.5 pM for MC-LR and 1.3 pM for MC-RR), compared with other recently reported SERS-based methods for MC-LR detection. The aptasensors show excellent selectivity to MC-LR/MC-RR and excellent recoveries (96-105%). The use of these SERS aptasensors to monitor MC-LR production over 1 week in a culture medium of M. aeruginosa cells demonstrates the applicability of the sensors in a realistic environment.

A Mini-Review on Detection Methods of Microcystins

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

Microcystins: Biogenesis, Toxicity, Analysis, and Control

Microcystins are cyclic peptide toxins formed by cyanobacteria. These toxins are recognized for their association with algal blooms, posing a significant threat to ecosystems and drinking water quality. Due to the growing environmental concerns they raise, a comprehensive review on microcystins' genesis, toxicity, and analytical methods for their quantitative determination is outlined. Genes, including the mcyABC cluster, regulate microcystin biogenesis. Bioanalytical experiments have identified key environmental factors, such as temperature and nitrogen availability, that promote microcystin production. Microcystin toxicity is explored based on its modulatory effects on protein phosphatases 1 and 2A in specific tissues and organs. Additionally, biochemical mechanisms of chelation, transportation, resultant oxidative stress, and tumor promotion abilities of microcystins are also discussed. Various analytical methods to separate, detect, and quantify microcystins, including the quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, nuclear magnetic resonance spectroscopy, and chromatographic platforms-linked tandem mass spectrometry (LC-MS) for unequivocal structural identification, are also reviewed. Since control of microcystins in water is of great necessity, both water treatment and mechanisms of abiotic transformation and microbial degradation are also discussed.

Recent developments in the methods of quantitative analysis of microcystins

Cyanotoxins are produced by the toxic cyanobacterial species present in algal blooms formed in water bodies due to nutrient over-enrichment by human influences and natural environmental conditions. Extensive studies are available on the most widely encountered cyanotoxins, microcystins (MCs) in fresh and brackish water bodies. MC contaminated water poses severe risks to human health, environmental sustainability, and aquatic life. Therefore, commonly occurring MCs should be monitored. Occasionally, detection and quantification of these toxins are difficult due to the unavailability of pure standards. Enzymatic, immunological assays, and analytical techniques like protein phosphatase inhibition assay, enzyme-linked immunosorbent assay, high-performance liquid chromatography, liquid chromatography-mass spectrometry, and biosensors are used for their detection and quantification. There is no single method for the detection of all the different types of MCs; therefore, various techniques are often combined to yield reliable results. Biosensor development offered a problem-solving approach in the detection of MCs due to their high accuracy, sensitivity, rapid response, and portability. In this review, an endeavor has been made to uncover emerging techniques used for the detection and quantification of the MCs.

Simultaneous analysis of current-use pesticides and their transformation products in water using mixture-sorbent solid phase extraction and high-performance liquid chromatography-tandem mass spectrometry

Pesticides have posed significant threats to aquatic ecosystems, yet little is known about their transformation products. The challenge is to simultaneously analyze various pesticides and transformation products in water as they have distinct physicochemical properties. A mix-mode solid phase extraction method was established to simultaneously analyze current-use pesticides and their transformation products using a mixture of hydrophile-lipophile balance, weak anion, and cation exchange resins (2:1:1, w/w/w) in combination with high-performance liquid chromatography and tandem mass spectrometry for chemical quantification. Neutral, acidic, and alkaline methanol were used as the elution solvent. Box-Behnken design was applied to optimize extraction conditions. Optimal conditions were as follows: sorbent mass, 200 mg; volume of elution solvent, 5 mL × 3; pH 4. The method was validated for compounds at concentrations from 20 to 1000 ng/L in different types of water samples, with recovery being from 43.5 ± 3.1 to 141 ± 35%. Low method detection limits (0.02-5.6 ng/L) implied that the developed method was sensitive. Finally, the method was applied to monitor current-use pesticides and their transformation products in natural waters. Frequent detection of transformation products of pesticides indicated that their contribution to aquatic risk should not be ignored.

Fluorescent enzyme-linked immunoassay based on silane-doped carbon dots for sensitive detection of microcystin-LR in water and crucian samples

In this work, a fluorescent nanoparticles labeling-free fluorescence enzyme-linked immunoassay (FELISA) has been established for the ultrasensitive detection of microcystin-LR (MC-LR) in water and fish samples. Polyclonal antibody against MC-LR was labeled with horseradish peroxidase (HRP) and used as signal probe for binding with analyte in sample or for coating antigen. After washing of the unbound antibody, the substrate system (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS)/H₂O₂) was added. The oxidation product of ABTS (ox-ABTS) catalyzed by HRP effectively caused the fluorescence quenching of subsequently added silane-doped carbon dots (Si-CDs), and the change in fluorescence intensity of Si-CDs was used to realize the quantitative detection of MC-LR. Under the optimum conditions, the Si-CDs based FELISA method showed a good linear relationship from 0.001 to 3.20 μg L^-1 (R² = 0.994) and provided a low detection limit of 0.6 ng L^-1, which was approximately 30-fold lower than that of traditional indirect competitive ELISA. Average recovery values from 79.9% to 109.2% was obtained from spiked water and crucian samples, suggesting its potential application on the monitoring of MR-LR at a trace level.

Determination of microcystins in environmental water samples with ionic liquid magnetic graphene

Microcystins is a class of monocyclic of heptapeptides with many different isomerides. It has become potential hazardous material in water environment for its toxic, distribution and stability. This project worked on a method for determination of trace microcystin (MC-LR and MC-RR) in environmental waters. The ionic liquid magnetic graphene (IL@MG) was prepared and applied to the concentration and determination of microcystins, based on magnetic solid phase extraction (MSPE), and coupled with ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The ionic liquid magnetic graphene was prepared by coprecipitatial synthesis and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR), specific surface area (BET), pore size distribution (BJH) and magnetic hysteresis loop. The experimental parameters of magnetic solid phase extraction, including amount of IL@MG, pH, extraction time and elution solvent were investigated by a univariate method and orthogonal screening. The method showed good linearity in the range of 0.01-10.0 g/L and 0.005-10.0 μg/L for MC-LR and MC-RR, when the pH of water samples was 4.00 and 10.0 mg adsorbents were used to extract targets for 18 min. The lowest detection limit was 0.414 ng/L and 0.216 ng/L for MC-LR and MC-RR respectively. The recoveries of the microcystins were in the range of 83.6-100.9%, and the relative standard deviation was less than 7.59%. The trace amount of MC-LR (0.020 μg/L) and MC-RR (0.003 μg/L and 0.021 μg/L) was detected in actural water samples. Attributed to its simple operator, low detection limit and high sensitivity, this method could be used for the detection of trace microcystins in water samples.

Highly sensitive detection of microcystin-LR under visible light using a self-powered photoelectrochemical aptasensor based on a CoO/Au/g-C3N4 Z-scheme heterojunction

Based on the unique photoelectrochemical properties of a CoO/Au/g-C₃N₄ Z-scheme heterojunction, a self-powered photoelectrochemical (PEC) aptasensor was constructed for the detection of microcystin-leucine arginine (MC-LR). Z-scheme heterojunctions can promote the separation of a photo-induced electron-hole pair, and the surface plasmonic resonance (SPR) of Au nanoparticles can significantly enhance the adsorption of visible light. Importantly, MC-LR molecules were captured by aptamers initially immobilized on the modified electrode due to their high affinity, and then oxidized by the photogenerated holes, which caused an amplified photocurrent signal, allowing the quantitative analysis of MC-LR by measuring the photocurrent intensity change. This PEC MC-LR aptasensor showed high sensitivity and selectivity within a wide linear response range from 0.1 pM to 10 nM and a detection limit of 0.01 pM. The application of this sensor in the analysis of lake water samples provided accurate results with a relative standard deviation (RSD) of 2.6%-4.2%.

Study on the cyanobacterial toxin metabolism of Microcystis aeruginosa in nitrogen-starved conditions by a stable isotope labelling method

In this study, the biosynthesis of microcystins (MCs) was investigated after long-term nitrogen-starved conditions in cyanobacterium Microcystis aeruginosa. The results demonstrated that the algal cells were able to survive in a non-growing state with nitrogen starvation for more than one month. The physiological properties of the algal cells were studied to elucidate the mechanisms of viability under nitrogen-deprivation conditions. After the state of nitrogen chlorosis, new toxins could be resynthesized and tracked using ¹⁵N-stable isotope-labelled nitrogen. Nitrogen starvation of nutritionally replete cells resulted in a significant increase of microcystin-LY (MC-LY), thereby suggesting that MC-LY may undergo catabolism to provide nitrogen or that MC-LY may be produced to play an important role in the cell in response to nitrogen deprivation. The rank order of different types of nitrogen in algal cells assimilation was N-ammonium > N-urea > N-nitrate > N-alanine. The relationship between the production of toxin variants and various environmental conditions is an interesting issue for future research and may help improve the understanding of the ecological role of cyanobacterial toxins.

Laser irradiation desorption of microcystins from protein complex in fish tissue and liquid chromatography-tandem mass spectrometry analysis

Microcystins are a group of cyanotoxins which interact with the C-terminal region of PP1 and PP2A proteins, so denaturation and inactivation are necessary for breaking covalent binding to release microcystins. In this study, a novel extraction method was developed by laser irradiation desorption of microcystins from fish protein. The sample was mixed with aqueous methanol and irradiated by a 450 nm laser, with an optimized value of laser power density at 8 W and exposure time at 5 min. ThenLC-MS/MS was applied for the determination of microcystins in fish extracts. The ionization behaviors of microcystins were investigated firstly, and doubly charged microcystins were selected as precursor ions in multiple reaction monitoring scan for quantification. This proposed quantitative method was well validated in terms of selectivity, linearity, sensitivity, accuracy, recovery, and stability. The successful application of this LC-MS/MS method showed its ability for the analysis of microcystins in low concentration, and it would be of significant interest for environmental and food safety applications to ensure the safety of fish and related products.

Occurrence of microcystin-LR in vegetated lagoons used for urban runoff management

Phytoremediation with aquatic macrophyte has been considered as an eco-friendly technique for controlling harmful cyanobacteria outbreak and proven to be effective. The conventional water quality parameters are frequently measured to evaluate the effectiveness of phytoremediation. However, the concentration of microcystin-leucine-arginine (MC-LR) in different vegetated water still remains uncertain. In this study, the contents of MC-LR in four macrophyte-vegetated lagoons were determined by solid phase extraction and ultra-high-performance liquid chromatography with tandem mass spectrometry technology. Results indicated that MC-LR was found in Nymphaea tetragona lagoon (lagoon-S), Vallisneria spiralis lagoon (lagoon-B) and another Vallisneria spiralis lagoon (lagoon-J). Only in lagoon dominated by Pistia stratiotes L. (lagoon-D), MC-LR concentration was undiscovered regardless of seasonal variation. The levels of MC-LR varied seasonally and were affected by the different vegetated aquatic macrophytes. The results suggest that in addition to conventional physicochemical parameters and indicators of water quality, MC-LR levels should be taken into consideration when the effectiveness of phytoremediation is assessed.

New Method for Simultaneous Determination of Microcystins and Cylindrospermopsin in Vegetable Matrices by SPE-UPLC-MS/MS

Cyanotoxins are a large group of noxious metabolites with different chemical structure and mechanisms of action, with a worldwide distribution, producing effects in animals, humans, and crop plants. When cyanotoxin-contaminated waters are used for the irrigation of edible vegetables, humans can be in contact with these toxins through the food chain. In this work, a method for the simultaneous detection of Microcystin-LR (MC-LR), Microcystin-RR (MC-RR), Microcystin-YR (MC-YR), and Cylindrospermopsin (CYN) in lettuce has been optimized and validated, using a dual solid phase extraction (SPE) system for toxin extraction and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) for analysis. Results showed linear ranges (5⁻50 ng g-1 f.w.), low values for limit of detection (LOD) (0.06⁻0.42 ng g-1 f.w.), and limit of quantification (LOQ) (0.16⁻0.91 ng g-1 f.w.), acceptable recoveries (41⁻93%), and %RSDIP values for the four toxins. The method proved to be robust for the three variables tested. Finally, it was successfully applied to detect these cyanotoxins in edible vegetables exposed to cyanobacterial extracts under laboratory conditions, and it could be useful for monitoring these toxins in edible vegetables for better exposure estimation in terms of risk assessment.

Removal of Microcystin-LR by a Novel Native Effective Bacterial Community Designated as YFMCD4 Isolated from Lake Taihu

Microcystin-LR (MC-LR) is the most toxic and frequently detected monocyclic heptapeptide hepatotoxin produced by cyanobacteria, which poses a great threat to the natural ecosystem and public health. It is very important to seek environment-friendly and cost-efficient methods to remove MC-LR in water. In this study, the MC-degrading capacities of a novel indigenous bacterial community designated as YFMCD4 and the influence of environmental factors including various temperatures, MC concentrations and pH on the MC-degrading activities were investigated utilizing high-performance liquid chromatography (HPLC). In addition, the MC-degrading mechanism of YFMCD4 was also studied using HPLC coupled with a mass spectrometry equipped with electrospray ionization interface (HPLC-ESI-MS). The data showed MC-LR was completely removed at the maximum rate of 0.5 µg/(mL·h) under the optimal condition by YFMCD4. Two pure bacterial strains Alcaligenes faecalis and Stenotrophomonas acidaminiohila were isolated from YFMCD4 degraded MC-LR at a slower rate. The MC-degrading rates of YFMCD4 were significantly affected by different temperatures, pH and MC-LR concentrations. Two intermediates of a tetrapeptide and Adda appeared in the degradation process. These results illustrate that the novel YFMCD4 is one of the highest effective MC-degrading bacterial community, which can completely remove MC-LR and possesses a significant potential to treat water bodies contaminated by MC-LR.

Dual-Modal Split-Type Immunosensor for Sensitive Detection of Microcystin-LR: Enzyme-Induced Photoelectrochemistry and Colorimetry

Microcystins, the lethal cyanotoxins from Microcystis aeruginosa, can inhibit the activity of protein phosphatase and promote liver tumors. Herein, a dual-modal split-type immunosensor was constructed to detect microcystin-LR (MC-LR), based on the photocurrent change of CdS/ZnO hollow nanorod arrays (HNRs) and the blue shift of the surface plasmon resonance peak from Au nanobipyramids@Ag. By using mesoporous silica nanospheres as the carrier to immobilize secondary antibody and DNA primer, a hybridization chain reaction was adopted to capture alkaline phosphatase, while its catalytic reaction product, ascorbic acid, exhibited dual functions. The detailed mechanism was investigated, showing that ascorbic acid can not only act as the electron donor to capture the holes in CdS/ZnO-HNRs, leading to the increase photocurrent, but also as the reductant to form silver shells on Au nanobipyramids, generating multiply vivid color variations and blue shifts. Compared with the traditional photoelectrochemical immunosensor or colorimetric method for MC-LR, a more accurate and reliable result can be obtained, due to different mechanisms and independent signal transduction. Therefore, this work can not only propose a new dual-modal immunosensor for MC-LR detection but also provide innovative inspiration for constructing sensitive, accurate, and visual analysis for toxins.

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.

Dispersive liquid-liquid microextraction as a new clean-up procedure for the determination of parabens, perfluorinated compounds, UV filters, biocides, surfactants, and plasticizers in root vegetables

An analytical method based on ultrasound-assisted extraction and dispersive liquid-liquid microextraction (DLLME) clean-up has been developed and validated for the determination of 31 emerging pollutants in root vegetables. The target compounds were four preservatives, six perfluoroalkyl compounds, six UV filters, two biocides, eight anionic surfactants, three nonionic surfactants, and two plasticizers. The type and volume of the extraction solvent, those of the disperser solvent, the pH and NaCl content of the DLLME aqueous phase, the amount of sample, and the sonication time were optimized. Box-Behnken experimental design was applied to select the best extraction conditions. Matrix-matched calibration curves were used for quantification. Four internal standards were used to compensate for residual matrix effects. Good linearity (R² > 0.990), accuracies (expressed as the relative recovery) of >82%, and precisions (expressed as the relative standard deviation) of <18% were achieved. Method quantification limits (MQLs), calculated from spiked samples as the concentrations corresponding to signal-to-noise ratios of 10, were in the range 0.1-25 ng g^-1 dry weight (d.w.). MQL values for 26 of the 31 target compounds were lower than 5 ng g^-1 d.w. The method was successfully applied to determine the target pollutants in carrots, potatoes, and turnips from a local market. To the best of our knowledge, the proposed method constitutes the first application of DLLME as a clean-up procedure for the multiresidue determination of emerging pollutants in vegetables. The method affords similar recoveries and method detection limits to previously reported methods but requires smaller solvent volumes and sample amounts and is less expensive.

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.

Validation and application of a multiresidue method based on liquid chromatography-tandem mass spectrometry for evaluating the plant uptake of 74 microcontaminants in crops irrigated with treated municipal wastewater

Reuse of treated wastewater for agricultural purposes can mitigate water stress in some regions where the lack of water is an extended problem. However, the environmental long-term consequences of this practice are still unknown. It is demonstrated that using reclaimed water for irrigation lead to accumulation and translocation of some microcontaminants (MCs) in soil and crops. However, so far, only a small group of contaminants has been investigated. This study aims to develop and validate a simple and efficient multiresidue method based on QuEChERs (Quick, Easy, Cheap, Effective and Rugged) extraction coupled to liquid chromatography tandem mass spectrometry (LC-MS/MS). The novelty of the study relays in the large number of MCs analyzed (74), some of them not previously investigated, in three commodities (lettuce, radish and strawberry). Optimized conditions yielded good results for the three commodities under study. Up to 84% of the compounds were recovered within a 70-120% range, with good repeatability (relative standard deviations below 20% in most cases). Method detection (MDLs) and quantification limits (MQLs) ranged from 0.01 to 2 ng/g. The proposed method was successfully applied to assess the potential uptake of MCs by lettuce and radish crops irrigated with wastewater under controlled conditions for 3 and 1.5 months, respectively. 12 compounds were detected in the crops with concentrations ranging from 0.03 to 57.6 ng/g. N-Formyl-4-aminoantipyrine (4FAA) was the most concentrated compound. The application of this method demonstrated for the first time the accumulation of 5 contaminants of emerging concern (CECs) not previously reported: 4FAA, N-Acetyl-4-aminoantipyrine (4AAA), hydrochlorothiazide, mepivacaine and venlafaxine.