microcystin-LR In Water Research Articles

Ozonation, biofiltration and the role of membrane surface charge and hydrophobicity in removal and destruction of algal toxins at basic pH values

Abstract This study was directed at the investigation of technologies for treatment of water containing algal toxins at basic pH values. Ozonation, biofiltration and membrane filtration were examined for the removal of algal toxins, specifically microcystin-LR (MC-LR). Results indicate that, as expected, ozonation completely destroyed MC-LR in water, while biofiltration using naturally-occurring bacteria did not show a significant reduction in MC-LR concentration after eight days of contact time. More compelling were the membrane filtration results, which showed that water-affinity interactions were not the only governing factor influencing the removal of MC-LR by membranes. It was found that charge interactions between membranes and MC-LR played an important role in the rejection. MC-LR was completely removed from the feed water only by hydrophobic neutrally and positively charged membranes. Furthermore, due to charge interactions, MC-LR reversibly adsorbed to neutral hydrophobic membranes, but it irreversibly adsorbed to positive hydrophobic membranes.

Using fluorescence immunochromatographic test strips based on quantum dots for the rapid and sensitive determination of microcystin-LR.

A novel immunosensor for the detection of microcystin-LR (MC-LR) was constructed with use of immunochromatographic test strips (ICTS). Quantum dots were chosen to be the fluorescent labels for the immune sensor in ICTS because of their excellent optical and electronic properties with a relatively narrow emission spectrum. The detection sensitivity of the ICTS was related to the concentration of the fluorescent probe and the amount of the MC-LR standards. Under optimal conditions, with MC-LR as the target, the ICTS sensor had a linear range from 0.25 to 5μg/L, with a correlation coefficient of 0.9901 and a detection limit of 0.1μg/L. Furthermore, the repeatability of the ICTS was good, and the coefficient of variation was 10%. The ICTS immunosensor allows the reliable detection of MC-LR in water, and has potential in simple, sensitive detection applications. Graphical Abstract A novel method was developed to detect MC-LR using QDs based immunochromatographic test strip.

Effectiveness and intermediates of microcystin-LR degradation by UV/H2O2 via 265nm ultraviolet light-emitting diodes.

Although the degradation of cyanotoxins by 254nm UV/H2O2 has been well elucidated, the efficiency and mechanism involved are not necessarily true for other UV wavelengths. The degradation of microcystin-LR (MC-LR), a representative cyanotoxin, was explored by UV/H2O2 using 265nm ultraviolet light-emitting diode (UV-LED). The results indicated that 265nm UV/H2O2 treatment had a high removal efficiency of MC-LR ([MC-LR]=0.1μM, apparent rate constants reached 0.2077min-1, half-time at 3.3min). The qualitative analyses demonstrated that three novel intermediates, C48H74N10O15 (molecular weight=1030.5335), C36H58N10O14 (854.4134), and C33H54N10O14 (814.3821), were generated in 265nm UV/H2O2. Five published intermediates were also confirmed. The generative pathway of these products mainly involved free hydroxyl radical oxidation, resulting in consecutive hydroxyl substitutions and hydroxyl additions of unsaturated bonds in MC-LR. The toxicity of MC-LR was weaken with a relative low mineralization. The electrical energy per order values were calculated to be in the range of 0.00447 to 0.00612kWhm-3order-1 for 100-5000μgL-1 MC-LR. Overall, 265nm UV-LED/H2O2 can be used as an alternative effective technology to improve the removal efficiency of MC-LR in water.

Iron based sustainable greener technologies to treat cyanobacteria and microcystin-LR in water

The presence of the toxic cyanobacteria and cyanotoxin, microcystin-LR (MC-LR) and other cyanotoxins, in drinking water sources poses a serious risk to public health. Iron based technologies using magnetic zero-valent iron nanoparticles (nZVI) and ferrate ion (Fe VI O 4 2− , Fe(VI)) represent greener approaches to remove cyanobacteria and degrade MC-LR in water. This paper reveals that nanoparticles of zero valent iron (nZVI) can destroy cyanobacteria in the source water and may play a preventive role in terms of the formation of cyanobacterial water blooms by removing nutrients like phosphate. Results on MC-LR showed that Fe(VI) was highly effective in removing MC-LR in water. Products studies on the oxidation of MC-LR by Fe(VI) demonstrated decomposition of the MC-LR structure. Significantly, degradation byproducts of MC-LR did not contain significant biological toxicity. Moreover, Fe(VI) was highly effective for the degradation of MC-LR in lake water samples. Mechanisms of removal and destruction of target contaminants by nZVI and Fe(VI) are discussed.

Cloning of scFv from hybridomas using a rational strategy: Application as a receptor to sensitive detection microcystin-LR in water

Single chain variable fragment (scFv), containing of heavy and light chains (VH and VL) joined by a short peptide linker, has been used widely for immunodetection. Nevertheless, cloning functional variable genes is still a bottle neck for the scFv generation technology. Here, a rational strategy for cloning and selecting variable region genes from an anti-microcystin-LR hybridoma was devised, then the functional VH and VL genes were recloned and assembled to scFv using splicing overlap extension PCR. The resulting scFv gene was recombinantly expressed as a soluble scFv-alkaline phosphatase fusion protein (scFv−AP) by vector PLIP6/GN. Then an indirect competitive chemiluminescent enzyme immunoassay (ic-CLEIA) for detection of microcystin-LR was developed. The half-maximum inhibition concentrations (IC50) and limits of detection (LODs, IC15) were 0.81 ± 0.04 μgL−1 and 0.13 ± 0.03 μgL−1, respectively. With the mean coefficient of variation lowing 8%, the mean recovery in intra-assay and inter-assay were 100.06% and 96.46%, The proposed strategy should be useful for generation scFv in a rapid and simple way.

Photocatalytic degradation of MC-LR in water by the UV/TiO2/H2O2 process

The ultraviolet (UV)/titanium dioxide (TiO2)/hydrogen peroxide (H2O2) process (UTHP) has been proven to be effective in removing organics because of its high production of free radicals. In this study, UTHP was further investigated for the photocatalytic degradation of microcystin-LR (MC-LR). Results showed that three mechanisms could realize MC-LR photocatalytic degradation using TiO2. H2O2 could effectively inhibit recombination and considerably improve the production of radicals and superoxides. From a correlation of the removal rate with the isomerization and decomposition of MC-LR under UV irradiation it was inferred that isomerization was crucial for MC-LR degradation during photocatalysis given the vulnerability of the exposed conjugated double bonds. The photocatalysis of MC-LR was apparently dependent on pH and MC-LR initial concentration. Under the optimum conditions of pH 3.5, 0.05 g/L TiO2, and 0.05 mmol/L H2O2, 100% MC-LR (308 μg/L) could be removed within 60 min. This process was accompanied by a synergistic effect during the initial 10 min.

Oxidation of microcystin-LR in water by ozone combined with UV radiation: The removal and degradation pathway

In this study, the performance of the combined UV/O3 process for the degradation of microcystin-LR (MC-LR) in water was investigated, and the possible degradation pathway of the toxin was elucidated according to reaction intermediates. Results demonstrated that the UV/O3 process was a more effective method for the removal and mineralization of MC-LR in water, compared with UV- and O3-alone processes. Increasing the solution pH (5–10) and dissolved organic carbon concentration (0–5.3mg/L) could inhibit the degradation of the toxin. Nine reaction intermediates of MC-LR were detected by LC/MS, and four initial reaction sites of the toxin were observed: the conjugated diene of Adda, the double bonds of Mdha and two free acid groups of MeAsp and Glu. The degradation pathways of the toxin during UV/O3 process involved isomerization, hydroxylation and oxidative cleavage of the Adda side chain, oxidation of Mdha and decarboxylation of MeAsp and Glu. The pathway of the oxidation and cleavage of Adda and Mdha could result from both HO and O3 oxidation, but the isomerization of Adda moiety and the decarboxylation of MeAsp and Glu mainly resulted from UV radiation. The yield trends of the intermediates indicated that the oxidation of Adda moiety was the dominant degradation pathway and that the combined UV/O3 process had a higher potential for the simultaneous degradation of MC-LR and its intermediates than the individual processes.

A hybrid adsorbent/visible light photocatalyst for the abatement of microcystin-LR in water

A hybrid adsorbent/photocatalyst was obtained and used for the removal of microcystin-LR, a potent toxin, from water via adsorption and photocatalyzed oxidation with singlet oxygen. The combined adsorption/photooxidation processes yielded a 500-fold decrease of the overall MC-LR concentration. The adsorbent/photocatalyst can be easily removed from the reaction system by sedimentation or centrifugation.

Oxidation of Microcystin-LR by Ferrate(VI): Kinetics, Degradation Pathways, and Toxicity Assessments

The presence of the potent cyanotoxin, microcystin-LR (MC-LR), in drinking water sources poses a serious risk to public health. The kinetics of the reactivity of ferrate(VI) (Fe(VI)O4(2-), Fe(VI)) with MC-LR and model compounds (sorbic acid, sorbic alcohol, and glycine anhydride) are reported over a range of solution pH. The degradation of MC-LR followed second-order kinetics with the bimolecular rate constant (kMCLR+Fe(VI)) decreasing from 1.3 ± 0.1 × 10(2) M(-1) s(-1) at pH 7.5 to 8.1 ± 0.08 M(-1) s(-1) at pH 10.0. The specific rate constants for the individual ferrate species were determined and compared with a number of common chemical oxidants employed for water treatment. Detailed product studies using liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) indicated the oxidized products (OPs) were primarily the result of hydroxylation of the aromatic ring, double bond of the methyldehydroalanine (Mdha) amino acid residue, and diene functionality. Products studies also indicate fragmentation of the cyclic MC-LR structure occurs under the reaction conditions. The analysis of protein phosphatase (PP1) activity suggested that the degradation byproducts of MC-LR did not possess significant biological toxicity. Fe(VI) was effective for the degradation MC-LR in water containing carbonate ions and fulvic acid (FA) and in lake water samples, but higher Fe(VI) dosages would be needed to completely remove MC-LR in lake water compared to deionized water.

Measurement of microcystin -LR in water samples using improved HPLC method.

Microcystins are a group of toxic compounds produced by freshwater cyanobacteria and cause diseases. World Health Organization has recommended a concentration of 1 µg/l for Microcystin-LR (MC-LR) in potable water as guideline value. The high performance liquid chromatography (HPLC) followed by C18 analytical column and ultra violet detector for detection of MC-LR. In this regard, 5 different concentrations of MC-LR solutions were injected into HPLC. MC-LR was detected in 5.33 minute retention time and Calibration curve was achieved with R2=0.988. Detection limit for this method was obtained by using acetonitrile solutions (32% and 55%) as a gradient run and a high silanol activity column equal to 0.02 µg/mL. Despite no acidic organic modifier being used in the mixture of solvents, the sensitivity of this method was appropriate for detection of MC-LR. Because of short retention time, reduction in number of solvents and high resolution and suitable sensitivity, this method is affordable and is fast for detection and determination of MC-LR in potable water.

Degradation of Microcystin-LR in water: Hydrolysis of peptide bonds catalyzed by maghemite under visible light

Maghemite, an abundant iron-oxide mineral, was investigated as a visible light catalyst for decomposing and mineralizing Microcystin-LR (MC-LR) in water using hydrogen peroxide (H2O2) as the initial oxidant. Interestingly, of the twelve intermediates identified by LC–MS, half were products of MC-LR peptide bond hydrolysis rather than the oxidation products typical of photocatalytic oxidation (PCO). The catalytic hydrolysis of MC-LR by maghemite and visible light has not been previously reported. Detailed examination of intermediates provided insight into the catalytic pathway. Electron spin resonance (ESR) spectra revealed that visible light irradiation does not increase hydroxyl radical (OH) production from H2O2 decomposition. Visible light appears to play a new role in this unique PCO system, generating Brønsted sites on the maghemite surface via a metal ligand charge transfer (MLCT), rather than producing OH from H2O2. Because opening the cyclic peptide structure detoxifies MC-LR, this catalytic system could be uniquely efficient in detoxifying MC-LR in the presence of relatively high levels of natural organic matter (NOM). This work introduces a new means of selectively and effectively detoxifying MCs in water using an inexpensive, environmentally friendly and bio-compatible mineral.

Revealing the degradation intermediates and pathways of visible light-induced NF-TiO2 photocatalysis of microcystin-LR

The effect of using only visible light to induce nitrogen- and fluorine-doped titanium dioxide (NF-TiO2) photocatalysis of degradation products of microcystin-LR (MC-LR), the most common problematic cyanotoxin, was explored by looking at the intermediate degradation products. Although the degradation mechanisms and products of conventional UV-based TiO2 photocatalysis of MC-LR have been well elucidated, the same is not true for visible light-based TiO2 photocatalysis. The results of LC/MS2 (and in one case LC/MS3) indicated that the intermediates are not drastically altered in comparison to traditional TiO2 photocatalysis using UV light. The data hint that the degradation is driven by hydroxyl radicals, as is UV-based TiO2 photocatalysis, although the mechanism for producing hydroxyl radicals is unclear since studies indicate drastically slower kinetics for visible light-based photocatalysis of MC-LR. Notably, the data indicate that visible light-induced NF-TiO2 photocatalysis degraded the portion of MC-LR that is responsible for biological toxicity. As a result of this, it was concluded that doping TiO2 with nitrogen and fluorine is an effective method for increasing utilization of visible light while degrading MC-LR in water, although it should still be noted that degradation kinetics are still slower than UV-based TiO2 photocatalysis.

A green synthesis of magnetic bentonite material and its application for removal of microcystin-LR in water

A simple and green method has been developed for in situ assembly of magnetic Fe3O4 on the pillared bentonite by a solvothermal reaction. Fe3O4 nanopaticles have a nearly uniform size of about 200nm, and they create the homogeneous structures distributed on the bentonite surface. The resulting magnetic material (Fe3O4@Al-B) has a surface area of 110 m2/g and a saturation magnetization of 36.18emu/g. At the same time, Fe3O4@Al-B has a strong surface affinity toward microcystin-LR (MC-LR) both in Mili-Q water and river water samples. Adsorption of MC-LR on Fe3O4@Al-B increases with pH decrease, with a maximum adsorption at pH 2.1. The equilibrium adsorption data are also analyzed by using the Langmuir and Freundlich models to evaluate the adsorption capacity of Fe3O4@Al-B and a result of 161.29mg/g is achieved. The pseudo-second-order kinetic model provides the best correlation of the experimental data. Therefore, Fe3O4@Al-B is an effective technology and has a great potential in removing MC-LR from drinking water resources.

Detoxification of microcystin-LR in water by Portulaca oleracea cv.

Microcystin-LR (0.02 μg/ml) in the hydroculture medium of Portulaca oleracea cv., became below the detection level (<0.0001 μg/ml) by HPLC analysis after 7 days. The toxicity of microcystin estimated with protein phosphatase inhibition assay, however, remained at 37% of the initial level, indicating that microcystin-LR was transformed by P. oleracea cv. into unknown compound(s) of lower toxicity.

Electrochemical immunosensor for ultrasensitive detection of microcystin-LR based on graphene–gold nanocomposite/functional conducting polymer/gold nanoparticle/ionic liquid composite film with electrodeposition

The study developed an electrochemical immunosensor for ultrasensitive detection of microcystin-LR in water. Graphene oxide and chloroauric acid were alternately electrodeposited on the surface of glassy carbon electrode for 20 cycles to fabricate graphene–gold nanocomposite. The composite was characterized and its apparent heterogeneous electron transfer rate constant (37.28±0.16cms−1) was estimated by Laviron's model. To immobilize microcystin-LR antibody and improve the electrical conductivity, 2,5-di-(2-thienyl)-1-pyrrole-1-(p-benzoic acid) and chloroauric acid were electrodeposited on the modified electrode in sequence. The ionic liquid was then dropped on the electrode surface and finally microcystin-LR antibody was covalently connected to the conducting polymer film. Experiment showed the electrochemical technique offers control over reaction parameters and excellent repeatability. The graphene–gold nanocomposite and gold nanoparticles enhance electron transfer of Fe(CN)63−/4− to the electrode. The ionic liquid, 1-isobutyl-3-methylimidazolium bis(trifluoromethane-sulfonyl)imide, improves stability of the antibody. The sensor displays good repeatability (RSD=1.2%), sensitive electrochemical response to microcystin-LR in the range of 1.0×10-16–8.0×10−15M and detection limit of 3.7×10−17M (S/N=3). The peak current change of the sensor after and before incubation with 2.0×10−15M of microcystin-LR can retain 95% over a 20-weeks storage period. Proposed method presents remarkable improvement of sensitivity, repeatability and stability when compared to present microcystin-LR sensors. It has been successfully applied to the microcystin-LR determination in water samples with a spiked recovery in the range of 96.3–105.8%.

Theoretical Spectroscopic Study of the Conjugate Microcystin-LR-Europium Cryptate

In this work, theoretical tools were used to study spectroscopic properties of the conjugate microcystin-LR-europium cryptate. The Sparkle/AM1 model was applied to predict the geometry of the system and the INDO/S-CIS model was used to calculate the excited state energies. Based on the Judd-Ofelt theory, the intensity parameters were predicted and a theoretical model based on the theory of the 4f-4f transitions was applied to calculate energy transfer and backtransfer rates, radiative and non-radiative decay rates, quantum efficiency and quantum yield. A detailed study of the luminescent properties of the conjugate Microcystin-LR-europium cryptate was carried out. The results show that the theoretical quantum yield of luminescence of 23% is in good agreement with the experimental value published. This fact suggests that this theoretical protocol can be used to design new systems in order to improve their luminescence properties. The results suggest that this luminescent system may be a good conjugate for using in assay ELISA for detection by luminescence of the Microcystin-LR in water.

Flow injection chemiluminescence immunoassay of microcystin-LR by using PEI-modified magnetic beads as capturer and HRP-functionalized silica nanoparticles as signal amplifier

A rapid sandwiched immunoassay of microcystin-LR (MC-LR) in water is proposed with flow injection chemiluminescence detection. The magnetic beads (MBs) were first modified with polyethyleneimine (PEI) by acylamide bond between the carboxyl group on the surface of MBs and the primary amine group in PEI, followed by immobilizing of anti-MC-LR (Ab1) onto PEI with glutaraldehyde as linkage. The resulting Ab1 modified MBs captured the target MC-LR in water, reacted with the horseradish peroxidase and anti-MC-LR co-immobilized silica nanoparticles, and were detected with flow injection chemiluminescence. When using PEI/MBs as the carrier of anti-MC-LR, the CL signal was greatly enhanced up to 9-fold compared to that using MBs without PEI modification. The CL signal was further amplified 13-fold when Si/Ab2 was used as the signal probe. Under the optimal conditions, the present immunoassay exhibited a wide quantitative range from 0.02 to 200 μg L(-1) with a detection limit of 0.006 μg L(-1), which was much lower than the WHO provisional guideline limit of 1.0 μg L(-1) for MC-LR in drinking water. The relative standard deviation was 4.8% and the recoveries for the spiked samples ranged from 84% to 115%, which indicated acceptable precision and accuracy for MC-LR. The present method is easier to perform and less time-consuming (the entire analysis process lasted about 40 minutes) and has been applied to the detection of MC-LR in different water samples successfully.

Determination of microcystin-LR in water by a label-free aptamer based electrochemical impedance biosensor

In this study, an electrochemical impedance biosensor for cyanobacterial toxin microcystin-LR (MC-LR) detection has been developed. MC-LR aptamers were immobilized on the gold electrode through Au–S interaction, in the presence of target (MC-LR); the binding of MC-LR and aptamers probe led to a complex formation change on the electrode surface and resulted in the impedance decreasing. The decrease rate had a linear relationship with logarithm of the MC-LR concentration in the range of 1.0×10−7–5.0×10−11mol/L, with a detection limit of 1.8×10−11mol/L. The sensor has good selectivity and stability, it has been applied to detect MC-LR in three kinds of real water samples with satisfying results.

Degradation of microcystin-LR in water by glow discharge plasma oxidation at the gas–solution interface and its safety evaluation

Microcystin-LR (MC-LR) is one of the most commonly found microcystins (MCs) in fresh water and it poses danger to human health due to its potential hepatotoxicity. In the present study, we employed a novel method by using discharge plasma taking place at the gas–solution interface in gas atmosphere to degrade MC-LR in aqueous solution. The initial degradation rate of MC-LR was fastest under acidic conditions (5.41 ± 0.17 × 10−3 mM min−1 at pH 3.04) and decreased to 2.22 ± 0.11 × 10−3 mM min−1 and 0.912 ± 0.02 × 10−3 mM min−1 at pH 4.99 and 7.02, respectively. The effects of total soluble nitrogen (TN), total soluble phosphorus (TP) and natural organic matter (NOM) on the degradation efficiency were studied. The degradation rate was remarkably affected by TP and TN. Mass spectrometry was applied to identify the products of the reactions. Major degradation pathways are proposed according to the results of liquid chromatography/mass spectrometry (LC/MS) results. It suggests that the degradation of MC-LR is initiated via the attack of hydroxyl radicals on the conjugated carbon double bonds of Adda and on the benzene ring of Adda. Finally, the toxicity of intermediates or end-products from MC-LR degraded by this method was assessed using Caenorhabditis elegans. Our findings demonstrates that discharge plasma oxidation is a promising technology for degradation and removal of MC-LR and it may lead us to a new route to efficient treatment of other cyanotoxins from aqueous solutions.

Selective Determination of Microcystin-LR Based on Proteasomal Trypsin-Like Activity Inhibition

A sensitive and selective method was developed for the determination of microcystin-LR (MC-LR) based on proteasomal trypsin-like activity inhibition. Under the optimized conditions, the detection limit for MC-LR was 0.18μg/L, The linearity range was 0.2-2 μg/L，and the average recovery for MC-LR in tap water was 128%. Microcystin-YR (MC-YR) and Microcystin-RR (MC-RR) have no inhibiting effect on the proteasomal trypsin-like activity in the concentration ranged between 0.1-100 nmol/L. This method could be applied for the selective, high-throughput, and rapid determination of MC-LR in waters.