Liquid chromatography/negative electrospray ionization ion trap MS2 mass spectrometry application for the determination of microcystins occurrence in Southern Portugal water reservoirs

The occurrence and human health risk assessment of microcystins in diverse food matrixes during production

Globally, the presence of cyanotoxins in water supplies and food has been widely investigated for over a decade. Cyanotoxins are harmful metabolites produced by toxic cyanobacterial genera. These metabolites belong to diverse chemical classes, with a variety of physicochemical properties, chemical structures, and toxic activities. The present study seeks to investigate the occurrence of cyanotoxins in water supplies destined for food processing and assess the human health risk from exposure to cyanotoxins. To achieve this, a simple, sensitive, and reliable analytical method was developed for the determination of microcystins (MC-RR, MC-LR, MC-YR) in process water, raw maize meal, and cooked maize (porridge) at ppb (parts per billion) levels. These compounds were extracted using Solid Phase Extraction (SPE) with optimized parameters; thereafter, Liquid Chromatography-tandem Mass Spectrometry (LC-MS/MS) was used for the rapid determination of the analytes selected for the present study. The method developed was applied to samples collected from the meal grinding station located in Mawoni village in South Africa; and was able to detect and quantify all the target cyanotoxins. MC-LR, MC-YR and MC-RR were detected at concentrations ranging from 10 to 11.2 μg/L, 9.1-9.4 μg/L, and 2.3-3.5 μg/L, in water samples, respectively. However, MC-YR was not detected in ground water sample. Moreover, MC-LR, MC-YR, and MC-RR concentrations in maize and porridge samples ranged between 9.2 and 11.2, 5.5-8.6, and 6.3-9.3 μg/kg dry weight, respectively. The hazard quotient index (HQi) levels found in the present study ranged between 2.2 - 8.4 and 0.11-8.9 for adults and children, respectively, representing potential risks to human health. Findings from LC-MS/MS reveal that cyanotoxins can be transferred from water to food during food processing using cyanotoxins contaminated water. Furthermore, the methods developed can be used by environmental and health agencies to strengthen the monitoring of cyanotoxins in water and food.

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.

Microcystin in source water: pollution characteristics and human health risk assessment

Frequent cyanobacterial blooms in eutrophic waters produce a variety of toxins such as microcystins (MCs), which are seriously harmful to waterbodies and human health. The spatiotemporal distribution characteristics of the MC-LR concentration in drinking water sources in seven river basins in China were investigated in this study. The removal rate of MC-LR in the purification process of water treatment plants and the human health risk of MC-LR in drinking water are also discussed. The results show that the detection frequency of MC-LR in source water was 55.46% and its concentration ranged from 0.06 × 10-3 to 52 × 10-3 μg L-1 (mean of 12.47 × 10-3 μg L-1), which are both below China's drinking water quality standard for algal toxins. The MC-LR concentration in lakes and reservoirs was higher than that in rivers, and exhibited an obvious spatiotemporal variation. The mean removal rate of MC-LR varied with river basin, and was also slightly higher for the advanced water treatment process (97.46%) in comparison to that of the conventional process (96.74%). The concentration of MC-LR in 8.26% of treated water samples was higher than that of raw water, thus indicating that MC-LR may be further released during the purification process. The risk index of MC-LR in treated water samples ranged from 2.29 × 10-3 to 8.40 × 10-3 (mean of 4.73 × 10-3), which corresponded to an extremely low level of risk. However, intensive monitoring should still be carried out in some high-concentration watersheds during the summer to ensure the safety of public drinking water.

High Levels of Anabaenopeptins Detected in a Cyanobacteria Bloom from N.E. Spanish Sau-Susqueda-El Pasteral Reservoirs System by LC-HRMS

The appearance of a bloom of cyanobacteria in the Sau-Susqueda-El Pasteral system (River Ter, NE Spain) in the autumn of 2015 has been the most recent episode of extensive bloom detected in Catalonia. This system is devoted mainly to urban supply, regulation of the river, irrigation and production of hydroelectric energy. In fact, it is one of the main supply systems for the metropolitan area of cities such as Barcelona and Girona. An assessment and management plan was implemented in order to minimize the risk associated to cyanobacteria. The reservoir was confined and periodic sampling was carried out. Low and high toxicity was detected by cell bioassays with human cell lines. Additionally, analysis studies were performed by enzyme-linked immunosorbent assay (ELISA) and liquid chromatography–high resolution mass spectrometry (LC–HRMS). A microcystin target analysis and suspect screening of microcystins, nodularins, cylindrosperpmopsin and related cyanobacterial peptides by LC–HRMS were applied. The results for the analysis of microcystins were negative (<0.3 μg/L) in all the surface samples. Only traces of microcystin-LR, -RR and -dmRR were detected by LC–HRMS in a few ng/L from both fractions, aqueous and sestonic. In contrast, different anabaenopeptins and oscillamide Y at unusually high concentrations (µg-mg/L) were observed. To our knowledge, no previous studies have detected these bioactive peptides at such high levels. The reliable identification of these cyanobacterial peptides was achieved by HRMS. Although recently these peptides are detected frequently worldwide, these bioactive compounds have received little attention. Therefore, more studies on these substances are recommended, especially on their toxicity, health risk and presence in water resources.

Development of a validated direct injection-liquid chromatographic tandem mass spectrometric method under negative electrospray ionization for quantitation of nine microcystins and nodularin-R in lake water

Microcystins (MCs) are cyclic heptapeptide toxins produced by various cyanobacterial genera that are toxic to both animals and humans. In this study, a novel strategy was proposed for the quantitation of nine MCs and Nodularin-R (NOD) in lake water using UHPLC-MS/MS under negative ionization mode, in which only centrifugation was employed during sample preparation. As a result, limits of quantification (LOQ) ranging from 0.05 to 0.1 μg/L for all studied compounds were obtained in water samples, which were lower than the results obtained using positive ionization mode. Additionally, validation was performed by spiking three different levels of MCs at 0.05 or 0.1, 0.5, 1.0 μg/L (n = 6). Recoveries ranged from 88.6% to 101.8%, and intraday and interday variability were lower than 12% and 14%, respectively, for all targeted compounds. Furthermore, the proposed method was applied to investigate microcystins contamination in fifty lake water samples collected in different regions in China. As a result, MC-LR, MC-RR, MC-YR, MC-WR, MC-LW, MC-LA, MC-LY, and MC-HilR were detected in lake water samples at trace level ranging from 0.06 to 0.37 μg/L. The obtained results indicated that it was necessary to monitor the presence of MCs in lake water, especially during regular cyanobacterial blooms during warmer months.

Detected cyanotoxins by UHPLC MS/MS technique in tropical reservoirs of northeastern Colombia

This study focused on the detection and quantification of eight cyanotoxins in water samples in three reservoirs located in the eastern department of Antioquia, Colombia. The reservoirs are a source of water supply and hydroelectricity, and also generate economic activities in fishing and recreation. Between May 2015 and October 2016, 8 samplings were carried out at times of high temperatures, which ranged from 20 to 29 °C. This period was selected because of a significant or strong El Niño phenomenon, according to the World Meteorological Organization. For the study, 270 integrated samples were taken from the photic zone (PZ) and the surface of the reservoirs, at each of the three sampling points. The samples were analyzed by the analytical technique of ultra-high-performance liquid chromatography coupled to triple quadrupole mass spectrometry (UHPLC MS/MS). The quantification performed for six microcystins (MCs), a nodularin (NOD) and a cylindrospermopsin (CYN), showed positive results well above 1 μg L^-1. In the water of the Abreo Malpaso and Peñol reservoirs, microcystin-LR (MC-LR), microcystin-YR (MC-YR) and [D-Asp³,(E)-Dhb⁷]- microcystin-RR toxins were detected at levels of considerable concentration, especially between May and September 2015, when there was no rainfall in this region. In the Playas reservoir, positive results for [D-Asp³,(E)-Dhb⁷]-MC-RR were detected from May to November 2015, with the highest concentrations being reached in dry season. The temperatures reached and the changes in climatic conditions witnessed during the monitoring period of this study were important factors in the production of cyanotoxins. This was evidenced in this work by the high concentrations of detected cyanotoxins and their absence in periods of rain, as happened from the second quarter of 2016 until the end of the study in October. This is the first study of the detection and quantification of cyanotoxins in tropical reservoirs of northeastern Colombia using the UHPLC MS/MS analytical technique, which allowed the toxins to be unequivocally detected and confirmed. A method was developed and validated, proving to be sensitive, reproducible and accurate. For each of the toxins (microcystin-LR (MC-LR), microcystin-RR (MC-RR), microcystin-YR (MC-YR), [D-Asp³,(E)-Dhb⁷]- microcystin-RR, microcystin-LW (MC-LW), microcystin-LF (MC-LF), nodularin (NOD) and cylindrospermopsina (CYN)) the correlation coefficients (R²) were in a range between 0.9907 and 0.9999. Verification of the accuracy of the method was performed through a calibration curve in solvent. The recovery percentages of the accuracy and precision tests of the method for low level, medium level and high level were in a range between 64% and 115% for all the cyanotoxins. The validation of the cyanotoxin method shows that it is possible to detect them individually in natural water with a quantification limit (LOQ) of approximately 0.05 μg L^-1.

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.

Microcystin-RR: Occurrence, content in water and food and toxicological studies. A review

Microcystins (MCs) are hepatotoxins, produced by various species of cyanobacteria, whose occurrence is increasing worldwide owing to climate change and anthropogenic activities. More than 100 variants have been reported, and among them MC-LR is the most extensively studied, but there are other MC congeners that deserve to be investigated. The need for data to characterize the toxicological profile of MC variants other than MC-LR has been identified in order to improve risk assessment in humans and wildlife. Accordingly, the aim of this study was to evaluate the information available in the scientific literature dealing with MC-RR, as this congener is the second most common cyanotoxin in the environment. The review focuses on aspects such as occurrence in water and food, and toxicity studies both in vitro and in vivo. It reveals that, although MC-RR is a real hazard with a high exposure potential in some countries, little is known yet about its specific toxicological properties that differ from those of MC-LR, and important aspects such as genotoxicity and chronic effects have not yet been sufficiently addressed.

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

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

Analysis of individual and total microcystins in surface water by on-line preconcentration and desalting coupled to liquid chromatography tandem mass spectrometry

A fast and high-throughput method is proposed for the determination of total microcystins (ΣMC) in environmental surface waters. After a 1-h Lemieux-von Rudloff oxidation step to yield the 2-methyl-3-methoxy-4-phenylbutyric acid (MMPB) moiety, samples were quenched, filtered, and directly analyzed. This was achieved via solid phase extraction (SPE) coupled on-line to ultra-high performance liquid chromatography electrospray ionization triple stage quadrupole mass spectrometry. The choice of on-line SPE settings was conducted using experimental designs. Given the matrix complexity of oxidation extracts, the on-line desalting step was found to be a critical parameter to ensure suitable method robustness. The on-line sample loading volume was 5mL, and the wash volume applied for on-line desalting was 3mL. Instrumental analysis was performed in just 8min. The method limit of quantification was 0.5ngL^-1 ΣMC (i.e. 2000 times lower than the current World Health Organization - WHO drinking water guideline). Excellent determination coefficients were observed for matrix-free and matrix-based calibration curves alike, and the linearity range tested spanned∼4 orders of magnitude. Accuracy and intermediate precision did not depend on the spike level and proved satisfactory (in the range of 93-110% and 3-6%, respectively). A thorough assessment of instrumental matrix effects was conducted by comparing standard additions curves in several lake and river oxidation extracts with the matrix-free reference. Regardless of the internal standard used (4-PB or D3-MMPB), instrumental matrix effects were efficiently compensated. The matrix effect that may occur at the earlier sample preparation stage was evaluated separately. While the oxidation step was generally not complete (yield ∼65%), the conversion rates of MCs into MMPB remained within a consistent range of values regardless of matrix type. No significant back-pressure was observed upon consecutive injections of oxidation-based samples, while the instrumental sensitivity remained unaffected. The herein described method could therefore be eligible for future large-scale monitoring surveys. The method was applied to a selection of surface water samples (n=30) collected across the province of Québec, Canada, and the results were compared to those achieved by an individual variant analysis of 8 MC congeners and a commercial ELISA kit.

Rapid Microcystin Determination Using a Paper Spray Ionization Method with a Time-of-Flight Mass Spectrometry System

The eutrophication of surface water sources and climate changes have resulted in an annual explosion of cyanobacterial blooms in many irrigating and drinking water resources. To decrease health risks to the public, a rapid real time method for the synchronous determination of two usually harmful microcystins (MC-RR and MC-LR) in environmental water samples was built by employing a paper spray ionization method coupled with a time-of-flight mass spectrometer system. With this approach, direct analysis of microcystin mixtures without sample preparation has been achieved. Rapid detection was performed, simulating the release process of microcystins in reservoir water samples, and the routine detection frequency was every three minutes. The identification time of microcystins was reduced from several hours to a few minutes. The limit of detection is 1 μg/L, and the limit of quantitation is 3 μg/L. This method displays the ability for carrying out rapid, direct, and high-throughput experiments for determination of microcystins, and it would be of significant interest for environmental and food safety applications.

An integrated strategy for rapid and accurate determination of free and cell-bound microcystins and related peptides in natural blooms by liquid chromatography-electrospray-high resolution mass spectrometry and matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry using both positive and negative ionization modes

An integrated high resolution mass spectrometry (HRMS) strategy has been developed for rapid and accurate determination of free and cell-bound microcystins (MCs) and related peptides in water blooms. The natural samples (water and algae) were filtered for independent analysis of aqueous and sestonic fractions. These fractions were analyzed by MALDI-TOF/TOF-MS and ESI-Orbitrap-HCD-MS. MALDI, ESI and the study of fragmentation sequences have been provided crucial structural information. The potential of combined positive and negative ionization modes, full scan and fragmentation acquisition modes (TOF/TOF and HCD) by HRMS and high resolution and accurate mass was investigated in order to allow unequivocal determination of MCs. Besides, a reliable quantitation has been possible by HRMS. This composition helped to decrease the probability of false positives and negatives, as alternative to commonly used LC-ESI-MS/MS methods. The analysis was non-target, therefore covered the possibility to analyze all MC analogs concurrently without any pre-selection of target MC. Furthermore, archived data was subjected to retrospective "post-targeted" analysis and a screening of other potential toxins and related peptides as anabaenopeptins in the samples was done. Finally, the MS protocol and identification tools suggested were applied to the analysis of characteristic water blooms from Spanish reservoirs.