Trace determination of multiple hydrophilic cyanotoxins in freshwater by off- and on-line solid phase extraction coupled to liquid chromatography-tandem mass spectrometry

High-resolution mass spectrometry-based suspect and nontarget screening of natural toxins in foodstuffs and risk assessment of dietary exposure

Daily dietary intake inevitably exposes individuals to various natural toxins, which may pose potential health threats. Focusing only on specific toxins could underestimate dietary risks. Therefore, we have developed a suspect and nontarget method based on ultrahigh-performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) to screen both known and unknown natural toxins in various foodstuffs. An in-house database containing 2952 natural toxins including fungal toxins, phytotoxins, animal toxins and cyanotoxins was established, facilitating suspect screening. Predicted retention time and mass spectrometry data were employed to enhance the confidence levels. Subsequently, Nontarget screening method was conducted based on molecular network analysis, annotating the edges and nodes through modified types and fragmentation characteristics. Finally, we analyzed 102 foodstuff samples and identified a total of 90 natural toxins, including mycotoxins and phytotoxins, with 65 identified by suspect screening and 25 by nontarget screening. Based on measured concentrations, the daily per capita dietary intake of total natural toxins was estimated, it was below risk doses for natural toxins with available reference values. Overall, this work established a novel method for the comprehensive identification of natural toxins in foodstuffs and emphasized the importance of dietary risk assessment for natural toxins.

Investigating the chemical space coverage of multiple chromatographic and ionization methods using non-targeted analysis on surface and drinking water collected using passive sampling

Multiple non-targeted analysis tools were used to look for a broad range of possible chemical contaminants present in surface and drinking water using liquid chromatography separation and high-resolution mass spectrometry detection, including both quadrupole time of flight (Q-ToF) and Orbitrap instruments. Two chromatographic techniques were evaluated on an LC-Q-ToF with electrospray ionization in both positive and negative modes: (1) the traditionally used reverse phase C18 and (2) the hydrophilic interaction liquid chromatography (HILIC) aimed to capture more polar contaminants that may be present in water. Multiple ionization modes were evaluated with an LC-Orbitrap, including electrospray (ESI) and atmospheric pressure chemical ionization (APCI), also in both positive and negative modes. A suspect screening library of over 1300 possible environmental contaminants, including pesticides, pharmaceuticals, personal care products, illicit drugs/drugs of abuse, and various anthropogenic markers was made with experimentally collected data with the LC-Q-ToF with both column types, with 227 chemicals being retained by the HILIC column. The non-targeted methods using multiple chromatographic and ionization modes were applied to environmental water samples collected with polar organic chemical integrative samplers (POCIS), including surface water upstream and downstream from wastewater effluent discharge, and the downstream drinking water intake and treated drinking water for three distinct sampling events. For the LC-Q-ToF, 442 chemical features were detected on the C18 column and 91 with the HILIC column in the POCIS extracts, while 556 features were found on the Orbitrap workflow by ESI and 131 features detected by APCI. Over 100 chemicals were tentatively identified by suspect screening and database searching. The comprehensive and systematic evaluation of these methods serve as a step in characterizing the chemical space covered when utilizing different chromatography and ionization methods, or different instrument workflows on complex environmental mixtures.

Elevated pCO2 may increase the edible safety risk of clams exposed to toxic Alexandrium spp

Toxic harmful algal blooms (HABs) have received increasing attention owing to their threat to the health of aquatic life and seafood consumers. This study evaluated the impacts of elevated atmospheric partial pressure of CO2 (pCO2) on the production of paralytic shellfish toxins (PSTs) in different Alexandrium spp. strains, together with its further effects on the bioaccumulation/elimination dynamics of PSTs in bivalves contaminated with PSTs from toxic dinoflagellates. Our results showed that elevated pCO2 stimulated the growth of the two Alexandrium spp. (A. catenella and A. pacificum) isolated from the northern and southern coastal areas of China, respectively, and affected PST production including content and toxicity of the two strains differently. Further PSTs bioaccumulation/elimination in PSTs-contaminated Manila clam, Ruditapes philippinarum under high pCO2 also occurred. It is worth noting the biotransformation of neosaxitoxin (NEO) with high toxicity through trophic transfer with effect of elevated pCO2. When in microalgae cultured under the control (410 ppm) and elevated pCO2 conditions (495 and 850 ppm), the proportion of NEO in the PST content produced by A. catenella was reduced from 11.1 to 6.4 and 2.6 %, while the proportion of NEO in A. pacificum was increased from 3.1 to 3.6 and 4.7 %, respectively. NEO accounted for >50 % of total PST contents in clams, which were biotransformed via transfer from dinoflagellates and higher pCO2 enhanced this biotransformation leading to increased NEO accumulation. The negatively affected elimination of PSTs, especially NEO, in clams fed with A. catenella or A. pacificum, indicates that the detoxification of PSTs-contaminated clams may be more difficult under elevated pCO2. This study provides reference for developing models to assess the safety of bivalves under the co-stress of environmental change and toxic HABs, suggesting that ocean acidification may lead to the higher safety risk of Manila clams exposed to toxic HAB dinoflagellates.

Ultrasensitive fluorescence detection of gonyautoxins in seawater using a novel molecularly imprinted nanoprobe

Gonyautoxins (GTXs), a group of potent neurotoxins belonging to paralytic shellfish toxins (PSTs), are often associated with harmful algal blooms of toxic dinoflagellates in the sea and represent serious health and ecological concerns worldwide. In the study, a highly selective and sensitive fluorescence nanoprobe was constructed based on photoinduced electron transfer recognition mechanism to rapidly detect GTXs in seawater, using specific entrapment of molecularly imprinted polymers (MIPs) combined with fluorescence analyses. The green emissive fluorescein isothiocyanate was grafted in a silicate matrix as a signal transducer and fluorescence intensity of the nanoprobe with a core-shell structure exhibited a strong enhancement due to efficient analyte blockage in a short response time. Under optimal conditions, the developed MIPs nanoprobe presented an excellent analytical performance for spiked seawater samples including a recovery from 94.44 % to 98.23 %, a linear range between 0.018 nmol L-1 and 0.36 nmol L-1, as well as good accuracy. Furthermore, the method had extremely high sensitivity, with limit of detection obtained as 0.005 nmol L-1 for GTXs and GTX2/3. Finally, the nanoprobe was applied for the determination of GTXs in seven natural seawater samples with GTXs mixture (0.035-0.058 nmol L-1) or single GTX2/3 (0.033-0.050 nmol L-1), and the results agreed well with those of a UPLC-MS/MS method. The findings of our study suggest that the constructed MIPs-based fluorescence enhancement nanoprobe was suitable for rapid, selective and ultrasensitive detection of GTXs, particular GTX2/3, in natural seawater samples.

Freshwater Cyanobacterial Toxins, Cyanopeptides and Neurodegenerative Diseases

Cyanobacteria produce a wide range of structurally diverse cyanotoxins and bioactive cyanopeptides in freshwater, marine, and terrestrial ecosystems. The health significance of these metabolites, which include genotoxic- and neurotoxic agents, is confirmed by continued associations between the occurrence of animal and human acute toxic events and, in the long term, by associations between cyanobacteria and neurodegenerative diseases. Major mechanisms related to the neurotoxicity of cyanobacteria compounds include (1) blocking of key proteins and channels; (2) inhibition of essential enzymes in mammalian cells such as protein phosphatases and phosphoprotein phosphatases as well as new molecular targets such as toll-like receptors 4 and 8. One of the widely discussed implicated mechanisms includes a misincorporation of cyanobacterial non-proteogenic amino acids. Recent research provides evidence that non-proteinogenic amino acid BMAA produced by cyanobacteria have multiple effects on translation process and bypasses the proof-reading ability of the aminoacyl-tRNA-synthetase. Aberrant proteins generated by non-canonical translation may be a factor in neuronal death and neurodegeneration. We hypothesize that the production of cyanopeptides and non-canonical amino acids is a more general mechanism, leading to mistranslation, affecting protein homeostasis, and targeting mitochondria in eukaryotic cells. It can be evolutionarily ancient and initially developed to control phytoplankton communities during algal blooms. Outcompeting gut symbiotic microorganisms may lead to dysbiosis, increased gut permeability, a shift in blood-brain-barrier functionality, and eventually, mitochondrial dysfunction in high-energy demanding neurons. A better understanding of the interaction between cyanopeptides metabolism and the nervous system will be crucial to target or to prevent neurodegenerative diseases.

A New Perspective: Revealing the Algicidal Properties of Bacillus subtilis to Alexandrium pacificum from Bacterial Communities and Toxins

Algicidal bacteria are important in the control of toxic dinoflagellate blooms, but studies on the environmental behavior of related algal toxins are still lacking. In this study, Bacillus subtilis S3 (S3) showed the highest algicidal activity against Alexandrium pacificum (Group IV) out of six Bacillus strains. When treated with 0.5% (v/v) S3 bacterial culture and sterile supernatant, the algicidal rates were 69.74% and 70.22% at 12 h, respectively, and algicidal substances secreted by S3 were considered the mechanism of algicidal effect. During the algicidal process, the rapid proliferation of Alteromonas sp. in the phycosphere of A. pacificum may have accelerated the algal death. Moreover, the algicidal development of S3 released large amounts of intracellular paralytic shellfish toxins (PSTs) into the water, as the extracellular PSTs increased by 187.88% and 231.47% at 12 h, compared with the treatment of bacterial culture and sterile supernatant at 0 h, respectively. Although the total amount of PSTs increased slightly, the total toxicity of the algal sample decreased as GTX1/4 was transformed by S3 into GTX2/3 and GTX5. These results more comprehensively reveal the complex relationship between algicidal bacteria and microalgae, providing a potential source of biological control for harmful algal blooms and toxins.