Determination of dissolved domoic acid in seawater with reversed-phase extraction disks and rapid resolution liquid chromatography tandem mass spectrometry with head-column trapping

Diversity and toxicity of the planktonic diatom genus Pseudo-nitzschia from coastal and offshore waters of the Southeast Pacific, including Pseudo-nitzschia dampieri sp. nov

To expand knowledge of Pseudo-nitzschia species in the Southeast Pacific, we isolated specimens from coastal waters of central Chile (36°S-30°S), the Gulf of Corcovado, and the oceanic Robinson Crusoe Island (700 km offshore) and grew them into monoclonal strains. A total of 123 Pseudo-nitzschia strains were identified to 11 species based on sequencing of the ITS region of the nuclear rDNA and on ultrastructural and morphometric analyses of the frustule in selected representatives of each clade: P. australis, P. bucculenta, P. cf. chiniana, P. cf. decipiens, P. fraudulenta, P. hasleana, P. multistriata, P. plurisecta, P. cf. sabit, the new species P. dampieri sp. nov., and one undescribed species. Partial 18S and 28S rDNA sequences, including the hypervariable V4 and D1-D3 regions used for barcoding, were gathered from representative strains of each species to facilitate future metabarcoding studies. Results showed different levels of genetic, and at times ultrastructural, diversity among the above-mentioned entities, suggesting morphological variants (P. bucculenta), rapidly radiating complexes with ill-defined species boundaries (P. cf. decipiens and P. cf. sabit), and the presence of new species (P. dampieri sp. nov., Pseudo-nitzschia sp. 1, and probably P. cf. chiniana). Domoic acid (DA) was detected in 18 out of 82 strains tested, including those of P. australis, P. plurisecta, and P. multistriata. Toxicity varied among species mostly corresponding to expectations from previous reports, with the prominent exception of P. fraudulenta; DA was not detected in any of its 10 strains tested. In conclusion, a high diversity of Pseudo-nitzschia exists in Chilean waters, particularly offshore.

Measuring Marine Biotoxins in a Hypersaline Coastal Lagoon

Marine biotoxins have posed a persistent problem along various coasts for many years. Coastal lagoons are ecosystems prone to phytoplankton blooms when altered by eutrophication. The Mar Menor is the largest hypersaline coastal lagoon in Europe. Sixteen marine toxins, including lipophilic toxins, yessotoxins, and domoic acid (DA), in seawater samples from the Mar Menor coastal lagoon were measured in one year. Only DA was detected in the range of 44.9-173.8 ng L-1. Environmental stressors and mechanisms controlling the presence of DA in the lagoon are discussed. As an enrichment and clean-up method, we employed solid phase extraction to filter and acidify 75 mL of the sample, followed by pre-concentration through a C18 SPE cartridge. The analytes were recovered in aqueous solutions and directly injected into the liquid chromatography system (LC-MS), which was equipped with a C18 column. The system operated in gradient mode, and we used tandem mass spectrometry (MS/MS) with a triple quadrupole (QqQ) in the multiple reaction monitoring mode (MRM) for analysis. The absence of matrix effects was checked and the limits of detection for most toxins were low, ranging from 0.05 to 91.2 ng L-1, depending on the compound. To validate the measurements, we performed recovery studies, falling in the range of 74-122%, with an intraday precision below 14.9% RSD.

[Determination of domoic acid in seawater by solid phase extraction-liquid chromatography-tandem mass spectrometry]

Domoic acid (DA) can poison or even be fatal to marine mammals, and poses a potential risk to human health via transmission through the food chain. The level of DA in seawater will affect the safety of seafood. Therefore, a powerful method for the detection of DA in seawater, especially in the coastal mariculture zone, is needed. In order to identify different concentration levels of DA in real seawater, in this study, a method was established for the determination of trace DA in seawater by SPE-LC-MS/MS. First, the LC-MS/MS instrument and sample pretreatment conditions were optimized. Subsequently, DA was separated on a 5 TC-C18 (2) analytical column (150 mm×4.6 mm, 5 μm), and multiple reaction monitoring (MRM) was conducted in the positive electrospray ionization mode. For off-line SPE, the HLB cartridge could enrich DA in seawater. The best enrichment of DA was obtained after adding 0.32 mL formic acid to an 80.0 mL seawater sample. Four on-line SPE columns from Agilent, namely, 5 TC-C18(2) (12.5 mm×4.6 mm, 5 μm), Zorbax Eclipse Plus-C18 (12.5 mm×2.1 mm, 5 μm), Zorbax Eclipse XDB-C8 (12.5 mm×2.1 mm, 5 μm), and PLRP-S (12.5 mm×2.1 mm, 15-20 μm), were tested to determine their suitability to trap DA from seawater samples. The 5 TC-C18 (2) column offered the best retention ability and good peak shape of DA, and was selected as the on-line SPE column. Validation was then performed to assess the sensitivity, linearity, matrix effects (MEs), recoveries, and precisions of the proposed method. After simple treatment of the seawater samples by filtration and acidification, 0.6 mL of the seawater sample was injected directly for on-line SPE-LC-MS/MS. The linearity was good, and ranged from 10.0 to 500.0 ng/L (correlation coefficient R2=0.9992). The limit of detection (LOD) and limit of quantification (LOQ) of DA were 4.0 and 10.0 ng/L, respectively, with good recovery (≥81.0%) and precision (RSDs≤4.2%) at three spiked levels in the blank seawater samples. After the DA in the 80.0 mL seawater sample was enriched by off-line SPE, a 0.6 mL sample was injected for on-line SPE-LC-MS/MS. The DA in the spiked blank seawater sample showed a good linear relationship in the range of 0.3-50.0 ng/L (R2=0.9990). The LOD and LOQ were 0.1 and 0.3 ng/L, respectively. The recoveries of DA at low, medium, and high spiked levels in the blank seawater samples were all ≥69.2%, and the RSDs were ≤4.4%. The MEs of DA with both methods were 18.3% and 13.7%, respectively, indicating that the ME was mild enough to be negligible. In summary, the proposed method is simple, sensitive, robust, and powerful for the detection of DA in inshore and offshore seawater.

First Report of Domoic Acid Production from Pseudo-nitzschia multistriata in Paracas Bay (Peru)

The Peruvian sea is one of the most productive ecosystems in the world. Phytoplankton production provides food for fish, mammals, mollusks and birds. This trophic network is affected by the presence of toxic phytoplankton species. In July 2017, samples of phytoplankton were obtained from Paracas Bay, an important zone for scallop (Argopecten purpuratus) aquaculture in Peru. Morphological analysis revealed the presence of the genus Pseudo-nitzschia, which was isolated and cultivated in laboratory conditions. Subsequently, the monoclonal cultures were observed by scanning electron microscopy (SEM), and identified as P. multistriata, based on both the morphological characteristics, and internal transcribed spacers region (ITS2) sequence phylogenetic analysis. Toxin analysis using liquid chromatography (LC) with high-resolution mass spectrometry (HRMS) revealed the presence of domoic acid (DA) with an estimated amount of 0.004 to 0.010 pg cell⁻¹. This is the first report of DA from the coastal waters of Peru and its detection in P. multistriata indicates that it is a potential risk. Based on our results, routine monitoring of this genus should be considered in order to ensure public health.

Capacity of the potentially toxic diatoms Pseudo-nitzschia mannii and Pseudo-nitzschia hasleana to tolerate polycyclic aromatic hydrocarbons

This study investigates the effects of polycyclic aromatic hydrocarbons (PAHs) on two potentially toxic Pseudo-nitzschia hasleana and P. mannii, isolated from a PAH contaminated marine environment. Both species, maintained in non-axenic cultures, have been exposed during 144 h to increasing concentrations of a 15 PAHs mixture. Analysis of the domoic acid, showed very low concentrations. Dose-response curves for growth and photosynthesis inhibition were determined. Both species have maintained their growth until the end of incubation even at the highest concentration tested (120 µg l^-1), Nevertheless, P mannii showed faster growth and seemed to be more tolerant than P. hasleana. To reduce PAH toxicity, both species have enhanced their biovolume, with a higher increase for P. mannii relative to P hasleana. Both species were also capable of bio-concentrating PAHs and were able to degrade them probably in synergy with their associated bacteria. The highest biodegradation was observed for P. mannii, which could harbored more efficient hydrocarbon-degrading bacteria. This study provides the first evidence that PAHs can control the growth and physiology of potentially toxic diatoms. Future studies should investigate the bacterial community associated with Pseudo-nitzschia species, as responses to pollutants or to other environmental stressors could be strongly influence by associated bacteria.

Simple determination of six groups of lipophilic marine algal toxins in seawater by automated on-line solid phase extraction coupled to liquid chromatography-tandem mass spectrometry

Lipophilic marine algal toxins (LMATs) are highly toxic secondary metabolites produced by marine microalgae that pose a great threat to marine aquaculture organisms and human health. In this study, a novel and automated method for the simultaneous determination of six groups of LMATs in seawater was developed by on-line solid phase extraction (SPE) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Condition optimization and method validation were performed, and the recoveries of all 14 target LMATs featuring different properties ranged from 83.5% to 96.0%. The limits of detection of most target compounds were within ≤3.000 ng/L with good precision (relative standard deviation ≤ 12.1%) and linearity (R²≥0.9916). Compared with off-line SPE methods, the proposed on-line SPE method has better recovery, sensitivity, repeatability, and throughput; in addition, the volume of seawater sample necessary to conduct determinations is greatly reduced in the present method. Finally, the method was applied to determine LMATs in actual seawater samples collected from the Bohai and South Yellow Seas of China in summer, and okadaic acid and pectenotoxin-2 were detected in all seawater samples. The highest concentration of ∑LMATs (22.23 ng/L) occurred in the coastal mariculture area of Shandong Province. Therefore, routine monitoring of LMATs in seawater of the coastal mariculture zone is necessary to prevent shellfish contamination especially in summer, and the proposed on-line SPE-LC-MS/MS method is a powerful way for direct and automatic detection of various LMATs in coastal mariculture area.

Effects of nitrogen supply on Pseudo-nitzschia calliantha and Pseudo-nitzschia cf. seriata: field and laboratory experiments

The effects of inorganic and organic nitrogen supply on the growth and domoic acid (DA) production of Pseudo-nitzschia cf. seriata and Pseudo-nitzschia calliantha from Bizerte Lagoon (SW Mediterranean Sea) were studied during field and laboratory experiments. Nitrogen enrichments (40 µM NO3 (-); 10 µM NH4 (+); 20 µM CH4N2O) and a control, with no added N, were carried out in separate carboys with seawater collected from Bizerte Lagoon. In the field experiments, all N-enrichments resulted in significant increases in chlorophyll a concentration, and maintained exponential growth until the end of the experiment. The initial diatom community was dominated by a bloom of P. cf. seriata (9.3 × 10(5) cells l(-1)). After 6 days of incubation, the abundance of P. cf. seriata was greatest in the urea addition (1.52 × 10(6) cells l(-1)), compared to the ammonium treatment (0.47 × 10(6) cells l(-1)), nitrate treatment (0.70 × 10(6) cells l(-1)) and control (0.36 × 10(6) cells l(-1)). The specific growth rates, calculated from increases in chlorophyll a and cell abundance, were statistically different across all treatments, with the highest in the urea and nitrate additions. Similar results were obtained from the laboratory experiments. These were carried out with P. calliantha isolated from Bizerte Lagoon and grown in f/2 medium enriched with 40 µM nitrate, 10 µM ammonium and 20 µM urea. The exponential growth rate was significantly faster for the cells cultured with urea (1.50 d(-1)) compared to the nitrate (0.90 d(-1)) and ammonium (0.80 d(-1)) treatments and the control (0.40 d(-1)). Analysis of DA, performed at the beginning and the end of the both experiments in all treatments, revealed very low concentrations (below the limit of quantification, 0.02- 1.310(-7) pg cell(-1), respectively).The field and laboratory experiments demonstrate that P.cf. seriata and P. calliantha are able to grow efficiently on the three forms of N, but with a preference for urea.

Multiplex biotoxin surface plasmon resonance method for marine biotoxins in algal and seawater samples

A multiplex surface plasmon resonance (SPR) biosensor method for the detection of paralytic shellfish poisoning (PSP) toxins, okadaic acid (and analogues) and domoic acid was developed. This method was compared to enzyme-linked immunosorbent assay (ELISA) methods. Seawater samples (n=256) from around Europe were collected by the consortia of an EU project MIcroarrays for the Detection of Toxic Algae (MIDTAL) and evaluated using each method. A simple sample preparation procedure was developed which involved lysing and releasing the toxins from the algal cells with glass beads followed by centrifugation and filtering the extract before testing for marine biotoxins by both multi-SPR and ELISA. Method detection limits based on IC20 values for PSP, okadaic acid and domoic acid toxins were 0.82, 0.36 and 1.66 ng/ml, respectively, for the prototype multiplex SPR biosensor. Evaluation by SPR for seawater samples has shown that 47, 59 and 61 % of total seawater samples tested positive (result greater than the IC20) for PSP, okadaic acid (and analogues) and domoic acid toxins, respectively. Toxic samples were received mainly from Spain and Ireland. This work has demonstrated the potential of multiplex analysis for marine biotoxins in algal and seawater samples with results available for 24 samples within a 7 h period for three groups of key marine biotoxins. Multiplex immunological methods could therefore be used as early warning monitoring tools for a variety of marine biotoxins in seawater samples.

Management of domoic acid monitoring in shellfish from the Catalan coast

Monitoring of amnesic shellfish poisoning (ASP) toxins in shellfish from the Catalan coast started in 2001. No ASP toxins were detected in any of the analyses performed before 2008. On 22 January 2008, domoic acid (DA) was detected in Donax trunculus (0.5 mg kg(-1)) and confirmed by rapid resolution liquid chromatography-tandem mass spectrometry (0.6 mg kg(-1)). A total of 974 shellfish samples were analyzed from January 2008 to December 2011, covering all the Catalan production areas and the most important marketed species. DA was detected in 23.8 % of the samples and was recorded every month in all areas and all species, except Ostrea edulis, although the percentage of samples with DA and DA content varied widely among samples. DA exceeded the regulatory level of 20 mg kg(-1) twice: in Callista chione sampled on February 2008 and in D. trunculus sampled on April 2010. DA content in Bolinus brandaris appeared constant and close to 4.5 mg kg(-1) for months in 2009. Mytilus galloprovincialis, Crassostrea gigas, and Ruditapes sp. presented very low concentrations of DA in the Ebro Delta bays, despite 113 alert situations according to Pseudo-nitzschia spp. abundances and the high number of shellfish samples analyzed. The origin of DA in Catalan shellfish remains unknown.

Domoic acid improves the competitive ability of Pseudo-nitzschia delicatissima against the diatom Skeletonema marinoi

Because domoic acid, a neurotoxic secondary metabolite produced by marine diatoms in the genus Pseudo-nitzschia, is hypothesized to be part of a high affinity iron uptake system, we investigated whether domoic acid could improve the competitive ability of Pseudo-nitzschia delicatissima, and whether the availability of iron changed the outcome of competition experiments. We found that domoic acid had a slight negative effect on growth of the diatom Skeletonema marinoi when it was grown in monocultures. However, when S. marinoi was cultured with P. delicatissima the presence of domoic acid resulted in a reduction of S. marinoi cells by up to 38% and an increase in P. delicatissima cell numbers by up to 17% under iron replete conditions. Similar effects were not observed in low iron treatments. Domoic acid was not taken up by P. delicatissima cells. Overall, our results indicate that domoic acid can improve the competitive ability of Pseudo-nitzschia spp. and that iron is likely to be involved. This study provides an unusual example of indirect inhibition of competitor growth mediated by a secondary metabolite.

Optimization of solid-phase extraction and liquid chromatography-tandem mass spectrometry for the determination of domoic acid in seawater, phytoplankton, and mammalian fluids and tissues

We previously reported a solid-phase extraction (SPE) method for determination of the neurotoxin domoic acid (DA) in both seawater and phytoplankton by liquid chromatography-tandem mass spectrometry (LC-MS/MS) with the purpose of sample desalting without DA pre-concentration. In the present study, we optimized the SPE procedure with seawater and phytoplankton samples directly acidified with aqueous formic acid without addition of organic solvents, which allowed sample desalting and also 20-fold pre-concentration of DA in seawater and phytoplankton samples. In order to reduce MS contamination, a diverter valve was installed between LC and MS to send the LC eluant to waste, except for the 6-min elution window bracketing the DA retention time, which was sent to the MS. Reduction of the MS turbo gas temperature also helped to maintain the long-term stability of MS signal. Recoveries exceeded 90% for the DA-negative seawater and the DA-positive cultured phytoplankton samples spiked with DA. The SPE method for DA extraction and sample clean-up in seawater was extended to mammalian fluids and tissues with modification in order to accommodate the fluid samples with limited available volumes and the tissue extracts in aqueous methanol. Recoveries of DA from DA-exposed laboratory mammalian samples (amniotic fluid, cerebrospinal fluid, plasma, placenta, and brain) were above 85%. Recoveries of DA from samples (urine, feces, intestinal contents, and gastric contents) collected from field stranded marine mammals showed large variations and were affected by the sample status. The optimized SPE-LC-MS method allows determination of DA at trace levels (low pg mL(-1)) in seawater with/without the presence of phytoplankton. The application of SPE clean-up to mammalian fluids and tissue extracts greatly reduced the LC column degradation and MS contamination, which allowed routine screening of marine mammalian samples for confirmation of DA exposure and determination of fluid and tissue DA concentrations in experimental laboratory animals.

Analytical approaches for an important shellfish poisoning agent: domoic Acid

Domoic acid (DA), a neurotoxic amino acid produced by some strains of phytoplankton, is responsible for the human toxic syndrome amnesic shellfish poisoning. This exocitotoxin results in neuronal degeneration and necrosis in specific regions of the hippocampus. Because DA accumulates mostly in shellfish, causing outbreaks in different countries, screening for DA has been carried out with various assays. Although bioassays and immunoassays have been developed, several liquid chromatographic methods for the determination of DA in different matrices such as shellfish, algae, or seawater have been reported. Additionally, other alternative methods such as capillary electrophoresis and capillary electrochromatography have been described. This paper summaries the toxicology, the chemistry, and the developed determination methods of DA.