Progresses of the Influencing Factors and Detection Methods of Domoic Acid

Domoic acid (DA) is a neurotoxin mainly produced by Pseudo-nitzschia diatom, which belongs to the genera Rhomboida. It can combine with the receptors of glutamate of neurotransmitters, then affecting the normal nerve signal transmission of the organism and causing nervous system disorders. However, as a natural marine drug, DA can also be used for pest prevention and control. Although the distribution of DA in the world has already been reported in the previous reviews, the time and location of its first discovery and the specific information are not complete. Therefore, the review systematically summarizes the first reported situation of DA in various countries (including species, discovery time, and collection location). Furthermore, we update and analyze the factors affecting DA production, including phytoplankton species, growth stages, bacteria, nutrient availability, trace metals, and so on. These factors may indirectly affect the growth environment or directly affect the physiological activities of the cells, then affect the production of DA. Given that DA is widely distributed in the environment, we summarize the main technical methods for the determination of DA, such as bioassay, high-performance liquid chromatography (HPLC), enzyme-linked immunosorbent assay (ELISA), biosensor, and so on, as well as the advantages and disadvantages of each method used so far, which adds more new knowledge in the literature about DA until now. Finally, the DA research forecast and its industrial applications were prospected to prevent its harm and fully explore its potential value.

Current Trends and New Challenges in Marine Phycotoxins

Marine phycotoxins are a multiplicity of bioactive compounds which are produced by microalgae and bioaccumulate in the marine food web. Phycotoxins affect the ecosystem, pose a threat to human health, and have important economic effects on aquaculture and tourism worldwide. However, human health and food safety have been the primary concerns when considering the impacts of phycotoxins. Phycotoxins toxicity information, often used to set regulatory limits for these toxins in shellfish, lacks traceability of toxicity values highlighting the need for predefined toxicological criteria. Toxicity data together with adequate detection methods for monitoring procedures are crucial to protect human health. However, despite technological advances, there are still methodological uncertainties and high demand for universal phycotoxin detectors. This review focuses on these topics, including uncertainties of climate change, providing an overview of the current information as well as future perspectives.

Paralytic and Amnesic Shellfish Toxins Impacts on Seabirds, Analyses and Management

Marine biotoxins have been frequently implicated in morbidity and mortality events in numerous species of birds worldwide. Nevertheless, their effects on seabirds have often been overlooked and the associated ecological impact has not been extensively studied. On top of that, the number of published studies confirming by analyses the presence of marine biotoxins from harmful algal blooms (HABs) in seabirds, although having increased in recent years, is still quite low. This review compiles information on studies evidencing the impact of HAB toxins on marine birds, with a special focus on the effects of paralytic and amnesic shellfish toxins (PSTs and ASTs). It is mainly centered on studies in which the presence of PSTs and/or ASTs in seabird samples was demonstrated through analyses. The analytical techniques commonly employed, the tissues selected and the adjustments done in protocols for processing seabird matrixes are summarized. Other topics covered include the role of different vectors in the seabird intoxications, information on clinical signs in birds affected by PSTs and ASTs, and multifactorial causes which could aggravate the syndromes. Close collaboration between seabird experts and marine biotoxins researchers is needed to identify and report the potential involvement of HABs and their toxins in the mortality events. Future studies on the PSTs and ASTs pharmacodynamics, together with the establishment of lethal doses in various seabird species, are also necessary. These studies would aid in the selection of the target organs for toxins analyses and in the postmortem intoxication diagnoses.

Current Trends and Challenges for Rapid SMART Diagnostics at Point-of-Site Testing for Marine Toxins

In the past twenty years marine biotoxin analysis in routine regulatory monitoring has advanced significantly in Europe (EU) and other regions from the use of the mouse bioassay (MBA) towards the high-end analytical techniques such as high-performance liquid chromatography (HPLC) with tandem mass spectrometry (MS). Previously, acceptance of these advanced methods, in progressing away from the MBA, was hindered by a lack of commercial certified analytical standards for method development and validation. This has now been addressed whereby the availability of a wide range of analytical standards from several companies in the EU, North America and Asia has enhanced the development and validation of methods to the required regulatory standards. However, the cost of the high-end analytical equipment, lengthy procedures and the need for qualified personnel to perform analysis can still be a challenge for routine monitoring laboratories. In developing regions, aquaculture production is increasing and alternative inexpensive Sensitive, Measurable, Accurate and Real-Time (SMART) rapid point-of-site testing (POST) methods suitable for novice end users that can be validated and internationally accepted remain an objective for both regulators and the industry. The range of commercial testing kits on the market for marine toxin analysis remains limited and even more so those meeting the requirements for use in regulatory control. Individual assays include enzyme-linked immunosorbent assays (ELISA) and lateral flow membrane-based immunoassays (LFIA) for EU-regulated toxins, such as okadaic acid (OA) and dinophysistoxins (DTXs), saxitoxin (STX) and its analogues and domoic acid (DA) in the form of three separate tests offering varying costs and benefits for the industry. It can be observed from the literature that not only are developments and improvements ongoing for these assays, but there are also novel assays being developed using upcoming state-of-the-art biosensor technology. This review focuses on both currently available methods and recent advances in innovative methods for marine biotoxin testing and the end-user practicalities that need to be observed. Furthermore, it highlights trends that are influencing assay developments such as multiplexing capabilities and rapid POST, indicating potential detection methods that will shape the future market.

Domoic acid depuration by intertidal bivalves fed on toxin-producing Pseudo-nitzschia multiseries

Domoic acid (DA), a neurotoxin produced by certain species within the diatom genus Pseudo-nitzschia, has caused numerous persistent harvest closures for razor clam Siliqua patula along the outer coast of Washington State (USA) over the last three decades. In comparison, bivalve harvest closures for DA have only occurred three times in Washington's largest inland estuary, Puget Sound, which has a variety of bivalve species excluding razor clam. While differing bloom dynamics in the two locations are responsible for much of the disparity in shellfish harvest closures, species-specific differences in DA depuration may affect the duration of harvest closures in the two regions. Toxin-producing Pseudo-nitzschia multiseries were fed to four species of bivalves, followed by measurement of tissue DA content over time to estimate depuration rate. Experimental species include razor clam and three species of intertidal Puget Sound bivalves: soft-shell clam Mya arenaria, purple varnish clam Nuttallia obscurata and Manila clam Ruditapes philippinarum. Using an exponential decay model, DA depuration rates were estimated as: 0.02·day^-1 ±0.08 for razor clam, 0.10·day^-1 ±0.07 for purple varnish clam, 0.37·day^-1 ±0.03 for soft-shell clam, and 0.44·day^-1 ±0.02 for Manila clam. Puget Sound species depurated DA between five and 22 times as fast as outer coast razor clam. Within Puget Sound species, slow DA depuration rates in purple varnish clam indicate that it may be a good sentinel organism for assessing beach-wide maximum DA concentrations in Puget Sound bivalves.

The Incidence of Marine Toxins and the Associated Seafood Poisoning Episodes in the African Countries of the Indian Ocean and the Red Sea

The occurrence of Harmful Algal Blooms (HABs) and bacteria can be one of the great threats to public health due to their ability to produce marine toxins (MTs). The most reported MTs include paralytic shellfish toxins (PSTs), amnesic shellfish toxins (ASTs), diarrheic shellfish toxins (DSTs), cyclic imines (CIs), ciguatoxins (CTXs), azaspiracids (AZTs), palytoxin (PlTXs), tetrodotoxins (TTXs) and their analogs, some of them leading to fatal outcomes. MTs have been reported in several marine organisms causing human poisoning incidents since these organisms constitute the food basis of coastal human populations. In African countries of the Indian Ocean and the Red Sea, to date, only South Africa has a specific monitoring program for MTs and some other countries count only with respect to centers of seafood poisoning control. Therefore, the aim of this review is to evaluate the occurrence of MTs and associated poisoning episodes as a contribution to public health and monitoring programs as an MT risk assessment tool for this geographic region.

Production of domoic acid from large-scale cultures of Pseudo-nitzschia multiseries: A feasibility study

The commercial demand for domoic acid (DA), the phycotoxin responsible for Amnesic Shellfish Poisoning, is currently met by extraction from a diminishing supply of stockpiled contaminated mussels (Mytilus edulis). As this supply becomes scarce, a more reliable source is needed. Purification of the toxin from an algal source would be easier and more economical than from shellfish tissue if algal growth and yield of toxin were maximized. This project was initiated to determine if DA could be produced using large-scale semi-continuous algal cultures, which should reduce labour and shorten the time required for biomass production. Pseudo-nitzschia multiseries was grown in 300-L fibreglass photobioreactors called a Brite-Box™. The effect of temperature and nutrient depletion on the yield of DA by P. multiseries was examined. A decline in maximum cell number without a substantial increase in cellular DA was associated with increased temperature. Maximum total cellular DA (8.8 pg cell^-1) was achieved at 20 °C. Semi-continuous culture of P. multiseries is accompanied by increasing amounts of DA lost to the medium. The process was deemed to be feasible for growing P. multiseries but methods to recover this extracellular DA are necessary for this process to be economical.

High-throughput quantitative analysis of domoic acid directly from mussel tissue using Laser Ablation Electrospray Ionization - tandem mass spectrometry

Eliminating sample extraction or liquid chromatography steps from methods for analysis of the neurotoxin Domoic Acid (DA) in shellfish could greatly increase throughput in food safety testing laboratories worldwide. To this end, we have investigated the use of Laser Ablation Electrospray Ionization (LAESI) with tandem mass spectrometry (MS/MS) detection for DA analysis directly from mussel tissue homogenates without sample extraction, cleanup or separation. DA could be selectively detected directly from mussel tissue homogenates using MS/MS in selected reaction monitoring scan mode. The quantitative capabilities of LAESI-MS/MS for DA analysis from mussel tissue were evaluated by analysis of four mussel tissue reference materials using matrix-matched calibration. Linear response was observed from 1 mg/kg to 40 mg/kg and the method limit of detection was 1 mg/kg. Results for DA analysis in tissue within the linear range were in good agreement with two established methods, LC-UV and LC-MS/MS (recoveries from 103 to 125%). Beyond the linear range, extraction and clean-up were required to achieve good quantitation. Most notable is the extremely rapid analysis time of about 10 s per sample by LAESI-MS/MS, which corresponds to a significant increase in sample throughput compared with existing methodology for routine DA analysis.

An analytical perspective on detection, screening, and confirmation in phycology, with particular reference to toxins and toxin-producing species

Knowledge concerning the ability of microalgae to produce metabolites of interest such as toxins or high-value secondary metabolites requires exhaustive details to be supplied on how the research was conducted. These should include the microalgal species and strain characterization, the culture conditions, the cell density, and physiological state at the time of harvesting, the harvesting method, the sample pre-treatment protocol, and the subsequent instrumental analytical separation/detection system. In this comment, we discuss issues that affect algal research from an analytical chemistry perspective, particularly (i) the need to specify detection capabilities of the entire method (i.e., limits of detection or threshold detection levels), which we illustrate in relation to classification of a species or strain as being "toxin producing" or "non-toxin producing"; and (ii) the requirements that have to be satisfied to confirm a microalgal species (new or not) as a producer of a particular chemical of interest for phycologists, which again we illustrate in relation to toxins. A successful collaboration among phycologists and analytical chemists will only be achieved as a result of a synergistic collaboration between the two disciplines, with a reciprocal understanding at least at a background level.

Innovative detection methods for aquatic algal toxins and their presence in the food chain

Detection of aquatic algal toxins has become critical for the protection of human health. During the last 5 years, techniques such as optical, electrochemical, and piezoelectric biosensors or fluorescent-microsphere-based assays have been developed for the detection of aquatic algal toxins, in addition to optimization of existing techniques, to achieve higher sensitivities, specificity, and speed or multidetection. New toxins have also been incorporated in the array of analytical and biological methods. The impact of the former innovation on this field is highlighted by recent changes in legal regulations, with liquid chromatography-mass spectrometry becoming the official reference method for marine lipophilic toxins and replacing the mouse bioassay in many countries. This review summarizes the large international effort to provide routine testing laboratories with fast, sensitive, high-throughput, multitoxin, validated methods for the screening of seafood, algae, and water samples.

Toxic diatoms and domoic acid in natural and iron enriched waters of the oceanic Pacific

Near-surface waters ranging from the Pacific subarctic (58°N) to the Southern Ocean (66°S) contain the neurotoxin domoic acid (DA), associated with the diatom Pseudo-nitzschia. Of the 35 stations sampled, including ones from historic iron fertilization experiments (SOFeX, IronEx II), we found Pseudo-nitzschia at 34 stations and DA measurable at 14 of the 26 stations analyzed for DA. Toxin ranged from 0.3 fg·cell(-1) to 2 pg·cell(-1), comparable with levels found in similar-sized cells from coastal waters. In the western subarctic, descent of intact Pseudo-nitzschia likely delivered significant amounts of toxin (up to 4 μg of DA·m(-2)·d(-1)) to underlying mesopelagic waters (150-500 m). By reexamining phytoplankton samples from SOFeX and IronEx II, we found substantial amounts of DA associated with Pseudo-nitzschia. Indeed, at SOFeX in the Antarctic Pacific, DA reached 220 ng·L(-1), levels at which animal mortalities have occurred on continental shelves. Iron ocean fertilization also occurs naturally and may have promoted blooms of these ubiquitous algae over previous glacial cycles during deposition of iron-rich aerosols. Thus, the neurotoxin DA occurs both in coastal and oceanic waters, and its concentration, associated with changes in Pseudo-nitzschia abundance, likely varies naturally with climate cycles, as well as with artificial iron fertilization. Given that iron fertilization in iron-depleted regions of the sea has been proposed to enhance phytoplankton growth and, thereby, both reduce atmospheric CO(2) and moderate ocean acidification in surface waters, consideration of the potentially serious ecosystem impacts associated with DA is prudent.

Naturally occurring food toxins

Although many foods contain toxins as a naturally-occurring constituent or, are formed as the result of handling or processing, the incidence of adverse reactions to food is relatively low. The low incidence of adverse effects is the result of some pragmatic solutions by the US Food and Drug Administration (FDA) and other regulatory agencies through the creative use of specifications, action levels, tolerances, warning labels and prohibitions. Manufacturers have also played a role by setting limits on certain substances and developing mitigation procedures for process-induced toxins. Regardless of measures taken by regulators and food producers to protect consumers from natural food toxins, consumption of small levels of these materials is unavoidable. Although the risk for toxicity due to consumption of food toxins is fairly low, there is always the possibility of toxicity due to contamination, overconsumption, allergy or an unpredictable idiosyncratic response. The purpose of this review is to provide a toxicological and regulatory overview of some of the toxins present in some commonly consumed foods, and where possible, discuss the steps that have been taken to reduce consumer exposure, many of which are possible because of the unique process of food regulation in the United States.

Biological methods for marine toxin detection

The presence of marine toxins in seafood poses a health risk to human consumers which has prompted the regulation of the maximum content of marine toxins in seafood in the legislations of many countries. Most marine toxin groups are detected by animal bioassays worldwide. Although this method has well known ethical and technical drawbacks, it is the official detection method for all regulated phycotoxins except domoic acid. Much effort by the scientific and regulatory communities has been focused on the development of alternative techniques that enable the substitution or reduction of bioassays; some of these have recently been included in the official detection method list. During the last two decades several biological methods including use of biosensors have been adapted for detection of marine toxins. The main advances in marine toxin detection using this kind of technique are reviewed. Biological methods offer interesting possibilities for reduction of the number of biosassays and a very promising future of new developments.

Comparative evaluation of enzyme-linked immunoassay and reference methods for the detection of shellfish hydrophilic toxins in several presentations of seafood

A comparative study was conducted to determine the feasibility of enzyme-linked immunosorbent assays (ELISAs) for the detection of amnesic shellfish poisoning (ASP) and paralytic shellfish poisoning (PSP) toxins in nine naturally contaminated species in fresh, frozen, boiled and canned fish and shellfish. PSP and ASP were analyzed in 138 shellfish samples (mussels, clams, barnacles, razor shells, scallops and cockles) and anchovies by mouse bioassay (MBA) and high performance liquid chromatography with ultraviolet detection (HPLC-UV), respectively. Results were compared with toxin concentrations obtained using two commercial competitive ELISAs, saxitoxin and ASP kits. Immunoassays were able to quantify toxins in different matrices showing excellent Pearson's correlation coefficients (r = 0.974 for saxitoxin ELISA and r = 0.973 for ASP ELISA) and to detect PSP and ASP with a lower limit of detection (LOD), namely, 50 microg saxitoxin equivalent/kg shellfish meat for PSP and 60 microg/kg domoic acid in shellfish flesh for ASP, than the reference methods (350 microg saxitoxin equivalent/kg shellfish meat and 1.6 mg/kg domoic acid in shellfish flesh, respectively). These results suggest that the ELISA method could be used as screening systems in a variety of species without matrix interference.

Requirements for screening and confirmatory methods for the detection and quantification of marine biotoxins in end-product and official control

An overview is given of the biological origin of phycotoxins, as well as their chemical characteristics. Major poisoning types are described and examples of poisoning events are given to illustrate the importance of the phenomenon to both shellfish consumers and the shellfish producing industry. The characteristics of phycotoxins as natural products, the lack of predictability of their occurrence, economic drivers and the freshness of shellfish consumed in many countries result in a number of requirements for methods to be used in the efficient detection of these compounds. Subsequently, the performance of mouse bioassays and mass spectrometry as detection tools are compared for examples from Irish and French monitoring programmes to assess the usefulness of qualitative and quantitative tools in official control, and their fitness for purpose compared with the requirements. The final part of the paper critically reviews methods available for the end-product and official control of shellfish toxins and their use in screening and confirmatory approaches in monitoring. Recent expert consultations on the methodology for phycotoxins at European and global level are summarised and recommendations are made for future progress in this area.

Use of biosensors as alternatives to current regulatory methods for marine biotoxins

Marine toxins are currently monitored by means of a bioassay that requires the use of many mice, which poses a technical and ethical problem in many countries. With the exception of domoic acid, there is a legal requirement for the presence of other toxins (yessotoxin, saxitoxin and analogs, okadaic acid and analogs, pectenotoxins and azaspiracids) in seafood to be controlled by bioassay, but other toxins, such as palytoxin, cyclic imines, ciguatera and tetrodotoxin are potentially present in European food and there are no legal requirements or technical approaches available to identify their presence. The need for alternative methods to the bioassay is clearly important, and biosensors have become in recent years a feasible alternative to animal sacrifice. This review will discuss the advantages and disadvantages of using biosensors as alternatives to animal assays for marine toxins, with particular focus on surface plasmon resonance (SPR) technology.

Decrease of marine toxin content in bivalves by industrial processes

Harmful algal blooms cause important economical losses due to the accumulation of toxins in shellfish. Natural detoxification occurs but this mechanism is very slow in most cases. The achievement of a method for the rapid detoxification of commercial bivalves would be very interesting for the shellfish harvesting sector in order to diminish economical losses due to harvesting areas closure. In this work, four different methods easily applicable in the food industry (freezing, evisceration, ozonization and thermal processing) were studied to gain the detoxification of four species of bivalves (mussels, scallops, clams and cockles) contaminated with the three main types of toxins (ASP, DSP, PSP). Results show that for ASP a significant decrease of the toxin levels below the legal limit (20 microg/g) is achieved by using hepatopancreas ablation or combination of simple steps (evisceration and/or thermal processing/and or freezing). In our hands, PSP toxin levels are sharply decreased under the limit of detection (35 microg STX eq/100g) after a thermal processing, inducing percentages of detoxification higher than 50%. The effect of freezing on the levels of PSP is very dependent on the matrix studied. DSP toxins are not significantly reduced with none of these methods.