Amnesic shellfish poisoning toxins in bivalve molluscs in Ireland

Spatiotemporal variations of domoic acid: New findings in the sedimentary environment of a typical nearshore mariculture bay, China

Domoic acid (DA) is a neurotoxin produced by marine microalgae. It tends to accumulate in marine shellfish and fish, posing a threat to aquaculture and seafood consumers' health. In this study, DA in the surface and bottom seawater, sediment, and porewater of the Jiaozhou Bay, a typical mariculture bay in China, was systematically investigated for the first time over different seasons. Surprisingly, a high concentration of DA was discovered in the marine sediment porewater (maximum detected concentration: 289.49 ng/L) for the first time. DA was found to be extensively distributed in the water body and sedimentary environment of the Jiaozhou Bay. DA in the surface and bottom seawater of Jiaozhou Bay in spring was uniformly distributed, whereas DA showed obvious spatial variations in summer and winter. The high concentration areas of DA are located in the north of Jiaozhou Bay and decreased to the south areas. DA was also distributed in the sediment (spring mean: 316.57 ng/kg; summer mean: 10.22 ng/kg; winter mean: 237.08 ng/kg) and porewater (spring mean: 129.70 ng/L; summer mean: 53.54 ng/L; winter mean: 19.90 ng/L) of Jiaozhou Bay. The DA concentrations in the surface sediment and porewater were higher in the spring than in the winter and summer, contrary to the seasonal variation pattern observed in the surface and bottom seawater. The DA concentration in porewater was significantly higher than in the surface and bottom seawater, indicating that the risk of pollution contamination from DA to benthic fishery organisms may be underestimated. Overall, DA is widely distributed in the seawater and also in the benthic environment of Jiaozhou Bay and exhibited potential harm to fishery organisms varied greatly with seasons. It is an important discovery for marine algae toxins and has important guiding significance and important indicative role for the routine monitoring and management of DA pollution in water and benthic environment.

Comparative study of domoic acid accumulation, isomer content and associated digestive subcellular processes in five marine invertebrate species

Despite the deleterious effects of the phycotoxin domoic acid (DA) on human health, and the permanent threat of blooms of the toxic Pseudo-nitzschia sp. over commercially important fishery-resources, knowledge regarding the physiological mechanisms behind the profound differences in accumulation and depuration of this toxin in contaminated invertebrates remain very scarce. In this work, a comparative analysis of accumulation, isomer content, and subcellular localization of DA in different invertebrate species was performed. Samples of scallops Pecten maximus and Aequipecten opercularis, clams Donax trunculus, slippersnails Crepidula fornicata, and seasquirts Asterocarpa sp. were collected after blooms of the same concentration of toxic Pseudo-nitzschia australis. Differences (P < 0.05) in DA accumulation were found, wherein P. maximus showed up to 20-fold more DA in the digestive gland than the other species. Similar profiles of DA isomers were found between P. maximus and A. opercularis, whereas C. fornicata was the species with the highest biotransformation rate (∼10 %) and D. trunculus the lowest (∼4 %). DA localization by immunohistochemical analysis revealed differences (P < 0.05) between species: in P. maximus, DA was detected mainly within autophagosome-like vesicles in the cytoplasm of digestive cells, while in A. opercularis and C. fornicata significant DA immunoreactivity was found in post-autophagy residual bodies. A slight DA staining was found free within the cytoplasm of the digestive cells of D. trunculus and Asterocarpa sp. The Principal Component Analysis revealed similarities between pectinids, and a clear distinction of the rest of the species based on their capabilities to accumulate, biotransform, and distribute the toxin within their tissues. These findings contribute to improve the understanding of the inter-specific differences concerning the contamination-decontamination kinetics and the fate of DA in invertebrate species.

Harmful algal blooms and shellfish in the marine environment: an overview of the main molluscan responses, toxin dynamics, and risks for human health

Besides human health risks, phycotoxins may cause physiological injuries on molluscan shellfish and, consequently, damages to marine ecosystems and global fisheries production. In this way, this review aimed to present an overview of HABs impacts on marine shellfish by evaluating the effects of cultivated molluscs exposure to microalgae and cyanobacteria that form blooms and/or synthesize toxins. More specifically, it was assessed the main molluscan shellfish responses to harmful algae, trophic transfer and dynamics of phycotoxins, and the risks for human health. Of the 2420 results obtained from literature search, 150 scientific publications were selected after thorough inspections for subject adherence. In total, 70 molluscan species and 37 taxa of harmful algae were assessed from retrieved scientific publications. A significant positive correlation was found between the marine production of molluscs and the number of available studies by molluscan category. Molluscan responses to HABs and phycotoxins were categorized and discussed in three sub-sections: effects on grazing and behavior, metabolic and physiological reactions, and fitness consequences. The main histopathological injuries and toxin concentrations in molluscan tissues were also compiled and discussed. Bivalves often accumulate more toxins than gastropods and cephalopods, occasionally exceeding recommended levels for safe consumption, representing a risk for human health. Harmful algae impact on molluscan shellfish are complex to trace and predict; however, considering the perspective of increase in the occurrence and intensity of HABs, the intensification of efforts to expand the knowledge about HABs impacts on marine molluscs is crucial to mitigate the damages on economy and human health.

Occurrence of domoic acid and cyclic imines in marine biota from Lebanon-Eastern Mediterranean Sea

Marine biotoxins are naturally existing chemicals produced by toxic algae and can accumulate in marine biota. When consumed with seafood, these phycotoxins can cause human intoxication with symptoms varying from barely-noticed illness to death depending on the type of toxin and its concentration. Recently, the occurrence of marine biotoxins has been given special attention in the Mediterranean as it increased in frequency and severity due to anthropogenic pressures and climate change. Up to our knowledge, no previous study reported the presence of lipophilic toxins (LTs) and cyclic imines (CIs) in marine biota in Lebanon. Hence, this study reports LTs and CIs in marine organisms: one gastropod (Phorcus turbinatus), two bivalves (Spondylus spinosus and Patella rustica complex) and one fish species (Siganus rivulatus), collected from various Lebanese coastal areas. The results show values below the limit of detection (LOD) for okadaic acid, dinophysistoxin-1 and 2, pectenotoxin-1 and 2, yessotoxins, azaspiracids and saxitoxins. The spiny oyster (S. spinosus) showed the highest levels of domoic acid (DA; 3.88 mg kg^-1), gymnodimine (GYM-B) and spirolide (SPX) (102.9 and 15.07 μg kg^-1, respectively) in congruence with the occurrence of high abundance of Pseudo-nitzchia spp., Gymnodinium spp., and Alexandrium spp. DA levels were below the European Union (EU) regulatory limit, but higher than the Lowest Observed Adverse Effect Level (0.9 μg g^-1) for neurotoxicity in humans and lower than the Acute Reference Dose (30 μg kg^-1 bw) both set by the European Food Safety Authority (EFSA, 2009). Based on these findings, it is unlikely that a health risk exists due to the exposure to these toxins through seafood consumption in Lebanon. Despite this fact, the chronic toxicity of DA, GYMs and SPXs remains unclear and the effect of the repetitive consumption of contaminated seafood needs to be more investigated.

Rapid Domoic Acid Depuration in the Scallop Argopecten purpuratus and Its Transfer from the Digestive Gland to Other Organs

Domoic acid (DA), the main toxin responsible for Amnesic Shellfish Poisoning, frequently affects the marine resources of Chile and other countries across the South Pacific, thus becoming a risk for human health. One of the affected resources is the scallop Argopecten purpuratus. Even though this species has a high commercial importance in Northern Chile and Peru, the characteristics of its DA depuration are not known. In this work, the DA depuration was studied by means of two experiments: one in controlled (laboratory) and another in natural conditions. All organs of A. purpuratus depurated the toxin very quickly in both experiments. In some organs, an increase or a very small decrease of toxin was detected in the early depuration steps. Several models were used to describe this kinetics. The one that included toxin transfer between organs and independent depuration from each organ was the model that best fit the data. It seems, therefore, that the DA in this species is quickly transferred from the digestive gland to all other organs, which release it into the environment. Physiological differences in the two experiments have been shown to have some effect on the depuration from each organ but the actual reasons are still unknown.

Domoic acid in California sea lion fetal fluids indicates continuous exposure to a neuroteratogen poses risks to mammals

Domoic acid (DA) is a neuroexcitotoxic amino acid that is naturally produced by some species of marine diatoms during harmful algal blooms (HABs). The toxin is transferred through the food web from plantivorous fish and shellfish to marine mammals resulting in significant morbidity and mortality. Due to the timing and location of DA producing HABs, it is well documented that pregnant female California sea lions (CSL) are regularly exposed to DA through their diet thereby posing exposure risks to a neuroteratogen in developing fetuses. In the present study, fluids from 36 fetuses sampled from naturally exposed pregnant CSLs were examined for DA. Domoic acid was detected in 79% of amniotic fluid (n = 24), 67% of allantoic fluid (n = 9), 75% of urine (n = 4), 41% of meconium (n = 17) and 29% of stomach content (n = 21) samples opportunistically collected from CSL fetuses. The distribution of DA in fetal samples indicates an increased prenatal exposure risk due to recirculation of DA in fetal fluids and continuous exposure to the developing brain.

Extended Targeted and Non-Targeted Strategies for the Analysis of Marine Toxins in Mussels and Oysters by (LC-HRMS)

When considering the geographical expansion of marine toxins, the emergence of new toxins and the associated risk for human health, there is urgent need for versatile and efficient analytical methods that are able to detect a range, as wide as possible, of known or emerging toxins. Current detection methods for marine toxins rely on a priori defined target lists of toxins and are generally inappropriate for the detection and identification of emerging compounds. The authors describe the implementation of a recent approach for the non-targeted analysis of marine toxins in shellfish with a focus on a comprehensive workflow for the acquisition and treatment of the data generated after liquid chromatography coupled with high resolution mass spectrometry (LC-HRMS) analysis. First, the study was carried out in targeted mode to assess the performance of the method for known toxins with an extended range of polarities, including lipophilic toxins (okadaic acid, dinophysistoxins, azaspiracids, pectenotoxins, yessotoxins, cyclic imines, brevetoxins) and domoic acid. The targeted method, assessed for 14 toxins, shows good performance both in mussel and oyster extracts. The non-target potential of the method was then challenged via suspects and without a priori screening by blind analyzing mussel and oyster samples spiked with marine toxins. The data processing was optimized and successfully identified the toxins that were spiked in the blind samples.

Distribution, occurrence and biotoxin composition of the main shellfish toxin producing microalgae within European waters: A comparison of methods of analysis

Harmful algal blooms (HABs) are a natural global phenomena emerging in severity and extent. Incidents have many economic, ecological and human health impacts. Monitoring and providing early warning of toxic HABs are critical for protecting public health. Current monitoring programmes include measuring the number of toxic phytoplankton cells in the water and biotoxin levels in shellfish tissue. As these efforts are demanding and labour intensive, methods which improve the efficiency are essential. This study compares the utilisation of a multitoxin surface plasmon resonance (multitoxin SPR) biosensor with enzyme-linked immunosorbent assay (ELISA) and analytical methods such as high performance liquid chromatography with fluorescence detection (HPLC-FLD) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for toxic HAB monitoring efforts in Europe. Seawater samples (n=256) from European waters, collected 2009-2011, were analysed for biotoxins: saxitoxin and analogues, okadaic acid and dinophysistoxins 1/2 (DTX1/DTX2) and domoic acid responsible for paralytic shellfish poisoning (PSP), diarrheic shellfish poisoning (DSP) and amnesic shellfish poisoning (ASP), respectively. Biotoxins were detected mainly in samples from Spain and Ireland. France and Norway appeared to have the lowest number of toxic samples. Both the multitoxin SPR biosensor and the RNA microarray were more sensitive at detecting toxic HABs than standard light microscopy phytoplankton monitoring. Correlations between each of the detection methods were performed with the overall agreement, based on statistical 2×2 comparison tables, between each testing platform ranging between 32% and 74% for all three toxin families illustrating that one individual testing method may not be an ideal solution. An efficient early warning monitoring system for the detection of toxic HABs could therefore be achieved by combining both the multitoxin SPR biosensor and RNA microarray.

Low-Molecular-Weight Metabolites from Diatoms: Structures, Biological Roles and Biosynthesis

Diatoms are abundant and important biological components of the marine environment that biosynthesize diverse natural products. These microalgae are rich in various lipids, carotenoids, sterols and isoprenoids, some of them containing toxins and other metabolites. Several groups of diatom natural products have attracted great interest due to their potential practical application as energy sources (biofuel), valuable food constituents, and prospective materials for nanotechnology. In addition, hydrocarbons, which are used in climate reconstruction, polyamines which participate in biomineralization, new apoptotic agents against tumor cells, attractants and deterrents that regulate the biochemical communications between marine species in seawaters have also been isolated from diatoms. However, chemical studies on these microalgae are complicated by difficulties, connected with obtaining their biomass, and the influence of nutrients and contaminators in their environment as well as by seasonal and climatic factors on the biosynthesis of the corresponding natural products. Overall, the number of chemically studied diatoms is lower than that of other algae, but further studies, particularly those connected with improvements in the isolation and structure elucidation technique as well as the genomics of diatoms, promise both to increase the number of studied species with isolated biologically active natural products and to provide a clearer perception of their biosynthesis.

Depuration and anatomical distribution of domoic acid in the surf clam Mesodesma donacium

In northern Chile, domoic acid (DA) has been detected in several bivalve species. In Mesodesma donacium, one of the most important commercial species for local fishermen, no information is available on depuration, or on the anatomical distribution of this toxin and its potential use as a palliative measure to minimize the consequences of ASP outbreaks. Deputation of DA is very fast in M. donacium, and can be adequately described by means of a two-compartment model. The estimated rates for the first and second compartments were 1.27 d(-1) and 0.24 d(-1), respectively, with a transfer rate between compartments of 0.75. Having high depuration rates protects this species from being affected by Pseudo-nitzschia blooms for an extended period of time. Taking this into account, the time in which the bivalves are unsafe for consumers is very short, and therefore the economic losses that could result by the DA outbreaks in local fisheries should be moderate. In relation to anatomical distribution, at least during the uptake phase, the toxin was evenly distributed within the soft tissues, with a total toxin burden corresponding to 27%, 32% and 41% for Digestive Gland (DG), Foot (FT) and Other Body Fractions (OBF), respectively. Since the contribution of each organ to the toxin concentration is a function of both weight contribution and toxin burden, the pattern of toxin distribution showed the following trend: "all other body fractions" (OBF) > Foot (FT) > Digestive Gland (DG). Thus, the highest concentration of DA, with a contribution close to 72%, corresponds to the edible tissues (OBF + FT), while the DG (non-edible tissue) only contributes the remaining 28%. Consequently, in view of the anatomical distribution of domoic acid in M. donacium, the elimination of the digestive gland does not substantially reduce the toxicity of the final product and therefore selective evisceration would not improve their quality for human consumption.

Molecular detection of a potentially toxic diatom species

A few diatom species produce toxins that affect human and animal health. Among these, members of the Pseudo-nitzschia genus were the first diatoms unambiguously identified as producer of domoic acid, a neurotoxin affecting molluscan shell-fish, birds, marine mammals, and humans. Evidence exists indicating the involvement of another diatom genus, Amphora, as a potential producer of domoic acid. We present a strategy for the detection of the diatom species Amphora coffeaeformis based on the development of species-specific oligonucleotide probes and their application in microarray hybridization experiments. This approach is based on the use of two marker genes highly conserved in all diatoms, but endowed with sufficient genetic divergence to discriminate diatoms at the species level. A region of approximately 450 bp of these previously unexplored marker genes, coding for elongation factor 1-a (eEF1-a) and silicic acid transporter (SIT), was used to design oligonucleotide probes that were tested for specificity in combination with the corresponding fluorescently labeled DNA targets. The results presented in this work suggest a possible use of this DNA chip technology for the selective detection of A. coffeaeformis in environmental settings where the presence of this potential toxin producer may represent a threat to human and animal health. In addition, the same basic approach can be adapted to a wider range of diatoms for the simultaneous detection of microorganisms used as biomarkers of different water quality levels.

Diversity and toxicity of the diatom Pseudo-nitzschia Peragallo in the Gulf of Maine, Northwestern Atlantic Ocean

Multiple species in the toxic marine diatom genus Pseudo-nitzschia have been identified in the Northwestern Atlantic region encompassing the Gulf of Maine (GOM), including the Bay of Fundy (BOF). To gain further knowledge of the taxonomic composition and toxicity of species in this region, Pseudo-nitzschia isolates (n=146) were isolated from samples collected during research cruises that provided broad spatial coverage across the GOM and the southern New England shelf, herein referred to as the GOM region, during 2007-2008. Isolates, and cells in field material collected at 38 stations, were identified using electron microscopy (EM). Eight species (P. americana, P. fraudulenta, P. subpacifica, P. heimii, P. pungens, P. seriata, P. delicatissima and P. turgidula), and a novel form, Pseudo-nitzschia sp. GOM, were identified. Species identity was confirmed by sequencing the large subunit of the ribosomal rDNA (28S) and the internal transcribed spacer 2 (ITS2) for six species (36 isolates). Phylogenetic analyses (including neighbor joining, maximum parsimony, and maximum likelihood estimates and ITS2 secondary structure analysis) and morphometric data supported the placement of P. sp. GOM in a novel clade that includes morphologically and genetically similar isolates from Australia and Spain and is genetically most similar to P. pseudodelicatissima and P. cuspidata. Seven species (46 isolates) were grown in nutrient-replete batch culture and aliquots consisting of cells and growth medium were screened by Biosense ASP ELISA to measure total domoic acid (DA) produced (intracellular + extracellular); P. americana and P. heimii were excluded from all toxin analyses as they did not persist in culture long enough for testing. All 46 isolates screened produced DA in culture and total DA varied among species (e.g., 0.04 to 320 ng ml^-1 for P. pungens and P. sp. GOM isolates, respectively) and among isolates of the same species (e.g., 0.24 - 320 ng ml^-1 for P. sp. GOM). The 15 most toxic isolates corresponded to P. seriata, P. sp. GOM and P. pungens, and fg DA cell^-1 was determined for whole cultures (cells and medium) using ELISA and liquid chromatography (LC) with fluorescence detection (FLD); for seven isolates, toxin levels were also estimated using LC - with mass spectrometry and ultraviolet absorbance detection. Pseudo-nitzschia seriata was the most toxic species (up to 3,500 fg cell^-1) and was observed in the GOM region during all cruises (i.e., during the months of April, May, June and October). Pseudo-nitzschia sp. GOM, observed only during September and October 2007, was less toxic (19 - 380 fg cell^-1) than P. seriata but more toxic than P. pungens var. pungens (0. 4 fg cell^-1). Quantitation of DA indicated that concentrations measured by LC and ELISA were positively and significantly correlated; the lower detection limit of the ELISA permitted quantification of toxicity in isolates that were found to be nontoxic with LC methods. The confirmation of at least seven toxic species and the broad spatial and temporal distribution of toxic Pseudo-nitzschia spp. have significant implications for the regional management of nearshore and offshore shellfisheries resources.

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.

Sex differences in effects of low level domoic acid exposure

Consumption of seafood containing the phytoplankton-derived toxin domoic acid (DOM) causes neurotoxicity in humans and in animals. It has been reported that DOM-induced symptoms may be more severe in men than women, but to date the effect of sex on DOM-induced effects in adults is not known. We investigated sex differences in DOM-induced effects in adult rats. Since low level exposure is of greatest relevance to human health (due to DOM regulatory limit), we examined the effects of low level exposure. Adult male and female Sprague Dawley rats were administered a single intraperitoneal injection of DOM (0, 1.0, 1.8 mg/kg). Behaviour was monitored for 3h and immunohistochemistry in the dorsal hippocampus and olfactory bulb was also examined. DOM increased locomotor and grooming activity, compared to vehicle group. DOM exposure also significantly increased stereotypic behaviours and decreased phosphorylated cAMP response element-binding protein immunoreactivity (pCREB-IR). There was no effect of sex on the magnitude of the behavioural responses, but the onset of DOM-induced locomotor activity and ear scratches was quicker in females than in males. Mixed effect modelling revealed the predicted peak in locomotor activity in response to DOM was also quicker in females than in males. Severe toxicity was evident in 2/7 male rats and 0/8 female rats dosed with 1.8 mg/kg DOM. These data suggest that males exposed to low level DOM may be more susceptible to severe neurotoxicity, whereas females are affected more quickly. Understanding sex differences in DOM-induced neurotoxicity may contribute to future protective strategies and treatments.

Exposure to domoic acid through shellfish consumption in Belgium

A main known culprit causing amnesic shellfish poisoning in humans is domoic acid (DA). The toxin appearance in sea waters (by counting the toxin producing algae) and consequently in shellfish is closely monitored to prevent acute intoxications with gastrointestinal symptoms and neurological signs. However it is assumed that there might be some chronic problems with repetitive exposures to the toxin in animals. In humans this is greatly unknown and it is mostly assessed by relating reported toxin episodes and representative consumption data. Although in Belgium no alarming outbreaks have been reported in recent years, different concentrations of DA have been found in shellfish samples. In this study the human acute and chronic exposure to DA through shellfish consumption was evaluated by linking the data of DA concentrations in samples collected in the scope of the National Food control program in the period 2004-2009 and consumption data obtained from the National Belgian Food Consumption Survey including 3245 adults. The found level of toxin was highest in scallops while lowest in mussels. The mean usual long-term intake of molluscs such as scallops, mussels and oysters for the whole Belgian population was from 0.10 g/day for scallops to 1.21 g/day for mussels. With average portion size estimated to be 56-108 g/day depending on the shellfish source it was calculated that less than 1% of the population would be at risk of acute intoxication. Using a medium bound approach, 5-6% of the population shows chronic exposure exceeding the tolerable daily intake of 0.075 μg/kg bw per day with scallops being the most probable toxin vector when using lower (68.5%) and medium (45.6%) bound concentrations.

Domoic acid--a new toxin in the Croatian Adriatic shellfish toxin profile

This is the first study that presents concentrations of domoic acid detected in the whole shellfish tissue from breeding and harvesting areas along the Croatian coast of the Adriatic Sea during the period 2006 to 2008. Shellfish sample analyses after SAX cleaning procedures, using a UV-DAD-HPLC system, showed the presence of domoic acid in four species. The most prevalent of those species were the blue mussel (Mytilus galloprovincialis), followed by European flat oyster (Ostrea edulis), Mediterranean scallop (Pecten jacobaeus) and proteus scallop (Flexopecten proteus). Domoic acid, a potentially lethal phycotoxin that causes amnesic shellfish poisoning (ASP), was detected for the first time in January 2006 with the highest value of 6.5486 μg g⁻¹ in whole shellfish tissue. Pseudo-nitzschia spp. bloom events preceded these high domoic acid concentrations. According to this study, retention of domoic acid in the blue mussel M. galloprovincialis is more than 42 days. This investigation indicates the first presence of domoic acid in Croatian shellfish, but in concentrations under the regulatory limit (20 μg g⁻¹), therefore shellfish consumption was not found to endanger human health.

Domoic acid as a developmental neurotoxin

Domoic acid (DomA) is an excitatory amino acid which can accumulate in shellfish and finfish under certain environmental conditions. DomA is a potent neurotoxin. In humans and in non-human primates, oral exposure to a few mg/kg DomA elicits gastrointestinal effects, while slightly higher doses cause neurological symptoms, seizures, memory impairment, and limbic system degeneration. In rodents, which appear to be less sensitive than humans or non-human primates, oral doses cause behavioral abnormalities (e.g. hindlimb scratching), followed by seizures and hippocampal degeneration. Similar effects are also seen in other species (from sea lions to zebrafish), indicating that DomA exerts similar neurotoxic effects across species. The neurotoxicity of DomA is ascribed to its ability to interact and activate the AMPA/KA receptors, a subfamily of receptors for the neuroexcitatory neurotransmitter glutamate. Studies exploring the neurotoxic effects of DomA on the developing nervous system indicate that DomA elicits similar behavioral, biochemical and morphological effects as in adult animals. However, most importantly, developmental neurotoxicity is seen at doses of DomA that are one to two orders of magnitude lower than those exerting neurotoxicity in adults. This difference may be due to toxicokinetic and/or toxicodynamic differences. Estimated safe doses may be exceeded in adults by high consumption of shellfish contaminated with DomA at the current limit of 20 microg/g. Given the potential higher susceptibility of the young to DomA neurotoxicity, additional studies investigating exposure to, and effects of this neurotoxin during brain development are warranted.

Neurological disease rises from ocean to bring model for human epilepsy to life

Domoic acid of macroalgal origin was used for traditional and medicinal purposes in Japan and largely forgotten until its rediscovery in diatoms that poisoned 107 people after consumption of contaminated mussels. The more severely poisoned victims had seizures and/or amnesia and four died; however, one survivor unexpectedly developed temporal lobe epilepsy (TLE) a year after the event. Nearly a decade later, several thousand sea lions have stranded on California beaches with neurological symptoms. Analysis of the animals stranded over an eight year period indicated five clusters of acute neurological poisoning; however, nearly a quarter have stranded individually outside these events with clinical signs of a chronic neurological syndrome similar to TLE. These poisonings are not limited to sea lions, which serve as readily observed sentinels for other marine animals that strand during domoic acid poisoning events, including several species of dolphin and whales. Acute domoic acid poisoning is five-times more prominent in adult female sea lions as a result of the proximity of their year-round breeding grounds to major domoic acid bloom events. The chronic neurological syndrome, on the other hand, is more prevalent in young animals, with many potentially poisoned in utero. The sea lion rookeries of the Channel Islands are at the crossroads of domoic acid producing harmful algal blooms and a huge industrial discharge site for dichlorodiphenyltrichloroethane (DDTs). Studies in experimental animals suggest that chronic poisoning observed in immature sea lions may result from a spatial and temporal coincidence of DDTs and domoic acid during early life stages. Emergence of an epilepsy syndrome from the ocean brings a human epilepsy model to life and provides unexpected insights into interaction with legacy contaminants and expression of disease at different life stages.

Marine toxins: chemistry, toxicity, occurrence and detection, with special reference to the Dutch situation

Various species of algae can produce marine toxins under certain circumstances. These toxins can then accumulate in shellfish such as mussels, oysters and scallops. When these contaminated shellfish species are consumed severe intoxication can occur. The different types of syndromes that can occur after consumption of contaminated shellfish, the corresponding toxins and relevant legislation are discussed in this review. Amnesic Shellfish Poisoning (ASP), Paralytic Shellfish Poisoning (PSP), Diarrheic Shellfish Poisoning (DSP) and Azaspiracid Shellfish Poisoning (AZP) occur worldwide, Neurologic Shellfish Poisoning (NSP) is mainly limited to the USA and New Zealand while the toxins causing DSP and AZP occur most frequently in Europe. The latter two toxin groups are fat-soluble and can therefore also be classified as lipophilic marine toxins. A detailed overview of the official analytical methods used in the EU (mouse or rat bioassay) and the recently developed alternative methods for the lipophilic marine toxins is given. These alternative methods are based on functional assays, biochemical assays and chemical methods. From the literature it is clear that chemical methods offer the best potential to replace the animal tests that are still legislated worldwide. Finally, an overview is given of the situation of marine toxins in The Netherlands. The rat bioassay has been used for monitoring DSP and AZP toxins in The Netherlands since the 1970s. Nowadays, a combination of a chemical method and the rat bioassay is often used. In The Netherlands toxic events are mainly caused by DSP toxins, which have been found in Dutch shellfish for the first time in 1961, and have reoccurred at irregular intervals and in varying concentrations. From this review it is clear that considerable effort is being undertaken by various research groups to phase out the animal tests that are still used for the official routine monitoring programs.

Shellfish toxicity: human health implications of marine algal toxins

Five major human toxic syndromes caused by the consumption of shellfish contaminated by algal toxins are presented. The increased risks to humans of shellfish toxicity from the prevalence of harmful algal blooms (HABs) may be a consequence of large-scale ecological changes from anthropogenic activities, especially increased eutrophication, marine transport and aquaculture, and global climate change. Improvements in toxin detection methods and increased toxin surveillance programmes are positive developments in limiting human exposure to shellfish toxins.

Distribution and linkage of domoic acid (amnesic shellfish poisoning toxins) in subcellular fractions of the digestive gland of the scallop Pecten maximus

The king scallop Pecten maximus accumulates domoic acid, the main amnesic shellfish poisoning toxin, in the digestive gland for a long time. To try to find if the cause of this characteristic is the binding of the toxin to some cellular component, the subcellular distribution of domoic acid in the cells of the digestive gland was studied, by means of serial centrifugation, ultrafiltration and size exclusion chromatography (SEC). Domoic acid was found to be present mostly in soluble form in the cytosol, as more than 90% was found in the supernatant after a centrifugation of 1h at 45,000 x g, and passed a 10 kDa ultrafilter. The retention time of the peak with an absorption maximum of 242 nm--the one characteristic of domoic acid--observed in the SEC chromatograms of the scallop samples was found identical to be one of a reference solution of the toxin, indicating therefore, that domoic acid is free in the cytosol of the digestive gland of Pecten maximus. This finding turns the focus from binding to the lack of membrane transporters in this species of the scallop as the cause of the long retention time of domoic acid in this species.

Domoic acid: neurobehavioral consequences of exposure to a prevalent marine biotoxin

Domoic acid (DA), the cause of Amnesic Shellfish Poisoning, is a naturally occurring marine biotoxin that is usually produced by the microscopic algae Pseudo-nitzschia. As is the case for other types of toxic algae, Pseudo-nitzschia outbreaks are becoming more frequent. Acute high-dose symptomology in humans includes vomiting, cramping, coma and death as well as neurological effects such as hallucinations, confusion and memory loss. Experimental studies and medical reports have collectively shown that DA exposure primarily affects the hippocampal regions of the brain and is associated with seizures and the disruption of cognitive processes. The neurobehavioral signature of DA is unique in that it includes transient and permanent changes in memory function that resemble human antegrade amnesia. Experimental studies with adult nonhuman primates have established that DA is a dose-dependent emetic that produces clinical and neuropathological changes consistent with excitotoxicity. Behavioral evaluations of treated rodents have shown that hyperactivity and stereotypical scratching are the first functional markers of toxicity. Mid-dose treatment is associated with memory impairment and behavioral hyperreactivity, suggesting changes in arousal and/or emotionality. At higher doses, DA treatment results in frank neurotoxicity that is characterized by seizures, status epilepticus and death in treated animals. The route of DA exposure is important and influences the severity of effects; intraperitoneal and intravenous treatments produce classic signs of poisoning at significantly lower doses than oral exposure. While developmental studies are few, DA readily crosses the placenta and enters the fetal brain. Domoic acid is not associated with congenital dysmorphia but is linked to persistent changes in motor behavior and cognition in exposed offspring. Comparative research suggests that functional losses associated with DA can be persistent and injuries to the CNS can be progressive. Long-term studies will be necessary to accurately track the expression of DA-related injury, in health and behavior, over the lifespan.

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.

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

Domoic acid (DA) is the principal neurotoxin responsible for amnesic shellfish poisoning (ASP) and is produced, among other species, by marine diatoms of the genus Pseudo-nitzschia. In this work, a method for the determination of dissolved DA and its isomers present in seawater has been developed, based on a solid-phase extraction (SPE) disks followed by rapid resolution liquid chromatography coupled with tandem mass spectrometry. SPE provided sample desalting and 20-fold concentration of dissolved DA, while complete resolution between DA and its isomers was achieved in less than 3 min with rapid resolution chromatography thus providing high sample throughput. Additionally, a simple on-column chromatographic procedure allowed head-column trapping of DA providing 15-fold higher sensitivity. The conditions developed in this work have shown appropriate quality parameters in a within-laboratory validation. The detection limit was 0.02 ng mL(-1) for the whole method, while trueness ranged between 92.1% and 110.6% recovery and precision between 8.4% and 19.0% relative standard deviation. Expanded uncertainty measured was 1.92, 0.23 and 0.03 for 10.0, 1.0 and 0.1 ng mL(-1) DA concentrations, respectively, which demonstrated the accuracy of this method for confirmation and quantification of DA present at very low concentration levels in seawater.

Domoic acid toxicologic pathology: a review

Domoic acid was identified as the toxin responsible for an outbreak of human poisoning that occurred in Canada in 1987 following consumption of contaminated blue mussels [Mytilus edulis]. The poisoning was characterized by a constellation of clinical symptoms and signs. Among the most prominent features described was memory impairment which led to the name Amnesic Shellfish Poisoning [ASP]. Domoic acid is produced by certain marine organisms, such as the red alga Chondria armata and planktonic diatom of the genus Pseudo-nitzschia. Since 1987, monitoring programs have been successful in preventing other human incidents of ASP. However, there are documented cases of domoic acid intoxication in wild animals and outbreaks of coastal water contamination in many regions world-wide. Hence domoic acid continues to pose a global risk to the health and safety of humans and wildlife. Several mechanisms have been implicated as mediators for the effects of domoic acid. Of particular importance is the role played by glutamate receptors as mediators of excitatory neurotransmission and the demonstration of a wide distribution of these receptors outside the central nervous system, prompting the attention to other tissues as potential target sites. The aim of this document is to provide a comprehensive review of ASP, DOM induced pathology including ultrastructural changes associated to subchronic oral exposure, and discussion of key proposed mechanisms of cell/tissue injury involved in DOM induced brain pathology and considerations relevant to food safety and human health.

Development of a pressurised liquid extraction and liquid chromatography with electrospray ionization-tandem mass spectrometry method for the determination of domoic acid in shellfish

Amnesic shellfish poisoning (ASP) is a potentially lethal human toxic syndrome which is caused by domoic acid (DA) that originates in marine phytoplankton belonging to the Pseudonitzschia genus. A confirmatory and sensitive procedure has been developed and validated for the determination of DA in shellfish. The proposed method includes pressurised liquid extraction (PLE) with methanol/acetone (9:1), florisil clean-up purification inside the PLE extraction cell and detection by liquid chromatography (LC) coupled to electrospray ionization in positive mode tandem mass spectrometry (ESI-MS-MS). Comparison of ionization sources (ESI, atmospheric pressure ionization (APCI) atmospheric pressure photoionization (APPI) and combined APCI/APPI) were carried out in order to improve the analytical signal. The main parameters affecting the performance of the different ionization sources and PLE parameters were previously optimised using statistical design of experiments (DOE). Linear calibrations were obtained using mussel tissue extracts 0.05-5 microg DA/ml (R2>0.999). The limits of detection (LOD) and quantitation (LOQ) of the method were 0.2 and 0.5 microg/g respectively and recoveries ranged from 81 to 95%. This method was successfully applied to determine DA levels in 46 shellfish samples collected from Valencian (Spain) supermarkets, showing high sample throughput.

Solid-phase extraction-fluorimetric high performance liquid chromatographic determination of domoic acid in natural seawater mediated by an amorphous titania sorbent

The feasibility of using sol-gel amorphous titania (TiO2) as a solid-phase sorbent for the pre-concentration of domoic acid (DA), a potent amnesic shellfish poisoning (ASP) toxin, directly from seawater was explored. The sol-gel titania material is able to adsorb DA from seawater, via the formation of ester-linkage between the carboxylic moieties of DA and the Ti-OH groups on the sorbent surface, at low pH and desorb it at high pH. The chemisorption process is not significantly interfered by the seawater matrix. The optimum pH values for the adsorption and desorption of DA were found to be pH 4 and 11, respectively. The optimal sorbent loading for the batch-type solid-phase extraction of DA was 0.67 mg-TiO2 ng-DA(-1) and adsorption equilibrium was achieved in 2 h at room temperature. The desorbed DA in 500 microL of 0.1 M alkaline borate buffer can be directly derviatized by 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) in aqueous media for fluorimetric HPLC quantification. Analyte recovery, repeatability and detection limit of this titania SPE-fluorimetric HPLC determination are 89%, 6.2% and 120 pg-DA mL(-1) (n=7, P<0.05), respectively, for a sample volume of 30 mL. This titania SPE technique should also be applicable to the pre-concentration of other polar carboxylate- and phosphonate-containing biomolecules and pharmaceuticals in complex and interfering environmental sample matrices.