Diarrhetic shellfish poisoning toxin esters in Danish blue mussels and surf clams

Variation profile of diarrhetic shellfish toxins and diol esters derivatives of Prorocentrum lima during growth by high-resolution mass spectrometry

Prorocentrum lima is a widely distributed toxigenic benthic dinoflagellate whose production of diarrhetic shellfish toxins threatens the shellfish industry and seafood safety. Current research primarily assesses the difference between free and post-hydrolysis total toxin methods, ignoring the impact of different detection methods on technical accuracy. After removing matrix interference with SPE extraction, a thorough HRMS strategy was created in this study. Alkaline hydrolysis could release the diol esters and played a crucial role in obtaining an accurate assessment of toxin levels, achieving satisfactory recoveries (74.0-147.0%) and repeatability (relative deviation <12.3%). The HRMS approach evaluated toxin profile variation during the growth of three P. lima strains from China. A total of 24 toxin contents varying in composition, content, and a high proportion were detected. The SHG, HN, and 3XS strains had total toxin contents of 23.3 ± 1.74, 19.8 ± 1.25, and 19.5 ± 1.58 pg cell^-1, respectively. The diol esters proportion varied among the strains, with SHG having 58.9-69.9, HN having 75.4-86.5, and 3XS having 91.0-91.7%. The variety of toxins produced by distinct P. lima strains highlighted the significance of this method for appropriately measuring the risks connected with DSTs manufacturing. The proposed approach provides a technical basis for gathering comprehensive and accurate data on the potential risks of P. lima DSTs production, with significant implications for ensuring food safety and preventing harmful toxins from spreading in the marine ecosystem.

Toxin accumulation, detoxification and oxidative stress in bivalve (Anomalocardia flexuosa) exposed to the dinoflagellate Prorocentrum lima

Prorocentrum lima is a cosmopolitan benthic dinoflagellate capable of producing the diarrhetic shellfish toxins (DSTs) okadaic acid (OA) and dinophysistoxin (DTX). These compounds may cause oxidative stress and accumulate in bivalve tissues, which become vectors of intoxication to human consumers. We investigated DST accumulation, detoxification and oxidative stress biomarkers in clams (Anomalocardia flexuosa) experimentally exposed to P. lima cells or their compounds. Experimental diets consisted of 6000 cells mL-1 of the non-toxic chlorophyte Tetraselmis sp. (C; control condition), and combinations of C with 10 P. lima cells mL-1 (T10), 100 P. lima cells mL-1 (T100), or to a toxin concentration of ∼4 μg OA L-1 and ∼0.65 μg DTX-1 L-1 (T100d). Clams were exposed to these diets for 7 days (uptake phase), followed by a 7-day depuration period. No DSTs were detected in clams exposed to treatments C (control) nor to T100d (dissolved compounds) during either uptake or detoxification phase. Conversely, clams exposed to T10 or T100 accumulated, on average, up to 2.5 and 35 μg DST kg-1 in their whole bodies at the end of the uptake phase. These concentrations are ∼64 and ∼4.5 times lower than the regulatory level of 160 μg OA kg-1, respectively. Accumulated OA quotas were 12-22 times higher in the digestive gland (DG) than in remaining tissues over the uptake phase. Quick toxin transformation was indicated by the early detection of conjugated compounds - DTX-1 and OA esters - in the DG after 6 h of exposure, with OA-ester representing the main compound (30 - 100 %) in that tissue over the experiment. During the depuration period, detoxification rates represented 0.024 h-1, 0.04 h-1 and 0.052 h-1 for OA, DTX-1 and OA-ester, respectively. The activities of catalase, glutathione S-transferase, glutathione peroxidase and the levels of oxidative stress by lipoperoxidation varied similarly in the DG of A. flexuosa individuals subjected to T100, T100d and the control condition. However, contrasting antioxidant responses were measured in those exposed to T10. These findings indicate that no oxidative stress was primarily induced by DST-producing dinoflagellates in this clam species under laboratory conditions representative of toxic bloom situations. Even though, possible interactions should be considered under multistressor scenarios.

Response of fatty acids and lipid metabolism enzymes during accumulation, depuration and esterification of diarrhetic shellfish toxins in mussels (Mytilus galloprovincialis)

Bivalve mollusks accumulate diarrhetic shellfish toxins (DSTs) from toxigenic microalgae, thus posing a threat to human health by acting as a vector of toxins to consumers. In bivalves, free forms of DSTs can be esterified with fatty acids at the C-7 site to form acyl esters (DTX3), presumably a detoxification mechanism for bivalves. However, the effects of esterification of DSTs on fatty acid metabolism in mollusks remain poorly understood. In this study, mussels (Mytilus galloprovincialis) were fed the DST-producing dinoflagellate Prorocentrum lima for 10 days followed by an additional 10-days depuration in filtered seawater to track the variation in quantity and composition of DST acyl esters and fatty acids. A variety of esters of okadaic acid (OA) and dinophysistoxin-1 (DTX1) were mainly formed in the digestive gland (DG), although trace amounts of esters also appeared in muscle tissue. A large relative amount of OA (60%-84%) and DTX1 (80%-92%) was esterified to DTX3 in the visceral mass (referred to as digestive gland, DG), and the major ester acyl chains were C16:0, C16:1, C18:0, C18:1, C20:1 and C20:2. The DG and muscle tissues showed pronounced differences in fatty acid content and composition during both feeding and depuration periods. In the DG, fatty acid content gradually decreased in parallel with increasing accumulation and esterification of DSTs. The decline in fatty acids was accelerated during depuration without food. This reduction in the content of important polyunsaturated fatty acids, especially docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), would lead to a reduction in the nutritional value of mussels. Enzymes involved in lipid metabolism, including acetyl-coenzyme A carboxylase (ACC), fatty acid synthase (FAS), lipoprotein lipase (LPL) and hepatic lipase (HL), were actively involved in the metabolism of fatty acids in the DG, whereas their activities were weak in muscle tissue during the feeding period. This study helps to improve the understanding of interactions between the esterification of DSTs and fatty acid dynamics in bivalve mollusks.

Shellfish contamination with marine biotoxins in Portugal and spring tides: a dangerous health coincidence

Bivalve molluscs can acquire marine biotoxins by filter-feeding upon certain toxin-producing microalgae. The two most common syndromes observed in temperate coastal waters have been diarrhetic shellfish poisoning (DSP) and paralytic shellfish poisoning (PSP). While DSP is a non-fatal gastrointestinal syndrome, PSP is a neurological syndrome which can lead to death by respiratory paralysis in high intoxication scenarios. In Portugal, the presence of both DSP and PSP toxins leads to recurrent seasonal bans of bivalve harvesting. On a few occasions, the bans were not placed in time, not properly disseminated to the public or were disregarded by recreational harvesters. Several cases of poisonings have been studied in collaboration between health authorities and the laboratory in charge of the biotoxin monitoring programme. Some of the outbreaks have even called the attention of the local media. In several of these recorded cases, a common trait has emerged throughout the years: bivalve harvest had often been done during very low tides attributed to either new or full moons. These tides expose intertidal bivalves more widely, increase harvesting time, and allow picking of larger-sized specimens. In some occasions, the consumers were extremely unfortunate because a noxious coincidence had occurred: larger-sized specimens were available but had attained the highest toxin content of the toxic season. This review alerts that despite costly monitoring programmes have been perfected through the years, human poisonings still take place due to the rapid increase in toxin levels and/or disrespect of harvest bans.

Fatty acid ester metabolites of gymnodimine in shellfish collected from China and in mussels (Mytilus galloprovincialis) exposed to Karenia selliformis

Marine shellfish exposed to the microalgae Karenia selliformis can accumulate gymnodimines (GYM). Shellfish samples collected from Beihai City in Guangxi Autonomous Region, and Ningde City in Fujian Province, in the South China Sea, as well as mussels Mytilus galloprovincialis fed on K. selliformis under laboratory conditions were analyzed. Gymnodimines and various fatty acid ester metabolites were detected in the clam Antigona lamellaris and pen shell Atrina pectinata, while no esters were found in the oyster Crassostrea sp. and the gastropod Batillaria zonalis despite positive detection of free GYM in both species. When present, the predominant acyl esters observed were 18:0-GYM-A and 20:1-GYM-A. Under laboratory conditions GYM-A was accumulated and metabolized to fatty acid esters in mussels exposed to K. selliformis, with 16:0-GYM-A and 20:1-GYM-A as the major variants. A novel compound with the same accurate mass as GYM-A and its 16:0 fatty acid ester were observed in the experimental mussels but was not present in the microalgal strain to which mussels were exposed. No significant differences of reactive oxygen species (ROS) levels and antioxidant enzymes were found between mussels fed on K. selliformis or GYM-free microalgae Isochrysis galbana. This suggests the accumulation of GYM and its metabolites does not significantly impact the physiological status of mussels. While it is currently not proven that GYM affects human health, risk assessments should consider the presence of GYM esters in naturally contaminated shellfish as part of exposure analysis.

Accumulation of Dinophysis Toxins in Bivalve Molluscs

Several species of the dinoflagellate genus Dinophysis produce toxins that accumulate in bivalves when they feed on populations of these organisms. The accumulated toxins can lead to intoxication in consumers of the affected bivalves. The risk of intoxication depends on the amount and toxic power of accumulated toxins. In this review, current knowledge on the main processes involved in toxin accumulation were compiled, including the mechanisms and regulation of toxin acquisition, digestion, biotransformation, compartmentalization, and toxin depuration. Finally, accumulation kinetics, some models to describe it, and some implications were also considered.

Spatial and seasonal variation of diarrheic shellfish poisoning (DSP) toxins in bivalve mollusks from some coastal regions of Vietnam and assessment of potential health risks

The occurrence of okadaic acid (OA) group toxins in bivalve mollusk collected from Vietnamese coastal areas was investigated from April 2016 to April 2017. OA group toxins were detected in mollusk by UPLC-MS/MS with the highest level of 11.3 ng/g and detection frequency of 11.8%. Toxins were detected more frequently in dry season (14.4% of analyzed samples) than in wet season (7.9%). Toxins were also detected more frequently at sampling locations in the northern parts (≥10.4%) than in the southern part (≤8.3%) of Vietnamese coastline. Results of this study were similar to those obtained in long-term studies in regions geographically close to Vietnam, confirming decisive influence of geographic location on the accumulation of toxins in mollusks. Within the scope of the study, toxin levels in all contaminated samples were below the regulation limit (160 ng/g), but the presence of OA group toxins in bivalve mollusk suggests the need of a more stringent control of toxins in bivalve mollusk in Vietnam.

Effect of Suspended Particulate Matter on the Accumulation of Dissolved Diarrhetic Shellfish Toxins by Mussels (Mytilus galloprovincialis) under Laboratory Conditions

In recent years, detection of trace amounts of dissolved lipophilic phycotoxins in coastal waters has been possible using solid phase adsorption toxin tracking (SPATT) samplers. To explore the contribution of dissolved diarrhetic shellfish toxins (DST) to the accumulation of toxins by cultivated bivalves, mussels (Mytilus galloprovincialis) were exposed to different concentrations of purified okadaic acid (OA) and dinophysistoxin-1 (DTX1) in filtered (0.45 µm) seawater for 96 h. Accumulation and esterification of DST by mussels under different experimental conditions, including with and without the addition of the food microalga Isochrysis galbana, and with the addition of different size-fractions of suspended particulate matter (SPM) (<75 µm, 75–150 µm, 150–250 µm) were compared. Results showed that mussels accumulated similar amounts of OA and DTX1 from seawater with or without food microalgae present, and slightly lower amounts when SPM particles were added. Mussels preferentially accumulated OA over DTX1 in all treatments. The efficiency of the mussel’s accumulation of OA and DTX1 from seawater spiked with low concentrations of toxins was higher than that in seawater with high toxin levels. A large proportion of OA (86–94%) and DTX1 (65–82%) was esterified to DTX3 by mussels in all treatments. The proportion of I. galbana cells cleared by mussels was markedly inhibited by dissolved OA and DTX1 (OA 9.2 µg L⁻¹, DTX1 13.2 µg L⁻¹) in seawater. Distribution of total OA and DTX1 accumulated in the mussel tissues ranked in all treatments as follows: digestive gland > gills > mantle > residual tissues. However, the percentage of total DST in the digestive gland of mussels in filtered seawater (67%) was higher than with the addition of SPM particles (75–150 µm) (51%), whereas the gills showed the opposite trend in filtered seawater with (27%) and without (14.4%) SPM particles. Results presented here will improve our understanding of the mechanisms of DST accumulation by bivalves in marine aquaculture environments.

Variability and profiles of lipophilic toxins in bivalves from Great Britain during five and a half years of monitoring: Okadaic acid, dinophysis toxins and pectenotoxins

Official control biotoxin testing of bivalve molluscs from Great Britain has been conducted by Cefas for over a decade. Reflecting the changes in legislation, bioassays were gradually replaced by analytical methods, firstly for analysis of Paralytic shellfish toxins, followed by introduction of liquid chromatography tandem mass spectrometric (LCMS/MS) method for lipophilic toxins (LTs) in 2011. Twelve compounds, representing three main groups of regulated lipophilic toxins, as well as two non-regulated cyclic imines were examined in over 20,500 samples collected between July 2011 and December 2016. The toxins belonging to Okadaic acid (OA) group toxins were the most prevalent and were quantified in 23% of samples, predominantly from Scotland. The temporal pattern of OA group occurrences remained similar each year, peaking in summer months and tailing off during autumn and winter, however their abundance and magnitude varied between years significantly, with concentrations reaching up to 4993 μg OA eq./kg. Three toxin profiles were identified, reflecting the relative contribution of the two main toxins, OA and dinophysis toxin-2 (DTX2). Dinophysis toxin-1 (DTX1) was less common and was never detected in samples with high proportions of DTX2. Inter-annual changes in profiles were observed within certain regions, with the most notable being an increase of DTX2 occurrences in north-west Scotland and England in the last three years of monitoring. In addition, seasonal changes of profiles were identified when OA, the dominant toxin in early summer, was replaced by higher proportions of DTX2 in late summer and autumn. The profile distribution possibly reflected the availability of individual Dinophysis species as a food source for shellfish, however persistence of DTX2 during autumn and winter in mussels might have also been attributed to their physiology. Mussels were the only species with higher average proportions of non-esterified toxins, while Pacific oysters, cockles, surf clams, razors and queen scallops contained almost exclusively ester forms. In addition, a temporal change in proportion of OA and DTX2 free form was observed in mussels. Pectenotoxin-2 (PTX2) was quantified only on rare occasions.

Contamination of raw bivalve molluscs available in Poland between 2009 and 2013 with marine biotoxins

Introduction: Growing consumption of shellfish is associated with an increased risk of food poisoning. The study was carried out on live bivalve molluscs available on the Polish market between 2009 and 2013. Material and Methods: ELISA was used for the determination of the following marine biotoxins: paralytic shellfish poison (PSP), amnaesic shellfish poison (ASP), and diarrhoeic shellfish poison (DSP). The molluscs, of which seven species were examined, were obtained from wholesale companies and markets. Results: Marine biotoxins were detected below the permitted levels in 67.6% of the samples. The maximum amounts of PSP and ASP biotoxins were found in great scallops (532.6 μg/kg and 1.0 mg/kg respectively) and the peak for DSP was in blue mussels (107 μg/kg). Conclusion: The analysis of toxicological status of raw bivalve molluscs available on the market in Poland indicates that they are safe for consumers.

Determination of typical lipophilic marine toxins in marine sediments from three coastal bays of China using liquid chromatography-tandem mass spectrometry after accelerated solvent extraction

A method based on sample preparation by accelerated solvent extraction and analysis by liquid chromatography-tandem mass spectrometry was validated and used for determination of seven typical lipophilic marine toxins (LMTs) in marine sediment samples collected from three typical coastal bays in China. Satisfactory specificity, reproducibility (RSDs ≤ 14.76%), stability (RSDs ≤ 17.37%), recovery (78.0%-109.0%), and detection limit (3.440 pg/g-61.85 pg/g) of the developed method were achieved. The results obtained from the analysis of samples from Hangzhou Bay revealed okadaic acid as the predominant LMT with concentrations ranging from 186.0 to 280.7 pg/g. Pecenotoxin-2 was quantified in sediment samples from Laizhou Bay at the concentrations from 256.4 to 944.9 pg/g. These results suggested that the proposed method was reliable for determining the typical LMTs in marine sediments and that the sediments obtained from Hangzhou Bay, Laizhou Bay and Jiaozhou Bay were all contaminated by certain amounts of LMTs.

Esterification of okadaic acid in the mussel Mytilus galloprovincialis

Okadaic acid and other toxins of the diarrheic shellfish poisoning (DSP) group are transformed mainly to their acyl-derivatives in bivalves. Some recent studies suggest that bacteria present in the bivalve gut could contribute substantially to the acylation of the toxins. By feeding microcapsules containing okadaic acid to mussels we have shown unequivocally that the ingested okadaic acid is nearly completely transformed to its fatty acid esters (acyl-derivatives). Treating mussels with antibiotics did not have any significant effect on the acylation of the supplied okadaic acid, suggesting that bacteria do not play any significant role in this process. The microsomal and mitochondrial subcellular fractions of the cells of the digestive gland have been shown to have contain enzymes that are able to transfer a fatty acid molecule from Coenzyme A to okadaic acid (so, that have Acyl-CoA:OA acyltransferase activity). This activity was related to that of the enzyme Cytochrome C reductase (NADPH), a marker of endoplasmic reticulum, suggesting that this organelle is the main responsible for the acylation process. Acylation of DSP toxins seems to be a key step in the depuration of these toxins from mussels, as these compounds are found in feces as acyl-derivatives. This is probably true for most bivalves. The proportion of acyl-derivatives accumulated can point to the key process of the depuration: acylation or excretion of acylated derivatives. In the mussels Mytilus galloprovincialis, Mytilus edulis and in Donax trunculus, the first process seems to be the most important, but in most bivalve species it seems to be the second one. Other aspects of the relationship between depuration and acylation are also discussed.

Profiles and levels of fatty acid esters of okadaic acid group toxins and pectenotoxins during toxin depuration. Part I: brown crab (Cancer pagurus)

In 2002, two outbreaks of diarrhetic shellfish poisoning (DSP) occurred in Norway, which was later confirmed to be caused by the consumption of brown crab (Cancer pagurus) contaminated predominantly by esters of okadaic acid (OA) after feeding on toxic blue mussels (Mytilus edulis). In addition to OA-group toxins, pectenotoxins (PTXs) are commonly detected in the toxin-producing algae (i.e. Dinophysis). In this paper, an experiment was set up to study the fatty acid ester profiles and depuration rates of OA-group toxins and PTXs from C. pagurus after feeding on M. edulis containing these toxin groups. OA, DTX1, DTX2 and PTX2 SA were all detected primarily in the form of fatty acid esters in the crab hepatopancreas (HP). Crabs preferentially assimilated toxins of the OA group after feeding on the mussels for 1 week. Detailed analysis of the fatty acid ester profile in crabs and mussels showed that the ester profiles in the crabs differed slightly from profiles of the fatty acid esters in M. edulis, but neither ester profile nor ester to free toxin ratio appeared to change in the crabs during the first 2 weeks of depuration. Calculations of depuration rates of the free forms of toxins resulted in similar reduction rates for OA and DTX2, whereas the depuration rate of DTX1, PTX2 and PTX2 SA was considerably faster. From the industrial perspective, the PTX-compounds are of minor importance compared to the OA group toxins in crabs, considering (1) the uncertainty regarding the oral toxicity of the PTXs, (2) the preferential ingestion of OA-group toxins compared to PTXs and (3) the faster depuration of PTXs.

Removal of lipids and diarrhetic shellfish poisoning toxins from blue mussels (Mytilus edulis) during acid and alkaline isolation of proteins

Diarrhetic shellfish poisoning (DSP) toxins pose a serious health risk for consumers of bivalves and other shellfish, as well as a huge economic burden for the bivalve-producing farmers. In this work, the aim was to utilize a solubilization-based protein-isolation method to produce a low-DSP toxin protein isolate from toxic blue mussels that are unsuitable for the whole shellfish market. A homogenate of whole mussel meat was solubilized at low pH (2.8) or high pH (11.1), followed by centrifugation and reprecipitation of the solubilized mussel proteins at the isoelectric pH. In a second centrifugation, precipitated proteins were collected. These processes resulted in 81 (acid solubilization) and 72% (alkaline solubilization) reduction in the initial DTX-1 toxin content of the mussel meat. No other DSP toxins were found in the protein isolates. Acid processing of mussel meat resulted in 50% reduction in the total lipid content, while alkaline treatment did not significantly affect the lipid content. The effect of citric acid and calcium chloride addition to the mussel meat-water homogenate on lipid and toxin content was also investigated. A poor correlation factor was surprisingly obtained between reductions in DTX-1 toxin and lipids in protein isolates from processed toxic mussels. Results from an analytical mass balance of the DTX-1 toxin during acid processing showed that 61% of this toxin ended up in the aqueous supernatant after the second centrifugation. The present study presents a promising alternative way of utilizing mussels for food production in periods when they are toxic.

Characterization of fatty acid esters of okadaic acid and related toxins in blue mussels (Mytilus edulis) from Norway

Marine algal toxins of the okadaic acid group can occur as fatty acid esters in blue mussels, and are commonly determined indirectly by transformation to their parent toxins by alkaline hydrolysis. Some data are available regarding the identity of the fatty acid esters, mainly of palmitic acid (16:0) derivatives of okadaic acid (OA), dinophysistoxin-1 (DTX1) and dinophysistoxin-2 (DTX2). Other fatty acid derivatives have been described, but with limited mass spectral data. In this paper, the mass spectral characterization of the [M-H](-) and [M+Na](+) ions of 16 fatty acid derivatives of each of OA, DTX1 and DTX2 is presented. The characteristic fragmentation of [M+Na](+) ions of OA analogues provided a useful tool for identifying these, and has not been described previously. In addition, a set of negative ion multiple reaction monitoring (MRM) methods was developed for direct determination of 16 fatty acid esters of OA, 16 fatty acid esters of DTX1 and 16 fatty acid esters of DTX2 in shellfish extracts. The MRM methods were employed to study the profiles of fatty acid esters of OA analogues in blue mussels and to compare these with fatty acid ester profiles reported for other groups of marine algal toxins.

Effects of the marine toxins okadaic acid and palytoxin on mussel phagocytosis

The present study analyzes the effects of the marine toxins okadaic acid (OA) and palytoxin (PTX) on the phagocytic activity of immunocytes from the mussel Mytilus galloprovincialis. In particular, we describe how the effects of the two biotoxins are influenced by the temperature and experimental stress applied before hemolymph withdrawal. The collected data indicate that OA increases phagocytic activity only when hemolymph incubation is performed at 25 degrees C, but not at 20 degrees C, suggesting a certain degree of dependence of OA effects from the status of mussel immunocytes. Conversely, PTX plays an active role in immunocyte signalling transduction pathways, increases the phagocytic activity and markedly promotes the involvement of p38 mitogen-activated protein (MAP) kinase in phagocytosis. Overall, we conclude that both OA and PTX influence mussel phagocytic activity, and the toxic effects may depend on both the mollusc conditions and the activation of specific signalling pathways.

Shellfish consumption: a major risk factor for colorectal cancer

In the last decades, relevant efforts have been made to reduce the cancer incidence in the European Union. The prevention programmes against cancer have obtained satisfactory results except for colorectal cancer (CRC). Identification of risk factors is primordial to plan preventive strategies for CRC. We hypothesize that shellfish consumption is increasing CRC incidence. DSP toxins, present in some seafood products, seem to behave like tumour agents. There are no relevant studies on real health-risk of consuming DSP toxins, just some experimental and ecological evidence. Preventive interventions for reducing CRC risk must be approached through the collaboration of governmental, health and environmental sectors as a single regulatory agency. Sometimes, shellfish accumulates diarrhetic shellfish poisoning (DSP) toxins (i.e. okadaic acid and its derivatives) which provoke a gastrointestinal illness (DSP syndrome). Furthermore, DSP toxins are tumour promoters that could increase CRC risk. The current regulation about level of DSP toxins in shellfish meat is only centred on reduction of the gastrointestinal symptoms. Unfortunately, legal levels of DSP toxins in shellfish are enough to increase CRC risk. A review of legislation on DSP toxins is urgent.

Lipophilic toxin profile in Galicia (Spain): 2005 toxic episode

By the end of 2005, a toxic episode of phytoplankton origin in bivalve shellfish led to the closing down of several shellfish production areas in Galicia (northwestern region of Spain). During this time, different kinds of shellfish were collected and analysed by LC-MS/MS to search for the following lipophilic toxins: okadaic acid (OA), dinophysistoxins (DTXs), pectenotoxins (PTXs), azaspiracids (AZAs) and spirolides. Samples were analysed before alkaline hydrolysis in order to investigate the presence of free OA and DTXs, AZAs, PTXs and spirolides, and after alkaline hydrolysis to detect OA and DTXs esters. All of the samples were found to be contaminated with OA and/or DTX-2, as well as esterified forms of these diarrhetic shellfish poison (DSP) toxins, at levels around and above European regulatory limit (160 microg of okadaic acid equivalents/kg). The analyses of mussels and razor clam also revealed the presence of 13-desmethyl spirolide C (SPX-1) at levels below 31 microg/kg. Likewise, in many of the samples different levels of pectenotoxin-2 secoacid (PTX-2sa) were detected. DSP toxin esters represent practically the 100% of the total OA equivalents for scallops, clams, razor clams and cockles.

Diarrheic shellfish poisoning due to toxic mussel consumption: The first recorded outbreak in Greece

During the week of 14-20 January 2000, 120 people visited the Emergency Departments of hospitals in Thessaloniki, northern Greece, complaining of acute gastrointestinal illness after eating mussels (Mytilus galloprovincialis). The symptoms indicated diarrhoeic shellfish poisoning, and the toxicity of mussels harvested from Thermaikos Gulf in Thessaloniki during the outbreak was investigated using mouse bioassays. The bioassays revealed toxicity to mice by the mussel samples; while high numbers of toxic algae Dinophysis acuminata were identified in water samples from Thermaikos Gulf. The harvesting of mussels was immediately suspended and a monitoring programme for algal blooms was established from then onwards. During a follow-up of the mussels' toxicity from January 2000 to January 2005, two more mussel samples were found positive for diarrheic shellfish poisoning: one harvested in March 2001 from the area of the outbreak (Thermaikos Gulf) and the other harvested in January 2001 from Amvrakikos Gulf in north-western Greece. However, no sporadic cases or outbreaks were reported during this period.