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Molluscs (particularly bivalves such as scallops, mussels and oysters) are a particularly strong area of growth in aquaculture. Production is forecast to rise to 10 million tonnes by 2010 (FAO statistics) but global market demand is consistently exceeding supply. Unfortunately bivalve molluscs can pose significant risks to human health. Shellfish are frequently consumed raw or only lightly cooked, allowing harmful bacteria and viruses to infect consumers. Bivalves can also very efficiently accumulate seafood toxins from the algae they eat. These toxins can sometimes produce severe, sometimes fatal poisoning in consumers and are unaffected by cooking. The major groups of toxins and their effects are shown in the table below (Table 1).
Amnesic shellfish poisoning (ASP), azaspiracid poisoning (AZP), diarrhetic shellfish poisoning (DSP) and paralytic shellfish poisoning (PSP) related toxins are all found in European waters, while neurotoxic shellfish poisoning (NSP) toxins could be found in imported shellfish. Actual clinical cases of shellfish poisonings are thankfully rare in Europe but there is concern that toxic algal blooms may be increasing in frequency with the prospect of an increase in poisonings.
TABLE 1: Phycotoxin Summary
| Toxin Group | ASP | DSP | PSP | AZP | | Principal Toxins | Domoic acid | Okadaic acid Dinophysis toxins Pectenotoxins and Yessotoxins | Saxitoxins
Gonyautoxins
C-Toxins
| Azaspiracid | | Origin | Diatoms | Marine Dinoflagellates | Marine Dinoflagellates | Marine Dinoflagellates | | Symptoms | Symptoms include nausea, vomiting, diarrhoea, amnesia and respiratory depression | Symptoms include nausea, diarrhoea, vomiting and abdominal pain | Tingling/ numbness in mouth, ataxia, dizziness, headache, respiratory distress and muscular paralysis | Similar symptoms to DSP, headaches & cramps | | Examples | Eastern Canada (1987): Human poisoning (104 people)- 2 deaths | UK (2006): 151 patients diagnosed as suffering from DSP resulting from high Okadaic acid levels in mussels | Annually results in approximately 300 deaths | Toxic outbreak in the Netherlands and England due to consumption of Irish mussels | | EU limits | 20 mg/kg | 160 µg/kg
(OA, DTXs & PTXs), 1 mg/kg YTX
| 0.8 mg/kg of tissue | 160 µg/kg
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Testing
Seafood toxins have traditionally been detected using the mouse bioassay, variations of which are still the international regulatory assay for PSP and DSP toxins. However, several countries have now banned its use in food testing, believing it to be an inappropriate use of live animals. We support this view and Integrin does not offer mouse bioassay testing.
Amnesic Shellfish Poisoning
We use the international regulatory HPLC method to detect and measure domoic acid (ASP). The method has been fully validated. The use of diode array detector allows the identification of possible co-eluting compounds.
 HPLC Method Specification:
Limit of quantitation: 1µg/g
Range: 1µg/g - 250µg/g
Paralytic Shellfish Poisoning
For PSP we use the Ridascreen quantitative immunoassay kit to detect PSP toxins. The kit is aimed at saxitoxin but will also cross react with a number of other PSP toxins, including Gonyautoxins II, III, C1 and C2 as well as Neosaxitoxin. This is a good coverage of the likely PSP toxins that have so far been found in European waters. We are currently involved in assessing and developing novel alternative assays for PSP.
Ridascreen Method Specification:
Limit of quantitation: 10µg/100g
Range: 10-160µg/100g
Diarrhetic Shellfish Poisoning
EU Council Directive 91/492, upon which current UK legislation is based, requires that ' the customary biological testing method must not give a positive result for the presence of Diarrheic Shellfish Poison (DSP). The regulations for DSP toxins have now been amended by Commission Decision 2002/225/EC of 15 March 2002. The DSP toxin complex has been split into four groups: Okadaic acid (OA) and dinophysistoxins (DTXs), pectenotoxins (PTXs), yessotoxins (YTXs), and azaspiracids (AZAs). Limits have also been set for each group: 160 micro g/kg OA equivalents for OA, DTXs & PTXs together, 1 mg yessotoxin equivalent / kg for YTXs, and 160 micro g azaspiracid equivalents / kg for AZAs. Specifications for alternative detection methods, to replace the mouse bioassay, have been provided in the decision but this decision has yet to be adopted in the UK.
Integrin has developed a fluorescent protein phosphatase inhibition assay which directly measures the toxic activity of OA and DTXs, giving a result in total OA equivalents per 100 grams of tissue. This assay meets all the Decision's analytical requirements for the OA / DTX group, and has been accredited by UKAS. DSP tests will normally be carried out by phosphatase inhibition assay. Integrin will continue to offer the DSP-check ELISA assay for customers who request it.
Other DSP toxins (YTX, PTX and AZP's) are tested for by LC-MS. Please contact us for prices.
Shellfish Protein Phosphatase Inhibition Assay Specification:
Species detected: OA, DTX1, DTX2 and DTX3
Limit of detection: 5µg/100g
Limit of quantitation: 10µg/100g
Range: 10 - 50µg/100g
Neurotoxic Shellfish Poisoning and other toxins
Please contact us if you have testing requirements for other toxins not stated above. There are assays available and we would be pleased to advise on the possibility of providing a testing service and likely costs.
For further information contact:
Dr J. Douglas McKenzie Tel:+44 (0) 1631 720765
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Seafood Safety 