Improving detoxification Efficiency of PSP-contaminated oysters (Crassostrea gigas Thunberg)
|Author(s)||Lassus Patrick, Bardouil Michele, Baron Regis, Berard Jean-Baptiste, Masselin Pierre, Truquet Philippe, Pitrat Jp|
|Source||Aquaculture Europe (European Aquaculture Society), 2005-06|
|Keyword(s)||Detoxification, PSP toxin, Toxic algae, Bioaccumulation, Contaminant, Clam, Mussel, Oyster, Shellfish culture|
|Abstract||Shellfish production, and production of marine bivalve molluscs in particular, is the main form of marine aquaculture in the European Union, with a production estimated at 1,200,000 tons in 1999 (Food and Agricultural Organization). Moreover, aquaculture production is rapidly expanding throughout Europe and is becoming a major economic resource in developing areas such as Northern Greece, Ireland, and northwestern Spain.
These shellfish, mainly mussels, oysters, and clams, are produced in a natural environment. Due to variations in their environment, these otherwise edible species may however become unsafe for human consumption.
Potential problems are amplified due to the nature of shellfish themselves: as they are filter feeders, they consume large amounts of algae. Contaminants, which are not harmful to them, therefore tend to concentrate in shellfish. Toxic algae have been a growing threat these last decades and at least three different types of shellfish poisoning, namely, diarrhetic, amnesic, and paralytic shellfish poisoning (DSP, ASP, and PSP), have been observed in Europe so far. Toxins that cause PSP are lethal compounds and first symptoms in man requires immediate medical attention due to the lack of specific antidotes. Accordingly, the Council of the European Communities have decided that live bivalve molluscs intended for immediate human consumption had to meet the following requirement regarding PSP toxins: "the total Paralytic Shellfish Poison content in the edible parts of molluscs must not exceed 80 microgrammes per 100 g of mollusc flesh" (Council Directives 91/492/EEC and 97/61/EEC). However, several weeks may be required for shellfish to eliminate saxitoxin or other analogs through a natural self-purification process termed depuration. Moreover, it is impossible to estimate the time required to reach regulatory PSP toxin levels in shellfish contaminated by the micro-alga Alexandrium, as there is no way to predict the size and duration of the bloom. No practical system exists that is capable of reducing this depuration/detoxification period. PSP toxin levels encountered in Europe typically range from 150 to 250 µg STX eq/100 g. They may, however, reach 1,000 µg STX eq/100 g, and even more in mussels. Although most of the time PSP toxin levels in oysters have been shown to be lower than that in mussels collected in the same area, they have often reached values either just above, or well above the regulatory limit (80 µg STX eq/100 g) and have been generally shown to range from 150-250 µg STX eq/100 g...