MAP Technical Reports Series No. 106 UNEP

7.2.2.5 DSP compromised seafoods
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Causative shellfish in Japan were the mussels Mytilus edulis and M. coruscum, the
scallops Patinopecten yessoensis and Chlamys nipponensis akazara, and the short-necked
clams Tapes japonica and Gomphina melaegis, while in European Atlantic coasts M. edulis and
in Adriatic and French Mediterranean coast M. galloprovincialis. In Japan and in the Atlantic
coast of Spain and France the infestation period ranges from April to September and the highest
toxicity of shellfish is observed from May to August, though it may vary locally (Yasumoto et al.,
1978, 1980, 1984; Campos et al., 1982; Berthomé et al., 1986; Delmas et al., 1993). In
Scandinavia, on the contrary, oysters in February and mussels in October have caused DSP
(Edebo et al., 1988). According to the provisions of the Italian Laws on toxic shellfish (Ministero
della Sanità, 1978; 1990a,b,c) the level of DSP biotoxins present in mussels from intensive
farms and natural beds along the coasts of Emilia-Romagna made them unsuitable for sale for
human consumption for a duration of 8 months (Viviani et al., 1990) for two consecutive periods,
from June 1989 to January 1990 and from June 1990 to January 1991. Okadaic acid and DTX-1
were found in Western European shellfish (Dahl and Yndestad, 1985), while YTX was detected
in Norwegian blue mussels in addition to acidic components (Lee et al., 1987). PTXs have not
been reported from European shellfish but few attempts have been made to detect these
components because of lack of routine methodology for their detection (Krogh, 1989). In
hepatopancreas of highly toxic mussels of Adriatic sea the presence of okadaic acid has been
evidenced through 1 H NMR spectroscopy. In addition, structural elucidation of the components
of two further toxic fractions is still in progress (Fattorusso et al., 1992).
The method of cooking did not alter toxicity of the causative shellfish but intoxication
could be avoided if the digestive glands were eliminated beforehand (Yasumoto et al., 1978;
1990). Comparative analysis for DSP in various shellfish collected from the same area was
conducted in Japan and the highest toxicity was found in the blue mussels, with less toxicity in
scallops, and very little in oysters. The differences were noted between mussels cultivated at
different depths, with concentrations differing by factors of two to three (Yasumoto et al., 1978;
1980). Also the first results obtained in the Adriatic sea (Boni et al., 1992) show that not all
species of bivalve molluscs, living in the same habitat infested by the microalgae, manifest an
analogous functional attitude towards the absorption and concentration of the enterotoxin in their
tissues. In particular, although they were drawn out of the same habitat, while values of 4 MU
(calculated according to IFREMER) were found in mussels, in Tapes semidecussatus the risk
level was never passed, in C. gallina, O. edulis and V. verrucosa DSP was not detected.
7.2.2.6 DSP detoxification in bivalve molluscs
Two DSP depuration experiments have been undertaken in 1989: one in laboratory
conditions and the other one in an oyster culture pond (Lassus et al., 1991). Two different sets
of diarrheic toxins (DSP) contaminated mussels have been used, respectively at high (3 MU)
and low (1 MU) initial toxic levels. These two sets were contaminated during two Dinophysis spp.
blooms, which occurred in June 1989 respectively along French Mediterranean (Sete) and West-
Brittany coasts (Douarnenex Bay). Depuration rates have been estimated simultaneously by
mouse test and high pressure liquid chromatography (HPLC). For highly toxic mussels, results
evidence a better depuration rate in the oyster culture pond with 0.5 MU g -1 in digestive glands
after 20 days and 1.0 MU g -1 in laboratory conditions after 42 days. For lower initial toxic level (1
MU), time needed for depuration is of course shorter but similar disparity is observed between
laboratory and pond experiments are assumed to be the causative factors for observed
differences in depuration rates (Lassus et al., 1991).