Studies on Paralytic Shellfish Poison (PSP) Toxification of Bivalves, in Association with Appearance of Alexandrium tamarense, in Hiroshima Bay, Hiroshima Prefecture

In April, 1992, paralytic toxicity substantially exceeding the quarantine limit of 4MU/g edible part as paralytic shellfish poison (PSP) was detected in cultured oyster Crassostrea gigas, mussel Mytilus edulis and short-necked clam Tapes (Amygdala) japonica from Hiroshima Bay, Hiroshima Prefecture concomitantly with the appearance of the toxic dinoflagellate Alexandrium tamarense. The toxicities were 31.4MU/g for oyster, 214.6MU/g for mussel and 20.3 MU/g for short-necked clam on 22nd April. Attempts were made to identify the paralytic toxin in these bivalves. They were extracted with 80% ethanol (pH 3.5), followed by defatting with dichloromethane. The aqueous layer obtained was ultrafiltered through a Diaflo YM-2 membrane (Amicon) to eliminate substances of more than 1,000 daltons, treated with activated charcoal and then applied to a Sep-Pak C18 cartridge (Waters). The unbound toxic fraction was analyzed by HPLC. In gonyautoxin (GTX) analysis of each toxin, protogonyautoxin-1,2 (PX12; epi-GTX8, GTX8; C1.2), GTX4, GTX1, GTX3 and GTX2 were detected. In saxitoxin (STX) analysis, a small peak of STX was detected in mussel and short-necked clam toxin, but not in the oyster toxin. Consequently, the toxin of the bivalves in Hiroshima Bay was found to be comprised of GTX1-4 as the major components, which accounted for approximately 92-95% (mole ratio) of all components, with a trace of STX. In all cases, GTX1 was the major component (approximately 51-55%; mole ratio). On the other hand, the content of PX1,2, which are N-sulfocarbamoyl derivatives, was 1.6-4.5% (mole ratio) irrespective of the sample. It was concluded from these results that the toxin of the above bivalves collected in Hiroshima Bay in April, 1992 consisted predominantly of PSP, possibly derived from the toxic plankton A. tamarense detected there.