Dinophysistoxin-2: the predominant diarrhoetic shellfish toxin in Ireland

Diarrhoetic shellfish poisoning (DSP) in Europe is due mainly to the presence of the dinoflagellate toxin, okadaic acid (OA). However, analysis of cultivated mussels (Mytilus edulis) from southwest Ireland revealed that an isomer of OA, dinophysistoxin-2, was the major toxin present during DSP episodes. Using fluorimetric HPLC, following derivatisation with 9-anthryldiazomethane, both OA and DTX-2 were found in shellfish during a prolonged toxic episode in 1991. However, examination of similar mussel cultivation locations in 1994 showed that DTX-2 was even more predominant. During this DSP period, OA levels were less than 0.7 microgram/g, whereas maximum DTX-2 levels of 6.3 micrograms/g hepatopancreas were recorded. This toxicity in shellfish occurred soon after high cell counts of Dinophysis acuta were observed. As well as large seasonal variability in toxin levels in rope cultured mussels, substantial variations were also observed, both horizontally and vertically, within the water column.