Liquid chromatography (HPLC) was used to search for
esters of DSP toxins in Portuguese bivalves.
Hexane-soluble derivatives of
okadaic acid (OA) and
dinophysistoxin-2 (DTX-2) were found. Presumably they are acyl derivatives, globally known as 'dinophysistoxin-3' (DTX-3). In certain instances DTX-3 content surpassed 50% of the total amount of DSP toxins. A human diarrhetic
poisoning (DSP) incident with Donax clams (Donax trunculus) harvested at Fuzeta (Algarve coast) was confirmed where the apolar (DTX-3 type) and other
esters remaining in the polar aqueous
methanol layer were implicated. The percentage of acyl
esters of OA was always higher than those of
DTX-2. An enzymic mechanism for the conversion of OA and
DTX-2 seems to be implicated in some kind of detoxification process because the percentage of
esters increases with the toxin amount ingested by the bivalve and there is some degree of selectivity as
DTX-2 seems more difficult to acylate. These findings pose a problem for the current assay methods used to detect DSP because mainly they are able to detect the parent toxins but not their
esters. The current bioassay method [Le Baut, C., Bardin, B., Bardouil, M., Bohec, M., Masselin, P., Truquet, P., 1990. Etude de la decontamination de moules toxiques. Rapport IFREMER DERO-90-02 MR. 21 pp.] used in Portugal includes a
hexane washing step that prevents interference from
free fatty acids. However, it cannot detect the presence of acyl derivatives because they are highly soluble in
hexane.