Esterification of DSP toxins by Portuguese bivalves from the Northwest coast determined by LC-MS--a widespread phenomenon.

Okadaic acid (OA) and dinophysistoxin-2 (DTX2) were confirmed by liquid chromatography with mass spectrometry detection both in extracts of digestive glands and edible parts of Portuguese shellfish. No dinophysistoxin-1 was found even in highly contaminated samples examined. However, only in blue mussel (Mytilus edulis) were these two parent toxins commonly found in a free form. Usually they were found largely esterified in all remaining shellfish species-common cockle (Cerastoderma edule), peppery furrow shell (Scrobicularia plana), carpet shell (Venerupis pullastra), oyster (Crassostrea japonica), razor clam (Ensisspp.), and clam (Ruditapes decussata). Oysters were the least toxic. In mussels esterified OA did not surpass 50% of the total OA found in edible parts, while DTX2 esterification rates were usually much lower. In remaining shellfish species usually more than 95% of the total OA was found esterified, while free DTX2 was rarely found. Also ratios of total DTX2/total OA were higher in mussels than in the remaining species examined. From all these species commercially exploited at the northern coast, mussels and cockles contained the highest levels of DSP toxins, thus representing the highest theoretical health risk. The previous association of DTX2 with the dinoflagellate Dinophysis acuta was confirmed with selective MS detection; while OA was the only parent diarrhoeic toxin found associated with Dinophysis acuminata.