Confirmed identification of gymnodimine in oysters from the west coast of South Africa by liquid chromatography–tandem mass spectrometry

Abstract

Mussels Choromytilus meridionalis and oysters Crassostrea gigas were suspended from a mooring off Lambert's Bay, South Africa, to study the kinetics of lipophilic phycotoxin accumulation and detoxification. The shellfish were subsequently harvested daily over approximately three weeks and analysed for lipophilic phycotoxins by liquid chromatography coupled with tandem mass spectrometry in the multiple reaction monitoring mode. A mass transition typical for the cyclic imine toxin gymnodimine was detected in low but consistent levels in all oyster samples throughout the sampling period, whereas this peak was detected with lesser intensity in only some mussel samples and was frequently below the limit of quantitation (0.02 μg g−1 fresh weight). Comparison of retention times and collision-induced mass spectra of a certified standard of gymnodimine and an oyster extract provided unambiguous confirmation of the identity of gymnodimine in the shellfish extracts. The absence of known producers of gymnodimine in the plankton, and the non-detection of gymnodimine in filtered water samples collected during the period of study, lead to the conclusion that the shellfish were contaminated at their site of initial collection in Saldanha Bay prior to deployment off Lambert's Bay. This finding is the first confirmed evidence of gymnodimine in the southern Benguela upwelling system.