Mouse Out! Chemistry In. Updates in Paralytic Shellfish Toxins

By Saji George

The paralytic shellfish toxins are a group of 18 secondary metabolites deposited in bivalve mollusks by dinoflagelates. Dinoflagelates blooms are seasonal, occurring during warm months. Since it is unpredictable whether an infestation will occur, the shellfish population should be regularly monitored for toxins. Ingestion of contaminated shellfish can lead to paralytic shellfish poisoning; a life-threatening illness.

Mouse bioassay is the official method of AOAC International, but the drawbacks associated with this method have led to exploration of chemical methods. The most common HPLC post-column method is to oxidize the separated toxins under alkaline conditions to a fluorescent compound. Sullivan et al. used this method to determine the gonyautoxins 1-6 (GTX1-6), saxitoxin (STX) and neosaxitoxin (neoSTX) but not the N-sulfocarbamoyl-11-hydroxysulfate toxins (C1-C4). Oshima et al. modified this method to determine the 3 toxin groups separately using isocratic elution with 3 different mobile phases. Further improvement by Jeffery van de Riet of the Canadian Food inspection Agency (CFIA) in collaboration with National Research Council Canada (CNRC) has led to a shorter analysis time to determine the 3 groups of toxins using step gradient and a switching valve.

Marine Biotoxins were a hot topic at the recent Pacific Northwest AOAC meeting in Tacoma, WA. According to Jeff, this method is also the topic of an AOAC interlaboratory study (currently underway) and has already been approved by the Shellfish Sanitation Program (NSSP) at the single laboratory validation (SLV) stage for use in the United States as a screening (type IV) method in shellfish monitoring. If approved by AOAC following the interlaboratory study as an official method of analysis (OMA) for shellfish, the method will then be eligible for consideration as a type II reference method by Codex Alimentarius This will also effectively end the use of mouse bioassays in shellfish monitoring within Canada.

This method was presented at the Annual Meeting of the Pacific NW Section, held at the University of Puget Sound (UPS) in Tacoma, which offered extensive laboratory training workshops this past June.