712 K. Campbell et al. which then progresses to the fingers and toes, followed by the loss of control of arms and legs. Difficulty in breathing ensues from paralysis of the muscles of the chest and abdomen, which results in death at high toxin doses. Fatal levels of less than 1 mg of the reference toxin saxitoxin (STX) have been reported (van Egmond et al. 2004). There is currently no antidote for intoxication with artificial respiration as the palliative care until the toxin is excreted from the body. PSP has major implications to public health and thereby seriously threatening economic consequences in coastal communities and aquaculture industries worldwide. Therefore, globally shellfish destined for human consumption are routinely monitored for PSP toxins by regulatory bodies. The internationally accepted and European Union reference method of analysis for PSP toxins in shellfish is the Association of Analytical Communities (AOAC)-accredited bio- logical method (AOAC 2005a) or more commonly referred to mouse bioassay. Using this method shellfish are deemed fit for consumption based on a regulatory limit, which in Europe is 800 mg of PSP toxins per kg of shellfish meat, a level which has been established for the prevention of acute poison- ing (European Commission 2004). In some other countries this limit is lower (Campas et al. 2007). However, both ethical issues relating to the use of animals and technical concerns unfolding in relation to interference and sensitivity of the assay, particu- larly if European Food Safety Authority (EFSA) recommendations for lowering the regula- tory limit are to be considered, is advancing the search for alternative methods of analysis (EFSA 2009). As a family group, both the chemical and biological properties of the PSP toxins categorise the task of developing an alternative method as extremely challenging from any analytical perspec- tive. Chemically, there are more than 20 common PSP toxins (Figure 1) that vary in structure at four main sites (R1–R4) of the parent compound STX (Llewellyn 2006a). The toxins are classified into groups based on the chemical substitutions at R4 as carbamate, decarbamoyl, sulfocarbamoyl and deoxydecarbamoyl. The carbamoyl and decarbamoyl toxins are the most toxic, whereas the sulfocarba- moyl toxins have a much lower potency. In contrast to the leaching of PSP toxins from shellfish to water it is interesting to note, however, that in the processing of canned seafood contaminated with PSP toxins, the sulfocarbamoyl toxins may be hydrolysed to the more toxic groups, which will increase the overall PSP toxicity (Christian and Luckas 2008). In the last number of years due to advances in mass spectrometry new structural ana- logues are also being identified (Dell’Aversano et al. 2008). Biologically, each analogue displays a different R1 +H2N Toxicity Factor 1.00 0.3382 0.6005 1.0911 0.8993 0.6569 R4 N N R3 H N N H OH R2 OH NH2+ R1 H H H OH OH OH R2 H H OSO3- H H OSO3- R3 H OSO3- H H OSO3- H OCRO4N:H2 STX GTX 2 GTX 3 NEO GTX 1 GTX 4 RMM 299 395.4 395.4 315.3 411.4 411.4 N-Sulfocarbamoyl toxins OCORN4H: SO3- RMM TFoaxcictoitry B1 (GTX 5) 379.4 0.0632 C1 475.4 0.0047 C2 475.4 0.0754 B2 (GTX 6) 395.4 0.0607 C3 491.4 0.0101 C4 491.4 0.0436 Decarbamoyl toxins RMM TFoaxcictoitry R4: OH dc-STX 256.3 0.7451 dc-GTX 2 352.3 0.1625 dc-GTX 3 352.3 0.3978 dc-NEO 272.3 0.7013 dc-GTX 1 368.3 ND dc-GTX 4 368.3 ND Deoxydecarbamoyl toxins R4: H RMM TFoaxcictoitry do-STX 240.3 ND do-GTX 2 336.3 ND do-GTX 3 336.3 ND Figure 1. Structure, relative molecular mass (RMM) and toxicity factor of paralytic shellfish poisoning (PSP) toxins.