MAP Technical Reports Series No. 106 UNEP

7.2.1.5 PSP compromised seafoods
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Saxitoxin and related toxins which cause PSP usually have little effect on shellfish but
are potent neurotoxins to vertebrates, including man, causing respiratory paralysis and death
by asphyxia. PSP are a group of toxins produced by certain species of dinoflagellates, present
in phytoplankton or in resting cysts. The toxins are taken up by predators feeding on plankton,
such as bivalve mollusc, but also as fish plankton feed. Human exposure is brought principally
about by consumption of PSP-containing shellfish which accumulate the toxins. The highest
concentrations of PSP have been found in these digestive organs, but PSP is also present in
other soft tissues. Since the sulfamate toxin is far less potent than its corresponding carbamatesulfgroup
it is easy to convert sulfamate to carbamate, the sulfamate toxins, when present in
bivalves constitute a reservoir of latent or cryptic toxicity (Hall and Reichardt, 1984).
7.2.1.6 PSP depuration of live stock of bivalve molluscs and of fish plankton feed
Owing to the importance of detoxification of toxic live shellfish, the effects of ozonation,
thermal shock, cation exchange and chlorination have been studied on the biological process
of detoxification (Viviani, 1981). Ozonation appears to be the most viable procedure to remove
low levels of the toxins from soft-shell clams (Blogoslawski and Neve, 1979), but is ineffective
when they have retained the toxins for long periods (White et al., 1985). Several observations
and studies in the past suggest that industrial processing (canning) may be a way of utilizing
contaminated shellfish resulting in a pronounced decrease in PSP concentration (Viviani, 1981).
In seafood a particular problem concerns finfish. Since finfish, unlike shellfish, are unable to
accumulate the toxins in their flesh, there would seem to be no problem in terms of the suitability
of fish plankton feed for human consumption, except possibly in instances where whole fish are
consumed without processing (White, 1984).
7.2.1.7 Methods of analysis for PSP
The most commonly employed methods is the mouse bioassay. All PSP components
are measured by this procedure (Viviani, 1981; WHO, 1984). The biological analysis is based
on the dose of PSP (expressed as the equivalent amount of saxitoxin), that provokes a fixed
death time in mice (from 1 to 60 minutes) injected intraperitoneally with an acid-soluble extract
of bivalve molluscs (Helrich, 1990; Hall, 1991). The mouse bioassay will be banned in Europe
in the coming years due to the public outcry over the use of animal in testing. Identification of
numerous saxitoxin derivatives during the last two decades has led to consider the mouse
bioassay for PSP detection a not entirely satisfactory assay for potentially contaminated food
sources in various PSP toxins. The development of assay procedures alternative to the in vivo
animal bioassay has gained increasing support (Shimizu and Ragelis, 1979). An improved high
pressure liquid chromatographic procedure (HPLC) for the PSP toxins has been developed by
Sullivan and Wekell (Sullivan and Wekell, 1984).
At present a radioimmunoassay (RIA) and indirect enzyme-linked immunoabsorbent
assay (ELISA) were developed only for the detection of saxitoxin but not for all PSP toxins
(Carlson et al., 1984; Chu and Fan, 1985). It appears that a relatively less expensive analytical
method is needed, simple to use and which can be employed in the field, comparable to or better
than the mouse bioassay in sensitivity and accuracy, and have the ability to cross react among
all the toxins likely to be present in marine shellfish affected by PSP.