Karenia mikimotoi

4.1 Possible exposure of bathers to free toxins
dissolved in the water
The possibility of bathers swallowing water containing dissolved phycotoxins must be
considered. Other than cyanobacterial toxins in fresh water (sect. 6.) there is a dearth
of information regarding the occurrence and stability of dissolved phycotoxins in natural
waters.
4.1.1 Domoic acid
Domoic acid (DA) is a water-soluble neurotoxin produced and released by several
species of the diatom Pseudo-nitzschia and by Nitzschia navis-varingica (Leftley and
Hannah, 2008). DA accumulates in the culture medium in dense laboratory cultures of
limited volume but there is no evidence that the free form of the toxin accumulates to
any significant concentrations in the ocean as it is photolabile (Bates et al., 2003;
Bouillon et al., 2006).
4.1.2 Okadaic acid and its congeners
Okadaic acid and its congeners are lipophilic compounds and of low solubility in water.
Their chemistry and stability has been discussed by Quilliam (2004). There appear to
be no reports of okadaic acid and related compounds being detected in significant
quantities in natural waters.
The extracellular production of okadaic acid by Prorocentrum lima in laboratory cultures
was observed by Rausch de Traubenberg et al. (1995). It was subsequently shown
that Prorocentrum spp. produce soluble sulphated diol esters of the parent acid
(Quilliam, 2004 and refs. therein).
4.1.3 The saxitoxins
No reports of the detection of the free toxin in natural waters were found.
4.1.4 Nodularin
Little toxicological data are available. It is considered equivalent in toxicity to
microcystin-LR produced by freshwater cyanobacteria (see Table 7). It is water soluble
and stable in solution (see 3.11).
30 A Literature review of the potential health effects of marine microalgae and macroalgae