MAP Technical Reports Series No. 106 UNEP

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Mechanism of action. While the PSP toxins act as non-depolarizing agents in the
membrane of the excitable cells, lipid-soluble neurotoxins, brevetoxins, responsible for NSP, act
as depolarizing substances. One of the toxic fractions (T 47) acts to open membrane channels
permeable to Na + , leading to a Na + influx. 42 K analysis precludes the effect of T 47 acting on the
K + channels (Risk et al., 1979).
According to more recent research, the lipophilic toxins profoundly affect Na + channels,
modifying virtually every aspect of their physiology and also the interaction of the channel with
nearly every other known class of active drug, including polypeptide toxins, local anaesthetics,
and the guanidinium toxins (Strichartz et al., 1987).
P. brevis cell fragments, upon becoming airborne in sea spray, elicit nonproductive
sneezing and coughing when inhaled (Music et al., 1973). The inhalation of the windsprayed cells
contaminated by the toxin(s) cells of P. brevis caused the opening of sodium channels by the
toxin(s), releasing acetylcholine and causing smooth tracheal muscle contraction. The effects
are only temporary (Krzanowski et al., 1981). All toxins isolated from P. brevis possess this
activity and during purification, if they become airborne on silica gel particles, cause the same
effect.
7.3.5.6 Tolerance levels and safety considerations
The Florida Department of Natural Resources (DNR) has run a general control program
since the mid 1970's. Only in 1984 were Ptychodiscus blooms specifically noted in control
regulations. Closures are made when the dinoflagellates exceed 5000 cells/litre near harvesting
areas. Closures have lasted between a few weeks and six months. Two weeks after
Ptychodiscus concentration drop below 5000 cells/litre, the first mouse bioassays of shellfish
are carried out. When levels are below 20 MU/100 g, the grounds are reopened (Beverly, 1985).
Also in Italy provision of law was based on this bioassay but established "no detectable amount"
(Ministero della Sanità, 1990c).
7.3.5.7 Gymnodinium spp. in the Mediterranean sea
The annual periodicity of Gymnodinium sp. indicated as Gymnodinium breve (Davis)
in an inshore eutrophic environment (Saronicos Gulf, Aegean Sea) from January 1977 to
December 1983 as well as during January to December 1985 has been studied. Spectral
analysis of the data as well as auto and cross correlation analysis confirmed the existence of
12 month cyclic variation of G. breve populations, regulated mainly by temperature (Pagou and
Ignatiades, 1990). Identification of G. breve Davis = Ptychodiscus brevis (Steidinger, 1979)
using electron microscopy was not performed. Effects on health implications (NSP) and fish kills
are to date not reported in the Aegean sea.
The other dinoflagellate of interest in the Mediterranean (Adriatic sea) is Gymnodinium
sp. responsible for "green tides" in 1976-77 (Viviani, 1981; Viviani et al., 1985, 1992) along the
Emilia-Romagna coast and in 1984 and 1988 in the Northern Adriatic sea (Artegiani et al., 1985;
Honsell et al., (in press); Regione Emilia-Romagna, 1985, 1989; Centro Studi Ricerche Risorse
Biologiche Marine Cesenatico, 1985; 1989). This species, at first regarded as similar to G. corii
and distinct from the toxic G. breve of Florida and also described in Japan, is now being studied
in order to define its taxonomy. The NSP and PSP toxins have never been detected in the cells
(Viviani, 1983). During the blooms of this Gymnodinium sp. in September 1977 symptoms of
respiratory irritation were reported in people, both along the coast and in the sea probably related
to the presence of seawater aerosols containing cell fragments or substances of this naked
dinoflagellate (Viviani, 1983;