Königswinterer Str. 37 a - D-53227 Bonn
Tel. +49-228-976396-0 - Fax +49-976396-12
Algal
toxins are a group of strongly toxic substances occuring in the cells of a number
of Cyanophyceae (blue-green microalgae). Lysis of the cells allows the release
of the substances into the water so that also cell free water can have a toxic
effect. Many toxic cyanophyceae, however, develop next to the toxins also
substances with an extremely strong odor which functions as a warning so that
poisoning of humans is relatively rare (while cattle poisoning is not
uncommon). In fresh water the following Algal toxin forming genera occur:
Microcystis, Anabaena, Planktothrix, Nostoc. Aphanizomenon and
Cylindrospermopsis. Nodularia is found predominantly in seawater (ZECH, 2001).
Algal toxins are either hepatotoxic (Microcystin, Nodularin) oder nerve
toxins (Anatoxin, Saxitoxin). The hepatotoxins are generally cyclic
oligopeptides which inhibit protein phosphatases. They may enter liver cells,
but not other cell types, which explains their specific liver toxicity. About
100 variants of this class of substances have been identified. All have in
common that they contain the rare C20 amino acid "Adda". The toxicity of
the algal nerve toxin is based on the fact that they either funtion as analogon
of acetyl cholin (anatoxin-a), as cholin esterase inhibitor (anatoxin-a(S)) or
that they block sodium channels (Saxitoxin) (WELLER, 2002).
Publications on algal toxins have caused a concern about potential Algal toxin
contamination of products used among others as supplement food for health
reasons. In this context the following has to be considered: Algal toxins occur
either in the intact cyanophycea cells or after lysis of the cells in the
surounding water. In products of low moisture content a contamination could
only be caused by the presence of algal cells.
In case of the cyanophycea Aphanizomenon flos-aquae (blue green alga, Klamath
alga) such a contamination can be imagined, although the actual hazard may be
insignificant. Aphanizomenon flos aquae is not cultivated but is harvested
"from the wild", that is, normally from the Upper Klamath Lake in
Toxic strains (of Microcystis aeruginosa, Anabaena flos aquae) can often
morphologically not be distinguished from the non-toxic ones. However, the
former common assumption that Aphanizomenon flos aquae itself has a toxic
variant (CARMICHEAL, 1997; MAHMOOD, 1087; RAPALA, 1993) has recently been
questioned (LI, 2000).
At any rate, manufacturers of Aphanizmenon have established an extensive
control program (Mouse bioassay, enzyme linked immuno sorbent assay (ELISA)
etc) in order to assure that commercial Aphanizomenon flos aquae is free of
toxins. In line with a recommendation of the World Health Organization the
Department of Agriculture of
In another commercially used algal product, Spirulina platensis (actually
Arthrospira) Phycotoxins cannot occur for the simple reason that Spirulina
grows in an alcaline medium of a pH of around 9 which prevents the growth of
other organisms. There are no toxic cyanophyceae known which would survive
under such circumstances and analyses of commercial samples of Spirulina have
always found to toxin free (KUIPER-GOODMAN, 2001;
Also in case of the kelp species Lithothamnium used as Calcium and Magnesium
source a Algal toxin contamination can be excluded. The partly fossilized
calcareous Lithothamnium leaves are collected from the sea bottom where
cyanophyceae never occur in noticeable concentrations (toxic cyanophyceae form
rather floating accumulations). Be it only for the difference in size the
microscopic cyanophycea cannot by chance be harvested together with
Lithothamnium leaves. The same applies also to various other kelp species (as
Laminaaria and Fucus) used on account of their Iodine content.
(Questions concerning algal toxins are answered by Dr. E.W. Becker, Tübingen,
email: wolfgang.becker@med.uni-tuebingen.de)
BECKER, E.W.(I), VENKATARAMAN, L.V. 1984: Production and utilization of the
blue-green alga Spirulina in
BECKER, E.W.(II), 1984: Biotechnology and exploitation of the green alga
Scendesmus obliquus in India, Biomass, 1-19
CARMICHAEL, W.W., 1997: The cyanotoxins. In Advances in Botanical Research,
Vol. 37 (Ed. by J.A. Callow), pp 211-256. Academic Press,
CARMICHAEL, W.W.; DRAPEAU, C.;
CHORUS, i., BARTRAM J. (eds). 1999: Toxic Cyanobacteria in water - A guide to
their public health consequences. Monitoring and Management. E & FN Spon,
KUIPER-GOODMAN, T., et al., 2001: Risk Assessment of microcystins in blue-green
algal health food products, in: Mycotoxins and phycotoxins in perspective at
the turn of the millenium. Proceedings of the Xth International IUPAC symposium
on mycotoxins and phycotoxins 21-25 May, 2000, Guarauja (Brazil), eds. W.J. de
Koe, R.A. Samson, H.P. van Egmond, J. Gilbert, M. Sabino, IUPAC and AOAC
International, Ponsen and Looyen, Wageningen, The Netherlands, pp.
549-556
LAWRENCE, J., et al., 2001: Comparison of Liquid Chromatography/Mass
spectrometry, ELISA, and Phosphatase assay for the determination of
microcystins in blue-green algae products. J. AOAC Int. vol. 84, no. 4,
1035-1044 LI,
R.H., CARMICHAEL, W.W., LIU, Y.D., WATANABE, M.M., 2000: Taxonomic
re-evaluation of Aphanizomenon flos aquae NH-5 based on morphology and 16S rRNA
gene sequences. Hydrobiologia, 438, 99-100
MAHMOOD, N.A. CARMICHEAL, W.W., 1987: Annatoxin-a(s), an anticholinesterase
from the cyanobacterium Anabaena flos aquae NRC-525-17. Toxicon, 25, 1221-1227
RAPALA, J.; SIVONEN, K., LYRA, C., NIEMELŽ S.I., 1993: Anatoxin-a concentration
in Anabaena and Aphanizomenon flos-aquae at different environmental conditions
and comparison of growth by toxic and non-toxic Anabaena strains, a laboratory
study. Applied Environmental Microbiology, 64, 99-105
WELLER, M.G., 2002: Algengifte im Wasser. Nachrichten aus der Chemie, 06/2002,
S. 700-7005
ZECH; CH., 2001: Entwicklung von immunanalytischen, chromatographischen und
massenspektrometrischen Methoden zur Bestimmung cyanobakterieller Hepatotoxine
(Microcystine und Nodularine). Dissertation, TU München, Nov. 2001, S.3