Neurotoxins are produced by several species of cyanobacteria, including species of Anabaena, Aphanizomenon and Oscillatoria. Several Anabaena neurotoxins exist, the most common of which (the alkaloid anatoxin-a) causes depolarisation block at neuromuscular junctions. Another Anabaena neurotoxin (anatoxin-a(s)) is a naturally-occurring organophosphate product which inhibits acetlycholinesterase. Aphanizomenon toxins have been identified as alkaloids (saxitoxins) of the same group as those responsible for paralytic shellfish poisoning. Signs of poisoning in animals that have ingested cyanobacterial neurotoxins have included paralysis, cyanosis, respiratory arrest, muscular tremor, hypersalivation, staggering and convulsions. Further neurotoxins (non-protein amino acids) are currently under investigation in cyanobacteria.
Hepatotoxins produced by several cyanobacteria, including species of Anabaena, Microcystis, Oscillatoria, Nostoc, Nodularia, Gloeotrichia, Coelosphaerium and Gomphosphaeria, have been identified as cyclic peptides. The hepatotoxins (microcystins) include over 90 variants; typically, several are present in a single hepatotoxic bloom. Signs of poisoning in animals have included weakness, vomiting, cold extremities, piloerection, diarrhoea, heavy breathing and death due to circulatory failure and respiratory arrest within 2 to 24 hours. Microcystins have also been associated with atypical pneumonia and are potent tumour promoters in laboratory animals. Nodularin, another hepatotoxic tumour-promoter, is also a carcinogen. All cyanobacteria also produce lipopolysaccarides (LPSs) as normal components for their outer layers. The chemical composition of LPS varies between strains of individual cyanobacterial species. LPS may have contributed to skin irritation observed in swimmers in contact with cyanobacterial blooms in the UK and to gastrointestinal disorders associated with blooms in several countries.
For sources of advice on toxicity see Annex C.
Email: Janet Sneddon
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