Saxitoxins have been found in Australian populations of the cyanobacterium Anabaena circinalis. The C-toxins (Cl and C2) and gonyautoxins (GTX2 and GTX3) are dominant components, while saxitoxin (STX), GTX5 and decarbamoyl gonyautoxins (dcSTX, dcGTX2 and dcGTX3) are minor constituents. Variation in the concentration and composition of saxitoxins has been observed in natural populations and cultured strains of A. circinalis and may reflect environmental conditions. Laboratory experiments were conducted with a single strain of A. circinalis to examine the effect of different nitrogen sources (dissolved atmospheric nitrogen, nitrate or ammonium) and varying concentrations of nitrate (0.0028, 0.28 and 28 mg N l(-1)) on growth and saxitoxin levels. Growth was determined by cell enumeration and saxitoxin concentrations were analysed by high-performance liquid chromatography. All experiments consistently showed a linear relationship between cell density and saxitoxin concentration (intracellular + extracellular). Growth of A, circinalis was depressed by addition of ammonium (0.04 mg N l(-1)) and by high levels of nitrate (28 mg N l(-1)), and these treatments were associated with an increased toxin release. The concentration of extracellular saxitoxins increased with the age of cultures. The composition of intracellular and extracellular toxin profiles was usually similar; however, the relative abundance of the different toxins was not always the same. Extracellular toxin profiles generally comprised a higher proportion of STX and GTX2 and less C-toxins. A strong correlation between toxin quota (saxitoxin concentration per cell) and logarithmic growth rate was found in three of four experiments. Saxitoxin concentrations in A. circinalis appear to be indirectly affected by the source and concentration of nitrogen through growth.

The occurrence of cyanobacteria (blue–green algae) blooms and the possibility of production of cyanotoxins (algal toxins) have become major concerns for drinking water providers worldwide. Ozone has been shown to be effective for the destruction of some classes of toxins under specific conditions, although most researchers agree that the dose and contact time required will depend on water quality. The clarification of the relative effects of water quality parameters such as dissolved organic carbon concentration and character, and alkalinity, has not been previously attempted. In this study the cyanotoxins microcystin LR and LA and anatoxin-a were ozonated at a range of ozone doses in four treated waters with very different water quality. For both the toxins, 100% destruction was related to a residual ozone concentration present after 5 min. This was, in turn, related to the water quality and indicated that a direct reaction with molecular ozone could be responsible for the destruction. The results confirmed that both the toxins would be destroyed under conditions usually utilised for ozonation prior to granular activated carbon (GAC) filtration. This will apply under a range of water quality conditions but not necessarily a range of temperatures. The saxitoxin class of compounds was very resistant to oxidation by ozone and would require further treatment such as GAC filtration.

The occurrence of cyanobacterial (blue-green algal) blooms and the possibility of the production of associated cyanotoxins (algal toxins) have become major concerns for drinking water providers. At least a third of the 50 known genera of cyanobacteria are capable of producing toxins and between 50 and 70% of blooms of those cyanobacteria are toxic. The most common types of cyanotoxins are neurotoxins such as the anatoxins and saxitoxins, and peptide hepatotoxins such as the microcystins, known to cause liver damage and promote tumours. The presence of cyanotoxins in water sources presents important implications for human health. A reliable method for the removal of commonly occurring toxins in a wide range of waters would be of great value to the international water industry. The ozonation of the cyanotoxins microcystin LR and LA, anatoxin-a and the saxitoxin group of compounds was studied in four different waters, sampled after treatment and before chlorination. The microcystins were most readily destroyed by ozone, while the saxitoxins showed considerable resistance to oxidation. The differences in the ease of oxidation can be attributed to the structural differences between the toxins. The four waters were chosen to represent a wide range of water quality, including high and low dissolved organic carbon (DOC) concentrations and high and low alkalinity. There was a significant effect of water quality on the ozonation of all toxins.

Cyanobacterial samples were collected between April 1989 and May 1997 from six drainage divisions in coastal areas of Australia: the northeast coast, southeast coast, Tasmania, Murray-Darling Basin, South Australian coast and southwest coast. Saxitoxins were detected in approximately 70% of all field samples and 57% of cultured strains of Anabaena circinalis. Maximum saxitoxin concentrations were 4466 and 2553 mug g(-1) dry weight cells in field samples and strains, respectively. Toxin profiles were similar in the majority of field samples and strains. The toxins were predominantly C-toxins (C1 and C2) and gonyautoxins (GTX2 and GTX3), with saxitoxin sensu stricto (STX). GTX5 and decarbamoyl gonyautoxins (dcGTX2 and dcGTX3) being present in minor amounts, A unique toxin composition (exclusively STX and GTX5) was Found in a geographically isolated strain from the southwest coast of Australia. N1-hydroxy saxitoxins (neoSTX, GTX1 and GTX4) were not detected in any field sample or cultured strain. Anabaena circinalis may not be the only Anabaena species producing saxitoxins, as very low concentrations of GTX3 (14 mug g(-1) dry weight cells or less) were detected in two other Anabaena species: A. perturbata var. tumida and A. spiroides. One decarbamoyl gonyautoxin (dcGTX3) was also present in one A. perturbata var. tumida strain. Anatoxin-a was not detected in Australian strains of Anabaena. Trace amounts of 0.23 and 0.10 mug microcystin-LR equivalents g(-1) dry weight cells were found in two cultured strains of Anabaena cylindrica. An increase in toxin concentration from 0 to 4423 mug saxitoxins gl dry weight cells was observed over a 3-month period in a series of samples collected from a persistent bloom of A. circinalis at Wongulla Lagoon. South Australia. This temporal variation in saxitoxin concentrations is similar to that reported for microcystins in Microcystis aeruginosa (Chroococcales, Cyanophyta).

The potential for the oxidant ozone used in water treatment, to destroy the various classes of toxins produced by cyanobacteria (blue-green algae) was investigated. Toxin destruction was determined by chemical analyses or mouse bioassay. Ozone was more effective than chlorine, hydrogen peroxide and potassium permanganate in destroying the peptide hepatotoxin microcystin-LR Ozone in combination with hydrogen peroxide was more effective than ozone alone. Ozone was capable of destroying the alkaloid neurotoxins anatoxin-a and paralytic shellfish poisons (PSPs), whereas chlorine has been previously reported to be ineffective (Rositano and Nicholson, 1994). Destruction of peptide hepatotoxins by ozone was pH-dependent. Ozone was less effective under alkaline conditions, consistent with its lower oxidation potential under these conditions (1.24V) compared with acidic conditions (2.07V).

Toxic cyanobacteria (blue-green algae) are becoming recognized as a greater water quality problem as blooms become more common in waters affected by increasing nutrient levels, and knowledge of the properties of the toxin increases. Of particular importance are the hepatotoxic cyclic peptides produced by certain strains of Microcystis species and by Nodularia spumigena. The effects of chlorine and chloramine on these hepatotoxins in both freeze-dried and intact material were investigated. The destruction of the toxins was monitored using HPLC analysis. In a number of cases mouse bioassays were used for confirmation of the destruction of the toxins and to ensure that toxic by-products, not detectable by HPLC, were not formed. Contrary to evidence reported in the literature, chlorine was effective in destroying toxins, as long as sufficient chlorine was used. Toxins were destroyed under conditions such that a chlorine residual of at least 0.5 mg/l was present after 30 min contact time. The destruction of toxins was pH dependent; chlorinating agents such as calcium and sodium hypochlorite were not as effective at high dose rates due to elevation of pH. Chloramination had little effect on toxins. Although the degradation mechanisms have yet to be established, the results show that chlorination may be an effective and practical method for the removal of cyanobacterial peptide toxins from drinking water.

Saxitoxin-group neurotoxins (paralytic shellfish poisons) have been identified in a cultured strain of Anabaena circinalis and in natural bloom samples in which this species was the dominant organism collected from widely distributed sites in the Murray-Darling Basin of Australia. These toxins have hitherto been isolated almost exclusively from 'red tide' dinoflagellates and contaminated shellfish. Two 'aphantoxins', which appear to be identical to two of the paralytic shellfish poisons, have been identified in a cyanobacterium from a small number of sites in New Hampshire, USA. The conclusions are supported by electrophysiological studies and by high-performance liquid chromatographic (HPLC) and fast atom bombardment-mass spectrometric (FAB-MS) analyses.

Medical Journal of AustraliaVolume 159, Issue 6 p. 423-423 Letters to the Editor Paralytic shellfish poisons from freshwater blue-green algae Ian R Falconer PhD, DSc, FRSC, Ian R Falconer PhD, DSc, FRSC Deputy Vice-Chancellor (Academic) University of Adelaide, Adelaide, SA, 5005Search for more papers by this author Ian R Falconer PhD, DSc, FRSC, Ian R Falconer PhD, DSc, FRSC Deputy Vice-Chancellor (Academic) University of Adelaide, Adelaide, SA, 5005Search for more papers by this author First published: 01 September 1993 https://doi.org/10.5694/j.1326-5377.1993.tb137930.xCitations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume159, Issue6September 1993Pages 423-423 RelatedInformation