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Toxic cyanobacterial blooms have occurred throughout recorded history in Australia, as causes of livestock deaths and water unpalatability. Human injury from cyanobacterial toxins is rarely recorded, but members of two local populations in Australia have suffered from an acute toxicity believed to be a consequence of copper sulphate treatment of water blooms. Minor health effects have been correlated with cyanobacterial contamination of drinking water drawn from rivers. Recreational exposure to toxic cyanobacteria is comparatively common, with demonstrated minor adverse effects on health. The World Health Organization has drawn up guideline values for microcystin in drinking water and recommendations for recreational waters. The major unknown is the potential for cancer stimulation by cyanobacterial toxins, particularly gastrointestinal cancers in Australia and other affluent countries and liver cancer in poorer nations.
INTRODUCTION
The people of Australia are very familiar with toxic cyanobacterial blooms, because they have been a long-standing problem for agricultural and human drinking water supplies, as well as for the recreational use of water. Livestock poisoning by cyanobacteria was first described in the 19th century near Adelaide (Francis 1878), and the names of water-courses across the country, such as `Poison Waterhole Creek,' may reflect the hazard from cyanobacterial toxicity. More recently, 1000 km of the Darling River carried a massive bloom of neurotoxic Anabaena circinalis Rabenhorst ex Bornet & Flauhault, which killed an estimated 10,000 livestock and required emergency water supplies for several towns (New South Wales Blue-green Algae Task Force 1992). In three successive summers (1998-2000) in the centre of the City of Adelaide, the Torrens Lake (no longer used for water supply) had a heavy bloom of toxic Microcystis aeruginosa (Kutzing) Lemmermann. This bloom was believed to be the cause of waterfowl deaths. Although livestock poisoning has been relatively common throughout farming history in Australia, cases of human and wildlife poisoning are rare, more through avoidance of drinking foul-smelling water than through an absence of toxicity in cyanobacterial blooms.
Effective assessment of the risk of cyanobacterial toxins to human health requires data that relate the dose of toxin to the clinical effects in a population. In general, when an adverse health effect has been suspected to have been caused by a cyanobacterial bloom in a water supply, no measurements of toxins have been...