Potential impact on human health of toxic cyanobacteria.

Most of the attention directed towards the adverse effects of cyanobacteria on human health has focussed on acute poisoning. In all cases of reported community poisoning, the cause was a chlorinated drinking water supply. The supply reservoir, or river, or lake had a water-bloom of toxic cyanobacteria. Several cyanobacterial species have been identified in human poisoning, the most frequently implicated being Microcystis aeruginosa (Kützing) Lemmermann. Individual poisoning has been largely due to recreational activities in rivers or lakes with water-blooms. Direct toxicity due to swimming in, and swallowing, cyanobacteria has been widely reported. Some cases appear to be primarily allergic responses. Neurotoxicity is also possible, from swallowed or inhaled cyanobacteria. In Australia the cyanobacterium Anabaena circinalis Rabenhorst ex Bornet et Flahault produces paralytic shellfish poisons (e.g. saxitoxin), and we have a report of severe respiratory distress from a water-skier who was inhaling water spray containing the organism. The mechanisms of toxicity of the diverse cyanobacterial toxins include nerve ion-channel blocking, neuromuscular blockade, anti-acetylcholinesterase activity, anti-phosphatase activity and protein synthesis inhibition. The liver is particularly damaged by the latter two activities, as well as the gastro-intestinal tract and, in the case of protein synthesis inhibition, the kidneys. The anti-phosphatase activity of microcystins and nodularin has significant potential for stimulating tumour growth. Experimentally this capacity is clearly demonstrated, and its mechanism is under detailed investigation. To assess the public health impact requires epidemiological investigation of human populations in areas known to be exposed to cyanobacteria in the water supply. Some evidence from China supports a link between contaminated surface water and primary liver cancer. The importance of cyanobacteria to human health requires further quantitation