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Blue-Green Algae (Cyanobacteria) in Inland Waters: Assessment and Control of Risks to Public Health
3 Public health concerns
3.1 Surveys in different parts of the world have found that between about 45% and 90% of blooms of blue-green algae produce toxins. These toxins are largely retained within the blue-green algal cells during their development and growth phases and are released, in the main, on cell death.
3.2 Blue-green algae of several genera can produce a range of toxins including neuro- and hepatotoxins and lipopolysaccharides. An algal bloom may contain more than one species, each producing different toxins. In addition, the toxicity of one species might change over time to a pattern that might vary for different places on a particular water body. Further information on algal toxins is given in Annex B.
3.3 Evidence of toxicity comes from reports of the effects of exposure of people and of animals to algal blooms and from laboratory investigations of algal toxins.
3.4 In 1989, a group of soldiers took part in canoe training, including rolling and swimming exercises, at Rudyard Lake in Staffordshire. Two became severely ill with atypical pneumonia; others reported abdominal pains, vomiting, diarrhoea, blistering of the mouth and sore throats. Further incidents of effects on human health have occurred after recreational contact with blue-green algal scums and blooms in UK inland waters in recent years. The effects were probably associated with exposure to blue-green algae and ingestion of the toxin-containing blue-green algal scum.
3.5 Gastroenteritis and acute hepatocellular damage have been reported from other countries. Deaths of haemodialysis patients, probably resulting from blue-green algal toxins in water substituted for the normal supply during a drought, occurred in 1996 in Brazil.
3.6 Ingestion of hepatotoxic and neurotoxic scums of blue-green algae are reported to have caused the deaths of cattle, sheep, dogs and birds. There is also evidence that algal toxins have been major contributors to fish kills.
3.7 Another potential source of intoxication for both animals and humans is bioaccumulation of algal toxins in the food chain. The principal concern here would be accumulation of algal toxins in shellfish such as freshwater mussels and in fish. However, no cases of intoxication from this source have been reported to date in Scotland.
3.8 For some two weeks, at the beginning of September 1997, a massive algal bloom on the main water supply loch on Westray, Orkney islands, resulted in a ban on the use of water for drinking, cooking and washing. Over the two preceding weeks, as the bloom developed, water treatment capacity had been progressively reduced due to clogging of the filters. Large quantities of water treatment chemicals were needed to reduce algal concentrations to a level where even a reduced throughput could be maintained and aluminium levels in the final water eventually rose to a level considered unfit for consumption. The water had also become unacceptable due to taste and odour. No algal toxins were detected. The water authority arranged for potable water to be transported as bottled water and in tankers to serve the human population. Fortunately, the very large cattle herd on the island at the time was able to continue to drink the loch water without ill effect.
3.9 Algal blooms are inherently complex (Paragraph 3.2) and assessment of the associated risks to public health is not straightforward. Such assessments should therefore take account of specialist advice ( Annex C). Where advice is not immediately available, action of the kind described herein might still be appropriate.
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