Toxic Cyanobacteria in Water and Their Public Health Consequences

Abstract

Cyanobacteria (blue-green algae) are natural inhabitants of fresh, brackish and marine waters, and they are worldwide in distribution. Cyanobacteria or blue-green algae occur worldwide especially in calm, nutrient-rich waters. Some species of cyanobacteria produce toxins that affect animals and humans. People may be exposed to cyanobacterial toxins by drinking or bathing in contaminated water. The most frequent and serious health effects are caused by drinking water containing the toxins (cyanobacteria) or by ingestion during recreational water contact. Cyanobacterial toxins are classified by how they affect the human body. Hepatotoxins (which affect the liver) are produced by some strains of the cyanobacteria Microcystis, Anabaena, Oscillatoria, Nodularia, Nostoc, Cylindrospermopsis and Umezakia. Neurotoxins (which affect the nervous system) are produced by some strains of Aphanizomenon and Oscillatoria. Cyanobacteria from the species Cylindrospermopsis raciborskii may also produce toxic alkaloids, causing gastrointestinal symptoms or kidney disease in humans. Not all cyanobacteria of these species form toxins and it is likely that there are as yet unrecognised toxins. People are mainly exposed to cyanobacterial toxins by drinking or bathing in contaminated water. Other sources include algal food tablets. Some species form a scum on the water, but high concentrations may also be present throughout the affected water. Surface scums, where they occur, represent a specific hazard to human health because of their particularly high toxin contact. Contact, especially by children, should be avoided. They produce a diverse range of small molecules which are hazardous to human and animal health. Their harmful effects range from mild to serious and include gastrointestinal upsets, skin irritations and liver and neurological damage. Reactive and proreactive measures of cyanobacteria are also defined. The reduction of cyanobacterial toxin problems in natural and controlled water as a potential benefit of eutrophication is also dealt with.