Cyanobacterial Toxins in Fresh Waters

Cyanobacterial blooms have been a growing problem in freshwater lakes, ponds, rivers, and reservoirs worldwide during the last half of the twentieth century. The increasing occurrence of cyanobacterial blooms is associated with human activities as they relate to global climate change, catchment disturbance, and water diversion and storage. Under bloom conditions, many species of cyanobacteria can produce toxins, primarily liver and nerve toxins. Exposure to these toxins in the natural environment through the skin, respiratory system, or digestive tract has been implicated in chronic and acute poisonings in invertebrates, fish, birds, and mammals, including humans. Cyanobacterial cells release toxins into the surrounding water when cells rupture, and these dissolved toxins can be stable and resistant to traditional drinking water treatment methods. In one case, renal dialysis exposure to contaminated drinking water resulted in human deaths. Biochemistry, chromatography, and molecular technology provide tools to monitor toxin concentrations in freshwater and phytoplankton samples. Chlorination and treatment with activated carbon and ozone are the most widely practiced options to remove toxins from drinking water supplies. Strategies to prevent human exposure to cyanobacterial toxins and directions for future research in this area are also reviewed.