ABSTRACT
Any substance that is poisonous in nature is termed as a toxin. Toxins produced by cyanobacteria are known as cyanobacterial toxins or cyanotoxins. Of the 150 known genera of cyanobacteria, 40 species of cyanobacteria have been implicated in the formation of toxic blooms in fresh, marine and estuarine waters (Carmichael, 1997; Saker et al., 1999). The bloom algae are characterized by the presence of reddish brown, refractile structures inside their cells known as gas vacuoles that help them to keep afl oat in water. Due to mixing of agricultural and industrial waste-water, the nutrient status of water bodies undergoes a change. In this context, nitrogen and phosphorus enrichment leads to the formation of nutrient saturated water bodies defi ned as eutrophic waters. The growth of bloom algae is thus dependent on variations in the nutrients especially of nitrogen and phosphorus, light intensity, temperature, pH and other factors. Prepas and Charette (2003) summarized the factors responsible for eutrophication of water bodies worldwide and suggested methods of control. The earlier concept that a low ratio of nitrogen to phosphorus (N:P) is responsible for the predominance of bloom algae has now been questioned. Downing et al. (2001) who analyzed data from 99 temperate lakes suggested that it is the variations in the total N and P contents in waters more important rather than their ratio. Due to their excessive growth, the waters emanate foul smell that is obnoxious in nature and the waters are unfi t for use in any manner either for animal or human consumption or for recreational purposes.
