Toxicity of Fresh Water Algal Toxins to Humans and Animals

Algae and cyanobacteria are responsible of the presence of toxins in fresh waters. Algae are considered less dangerous than cyanobacteria, because even if they can proliferate quite intensively in eutrophic fresh waters, they rarely accumulate to form dense surface blooms like blue-green algae do. Thus the toxins they produce do no accumulate to levels high enough to become hazardous to human and animals health. Cyanobacteria, both planktonic and benthic species, can instead form huge agglomeration close to the shore, which can become very dense and concentrated. This material can take a long time to disperse and so become a risk for human health and mainly for animals, which can easely enter in contact with poisoned water. Lots of blue-green algae species have been found to produce toxins, and some authors assume that it could be prudent to assume that any cyanobacterial population can have a toxic potential. At present known toxins are classified as neurotoxins (anatoxin-a, anatoxin-a(s) and saxitoxin), cytotoxin or cylindrospermopsin and microcystins or nodularins. Anyway, starting from existing studies, it seems likely that other unidentified toxins exists.