Cyanobacteria and Cyanotoxins
Based on the health advisory released by EPA in June 2015, the area of cyanotoxins has emerged as a large concern for all organizations providing water to the public from surface water systems. The health effects that can result from ingestion can be very severe, inclusive of gastroenteritis, liver and kidney damage.
The noted increase in concern has been attributed to the degradation of aquatic ecosystems by nutrient pollution resulting in massive cyanobacterial water blooms. Cyanobacteria are usually unicellular, photosynthetic and can be found in limnic and marine environments as well as terrestrial habitats.
Cyanotoxins are secondary metabolites produced by cyanobacteria. According to their chemical structures, cyanotoxins fall into several main groups: peptides, heterocyclic compounds (alkaloids) or lipidic compounds. The most prevalent cyanotoxins are monocyclic heptapeptides classified as microcystins.
Current studies have identified more than 70 variants in the family of microcystins. The toxicity of many of these variants has still to be determined. Three of the most predominant microcystins are microcystin-LR, microcystin-RR, and microcystin-YR. The most studied and most prevalent of which is microcystin-LR. The World Health Organization has set guidelines for microcystin-LR based on toxicity to humans.
Most discussions on cyanotoxins present microcystins; however the less discussed, and in some cases the more difficult to treat, cyanotoxins are anatoxin-a and cylindrospermopsins. The aforementioned compounds are also found frequently, but not in concentrations as elevated as microcystins.
It is important for water utilities to know what the concentration of cyanotoxins is in their supply as well as in their treated water. It is even more important to know the different cyanotoxins that are present. The need for determining which compounds are present is to ensure that the treatment technique in use is adequately removing all the compounds of concern. In cases where microcystins only are present GAC will provide adequate removal; however if anatoxin-a or cylindrospermopsins is present PAC is necessary because GAC has been found to be not effective.