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 from surface water systems to the public. The health effects that can result from ingestion can be very severe and include 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 three 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 is 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 these 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. These compounds are also found frequently, but not in concentrations as elevated as microcystins.
It is important for water utilities to know the concentration of cyanotoxins in their supply as well as in their treated water. It is even more important to know the different cyanotoxins that are present. This will ensure that the treatment technique in use is adequately removing all the compounds of concern. In cases where only microcystins only are present, GAC (granular activated carbon) will provide adequate removal; however if anatoxin-a or cylindrospermopsins is present, PAC (powdered activated carbon) is necessary, because GAC is not effective.