Cyanotoxins are secondary metabolites produced by cyanobacteria, a group of photosynthetic prokaryota especially found in freshwater. In favourable conditions (i.e. high nutrient levels, light intensity, water temperature), cyanobacteria can form blooms, a natural phenomenon characterised by an algal biomass accumulation and the possible release of cyanotoxins in water ecosystems. Toxins represent an emerging threats for the aquatic organisms which can bioaccumulate these compounds and transfer them throughout the food chain to wildlife and humans. Other ways of exposure for humans include the oral, dermal and inhalation route.
The consumption of contaminated drinking water, skin contact and swallowing water during recreational activities are among the most frequently reasons for human poisonings caused by cyanotoxins. The associated symptoms usually range from severe headache to fever, respiratory paralysis and in rare case, death. The World Health Organization (WHO) has issued a provisional guideline value of 1 µg/L in drinking water for Microcystin-LR (MC-LR), the most toxic, widespread and common toxin in water supplies. Due to the lack of complete toxicological data for a range of cyanotoxins, their concentration in drinking water is not yet well regulated even in countries belonging to the European Union (EU).
In this report, attention is focused on the methodologies commonly used to detect cyanotoxins in water environments. These applications can be grouped in: I) microscopy analysis II) physicochemical methods III) molecular-based methods IV) biochemical-based methods V) chemical methods. Each technique shows specific limitations in terms of sensitivity, reliability and limit of detection. The choice of the best one to use is determined in accordance with the information they provide, the availability of facilities and the technical expertise of the operators. Most of the research about cyanotoxins has been mainly focused on microcystins (MCs). The other cyanotoxins have been much less investigated and more tools need to be developed to overcome this problem. Notwithstanding there is no a single analytical application able to detect all cyanotoxin variants in an environmental sample. Some current methods described in this report show great promise in terms of being simple, cost-effective, specific and sensitive for the analysis of a defined toxin.