microcystins

Microcystins are a family of cyclic heptapeptide toxins produced by certain freshwater cyanobacteria, especially during harmful algal blooms. They are potent hepatotoxins that can contaminate drinking water and recreational waters when blooms form, posing risks to humans and animals.

Chemically, microcystins are distinguished by a cyclic structure and a unique amino acid called Adda, which is essential for their inhibitory activity. More than 200 congeners have been identified, with microcystin-LR (leucine-arginine) being the best studied and frequently used as a reference for toxicity. The primary mechanism of action is inhibition of protein phosphatases 1 and 2A in liver cells, leading to cellular damage, cytoskeletal disruption, and potentially liver failure after significant exposure.

Cyanobacteria such as Microcystis, Dolichospermum (formerly Anabaena), and Nostoc can produce microcystins. Blooms are favored by warm conditions, high nutrient levels (nitrogen and phosphorus), and sunlight, and they can occur in lakes, reservoirs, and occasionally in drinking-water reservoirs. Human exposure occurs mainly through ingestion of contaminated water or food, with aerosol inhalation and dermal contact being potential but less common routes.

Detection and regulation vary by country, but monitoring often uses LC-MS or immunoassays to quantify microcystin concentrations, typically reported as microcystin-LR equivalents. World Health Organization guidance for drinking water commonly cited is around 1 µg/L as a reference limit, with national standards differing.

Treatment approaches emphasize removal before consumption. Conventional coagulation and filtration can reduce some cyanotoxins, but microcystins are relatively stable; advanced treatments such as activated carbon, ozonation, advanced oxidation processes, or membrane filtration are more effective at degrading or removing them. Public health actions focus on monitoring blooms, issuing advisories, and providing safe water alternatives during elevated risk periods.