microcystin

Microcystin refers to a family of hepatotoxic cyclic peptide toxins produced by freshwater cyanobacteria, especially genera such as Microcystis, Planktothrix, Anabaena, and Nostoc. More than 100 congeners have been identified, with microcystin-LR (LR) being the most studied. These toxins are produced during cyanobacterial blooms and can persist in water bodies even after the bloom declines. They are relatively stable to heat and common water treatments, which can complicate removal from drinking water and recreational waters.

Toxicology and mechanism: Microcystins primarily affect the liver. They inhibit protein phosphatases 1 and 2A (PP1 and PP2A) by binding to their active sites, a process that disrupts cellular signaling, causes cytoskeletal damage, oxidative stress, and hepatocellular necrosis. The Adda-containing structure is essential for activity. Acute exposure can cause gastrointestinal symptoms and liver injury; chronic exposure has been associated with adverse health effects in animals and concerns about cancer promotion in long-term studies.

Exposure and monitoring: Humans are exposed through ingestion of contaminated drinking water or water used for recreation, as well as through consumption of fish or shellfish from affected waters. Detection methods include immunoassays that measure total microcystins and liquid chromatography–mass spectrometry for congener-specific analysis.

Regulation and prevention: Guidance values exist for drinking water, with common recommendations around 1 microgram per liter for total microcystins, though regulations vary by country. Prevention focuses on bloom monitoring, source-water management, and multi-barrier water treatment approaches, including activated carbon, ozonation, and advanced oxidation to reduce toxin levels in water supplies.