Microcystin

Microcystins—or cyanoginosins—are a class of toxins produced by certain freshwater cyanobacteria; primarily Microcystis aeruginosa but also other Microcystis, as well as members of the Planktothrix, Anabaena, Oscillatoria and Nostoc genera. Microcystin-LR (i.e. X = leucine, Z = arginine) is the most toxic form of over 80 known toxic variants, and is also the most studied by chemists, pharmacologists, biologists, and ecologists. Microcystin-containing 'blooms' are a problem worldwide, including China, Brazil, Australia, South Africa, the United States and much of Europe. Hartebeespoort Dam in South Africa is one of the most contaminated sites in Africa, and possibly in the world. == Chemistry ==

Microcystins have a common structural framework of D-Ala1-X2-3-Z4-Adda5-D-γ-Glu6-7, where X and Z are variable amino acids; the systematic name "microcystin-XZ" (MC-XZ in short) is then assigned based on the one letter codes (if available; longer codes otherwise) of the amino acids. • D-Masp is D-erythro-β-methyl-isoaspartic acid, a derivative of aspartic acid in β-amino acid form; == Mechanism of action ==

Microcystins covalently bond to and inhibit protein phosphatases PP1 and PP2A and can thus cause pansteatitis. ==Factors affecting production==

bacterium The microcystin-producing Microcystis is a genus of freshwater cyanobacteria and thrives in warm water conditions, especially in stagnant waters. Algal growth is also encouraged through the process of eutrophication (oversupply of nutrients). Microcystins may have evolved as a way to deal with low iron supply in cyanobacteria: the molecule binds iron, and non-producing strains are significantly worse at coping with low iron levels. Low iron supply up-regulates McyD, one of the microcystin synthetic operons. Sufficient iron supply, however, can still boost microcystin production by making the bacterium better at photosynthesis, therefore producing sufficient ATP for MC biosynthesis. Microcystin production is also positively correlated with temperature. Bright light and red light increases transcription of McyD, but blue light reduces it. A wide range of other factors such as pH may also affect MC production, but comparison is complicated due to a lack of standard testing conditions. ==Exposure pathways==

There are several ways of exposure to these hepatotoxins that humans can encounter one of which is through recreational activities like swimming, surfing, fishing, and other activities involving direct contact with contaminated water. Another rare, yet extremely toxic, route of exposure that has been identified by scientists is through hemodialysis surgeries. One of the fatal cases for microcystic intoxication through hemodialysis was studied in Brazil where 48% of patients that received the surgery in a specific period of time died because the water used in the procedure was found to be contaminated. Microcystins are chemically stable over a wide range of temperature and pH, possibly as a result of their cyclic structure. Microcystin-LR water contamination is resistant to boiling and microwave treatments. Microcystin-producing bacteria algal blooms can overwhelm the filter capacities of water treatment plants. Some evidence shows the toxin can be transported by irrigation into the food chain. Lake Erie blooms In 2011, a record outbreak of blooming microcystis occurred in Lake Erie, in part related to the wettest spring on record, and expanded lake bottom dead zones, reduced fish populations, fouled beaches, and damaged the local tourism industry, which generates more than $10 billion in revenue annually. An Ohio state task force found that Lake Erie received more phosphorus than any other Great Lake, both from crop land, due to the farming practices, and from urban water-treatment centers. Iowa In 2018, the Iowa Department of Natural Resources found microcystins at levels of 0.3 µg/L, or micrograms per liter (ppb), in the raw water supplies of 15 out of 26 public water systems tested. Oregon In 2023, the Oregon Department of Environmental Quality (DEQ) and Oregon Health Authority issued a cyanobacteria advisory for much of the Willamette River as it runs through Portland. The advisory affected the Willamette from the Ross Island Lagoon through Cathedral Park. Testing by the DEQ showed microcystin levels at 549 ppb. ==Human health effects upon exposure==

Microcystins cannot be broken down by standard proteases like pepsin, trypsin, collagenase, and chymotrypsin due to their cyclic chemical nature. Acute health effects of Microcystin-LR are abdominal pain, vomiting and nausea, diarrhea, headache, blistering around the mouth, and after inhalation sore throat, dry cough, and pneumonia. There appears to be inadequate information to assess the carcinogenic potential of microcystins by applying EPA Guidelines for Carcinogen Risk Assessment. A few studies suggest a relationship may exist between liver and colorectral cancers and the occurrence of cyanobacteria in drinking water in China. Evidence is, however, limited due to limited ability to accurately assess and measure exposure. ==Regulation==

In the US, the EPA issued a health advisory in 2015. A ten day Health Advisory was calculated for different ages which is considered protective of non-carcinogenic adverse health effects over a ten-day exposure to microcystins in drinking water: 0.3 μg/L for bottle-fed infants and young children of pre-school age and 1.6 μg/L for children of school age through adults. ==See also==