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Source in nature

Saxitoxin is a neurotoxin naturally produced by certain species of marine dinoflagellates (Alexandrium sp., Gymnodinium sp., Pyrodinium sp.) and freshwater cyanobacteria (Dolichospermum cicinale sp., some Aphanizomenon spp., Cylindrospermopsis sp., Lyngbya sp., Planktothrix sp.) Saxitoxin accumulates in "planktivorous invertebrates, including mollusks (bivalves and gastropods), crustaceans, and echinoderms".

Saxitoxin has also been found in at least 12 marine puffer fish species in Asia and one freshwater fish tilapia in Brazil. However, the ultimate source of STX is often still uncertain. The dinoflagellate Pyrodinium bahamense is the source of STX found in Florida. Recent research shows the detection of STX in the skin, muscle, viscera, and gonads of "Indian River Lagoon" southern puffer fish, with the highest concentration (22,104 μg STX eq/100 g tissue) measured in the ovaries. Even after a year of captivity, Landsberg et al. found the skin mucus remained highly toxic. The concentrations in puffer fish from the United States are similar to those found in the Philippines, Thailand, Japan, and South American countries. Puffer fish also accumulate a structurally distinct toxin, tetrodotoxin.

""Saxitoxins are found in butter clams native to Alaska. The Alaskan butter clams have cyclical highs and lows in their total toxin concentrations that coincide with the occurence of Alexandrium blooms. These cycles follow baisc seasonal patterns. They are the highest during the summer season(may-august). They are the lowest during the winter season( December- February). ^[1] ""

Cusick, Kathleen D.; Sayler, Gary S. (2013-03-27). "An Overview on the Marine Neurotoxin, Saxitoxin: Genetics, Molecular Targets, Methods of Detection and Ecological Functions"^[2]

Kibler, Steven R.; Litaker, R. Wayne; Matweyou, Julie A.; Hardison, D. Ransom; Wright, Bruce A.; Tester, Patricia A. (2022-01-01). "Paralytic shellfish poisoning toxins in butter clams (Saxidomus gigantea) from the Kodiak Archipelago, Alaska"^[1]

Military interest

Saxitoxin, by virtue of its extremely low LD50, readily lends itself to weaponization. In the past, it was considered for military use by the United States and was developed as a chemical weapon by the US military. It is known that saxitoxin was developed for both overt military use as well as for covert purposes by the CIA. Among weapons stockpiles were M1 munitions that contained either saxitoxin or botulinum toxin or a mixture of both. On the other hand, the CIA is known to have issued a small dose of saxitoxin to U-2 spy plane pilot Francis Gary Powers in the form of a small injection hidden within a silver dollar, for use in the event of his capture and detainment.

After the 1969 ban on biological warfare by President Nixon, the US stockpiles of saxitoxin were destroyed, and development of saxitoxin as a military weapon ceased. However, in 1975 the CIA reported to Congress that it had kept a small amount of saxitoxin and cobra venom against Nixon's orders which was then destroyed or distributed to researchers.

It is listed in schedule 1 of the Chemical Weapons Convention. The United States military isolated saxitoxin and assigned it the chemical weapon designation TZ.

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