saxitoxins

Saxitoxins are a group of potent neurotoxins produced by certain aquatic microorganisms, most notably marine dinoflagellates such as Alexandrium and Gymnodinium, and some freshwater cyanobacteria. They accumulate in shellfish and other filter feeders during algal blooms, and can cause paralytic shellfish poisoning (PSP) in humans who consume contaminated seafood. The family includes saxitoxin and numerous congeners, such as GTX1–4 and neoSTX, many of which share a common guanidinium structure critical for their activity. The toxins are heat-stable and cooking does not reliably destroy them.

Saxitoxins exert their effects by binding to voltage-gated sodium channels in nerve and muscle cells, blocking sodium influx and preventing action potential conduction. This disruption of neural signaling leads to early symptoms such as tingling around the mouth and lips, followed by dizziness, ataxia, limb weakness, and in severe cases respiratory failure and death.

Saxitoxins occur worldwide, associated with harmful algal blooms in coastal waters and, less commonly, in freshwater systems. Humans are mainly exposed through the consumption of contaminated shellfish, including clams, mussels, and oysters. Onset of symptoms is typically minutes to hours after ingestion.

Public health agencies monitor shellfish toxins using chemical analyses, such as LC-MS, with regulatory limits expressed as saxitoxin equivalents. Limits vary by region but are generally set to protect consumers, often in the hundreds of micrograms per kilogram of shellfish meat.

There is no antidote; treatment is supportive, with emphasis on airway and respiratory support as needed. Prevention relies on area closures during blooms and ongoing toxin monitoring.