Paralytic Shellfish Poisoning (PSP) is caused by toxins that are produced by oceanic phytoplankton or dinoflagellates. The toxin most commonly associated with paralytic shellfish poisoning is saxitoxin. Saxitoxin is water-soluble and heat-stable. There are over 20 known toxins formed from either saxitoxin or its derivatives.
The Paralytic Shellfish Poisoning is caused by toxins produced by certain species of dinoflagellates, diatoms and freshwater/marine cyanobacteria. The chief among these toxins is Saxitoxin, a sodium channel blocker in neurons. Other such neurotoxins are neosaxitons and gonyautoxins series, all of which are sodium channel blockers. These toxins are mostly formed by Alexandrium tamarense species complex in the higher latitudes and by the like of Pyrodinium is tropical Asiatic waters.
Brevetoxins synthesized by certain dinoflagellates also cause Neurotoxic Shellfish Poisoning. Amnesic Shellfish Poisoning is also caused by freshwater, marine or euryhaline diatom species belonging to Nitzschia and Pseudonitzschia and the causal agents are Kainic acid analog neurotoxins such as Domoic Acid. Okadaic acid porduced by several dinoflagellates causes Diarrhetic/Diarrheal Shellfish Poisoning. Microcystins/Nodularin and other Cyanoginosins are Cyanotoxins formed by quite a few freshwater/estuarine cyanobacterial species
All or most of these of these so called toxins are readily soluble in water, acid stable and are thermotolerant. Saxitoxin is water soluble and heat and acid stable. Brevetoxins are acid, heat stable and lipid soluble in general with some members being water soluble. Domoic acids are water soluble and extremely heat stable compounds. Microcystins are highly water soluble and stable but not so thermotolerant as some of the other toxins.
These toxins are synthesized in response to dissolved nutrient concentrations in ambient environment of their respective source organisms. For example, it has been documented that nitrate-nitrogen limitation normally triggers a rise in saxitoxin production. Hence monitoring of eutrophication mediated algal blooms should be one of the quintessential priorities of all governing bodies to combat shellfish borne toxicities. Organisms that synthesize these compounds do so at far less intensities under oligitrophic conditions and in nutrient polluted environments.