World’s 2nd deadliest poison, in an aquarium store near you

By Ed Yong | April 5, 2011 8:47 am

In 2007, a man from Woodbridge, Virginia was rushed into hospital after inhaling an aerosolised version of one of the deadliest poisons on the planet. He was not the victim of a terrorist attack. He wasn’t working in a biohazard laboratory. He was trying to clean out his fish tank.

The man, who posts on the Reef Central Forums as Steveoutlaw, was trying to get rid of a colony of zoanthids – a relative of corals and sea anemones – that was infesting his aquarium rocks. He had heard that boiling water would do the trick. When he tried it, he accidentally inhaled some of the steam.

Twenty minutes later, his nose was running and he had a cough. Four hours later, his breathing was laboured and he was headed to the emergency room. By the time he arrived, he was suffering from severe coughing fits and chest pains. He was stabilised, but he developed asthma and a persistent cough, and had to use steroids and an inhaler for at least two months.

The reason for his sudden illness was palytoxin, a speciality of zoanthids, and the second deadliest poison in the natural world. One gram of the stuff will kill more than a hundred million mice. This poison, liberated by the boiling water, had risen into Steveoutlaw’s airways in a cloud of steam.

Palytoxin is shrouded in legend. Hawaiian islanders tell of a cursed village in Maui, whose members defied a shark god that had been eating their fellow villagers. They dismembered and burned the god, before scattering his ashes in a tide pool near the town of Hana. Shortly after, a mysterious type of seaweed started growing in the pool. It became known as “limu-make-o-Hana” (deadly seaweed of Hana). If smeared on a spear’s point, it could instantly kill its victims.

The shark god may have been an elaborate fiction, but in 1961, Philip Helfrich and John Shupe actually found the legendary pool. Within it, they discovered a new species of zoanthid called Palythoa toxica. The limu-make-o-Hana was real, but it wasn’t seaweed – it was a type of colonial anemone. In 1971, Richard Moore and Paul Scheuer isolated the chemical responsible for the zoanthid’s lethal powers  – palytoxin. Now, Jonathan Deeds from the US Food and Drug Administration has found that the poison is readily available in aquarium stores.

Deeds was investigating a case of palytoxin poisoning when he heard about Steveoutlaw’s unfortunate incident. He visited the man, collected a sample of the offending zoanthid, and found that it was indeed heavy with palytoxin. It wasn’t hard to get his hands on more. Deeds bought 15 more colonies from three aquarium stores in the Washington DC area, of the same species that gave Steveoutlaw his whiff of toxic steam. Three of the samples yielded even more poison. Every gram contained enough palytoxin to kill 300,000 mice, or around 80 people.

Unfortunately, Deeds has no clear message for aquarium owners. Some of the zoanthid species that he tested weren’t toxic at all, and indeed, many people claim to have handled zoanthids for years without problems. However, those that contain palytoxin can kill if even a small amount of the poison gets on the skin. And, as Steveoutlaw found, even breathing in an aerosolised version of the poison is a bad idea. The problem is that telling zoanthids apart is incredibly difficult – Deeds only did it with any degree of certainty using genetic analysis.

And tracing the origins of these animals isn’t easy either. One of the aquarium owners who Deeds visited said that he got his zoanthids through mixed containers of corals and rock fragments, known as “frags”, with no information about their origins. The animals can be accidentally introduced on unsuspecting rocks. And many aquarium owners will break the rocks up themselves and exchange them between friends.

As Deeds wrote, “the legendary limu appears to be exacting its ancient curse once again, but this time upon unsuspecting marine home aquarists.” Owners are “often unaware  of the deadly poisons they are being exposed to”.

PS Venom enthusiasts know that the potency of poisons is measured using the LD-50 – the dose that will kill half a group of mice after a set time. The most venomous snake has an LD-50 of 25 micrograms per kilogram of body weight. For tetrodotoxin, the equivalent figure is 8 micrograms. For batrachotoxin, the poison from the skin of poison dart frogs, it’s 2-7 micrograms. For palytoxin, it’s 0.3 micrograms (or 300 nanograms).

Reference: Deeds, J., Handy, S., White, K., & Reimer, J. (2011). Palytoxin Found in Palythoa sp. Zoanthids (Anthozoa, Hexacorallia) Sold in the Home Aquarium Trade PLoS ONE, 6 (4) DOI: 10.1371/journal.pone.0018235

More on poisons and venoms:


Comments (50)

  1. Greg

    This story was just awesome and informative and it would have totally been ignored, I bet, if you weren’t blogging.

    Lord knows what deadly poison is growing in my fishtank…

  2. I have nothing intelligent to add. But: awesome.

  3. natselrox

    Enough material there to write a thriller novel. Or to murder someone! 😛

  4. Steve Outlaw and the Angry Shark God. Coming soon to your Kindle…

  5. Sam

    Interesting read! Glad I don’t own an aquarium…What’s the world’s deadliest poison then?

  6. I should add *naturally occurring* poison. But the number one is maitotoxin, produced by a marine dinoflagellate (type of plankton) called Gambierdiscus toxicus. It has an LD50 of 50ng/kg, making it six times more potent than palytoxin.

  7. Funny coincidence, I stumbled on the case study of this guy this morning. The train of thought was: friend’s post about crown-of-thorns starfish on Facebook -> Wikipedia entry on crown-of-thorns -> there’s some big-ass polyp that eats COTs -> ended up on article about palytoxin.

  8. The synthesis of palytoxin by the Harvard chemist Yoshito Kishi was a landmark. It remans the largest non-protein molecule to be synthesized in a laboratory.

  9. I think botulinum toxin can be more potent than maitotoxin. That’s intravenous.

  10. Sven DiMilo

    Very interesting. I was unfamiliar with this toxin…it’s cool.
    For one thing, check out the outrageous chemical structure. For another, its mechanism: binding to sodium-potassium-ATPase pumps and converting them into open ion-leakage channels, wow! No ion gradients, no neuron or muscle function.

  11. My wife and I both got hit with palytoxin. We had a zooanthid colony that had come in with zoopox (an infection of zooanthids). We removed the clearly dying colony, but some of our other colonies had already been infected.

    So we got some antibiotic/anti-fungal dip and ripped the colonies from their attachment on the rock, dipped them in the medication (in a seperate tank) for about 20 minutes then put them back. I monitored the medication and kept the water circulating, usually by sticking my hands in the tank and swirling the water. My wife was moving the colonies to and from the display tank.

    BTW: Palytoxin is skin permeable.

    The results sucked. It was like the worst case of food poisoning ever. Joint and muscle pain you wouldn’t believe. We were basically flat on our backs for three days. We couldn’t figure out why we were so sick and our little boy wasn’t.

    Finally, after got better, I found out about palytoxins.

    It was very, very bad.

  12. megan


  13. BTW: The blue bit is not the zooanthid. That’s a clam. The round things with the frills are the zooanthids.

    Just wanted to make sure everyone realized.

  14. @OgreMkV – Thanks for sharing your story.

    And to clarify, because someone raised this on Twitter, the photo shows the actual zoanthoid implicated in the opening case study.

  15. Jon F

    Awesome. We keep tetrodotoxin in our lab (it comes in 1 mg vials, so at 8 ug/kg for the LD50 that’s enough to kill 4 or 5 people) and I’ve marked it all up with a bunch of warnings to handle it with care. And that stuff’s over 20 times as potent. Dang, sea creatures, why you gotta be like that?

  16. Lila Guterman

    As an undergraduate, I did research in the lab of Yoshito Kishi, a chemist at Harvard, not long after he published the first total synthesis of palytoxin. There was a fun story about him:

    When his grad student was almost done with the synthesis, he’d walk into lab every day, scratching his arms and asking, “Is it done yet? I CAN FEEL IT!”

  17. Daniel

    I’ve always been tempted to touch zooanthids when diving. I guess I’ll stay clear of them.

  18. Jason R

    Title your posts with care. The social media daemons are displeased with your invalid use of an apostrophe in the URL of this story.

  19. M.Semones

    LD50s aren’t always comparable or realistic. Route of exposure makes a big difference. Some toxins can be swallowed with minimal harm, but are much more potent intravenously. So, unless you’re using it as a deliberate poison, the natural exposure route makes a big difference on the toxicity. It can make a difference between LD50 studies, too, depending on how the experimenter decides to administrate the poison (i.e., results from orally and intravenously administered poisons aren’t going to be comparable, and may not be realistic if the natural exposure route is drastically different. The body’s got some pretty nice defenses). Thought I’d toss that in; the LD50 is a bit more complex when you start taking it apart.

    Also, the Organization for Economic Cooperation and Development (which the US is a part of) agreed to phase out the LD50 in 2000. Didn’t have time to dig it out on their website, but here’s a quick link that sums up what I talked about above better and notes the OECD decision: You can find other articles online about it, too, though I don’t know how effective it’s been since LD50 is still the biggest number commonly used for toxicity.

  20. LD-50s are pretty ‘old-school’ and a very simplistic, crude measure of toxicity… I’d hesitate to call any agent the “world’s 2nd deadliest poison” if it’s merely based on LD-50 results. But nonetheless, a very interesting piece!

  21. R

    This guy you kindly refer to is a friend as well as a member of the Washington DC Marine Aquarist Society (WAMAS), also an accomplish marine reef keeper who is knowledgeable and as well as an avid aquaculturist.

  22. Shawn

    Awesome article! I can’t wait until we see this on Bones or Castle or CSI.

  23. Nathan Myers

    I’d like to read a story on the mechanisms of action of these extreme toxins. What do they stick to, interfere with, substitute for, catalyze, lyse, clog up, or what-have-you? I’ve been reading about mitochondria, and their role in programmed cell death. (“Sex, Power, Suicide” by Nick Lane; recommended!) Something that tipped the balance in favor of mitochondria releasing cytochrome c into the cytoplasm could have cells throughout the body pining for the fjords in no time.

    OgreMkV: The expression to sum up with is, “No, sir, I didn’t like it.”

  24. @Nathan Myers – Sven covered this above, but basically, palytoxin sticks to a protein called Na+/K+-ATPase, which is a pump that shunts sodium ions out of a cell and potassium ions into it. Palytoxin turns the pump into an open gate, allowing both types of ions to flow in both directions. Without these differences in ion concentration, muscles can’t twitch, nerves can’t fire. Palytoxin kills with equality.

    Also, check out the absolutely insane chemical structure127 129 carbon atoms joined together in a barmy conga line of death.

  25. Blondin

    What’s in your aquarium? Poisson or poison?

  26. tbone

    Hmm, are these the same things as the sea anemones you find at the tide pools at the beach? I have touched plenty of those. must not be. Someone can clarify please. Thx.

  27. NeoTechni

    Sounds like this needs to be a controlled substance, its already weaponized!

  28. clstreak

    The Blue Ringed Octopuss is the deadliest sea creature.. But it has to bite you with its beak and inject you with venom. I have personally seen these in the US but they were by compelet accident.. and the Aquarium stores that recieved these specimines destroyed them when they were found. They cay come in hiding in the Live Rock. Heck being only 4-6″ across they can hide pretty well.

    When I handle my Zoo’s I always were gloves and goggles.. as they can also squirt there toxin when pulled outta the water. And the blogger says you never know which varity might have the toxin by looking at it.

  29. Obviously smarter than ya'll

    It’s funny, because I don’t know a single salt water aquarium owner who DOESN’T know about this. Way to present this rather banal story as some riveting late-breaking news piece.

  30. Nice post, “Obviously”. There might be a few aquarium owners that are unaware, so how about finding something more significant to complain about?

  31. Thankfully, I didn’t post this to my other blog – Not Exactly Salt Water Aquarium Owning – or I’d have been the laughing stock

  32. I quite like the description of palytoxin’s structure as ‘127 carbon atoms joined together in a barmy conga line of death’ – but I’m going to be picky and point out that it’s 129 carbon atoms… and if you think that structure’s impressive, check out maitotoxin’s –

  33. That. Is. Mental.

  34. After reading this we did a write-up on one of our readers that experienced something similar while working for one of the large marine aquarium suppliers in California:

  35. @Obviously: Deeds (the author of the cited paper) states ““the legendary limu appears to be exacting its ancient curse once again, but this time upon unsuspecting marine home aquarists.” Owners are “often unaware of the deadly poisons they are being exposed to”.” Deeds is actually making this statement that marine aquarists are unaware of this and not Ed. Deeds is the one that’s mis-informed. For any of us that frequent the numerous reefkeeping forums, we’ve occasionally come across posts about this in addition to remarks about palytoxin. A number of the reef aquarium hobbyist books also make mention of this. What’s surprising is that the US FDA didn’t.

  36. gillt

    Nevermind the troll.

    I was in the salt water aquarium trade for over a decade and never heard of this. It was never brought up in the store I worked at and I never read about it until now.

    This article will be making the rounds at my local aquarium society.

  37. MP

    Hate to be picky, but it’s not the world’s second-deadliest poison…it’s the second-deadliest NONPROTEIN toxin. Tetanospasmin and botulinum toxin are even more lethal if you’re going by LD50. Other than that, though, nice post.

  38. Peter B

    The structures given as a link in 24 and 33 made me wonder what their IUPAC names are. Al I could think of was “oh, my.” My BS Chem was ’65 and even then I would not have had a clue how to name those compounds.

    Software engineering is so much safer. Although one place where I consulted had a wet chemistry lab. I looked around thinking about asking for a favor. I saw HF bottles and tanks of gases that would kill you faster. My pH meter did not need calibrating after all.

  39. tbone, while palys and zoos are in the same phylum as jellies and similar species, they are not even in the same family.

    So, yes, they all have toxins, but the palys and zoos are a toxic bunch unto themselves.

    I have a working hypothesis that, like some vertebrates, the brighter the zoo or paly, the more toxic they are. This based on a sample size of two, so take with a 2 kilo block of halite.

    The ones that got us were radioactive dragon’s eyes, which are generally very bright green.

  40. Eric

    So let me get this straight: First, 1g kills a million mice. Next, 1g kills 300,000 mice. Explain that to me.

  41. Pooua

    @Eric: The way I understand it is, 1 gram of pure palytoxin can kill a million mice. 1 g of the unpurified sample of zoanthid (marine organism) the researcher collected could kill 300k mice. I briefly wondered the same thing as you when I read the article.

  42. Linda

    Eric, I suppose the 1g killing 100 million mice is the toxin in its purest form. The 1g killing 300.000 mice was one of the samples Deeds got, not pure toxin.

    Ed, wonderful read as always, and a very inspiring one too! I google-image’d “zoanthid” and got a plethora of immensely beautiful pictures of the most colourful creatures. This needs to be written in my notebook (I’m an art student)!

  43. Slyph

    Very interesting article, glad I have stuck to freshwater aquariums :)

  44. Bruno Orsini

    Am I the only one who was left wondering what is the world’s 1st deadliest poison?


  45. Max Normal

    “Hate to be picky, but it’s not the world’s second-deadliest poison…it’s the second-deadliest NONPROTEIN toxin. Tetanospasmin and botulinum toxin are even more lethal if you’re going by LD50. Other than that, though, nice post.”

    hate to be pickier, but unless the author has got his facts wrong, the first quoted lethal dose is 10 ng. 300 ng is the LD50, a measurement of lethality over time, not overall palytoxin-dependent lethality after exposure with no time reference. This suggests that if you let things take their course, a 30-fold lower dose is lethal. The author also fails to mention whether the mice received an oral, intravenous, intramuscular or epithelial dose. Obviously, being a protein, this molecule with be highly sensitive to proteases and pH differences in the digestive tract, so a lethal oral dose is likely to be much higher that a lethal intravenous dose. Given that, quoting LD50 numbers and death rates is fairly meaningless without further information. This is the problem with mixing journalistic articles like this one with some science, the science becomes meaningless. As this article is pretty uncertain about what is really happening, I don’t think you can draw any negative conclusions about it either. Other than that, good point.

  46. Lorra

    So if it’s so deadly how come fish around it don’t die?

  47. Oxymoronic

    @ Eric

    One gram of pure palytoxin will kill one-hundred million mice.

    The zoanthids gathered from D.C. area aquarium supply stores, when tested, had enough palytoxin to kill 300,000 mice.

    Obviously zoanthids aren’t made from pure palytoxin.

  48. dan

    I was breaking down my tank as a sale to a friend. I seperated a bunch of brownish and teal stripped palythoas from the tank into another tank so I could keep a large colony. Apparently while we waited for the water to drain into buckets my hands dried off. Because it was around 8:30 in the morning I was wiping the corners of my eyes. Within 5 minutes I started feeling like a strong allergy came over me. I sneezed, coughed and iched the hell out of my eyes(only putting more toxins in the left as I rubbed). Within 1 hour I was at the ER getting my eye flushed. They gave me eye drops and pain reliever naproxin and vicoden. Neither worked for shit. By 4am the pain was 10 out of 10. The next day around 12:30 went to the eye center and within 15 minutes of giving me drops the pain stopped. My eyelids were swollen shut like frog eyes. But no more pain. He gave me a steroid drop , dilated my pupils so the eye would not continue to expand and contract and also gave me a eye antibiotic. He said the pain reliever the ER gave me didn’t work for eye pain but Tylenol would.. Also told me most eye centers have on call doctors for the ER and to insist to contact that eye doctor as ER peolpe aren’t prepared to handle eye injuries. It took two full weeks to regain about 99% of my vision back. I think it’s still just slightly blurry. Anyhow lesson learned Wash your hand after touching any coral.

  49. Harry

    I almost lost my austrailian shepherd because of pressure washing these polyps off of my live rock. Her heartbeat was so low that they had to give her adrenalin. Also she apparently gotten some in her eyes, which caused a ulcer on her cornea. I had to rush her to LSU animal clinic, where they treated the toxin and had to sew a collagen patch to her cornea…..I had saltwater aquariums for 16 years and never had problems like that….I now realize all the flu-like symptoms i had were because of these palythoas…..


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