The Most Toxic Chemicals to Humans Are Natural!

This is to correlate with my Scientific American guest blog post, “Natural versus Synthetic Chemicals Is a Gray Matter”.

Please not that I will update this list soon to include more information!


Botulinum toxin (aka Botox)- botulism is caused by this protein and neurotoxin produced by bacteria spores

Tetanospasmin– A neurotoxin produced by bacteria that causes Tetanus

Palytoxin– narrows the blood vessels particularly large arteries and is found in a variety of marine life

Diphtheria toxin– Is secreted by bacteria and causes diphtheria

Ciguatoxin– A class of toxins found in certain fish that cause a food-borne illness called Ciguatera

Batrachotoxin- A cardiotoxin and neurotoxin found in poison-dart frogs, melyrid beetles and certain birds

Saxitoxin– a paralytic produced by shellfish

Tetrodotoxin– A neurotoxin produced by a variety of marine life, most notably the puffer fish

Ricin– (Breaking Bad fans may remember this one! ) It comes from castor beans and damages the ribosomes that carry out protein synthesis in cells

Alpha-Amanatin– Causes liver failure and death and is found in mushrooms of the genus Amanita including the Death Cap

Muscarine– a cardio and neuro toxin produced by certain mushrooms

Aflatoxins– A class of fungal produced toxins and carcinogens that contaminate grains, peanuts and corn (Aflatoxin B1 is the most toxic in this class) 

 for separate blog post



* Merck Index

** Winder, C., Toxin Reviews, 2004, Vol. 23, No. 1 , Pages 97-103

*** University of Florida, Environmental Health & Safety



  1. Chris says:

    Yes but risk is from toxicity and exposure. Got to consider how much of the chemicals are getting into living things. Not disagreeing with your premise, just saying risk assessment includes exposure assessment as well as health effects information.

    Also using only LD50 (acute effects information) is incomplete. Chronic effects risk assessment requires comparisons of reference dose, reference concentration or slope factors.

  2. nicoconut says:

    What species were used to determine the LD50 values in the graph? The LD50 can vary widely between species, and can vary depending on the route of exposure, so unless the exposure routes and animals used are all the same between these studies, I’m not sure you can compare them this way. A low LD50 in an animal doesn’t necessarily mean the substance will be as lethal to humans, just as a high LD50 in animals doesn’t mean that the substance will not be a cause for concern to people.

  3. nicoconut says:

    Please also note that lethality is not the only endpoint that toxicologists are concerned about!! Yes, bolutinim toxin is one of the deadliest substances out there, but that doesn’t mean that the above chemicals don’t have other toxic endpoints of concern (e.g., cancer, genotoxicity, reproductive or developmental toxicity, etc.). Perhaps you should revise your post to say that the most *lethal* chemicals are natural…

  4. […] and that synthetic chemicals are not a priori worse than organic chemicals, in fact, quite the opposite. In other words, we need to get real, and deal with the facts as they are, not as we want them to […]

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  6. Duperray says:

    Good site indeed, quantification does mean something, unlike the media’s propaganda about anything which displease them…
    Perhaps one shall also consider existing and worldwide manufactured quantities. I dont believe botulic toxin is manufactured by tons. Therefore if we multiply the a.m. toxicity index by produced quantities (industrial use) I think that Sodium Cyanide or DDT be of top class.
    As someone told before, what does really count is the probability that each Lethal Dose be absorbed by random persons: Both cyanide and arsenic oxyde require circa 250mg per person in one chunk to be lethal. This is why lethal probability is extremely low, despite huge tonnage manufactured.
    Also, when absorbe dose is much smaller, these inorganic chemicals are no longer a danger but are welcomed by our body which does need 2mg arsenide per day (garlic, ognons,..) !! Cyanide CN- is a very active ion in ordinary human chemistry…

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