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Toxicology Question About Dosage

Kahalachan

Illuminator
Kahalachan
Joined
May 21, 2007
Messages
4,237
Is there any substance out there in which one molecule of it can be fatal?

I think we've all heard the axiom about dosage being everything.

This can be proven wrong if there is even just one substance where the indivisible part of it would be fatal.

So just looking for any positive evidence that would contradict this.
 
But seriously, many sources I've encountered say botulinum toxins are the most poisonous substance, and they're fatal at considerably more than a dose of one molecule, as we can tell from the popularity of Botox treatments!

According to this source,
These are a family of seven different proteins produced by the Clostridium botulinum bacterium. We are all aware of the horror of the affliction known as botulism. These seven toxins have a median lethal dose in mice of 0.0000003 mg of botulin/kg of body mass in mice. In other words, they are about 10,000 times more toxic than either TCDD or plutonium.
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Gravy said:
I don't think one prion is a fatal dose.
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I don't have a clue.

I know that a prion is a protein in a configuration that can induce other molecules of the same protein in a 'healthy' configuration to change to the configuration that the prion is in. The prion configuration of the protein is either non-functional or malfunctional.

If I'm right, it would be possible for a single prion to start a chain reaction of configuration shifts. Possible rather than likely, but, perhaps, possible.
 
Yes, I'll retract my statement and and agree that you may have something there.
 
I don't know if I'm even close to right, but it was the first thing that came to mind when the question arose.
 
"Dose makes the Poison" is an axiom from toxicology, not the study of infectious disease. It's possible one bacterium, virus or prion can cause death under really, really unusual circumstances. (Let's also keep in mind that human pathology caused by prions is still hypothetical.) Infectious agents are not considered substances in the science of toxicology.

To answer the OP, no. there are no known substances that will kill with only one molecule. Not only would that disprove the axiom but it would also disprove the Receptor Theory of Pharmacology.
 
Kahalachan said:
I think we've all heard the axiom about dosage being everything.

This can be proven wrong if there is even just one substance where the indivisible part of it would be fatal.
Click to expand...

Firstly, dosage clearly isn't everything since the substance being dosed is pretty damn important as well. Secondly, this wouldn't be proven wrong by finding something that could be fatal with one molecule. All that would prove is that one particular substance is so deadly that even the minimum dose possible is still fatal. The does would still be important for things like the speed of fatality and the possibility of an antidote.

Finally, no. It is simply not possible for a single molecule to kill someone. There are a huge number of cells in the human body, and killing one or two will not even be noticeable, let alone fatal. Just look at the example of botulinum toxin Gravy provided. About 10-7g/kg for a fatal dose. That makes something like 1020 molecules. Single atoms and molecules are just not relevant when it comes to living systems.

Of course, as already mentioned, if you include self-replicating systems then introducing a single one could result in it reproducing and building up to a fatal dose. However, I wouldn't count this as a single molecule being fatal, since death won't occur until there are a hell of a lot more than one of it.

Edit: I suppose if you want to be really picky there are some possibilties. For example, ionic substances exist as crystals. Although various flaws usually mean the crystal we see are made up of many different small crystals, it is entirely possible for a single macroscopic crystal to be a single molecule. So you could technically die from having a single molecule of salt dropped on your head. The same sort of logic can apply to various other things as well, carbon, for example, can form arbitrarily long chains as far as we know. However, most people probably wouldn't count this sort of thing as an answer to the OP.
 
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Cool. Thanks for the responses.

I wasn't counting anything that borders on life, like a virus or some other self-replicating chemical structure that doesn't fit all the definitions of life.

I don't know much about toxicology, so it's good to learn a few tidbits from here.

Would probably make for some good science fiction to have a toxin that lethal.
 
Um, in fact there is geuss what a range of statistics (just like the 60hz being the 99% persitant vision level) there is the LD50,

Lethal Dose 50%, due to size and metabolism (especialy metabolism) there is a dose at which 50% of the subjects receiving the dose will die from that application of material. So it is again the application of statistics.

I do know that some neurotoxins require very low doses but I am not sure what the gubbiment wants you to know about that. A single small drop still contains thousands and thousands of molecules.
 
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Kahalachan said:
Is there any substance out there in which one molecule of it can be fatal?
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You didn't specify "fatal" to what? A person, a dog, a mouse, a paramecium, a bacterium, a virus? There is probably no answer to this question since there are thousands, probably tens of thousands of substances (& their molecules) which haven't been discovered yet, nor tested against every organism. And the number of peptides and polypeptides, many of which constitute natural toxins at higher doses than a molecule, is literally infinite.

I think we've all heard the axiom about dosage being everything.
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The axiom was first uttered by Paracelsus ....Google him.
 
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Cuddles said:
For example, ionic substances exist as crystals. Although various flaws usually mean the crystal we see are made up of many different small crystals, it is entirely possible for a single macroscopic crystal to be a single molecule. So you could technically die from having a single molecule of salt dropped on your head. The same sort of logic can apply to various other things as well, carbon, for example, can form arbitrarily long chains as far as we know.
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Even pickier, ionic compounds do not contain anything considered molecules. Molecules are covalently bound; ionic compounds are not.

You can, however, have macromolecules such as diamonds, which are covalently bonded. A single crystal of diamond or silica could be considered a single molecule, and could easily be large enough to be lethal.
 
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