Oh, my friend, where do I even start? Toxics? Corrosives? Explosives? There are so many options!
I’ll actually be breaking this reply up into several pieces because I feel like you should have a response sooner rather than later. Plus, this way, we can spend more time on the many different kinds of dangerous available to us. The first part of my quick reply is to point you towards this video:
The second part of the short answer (I am bad at giving short answers!) is a quick list of some seriously nasty chemicals that are fairly common.
I know, right? Most of us remember hydrogen peroxide as that stuff we poured on cuts as kids in order to disinfect them. It stung, sure, but dangerous?
Hydrogen peroxide is a good disinfectant for the same reason that it’s dangerous in high concentrations. The peroxide bond (two oxygen atoms single-bonded to each other and to one other element) is not very stable, and so whenever there’s something nearby that offers a more stable bond, peroxides react immediately and often explosively. Old bottles of laboratory-grade peroxides have to be handled by HAZMAT teams because the residue left between the bottles and their caps forms a contact explosive that can detonate with the slightest touch. There’s a reason why good old hydrogen peroxide, at high concentrations, is used a rocket propellant.
Commonly used for etching glass, hydrofluoric acid is generally not considered a strong acid in chemistry circles. Compared to its sibling hydrochloric acid, it isn’t a strong acid. It doesn't damage the skin, it doesn’t react strongly with organic compounds or many metals, and in general it’s just not as reactive as stronger acids.
It is, however, exceptionally reactive with calcium salts, including calcium carbonate and calcium phosphate, which are the primary building blocks for bones. Remember how I said hydrofluoric acid wouldn't burn your skin? It won’t, so if you accidentally come in contact with it, you won’t notice right away. It will pass right through your skin and muscle until it hits bone, which it promptly begins to dissolve.
Dimethylmercury is a nasty compound. To be fair, most organomercury compounds are, because a mercury atom bonded to an organic compound is much more bioavailable than a mercury atom in its elemental form. Mercury is poisonous no matter how you look at it, but it’s much more dangerous when it can hitch a ride into your body on some non-threatening molecule.
Dimethylmercury is the perfect example of this. It is easily vaporized (so you can inhale it) and it readily passes through many commonly used types of protective equipment, including several of the most common glove types. This means if you splash it on your gloves it will pass right through and be absorbed into your body, where it can then reach fatal mercury levels very quickly. This was tragically demonstrated by the death of Dr. Karen Wetterhahn of Dartmouth College in 1997.
I’ll leave you with those for now. In the next few weeks, I’ll be doing a few posts on other compounds and the many and varied ways they can be dangerous. Until then!
