Toxic vs Non-toxic.

Finally I have time to write something here after long absence.I come across this small Q&A on New York Times which distinguished for the readers the difference between diethyl glycol and polyethyl glycol. This caught my sight because it is Chinese related – the toxic toothpaste scandal. However, to explain the non-toxic polyethyl glycol the author stated that:

Polyethylene glycol, which has nitrogen in addition to diethylene glycol’s carbon, hydrogen and oxygen, is safe…

This got me in puzzle for a while, before I realized what he was mentioning was one of the most industrially common derivatives of polyethylene glycol – polyethylene glycol diamine, where the two hydroxyl end groups are replaced by amino groups, in order to facilate further functionalization.

But this is not exactly the reason why polyethylene glycol or most of its common derivatives are non-toxic. Doping a toxic molecule with nitrogen does not render it non-toxic, in contrast a lot of nitrogen-containing substances are extremely toxic (e.g. KCN).

The toxicity of polymers and their corresponding monomer is one of the most puzzling issue among the public science literacy. Polymers are not necessarily toxic if their monomers are toxic. Examples include polyvinyl chloride (old school plastics), polytetrafluoroethylene (DuPont’s nonstick coating), and even simply polystyrene. Mostly when toxic monomers polymerize into a polymer the original reactivity is lost. Industrial polymers are sometimes regarded toxic because the possibility of some monomer residues as well as other additives obtained during the manufacturing process. Sometimes these monomer residues or additives are industrially unavoidable, the polymer having to be banned as toxic chemical by the government. But this doesn’t mean the polymer itself is toxic if carefully purified.

These said, those Chinese toothpastes are still toxic, indeed. What a shame!