Does anybody know exactly how dangerous ~2ml of Didecyl Dimethyl Ammonium Chloride is to human health? I recently saw this chemical is the active ingredient in Febreze Antimicrobial.

I doubt that you have the pure substance. The pure substance (a quaternary ammonium salt) is a solid, which dissolves in water as an ionic salt. You most likely have a solution, which contains 1 to 2% of the substance, probably together with some other quaternary ammonium salts.

 

Quaternary ammonium salts are toxic to humans, but not insanely toxic.

 

Here is a link to an MSDS of a product, containing around 15% of quat. amm.

 

http://www.pharmacal.com/MSDS/US/MSDSQUATPV15.pdf

 

The LD50 for rats of the solution is between 1 and 2 gram per kg of body weight in general. As with many chemicals, a single exposure to a small amount of this is not a problem.

 

It hardly ever happens that a person gets a lethal dose at once of a certain chemical. You have to be careful not to be exposed to this on a regular basis with small quantities. Long-term low-level exposure may be harmful.