Factual error: While it is true that lithium carbonate can be used to treat depression and other psychiatric disorders, it cannot be administered in gaseous form. It is a very stable salt and only starts to form vapour at 1,310 degress Celcius. Spraying it about as a 'mood stabliser' at that temperature, as Kryten does, is going to kill everyone on the spot.
Suggested correction: A couple of explanations come to mind. After 3 million years, the lithium carbonate may have become contaminated or mutated, resulting in it becoming a less stable salt and/or a change in its chemical structure. Another explanation is that Holly just made a mistake. They have a proven track record of mistakes, saying the wrong things, and generally being stupid.
Salts don't mutate - they don't have genes. If Holly "just made a mistake" and the chemical being sprayed about by Krtyen wasn't lithium carbonate (or it was contaminated), then it would not work as a mood stabiliser. Since it does, it was lithium carbonate and the Boys From The Dwarf are going to die horribly.
All good points. Sounds like contamination is the most likely answer, then.