Here’s an article from The Scientist. It discusses, among other things, the science of Jill Masterson’s body paint murder in Goldfinger, and of the poisonous orchids in Moonraker. More disturbing is the mention in this article of a chemical that is a more practical way to kill human beings en mass. It is called ricin, is fatal in fairly small doses (a few milligrams or less) , can be spread easily in aerosol form, and has no known antidote. It comes from castor-oil plants.
I wish they hadn’t been so explicit about it; but then again I never really liked castor oil.
P.S. I checked that infallible source of information, Wikipedia, and it says that ricin isn’t that bad compared to things like Anthrax and Botulinum, so belligerent countries or organisations with the technology would go for the latter substances. However, it is twice as deadly as Cobra venom, is easy to process from castor beans, and there is no known antidote, making it risky and also attractive to lower tech belligerents.