tl;dr damn Gov’t, you scary!
Prior to the fictional events in “Breaking Bad” ricin was used several times as both a tool of assassination as well as a weapon of terrorism. It’s cheap and easy to make and no known antitoxins existed until just a couple of years ago.
The beans themselves can kill an adult if injested, and the amount of pure ricin extract that’s lethal is less than the amount of venom a bee stings you with.
And in 1944 the U.S. government was producing 26 pounds of ricin a day at an experimental weapons facility in Utah. It was simply called “Agent W.”