As a jaded observer of the meat industry, even I'm flummoxed by this fact: It's standard practice on factory chicken farms to dose those unfortunate birds with arsenic. The idea is that it makes them grow faster -- fast growth being the supreme goal of factory animal farming -- and helps control a common intestinal disease called coccidiosis.
The industry emphasizes that the arsenic is applied in organic form, which isn't immediately toxic. "Organic" in the chemistry sense, that is, not the agricultural sense -- i.e., molecules containing carbon atoms as well as arsenic. Trouble is, arsenic shifts from organic to inorganic rather easily. Indeed, "arsenic in poultry manure is rapidly converted into an inorganic form that is highly water soluble and capable of moving into surface and ground water," write Keeve E. Nachman and Robert S. Lawrence of the Johns Hopkins Center for a Livable Future.
Inorganic arsenic is the highly poisonous stuff -- see the absurd and wonderful Cary Grant classic Arsenic and Old Lace, or the EPA's less whimsical take here and here [PDF]. The fact that the organic arsenic added to feed turns inorganic when it makes its way into manure is chilling, given the mountains of concentrated waste generated by factory poultry farms.