In a news story (see below), Po-210 was indicated as a weapon in an assassination. To recieve an annual legal limit from Po-210, a worker would have to ingest 3 uCi (microcuries). Biological half life for Po-210 is 50 days (ICRP Publication 67) and the effective half life would be about 36 days. With death within 1 effective half life and the dose protracted over a month, I would have to guess the amount ingested would need to be over a thousand ALI, possibly several thousand (note: 100% conjecture on my part). Still, that would be something like a microgram of Po-210.
Polonium-210 is used mainly in static eliminators, ie, used to eliminate static electricity in processes such as paper rolling, manufacturing plastics and photography.