> Alpha radiation is completely harmless and doesn’t even get through a sheet of paper. It is indeed harmless outside of your body, but it is devastating inside of your body. The reason is that outside of your body, it is blocked by your layer of dead skin, if it gets to it, your dead skin ends up pretty messed up as it absorbs all the energy of the alpha particle. But no big deal, it is dead, doesn't take part of yo…
How leathal? Roughly 6.8 trillionths of a gram [1].
Luckily Po-210 isn't a huge danger because of the short half life and it's really only produced by governments in very small quantities. But the point is that any alpha particle emitter ingested is potentially a massive health risk.
And what happens at an accident like Chernobyl? It scatters a ton of dust over a huge area that consists of many radioactive isotopes, some of which are just toxic by themselves (eg Caesium) but also some of them are alpha particle emitters. That dust gets into the food chain.
[1]: https://www.reuters.com/article/palestinians-arafat-swiss-po...