It's complex, but the fertilizer itself is actually the source of the radioactive stuff. Tobacco has the odd characteristic of capturing that and the decay products are things like polonium
That doesn't say anything about Polonium being selectively taken up by the plant and used for growth. Just contamination on the sticky covering of the plants. Which doesn't make smoking tobacco good in any way, shape or form whatsoever, but it's not at all the same claim.
https://news.cancerresearchuk.org/2008/08/29/radioactive-pol...