You can basically take two paths here. What you’re currently trying to do is move from downstream to upstream: starting with a very detailed mechanism (radon → specific progeny → deposition → uptake → dose) and then working backwards to argue that this must be a serious health risk. That might feel logical, but it’s also the kind of approach that can take a lifetime, because every link in the chain becomes its own complex project. Also the underlying question is whether there is an health risk.
The other path is to go from upstream to downstream, and that would be my advice. Start with the big, upstream question: do we actually see a measurable effect in the real world among people who work in these facilities (e.g., higher lung cancer risk or higher measured occupational dose compared to a comparable group, controlling for smoking and other confounders)? If you see a signal there, then it makes sense to go downstream and ask which part of the mechanism explains it. If you don’t see a signal, then you’ve learned something important early, and you can reframe the whole question.
Now if this is something that can be done just by reading literature is the question, but I suspect that it would have been known by now, if significant, especially in these familie operations, growing mushrooms, in Italy.