My opinion is boiling kills everything. If you boil long enough to sink deep into the wood, nothing will survive, so I wouldn't stress that much over it. Many people get their wood they use in aquariums from rivers etc. I wouldn't mess with anything but boiling it, IMO.
If you're worried, buy a piece of wood, but like you said, you may find a very interesting piece. You know what is down by your river, more than we do :) Best of luck!
that sums it up. nothing can survive boiling. thank you gwen.