Is this mold? What do I do?

I recently found mold under my mattress. The mattress was sitting on another thinner mattress on the floor, and the mold was between the thin mattress in the floor and the floor. I got rid of that mattress and contaminated floor boards and cleaned the cement underneath, but now I see some grey on this piece of wood which is stuck in the floor. Is that mold on the wood or just dirt or something? I’ve been having mold exposure symptoms for months so I’m trying to get rid of all the mold but don’t know what to do if it’s on the wood. I’ve got a bedframe now but don’t know how to get rid of the rest. I also don’t know if I need a new mattress, there was a mattress protector on my mattress and no visible mold on the mattress or protector, but I don’t know if mold spore could have spread from the thinner mattress underneath. I would appreciate any help, thank you!