Mold growth on insulation

[quirkzoo]

I poured my hearth and laid down the FB Board insulation but was unable to lay down my floor tiles soon after. In the meantime I covered the insulation with a tarp. When I removed the tarp there are some spots of black mold on the insulation. My plan was to wash the insulation with some bleach and perhaps apply a fungicide. I am assuming that the insulation won't break down with mold but I don't want to assume that and then have the insulation crumble and my entire oven disturbed a year or two down the road.

Should I be worried?
Any other suggestions for what to do with the moldy insulation?

(apologies if this is a double post, I wasn't sure if I created the first one correctly)