If these fungi are really capable of eating polyurethane in anaerobic environments, we'd better hope they can't do the same with polypropylene and polyethylene, because if so the polypropylene liners modern landfills depend on to keep their contents out of the groundwater are going to start leaking pretty soon.
(Some landfills use geomembranes of other polymers, too.)
It reads like a summer disaster movie, entertaining but mostly forgettable. What was interesting about the book was as a thought experiment about the use of plastics in critical infrastructure and how much of a nightmare plastic-eating anything could be.
I think the backstory of the Ringworld series was that a superconductor-eating microbe destroyed civilization on the Ringworld, and restarting it was impossible because there were no metals or fossil fuels to mine. On the plus side, on actual Earth, at least most of the metals are still in the landfills.
(Some landfills use geomembranes of other polymers, too.)