The problem with petroleum-eating microbes is that they flood the local area with waste products. That it's no longer petroleum doesn't mean it won't still wipe

The problem with petroleum-eating microbes is that they flood the local area with waste products. That it's no longer petroleum doesn't mean it won't still wipe out the local ecosystem - i.e. how fertilizer run-off destroys estuaries because it triggers an algal bloom which promptly chokes off everything else.