The Sixth Edition of the PMBOK® Guide does not, sadly, even mention sustainability. One could read it thinking that unlike other PM standards, for example Prince2 and IPMA and ISO21500, they simply forgot about it.
It’s just hiding. And you just need to know where to look.
I can help. Please see these two posts (Links below from a two-part series) from my companion blog on People, Planet, Profits, and Projects.