I've been hearing this sentence for a few years now. I'm a native English speaker from South Africa and it just sounds wrong to me.
Am I being stupid about the whole thing? "It's not environmental," is used as meaning, "It's not friendly to the environment," "It's not environmentally friendly." For example a girl sees smoke billowing out of a passing scooter and mutters, "That's not very environmental." Or a boy throws a bit of recyclable trash in the general wastebin and the teacher says, "Johnny, put the trash in the correct bin. We have to be more environmental. What you did was not environmental, now was it?"
Should I let it go and start using the word in the same way that everyone else seems to be using it? Or stick to, "It's not good for the environment," "It's wasteful," "It's harmful to the environment," or something like that? I don't like the ambiguity of, "It's not environmental." This sentence could mean the 'the problem isn't in the environment,' not necessarily 'it's harming the environment' (ie Nature).