According to a quick google search, toxic is always associated with poison or toxins. It is harmful and unhealthy. So, when a school's environment "goes toxic" whose job is is to cure it? Who is responsible for this outcome? How did it get to be that way? And, does it matter why it's that way or is it more important to figure out what to do to turn things around?
I've been in toxic school environments that seem to get worse before they get better. Often, this starts out with teachers feeling that they are not being respected by the administration. Then, teachers start talking to each other because, more often than not, this is the only outlet they have to check their perceptions about what's going on. Sometimes teachers will feel like they're alone in their feelings or like there's something wrong with them. So, one brave soul will test the waters by bringing up a concern in casual conversation. Soon after, another conversation will ensue about the same or a similar topic with the same colleague or a different one. And, then there is a snowball effect.
If administration wants to change this climate then it must first be aware that it's happening. Otherwise, nothing will change. So, who will be the brave soul to broach this in a meeting or in a private conversation? And will this be enough?