Google's John Mueller said on Twitter "we don't have a concept of toxic domains." It was in a reply about a third-party SEO tool saying some of the links to his site are low quality and maybe toxic.
Google said previously most site do not have toxic links. So I guess there is some sort of "concept" around a toxic link but I doubt Google classifies those links internally as toxic.
PageRank by definition gives different weights to links based on the reputation of those links. But could those weights be negative? I doubt it, not since Penguin 4.0.
In any event, sure, I think with manual actions, some links can be "toxic" in terms of hurting a site from ranking. But with Penguin 4.0, Google now algorithmically just ignores bad links to your site.
Here are those tweets:
We don't have a concept of toxic domains. It's fine to use tools to work on your site, but you should understand what the tool does, interpret the output, and not just blindly follow along.
— 🍌 John 🍌 (@JohnMu) September 2, 2020
Forum discussion at Twitter.