"Planetary boundaries is a concept highlighting human-caused perturbations of Earth systems [...] The framework is based on scientific evidence that human actions, especially those of industrialized societies since the Industrial Revolution, have become the main driver of global environmental change. According to the framework, "transgressing one or more planetary boundaries may be deleterious or even catastrophic due to the risk of crossing thresholds that will trigger non-linear, abrupt environmental change within continental-scale to planetary-scale systems."[2]"
The first sentence suggests that the study's authors are concerned that PFAS and its similar cousins represent a non-linear, large-scale environmental threat.
An additional thing to understand here is that PFAS is not a new boundary at all in the context of the planetary boundaries framework - they fall under the already defined category of Novel Entities.
Since that's a catch all category for many things (nuclear waste, other synthetic chemicals, there's even debate with the original authors of the framework if Artificial Intelligence should be considered), the boundary value itself is not currently defined.
One school of thought is that the boundary value for this category should be zero - as any synthetic substance is more than nature generates.
Regardless, papers like this one are helpful to piece together all of the novel entities research amd get a better picture of how this boundary interacts with the rest of the Earth System.
Ah, so a boundary is between continuous "regimes" governed by a single behavior; crossing the boundary means moving into a different, as-yet unexplored regime.
Indeed -- in this case, a large-scale diffusion of a very stable family of waterproofing chemicals into the, uh, global water cycle. The idea is that it's possible for human activity to fundamentally change the nature of some system whose behaviour we think of as stable and inviolable. Considering how goddamn important water is to basically everything in the biosphere, I think of it as more an eaten-by-a-grue "unexplored", rather than enticing-terra-nova, style of thing.
It's interesting how humanity will accept this kind of "experiment" when it's a side-effect of something designed to give a little convenience, or for somebody to make a bit more profit. If a scientist proposed doing it on purpose, just to find out what would happen, there would probably be less enthusiasm.
It's also interesting how it's the political "conservatives" who seems to be most accepting of these kinds of environmental changes, when "conservatism" is supposed to be about preserving the way things are now, or perhaps how they were in some recent "golden age" past, as I understand the term.
"Planetary boundaries is a concept highlighting human-caused perturbations of Earth systems making them relevant in a way not accommodated by the environmental boundaries separating the three ages within the Holocene epoch."
