I'd just like to add that, at least for me, the alarming part is regarding the distribution of these, they seem to be not only lipophillic (which would be expected, considering the nature of them), but also able to cross the blood-brain barrier, something evolved in order to keep bad stuff out (sure, the lipophillic nature explains that part as well, but presumably the fact that they are undissolved but basically very small particles, there was probably some hope towards them not being able to cross).

To me, this raises some questions regarding what else travels with them, and are they inadvertently becoming a vector for stuff that would normally be more easily disposed of? Thinking of things like the first pass effect here, in the liver where things like 'naked' pollutants would be processed/eliminated 'on sight'; then, if something comes along adsorbed/absorbed into a 3D structure that hides it from the body long enough and then reaches the brain, that something could be potentially leached in a highly unfortunate place. Think targetted drug delivery - only random and with whatever happened to be around while the microplastic was forming.

Add to this the fact that any and all studies lack a control group since the things are in everything and everyone. Would it even be possible to grow plastic-free lab animals to test them? How would you even isolate the area without using any sort of plastic?

I predict that behavioral studies are more likely than not to show erratic results due to having different baselines of comparison for each subject because of the heterogeneity of contamination, so even spiking with the same agent in the same manner, you'd be either compounding an effect, potentially countering another or perhaps just eliciting a totally different response. How would one control for that? Maybe get as uniform a starting group as possible but how would you prove that uniformity?