Yes, microplastics accumulate in the brain over the years [PMID: 38765967]. They cause anxiety [PMID: 37269995] and brain inflammation [DOI: 10.3390/ijms241512308]. There is a lot more research on them than I am quoting here.

When someone is suffering from crippling anxiety, if you have ever suffered from it, the last thing on their mind will be to develop anything cool.

Moreover, microplastics accumulate and harm various organs, not only the brain. They also cause generational infertility due to the pervasive co-presence of toxins like phthalate in them [PMID: 39446714].

Similarly, higher CO2 levels are detrimental to cognition. This has been known for years and is established knowledge.